B u reau of Resource Sciences

Managing Vertebrate Pests: Feral Pigs

David Choquenot, John McIlr oy and Terry Korn

Scientific editing by Mary Bomford

Australian Government Publishing Service C a n b e r r a © Commonwealth of Australia 1996

ISBN 0 644 29240 7 (set)

ISBN 0 644 35847 5 (this publication)

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be re p ro d u c e d by any process without prior written permission from the Australian Government Publishing Service. Requests and inquiries concerning re p roduction and rights should be addressed to the Manager, Commonwealth Inform a t i o n Services, Australian Government Publishing Service, GPO Box 84, Canberra ACT 2601.

Publication design by Bob Georgeson, Bureau of Resource Sciences Design Studio.

C redits for cover photograph. Main: J. Mitchell, DNR. Insert: P. Pavlov.

C o v e r, typesetting and diagrams by Henryk Dekker.

The Bureau of Resource Sciences is a re s e a rch bureau of the Department of Primary Industries and Energy. Its mission is to enhance the sustainable development of Australia’s agricultural, fisheries, mineral and petroleum re s o u rc e s and their industries by providing scientific and technical advice to government, industry and the community.

A ff i l i a t i o n s

A u t h o r : David Choquenot, New South Wales Agriculture; John McIlroy, CSIRO Division of Wildlife and Ecology, Canberra; Terry Korn, New South Wales Agriculture .

E d i t o r : Mary Bomford, Bureau of Resource Sciences, Canberra.

Publication to be cited as:

Choquenot, D., McIlroy, J. and Korn, T. (1996) Managing Vertebrate Pests: Feral Pigs. B u reau of Resource Sciences, Australian Government Publishing Service, Canberra.

AGPS Reference A61984 P roduced for the Bureau of Resource Sciences by the Australian Government Publishing Service, Canberra. FOREWORD

Feral pigs cause problems for farmers because or hunting is humane. The authors have they eat crops, pasture and lambs. Conser- attempted to take all these divergent views vation authorities are concerned that feral and objectives into account in compiling these pigs, through selective feeding, trampling and g u i d e l i n e s . rooting, could have negative impacts on a The principles underlying the strategic range of native plants and animals, including management of vertebrate pests have been invertebrates. Quarantine authorities need to described in Managing Vertebrate Pests: manage the risk that feral pigs could be Principles and Strategies (Braysher 1993). involved in exotic disease outbreaks, such as The emphasis is on the management of pest foot-and-mouth disease or swine fever, should damage rather than on simply reducing pest such diseases enter Australia. On the other density. The guidelines recommend that, hand, feral pigs are valued by those who hunt w h e rever practical, management should them commercially or rec reationally and feral concentrate on achieving clearly defined pig meat is exported to Europe as wild boar. conservation or agricultural pro d u c t i o n T h e re is little reliable information about b e n e f i t s . the extent and nature of many of the prob l e m s This publication, which is one in a series, caused by feral pigs and how they can best p rovides land managers with ‘best practice’ be solved. This has led to diverse views about national guidelines for managing the feral pig management. Although spending agricultural and environmental damage on pest control should be justified in term s caused by feral pigs. Others in the series of economic re t u rns on such investments, include guidelines for managing feral horses, this is clearly difficult when the impacts of rabbits, foxes, feral goats and rodents. The feral pigs on both agricultural and publication was developed and funded by conservation values, and the responses of pig the Vertebrate Pest Program in the Bureau of populations to control operations, are often R e s o u rce Sciences. poorly quantified. Conservation orga n i s a t i o n s would like to see pig populations eradicated To ensure that the guidelines are widely or reduced to low numbers in areas where accepted as the basis for feral pig they pose a particular threat to conservation management, comment has been sought from values. Pastoralists would like to have cost- State, Territory and Commonwealth e ffective means for reducing pig pre d a t i o n Go v e rnment agricultural, environmental, and on lambs. Quarantine authorities wish to re s o u rce management agencies. Comments e n s u re that feral pigs could be controlled if w e re also sought from land managers and they were involved in an exotic disease community organisations, including the o u t b reak. People interested in hunting feral Australian Conservation Foundation, the pigs for commercial use, re c reation or National Farmers’ Federation, the National subsistence food want to retain them as a Consultative Committee on Animal We l f a re , re s o u rce. Those concerned with animal the Australian Veterinary Association, the w e l f a re want to ensure that feral pig contro l N o r t h e rn Aboriginal Land Council and four

Bureau of Resource Sciences iii res e a rch and development corporations. The reduce damage to agriculture and the natural Standing Committee on Agriculture and e n v i ronment caused by feral pigs thro u g h R e s o u rce Management has endorsed the the use of scientifically based management a p p roach to managing feral pig damage set that is humane, cost-effective, and integrated out in these guidelines. with ecologically sustainable land m a n a g e m e n t . These guidelines will help land managers

Peter O’Brien Executive Dire c t o r B u reau of Resource Sciences

iv Managing Vertebrate Pests: Feral Pigs CONTENTS

FOREWORD iii ACKNOWLEDGMENTS ix SUMMARY 1 INTRODUCTION 7

1. HISTORY 11 Summary 11 1.1 Origin of feral pigs in Australia 11 1.2 Introduction and spread in Australia 11

2. DISTRIBUTION AND ABUNDANCE 13 Summary 13 2.1 Distribution in Australia 13 2.2 Changes in abundance 15

3. BIOLOGY AND ECOLOGY 17 Summary 17 3.1 General description 18 3.2 Habitats 20 3.3 Food and movements 20 3.4 Social organisation and behaviour 23 3.5 Reproduction 25 3.6 Diseases and parasites 25 3.7 Mortality 26 3.8 Population dynamics 26

4. ECONOMIC AND ENVIRONMENTAL IMPACTS AND COMMERCIAL USE 33 Summary 33 4.1 Economic Impact 33 4.2 Environmental impact 41 4.3 Impact of diseases and parasites 43 4.4 Resource value and commercial use 47 4.5 Implications of harvesting for damage control 50

5. COMMUNITY ATTITUDES AFFECTING FERAL PIG MANAGEMENT 51 Summary 51 5.1 Community perceptions 51 5.2 Animal welfare issues 51 5.3 Attitudes in the rural community 52 5.4 Attitudes of the general public 53 5.5 Attitudes to multiple-use management 53

6. PAST AND CURRENT MANAGEMENT 55 Summary 55 6.1 Past management 55 6.2 Current management and legal status 56

Bureau of Resource Sciences v 7. TECHNIQUES TO MEASURE AND MANAGE IMPACT AND ABUNDANCE 61 Summary 61 7.1 Introduction 62 7.2 Estimating pig abundance 62 7.3 Simple estimates and indices of pig abundance 64 7.4 Estimating agricultural and environmental damage 64 7.5 Use of impact, distribution and density measurements 72 7.6 Control techniques 74 7.7 Cost of control 88 7.8 Monitoring 91 7.9 Evaluation 92

8. STRATEGIC APPROACH TO MANAGEMENT AT THE LOCAL AND REGIONAL LEVEL 94 Summary 94 8.1 Economic frameworks 94 8.2 Strategic approach 95 8.3 Defining the problem 96 8.4 Management plan 96 8.5 Implementation 104 8.6 Monitoring and evaluation 104 8.7 Example of the strategic planning process centred on the wet tropics World Heritage Area of north Queensland 105 8.8 Example of costs and benefits of controlling feral pigs in rangelands woolgrowing enterprises 107

9. IMPLEMENTING A MANAGEMENT PROGRAM 117 Summary 117 9.1 The role of extension services 117 9.2 Around the states 118 9.3 Stakeholders 119 9.4 Identification of goals 120 9.5 Government involvement 120 9.6 Partnerships are needed 121 9.7 Facilitation of effective groups 123

10. DEFICIENCIES IN KNOWLEDGE AND PRACTICE 126 Summary 126 10.1 Biology of feral pigs in Australia 126 10.2 Agricultural impact 127 10.3 Environmental impact 127 10.4 Impact of diseases and parasites 127 10.5 Assessment of non-target impact of CSSP 128 10.6 ‘Real world’ costs of feral pig control 128 10.7 Training 129

vi Managing Vertebrate Pests: Feral Pigs REFERENCES 130

APPENDIX A Best practice extension in pest management 142

APPENDIX B Economic framework for feral pig management 144

APPENDIX C Criteria for eradication 147

ACRONYMS AND ABBREVIATIONS 148

GLOSSARY 149

INDEX 154

FIGURES Figure 1 Strategic approach to managing feral pig damage. 8 Figure 2 Distribution of feral pigs in Australia. 14 Figure 3 Variation in protein content of food consumed by pigs in north-west New South Wales. 28 Figure 4 The numerical response of pigs to pasture biomass in north-west New South Wales. 29 Figure 5 The relationship between total mortality rate for pigs and number of dingo bounties paid. 32 Figure 6 Probability of different rates of lamb predation at three pig densities. 36 Figure 7 Sugarcane production losses attributed to feral pigs in Queensland. 38 Figure 8 Decision tree for determining the cause of lamb death. 65 Figure 9 Generalised relationship between pig density and reduction in yield. 66 Figure 10 Relationship between pig density and reduction in yield in maize and sorghum crops in the wet–dry tropics. 66 Figure 11 Relationship between pig density and reduction of lamb predation in western New South Wales. 67 Figure 12 Effect of assuming a linear relationship between pig density and reduction in yield when the relationship is curvilinear. 68 Figure 13 Effect of assuming a linear relationship between pig density and reduction in yield passes through the origin when it passes through the density axis. 69 Figure 14 Variation in pig density and the extent of new rooting activity predicted for an erupting interactive pig–vegetation system. 71 Figure 15 Generalised relationship between pig density and cost-per-removal. 72 Figure 16 Effect of density-dependent cost recovery on the relationship between pig density and cost-per-removal for a given control technique. 72 Figure 17 Pig fence constructed with 8/80/15 hingejoint and steel posts. 78 Figure 18 A fully electrified fence with off-set trip wires. 79 Figure 19 Feral pig trap designs and specifications. 82 Figure 20 Variation in marginal benefits and costs of simulated programs for shooting from helicopters. 113 Figure 21 Ratio of benefits and costs of a simulated program for shooting from helicopters. 114 Figure 22 Ratio of benefits and costs of a series of simulated 1080 poisoning programs. 115 Figure 23 Selection of control area size relative to the home range of feral pigs. 122 Figure B1 Possible relationships between pig density and the damage they cause. 144 Figure B2 Marginal analysis plotting cost of reducing pigs and cost of damage caused by pigs against level of control activity. 145

Bureau of Resource Sciences vii TABLES Table 1 Estimates of abundance of feral pigs in various locations and habitats in Australia. 16 Table 2 Chemical constituents of tropical and temperate fruits eaten by feral pigs. 21 Table 3 Daily nutrient requirements of domestic pigs. 22 Table 4 Home ranges of feral pigs. 24 Table 5 Estimates of feral pig damage to sugarcane in Queensland. 38 Table 6 Typical prices paid by Australian chiller operators for wild boar meat. 49 Table 7 Status of the feral pig in Australia. 60 Table 8 Studies using ground survey techniques to assess feral pig abundance. 63 Table 9 Subjective assessment of the likely shape of the relationship between reduction in yield and pig density for agricultural products and resources affected by pigs. 69 Table 10 Comparative costs of feral pig control methods in different habitats. 89 Table 11 Costs for control strategies associated with varying levels of population reduction. 90 Table 12 Costs per kilometre of fences tested and their cost efficiencies. 91 Table 13 Costs and benefits derived by computer simulation for a no pig control strategy on a woolgrowing enterprise. 110 Table 14 Costs and benefits derived by computer simulation for a sustained pig control strategy to restrain pigs at a moderate density on a woolgrowing enterprise. 110 Table 15 Costs and benefits derived by computer simulation for a sustained pig control strategy to restrain pigs at a low density on a woolgrowing enterprise. 111 Table 16 Costs and benefits derived by computer simulation for a local pig eradication strategy on a woolgrowing enterprise. 111 Table 17 Comparative ratio of benefits to costs of control strategies. 112

All dollar values have been converted to 1994–95 Australian dollars unless otherwise stated in the text.

viii Managing Vertebrate Pests: Feral Pigs ACKNOWLEDGMENTS

The Vertebrate Pests Committee’s Wo r k i n g •Vertebrate Pests Committee G roup — Peter Allen, Roger O’Dwyer, •Australia and New Zealand Enviro n m e n t A n d rew McNee, Don Pfitzner and Jason and Conservation Council Alexandra — oversaw the preparation of – Standing Committee on Conservation these guidelines and provided valuable input – Standing Committee on the and comments. Environment We especially acknowledge the following •Land and Water Research and Development people who made helpful comments on the Corporation draft manuscript or gave advice: Ross Blick, Mike Braysher, Peter Caley, Judy Caughley, •Meat Research Corporation Nick Dexter, Chris Dickman, Don Fletcher, •Rural Industries Research and Development Graeme Garn e r, Jack Giles, Garry Grant, Corporation Robert Hadler, Jim Hone, Onko Kingma, Jim Mitchell, Colin Mues, Peter O’Brien, Glenys •International Wool Secretariat Oogjes, John Parkes, Brian Ramsay, Glen •Australian Conservation Foundation Saunders, and Jim Thompson. Dana Kelly contributed significantly to Chapter 9, and •National Consultative Committee on Animal both she and Quentin Hart wrote Appendix A. Welfare Several individuals from the Bureau of •Australian and New Zealand Federation of Re s o u rce Sciences deserve mention. Quentin Animal Societies Hart and Dana Bradford helped copy edit the •National Farmers’ Federation manuscript and figures, and assisted with the final collation and publication. Gregg Berry •Australian Veterinary Association also assisted with copy editing. •Northern Land Council The draft manuscript was circulated to the We thank these groups for their following organisations for comment: contributions. Many other people, too •Commonwealth Department of Primary nu m e rous to acknowledge individually, also Industries and Energy gave us the benefit of their experiences by commenting on drafts of the manuscript. •Standing Committee on Agriculture and Resource Management

Bureau of Resource Sciences ix SUMMARY on reliable quantitative information about the damage caused by pigs, the cost of contro l m e a s u res and the effect that implementing The introduced feral pig or wild boar (Sus c o n t rol has on reducing damage. In s c ro f a) is widely distributed thro u g h o u t developing these guidelines the authors have eastern and northern Australia, with smaller used all such available information. In some populations in the west. Their distribution in instances, however, where reliable infor- inland or seasonally dry areas of Australia is mation is not yet available, land managers restricted to the vicinity of watercourses and responsible for feral pig management will their associated floodplains. In the more have to make assumptions about feral pig forest-covered parts of eastern Australia and south-west We s t e rn Australia, populations impact and the efficacy and cost-effe c t i v e n e s s are still spreading, often through deliberate of control techniques. or accidental releases. Feral pigs prey on lambs and some native animals, trample and Who will use the guidelines? eat crops, could play a role in spreading exotic The guidelines have been prep a red primarily diseases such as foot-and-mouth disease for state and territory land management (should they enter Australia), and cause an agencies as a basis on which to consult with unknown amount of land degradation. Feral private land managers and other re l e v a n t pigs are also an economic resource and are i n t e rest groups and pre p a re state, re g i o n a l hunted commercially and recreationally. and local strategies for reducing the damage These guidelines are a compre h e n s i v e feral pigs cause to agricultural production and review of the history of feral pigs in Australia, the environment. The guidelines should be their biology, the damage they cause, and read in conjunction with Managing Ver t e b r a t e past and current management. The attitudes Pests: Principles and Strategies ( B r a y s h e r of landholders, conservationists, animal 1993), which explains why national pest we l f a re groups, commercial and rec re a t i o n a l guidelines were developed, their aims, the hunters, Aboriginal peoples and other interes t planning process, their use and the principles groups were sought during their prod u c t i o n . on which pest management should be based. Techniques and strategies for feral pig management are recommended and The feral pig problem illustrated by case studies. Deficiencies in Feral pigs are responsible for several types knowledge, management and legislation are of agricultural damage. They prey on identified. ne w b o rn lambs, eat and destroy grain crop s , damage fences and water sources, re d u c e Why develop national guidelines? yields of sugarcane and some tropical fruit These guidelines for managing the impact of c rops, and compete with stock for feed by feral pigs were developed as part of the eating or damaging pasture. There are no Vertebrate Pest Program administered by the reliable estimates of the cost of feral pig B u reau of Resource Sciences. The VPP, in damage to agricultural production, although cooperation with the Vertebrate Pests it is likely that the damage is at least of the Committee of the Standing Committee on order of $100 million annually, and it may be Agriculture and Resource Management, has much more. p roduced a series of pest management Although feral pigs are often regarded as guidelines including ones for feral horses, having deleterious effects on the environ m e n t , rabbits, foxes, feral goats and rodents. there is little objective information available The purpose of these guidelines is to assist on their impact. The most important in developing the most cost-effective strategies en v i ronmental impacts are likely to be habitat to reduce feral pig damage to production and modification through selective feeding, conservation. Ideally, such strategies are based trampling damage and rooting for under-

Bureau of Resource Sciences 1 ground parts of plants and invertebrates; as derived from the export market of wild pig well as predation on, competition with, or meat is paid to shooters and chiller disturbance of, a range of native animals. Most operators, and that re c reational hunting of pe rceptions of environmental damage caused feral pigs also injects considerable funds by pigs focus on their rooting up of soils, into the general community each year grasslands or forest litter, particularly along t h rough money spent by pig shooters. drainage lines, moist gullies and aro u n d swamps and lagoons, or after rain, when the History and biology g round is softer. Their impact on diff e re n t plants is largely unknown, as is the extent of Most feral pigs in Australia are descendants their role as seed eaters or dispersers, and in of various breeds of the Eurasian wild boar s p reading ro o t rot fungus (P h y t o p h t h o r a or the domestic pig, which for various rea s o n s , ci n n a m o m i ), responsible for dieback disease particularly lack of restraint and deliberate in native vegetation. Feral pigs readily eat releases, reverted to living in the wild. animal material, but are probably not Horizontal black stripes on the piglets of many significant predators of most fauna except feral pigs indicate the infusion of Eurasian local populations of earthworms. wild boar genes. Initially, the distribution of pigs was close to major settlements Feral pigs are the main wild animal of th roughout Australia, but as changes occurred co n c e rn in Australia in relation to the potential in the management of rural properties, many s p read of exotic diseases, particularly foot- pigs were left unattended, wandered away and-mouth disease (FMD), the main exotic and established truly feral colonies. disease of concern in Australia. Feral pigs can act as hosts or vectors of several endemic and Once established, colonies of feral pigs exotic diseases and parasites that can affect rapidly built up in many areas. Estimates of other animals, including domestic livestock population size vary between 3.5 million and and people. The major endemic diseases and 23.5 million, inhabiting 38% of Australia, but parasites of concern are leptospiro s i s , their distribution and abundance can vary brucellosis, melioidosis, tuberculosis and markedly from year to year according to sp a rganosis. The involvement of feral pigs in environmental conditions. an exotic disease outbreak could delay The biology and ecology of feral pigs are disease detection; increase the rate and extent two of the major reasons why they are such of disease spread; make disease eradication an important and successful vertebrate pest m e a s u res expensive, time-consuming or in Australia. Their large robust bodies, snouts impossible; and have severe re p e rc u s s i o n s specially developed for rooting up the grou n d , for Australia’s livestock industries. Although om n i v o rous diet and adaptive activity patterns Commonwealth, State and Te r r i t o r y allow them to live in a wide range of habitats. authorities have prep a red contingency plans Feral pigs are habitat generalists and have for dealing with outbreaks of exotic diseases, colonised subalpine grasslands and fore s t s , and have also developed stringent quarantine dry woodlands, tropical rainforests, semi-arid regulations, recent re s e a rch indicates that and monsoonal floodplains, swamps and ou t b reaks of FMD could establish in feral pig other wetlands in many parts of the Northern populations in parts of Australia. Territory, Queensland, New South Wa l e s , other states and the Australian Capital Resource value Territory. Their prime re q u i rements are a The Australian feral pig is taxonomically, reliable and adequate supply of water, food ecologically and physically comparable to and cover. Temporal changes can occur in the European wild boar and there is a their use of habitats to satisfy these significant export of wild pig meat fro m re q u i rements, particularly to obtain shade Australia to European markets. It is estimated and water and exploit seasonally abundant about $5 million of the $10–20 million food sources.

2 Managing Vertebrate Pests: Feral Pigs The re p roductive potential of feral pigs T h e re are currently no biological or is more similar to that of rabbits than to that fertility control agents suitable for use against of other large mammals in Australia. feral pigs. Fecundity increases with age and body weight but can be strongly affected by Integrated management using a range seasonal conditions. Under favourable of c o n t rol techniques produces the best conditions, breeding can occur thro u g h o u t results, but a lack of reliable information on the year and sows can produce two weaned ‘ o n - f a rm’ control costs is seen as a barrier litters every twelve to fifteen months, with to adoption of some techniques. This an average of six piglets per litter. This gives deficiency should be addressed if best feral pigs the capacity to recover quickly practice management is to be widely f rom the effects of management pro g r a m s a d o p t e d . or other setbacks such as droughts. Development of a strategic Techniques to control feral pigs management approach Management of the feral pig problem has Poisoning is a control technique that is been traditionally ad hoc but there is now widely accepted throughout rural a trend towards more strategic and scientific communities. It is perceived as a method management. Before the 1970s no re s e a rc h which, if properly used, can produce a quick had been conducted on feral pig biology, knockdown of feral pig populations. The ecology or management and land managers negative aspects of poisoning are associated typically used shooting, bounties and with its non-specificity and welfare poisoning with either strychnine, arsenic or implications. The success of a 1080 poisoning phosphorus, as control tools. p rogram revolves around adequate fre e - feeding with non-toxic bait to attract pigs. Since the 1970s considerable work has C S S P, a yellow phosphorus-based poison, is been done to evaluate and impro v e e ffective in killing pigs but there are serious trapping, poison efficacy and bait doubts about its humaneness. Wa rfarin, an acceptance, fence design and shooting fro m anticoagulant, is a poison readily accepted helicopters as control tools. This work has by feral pigs. It is very effective if extended coincided with the phasing out of bounties feeding is practiced. Despite this, no and the introduction of coord i n a t e d Australian states or territories have reg i s t e re d management using landholder groups. The w a rfarin for feral pig contro l . success of the coordinated approach was validated by numerous programs conducted Shooting from helicopters is time-effi c i e n t in New South Wales which pro d u c e d and provides a quick knockdown to pro t e c t positive outcomes in the way of decre a s e d susceptible enterprises from short-term lamb predation and crop damage for damage. Pig populations recover rapidly participants. Both Queensland and New between shooting episodes. Shooting fro m South Wales have a policy of encouraging the ground, with or without dogs, is the use of coordinated management. generally considered to play an insignificant role in damage control except where it is C u r rent management is incre a s i n g l y intensively conducted on small accessible sensitive to environmental and animal welfare p o p u l a t i o n s . issues. Increasing effort is expended to ensure that techniques and methods are sensitive to Trapping can be effective, but results are the community’s needs in this regard. variable, being affected by season, trap type and site, pre-baiting techniques and trapping F u t u re management of feral pig damage f requency. Trapping is a flexible technique can be enhanced by improved training of that can be fitted into routine pro p e r t y c o n t rol agency staff in extension and the a c t i v i t i e s . facilitation of stakeholder groups. Lack of

Bureau of Resource Sciences 3 such skills can be a serious barrier to the rapid feral pig management strategies; an adoption of best practice management by understanding of why the actions of landholders. individual land managers may not lead to optimum levels of pig control; and how What is the strategic management such problems can be addressed. approach? Implementation — The most eff e c t i v e The emphasis in these guidelines is on the approach is to coordinate management of strategic management of feral pigs to minimise feral pig damage on a local and re g i o n a l the damage they cause to production and level, involving cooperative action by land conservation values, not merely to kill pigs. managers, both private and public, Feral pigs need to be considered as one factor government agencies and industry. in a complex and changing system which Monitoring and evaluation — Monitoring includes a highly variable climate, fluctuating has two aspects. Operational monitoring commodity prices, other animal and plant assesses the efficiency of the management pests, the number and quality of farm stock, strategy over time, particularly to determi n e and the profitability of farming businesses. whether it is being carried out in the most Achieving a strategic approach to the c o s t - e ffective manner. Perf o rm a n c e management of feral pigs and other vertebrate monitoring gathers information by which pests involves four key components. These the effectiveness of the strategy in meeting are: the desired long-term production or conservation objectives can be determi n e d . Defining the pro b l e m — The problem first Evaluation of data from both forms of needs to be determined in terms of the monitoring can help determine if and how impact of feral pigs on a valued resource, the management strategy should be be it economic or environmental. The next modified. step is to quantify the impact which may re q u i re experimental assessment of the The above approach has been adopted for damage. developing these national guidelines, and the information in this publication is Management plan — In developing a designed to facilitate the development of management plan, it is essential that clear strategies for managing feral pigs at the local objectives are established, where v e r and regional level. practicable in terms of the desire d p roduction and/or conservation outcome Community attitudes sought, relative to the costs of contro l . Options for feral pig management include The feral pig is considered by the community local eradication, strategic management to be many things: agricultural pest, endemic ( t a rgeted, sustained or one-off), crisis and exotic disease hazard, enviro n m e n t a l management, commercial harvesting or no liability, export commodity and recreational management. In light of the objectives, and res o u rce. These attitudes have varied throu g h the choice of management options, a time and location. Although the status of feral management strategy should be developed pigs as an agricultural pest was responsible based upon the techniques available for pig for raising their profile initially, the feral pig control. is no longer simply reg a rded as an agricultural pest and environmental threat, but also as a Economic frameworks need to be contributor of significant income to rural developed to assist land managers to assess communities through re c reational and the relative value of alternative contro l commercial hunting. strategies. Such frameworks re q u i re : definition of the economic problem; data The multiple use of feral pigs leads to on relative costs and benefits of diff e re n t conflict within the rural community as well

4 Managing Vertebrate Pests: Feral Pigs as within the general community. The en v i ronmental damage with economic losses significant benefits from the game meat caused by pigs to agriculture. export industry and re c reational hunting are The major poisons used to control feral politically attractive. Despite arguments from pigs in Australia are 1080 and CSSP. Extensive some rural groups that commercial and work has been conducted on the threat 1080 re c reational use of feral pigs is incompatible poses to non-target species but no studies are with their effective management, experience known to have been conducted or reported suggests otherwise. There is an incre a s i n g on CSSP, despite its longstanding and acceptance among communities that widespread use as a feral pig control agent. multiple-use management of feral pigs is both practical and appro p r i a t e . There are no reliable data on how much it costs property managers to control feral The future pigs. Land managers need better informa t i o n on the types and extent of damage caused by M o re information in some key areas is feral pigs and on control costs. This will essential if the strategic approach to feral pig enable a change in management philosophy management is to be developed further. f rom one focussed on killing more pigs to Although the biology and ecology of feral one focussed on cost-efficiently reducing the pigs in most major habitats in Australia is damage caused by pigs. generally well understood, there is limited i n f o rmation about pigs for some parts of Adoption of the national guidelines will re q u i re a change in understanding and tropical Australia, especially in rainforests. behaviour at various levels, ranging from land Two of the basic weaknesses in being able managers to policy makers and officers of to determine priorities for where to contro l state agencies. Currently, few extension staff feral pigs in many areas of Australia are the a re trained in the principles of education, lack of objective, quantitative data on the sociology or psychology, all key elements impact of pigs on the environment, and a associated with facilitating a change in means of comparing the cost of this behaviour in individuals or groups.

Bureau of Resource Sciences 5 INTRODUCTION Conservation of Australia’s Biological Diversity. Applying the strategic appro a c h to the management of pigs and other These guidelines for managing feral pigs vertebrate pests involves four key com- a re one in a series pre p a red as part of the ponents as shown in Figure 1. This approa c h Vertebrate Pest Program of the Bureau of f o rms the basis of these national guidelines. R e s o u rce Sciences in cooperation with the Vertebrate Pests Committee of the Standing Committee on Agriculture and Resourc e Defining the problem Management. Other guidelines include feral Feral pigs are estimated to cause losses to horses, rabbits, feral goats, foxes and agricultural production in Australia in the rodents. o rder of at least $100 million each year, The need for a new approach to although this might be a substantial under- vertebrate pest management is described in estimate. Although feral pigs are often Managing Vertebrate Pests: Principles and re g a rded as having deleterious effects on S t r a t e g i e s (Braysher 1993), which explains the environment, there is little objective why national guidelines for managing pest i n f o rmation. Determining the nature and animals were developed, the management extent of the economic or enviro n m e n t a l p rocess, and the principles on which pest t h reat due to feral pigs re q u i res knowledge management should be based. The need to of their status and biology. Thus, Chapter 1 focus on the damage caused by the pest and describes the history of their intro d u c t i o n not the pest itself is stre s s e d . and spread; Chapter 2 their distribution and abundance; and Chapter 3 their biology. As acknowledged in Managing Ver t e b r a t e Pests: Principles and Strategies, a set of Chapter 4 reviews the evidence concerni n g guidelines for all vertebrate pests, taking the economic and environmental impact of into account the links between them, and feral pigs in Australia. It also re v i e w s other aspects of land management, would co m m e rcial use of feral pigs. Public attitudes have been more desirable than the single can strongly influence the perceived nature species approach adopted in these of feral pigs as a re s o u rce or as a pro b l e m , guidelines. This would have been consistent and these issues are reviewed in Chapter 5. with the holistic approach to land manage- Past and current management of feral pigs ment advocated under the Ecologically and their legal status are discussed in Chapter Sustainable Development (ESD) Strategy 6. The impact of feral pigs can be assessed in and the National Landcare Program (NLP). several ways, and these are reviewed in Although this was not practicable, all the Chapter 7, together with the efficacy of guidelines, including this one for feral pigs, techniques to reduce these impacts. In many consider interactions between species and cases, feral pig impact on one property or other aspects of land management. a rea is influenced by their presence in neighbouring properties or areas. Thus many The guidelines are principally for state people or agencies, including governments and territory land management agencies to and the community, jointly own feral pig assist them more effectively manage feral p roblems and need to seek solutions pig damage through better coord i n a t i o n , cooperatively. planning and implementation of local and regional management programs. The Commonwealth Government also has a Management plan major interest in the effective management The objective of the national guidelines is to of feral pest damage both through its stimulate a change in approach to feral pig responsibilities as a land manager, and management from ad hoc measures by t h rough various initiatives such as the NLP individuals and agencies to a strategic and the National Strategy for the management approach based on cooperative

Bureau of Resource Sciences 7 Fi g u re 1: Strategic approach to managing feral pig damage (after Braysher 1993). action. Adopting a whole property approa c h p roduction or conservation outcome by the to management, preferably integrated into a most cost-effective means consistent with regional or total catchment plan, is advocated ecologically sustainable use of the since it can help manage the risks posed by management system. In many cases lack of feral pigs. knowledge may initially prevent ident- The guidelines will have succeeded in ification of the best strategy. A flexible meeting this objective when the strategic ap p roach, however, where the land manager a p p roach they advocate is accepted and evaluates the benefits of management action implemented by a significant number of and continually modifies it in the light of agencies and individuals. experience (that is, ‘learning by doing’) is often the best approach. Chapter 8 describes Several management options are identi- how such a management strategy can be fied and discussed in Chapter 8, including d e v e l o p e d . local eradication, strategic sustained management, commercial management, Implementation crisis management and no management. T h e re are many ways of managing pig These guidelines for managing feral pig damage, including poisoning, exclusion, damage encourages the group approach at trapping, and shooting from the ground or the local and regional level. This involves helicopters. Ideally the management strategy all land managers and others with a should aim to achieve the desire d significant interest in feral pig management

8 Managing Vertebrate Pests: Feral Pigs cooperating at an early stage in planning Chapter 10 looks to the future and and implementation. Chapter 8 describes a d d resses re s e a rch and management the features of such an approach for d e v e l o p m e n t s . implementing management plans. At the national level, such an appro a c h Strategic management at the local re q u i res that the various roles and and regional level responsibilities of government agencies, This document sets out best practice feral g roups and individuals are taken into pig management at the national level based account and integrated. The Commonwealth on current knowledge. It brings together Go v e rnment is involved in pest management the best available information on eff e c t i v e as a manager of Commonwealth land, feral pig management, as a basis for better t h rough its responsibilities in exotic disease management of the damage they cause. p re p a redness and overseas trade and t h rough the threat that pests pose to such The challenge for local and regional land national initiatives as the National Landcare managers and others with a major stake in P rogram, the ESD strategy and the National the outcome of feral pig management is to Strategy for the Conservation of Australia’s use the information and processes described Biological Diversity. State and territory in this book to develop a strategic g o v e rnments are responsible for pro v i d i n g management plan to address the damage the legislative and regulatory framework, caused by feral pigs. Chapter 8 explains how a d m i n i s t e red through pest control agencies. this might be achieved, and pro v i d e s hypothetical examples of its application. At the local level, responsibility for pest management lies with the landholders and occupiers, whether government or private. Vertebrate Pest Program The active participation of the Ve r t e b r a t e In its Environment Statement of December Pests Committee in developing these 1992, the Commonwealth Govern m e n t guidelines is thus important in obtaining their p rovided increased re s o u rces to complete acceptance and implementation. Chapter 9 the guidelines for managing Australia’s major reviews these issues and also addresses the vertebrate pest species and to establish key role of extension services and group action demonstration projects to facilitate adoption for implementing effective feral pig of best practice pest management. Pro j e c t s m a n a g e m e n t . draw on the management strategies outlined in the relevant guidelines for each species. Monitoring and evaluation For most projects, including management of feral pigs, it is anticipated that best practice Monitoring is an essential component of the management will evolve based on experience strategic management approach to enable gained from strategic management. Using managers to determine whether their the management system to refine pest management strategy needs to be modified. management strategies is called adaptive Operational monitoring aims to assess the management, or ‘learning by doing’. e fficiency of the implementation of the management strategy so that areas where It is expected that community-based e fficiency can be improved are identified. g roups will become more involved in the Chapter 7 reviews techniques for assessing strategic management of vertebrate pests. the cost-effectiveness of control. Perf o r- The guidelines are designed to facilitate the mance monitoring seeks to evaluate the ownership of the pest problem by such local outcome of the management plan; that is, groups, and the management strategy which whether the goals set initially in terms of might be developed and implemented based p roduction or conservation outcomes are on them. Accordingly, the Vertebrate Pest being met. Methods of evaluating such P rogram (VPP) gave pre f e rence to pro j e c t s outcomes are also described in Chapter 7. which involved collaboration between

Bureau of Resource Sciences 9 several appropriate government and/or non- in areas primarily used for conservation. g o v e rnment agencies and involved P rojects which addressed both agricultural community-based groups in their design and and conservation damage by pests were implementation. The VPP supported proj e c t s jointly funded. It is intended that these which addressed the impact pests have on guidelines and the results of the VPP and FPP primary production. The complementary p rojects will assist state and territory Feral Pests Program (FPP) administered by g o v e rnments in their role of pro v i d i n g the Australian Nature Conservation Agency legislative, technical and policy support for gave priority to strategic pest management feral pig management.

10 Managing Vertebrate Pests: Feral Pigs 1. History pigs, and hence to feral pigs in Australasia, the Americas and Oceania (Clarke and Dzieciolowski 1991). During the 18th and Summary early 19th centuries, European domestic pigs Most feral pigs in Australia are descendants (S. scrofa scro f a), such as the Berkshire , of various breeds of the domestic pig S u s we re extensively modified by cros s - b re e d i n g s c ro f a , which for various re a s o n s , with Chinese S. scrofa moupinensis, Indian particularly lack of restraint and deliberate S. scrofa cristatus and pigs from Naples and releases, reverted to living independently of Portugal (Epstein and Bichard 1984). Such people. The main founder breeds were highly modified domestic breeds, many of p robably the European Berkshire and which were partly or wholly Asian in origin, Tamworth, which had already been gre a t l y f o rm the basis for the modern European pig modified by cros s - b reeding with other bree d s industry. These and other impro v e d from China, India, Italy and Portugal. Some E u ropean breeds (for example, the S. celebensis, brought from Timor and Kisar Tamworth) were the pigs mostly taken by to early settlements on the Coburg Peninsula e x p l o rers, mariners and settlers on 18th and last century, may also have established in early 19th century voyages to Australia and the Northern Territory and ‘S. papuensis’, New Zealand (Clarke and Dzieciolowski a hybrid between the two species from New 1 9 9 1 ) . Guinea may have been released in some a reas of Queensland in the past. Initially, 1.2 Introduction and spread the distribution of pigs was closely correl a t e d with major settlements throughout Australia, in Australia but as changes occurred in the management It is not known when pigs were first of rural properties, many pigs were left successfully introduced into Australia. unattended, wandered away and Captain Cook presented some pigs to the established truly feral colonies. Maori and released others during his second and third voyages to New Zealand during 1.1 Origin of feral pigs in 1773–1777 (McIlroy 1990; Clarke and Australia Dzieciolowski 1991). These included pigs f rom Capetown (presumably of Euro p e a n Feral pigs (Sus scro f a) belong to the small origin) and some Polynesian pigs of Indo- Old World Family Suidae of nine species Malay origin (possibly Sus scrofa vittatus) , classified into five genera: B a b y ro u s a obtained from Tongatapu (Tonga Islands) (babirusa); Phacochoerus (wart hogs); and Huahine (Society Islands). Cook’s Hylochoerus (giant forest pigs); diaries, however, make no mention of the Potamochoerus (bush pigs); and Sus ( w i l d release of pigs in Australia except for a boar bo a r, feral and domestic pigs). All have large , and a sow that were set free on Bruny Island long heads with mobile snouts used for in Tasmania in 1777, which he expected to rooting up the ground, short necks and be killed by the Aborigines (no signs of pigs p o w e rful, stocky bodies with coarse, bristly w e re seen on the island by the Baudin c o a t s . expedition in 1802; Statham and Middleton Feral pigs can be distinguished from three 1987). The diaries also note that one piglet, of the four other species of Sus (S. barbatus, f rom a sow and piglets being kept ashore S. celebensis and S. verrucosus) by their lack while Cook careened the Endeavour near of facial warts, hair type and skull characters the present Cooktown in north Queensland, ( G roves 1981), and from the fourth, the was scorched to death by a fire deliberately pygmy hog (S. salvanius), by their larg e r lit by the Aborigines (Pullar 1953). Pigs could size, longer tail and six pairs of nipples have been introduced onto Cape York fro m instead of three (Cumming 1984). Sus scro f a Papua New Guinea before then, but this and its subspecies gave rise to most domestic seems unlikely given the apparent lack of

Bureau of Resource Sciences 11 a word for ‘pig’ in the languages of the Pigs became feral and subsequently Aboriginal peoples (Pullar 1950; Pavlov et s p read by unrestrained domestic stock al. 1992). Pullar (1953), however, re c e i v e d wandering away, accidental escape of reports indicating pigs may have been domestic stock when farm buildings were i n t roduced into Cape York from Papua New i n s e c u re or when trucks were damaged or Guinea late last century. o v e r t u rned, and deliberate releases of feral pigs to start new colonies or to improve the The New Guinea pig (the so-called S u s c o n f o rmation of existing feral pigs (Pullar pa p u e n s i s ) is a hybrid between domesticated 1953). Such releases and spread continue S. celebensis and imported, domesticated S. t o d a y . s c rofa vittatus ( G roves 1981). Some S. c e l e b e n s i s w e re brought to the Melville ‘The first official r e c o rd of Island and Coburg Peninsula settlements in pigs in Australia is that of 49 the Northern Territory from Timor and Kisar, hogs in the First Fleet.’ between 1824 and 1843 (Letts 1962; Calaby Initially, the distribution of feral pigs was and Keith 1974). Some of the pigs on Melville closely correlated with settlement, where Island wandered at liberty, while pigs until about the middle of the 19th century considered to be the offspring of a boar and they were kept under semi-feral conditions. several sows left at Raffles Bay in 1829, when In some areas they quickly became the settlement was abandoned, were nuisances, such as around the settlement of observed in the forests around Port Essington Sydney Cove by 1795 and in Lonsdale Stree t , in 1843 (Letts 1962). Leichhardt reported that M e l b o u rne in the 1840s. After about 1865, at Port Essington a good number of pigs when the fencing-in of properties became strayed away into the bush (Calaby and Keith general practice and many original runs and 1974). Although signs of pigs are not common stations were subdivided, a considerable in the area today (Calaby and Keith 1974), number of pigs were left unattended and there is a chance that S. celebensis, S. scrofa became truly feral. The main established and ‘S. papuensis’ may all occur in some colonies of pigs then, according to Pullar northern parts of Australia (Groves 1981). (1950, 1953), were in the greater part of The first official record of pigs in Australia Queensland and the Northern Territory, the is that of 49 hogs (one boar, nineteen sows, Upper Darling and Lachlan–Murrumbidgee others not defined) after the arrival of the First Junction, the Darling Ranges in We s t e rn Fleet in Sydney (Rolls 1969). From then on Australia and on Flinders and Kangaro o the introduction and spread of pigs is unclear, Islands (in the latter two cases, aided by but various breeds or subspecies of S. scrofa releases from sealers and other mariners). w e re probably brought to Australia fro m By the 1880s pigs had run wild in New South di ff e rent countries by trading ships and many Wales and were such a nuisance that they pedigree pigs were imported from England w e re being shot (reportedly in thousands in the 1820s (Anon. 1983). in the Riverina) and poisoning of them was about to begin (Rolls 1969).

12 Managing Vertebrate Pests: Feral Pigs 2. Distribution and Wales is directly related to the location of inland watercourses and their associated abundance flood plains. Feral pigs can tolerate high ambient temperatures only where both Summary drinking water and dense vegetation for Feral pigs are generally sedentary animals, shelter are available (Wilson et al. 1992a). but may become semi-nomadic in Natural spread along watercourses into these e n v i ronments where there are marked a reas depends on good seasons and has changes in the availability of food and l a rgely occurred only during the last 40 to w a t e r. The most critical factors aff e c t i n g 80 years (Pullar 1953). McKnight (1976), for their distribution in Australia are their poor example, provides reports of feral pigs heat tolerance and the accompanying need s p reading widely throughout Queensland’s for access to daily water and dense shelter. Channel Country between 1913 and 1921, This largely restricts their distribution to the to the Cobar and Hillston districts of New vicinity of watercourses and associated South Wales and well back from the Darling floodplains in inland or seasonally dry River around Bourke (from the Walgett and a reas of Australia. These factors are less M o ree districts and marshes on the critical in the more fore s t - c o v e red parts of Macquarie and Lachlan Rivers) during a e a s t e rn Australia and south-west We s t e rn succession of good seasons in the early Australia, where populations are still 1950s, and into the Cunnamulla area since s p re a d i n g . 1 9 5 0 . Once established, colonies of feral pigs ‘The distribution and spread of rapidly build up in many areas. Because feral pigs in inland Queensland estimates of pig numbers are subject to and New South Wales is along many sources of variation, total numbers w a t e rcourses and their of pigs in Australia could be anywhere flood plains.’ between 3.5 million and 23.5 million. They N u m e rous isolated populations of feral inhabit 38% of the continent, but their pigs have also appeared in eastern distribution and abundance can vary Queensland and New South Wales over the markedly according to enviro n m e n t a l last 30 years, particularly in the tablelands conditions from year to year. Densities in and coastal areas (Hone and Waithman 1979; d i ff e rent habitats vary from about one pig Wilson et al. 1992a). In many cases the per square kilometre in drier eucalyptus founding animals for these populations were woodland, forests and grazing land to ten p robably deliberately released by hunters, to twenty pigs per square kilometre, and rather than being a product of natural possibly higher, in wetlands and seasonally d i s p e r s a l . inundated floodplains. In the Australian Capital Territory an unstated number of pigs were released in 2.1 Distribution in Australia the Boboyan district in 1900 and others Feral pigs are now widely distributed in escaped or were released into the general Queensland, the Northern Territory, New a rea between 1959 and 1968 (Bore h a m South Wales, and the Australian Capital 1981). Since then, the pigs have dispersed Territory (Figure 2). Isolated populations th roughout most rural areas in the Australian occur in Victoria, Kangaroo Island in South Capital Territory and adjacent parts of New Australia, in Wes t e rn Australia and on Flinders South Wales. Some unauthorised re l e a s e s Island in Bass Strait. In Tasmania, accidental still occur. releases lead to small, temporary populations. Populations of feral pigs in Victoria are The distribution and spread of feral pigs small, local, but widespread, and are in western Queensland and New South indicative of deliberate liberations

Bureau of Resource Sciences 13 Fi g u re 2: Distribution of feral pigs in Australia (after Wilson et al. 1992a).

( Townsend 1981). Accidental releases in the extensive floodplains and adjacent Tasmania lead to small populations woodlands close to the coast (Bayliss and occupying areas of private and Crown land. Yeomans 1989). They tend to concentrate Dispersal is contained by rangers and local near watercourses and billabongs, but during hunters (G. Atkinson, NPWS, Ta s m a n i a , the wet season they range further throu g h o u t pers. comm. 1995). On Flinders Island in the open forest country. Their main Bass Strait about 1000 pigs inhabit the north distribution extends from the Moyle River and and east coast lagoon areas, Strzelecki the northern catchment of the Victoria River National Park and Darling Range (Statham to the eastern edge of the Arnhem Land and Middleton 1987). In We s t e rn Australia escarpment, but occasionally they are feral pigs occur in four main areas: the river observed further east of this, including along systems of the east and west Kimberley; the the Roper River (Letts 1964; Bayliss and Pilbara; north-west lower Murchison and Yeomans 1989). Like buffalo (B u b a l u s Geraldton areas; and the river systems, b u b a l i s), they have colonised forest and swamps and forest country in the south- woodland scattered throughout the sandstone west of the state (Long 1988). plateau. Feral pigs also occur on Bathurst In the Northern Territory feral pigs occur Island but none are now known to occur on mainly in higher rainfall areas, particularly on Melville Island (Bayliss and Yeomans 1989).

14 Managing Vertebrate Pests: Feral Pigs ‘Feral pigs are still colonising (Caughley 1970). Once established, they parts of Australia.’ i n c reased rapidly. In some areas pig populations remained high for a period and Feral pigs are normally sedentary animals, then declined, through either depletion of generally confining their movements to a their pre f e r red foods or cover by land defined home range. This reluctance to leave development, increased control efforts or their home range may explain why they are the effect of droughts. In other are a s still colonising parts of Australia. In the management practices, particularly crop p i n g N o r t h e rn Territory feral pigs were observed and the provision of stock watering sourc e s , near the Liverpool River in east Arn h e m have allowed pigs to remain at moderately Land for the first time during the mid-1980s high densities, while in some areas they are (Caley 1993). If these pigs were descendants still increasing and spre a d i n g . of the original pigs that escaped or were released at Port Essington 240 kilometre s In many areas major concentrations of away in the mid-1800s, the dispersal rate feral pigs built up during both World Wa r s would be about two kilometres per year. (as also occurred in New Zealand, McIlro y 1990), because of a shortage of hunters, rifles, ammunition and petrol for transport 2.2 Changes in abundance (Pullar 1953). Since then, their numbers have The changes in abundance of feral pigs in fluctuated. Some colonies have died out, Australia, both in time and location, are while others have started, particularly similar to the irruptive pattern observed in t h rough releases, and there has been pig and other ungulate populations considerable variation in the extent of range following their liberation in other countries they inhabit from year to year. Hone (1990a)

Feral pigs are widely distributed in Queensland, the Northern Territory, New South Wales and the Australian Capital Te r r i t o r y . Source: P. O'Brien, BRS

Bureau of Resource Sciences 15 estimated that feral pigs now inhabit about be interpreted with great caution because 38% of Australia and there could be 13.5 of the inadequate data that can be used as million (with 95% confidence intervals of 3.5 a basis for such estimates and the stro n g million to 23.5 million) of them in Australia. evidence that population size of feral pigs This estimate encompasses the three other is not constant from year to year, but is most recent estimates of the numbers of pigs d e t e rmined by environmental influences. in Australia (Flynn 1980; Tisdell 1982; Cutler 1989). Hone (1990a), however, re c o m - Estimates of the abundance of feral pigs mended that any current estimates of in diff e rent habitats at diff e rent locations abundance of feral pigs in Australia should t h roughout Australia are shown in Table 1.

Table 1: Estimates of abundance of feral pigs in various locations and habitats in Australia.

Location Density (pigs per Habitat Source square kilometre)

South-west Western Australia 1–4 Forest Masters (1979) Warren, New South Wales 8.0–17.5 Wetlands Giles (1980) Yantabulla, New South Wales 0.2–0.8 Semi-arid Giles (1980) rangelands Flinders Island, Tasmania 0.5–3.0 Forest and swamp Statham and Middleton (1987) Goondiwindi, Queensland 0.1–3.9 Pasture, woodland, Wilson et al. (1987) forests and wheat crops Kosciusko National Park, 1.1 Forest Saunders (1988) New South Wales Macquarie Marshes, 10.3 Wetlands Saunders and Bryant New South Wales (1988) Namadgi National Park, 1.8 Forest McIlroy et al. (1989) Australian Capital Territory Aurukun, Queensland 1–>20 Floodplain, swamp Dexter (1990) and woodland Adelaide River, 2.6–10.9 Paperbark swamp Hone (1990b) Northern Territory 2.2–10.2 Open floodplain 0–1.2 Dry woodland Mary River, 6.1 Floodplain and Hone (1990c) Northern Territory woodland Sunny Corner, 2 Pasture, forest Saunders and Kay New South Wales and woodland (1991) Kapalga, <1 Open forest and Ridpath (1991) Northern Territory woodland Douglas–Daly area, 0.8–3.5 Woodland and Caley (1993) Northern Territory crops Nocoleche Nature Reserve, 0.2–1.5 Semi-arid Choquenot (1994); New South Wales rangelands Dexter (1995) Paroo River, 0.2–1.2 Floodplain and Dexter (1995) New South Wales woodland

16 Managing Vertebrate Pests: Feral Pigs 3. Biology and ecology a n o t h e r, in their search for food, or in response to major prolonged disturbance by people. But most pigs retain a stro n g Summary fidelity to their home ranges, even when The biology and ecology of feral pigs make subjected to minor disturbance, such as them important and successful pests in i n f requent hunting by people and dogs. Australia. Their large robust bodies, Although adult boars are invariably specially developed snouts for rooting up solitary, and farrowing sows will tem- the ground, omnivorous diet and adaptive porarily separate themselves from other pigs, activity patterns allow them to live in a wide feral pigs are mostly social, gre g a r i o u s range of habitats. Some variation occurs in animals. The basic group consists of one or physical size, shape and coat colour between mo re sows and their piglets, but other grou p s d i ff e rent regional populations. Overall, feral consist of young females, bachelor gro u p s pigs are smaller, leaner and more muscular of young males and other combinations. than domestic pigs, with well developed Group sizes vary considerably, ranging from shoulders; longer, larger snouts and tusks; 1–12 up to 40 –50 in diff e rent seasons and s m a l l e r, mostly pricked ears; coarser hair a reas. Mobs of more than 100 can gather and straight rather than curly tails. Males a round remaining waterholes in dry tend to be longer and heavier than females s e a s o n s . and have larger heads and tusks. Home range sizes are determ i n e d Feral pigs are habitat generalists and primarily by re s o u rce abundance, and have colonised subalpine grasslands and secondarily, by population density and body f o rests, dry woodlands, tropical rainfore s t s , size. Boars have larger daily, seasonal and semi-arid and monsoonal floodplains, overall home ranges than sows. Activity swamps and other wetlands in many parts p a t t e rns depend on the location, weather of Australia. Their prime re q u i rements are and the degree of disturbance from people. a reliable and adequate supply of food, Feral pigs tend to be more nocturnal or water and cover. Their opportunistic feeding c repuscular during hot weather or when habits and omnivorous diet allow them to they are subjected to disturbance, and more exploit various temporarily abundant food d i u rnal in cooler climates. s o u rces, such as fruits and seeds, foliage The re p roductive potential of feral pigs and stems, rhizomes, bulbs and tubers, is more similar to that of rabbits than to fungi and animal material. Feral pigs have that of other large mammals in Australia. relatively high energy and pro t e i n Under favourable conditions, breeding can re q u i rements, particularly during pre g - occur throughout the year, but where food nancy and for successful lactation and availability and quality is variable, bree d i n g g rowth of young. These re q u i re m e n t s is usually seasonal. Adult females have a cannot always be met by the seasonal 21-day oestrus cycle, a gestation period of availability of foods in any particular are a . about 113 days, and as soon as they re a c h Consequently feral pigs often move to other 25 kilograms in weight are able to give birth parts of their home range that are better to an average of five or six piglets. Fecundity s o u rces of the foods they re q u i re, including i n c reases with age and body weight but can agricultural crops. This seasonal need for be strongly affected by seasonal conditions. either more food, or high energy or pro t e i n - Under favourable conditions sows can rich food, is both the reason for their impact p roduce two weaned litters every 12–15 on agriculture and the environment and months, providing them with the capacity a weakness in their ecology that can be to recover quickly from control pro g r a m s exploited for management purposes. or other setbacks such as droughts or floods. Individuals can move up to 55 kilometre s , Mortality of young piglets is generally high, particularly from one watercourse to especially from starvation and loss of

Bureau of Resource Sciences 17 contact with their mothers, ranging fro m tusk-like canines, rounded body contours, 10 –15% when food supplies and weather and short legs with four toes (two of which are favourable, up to 100% when conditions have been modified to large dewclaws in a re poor. Adult mortality can vary fro m pigs). In contrast, the ruminant artiodactyls 15 –50% with few pigs living beyond five (for example, camels, deer, giraffes, cattle, years of age. Dingoes and feral dogs can sheep and goats) are specialist herbivore s , p rey on substantial numbers of young pigs with ridged, often high-crowned molars, a but it is not clear if they limit the size or m u l t i - c h a m b e red stomach, and often longer distribution of pig populations. legs and only two functional toes. Feral pigs are subject to many infectious diseases and parasites, including some 3.1.1 Morphology economically important exotic diseases, Feral pigs in Australia are smaller, leaner and such as foot-and-mouth disease, and mo re muscular than domestic pigs, with well endemic diseases and parasites, such as developed shoulders and necks and smaller, l e p t o s p i rosis, brucellosis, and melioidosis, shorter hindquarters. They also have longer, that can affect the health of domestic l a rger snouts and tusks, smaller, mostly livestock or people. Several parasites are pricked ears (not pendant like those of many important in terms of domestic livestock or domestic pigs) and much narrower backs. public health. Older boars usually develop keratinous The population dynamics of feral pigs plaques or shields up to three centimetre s have been studied in various habitats in thick on their shoulders and anterior flanks, Australia, although in detail only in the which provide some protection from serious semi-arid rangelands and the wet–d r y injury during fights with other boars. Their t ropics. In both of these habitats rate of hair is sparse and longer and coarser than that change in population abundance is driven of domestic pigs. Some individuals develop by food availability. In the wet–dry tro p i c s , a crest or mane of bristles extending fro m food availability varies in a re a s o n a b l y their neck down the middle of their back; up consistent pattern with the annual cycle of to ten centimetres long on the neck, wet and dry seasons. In the rangelands, diminishing to one centimetre nearer the tail, food availability varies with rainfall and hence the nickname razorback. These bristles flooding. There is evidence that food and often stand erect when the pig becomes p redation operate together to regulate the enraged (Giles 1980). The tails of feral pigs abundance of feral pig populations in the a re usually straight with a bushy tip rather south-east tablelands and subalpine reg i o n s . than curly as in domestic pigs. Little is known about the dynamics of feral ‘Feral pigs in Australia pig populations in the wet tro p i c s . a r e smaller, leaner and m o re muscular than 3.1 General description domestic pigs.’ Feral pigs in Australia generally more closely Males tend to be longer and taller than resemble Eurasian wild boar than domestic females, have larger heads, and are up to pigs. Pigs belong to the Order Artiodactyla, 10–20 kilograms heavier when one year old or even-toed ungulates, the largest and most (Australian Meat Research Committee 1978, diverse group of large land-dwelling Masters 1979, 1981; Pavlov 1980, 1983). mammals living today. Like their closest Body weight depends on habitat conditions relatives, peccaries (Family Ta y a s s u i d a e ) but adults generally range up to 115 and hippopotamuses (Family Hippopota- kilograms for males and 75 kilograms for midae), they are non-ruminant mammals females. Feral pigs in the temperate fore s t s that are primarily omnivorous, with low- of New Zealand may grow to over 200 c rowned molars with simple cusps, larg e kilograms (McIlroy 1990) and in Namadgi

18 Managing Vertebrate Pests: Feral Pigs National Park, near Canberra, a 175 kilogram to poorly developed domestic pigs, are boar was caught (J. McIlroy, unpublished). p robably progeny of more recent additions Lactating sows usually weigh less than non- (Pullar 1953). Colour patterns vary both lactating sows of the same age. Av e r a g e within and between areas. Black is, and body length of adults is 105–155 centimetres a p p a rently always has been, the most for males and 100–130 centimetres for common colour (Pullar 1953; Pavlov 1983). f e m a l e s . Other colours include rusty red and a high p roportion of lighter or mixed colours, 3.1.2 Colour including white, light ginger, brown and white, brown with black spots and agouti Regional populations of feral pigs vary in pa t t e rned (brown or black hair with a lighter physical size, shape and coat colour, tip). The agouti pattern is more typical of d i ff e rences probably inherited from the pigs in north-west New South Wa l e s , b reeds which initially escaped or were wh e reas black pigs predominate further east released. Pullar (1953) described two (Australian Meat Research Committee 1978). e x t remes of feral pigs as early and re c e n t Some piglets are marked with dark types but recognised that there was a larg e longitudinal stripes, which disappear as they and varied range of intermediate forms. The grow older (Wilson et al. 1992a). Such stripes sm a l l e r, mainly black or dark red early types, a re rarely seen in domestic pigs, but occur which were in decline in the 1950s, were in wild Sus scrofa, S. celebensis a n d p e rhaps the direct descendants of pigs ‘ S. p a p u e n s i s ’ . which escaped or were liberated 90 to 140 years ago. The larger recent types, similar 3.1.3 Facial characteristics

The young of some feral pigs are marked with longitudinal stripes which are rarely seen in domestic p i g s . Source: P. O'Brien, BRS

Bureau of Resource Sciences 19 The nostrils of pigs face forward on the end water and cover for seclusion and prot e c t i o n of their blunt, rounded snouts, which are f rom extremes of temperature (Pullar 1950; flattened and strengthened by a cartilaginous Australian Meat Research Committee 1978). plate supported by prenasal bones (Gro v e s Details on movements of pigs between and Giles 1989). Their eyes are small and habitats are given in Section 3.3.2. their eyesight poor, but their senses of smell and hearing are well developed. Their dental 3.3 Food and movements f o rmula is I 3/3 C 1/1 PM 4/4 M 3/3 = 44. The permanent teeth are in place by 20– 2 2 3.3.1 Food months old. The continuously gro w i n g Pigs have a single stomach, with a poor canine teeth (tusks) of adult males are larg e r capacity to digest cellulose, so they cannot than those of domestic pigs and project from feed solely on roughage as ruminants do. the sides of the mouth. The lower tusks are Instead, they are opportunistic omnivore s , triangular in cross section and curve with strong pre f e rences for succulent gre e n up w a rds, outwards and backwards, formi n g vegetation, a wide variety of animal material, an arc of a circle up to 60 centimetres in fruit and grain (Giles 1980). Other foods c i rc u m f e rence (Pullar 1953; McIlroy 1990). include underg round starch-rich plant Their total length is up to 30 centimetre s , material, such as roots, bulbs and corm s . but up to 80% is embedded in the lower jaw (Pullar 1953; McIlroy 1990). The upper The items eaten by feral pigs in Australia canines are considerably shorter; up to nine vary from region to region, but include: c e n t i m e t res long (Pullar 1953; McIlroy 1990) (a) Fruits and seeds: and oblong in cross section. They curve Figs, palms, pandanus and other rainforest o u t w a rds and back, functioning as t rees; cycads ( M a c rozamia spp.); bush whetstones or grinders to the lower tusks. peanuts (Elaeocarpus spp.); sweet briar If an upper tusk is broken or deformed, the (Rubus rubiginosa); Acacia spp.; Pe r s o o n i a c o r responding lower one can continue to and C o p ro s m a; bananas, mangoes and a g row in a complete circle, ultimately re - wide range of orc h a rd fruit; grasses; and entering the lower jaw. c rops such as pumpkins, waterm e l o n s , potatoes, peanuts, maize, wheat, oats, 3.2 Habitats sorghum and other cereals. Feral pigs occupy a wide range of habitats (b) Foliage and stems: in Australia, including the subalpine Small palms, pandanus and other rainfores t grasslands and forests of Kosciusko National seedlings; young coconut and banana tree s ; Park, the semi-arid floodplains (often s u g a rcane; succulents such as P o r t u l a c a dominated by lignum — M u e h l e n b e c k i a oleracea; semi-aquatic ferns (for example, c u n n i n g h a m i i) in western New South n a rdoo — Marsilea drummondii); and a Wales, the Typha and Phragmites re e d - b e d s range of forbs, grasses and legumes, of the Macquarie Marshes in central New including native medics, introduced clovers South Wales, the rainforests in the wet and lucerne, Paspalum paspaloides, P o a t ropics of northern Queensland, and the spp. and young wheat. paperbark (Melaleuca spp.) swamps, open (c) Rhizomes, bulbs and tubers: floodplains, monsoon forest patches, Lilies (for example, Helmholtzia spp. and Mimosa pigra thickets and dry woodlands vanilla lily — Arthropodium milleflorum); in the Northern Territory (Australian Meat grasses, sedges and rushes such as R e s e a rch Committee 1978; Giles 1980; Eleocharis spp., Cyperus rotundus, Setaria Saunders 1988; Hone 1990b; Bowman and sphacelata, Phragmites spp., Typha s p p . , McDonough 1991; McIlroy 1993; Dexter Scirpus spp. and Juncus spp.; bracken 1995). They prefer moist areas that pro v i d e (Pteridium esculentum); dock (Rumex sp p . ) a reliable and adequate supply of food, and thistles (Family Asteraceae); native

20 Managing Vertebrate Pests: Feral Pigs geranium (Geranium solanderi); O x a l i s 1991). Fruits, however, usually contain far spp.; yams and other tropical ro o t s t o c k s less protein than foliage, although the (Ipomoea, Dioscore a and A m p e l o c i s s u s amount that pigs may obtain from fruit could spp.); and Macrozamia spp. vary according to whether it contains larg e seed capsules and if the pigs chew and (d) Fungi: digest these as well as the softer pericarp. Underground fungi. ‘Feral pigs have high pr o t e i n (e) Animal material: re q u i rements, particularly for Earthworms, snails, arthropods (especially successful lactation and beetles), crustaceans, shellfish, frogs, fish, g rowth of young.’ reptiles (including turtle eggs), eggs of Feral pigs probably have relatively high g round-nesting birds, birds, mice, young p rotein re q u i rements, similar to those of rabbits, lambs and other small mammals domestic pigs (Table 3), particularly for and carrion. successful lactation and growth of young. ( S o u rces of information: Pullar 1950; If intake of crude protein falls below 15% Masters 1979, 1981; Giles 1980; Bore h a m of the diet, lactation can cease and piglets 1981; Alexiou 1983; Hopkins and Graham may die (Giles 1980). The dietary energ y 1985; Statham and Middleton 1987; Bowman needs of feral pigs are also relatively high, and McDonough 1991; Pavlov 1991; Ridpath particularly for sows in the last month of 1991; Pavlov et al. 1992; Mitchell 1993). p regancy, which re q u i re about twice the digestible energy of non-breeding sows, and The nutrient levels in these diffe rent foods lactating sows which re q u i re up to thre e can vary considerably (Table 2). Fruits times the non-breeding energy re q u i rm e n t s . usually contain much higher concentrations If these re q u i rements are not met by dietary of readily digestible carbohydrates (sugars intake, they must be met by mobilising tissue and starch) than foliage, and some are reserves (Giles 1980). Puberty in feral pigs especially high in lipids which pro v i d e may also be delayed by severe re s t r i c t i o n readily available energy (Cork and Foley in energy intake.

Table 2: Chemical constituents (ranges) of tropical and temperate fruits and other items likely to be eaten by feral pigs. Adapted from Bolton and Phillipson (1976), Barrett (1978), Lee (1985), Bell (1990) and Cork and Foley (1991). Dashes indicate no data available.

Constituent (% dry matter)

Food item Crude protein Sugars and starch Cellulose

Tropical and temperate: Fruits 3–12 12–78 1–8 Seeds 3–15 2–16 – Grasses 4–17 3–19 15–40 Forbs 4–35 2–18 6–33 Tropical trees and shrubs: Young leaves 7–55 0–33 6–25 Mature leaves 5–36 1–15 11–30 General: Bulbs 12–15 – – Legumes 24–25 – – Earthworms 54–80 – – Insects 60 7 – Carrion (cow) 57 – –

Bureau of Resource Sciences 21 Table 3: Daily nutrient re q u i rements of domestic pigs for diff e rent weight classes (Barrett 1978).

Growing Breeding Lactating Boars pigs sows sows 5–10 10–20 20–35 110–160 136–200 110–180 kg kg kg kg kg kg

Digestible energy: Kilocalories per 3500 3500 3300 3300 3300 3300 kilogram forage Kilocalories 2100 4370 5610 6600 16 5008250 per day Total feed: Air dry weight 0.6 1.3 1.7 2.0 5.0 2.5 (kilograms) Crude protein: Percentage 22 18 16 14 15 14 of diet Grams per day 132 225 272 280 750 350

Both the availability and nutrient levels Movements are also influenced by in the diffe rent foods and their consumption req u i rements for shelter, including wallowing by pigs change seasonally. For example, in areas, during different times of the year, and central and western New South Wales, feral to a lesser extent by the local topography and pigs feed mainly on green herbaceous disturbance. For example, McIlroy (1989) material when it becomes available after found that in New Zealand feral pigs were heavy rain or floods (Giles 1980). During sedentary in a relatively undisturbed are a dry periods they eat roots, carrion and little containing improved pasture, bracken and else. In the Girilambone area in central New fo rest with abundant food, water and shelter. South Wales, they mainly eat forbs such as H o w e v e r, some pigs moved to more open Solanum ellipticum and insects in autumn, lambing paddocks in late winter when food native medics (Medicago spp.) with their became less abundant. high protein content in winter, and wheat ‘Feral pigs readily switch foods in spring and summer. Roots, however, are and feeding places.’ the most consistent food item in all seasons (Pavlov 1980). Consumption of animal Most observed movements of feral pigs m a t t e r, with its high protein content, varies in the wet tropics of northern Queensland g reatly between seasons and rarely exceeds similarly appear to be seasonal and re l a t e d 5–18% of the diet (Giles 1980; Pavlov 1980). to food supplies (McIlroy 1993). In more settled areas pigs are reported to move fro m r a i n f o rests to sugarcane, banana and other 3.3.2 Movements c rops, orc h a rds and other areas during the Feral pig movements are largely driven by dry season and back into the rainforest once the location of food, and there is often a the wet season begins. Common routes for t r a d e - o ff between the energy needed to movements are the drier, more open ridges obtain food and the protein and energ y leading down to cane fields. Examples of derived from it. Hence feral pigs re a d i l y such movements are to cane fields in April switch foods and feeding places, and they o n w a rds, when the cane has a high sugar may move correspondingly little or content; to house gardens and small extensively, depending on variations in o rc h a rds in August–November, when ripe locally or seasonally abundant food source s . fruit is available; and to irrigated pasture s ,

22 Managing Vertebrate Pests: Feral Pigs municipal parks and golf courses in Feral pigs generally do not move very far S e p t e m b e r– O c t o b e r, when the ground in in response to minor disturbance, including many other areas is too hard to root up for i n f requent hunting by people, and usually e a r t h w o rms. Diong (1973) similarly found re t u rn to their home ranges shortly in Malaya that some feral pigs moved up to a f t e r w a rds (Pullar 1950; Masters 1979; 16 kilometres to feed on sugarcane and Saunders and Bryant 1988; McIlroy and other crops when their food in the native S a i l l a rd 1989; Caley 1993). Feral pigs can, f o rest became limited. The pigs generally h o w e v e r, shift permanently to more re m o t e moved along well-marked customary trails a reas, for example, up to five kilometre s to these feeding areas, and were usually in away in forest, if subjected to intensive or a better condition than pigs that re m a i n e d p rolonged disturbance, such as larg e - s c a l e feeding in the native vegetation. In less hunting or other control activities (Pullar settled areas of northern Queensland pigs 1950; McIlroy 1989; McIlroy et al. 1989; Caley regularly forage for soil invertebrates in 1993). Maximum linear distances that feral ephemeral swampy areas of the coastal pigs are known to have covered in Australia plains during the early dry season, as well a re 55 kilometres for a sow from one as scavenging food from orc h a rd s , w a t e rcourse to another over open plains in household compost heaps, open garbage w e s t e rn New South Wales after a major dumps and tourist areas, but move into c o n t rol operation (Saunders and Bryant higher rainforest areas once conditions 1988) and 23 kilometres, over a period of become drier (Pav Ecol 1992). Seasonal at least two years, for two boars in similar changes in habitat use also occur in the country, probably in response to flooding South Coast area of New South Wales. Here (Giles 1980). feral pigs tend to ret i re to the thickly fores t e d headwaters of creeks or swamps, where 3.4 Social organisation and water is permanent during dry periods; but behaviour re t u rn to the coastal plain where food supplies are more abundant during rainy Although adult boars over 18 months old weather (Hart 1979). In the Northern a re invariably solitary, and farrowing sows Territory, feral pigs primarily exploit the will temporarily separate themselves fro m seasonally flooded swamp communities other pigs, feral pigs are gregarious animals. during the dry season and the open The basic group consists of one or more floodplains and dryland forests during the sows and their piglets, but groups may also consist of young females, bachelor males wet season (Hone 1990b; Bowman and or other combinations. Interactions with McDonough 1991). individuals from other litters begin early in ‘Feral pigs can shift home life and often persist into adulthood (Graves range if they are subjected to 1984). Weaned piglets remain with their intensive or pro l o n g e d mother until the next litter is due and then disturbance, such as hunting run together until the young sows mate. or other control activities.’ Bachelor groups of males remain together Temporal changes can also occur in the until they are about 18 months old (Masters 1979; Giles 1980; Pavlov 1980). After that use of habitats by feral pigs. During hot they generally only rejoin groups for mating w e a t h e r, for example, feral pigs may re s t or to feed on localised food re s o u rc e s . during the day in shady places under thick lignum bushes, in riverine woodland G roup sizes can vary considerably in communities, or in patches of monsoon di ff e rent areas and with seasons. In the fores t s f o rest and then move to more open of south-west Western Australia, group sizes grasslands, sedgelands and waterholes to r a rely exceed 12 pigs, but in more open drink and feed after dark (Giles 1980; country mobs of 30–40 have been reported Ridpath 1991; Dexter 1995). (Masters 1979). Caley (1993) re c o rded the

Bureau of Resource Sciences 23 l a rgest group sizes, 12–45, during the mid- Both boars and sows have carpal glands dry season in the Douglas–Daly are a , ( S i g n o ret et al. 1975) which, along with N o r t h e rn Territory, and the smallest, 5–3 0 , saliva, are used as scent markers. Despite during the late wet season and early dry this, there is no evidence of territorial season. In contrast, Hone (1990b) re p o r t e d behaviour (Barrett 1978; Giles 1980). that the most frequently observed group size The size of home ranges is primarily near the Mary and Adelaide rivers, further d e t e rmined by the abundance of food and east, was 1–10 pigs (maximum 50) in both is correlated with body weight and the dry and wet seasons. These are similar to population density (Saunders 1988; Caley those reported for parts of western New South 1993). Boars have larger daily, seasonal and Wales by Hone and Pedersen (1980) and for overall home ranges than sows, particularly Kosciusko National Park by Saunders (1988). recently farrowed sows which stay close to Ridpath (1991) likewise reported that in their young for the first two weeks or so tropical northern Australia often only single after farrowing (Saunders 1988; McIlroy et pigs were observed and groups rarely exceed al. 1989; Caley 1993). Daily home ranges 20 individuals, but that in times of severe a re generally small (0.7–1.4 square d rought, groups of over 100 could gather k i l o m e t res) compared with seasonal and around remaining waterholes. a g g regate home ranges, indicating that pigs ‘The size of a feral pig’s home do not cover their entire range over short range is mainly determined by periods as territory-holding animals food abundance.’ generally do. The home range of a re c e n t l y fa r rowed sow may be as small as 0.16 square Feral pigs make consistent use of trails k i l o m e t res (Saunders 1988). Where food to travel from one area of specific use to supply is poor, such as in Kosciusko a n o t h e r, such as from refuge or bedding National Park and during the early dry sites to feeding grounds or water (Saunders season in the Northern Territory, average 1988). Signs of rubbing or tusking are often home ranges can be quite large (Table 4). found on trees or logs along these trails. Wallowing in dust or muddy depressions is Activity patterns of feral pigs depend on also common and serves as both a method location, season, weather and degree of to reduce ectoparasite infection (as does disturbance from people. Generally, pigs rubbing) and a means of therm o re g u l a t i o n . a re nocturnal or restrict their activity to the

Table 4: Home ranges of feral pigs.

Home range Area (square kilometres) Source Male Female

Western New South Wales 43 6.2 Giles (1980) Sunny Corner, 10.7 4.9 Saunders (1988) New South Wales Kosciusko National Park, 34.6 10.2 Saunders (1988) New South Wales Namadgi National Park, 1.4–6.6 1.5–5.5 McIlroy and Saillard (1989); Australian Capital Territory McIlroy et al. (1989) Douglas–Daly area, 31.2 19.4 Caley (1993) Northern Territory North-west New South Wales 8.9–11.6 4.9–8.1 Dexter (1995)

24 Managing Vertebrate Pests: Feral Pigs early morning, late afternoon, evenings and especially in younger sows (Section 3.3.1; early night in hot weather, or when they are Giles 1980). subjected to hunting or other disturbances The average number of viable embryos (Pullar 1950; Giles 1980; Saunders and Kay in feral pigs in Australia (4.6– 8.2) is far fewer 1991). They are more diurnal in cloudy or than that for domestic pigs (14 –22 for a large rainy conditions, or in cooler seasons or white sow on a high nutrition diet) (Masters a reas, although they are not usually active 1979; Giles 1980; Pavlov 1980). Fecundity during the middle of the day (Saunders 1988; i n c reases with age and body weight. In M c I l roy et al. 1989; Saunders and Kay 1991). domestic pigs sexual maturity occurs at 4–9 In the Northern Territory feral pigs are most months old but in feral pigs body weight is active during the early dry season and least m o re important; in Australia feral sows only active during the late dry season (Caley b reed when they have reached 25–3 0 1 9 9 3 ) . kilograms, usually at about 7–12 months old (Masters 1979; Giles 1980; Pavlov 1980). 3.5 Reproduction Average litter sizes vary from 4.9 to 6.3 Feral pigs are polyoestrous: adult females piglets, but up to 10 piglets can be born in have a 21-day oestrus cycle and a gestation good conditions. period of 112–114 days. Under favourable ‘Breeding can occur throughout conditions breeding can occur thro u g h o u t the year in good conditions but the year but is usually seasonal where food it is usually seasonal.’ availability and quality are variable. In the high country of Kosciusko National Park, Weaning age can vary from two to thre e for example, most births occur in summer months. The time for a feral sow to re t u rn and autumn, in response to the spring flush to oestrus after parturition is also variable, of growth (Saunders 1988). Reduced rates being up to 94 days compared with a of conception occur in autumn and winter minimum of 18–22 days for domestic sows because of the decreasing availability of (Giles 1980; Pavlov 1983). Under favourable h i g h - p rotein food. Feral pigs living on the conditions, sows can produce two weaned semi-arid floodplain of western New South litters every 12–15 months (Giles 1980; Wales generally breed continuously, but Pavlov 1983; Ridpath 1991) but, where m o re conceptions tend to occur after b reeding is seasonal, only 0.85 litters per flooding when more food is available (Giles year are produced (Saunders 1988). This 1 9 8 0 ) . potentially high re p roductive rate, closer to that of rabbits than that of other feral B reeding also occurs throughout the year ungulates in Australia, gives feral pig in feral pigs in the monsoonal lowlands of populations the capacity to recover quickly the Northern Territory, with a peak in births f rom natural setbacks or control pro g r a m s during the early dry season (Caley 1993). and is a major factor to be considered in This is because many sows come into strategies for their management. oestrus and mate during the wet season when food is abundant. In comparison, during the late dry season many adult sows 3.6 Diseases and parasites a re in poor condition due to the nutritional Feral pigs are susceptible to many infectious demands of previous pregnancies and exotic diseases and parasites, including lactation and a shortage of high quality food, those specific to pigs, such as swine fever, so fewer piglets are born during the wet and others that are widespread among other season. Droughts and shortage of food can animals such as foot-and-mouth disease delay the onset of breeding by young sows (FMD) (Section 4.3.2). The exotic diseases and increase the length of post-partum and parasites that can occur in feral pigs that anoestrus in older sows, as well as re d u c i n g attract most attention in Australia include the number of foetuses and piglets born , FMD, other vesicular diseases, classical

Bureau of Resource Sciences 25 swine fever (CSF), African swine fever, of Australia, and high during the late dry Aujeszky’s disease, trichinosis and scre w - season (Caley 1993). Adult mortality can w o rm fly. Several of these, such as FMD and vary from 15 to 50% between age cohorts, swine fever, were accidentally intro d u c e d with few feral pigs in western New South into Australia in the past, but were prev e n t e d Wales living beyond five years old (Giles f rom establishing (Robertson 1932; Pullar 1 9 8 0 ) . 1 9 5 0 ) . The main mortality factors are loss of Feral pigs in Australia also carry several foetuses, accidental suffocation of piglets endemic diseases and parasites of economic by sows, loss of contact between piglets and importance to the livestock industries and sows and starvation at all ages, including some of importance to human health old pigs when excessive tooth wear (Section 4.3.1). These include leptospiro s i s , i n t e rf e res with chewing. Sows whose crude brucellosis, tuberculosis, melioidosis, p rotein intake drops below critical levels s p a rganosis, porcine parvovirus, Murray cease to lactate, resulting in high piglet Valley encephalitis and other arborviruses. mortality (Giles 1980; Pavlov 1980). Lack of Other parasites of feral pigs of less adequate protein also affects the general importance economically include helminths health of pigs of all ages, increasing their such as A s c a rops stro n g y l i n a a n d susceptibility to parasites and diseases. Simmondsia paradoxa, the stomach worm Dingoes (Canis familiaris) and feral dogs (Physocephalus sexalatus), red stomach prey on piglets and are probably res p o n s i b l e w o rm (H y o s t rongylus rubidus), kidney for the frequent high mortality of immature w o rm (Stephranus dentatus), lungworm s pigs and sometimes sows, but there is (M e t a s t rongylus spp.), thorny-headed worm conflicting opinion about whether dogs limit (M a c r a c a n t h o rhyncus hirudinaceus) , the size or distribution of pig populations hydatid cysts (Echinococcus granulosus) , (Pavlov 1983, 1991; Woodall 1983; Saunders cysts of bladder worm (Taenia hydatigena), 1988; Corbett 1995). l i v e rfluke (Fasciola hepatica), pig lice (Haematopinus suis), mange mite (Sa rc o p t e s 3.8 Population dynamics s c a b e i) and various ticks (Pullar 1950; Masters 1979; Giles 1980; Saunders 1988; 3.8.1 Overview of large mammal Thompson et al. 1988; Pav Ecol 1992; Pavlov population dynamics et al. 1992; D. Spratt, CSIRO, Australian Animal populations are often described as Capital Territory, pers. comm. 1994). being regulated by intrinsic and/or extrinsic factors. The rate of increase of an intrinsically 3.7 Mortality regulated population slows through the e ffect of some sort of spacing behaviour as Mortality among young feral pigs during density increases. Such populations can be their first year of life, particularly from the thought of as being self-regulated; rate of foetal stage to weaning, is generally high, change in their abundance at any time being but can vary considerably from 10– 1 5 % a consequence of prevailing density. The when food supplies and weather are rate of increase of an extrinsically re g u l a t e d favourable, to 90% where conditions are population, on the other hand, is imposed p o o r, and even 100% during dro u g h t by some limiting environmental re s o u rc e (Masters 1979; Giles 1980; Saunders 1988). (such as food or nesting sites), or the eff e c t In Kosciusko National Park, piglets born of some limiting environmental factor (such during the summer have a greater chance as a pathogen or predator). The abundance of survival than those born in the cold of these populations at any time is months (Saunders 1988). Mortality of feral de t e rmined by the availability of the limiting pigs, particularly piglets less than two re s o u rce or the effect of the limiting factor. months old, is similarly low during the wet and early dry seasons in the tropical north Animal populations may also be described

26 Managing Vertebrate Pests: Feral Pigs as being density-dependent or density- dependence. independent. Density-dependence means that a population’s rate of increase is affe c t e d 3.8.2 Dynamics of feral pig by density. Conversely, density- populations independence means that no re l a t i o n s h i p exists between population density and Variations in the rate of change in pig p revailing rate of increase. Intrinsically abundance need to be known as they regulated populations by definition display d e t e rmine re q u i rements for eff e c t i v e density-dependence, their rate of incre a s e management of pig impacts (Section 7.4) being a direct function of their density. and may also influence the capacity of feral Ho w e v e r, extrinsically regulated populations pigs to harbour and transmit exotic livestock can also (although not always) display diseases (Sections 3.6 and 4.3.2). Detailed density-dependence, when their pre v i o u s studies of the dynamics of feral pig density influences the current availability of populations in Australia have been a limiting re s o u rce or the effect of a limiting conducted in the semi-arid rangelands (Giles f a c t o r. To illustrate this latter case, Caughley 1980; Woodall 1983; Choquenot 1994; (1987) described the example of a population Dexter 1995), in a subalpine area (Saunders of deer (Family Cervidae), extrinsically 1988, 1993a), and in tropical woodland and regulated by the availability of grass. At any floodplain habitats (Caley 1993; Corbett given time, the population’s rate of incre a s e 1995). Hone (1987) also studied aspects of is determined by the biomass of grass, but the population dynamics of feral pigs while that biomass is influenced by the pre v i o u s evaluating strategies for management of their history of grazing. Hence present rate of impacts in a highland forest area in south- i n c rease might well be predicted from either east Australia, and on a tropical flood plain c u r rent or past population densities, using in the Northern Territory. What is known of an appropriate population model, and in that the dynamics of feral pig populations in sense the dynamics of the population are each of these regions is summarised below. said to be density-dependent. ‘Good management Populations of large mammals are re q u i res knowledge of generally believed to be regulated by extrinsic changing rates of population factors, most commonly food supply, g rowth and decline.’ p redation, or both. Regulation of larg e mammal populations by extrinsic factors is The semi-arid rangelands c o n s i d e red to be manifested through dire c t Giles (1980) studied feral pig population effects of food shortage and/or predation on dynamics in the semi-arid rangelands, based the population’s demographic rates, which on extensive mark–re c a p t u re and autopsy d e t e rmine its prevailing rate of incre a s e . of large shot samples. Although Giles used Hypotheses relating large mammal four study sites, most of his information on abundance to food supply have been population dynamics came from two generalised to propose that density- locations: War ren on the Macquarie Marshes dependent mortality regulates population and Yantabulla in the Cuttaburra Basin. Both abundance through food shortage (Sinclair sites were within the wild dog exclusion et al. 1985). In this context, density- fence, which separates the sheep rangelands dependence refers not to a direct causal link of western New South Wales from the more between current population density and rate extensive rangelands of south-west of increase (self-regulation), but to the Queensland and north-east South Australia. negative effect on prevailing mortality rates Hence, feral pigs were not preyed on by of a correlation between previous population dingoes at either site. density and current food supply. Caughley’s (1987) example of a deer population would Giles (1980) reported population densities c o n f o rm to this definition of density- which varied between 8.01 and 17.47 pigs

Bureau of Resource Sciences 27 Fi g u re 3: Variation in protein content of food consumed by pigs in relation to rainfall and flooding at Yantabulla in north-west New South Wales (after Giles 1980). per square kilometre over three years for for feral pigs, their body the Wa r ren study site, and between 0.24 and condition and survival 0.77 pigs per square kilometre over two rates decline.’ years for the Yantabulla study site. Giles Giles (1980) found that the flush of gre e n concluded that the variability in pig density vegetation which followed heavy rains or at both sites was due to chance variation in flooding led to increasing body condition. p revailing seasonal conditions, rate of This improved body condition, and an change in pig abundance being determ i n e d associated decrease in juvenile and adult l a rgely by the influence of dietary pro t e i n mortality, continued as long as favourable availability. Protein was most commonly seasonal conditions ensured green feed was obtained from fresh green legumes, grasses available. When green feed was inadequate and forbs. Animal matter, mostly carrion, to maintain body condition, adult survival f rogs and earthworms, re p resented an fell and juvenile survival declined important secondary source when it was dramatically. Using a combination of available. Giles linked availability of fre s h m a r k – re c a p t u re data and reconstructed age g reen vegetation to flooding or heavy rain. distributions, Giles demonstrated that F i g u re 3 relates changes in an index of the juvenile survival increased from 0% when p rotein content of food consumed by pigs little or no green feed was available, to 60% at Yantabulla to the incidence of rainfall and when rains or floods prompted rapid flooding over six years. When adequate vegetation growth. Mark–re c a p t u re studies green feed was not available, pigs consumed indicated adult survival varied from 50% to mostly roots and tubers which were rich in 85% over a similar range of seasonal digestible carbohydrate but contained little conditions. Giles suggested that a lack of p ro t e i n . p rotein-rich green feed reduced juvenile ‘When green feed is inadequate survival by affecting the quality and/or

28 Managing Vertebrate Pests: Feral Pigs quantity of milk produced by lactating this rep resents a maximum rate of decline for females, and/or by providing inadequate the populations studied by Giles. food re s o u rces for recently weaned piglets. Choquenot (1994) described a large - s c a l e In either case, maximum juvenile mortality field experiment to test the nature of o c c u r red at or close to weaning. A series of interaction between pig populations and sensitivity analyses indicated that variation their primary food supply in a western river in juvenile mortality was the key factor system. In the experiment the density of influencing the prevailing rate of population pigs was manipulated such that there were in c rease, suggesting that food was a primary t h ree levels of reduction from initial density limiting factor, and rainfall or flooding was in a replicated design. Pig abundance and an indirect limiting factor for these vegetation biomass were estimated p o p u l a t i o n s . quarterly. These data indicated that pigs had Giles (1980) estimated that, under seasonal little or no influence on the amount or rate conditions leading to high survival of adults of change in pasture available to them, and and juveniles, populations attained an annual that pasture availability influenced rate of exponential rate of increase (r ) of 0.6–0 . 7 , change in pig abundance. The re l a t i o n s h i p equivalent to a finite rate (er ) of 1.82–2. 0, an d was a curvilinear numerical re s p o n s e that this re p resented a probable maximum (F i g u re 4). The maximum instantaneous rate

(intrinsic) rate of increase (rm). Hone and of increase of 0.68 (97% per year) was Pederson (1980) estimated r to be 0.57 realised when pasture biomass exceeded (a finite rate of 1.77) for a pig population at about 450 kilograms per hectare. Choquenot Yantabulla in north-west New South Wa l e s (1994) used a series of stochastic population which was recovering following a poisoning models to demonstrate that the lack of program. Although not specifically estimated, influence which pigs appear to exert over data presented by Giles (1980) suggest that, p a s t u re availability in the rangelands was under poor seasonal conditions, pig because of their low overall density in the populations decreased at an annual a rea relative to other herbivores such as exponential rate of – 0.62. It is not known if k a n g a roos and sheep. The low abundance

Fi g u r e 4: The numerical response of pigs to pasture biomass along the Paroo River in north-west New South Wales. Pig population data is lagged by three months (after Choquenot 1994).

Bureau of Resource Sciences 29 of pigs relative to other herbivores appeared The wet-dry tropics due to their higher rates of population decline during dro u g h t s . Caley (1993) used the mark–re c a p t u re technique to estimate a feral pig density of 2 .2–3.5 pigs per square kilometre in a The slopes, tablelands and t ropical woodland habitat from which he subalpine areas derived estimates of r for the population. Saunders (1993a) described the demography Caley (1993) related r to rainfall over the of a pig population in a subalpine enviro n - six months prior to and including the interval ment during a three year mark–re c a p t u re between successive estimates of population study and concluded that the population abundance to derive a numerical re s p o n s e . was relatively stable at a density of 1.6 pigs Rainfall was used as an index of food per square kilometre. Two studies of pig availability because the abundance of food abundance in a highland forest area at a re s o u rces was not measured. The numerical slightly lower altitude than Saunders’ (1993a) response indicated a maximum rate of subalpine study site (Hone 1987; McIlroy et population increase of rm = 0.78 when al. 1989) gave similar estimates of density rainfall in the six months prior to the interval ( 0 .9–2.4 pigs per square kilometre ) . of population growth exceeded 600 Seasonal variation in body condition m i l l i m e t res. Rainfall variation (and hence indicated that the subalpine population was food availability) in the wet–dry tropics has limited by food availability and/or quality a very predictable temporal pattern re l a t i v e over autumn and winter. A life table for the to that in rangelands habitats, and Caley population, estimated from the standing age (1993) found that this had important distribution, indicated that mortality was consequences for variation in pig very high for juveniles (85% over the first abundance. The population he studied year of life), declining through middle ages. moved from phases of population gro w t h Saunders (1993a) presented indire c t to population decline over the re g u l a r evidence that at least some piglet mortality annual cycle of wet and dry seasons. This was due to predation by dingoes. He is in distinct contrast to the unpre d i c t a b l e suggested that this, along with over- w i n t e r variation in rates of change in rangelands food shortage, meant populations in habitats (Choquenot 1994). subalpine areas probably had lower rates Corbett (1995) used natural variation in of increase than populations in the semi- the abundance of primary prey for dingoes arid rangelands. and an experimental manipulation of the Saunders et al. (1990) estimated a rate of abundance of feral water buffalo (B u b a l u s population increase r = 0.25 for a population b u b a l i s) to test the effects of predation and of feral pigs near Bathurst in the central competition from buffalo on pig abundance tablelands recovering from a poisoning in an area of mixed tropical woodland and p rogram. This estimate encompassed 12 floodplain in northern Australia. The total months only, and the increase appeared to response of dingoes to pigs, derived fro m have occurred more through recolonisation an estimate of the number of pigs eaten per of the area than by intrinsic increases in the dingo multiplied by the number of dingoes resident population. Hone (1995) monitored p resent, was negatively related to pig the feral pig population in Namadgi National density, suggesting an inverse density- Park (Australian Capital Territory) over 5.5 dependent relationship. Corbett (1995) years and reported a decline in abundance. concluded that dingo predation could not The observed rate of increase was r = – 0. 4 4 regulate the abundance of pigs although it per year, corresponding to a decline of 64% could limit the size of the pig population. per year. Pigs increased in abundance following

30 Managing Vertebrate Pests: Feral Pigs b u ffalo removal and Corbett (1995) found saturated soil in this ecotone. In the late dry a significant negative effect of buff a l o season, protein-rich food is scarce and density on pig density. Both species limited access to underg round vegetation c o n g regate in the ecotone which moves reduces the ability of pigs to successfully a c ross the floodplain with the drying of lactate and wean their offspring. Corbett inundated areas as the dry season (1995) suggested that such interf e re n c e p ro g resses. Corbett (1995) suggested that competition where buffalo occurred may w h e re buffalo are present they limit access limit feral pig populations in tro p i c a l by pigs to underg round vegetation in the floodplain enviro n m e n t s . late dry season through compaction of the

The role of predation In contrast to the studies of Giles (1980) and Choquenot (1994), the analysis of feral pig population dynamics conducted by Woodall (1983) was based on data from central and w e s t e rn Queensland where pigs and dingoes co-exist. Woodall (1983) used annual tre n d s in bounty payments for dingoes and pigs to index their relative abundance ( N ) b e t w e e n 1 1949 and 1973. Total mortality rate ( Mt) was estimated as the diff e rence in successive l o g1 0 t r a n s f o rmed abundance indices (Varley and Gradwell 1968):

Mt = log1 0Nt–l o g1 0Nt + 1 Woodall (1983) found:

• a significant positive relationship between pig density and Mt suggesting density-dependent mortality consistent with population regulation; • some evidence of delay in density dependence from the chronological sequence of

changes in density related Mt , which could indicate delayed density dependence and that equilibrium density (K) was unstable;

• a significant positive relationship between dingo density and Mt for pigs suggesting predation by dingoes was a limiting and potentially regulating factor for pig populations; and

• a significant negative relationship between rainfall and Mt for pigs suggesting food availability was also a limiting and potentially regulating factor for pig populations. Unfortunately, Woodall (1983) overlooked the existence of a significant negative relationship between his measure of dingo abundance and rainfall over the previous 12 months (F =9.220, df =1,16, P > 0.01). This relationship suggests that high rainfall in the p receding year led to either lower dingo density (Woodall’s implicit assumption), or fewer dingoes caught or shot for bounty payment. Because there is no significant

relationship between Mt for pigs and the number of bounties paid for dingoes (F =2 . 2 5 7 , df = 1,15, NS), the latter is probably true. When the annual number of bounties paid on dingoes is corrected for the effects of rainfall, the apparent relationship between dingo

density and Mt for pigs disappears (Figure 5) (F =0.097, df = 1,16, NS). Hence, Wo o d a l l ’ s (1983) study suggests a negative relationship between pig mortality rate and pre v i o u s rainfall which may show delayed density dependence (consistent with the hypothesis that pig density is limited and potentially regulated by food availability) but no effect of p re d a t i o n .

1 Mt is used for total mortality rather than the usual K to avoid confusion with equilibrium density at carrying capacity K.

Bureau of Resource Sciences 31 Fi g u re 5: The relationship between total mortality rate (Mt ) for pigs and the number of dingo bounties paid, corrected for rainfall effects (after Woodall 1983).

The wet tropics is of insufficient quantity/quality to maintain

Variation in rates of increase in the wet lactation, juvenile mortality will be high, t ropics are probably driven by food availability and/or quality. In a sample of and rates of population increase will be low 23 mature sows collected from the Cape Tribulation area in northern Queensland in or negative. It is unknown whether the the first half of 1992, half were pregnant and none were lactating (Pav Ecol 1992; McIlro y 1993). Stomach contents of non-pre g n a n t variation in food supply in the wet tro p i c s sows indicated insufficient protein to maintain lactation, suggesting that at least is regular as in the wet–dry tropics or some of the time, food quantity or quality a ffects re p roduction. It is likely that if food i r regular as in the semi-arid rangelands.

32 Managing Vertebrate Pests: Feral Pigs 4. Economic and temporarily abundant food supply, such as fallen rainforest fruits, until the source is environmental almost depleted, could affect specialist feeders, impacts and such as cassowaries (Casuarius casuarius) commercial use which are largely frugivorous. Feral pigs can act as hosts or vectors of Summary several endemic and exotic diseases and Feral pigs cause damage to both agriculture parasites that can affect other animals, and the environment, but they are also an including domestic livestock and humans. economic res o u rce. Feral pigs are res p o n s i b l e The major endemic diseases and parasites of for economic losses in three ways: direct losses c o n c e rn are leptospirosis, brucellosis, to agricultural production; thro u g h melioidosis, tuberculosis and sparg a n o s i s . continuing expenditure of resources on pig An outbreak of exotic disease amongst feral c o n t rol; and the value of lost opportunities pigs, such as foot-and-mouth disease, could to take profit from alternative investment of delay its detection, increase the rate and this expenditure. extent of its spread, make eradication m e a s u res more expensive, time-consuming Feral pigs eat newborn lambs, reduce yields or difficult, and have severe re p e rc u s s i o n s of crops, damage fences and water source s , for both Australia’s domestic and export and compete with stock for feed by consuming livestock industries. Although Commonwealth or damaging pasture. There are no rel i a b l e and State authorities have pre p a re d estimates of the cost of feral pig damage to contingency plans for dealing with outbrea k s agricultural production, although it is likely of exotic diseases, as well as maintaining that the damage is at least of the order of $100 stringent quarantine regulations, re c e n t million annually, and it may be much more. re s e a rch indicates that outbreaks could Although feral pigs are often regarded as establish in feral pig populations in Australia. having deleterious effects on the environ m e n t , It is estimated that about $5 million of the very little objective information on their $ 10–20 million derived from the export impact is available. The most important market of wild boar meat is paid to shooters en v i ronmental impacts they are likely to have and chiller operators, and that recreational a re habitat degradation through selective hunting also injects considerable funds into feeding, trampling damage and rooting for the general community each year thro u g h u n d e rg round parts of plants and inver- money spent by pig shooters. tebrates, as well as predation on, competition with, or disturbance of a range of animals. Most people’s perceptions of enviro n m e n t a l 4.1 Economic Impact damage by feral pigs focus on their rooting Economic impacts of pigs are of three types: up of soils, grasslands or forest litter, particularly along drainage lines, moist gullies (1) value of the direct losses to agricultural and around swamps and lagoons, or after production; rain, when the ground is softer. Their impact (2) value of the continuing expenditure on on plants is largely unknown, as is the extent pig control; and of their role in eating or dispersing seeds, and (3) value of lost opportunities to take profit s p reading ro o t rot fungus ( P h y t o p h t h o r a from alternative investment of this cinnamomi), responsible for dieback disease expenditure. in native vegetation. Estimates of the economic impact of wild Feral pigs eat a range of animal material, animal pests are of two types, gross estimates but are probably not significant predators of and per capita estimates. Gross estimates most fauna except for local populations of value economic losses attributable to the e a r t h w o rms. Their habit of feeding on one p resence of the animal pest. Per capita

Bureau of Resource Sciences 33 estimates value economic losses attributable ( Tisdell 1982; O’Brien 1987); and compete to each individual animal present (or to each with stock for feed by consuming or unit of pest density). In developing manage- damaging pasture (Hone 1980). There are ment strategies for animal pests the form e r no reliable estimates of the cost of feral pig measure is of little use because it only gives damage to agricultural production, but it is an estimate of gain related to the total likely that the damage is at least of the ord e r eradication of the pest animal population. In of $100 million annually and it may be contrast, the second measure allows estimates considerably more. Feral pig contro l of economic gain associated with any activities also add to the costs of landholders. reduction in pest animal density. Predation of newborn lambs The predation of newborn lambs by feral 4.1.1 Agricultural damage pigs has long been recognised as a Feral pigs are responsible for several types significant problem for many sheep graziers of agricultural damage. Pigs prey on (Moule 1954; Rowley 1970). Lamb n e w b o rn lambs (Plant et al. 1978; Pavlov et p roduction is considered critical to the al. 1981; Hone 1983b; Choquenot 1993); viability of woolgrowing enterprises in many reduce yields of grain crops (Benson 1980; parts of Australia because most flocks are Caley 1993), sugarcane and some tro p i c a l s e l f - replacing, graziers rely on a bro a d fruit crops such as bananas, mangoes, genetic flock base to exercise selection for pawpaw and lychees (McIlroy 1993); c o m m e rcially important wool quality traits, damage fences; damage and pollute water and the sale of excess lambs is an important s o u rces such as bore drains and dams s o u rce of cash flow (Alexander 1984).

Feral pig predation on lambs may be significant in some are a s . Source: P. Pavlov

34 Managing Vertebrate Pests: Feral Pigs Quantitative assessment of lamb F a rmers must make essentially ad hoc p redation by feral pigs has been re s t r i c t e d decisions about the appropriate amount of to the semi-arid rangelands where the pig control to undertake because (a) they p roblem is considered most critical. By lack information relating feral pig density contrasting the rearing perf o rmance of and seasonal conditions to rates of lamb lambing flocks from which pigs were p redation; and (b) season-to-season excluded, with flocks to which pigs had variation in predation rates are unpre - access, Plant et al. (1978) measured 32% d i c t a b l e . p redation of newborn lambs by feral pigs and Pavlov et al. (1981) measured an ‘Although lamb survival could average level of predation of 18.7% over be increased by removing feral four lambing seasons (range 0–38%). Both pigs from rangeland authors speculated that prevailing seasonal p roperties, this is not a conditions affected the foraging behaviour practical option.’ and demography of feral pigs which In two large-scale field experiments, influenced the level of lamb predation. Choquenot (1993) measured pig density to Although both studies demonstrated that assess variation in lamb predation rates due lamb rearing rates could be significantly to pigs, and to prevailing seasonal i m p roved by excluding or eradicating feral conditions. In the first experiment, pred a t i o n pigs, neither management option is rate was found to be proportional to pig c o n s i d e red realistic or practical for sheep density when other sources of lamb loss graziers under rangeland conditions w e re experimentally removed from flocks (Choquenot and O’Brien 1989). Usually the of ultrasonically scanned lambing ewes. e ffort expended by graziers to manage pig Comparison of scanning results with udder- numbers varies according to the perc e i v e d s c o res allowed the fate of lambs born to impact of the pigs, and the cash flow individual ewes to be determined. Tw i n - available to the farmer (Tisdell 1982). b o rn lambs were found to be 1.75 times

The rooting up of pasture by feral pigs reduces the amount of feed available to stock and may i n c rease the establishment of weeds. Source: NSWAF

Bureau of Resource Sciences 35 m o re likely to be preyed on by feral pigs decisions about investment on pig contro l than were their single-born counterparts. will then depend on their attitude to risk and ‘Graziers’ decisions about their available finances. investment in pig control will depend on their attitude to Damage to grain crops risk and their financial re s o u rc e s . ’ Pigs reduce yields in grain crops by consuming grain or trampling plants to form In the second experiment on four bedding or to gain access to the centre of the p roperties, seasonal conditions did not crop. Tisdell (1982) estimated that the overall significantly affect lamb loss, over and above impact of feral pigs on grain crops in 1979 – 80 that due to prevailing pig density. It was was $41.4 million (approximately equivalent possible to calculate the probability of to $105 million in 1994–95 values). The d i ff e rent lamb predation rates at given pig greatest economic impact was on the wheat densities (Figure 6). The results suggest that industry (3% of the crop in New South Wales managers could determine specified rates of and Queensland, worth $34 million, lamb predation matched to the lamb equivalent to $86 million in 1994–95 values). p roduction re q u i rements of the grazing Significant losses also occurred in sorg h u m enterprise. For a given rate of lamb loss, the crops (5% reduction in yield, worth $5 million, cost of managing pigs to the density which $13 million in 1994–95 values). Other major matches the appropriate probability to the losses in grain crops were: barley (1% specified rate of predation (Section 7.4) can reduction in yield, $1.5 million loss, be directly equated with the value of the a p p roximately $4 million converted to lambs saved. The value of lambs saved 19 94–95 values); oats (1% reduction in yield, depends on the lamb production re q u i re - $0.5 million loss); and maize (3% reduction ments of particular grazing enterprises. In this in yield, $0.4 million loss). The figures Tis d e l l way, the cost of pig control becomes a (1982) gave for oats and maize are both premium to insure against unacceptable risks ap p roximately equivalent to $1 million when of given rates of lamb predation. Graziers’ converted to 1994–95 values.

Fi g u r e 6: P robability of diff e rent rates of lamb predation at three pig densities (after Choquenot 1 9 9 3 ) .

36 Managing Vertebrate Pests: Feral Pigs Tisdell (1982) suggested that pigs also rooting of bore drains and bore outlets, affected rice production, but did not estimate damage to water supply channels in irrigation the economic impact or the perc e n t a g e areas, damage to flood gates and levy banks reduction in yield. Tisdell’s data on cro p around flood-prone property, disturbance to damage were derived from the perceptions water trough and distribution pipes, and of landholders and various experts. On the fouling of farm dams and waterholes by basis of landholder estimates obtained by a wallowing and defecation. Again, these mail-back survey, Benson (1980) estimated impacts, their cost, and their mitigation that feral pigs reduced wheat yields in north- t h rough pig management have not been west New South Wales by 5.6%, somewhat quantified. higher than the estimate of Tisdell (1982). Reduced yields of sugarcane, fruit Caley (1993) derived per capita estimates and vegetable crops of the damage to maize and sorghum crops in the wet– dry tropics of the Northern Tisdell (1982) reported that the Queensland Territory, using a combination of exclosure Sugar Research Stations (SRS), now the trials and visual estimates of crop damage. Bu reau of Sugar Experiment Stations (BSES), Maize and sorghum yields were reduced by e n c o u n t e red problems with pigs re d u c i n g 100 kilograms per pig (equivalent to $28.50, yields by consuming cane or knocking it or $32 when converted to 1994–95 values) down. In 1982 the SRS estimated that about w h e re crops were unprotected. This was 20 000 tonnes of cane (0.1 to 0.15% of equivalent to each pig taking 0.035 hectares Queensland production) were being lost out of production. A trapping program which annually to pigs. This re p resented a reduced pig density in an area adjacent to considerable increase in lost tonnage fro m c ropping areas by 76% reduced estimated the early sixties when estimates of cane crop losses due to feral pigs by 71% in one damage began (Figure 7). y e a r. Caley (1993) conducted cost–b e n e f i t ‘Feral pigs were estimated to analyses of various pig control techniques cause annual losses of 20 000 based on these data (Section 7.4.1). tonnes of sugarcane in ‘Feral pigs cause considerable Q u e e n s l a n d . ’ damage to grain crops but few M c I l roy (1993) reported estimates for of these economic impacts s u g a rcane losses to pigs in Queensland have been measure d . ’ between 1989 and 1991 (Table 5). On average Although the economic impact of pigs on these estimates are slightly higher than grain crop production has only been those reported by Tisdell (1982), indicating examined in one study (Caley 1993), it is that a small increase may have occurred over likely that considerable damage occurs. The the intervening eight to ten years. McIlroy’s lack of specific data on per capita impacts (1993) data also indicate that most sugarca n e on grain crop production precludes useful damage occurs in the wet tropics area in the discussion of cost-effective strategies for north of Queensland. Within that area, the managing these impacts. M o s s m an–Herbert River area consistently sustains more damage to cane than other cane Damage to fences and water sources growing areas. McIlroy (1993) attributes this Pigs are known to damage fences by tearing to the presence of extensive areas of trop i c a l holes in lighter netting, and weakening wires r a i n f o rest adjacent to and adjoining cane and posts (Pullar 1950). No quantified farms. No per capita estimates of sugarcane assessment of these impacts, or the damage damage caused by feral pigs are a v a i l a b l e . caused by other animals passing thro u g h M c I l roy (1993) reported that the main b reaches in fences has been made. Ti s d e l l damage to cane crops by pigs occurs fro m (1982) catalogued the impacts pigs are known the start of the dry season (April–M a y ) to have on water sources. These include o n w a rds, although some damage to cane

Bureau of Resource Sciences 37 Fi g u re 7: S u g a rcane production losses attributed to feral pigs in Queensland between 1961 and 1979 (after Tisdell 1982). has occurred as early as January. By the end cane in one location, but over the course of of October when the cane has been several weeks they may affect 2–3 hectare s harvested, pigs move back into the rainfores t of a cro p . and remain there until the end of the wet season in the following year. Damage Pigs also damage fruit and vegetable crop s , p redominantly occurs to older plants with although no data on the extent of such a higher sugar content, but some younger damage are available (Tisdell 1982, McIlroy first-year plants may also be damaged, 1993). Crops known to be affected include p reventing their use in the cane harvesting bananas, pumpkins, watermelons, mangoes, cycle of 2–4 years. It is believed that pawpaws, lychees, and pineapples. Ti s d e l l generally only 1–2 pigs cause damage to (1982) reports an apparently isolated instance

Table 5: Estimates of feral pig damage to sugarcane in Queensland (after McIlroy 1993).

Area 1989 1990 1991 Tonnes Value Tonnes Value Tonnes Value lost ($)a lost ($)a lost ($)a

North Queensland 17 272 530 000 24 940 690 000 20 070 485 000 wet tropics area Other areas 1 520 52 000 3 940 117 000 5 440 143 000 Total 18 792 582 000 28 880 807 000 25 510 628 000

a Financial losses to sugar millers and to the industry in sugar foregone are not included in costings. Millers make about $20 per tonne for processing, and seven tonnes of cane makes about one tonne of sugar, valued at $390 per tonne.

38 Managing Vertebrate Pests: Feral Pigs of pigs destroying potato crops near relative importance of rainfall as compare d Tamworth in New South Wales. to grazing pre s s u re in causing variation in p a s t u re biomass in diff e rent enviro n m e n t s . Competition with livestock and T h e o retically, in more stable enviro n m e n t s damage to pastures such as that in which Hone’s (1980) study Pigs, being primarily herbivorous, can eat was conducted, the biomass of the standing or root up pasture which could otherwise c rop of pasture is closely related to the be used by domestic stock to grow wool or grazing pre s s u re placed upon it. In such meat. Pigs may also affect livestock en v i ronments, reductions in pasture biomass p roductivity by initiating trends in pasture due to pigs is likely to be important for species composition which ultimately p a s t u re availability and consequent pro d u c - degrade pasture quality. Hone (1980) tivity of domestic grazing animals at any assessed the reduction in native and point in time. In contrast, prevailing pasture i n t roduced pasture attributable to ro o t i n g biomass in less predictable enviro n m e n t s by feral pigs near Te n t e rfield in northern such as the semi-arid rangelands, depends New South Wales. On native pasture, ro o t e d upon rainfall such that grazing pre s s u re has a reas had green feed reduced by 98%, a lesser role in determining day-to-day standing dry matter reduced by 74%, and variation in pasture availability (Caughley the abundance of weeds, pre d o m i n a n t l y 1987; Choquenot 1994). In semi-arid bracken fern and blady grass, also declined. en v i ronments, reductions in pasture biomass On the introduced pasture, green feed was due to pigs will have, at best, a minor reduced by 74% in rooted areas, standing influence on pasture availability. Pre v a i l i n g dry matter by 37%, and the abundance of productivity of domestic grazing animals will non-grass matter, predominantly bro a d l e a f be determined predominantly by rainfall- weeds, increased ten-fold. The appare n t driven variation in pasture biomass. These contrast in rooting impact on native re l a t i v e d i ff e rences between stable and unstable to introduced pasture was attributed to e n v i ronments probably account for the d i ff e rences in the standing crop of the two d i ff e rent effects of feral pigs on pasture p a s t u re types due to pre f e rential grazing of described by Hone (1980) and Choquenot the introduced sub-clovers. It was concluded ( 1 9 9 4 ) . that the potential for pig rooting to aff e c t pa s t u re productivity in this environment was Roshier (1993) reported no variation in considerable. wool cut per head of sheep and pasture biomass in semi-arid western New South ‘Pigs root up and eat pasture Wales, over a range of pasture availability and this can affect pasture f rom less than 10 kilograms per hectare to species composition and also mo re than 1500 kilograms per hectare. There reduce the food supply was, however, a strong relationship between f or l i v e s t o c k . ’ p a s t u re availability and mortality rates in Choquenot (1994) could not demonstrate sheep (indicating a numerical response by any relationship between feral pig sheep). If reduction in pasture availability abundance and pasture availability in due to pigs (or any other wild grazer) is to rangeland habitat in western New South a ffect productivity in this environment, it Wales (Section 3.8.2). Similarly, the outcomes will most likely be through impacts on of a grazing model (Section 7.4.1) suggest p revailing sheep stocking rates rather than that grazing by unmanaged densities of pigs wool production per head. Given the reduce long-term average pasture availability relatively minor potential pigs have to red u c e by less than 3%. p a s t u re biomass in semi-arid enviro n m e n t s , this impact is likely to be negligible. The nature of the competition between feral pigs and livestock for pastures is To assess the impact of pigs on livestock complex, and is largely dependent on the p roductivity through reduction in available

Bureau of Resource Sciences 39 p a s t u re, several relationships must be spent by New South Wales, and the Northern established, including that between: Territory spent 20% of what New South Wales spent ($220 000), and Victoria and • p a s t u re availability and livestock We s t e rn Australia combined spent 10% p roductivity, or alternatively between ( $ 1 10000) of this amount, the total pa s t u re availability, intake rate of livestock, ex p e n d i t u re for Australia in 1984 would have and subsequent productivity; been about $2.5 million. Clearly, with so •pa s t u re availability and intake rate of pigs; many assumptions, this is an extre m e l y rough estimate. • pasture availability and rate of change in pig abundance; and The re t u rn on expenditure on pig contro l •pa s t u re biomass variation and the influence depends upon how it is spent. For instance, of climatic factors and grazing pressure. g o v e rnment spending goes into re s e a rc h and extension activities, as well as pig How all of these factors operate for sheep c o n t rol on national parks and state re s e r v e s . and pig grazing systems in the semi-arid Accurately estimating the re t u rn on this rangelands is reasonably well known, but e x p e n d i t u re is very difficult. Similarly, much less is known for other environments. investment in pig control by a western grazier will net a very diff e rent re t u rn fro m 4.1.2 Expenditure on pig control that arising from investment in pig contro l by a banana grower in northern Queens- T h e re has been virtually no assessment of land, or a rice grower in the Murray Irrigation ex p e n d i t u re on feral pig control in Australia. A rea. No conclusion about the re t u rn on Saunders and Korn (1986) estimated that c u r rent investment in pig control can be a round $4 million was spent on contro l l i n g made until information is available on the pigs, rabbits and wild dogs in New South n a t u re of expenditure and per capita Wales in 1984. This comprised $2.3 million estimates of the effectiveness of techniques of government expenditure and $1.7 million employed to mitigate damage. of landholder expenditure, not including labour costs. They estimated that 428 days The value of foregone profits fro m of labour and $60 000 were spent by re s o u rces expended on pig control can be landholders on 1080 programs for feral pigs estimated by calculating the ret u rn on capital alone, and this estimate could be doubled outlay invested in various commodities such to account for expenditure of re s o u rces on as new farm equipment, new property or other forms of control such as shooting from o ff - f a rm investments such as govern m e n t helicopters, trapping and poisoning with bonds. Similarly, the value of labour CSSP (Sections 7.6.3, 7.6.7 and 7.6.8). If these f o regone through investment in pig contro l 1984 estimates are reasonably accurate, and can be estimated by calculating the value assuming 33% of government expenditure of time spent on other activities such as was directed to feral pig related activities, repairing fences, tending stock, fertilising the New South Wales Government and p a s t u re or crops, book-work or watching N ew South Wales landholders spent about the cricket. The value of these fore g o n e $1.1 million on pig control in 1984. This re t u rns on re s o u rces expended on pig would consist of $750 000 govern m e n t c o n t rol must be added to the total cost of e x p e n d i t u re2, and $365 000 of landholder c o n t rol when calculating total expenditure . e x p e n d i t u re ($125 000 materials and Total expenditure on pig control is additive $ 2 40000 labour at $35 per hour). If to estimates of economic losses through the Queensland spent a similar amount to that d i rect impact of pigs.

2 Estimates by T. Korn for New South Wales Government expenditure on feral pig control in 1995 totalled approx i m a t e l y $250 000.

40 Managing Vertebrate Pests: Feral Pigs 4.2 Environmental impact floor litter, or periodic, such as diff e re n t i a l impacts during dry and wet seasons or 4.2.1 Real or perceived? impacts on valley floors during winter. Many members of the public, conservationists The most important enviro n m e n t a l and land managers believe that feral pigs have impacts that feral pigs are likely to have are a major impact on the environment in habitat degradation and pre d a t i o n . Australia. There are, however, few quantitative data on actual impacts, and perceptions of 4.2.2 Habitat degradation damage may not always be correct. For Most perceptions of damage by pigs focus example, in the Top End of the Northern on their rooting up of soils, grasslands or Territory, there was concern about the impact f o rest litter. Such disturbance can be locally of pigs on lowland everg reen monsoon extensive, such as in or around swamps and ra i n f o rests because the forests typically occur lagoons, or after rain, when the ground is in small patches (0.5 square kilometres) and s o f t e r, and is often associated with sites a re of high conservation value. Studies by modified by people, or close to roads, tracks Bowman and McDonough (1991), though, and waterc o u r s e s . showed that pigs mainly use the forests for shade during the day and have only limited Mitchell (1993) found that during the late e ffects on them, because greater food dry season (August–November) lowland re s o u rces are available in adjacent are a s . a reas in the wet tropics of Queensland’s Similarly, extensive trampling or rooting of World Heritage Area were more affected by vegetation or the ground by pigs and the rooting than highland areas (8% compare d succeeding invasion of weeds may be to 2.2% of the ground surface). Coastal dramatic evidence of the presence of pigs, woodlands and swamps were more affe c t e d but may not necessarily be important in terms than other broad habitat types like of the long-term processes of plant dynamics r a i n f o rests. Overall, he found that only 4.3% or community structure. of the ground surface at 31 random sites t h roughout the World Heritage Area had ‘Habitat degradation and been rooted up, despite other signs of pigs p redation on native species being re c o rded along 157 (67%) of the a r e probably the most transect lines at the sites. Most pig diggings important enviro n m e n t a l (69%) were within ten metres of a ro a d , impacts of feral pigs.’ track, surface water or a drainage line, Measuring or identifying enviro n m e n t a l particularly along watercourses (36%) and impact by feral pigs can be difficult. In some table drains (8%). Only 1% of the gro u n d cases their impacts may be direct or obvious, s u rface more than ten metres away fro m such as damage to turtle nests and eggs, roads and watercourses had been ro o t e d although the significance of this impact on up. Although not proven, there appears to turtle populations is uncertain, given the be a strong correlation between ro o t i n g intrinsically high juvenile mortality of turtles. damage and soil moisture (Hone 1988a, In other cases, pig damage could be indirec t . 1995), soil friability and probably the For example, rooting up of the gro u n d , p resence of large numbers of earthworm s , which leads to siltation, ultimately aff e c t s other invertebrates and bulb-pro d u c i n g the habitats of aquatic life. Impacts of pigs p l a n t s . can also vary over time. They can be acute, Similarly, Alexiou (1983) found that the such as the destruction of the last re m a i n i n g a reas of subalpine vegetation most specimens of a rare plant, or chronic, such susceptible to damage by pig rooting at as the gradual degradation of a subalpine Smokers Gap, in the Australian Capital swamp. Impacts can be almost constant in Territory, were along drainage lines, in intensity, such as the disturbance of fore s t d e p ressions and around grassy flats. About

Bureau of Resource Sciences 41 32% of these areas showed signs of pig un d e rg round parts (Section 3.3.1). The effe c t damage. Revegetation was slow and the of pigs on rare or endangered plants and dominant grassy vegetation and some small on plant succession in Australia, however, native herbs were greatly reduced in is unknown. Extrapolation of inform a t i o n abundance at disturbed sites. Several native on the impact of pigs on vegetation in other plants, however, became vigorous colonisers countries may not be valid because of of damaged areas. Hone (1988a) found feral d i ff e rences between the enviro n m e n t s , pig rooting in Namadgi National Park in the particularly the relative availability of Australian Capital Territory occurred mainly d i ff e rent foods, and between the ecology in rocky areas where leaf litter accumulated. of feral pigs in these environments. For He also found the amount of rooting was example, the consensus of opinion is that a ffected by altitude. feral pigs do not damage or eat tre e - f e rn s in the wet tropics of Queensland, in contrast Feral pigs have also damaged the Strzelecki to their behaviour in Hawaii and New National Park on Flinders Island (Statham and Zealand (McIlroy 1993). If correct, this may Middleton 1987). Extensive rooting in the be because there are more palms for them moist rich gullies led to erosion, loss of to eat in the wet tropics of Queensland than regenerating forest plants and their in the other countries, or because they have replacement by thick, impenetrable stands of access to other starch-rich foods such as bracken fern (Pteridium esculentum). bananas and sugarc a n e . ‘Extensive rooting by feral pigs in moist gullies led to ero s i o n The extent to which feral pigs eat or and loss of native forest plants disperse seed is unknown. Feral pigs are in Strzelecki National Park on likely to eat a much greater range of fruits Flinders Island.’ and seeds than has been reported, but the viability of the seeds in pig faeces may The effect of rooting by pigs on soil depend on the size of the seeds, the feeding nutrient cycling and erosion is larg e l y behaviour of the pigs and where the faeces unknown. Feral pig rooting may cause a re deposited. The ingestion by pigs of fruit significant erosion of creek banks in the containing small (less than five millimetre s r a i n f o rests of Queensland, leading to the diameter) seeds from plants such as trunk- silting of downstream swamps (McIlro y fruiting figs (Ficus variegata), umbrella tree s 1993) or the lowering of water quality in (S c h e fflera actinophylla) and guavas catchments (Oliver et al. 1992). This may be (Psidium guajava), appears to cause no minor though, compared to the concen- physical damage to most of the seeds, but tration of suspended sediment in streams in t h e re are conflicting reports on the fate of the area from vehicles crossing them, and l a rg e r, soft seeds (McIlroy 1993). Guava and f rom the widespread overland flow of water other unidentified seeds have been observed and saturated soil profiles associated with g e rminating in pig faeces, but their viability t o r rential rainfall, particularly from cyclones appears to be low (Pav Ecol 1992; Pavlov during the wet season (Gilmour 1971; et al. 1992; Mitchell 1993). Gillman et al. 1985; Rainforest Conservation T h e re is growing evidence that feral pigs Society of Queensland 1986). Rooting by may help spread ro o t rot fungus pigs is more likely to affect litter composition (Phytophthora cinnamomi), responsible for d i rectly through its mixing and aeration dieback disease in native vegetation. e ffects and indirectly through its facilitation Although there is still no evidence of spre a d of predation on worm s . via the gut, following ingestion of infected Feral pigs are known to eat a range of material (Masters 1979), three of four feral native and exotic plants, including their pigs examined in Hawaii were found to be foliage and stems, fruits and seeds, and carrying the organism in soil on their hooves rhizomes, bulbs, tubers, roots or other (Kliejunas and Ko 1976). Pigs could also

42 Managing Vertebrate Pests: Feral Pigs carry infected material on other parts of their The effect of pig predation on other body, particularly after wallowing during invertebrates and small vertebrates in w a rmer conditions when sporulation may Australia is not known. Without data on occur (Masters 1979). The spread of the what prey are actually eaten, the rates of fungus has also been associated with soil predation, the density and status of the prey , disturbance and reduction of litter cover by and whether or not predation by pigs is pigs (Brown 1976). Pigs also chew or tusk density dependent, it is pre m a t u re to judge the bark on buttress roots and lower trunks whether pigs are a serious threat to the of trees, which might allow the entry of animals concerned. This also applies to their fungi. They also undermine shrubs and tree s impact on larger ground-nesting birds, such by their digging, causing them to topple as cassowaries (Casuarius casuarius) , (Pav Ecol 1992; Mitchell 1993), but it is not scrubfowl (Megapodius re i n w a rd t) and clear if other factors, such as cyclone brush-turkeys (Alectura lathama), despite damage, may also have had a contributory reports of pigs destroying their nests and e ffect (McIlroy 1993). eating their eggs and young (Hopkins and Graham 1985; Crome and Moore 1990; Mitchell 1993). Laurance et al. (1993) and 4.2.3 Predation, competition and Laurance and Grant (1994) suggested that disturbance of other animals opportunistic, omnivorous ro d e n t s , Live animals reported to be eaten by feral pigs especially white-tailed rats (U ro m y s include earthworms, amphipods, centipedes, c a u d i m a c u l a t u s) may be the dominant beetles and other arthropods, snails, fro g s , p redators of some bird nests, particularly l i z a rds, snakes, the eggs of the fre s h w a t e r ground nests, in north Queensland rainfores t crocodile (Crocodylus johnstoni), turtles and and secondary fore s t . their eggs, small ground-nesting birds and T h e re is also insufficient information to their eggs, young rabbits and newborn lambs evaluate whether pigs adversely compete (Pullar 1950; Tisdell 1984; McIlroy 1990; with native animals for food. Their habit of Mitchell 1993; Roberts et al. 1996). feeding on one temporarily abundant food E a r t h w o rms are one of the most common s o u rce, such as fallen rainforest fruits, until s o u rces of animal protein in the diet of feral the supply is almost depleted, before pigs and it is possible that pigs could switching to others, such as sugarcane, could significantly reduce the numbers of worm s a ffect more specialist feeders, such as the in some localities. Pav Ecol (1992) found l a rgely frugivorous cassowaries. Ti s d e l l that feral pigs harvested over 95% of the (1984) suggests possible competition with available worms at paired quadrat sites in brolga (Grus rubicundus) and magpie geese lowland ephemeral swamps near Cape (Anseranas semipalmata) for tubers and Tribulation during April–July 1992. Although bulbs in northern Australia. the number of worms at diffe rent sites varied g reatly, few adult worms occurred in fre s h l y 4.3 Impact of diseases and rooted up areas. Mitchell (1993), in contrast, parasites found identical numbers of earthworms in feral pig diggings and surrounding areas in 4.3.1 Endemic diseases and the same general region south of Cape parasites Tribulation. Frogs may also be a common Feral pigs can be hosts or vectors of several food item for pigs in some areas. Richard s endemic diseases and parasites that can et al. (1993) suggest that feral pigs, thro u g h a ffect other animals, including domestic either direct predation or habitat distur- livestock and people. The major diseases of bance, may have contributed to the declines c o n c e rn are leptospirosis (L e p t o s p i r a s p p . ) , in some populations of endemic tro p i c a l brucellosis (Brucella suis), melioidosis r a i n f o rest fro g s . (Pseudomonas pseudomallei), tuberc u l o s i s

Bureau of Resource Sciences 43 (M y c o b a c t e r i u m spp.), sparganosis (S p i ro - 1980; Caley 1993). The risk of people getting metra erinacei), porcine parvovirus, Murray porcine brucellosis from eating infected pig Valley encephalitis and other arboviruses meat is extremely low, particularly if it has (Pavlov et al. 1992; Caley et al. 1995; been well cooked. M c I n e rney et al. 1995). Tu b e rculosis was common in feral pigs ‘Feral pigs can be hosts or in the Northern Territory and also occurre d vectors for several endemic in pigs in We s t e rn Australia (Masters 1979; diseases that can af f e c t C o rner et al. 1981). The main source of livestock and people.’ infection was probably the carcasses of feral Le p t o s p i rosis is the most common bacterial cattle and buffalo. This source is likely to disease in feral pigs. Strains of p o m o n a , have diminished greatly following the tarassovi and hardjo were found by Masters bovine brucellosis and tuberc u l o s i s (1979) in 2–9% of pigs examined in Western eradication campaign (BTEC) thro u g h o u t Australia and in 4–22% of pigs examined by Australia and more intensive management Pav Ecol (1992) in north Queensland. Giles of buffalo. Comparative surveys of feral pigs (1980) re c o rded pomona in 2–51% of pigs over an extended period has shown that the examined in western New South Wales and p revalence of tuberculosis has dro p p e d Pavlov (1980) found pomona in 20% of pigs dramatically with the eradication of the and tarassovi in 6.8% of pigs from the same disease in cattle and buffalo. Pigs are general area. This bacterium, which causes re g a rded as an end host for the disease Weil’s disease in humans, was well known in (bovine, avian and human types) and are north Queensland as canecutter’s disease not a significant source of infection for cattle. when sugar was harvested manually. Infection People can be infected by eating inade- usually follows contact with the urine of quately cooked flesh of pigs suffering fro m infected animals through broken skin, or the disease. t h rough intake of urine-contaminated food People can get sparganosis (caused by or water. It can occur from living in close infection with the spargana or larval plero - association with infective pigs or handling ce roid of the tapeworm Sp i rometra erinacei) them during hunting or field butchery. A range f rom a number of sources including eating of other animals can also be infected with feral pig meat. While this parasite, which leptospirosis, particularly cattle and rodents. travels through the tissues of the body, is In pigs, leptospirosis can cause infertility, wi d e s p read in pigs frequenting many swampy abortions, stillbirths and post-partum death a reas of Australia, it is not a human health of young piglets. ha z a rd if meat is adequately frozen or cooked. P o rcine brucellosis, a serious and long- lasting illness in people, is a notifiable disease 4.3.2 Exotic diseases and parasites in Australia that results from people coming Feral pigs are the species of most concern into contact with animals or animal prod u c t s in Australia for their potential to harbour or infected with Brucella suis (Stevenson and s p read exotic diseases. Feral pigs can act as Hughes 1988). Infection may occur in people hosts or vectors of several exotic diseases handling raw feral pig meat, such as meat and parasites of livestock, of which the most industry workers and hunters. Although the significant are described by Geering et al. disease is still rare in both people and (1995) and Wilson and Choquenot (1996). domestic pigs in Australia, and has a limited These diseases include: regional distribution within the tropical and no r t h e rn temparate zones, it is being detected • Foot-and-mouth disease (FMD) is a highly in increasing numbers of people (Robson et contagious viral disease of ungulates al. 1993). No evidence of the organism has (including pigs, cattle, sheep, goats and been found in pigs in We s t e rn Australia or deer) that can also infect some ro d e n t s . the Northern Territory (Masters 1979; Giles Although not often lethal in adult animals,

44 Managing Vertebrate Pests: Feral Pigs it causes serious production losses and is countries in the temperate regions of the a major constraint in international trade world including North Amercia, Egypt, in livestock and livestock products. FMD Kenya, Spain, Thailand and New Zealand, is endemic at a high prevalence in many and may also occur in the western prov i n c e countries in Africa, Asia, the Middle East of Papua New Guinea. In Australia, an and South America. In Europe, FMD abattoir survey of pigs in the 1960s yielded p revalence has decreased markedly in negative results. One species of trichinosis recent years, and Pacific nations, and has been found in wild animals in North and Central America are free of the Tasmania, but this species is not considered disease; to be a risk to public health or production animals (Geering et al. 1995); • Swine vesicular disease is a viral disease and outbreaks have occurred in Euro p e • Classical swine fever (CSF) is a highly and Asia. Pigs are the only livestock contagious, generalised viral disease of a ffected. Infection rates may be high in pigs that is also called hog cholera. It is a ffected pens, but mortality is negligible; clinically similar to ASF but is caused by a different virus. Pigs are the only livestock • African swine fever (ASF) is another highly a ffected. CSF has been eradicated fro m contagious viral disease that affects only most of western Europe, although it pigs. Mortality rates can be high. ASF occurs remains in Germany and eastern Europe. in most of sub-Saharan Africa, and in 1957 It is also present in east and central Africa, it spread to Portugal and later to Spain, and Asia and Central and South America. In the over the following decades outbre a k s acute form of CSF, the mortality rate may o c c u r red and were eradicated in many reach 90%. There are also chronic and mild E u ropean and other countries. Although forms, both of which can kill pigs. ASF is now under control in domestic pigs in Spain and Portugal, it remains in feral O u t b reaks of any of these diseases or pig (wild boar) populations, and may be parasites could have severe re p e rc u s s i o n s a reservoir for domestic pigs in these for both Australia’s domestic and export countries; livestock industries (Pech and McIlroy 1990). For example, an outbreak of FMD, the exotic • Aujeszky’s disease is a highly contagious disease of most concern, could cost Australia herpes viral disease that affects several m o re than $3 billion in lost export trade, livestock and wild species, although its even if the outbreak of the disease was greatest economic significance is in pigs. eradicated immediately (Wilson and It occurs in most European, and several Choquenot 1996). If the outbreak persisted, Asian and American countries, and also in continuing losses could be $0.3–4 billion a New Zealand and Samoa. Cases in cattle y e a r, depending on whether trade was and sheep are sporadic and they are a ffected in just one state or territory or generally reg a rded as dead end hosts. Rats country-wide (Barry et al. 1993). Av e r a g e and wildlife may have some role as incomes for beef producers could fall by reservoirs and vectors. The mortality rate almost $60 000 annually (Lembit and Fisher varies with age in domestic pigs, declining 1992; approximately equivalent to $65 000 from close to 100% in young piglets to low in 1994–95 values). Significant social levels in adults; upheaval could follow, as well as major • Trichinosis (or trichinellosis) is a helminth changes in land use in some parts of Australia. Less significant exotic diseases ( ro u n d w o rm) disease that results fro m which could involve feral pigs are rabies eating raw or improperly cooked meat. All and infestation with scre w - w o rm fly mammals are susceptible, but infestation (Chrysomya bezziana) . is most common in carn i v o res and o m n i v o res, including people, pigs, cats Australia maintains stringent quarantine and dogs. Trichinosis is present in many regulations to prevent the introduction of

Bureau of Resource Sciences 45 exotic diseases. Commonwealth and State ments, but this req u i res information on factors animal health authorities have also developed such as the disease transmission coeff i c i e n t a nationally agreed approach for managing o r, failing that, the rate of contact between contingency plans — the Australian Vet e r i n a r y feral pigs (Pech and McIlroy 1990). This, and E m e rgency Plan (AUSVETPLAN) — for other information, is also re q u i red to ou t b reaks of FMD and other exotic diseases. de t e rmine the threshold density of susceptible Ideally, any outbreak would be contained individuals, below which the disease will die within a small area, affected and in-contact out naturally, and the culling rates necessary animals would be immediately slaughtere d , to eradicate the disease within certain periods and the disease organism would be of time. A full list of factors likely to affect the eliminated from the environment by p ro g ress and management of an outbreak of cleaning, disinfection, and spelling the land. FMD in a feral pig population is provided by Pech and Hone (1988). The potential role of feral pigs in an o u t b reak of FMD is unclear. Although feral If active disease eradication was not pigs are highly susceptible to FMD, and c o n s i d e red feasible or practical as a s e c rete copious quantities of the virus in management option, it could be contained their urine and saliva for a short period, within a confined zone until it died out t h e re is no evidence that they act as a naturally. Stock movement out of the reservoir of infection or cause re c u r re n t containment zone would be banned. o u t b reaks. Feral pigs are, however, diff i c u l t Based on studies reported by Hone and to manage and an outbreak of FMD in feral Pech (1990), the probability of detecting an pigs could delay its detection, increase the individual feral pig infected with FMD using rate and extent of spread, make eradication the current opportunistic surveillance scheme of disease expensive, time-consuming or is less than 1.5 in 1000. This could mean that, impossible, and complicate and delay for a feral pig population subject to re g u l a r declaration of disease-free status following hunting and occupying 100 square kilometres an outbre a k . of western New South Wales at a density of ‘An outbreak of an exotic 15 per square kilometre, it would take disease such as foot-and- between 23 and 358 days, most pro b a b l y mouth disease in feral pigs seven months, to detect an outbreak of FMD. could have severe Time to detection could be greater still in consequences for Australia’s sparser populations and in the absence of livestock industries.’ hunters. Given, however, that FMD is a multi- species disease, and that cattle are more The success of an eradication campaign susceptible than pigs, it is most likely that an against an outbreak of an exotic disease o u t b reak would be first detected in cattle. amongst feral pigs is likely to depend on several factors, including the delay in first Not enough is known about the continuity detecting infected animals, the prevalence of of distribution of feral pigs in diff e rent are a s infection and the size and location of the area of Australia to accurately predict the bro a d - to be decontaminated (Pech and McIlro y scale rate of spread of a FMD outbre a k . 1990). Under present policy, an outbreak of C u r rent estimates suggest an outbreak could a disease, such as FMD, amongst feral pigs s p read at a rate of about 2.8 kilometres per could be eradicated by slaughter of all host day in Namadgi National Park in the animals within a tightly managed core are a Australian Capital Territory (Pech and McIlroy encompassing all detected cases. In a buff e r 1990), about 2.5 kilometres per day in zone outside this, host animals would be Nocoleche Nature Reserve in the semi-arid tested to ensure the continued absence of rangelands of north-west New South Wa l e s FMD. A knowledge of the rate of spatial (Dexter 1995), and between 0.2–2 . 3 sp read of FMD would be valuable in helping k i l o m e t res per day in the Top End of the to define these zones in diff e rent enviro n - N o r t h e rn Territory, in areas where the

46 Managing Vertebrate Pests: Feral Pigs distribution of pigs is continuous (Caley 1993). Results of studies by Saunders (1988) and M c I l roy et al. (1989) indicate that targ e t An outbreak of FMD in pigs inhabiting the reductions can be achieved in the hill country Douglas River area in the Northern Te r r i t o r y of south-east New South Wales, but a suite could establish during any part of the dry of control methods need to be used and it season as the predicted threshold densities takes considerable time. Other factors that for FMD establishment (0.6–2.0 pigs per need to be considered include how far pigs s q u a re kilometre, or group sizes of 52–1 9 2 move, their propensity to come into contact pigs, where there is discontinuous with other pigs (that is, how isolated the distribution) are below the observed population is), and the presence and density population densities (Caley 1993). Outbrea k s of other potential host animals and their of the disease in the Northern Territory could interactions with feral pigs (Wilson and die out naturally if they occurred in only small Choquenot 1996). For these reasons, the isolated populations of pigs, particularly those option of containment of FMD, rather than in the woodlands where the density of pigs eradication, might be more practical for is 0–1.2 per square kilometre (Hone 1990b; managing an outbre a k . Caley 1993), but FMD could establish over a wide area of the coastal open floodplains of ‘The key to eradication of an the Top End, where densities range fro m o u t b reak of foot-and-mouth 2 .2–10.9 per square kilometre thro u g h o u t disease in feral pigs is to the year (Hone 1990b). Outbreaks of FMD reduce their density below the could similarly establish in the hill country of disease thr e s h o l d . ’ south-east Australia where there are one to Not only will FMD need to be eradicated two pigs per square kilometre (Saunders 1988, f rom feral pigs, it will also be necessary to Mc I l roy et al. 1989) and the threshold density demonstrate to Australia’s trading partners that (at least for pigs in Namadgi National Park) all feral pig populations in affected zones are is 0.037 pigs per square kilometre (Pech and free from FMD. This could be a protracted and Mc I l roy 1990). The probability of an outbrea k di fficult process (Wilson and Choquenot 1996). establishing in western New South Wa l e s , w h e re the threshold density is about seven Little information is available on the likely pigs per square kilometre (range: 2.3–24 pigs dynamics and rate of transmission of other per square kilometre) (Pech and Hone 1988) exotic diseases between feral pigs in Australia. would depend on the density of the pigs Re s e a rch by Hone et al. (1992) suggests that occurring at the particular time and site. The classical swine fever is only likely to establish t h reshold densities of feral pigs in semi-arid in pigs occupying good quality habitats such rangelands was estimated to be 0.24–0 . 2 6 as wetlands and river systems where the pigs per square kilometre (Dexter 1995). carrying capacity for pigs is probably well above the threshold density for the disease. The key to eradication of an outbreak of In such cases, eradication of outbreaks would FMD in feral pigs is to reduce their density req u i re active culling or vaccination. below the disease threshold in the given area . Some modelling, however, indicates that this re q u i res very heavy culling, of the order of 4.4 Resource value and 95% of pigs for short-term management, but commercial use p e rhaps half this for a long-term (two year) FMD eradication campaign (Pech and Hone 4.4.1 Introduction 1988). Achieving target reductions to these The Australian feral pig is both ecologically pig densities has proven difficult. Three full- and physically similar to the European wild scale FMD eradication exercises in western boar and there is a significant export of wild New South Wales, the Northern Territory and pig meat from Australia to Euro p e a n Queensland, achieved only 40–8 0 % markets. Commercial use of feral pigs began reductions in pig numbers (Davidson 1990). in 1980 following amendments to the export

Bureau of Resource Sciences 47 meat regulations in 1979 to include the a total expenditure of $45 million (equivalent export of game meat. Game Management to $95 million in 1994–95). No current figures Australia Pty Ltd, a Queensland company, are available. was re g i s t e red in 1980 for the purposes of In October 1994, the Standing Committee exporting game meat. At present, there are on Agriculture and Resource Management t h ree major players involved in the (SCARM) considered the development of harvesting and export of wild boar meat sustainable industries based on both native f rom Australia (P. Vitolovich, AQIS, and introduced wild and feral animals. Australian Capital Territory, pers. comm. 1 9 9 6 ) . SCARM supported the commercial use of wild animals, with due reg a rd to ecologically ‘There is a significant export of sustainable development principles and feral pig meat from Australia to consideration of animal welfare. Further, European markets where it is SCARM agreed that the development of sold as “wild boar” meat.’ c o m m e rcial industries using feral pest The feral pig is re g a rded as the most species should include the objective of important game animal in Australia (Ti s d e l l c o n t rolling damage due to the pest rather 1982, 1983/84), and is most commonly taken than encouraging their propagation in the by hunting on foot, with or without dogs, or wild. Both public and private landholders f rom vehicles. Tisdell (1982) reports re s u l t s have concerns about some aspects of of extensive surveys of recreational shooters c o m m e rcial use of feral pigs. These include in the late 1970s at which time the average p roblems with trespassing and pro p e r t y hunter took 73 pigs per year from 8–11 trips. damage by hunters. Most of the hunters act on their own, stron g l y believing that they have a useful role to play 4.4.2 Industry structure in feral pig control, and that there is potential for wild pig hunting as a tourist attraction. C o m m e rcial harvesting operations are Tisdell (1982) suggested that amateur hunters restricted to those areas of New South Wal e s , may kill 15–20% of the feral pig population Queensland and the Northern Te r r i t o r y annually. He estimated that this rate of culling w h e re feral pig populations persist despite would reduce feral pig populations by about harvesting and management pro g r a m s 7.5%, and that if each pig caused $15 (1982 conducted by landholders and govern m e n t values, approximately equivalent to $30 in agencies. Australia’s feral pig industry has 1 9 94–95 values) worth of damage to a simple structure consisting of shooters and landholders, then amateur shooters were chiller operators who are based in rural producing an indirect benefit to landholders towns, and game meat processors based in of $3.75 million annually (1982 values, Sydney and Brisbane (Ramsay 1994). The a p p roximately equivalent to $8 million in total value of feral pig meat exports varies 1 9 94–95 values). Added to this is the flow- between $10 million and $20 million on from the expenditure of hunters in the annually, mostly gained from Australian wild community; Tisdell (1982) suggested that b o a r4 exported to Europe (Ramsay 1994). there were about 100 000 feral pig hunters3, In comparison, Australia’s domestic pig meat who each spent an average of $447 annually industry is worth about $700 million (equivalent to about $950 in 1994–95), giving annually (B. Ramsay, Pork Council of

3 Tisdell (1982) suggested there were at least 100 000 pig hunters in Australia and that they each took an average of 73 pigs per year — a total of 7.3 million pigs. Tisdell (1982) also suggested that feral pig hunters kill about 15–20% of Australia’s feral pigs each year — a total of 0.5 million to 4.7 million pigs based on Hone’s (1990a, Section 2.2) estimate that Australia’s feral pig population is in the range of 3.5 million to 23.5 million. Given the discrepancy of these total kills, it is probable that Tisdell greatly overestimated the number of hunters or the number of kills per hunter, or both. 4 Wild boar is the preferred term of the export trade because it is understood by clients in Europe. Feral pig is a term with which they are not familiar.

48 Managing Vertebrate Pests: Feral Pigs Feral pig meat exports are worth $10 –20 million annually. Source: P. O'Brien, BRS Australia, Australian Capital Territory, pers. market factors. For example, eastern comm. 1995). In 1989, a peak year for feral E u ropean countries such as Poland and pig harvesting, game meat companies paid Hungary compete against Australia in this at least $5 million to shooters and chiller operators. In 1993 there were about 200 p e rmanent and intermittently operating Table 6: Typical prices paid by Australian chillers spread throughout rural New South chiller operators for wild boar meat in 1987 Wales, Queensland and the Northern and 1992 (from Ramsay 1994). Territory (Ramsay 1994). Wild Game R e s o u rces (WGR, previously called Year Weight Price Price B a n n e rgame and owned by Southern Game of per kg per Meat) is one of the major companies carcassa carcass involved in the harvesting of wild boar. In (kg) ($) ($) June 1993, WGR had 81 chillers operating 1987b 22–30 0.40 8.80–12.00 pe rmanently at locations in Queensland and 31–40 0.60 18.60–24.00 New South Wales. Typical prices paid by 41–61 0.70 28.70–42.00 ≥ ≥ Australian chiller operators for feral pig meat 61 0.80 48.80 in 1992 are shown in Table 6. 1992 23–30 0.30 6.90–9.00 31–50 0.60 18.60–30.00 Most wild boar meat is exported between 51–80 0.70 35.70–56.00 May and December to catch the winter ≥81 1.00 ≥81.00 market in Europe when consumption is g reatest. There is a fluctuating demand for a Partly eviscerated feral pig from Australia because of other b from Takahashi and Tisdell (1989)

Bureau of Resource Sciences 49 market. In addition, seasonal conditions based on a hypothetical wild pig harvest. such as prolonged droughts or extensive Their example is imaginary because the flooding affect the quality and quantity of relationship between pig density and the pro d u c t . e n v i ronmental damage is unknown. In Queensland commercial feral pig Choquenot et al. (1995) concluded hunters have been req u i red to be accred i t e d , conventional control is a sensible option as from May 1995, which allows the sale of w h e re: (a) commercial harvesting does not pig meat for domestic consumption in achieve the reduction in pig density necessary Q u e e n s l a n d . to reduce impacts to acceptable levels or over large enough areas; and (b) where it follows an unsustained harvest of pigs. In the forme r 4.5 Implications of case, the relative efficiencies of substituting harvesting for damage conventional control for harvesting or control subsidising the harvest to increase its capacity If intense and frequent enough, commerc i a l to reduce pest density should be examined. harvesting has the potential to lower feral In Choquenot et al.’s (1995) hypothetical pig densities to a level where the damage example, a 15% subsidy on the value of they cause is reduced. Annual rates of harvested pigs increased the area over which i n c rease of feral pig populations in Australia acceptable reductions in density occurred by can be as high as 86% (Giles 1980), so culling 52%. In a review of such subsidies or ‘smart rates would need to be sustained at high bounties’, Hassall and Associates (1996) levels to keep populations down. There concluded they were unlikely to result in have been no studies in Australia to significant or long-term damage re d u c t i o n d e t e rmine whether current levels of (Section 6.1.1). Choquenot et al. (1995) c o m m e rcial harvesting of feral pigs are concluded that commercial harvesting of pigs reducing agricultural and enviro n m e n t a l could contribute to conservation objectives, damage. though there was insufficient data to quantify ‘For commercial harvesting to the contribution, but they also recognised that reduce feral pig densities placing an economic value on pigs through s u fficiently for the damage commercial harvesting could (a) encourage they cause to be r e d u c e d , maintenance of a pig density sufficient to culling rates would need to be meet harvesting needs, and/or (b) discourage sustained at high levels.’ f u t u re attempts at high level control or Because harvesting pests reduces their eradication (Tisdell 1982; Ramsay 1994). If density, it follows that where there is a realised, these factors could offset the relationship between pest density and potential contribution of feral pig harvesting e n v i ronmental or agricultural impact, to achieving conservation objectives. These co m m e rcial or rec reational harvesting has the conclusions can be expected to apply equally potential to contribute to conservation or to impacts of commercial harvesting of feral agricultural production objectives. Choquenot pigs on agricultural production. It may be et al. (1995) developed a conceptual model easier to quantify the agricultural benefits of of how harvesting might reduce the co m m e rcial harvesting as there are some data distribution of feral pig damage to the on the relationship between feral pig density e n v i ronment, and developed an example and agricultural damage (Section 4.1.1).

50 Managing Vertebrate Pests: Feral Pigs 5. Community attitudes and observer perception, and in so doing affecting feral pig give rise to conflict. management 5.2 Animal welfare issues Animal welfare groups aim to pro t e c t Summary animals from cruelty and improper exploita- The feral pig is considered by the community tion, encourage considerate treatment of to be many things: agricultural pest; endemic animals and denounce practices perc e i v e d and exotic disease hazard; enviro n m e n t a l as causing animals unnecessary suff e r i n g . liability; export commodity; and rec re a t i o n a l The Australian and New Zealand Federation resource. These attitudes vary with time and of Animal Societies (ANZFAS) accepts that location, although the feral pig’s status as an some feral animals such as feral pigs cause agricultural pest was responsible for raising agricultural or environmental damage, and its profile initially. The feral pig management that where this occurs there is a case for debate has become more complex because of reducing their numbers (ANZFAS 1990). changing values in the community. No longer Their view, however, is that only humane simply re g a rded as a threat to agriculture methods conducted under the supervision and the environment, the feral pig now also of government authorities, and within long- represents a source of significant income to t e rm population reduction programs, are rural communities through re c re a t i o n a l a c c e p t a b l e . hunting and commercial harvesting. Multiple Generally, the humaneness of techniques use of feral pigs leads to conflict in the rural associated with the management of community as well as in the general i n t roduced pest species has received little community. Benefits from the game meat attention, with most emphasis being placed export industry and re c reational hunting upon the methods used to cull native species are attractive. Despite arguments from some such as kangaroos and wallabies. The Sub- rural groups that commercialisation and committee on Animal Wel f a re (SCAW) of the rec reational use of feral pigs is incompatible Standing Committee on Agriculture and with effective feral pig management, R e s o u rce Management (SCARM) has experience suggests otherwise. There is an p roduced a Code of Practice on F e r a l increasing acceptance among communities Livestock Animals — Destruction or that multiple-use management of feral pigs Ca p t u re, Handling and Marketing (S t a n d i n g is both practical and appropriate. Committee on Agriculture 1991). Feral pigs Animal welfare groups accept there may a re discussed in this publication. The be a need to reduce feral pig numbers where National Consultative Committee on Animal they cause agricultural or enviro n m e n t a l We l f a re (NCCAW 1992) has called for the damage, but consider only humane control banning of use of yellow phosphorus poison techniques are acceptable, and that the goal or CSSP against feral pigs (Section 7.6.8). should always be a sustained reduction in A N Z FAS does not support shooting fro m pig numbers. helicopters, due to the risk of pigs being wounded rather than humanely killed, and suggests the need for helicopters to take a 5.1 Community perceptions second run over the control area to check C u r rently, feral pigs are perceived to be an for wounded pigs and reshoot them if agricultural pest, an endemic and exotic necessary. ANZFAS only considers trapping disease hazard, an environmental liability, is humane if the trap is in a sheltered are a , an export commodity and a re c re a t i o n a l is checked frequently, and the pigs are killed re s o u rce (Tisdell 1982). According to humanely (G. Oogjes, ANZFAS, Vi c t o r i a , O’Brien (1987) and Izac and O’Brien (1991) pers. comm. 1995). The use of dogs to these attributes can vary with location, time pursue and hold feral pigs is opposed by

Bureau of Resource Sciences 51 A N Z FAS due to the stress of capture and the lambing rates. The owners concluded that injuries inflicted upon pigs prior to death. unless pig and kangaroo numbers were The dogs used are also subject to a high risk substantially reduced, they would not be able of injury or even death in the struggle with to show a satisfactory re t u rn on their the captured pig (G. Oogjes, ANZFA S , investment in sheep. Other properties, where Victoria, pers. comm. 1996). Both ANZFA S feral pigs were not evident, had a 79–8 0 % and RSPCA Australia strongly oppose the lamb survival rate at marking. hunting of animals for sport. Feral pigs were declared noxious in the ‘Consideration of animal first Rural Lands Protection Board district in w e l f a re issues should be an New South Wales in 1936. Other Boards in integral part of any feral north-west New South Wales followed suit animal management plan.’ until a statewide noxious declaration for the Consideration of animal welfare issues feral pig was made in 1955. This declaration should be an integral part of any feral animal followed submissions from Rural Lands management plan. ANZFAS considers that P rotection Boards and landholders, and the current approach to feral animal complaints from councils including the management, namely ad hoc, opportunistic Baulkham Hills Shire in north-west Sydney. actions based on short-term reduction in Councillors stated that feral pigs were populations, are inappropriate. ANZFA S p resent in dense bushland, periodically considers that a well planned and e m e rging to raid crops and damage fences c o o rdinated strategy, as advocated in these and outbuildings on isolated farms. It was guidelines, is likely to be more humane. further claimed that speculators bro u g h t Ac c o rding to Wirth (1995), public opposition pigs from country areas in western New to some pest control operations is based on South Wales, released them in bush country the lack of objective assessment of the to breed and fatten for sale, and made agricultural or environmental impacts of considerable profits from the operation. pests, and a belief that the animal welfare Some farmers suggested recent immi- costs of the control operations are often grants were dumping the pigs. This is of unjustified. NCCAW considers that animal i n t e rest because it exemplifies the w e l f a re issues should be taken into account d i ff e rences in perceptions by diff e re n t when management progams are designed cu l t u res towards use of wild res o u rces. Many and that control techniques must be as immigrants from continental Euro p e humane as is feasible (Wirth 1995). consider game meat a delicacy, unlike many people of British origin. Many indigenous 5.3 Attitudes in the rural peoples of Australia, such as those living in community north-west Arnhem Land, perceive the feral pig as a re s o u rce (Roberts et al. 1996; Rose Rolls (1969) states that pigs were shot in their 1995) whereas others in central Arn h e m thousands in the Riverina in the 1880s and Land see them as a pest because they again in the 1950s. It is not clear whether they damage bush tucker (Wilson et al. 1992b). w e re shot because they were perceived as agricultural and environmental pests or Rural Lands Protection Boards in New whether they were shot for sport. In some South Wales still view feral pigs with cases it was clear that many lambs were being c o n c e rn, but according to Grant (1982) lost to feral pigs. One property owner in 1954 (Section 6.2.3) this concern is more evident reported feral pigs were so numerous that in We s t e rn compared to Central and Eastern high lambing success in the vicinity of the B o a rds. From 1979 to 1982, the New South Macquarie Marshes was not possible. Five Wales government funded the pilot north- other properties where feral pigs were pres e n t west New South Wales feral pig contro l reported either very low (28%) or negligible scheme described by Bryant et al. (1984).

52 Managing Vertebrate Pests: Feral Pigs In general farmers re g a rd feral pigs as a they have become highly prized hunting pest requiring some control (Oliver et al. t rophies. According to Tisdell (1982), they 1992). Due to feral pig mobility, farm e r s are affo rded special status by amateur hunters. have difficulty controlling pigs when they In the wet tropics of north-east also live on neighbouring land. This can Queensland, control of feral pigs was the lead to disputes. Managers of public lands highest priority issue raised by community including state forests and national parks g roups consulted during the development also need to account for feral pigs in their of the Wet Tropics Plan: Strategic Dire c t i o n s management plans. ( Wet Tropics Management Authority 1992). ‘ F a r mers generally This has led to a strategy aimed at defining re g a r d feral pigs as pests the problem, filling in knowledge gaps by requiring contro l . ’ re s e a rch at various levels and implementing Feral pigs are not only viewed negatively management strategies with a stro n g by the agricultural community because of the community participation (Section 8.7; damage they cause to livestock and cro p M c I l roy 1993; P. Salleras, C4, Queensland, enterprises, but also because of their potential pers. comm. 1993) through established role in an outbreak of exotic disease, such as g roups such as the Consultative Committee foot-and-mouth disease (FMD). Pullar (1950) for the Conservation of Cassowaries, now and Keast et al. (1963) identified feral pigs as the Committee for Coastal and Cassowary efficient vectors for some diseases, and Wil s o n Conservation (C4). and Choquenot (1996) identified them as the species of most concern in relation to wildlife 5.5 Attitudes to multiple-use harbouring or spreading exotic disease in management Australia (Sections 3.6 and 4.3.2). This has led The main issue associated with commerc i a l to considerable Commonwealth funds being harvesting of feral pigs is the conflict which allocated to feral pig re s e a rch through the Wildlife and Exotic Disease Pre p a re d n e s s arises between those who seek eradication, Program from the mid-1980s to the present. those who view feral pigs as a re s o u rce, and those who view feral pigs as both a res o u rc e and pest. 5.4 Attitudes of the general public This conflict exists between management o rganisations within the same state. For Feral pigs are perceived to have a negative example, New South Wales Agriculture impact on the environment (Section 4.2). recognises that commercial harvesting has Both Pullar (1950) and Tisdell (1984) a role to play in feral pig management. e x p ressed concern about the enviro n m e n t a l H o w e v e r, Rural Lands Protection Board s , impacts of feral pigs and provided some who are responsible to the Minister for evidence that feral pigs prey on, or have A g r i c u l t u re, have a policy of eradication potential to prey on, native fauna (Section (Section 6.2.3). Even landholders who are 4.2). Conservationists consider feral pigs highly organised into feral pig management should not only be prevented fro m g roups are split on this issue. In the More e expanding their range but populations Rural Lands Protection Board, about 40 feral should be reduced (if eradication is not pig management groups exist. When the possible) in areas where they cause damage views of group leaders were sought on the to native flora and fauna (Oliver et al. 1992). desirability of banning commerc i a l i s a t i o n Damage to newly planted trees also of feral pigs, their views were evenly split. c o n c e rns foresters and others involved in Pest control agencies generally oppose t ree planting. c o m m e rcialisation because some believe T h e re is a strong perception in the that it is incompatible with eradication and community that feral pigs are dangerous, and that it interfe res with management prog r a m s .

Bureau of Resource Sciences 53 O’Brien (1987) argues that commerc i a l - The Standing Committee on Agriculture isation of feral pigs has significant social and Resource Management (SCARM) supports implications because of the injection of the development of commercial industries funds into rural communities (Section 4.4.1), based on the harvest of feral pigs (Section many of which are economically depre s s e d . 4.4), although SCARM considers these Some land managers in north-west New industries should not support the maintenance South Wales readily use feral pigs as a of feral pig populations. In supporting re s o u rce but others refuse to adopt the co m m e rcial use of feral animals, the position multiple-use approach proposed by O’Brien of SCARM differs from that of ANZFA S (1987). O’Brien and Meek (1992) argue that (Section 5.2). The policy of the National c o m m e rcialisation adds to the present ad Farmers’ Federation is to support control of hoc multiple-use management of feral pigs. feral pigs and to allow commercial use where Other components are re c reational hunting it assists control (R. Hadler, NFF, Australian and pest control (environmental, agricul- Capital Territory, pers. comm. 1995). tural, epidemiological). Ramsay and O’Brien (1991) provide a list of generic objections It is unlikely that the debate between to commercial use and identify elements those advocating sustained management of important to the integration of control and feral pigs to low densities and those c o m m e rcial use. Attitudes to commer- supporting their commercial use will be cialisation vary according to economic resolved in the near future. The pro b a b l e c i rcumstances of rural communities, answer lies with local landholder manage- individual landholders and the prices paid ment groups who can set their own agenda for feral pigs. A value of $1.00 per kilogram on the extent commercialisation is to play d ressed for captured pigs is a stro n g in local management of feral pigs. There economic incentive for landholders, their would be little political support to ban families or staff, to set traps to manage feral c o m m e rcialisation of feral pigs because of pigs or hunt re c reationally (Table 6). Most the export income and local employment it readily deliver pigs to chillers. g e n e r a t e s .

54 Managing Vertebrate Pests: Feral Pigs 6. Past and current C u r rent management is incre a s i n g l y sensitive to environmental and animal management w e l f a re issues associated with contro l . Considerable effort is made to ensure that Summary techniques and methods are sensitive to the Management of feral pigs has varied community’s needs in this re g a rd . depending on the balance between their pest and re s o u rce status, their legal 6.1 Past management definition in diff e rent states, and ad hoc Feral pigs are relatively recent agricultural policies or regulations developed by diffe re n t and environmental pests that have achieved state agencies. Most land managers now p rominence over the last 50 years. They view feral pigs as pests and this has led to appear to have dispersed widely in eastern campaigns in some states and territories to Australia following the decade of wet years manage them. The legal status of feral pigs in the 1950s. In addition, the incre a s e d d i ffers within and between states and mobility of hunters resulted in the territories, and this affects management transportation of feral pigs to uncolonised practices. Some laws prescribe how feral locations in eastern New South Wales and pigs are to be managed; others merely define parts of Victoria. them as pests and leave management to the d i s c retion of landholders or the changing E ffective control practices have only policies of public agencies. evolved over the last 20 years as governm e n t s and industry bodies accorded feral pigs a high State and territory governments pro v i d e priority and allocated funds for research and legislative, technical, policy and possibly extension. Techniques for the control of feral financial support for feral pig control, and pigs are described in Section 7.6. a re also responsible for feral pig management on land held by their agencies. This section provides an overview of Although management of the feral pig co n t rol practices as they have developed and problem has been traditionally ad hoc, there been reported in the literature. is now a trend towards more strategic management. Before the 1970s, no re s e a rc h 6.1.1 Bounties had been conducted on feral pig biology, Pullar (1950) reports that payment of ecology or management and land managers bounties to control feral pigs dates back to typically used shooting, bounties and 1870 but they were not given govern m e n t poisoning with either strychnine, arsenic support until 1945 when a two-shilling or phosphorus, as control tools. Since the bounty (about $2.50 in 1994–95 values) was 1970s, considerable re s e a rch has been i n t roduced in Queensland. The number of conducted on trapping evaluation, poison bounties payed in Queensland between e fficacy and bait acceptance, fence design, 1945 and 1977 annually ranged from 25 504 and shooting from helicopters as contro l to 131 740 (Anon. 1980). tools. This work coincided with the phasing out of bounties and the introduction of Bounties have been viewed favourably co o rdinated management using landholder at various times as providing several g roups. The success of the coord i n a t e d benefits. These include pro v i d i n g : a p p roach is validated by numero u s • additional income for farmers, graziers and p rograms conducted in New South Wa l e s trappers, who in some cases depend on which produced positive outcomes in the the extra income for a living (Laun 1971); way of decreased lamb predation and cro p damage. Both Queensland and New South • assistance to farmers and graziers by Wales have a policy of encouraging the use meeting part of the cost of contro l of coordinated management. (Tomlinson 1957);

Bureau of Resource Sciences 55 • data on distribution, numbers, food habits, other less successful control measures in taxonomy and other important scientific o rder to claim the bounty (Smith 1990). information (Laun 1971); G o v e rnments now generally re c o g n i s e • an incentive to agricultural workers/ that traditional bounties are ineffective as a employees to become more involved in pest control method. In 1975, a re s o l u t i o n animal pest control than may otherwise be was passed by the Vertebrate Pests the case (Smith 1990); Committee recommending that bounty payments should be phased out completely. • an incentive for individual ‘killer pigs’ to This has been implemented for pigs, with be destroyed (Tomlinson 1957); and the exception of a few small-scale bounty • a measure of effectiveness or otherwise of schemes targeted at localised feral pig current and past control programs (Smith p ro b l e m s . 1990). ‘ G o v e rnments generally It has been recognised for some time, recognise that traditional h o w e v e r, that bounties have a substantial bounty schemes are ineff e c t i v e number of weaknesses as a means of for controlling pest animals c o n t rolling vertebrate pests. These include: such as feral pigs.’ • susceptibility to fraud (for example, Choquenot et al. (1995) investigated how transferring scalps from other areas where a bounty subsidy could be used to incre a s e t h e re is no (or less) bounty paid and c o m m e rcial harvesting of feral pigs to meet substituting scalps of other animals) (Balser damage control goals (Section 4.5). and Moyle 1958; Latham 1960; Rolls 1969; Ho w e v e r, a review by Hassall and Associates Breckwoldt 1988; Smith 1990; Hassall and (1996) of such ‘smart bounties’ concluded Associates 1996); that while they are capable of ‘off e r i n g positive benefit–cost ratios’, they are a •f a i l u re to cause a significant decrease in ‘clumsy tool requiring considerable pest animal populations (Balser and Moyle supervision’ and the authors considered it 1958; Rolls 1969; Smith 1990; Hassall and unlikely that bounty payments would deliver Associates 1996); l o n g - t e rm reductions in damage. • deliberately spreading pest animals (for example, rabbits) throughout the continent 6.2 Current management (Rolls 1969); and legal status • deliberately setting free females and young 6.2.1 Introduction to provide future income (Balser and Moyle 1958; Rolls 1969); and Feral pigs numbers are greatest in Queensland, New South Wales, Northern • bounties have to be very high to induce Territory and We s t e rn Australia, pro b a b l y participation, at which point costs exceed in that ord e r. Victoria has far fewer feral the total predation losses (Laun 1971). pigs, South Australia has isolated Bounties may be effective in managing populations, including on Kangaroo Island, feral animals if bounty payments incre a s e and there is a permanent feral population in value substantially as the pest population on Flinders Island in the Bass Strait. d e c reases, thereby inducing hunters to seek Historically, feral pigs have been out the few remaining animals before c o n s i d e red an agricultural pest and this has dishonest and fraudulent practices creep in been reflected in their management where (Jacobsen 1945; Gosling and Baker 1989; l a rge-scale reductions in numbers has been Smith 1990). For example, bounties could the primary aim. There is an incre a s i n g j e o p a rdise more effective management a p p reciation in rural communities that feral p rograms if some landholders wish to try pigs are an important export commodity

56 Managing Vertebrate Pests: Feral Pigs and an important rec reational res o u rce. This e x e rcises conducted by other states. has led to conflict and the need to re - a s s e s s l o n g - t e rm management of feral pigs (Izac 6.2.3 New South Wales and O’Brien 1991). The attitude to feral pig management taken by various state and Under the Rural Lands Protection Act 1989, territory governments within Australia is management of feral pigs on private or reflected in their legislation (Table 7). leased land in New South Wales is the responsibility of the occupier or owner of the land. On land owned by the Crown, the 6.2.2 Queensland agency responsible for that land may or may The official policy of the Queensland not allocate funds for feral animal Department of Lands is to reduce the impact management. Most government agencies of feral pigs through coordinated and respond to public pre s s u re and allocate sustained control programs in areas where either physical or financial re s o u rces to feral feral pigs constitute a high risk to agricultural pig management. For example, the New p roduction and/or the environment. The South Wales National Parks and Wi l d l i f e Department of Lands recognises that feral Service contributes about $350 000 to feral pigs are the basis of an important animal control each year. Control of feral c o m m e rcial harvesting industry and that the animals on unoccupied Crown land is harvesting of feral pigs contributes to their funded through a grant system administered management in Queensland. by New South Wales Agriculture . The Rural Lands Protection Act 1985 ‘New South Wales Agriculture re q u i res landholders in Queensland to recognises the role commerc i a l d e s t roy feral pigs on their properties. This harvesting can play in Act is overseen at a regional level by managing feral pig damage.’ inspectors of the Land Protection Branch of The Rural Lands Protection Board s the Department of Lands. The Inspectors administer the Rural Lands Protection Act operate from Department of Lands off i c e s 1 9 8 9 t h rough Noxious Animal Inspectors and work in Department of Lands re g i o n s . and Directors. Noxious Animal Inspectors The inspectors act as advisers to landholders a re trained by New South Wales Agriculture and provide additional services by issuing in basic vertebrate pest control, then learn poison bait and assisting landholders to form on the job while working with landholders and operate pig management groups. and other government agencies. Rural Lands Despite the pre s s u re of a legal P rotection Boards are autonomous bodies, re q u i rement, landholders control feral pigs answerable for their policies only to the because they perceive they have a negative Minister for Agriculture. In an attempt to economic impact on their enterprises. In have Boards develop and implement one survey (Appleton 1982) not one management plans which contain key landholder gave legal liability as a re a s o n elements, model plans were drafted by New for controlling feral pigs. South Wales Agriculture and distributed to all Boards. The adoption of these plans has One of the major concerns about feral met with limited success, despite the fact pigs in Queensland is their possible that the plans were developed in involvement in an exotic disease outbre a k . consultation with re p resentatives from the In an attempt to improve the pre p a re d n e s s Rural Lands Protection Board s . of government agencies for such an event, two major exercises have been conducted New South Wales Agriculture has a policy within the last ten years: one at Charleville on feral pigs that is control oriented but and another at Byfield (Allen 1985). In which recognises the role that commerc i a l addition, staff from the Queensland harvesting can play in managing feral pig Department of Lands have attended damage. On the other hand, the form a l

Bureau of Resource Sciences 57 policy of the Executive Council to Rural 6.2.5 Western Australia Lands Protection Boards is one of eradication. In practice, the eradication Feral pigs are declared in categories A4, A5, policy of Rural Lands Protection Board s and A6 under the A g r i c u l t u re and Related cannot be implemented. The Boards do not R e s o u rces Protection Act 1976 in We s t e rn have the re s o u rces to pursue an eradication Australia, which means that landholders are legally obliged to comply with the following policy, although they feel an obligation to c o n d i t i o n s : follow a 1950s legal ruling that eradication is the specified objective under the Act. • i n t roduction of feral pigs is subject to Notwithstanding this, most Boards accept conditions and restrictions; that damage control is the real objective, • numbers of feral pigs should be reduced even if not explicitly stated; eradication is and kept under restriction; and seen as the ultimate, but impro b a b l e objective (Section 8.4.2; Appendix C). • keeping of feral pigs is subject to conditions and restrictions. 6.2.4 Northern Territory In Wes t e rn Australia, direct losses of grain c rops are probably the most significant The feral pig is declared as a pest under the damage and individual losses to lupin cro p s Territory Parks and Wildlife Conservation may reach tens of thousands of dollars. Act 1988. This places no legal obligation on D i rect predation on livestock is very rare in land managers to manage feral pigs, unless We s t e rn Australia. There is circ u m s t a n t i a l the area in which they manage land is a evidence that pigs spread the fungal d e c l a red area. Landholder attitude is pathogen (Phytophthora cinnamomi) which orientated to reducing crop damage which causes jarrah (Eucalyptus marg i n a t a) can be significant (Caley 1993). The official dieback disease in Wes t e rn Australia (Section go v e rnment policy is to encourage control of 4 . 2 . 2 ) . feral pigs by land managers but there are no re c o rds of land managers being forced to Baiting with 1080 poison is a major tool in feral pig control and re c reational hunting undertake management programs (G. Davis, is a popular activity. CCNT, Darwin, pers. comm. 1994).

C o m m e rcial harvesting is an interm i t t e n t 6.2.6 Victoria management tool despite the relatively high Feral pigs are declared as Established Pest density of feral pigs in the Top End of the Animals under the Catchment and Land Northern Territory. Its intermittent nature is Protection Act 1994 and all landowners have simply due to difficulties of access because a legal responsibility to take reasonable steps of topography and weather pattern s . to manage them. Feral pigs are dispersed in Co m m e rcial harvesting provides an irreg u l a r isolated populations in the north-west, source of income for some itinerant hunters, south-west, north-east and eastern parts of including Aboriginal peoples. Recre a t i o n a l the state. However, it is in the last two are a s hunting is a popular activity, but is considered that feral pigs are increasing in both numbers to have no effect on the feral pig population. and distribution, and pose a potential major Feral pigs are of particular concern in the t h reat in the next five to ten years. Top End because of their potential Accessibility and size of populations involvement in exotic disease outbre a k s d e t e rmine the appropriate control tech- such as foot-and-mouth disease (Section niques. Where feral pig activity is evident on 4.3.2). Several simulated exotic disease public land, the setting of cage traps by local c o n t rol exercises have been conducted in staff of the Department of Conservation and the Northern Territory, in an effort to train Natural Resources is the main method used s t a ff for such events. to protect farmland throughout Victoria. Some

58 Managing Vertebrate Pests: Feral Pigs opportunistic shooting is conducted by level and the impact on the enviro n m e n t Department staff, but control of populations has been re d u c e d . on private land is predominantly carried out by re c reational shooters and adjoining 6.2.8 Tasmania landholders. Shooting is the pref e r red option when there are scattered sightings, particularly Feral pigs are declared stock under the in rough country. Stock Act 1932. This means landholders can muster animals on their land, and local 6.2.7 Australian Capital Territory councils are responsible for the trans- portation, disposal or destruction of these Leaseholders in the Australian Capital Ter r i t o r y animals. Due to the need to eff i c i e n t l y are not legally required to control feral pigs. c o n t rol feral pig populations, the N a t i o n a l Ho w e v e r, the Parks and Conservation Service Parks and Wildlife Act 1970 allows rangers provides support and assistance to Landcare to destroy pigs in national parks. At this g roups and individuals for pig control on stage, funding is not provided for contro l leasehold land by providing poisoned bait p rograms and government coord i n a t e d and traps to lessees. p rograms have not yet been developed. Feral pigs are widespread throughout the f o rested and pastoral areas of the Australian 6.2.9 South Australia Capital Territory. They destroy pasture and Pigs are proclaimed in Class 4 (which damage sensitive native plant communities includes livestock, domestic and companion t h rough their feeding and wallowing. They animals) under the Animal and Plant a re a high priority for control in the C o n t rol (Agricultural Production and other Australian Capital Territory due to their Purposes) Act 1986, for the whole of South e n v i ronmental and agricultural impacts and Australia. The only provision of the Act potential as a reservoir or vector for exotic which applies to pigs is Section 44 which d i s e a s e . p rohibits the release of pigs into the wild as Since 1985, warfarin poison (Section a wilful or negligent act. Landholders are 7.6.8) has been used successfully in not compelled to take action to control feral Namadgi National Park, other reserves, pine pigs. Control is organised by landholder f o rests and rural areas. The number of pigs g roups and is carried out on a voluntary has been consistently maintained at a low b a s i s .

Bureau of Resource Sciences 59 60 Managing Vertebrate Pests: Feral Pigs 7. Techniques to Management units or control areas must be both sociologically and geographically measure and manage based and the local land management grou p , impact and constituting the management unit, must have abundance strong ownership of the project and must set priorities. Summary Several techniques can be used for T h e re are many techniques available to c o n t rolling pigs. Shooting from the gro u n d is generally ineffective for damage contro l estimate or index pig abundance. Complex techniques require many resources but can except where it is intensively conducted on provide absolute estimates of abundance with small populations. Shooting from helicopters can protect susceptible enterprises from short- measurable levels of precision. These can be used to compare pig densities between term damage, although annual campaigns are unlikely to result in long-term red u c t i o n s locations, habitats, and times. Such of pig numbers because the populations techniques are of use for the more accurate generally recover during the intervening 12 assessment of control operations and res e a rc h . months. Simpler techniques usually provide useful indices of abundance which can indicate Poisoning is a control technique that is broad changes in pig density over time. widely accepted throughout rural com- munities. It is perceived as a method which, The assessment of the agricultural impact if properly employed, can produce a quick of pigs should focus on per capita estimates knockdown of the feral pig population. The of reduction in yield of the given commodity. negative aspects of poisoning are associated M e a s u res of year-to-year variation in with its non-specificity and welfare impli- reduction of yield, over and above that due cations. to feral pig density and other sources of systematic variation in yield, can be used to Trapping is best used where poisoning is p redict probabilities of yield re d u c t i o n s impractical or as a follow-up control measure associated with given feral pig densities. after poisoning. Fences are of limited value Probability or risk of impacts rep resent a more because no designs keep feral pigs out useful basis for managing pig impacts, as indefinitely. they allow measures of acceptable uncertainty No research for biological control of feral and risk to be incorporated into management pigs is currently being undertaken. While decisions. v i r a l - v e c t o red immunocontraceptives have Feral pigs can affect the environment by been proposed as a means of controlling some consuming or destroying native plants and feral animals, no such technique has yet been animals or their habitats. The same proc e s s e s successfully developed for controlling any underlying the relationships between pig pest species. density and reduction in yield for agricultural Integrated management using a range of enterprises can be used to understand control techniques produces the best results, consumptive environmental impacts of pigs. but a lack of reliable information on on-farm The persistence of destructive impacts control costs is seen as a barrier to adoption complicates their relationship with pig density. of some techniques. This needs to be addres s e d This creates problems when contemplating if best practice management is to be widely their management through pig control. More adopted. i n f o rmation on ecological factors aff e c t i n g the occurrence of destructive impacts, and Monitoring techniques exist which permi t their effects on ecosystem processes, is req u i re d management programs to be eff e c t i v e l y to resolve some of these management evaluated over time and location. These problems. techniques are more appropriate and

Bureau of Resource Sciences 61 meaningful for evaluating the impact of feral estimates of true feral pig abundance fro m pig management in agricultural enterprises these counts. Wilson et al. (1987) counted rather than natural or enviro n m e n t a l l y pigs in wheat fields during fixed-wing surveys sensitive areas. of kangaroos in south-west Queensland. Counts were presented as uncorrected indices 7.1 Introduction of abundance and it was concluded that fixed- wing counts would probably be of little value Techniques are described in this chapter for for determining pig abundance in all but the estimating the abundance of feral pigs, for most open habitats. Bayliss (1985) also noted assessing their agricultural and enviro n - observations of pigs while conducting fixed- mental impact, for managing these impacts, wing counts of feral livestock in the Top End and for monitoring the effectiveness of of the Northern Territory. Counts were management programs. presented as simple occurrences, and Bayliss recommended that helicopter counts be 7.2 Estimating pig e x p l o red as a means of obtaining more abundance accurate population estimates. Estimates or indices of feral pig abundance Re s e a rch on helicopter surveys to estimate and distribution will assist planning and pig abundance was subsequently conducted implementation of pig management by Hone (1987). He used a known-size programs. Estimates or indices of abundance population of pig carcasses to test two options and distribution can be used in conjunction for correcting visibility associated with counts with local knowledge to: determine the need of pigs on an area of the Top End consisting for pig management; identify an approp r i a t e of a combination of flood plains and open management strategy; determine re s o u rc e woodland. The project also assessed the effe c t s re q u i rements for management; and assess of cloud cover, time of day, and observer the pro g ressive reduction in feral pig e ffects on visibility bias. Both methods abundance over the course of the p rovided reasonably accurate population management pro g r a m . estimates. No effects of cloud cover or time of day on visibility bias were detected, Abundance estimates and indices can be although significant observer diff e rences in complex, requiring systematic measurem e n t , the shape of sightability functions for line repeated sampling and usually some form transect counts were detected. Surveys of live of numerical analysis; or simple, re q u i r i n g pigs in the same area showed them to be less less complex measurement and no visible than pig carca s s e s . numerical analysis. Complex estimates are better for formal assessment of the pro g re s s Recent re s e a rch has focussed on or outcomes of management programs, for development of helicopter survey techniques detailed estimation of re s o u rce re q u i re - for estimating pig abundance in semi-arid ments, and for re s e a rch. Simple estimates floodplain habitats (Choquenot 1995). The a re better for providing simple indices of techniques provide accurate estimates of pig abundance so landholders can monitor visibility bias associated with standard i s e d the pro g ress of management pro g r a m s . transect counts, and correction factors for the effects of habitat. 7.2.1 Aerial survey techniques Most re s e a rch on survey methods for feral 7.2.2 Ground survey techniques pigs has focussed on aerial techniques, Various ground survey techniques for feral primarily counts from helicopters. Hone pigs have been used during assessment of (1983a) used fixed-wing aircraft counts of c o n t rol techniques and/or campaigns, or in pigs to assess the efficacy of a 1080 poisoning studies of the population dynamics and p rogram. No attempt was made to derive behaviour of feral pigs (Table 8).

62 Managing Vertebrate Pests: Feral Pigs Table 8: Studies using ground survey techniques to assess feral pig abundance.

Study Technique Habitat/location

Giles (1980) Mark–recapture Semi-arid riverine (New South Wales) Hone and Pederson (1980) Counts at water Semi-arid riverine (New South Wales) Hone (1983a) Direct counts Semi-arid riverine (New South Wales) Hone (1988a,b, 1995) Direct counts, dung counts, Mountain forests extent of rooting (Australian Capital Territory) Saunders (1988) Mark–recapture, Mountain forests, open farmlands catch-per-unit-effort (New South Wales) McIlroy et al. (1989) Mark–recapture Mountain forests (Australian Capital Territory) Choquenot et al. (1990); Mark–recapture, trap success, Semi-arid riverine Choquenot (1995) direct counts, bait consumption (New South Wales) Saunders et al. (1990) Direct counts Mountain forests (New South Wales) Ridpath (1991) Direct counts Tropical woodlands, sedgelands (Northern Territory) Caley (1993) Mark–recapture, Tropical woodlands catch-per-unit-effort (Northern Territory) Choquenot et al. (1993) Direct counts Tablelands forests (New South Wales) Dexter (1995) Mark–recapture Semi-arid riverine (New South Wales)

Four issues are apparent from these continue, and may provide an estimate of studies. Firstly, all ground survey techniques p re - c o n t rol abundance re t rospectively. assessed are labour intensive, most involving repeated measures or repeated capture of T h i rdly, re g a rdless of the technique used, individual animals, and detailed numerical the design and intensity of the survey will analysis. As such, an experienced wildlife depend on the nature of the inform a t i o n biologist will usually be needed to plan, sought. For instance, general inform a t i o n implement and interpret the results of on the broad distribution of pigs will entail g round surveys. w i d e s p read application of low-fre q u e n c y sampling, probably without re p e a t e d Secondly, the choice of techniques will m e a s u res. Detailed information on rate of depend on the context within which the change in pig abundance, on the other hand, survey is to be undertaken. For example, will re q u i re intensive directed sampling, surveys of ground disturbance will usually p robably on marked plots. not provide an accurate estimate of pig abundance before pigs are controlled. Such Finally, none of the ground survey a survey may, however, provide valuable techniques assessed so far can be used to i n f o rmation on the rate of reduction in pig rapidly provide accurate data on pig abundance as pig control operations abundance and distribution.

Bureau of Resource Sciences 63 7.3 Simple estimates and Choquenot (1993) advocates the use of indices of pig kill rates during shooting from helicopters abundance to index pig abundance. Depending on canopy cover, prevailing kill rate (measure d 7.3.1 Surveys of feral pig signs as kills per hour over at least two hours) will start to decrease exponentially at some Pavlov et al. (1992) used a simple scoring t h reshold density. A sudden decrease in kill system for sign of pig activities along semi- rate usually indicates that pig density has random transects in wet–tropical rainfore s t s declined below this threshold density and to index the relative abundance and the cost per kill of continuing to shoot distribution of pigs in north Queensland. beyond this point will rise dramatically. Simple assessments of the spatial extent and/or frequency of pig signs can be used to provide an index of pig abundance. 7.4 Estimating agricultural Because, however, pig activities such as and environmental rooting vary with prevailing season (as do damage habitat pre f e rence and rates of movement), Many factors of experimental design and assessments should be made as far as sampling impinge upon processes for possible under similar seasonal conditions obtaining reliable estimates of pest impacts and in similar habitats (Hone 1995). The use (Hone 1994). Although this section deals with of pig signs will be much more accurate for estimating feral pig impacts, no consideration monitoring changes in pig abundance at a is given to these factors. Rather, pro c e s s e s single location than it will be for comparing involved in estimating the impact of feral pigs pig abundance between locations. on agriculture and the environment are examined, emphasising the consequences of 7.3.2 Indices based on responses these processes for development of effe c t i v e to management management strategies. Damage caused by feral pigs varies both spatially and temporally Several aspects of normal control proc e d u re s (Hone 1995), and this needs to be taken into will vary systematically with pig abundance. account when estimating impact. F ree-feeding carried out before trapping or poisoning provides a useful technique for monitoring changes in pig abundance. If 7.4.1 Estimating agricultural the quantity of bait or percentage of bait impacts trails being consumed before and after As previously outlined (Section 4.4.1), feral poisoning or trapping is re c o rded, some pigs reduce the profitability of agricultural idea of the effectiveness of the program can enterprises through reduced yields and/or be obtained. Conducting periodic fre e - i n c reased costs. With the exception of feeding programs over three or four days damage to fences and water sources, all the t h roughout the year will allow landholders agricultural impacts of pigs are the result of to identify when pig numbers are on the their consumptive habits. Pigs eat cro p s , i n c rease before significant damage occurs. which would otherwise be harvested; grass, In using this technique, however, care must which would otherwise be used to gro w be taken to ensure that seasonal variations wool or meat; and kill lambs. First it is in bait consumption and seasonal habitat essential to verify that the damage being use are taken into account (Choquenot and c o n s i d e red is due to feral pigs. The decision Lukins 1996). This technique has the t ree in Figure 8 can be used to determ i n e advantage of having pigs consuming bait the cause of lamb death. Similar when control is considered timely, c o n f i rmations are re q u i red for crop losses, accelerating the trapping or poisoning for example, checking to ensure pig signs p ro g r a m . a re present at damage sites.

64 Managing Vertebrate Pests: Feral Pigs Fi g u r e 8: Decision tree for determining the cause of lamb death (after Agriculture Protection Board 1 9 9 1 a ) .

Bureau of Resource Sciences 65 Reduction in yields of commodities due dividing damage due to pigs by the known to feral pigs can be estimated on a gross or number of pigs in the immediate area. This per capita basis. Gross estimates of impact per capita estimate assumes the re l a t i o n s h i p a re of dubious value in developing manage- between reduction in crop yield and pig ment strategies. Hence, in this section the density is linear, and the line describing derivation of per capita estimates of d e n s i t y - related reduction in yield passed agricultural impacts is emphasised. t h rough its origin (Figure 10). The first assumption is likely to be valid because Any assessment of the agricultural impacts Caley measured per capita reduction in crop of feral pigs must be able to estimate yield yield where crop abundance would have in the absence of pigs either directly or satiated the intake rate of all pigs pre s e n t , i n d i rectly through extrapolation of some p recluding competition. At higher pig density-dependent relationship. Per capita densities where the abundance of the cro p estimates of impact further req u i re that yield would not satiate the intake rate of all pigs in the absence of pigs can be contrasted p resent, the relationship between re d u c t i o n with that when pigs are present at a range in yield and pig density would become of densities so that per capita reduction in yield can be estimated for each pig density. The relationship between feral pig density and reduction in yield will generally be the same for all consumptive impacts such as lamb predation, damage to grain, sugarca n e , fruit or vegetable crops (Figure 9). This relationship reflects the density-re l a t e d consumptive impacts of most pest species (Southwood and Norton 1973). When the density of pigs is low, crop availability per head is high, precluding inter- p i g competition for the res o u rces on offe r. While pig density is low enough to pre c l u d e competition, the crop intake rate of Fi g u r e 9: Generalised relationship between individual pigs will be satiated (that is, all pig density and reduction in yield. pigs can eat all they want), and the relationship between reduction in yield and pig density will be linear. When pig density i n c reases past the point where competition for available re s o u rces begins to occur, the c rop intake rate of individual pigs will no longer be satiated and the rate at which yields are reduced with increasing pig density will slow, eventually reaching an asymptote. The rate of slowing will depend on the functional response of pigs to cro p availability. The position of a crop along the line plotted in Figure 9 will depend on the abundance of the crop relative to pig density. Two case studies will illustrate these p o i n t s . Fi g u r e 10: Relationship between pig density Caley (1993) obtained a per capita and reduction in yield implied in a study of estimate of the impact of pigs on maize and impacts on maize and sorghum crops in the s o rghum crops in the wet–dry tropics by w e t–dry tropics (Caley 1993).

66 Managing Vertebrate Pests: Feral Pigs Fi g u r e 11: Relationship between pig density and reduction in yield measured in a study of lamb p redation in western New South Wales (Choquenot et al. 1996). c u r v i l i n e a r. However, reduction of cro p by pig-proof electric fencing, or a paddock abundance to the point where competition enclosed by conventional fencing which did between pigs would lead to decreased per not exclude pigs. The two flocks were capita rate of consumption would involve maintained under identical conditions for very high levels of crop damage. The second the duration of lambing. At the conclusion assumption made by Caley was supported of the experiment gross lamb pro d u c t i o n by the behaviour of radio-collared pigs in for each flock, estimated from scanning the immediate area of the crops, all of which results, was contrasted with net lamb spent considerable time feeding in the cro p . p roduction from counts of lambs leaving each paddock. Because flocks were If the relationship between reduction in maintained under identical conditions at yield and pig density over the range of each site, diff e rences in lamb pro d u c t i o n densities normally affecting a particular crop between protected and unprotected flocks can be safely assumed to be linear, and all d i rectly measured the predation rate of pigs present are likely to contribute to the lambs by pigs. Predation rate was expre s s e d reduction in yield, the relatively simple as a function of prevailing pig density, and technique of estimating per capita re d u c t i o n a relationship estimated which allows the in yield adopted by Caley may be impact of pigs on lambing rates to be a p p ropriate. If, however, a linear estimated on a per capita basis (Figure 11). relationship through its origin cannot be A curved line was fitted to the re l a t i o n s h i p assumed, a more complex approach to between pig density and reduction in lamb obtaining per capita estimates of re d u c t i o n yield (predation rate) because not all in yield will be re q u i red. Choquenot et al. n e w b o rn lambs are equally susceptible to (1996) estimated lamb predation by fre e - predation. Pavlov and Hone (1982) rep o r t e d ranging pigs at three locations, each with a that only 23.8% of observed attacks by pigs d i ff e rent pig density. Sites were selected to on lambs were successful. encompass the normal range of pig abundance encountered in the semi-arid The curvilinear relationship between rangelands. At the three sites, two flocks of reduction in yield and pig density in this about 150 ultrasonically scanned ewes were study contrasts with the linear re l a t i o n s h i p placed alternately in a paddock enclosed i n f e r red in Caley’s (1993) study. In the study

Bureau of Resource Sciences 67 on lamb predation it was argued that pigs will pass through the origin, a single estimate can only catch some of the lambs born of reduction in yield due to pigs in re l a t i o n (about 20% in this study), because many to the number or density of pigs present will n e w b o rn lambs are sufficiently fast and fit p rovide sufficient information to derive the to evade capture. At low pig densities, there relationship. If, however, a linear rel a t i o n s h i p a re probably sufficient accessible lambs to cannot be assumed, then reduction in yield satiate the intake of the pigs which are must be estimated for at least three densities p resent and the relationship between of pigs, preferably with replication, so that reduction in yield and pig density will be an adequate test of curvilinearity can be ap p roximately linear. At higher pig densities, p e rf o rmed. If the relationship between h o w e v e r, there are likely insuff i c i e n t reduction in yield and pig density is assumed accessible lambs to satiate the intake of all to be linear when it is in fact curvilinear, pigs present and the relationship between p redicted per capita reductions in yield at reduction in yield and pig density will re a c h higher pig densities will be incre a s i n g l y a maximum level. In Choquenot et al. o v e restimated when per capita impact is (1996), this maximum level occurred at m e a s u red at low pig densities, and a round 5.5 pigs per square kilometre . u n d e restimated when per capita impact is The shape of the relationship between m e a s u red at high pig densities (Figure 12). reduction in yield and pig density is important If all pigs present contribute to the yield when considering how to evaluate reduction, the line describing the rel a t i o n s h i p agricultural damage due to pigs on a per between reduction in yield and pig density capita basis. If it can be assumed that the passes through its origin reg a rdless of whether relationship will be linear over the range of the relationship is linear or curvilinear. If not pig densities likely to be encountered, and all pigs contribute to reduction in yield (for

Fi g u r e 12: E ffect of assuming a linear relationship between pig density and reduction in yield when the relationship is actually curvilinear. Per capita estimates of reduction in yield will be increa s- ingly overestimated when per capita impact is measured at low pig densities (above point A), and u n d e restimated where per capita impact is measured at high pig densities (below point B).

68 Managing Vertebrate Pests: Feral Pigs Table 9: A subjective assessment a of the likely shape of the relationship between reduction in yield and pig density for agricultural products and re s o u rces affected by pigs.

Resource Low density of pigs High density of pigs

Lambs Linear Curvilinear Grain crops Linear Linear Sugarcane Linear Linear Fruit or vegetables Linear Curvilinear Livestock productivity Linear Curvilinear (temperate environment) Livestock productivity Linear Linear (semi-arid environment) Fences and water sources Linear Curvilinear

a That is, not based on measurements. example if only some pigs kill lambs) the line reductions in lambing percentages associated describing its relationship with pig density with pig densities lower than that where per will pass through the x-axis, the intercept of capita impact was measured and would the line being negative. If pigs that do kill u n d e restimate reduction in lambing lambs are removed by trapping in and arou n d p e rcentages associated with higher pig lambing paddocks, the reduction in yield densities (Figure 13). It is less likely that such would reduce to zero, but there would still an error would be made when a curvilinear be pigs present. If a linear relationship force d model is fitted because the significance of t h rough the origin was incorrectly fitted to the contribution made by the intercept to the relationship between yield reduction and explain variation in yield reduction would be pig density, the line would overe s t i m a t e t e s t e d .

Fi g u r e 13: E ffect of assuming a linear relationship between pig density and reduction in yield passes through the origin when it actually passes through the density axis (that is, the y-i n t e rc e p t is negative).

Bureau of Resource Sciences 69 Table 9 gives a subjective assessment of consumption of desirable plant species) or the likely shape of the relationship between destructive (usually ground disturbance reduction in yield and pig density for some t h rough rooting). Most destructive impacts of the products and re s o u rces known to be of pigs are an indirect consequence of a ffected by pigs. foraging activity, so consumptive and destructive impacts may often be closely ‘It may be better to pre d i c t p robabilities of reductions in related. As for agricultural impacts, e n v i ronmental impacts can be estimated on yield associated with pig a gross or per capita basis. Per capita density rather than the estimates of environmental impacts will be average reduction in yield.’ of most use in developing strategies to Depending on the degree of the random manage these impacts. variation associated with specific agricultural The relationship between pig density and impacts, it may be better to pre d i c t reduction in yield detailed for agricultural probabilities of reductions in yield associated impacts in Figure 9 applies equally well to with pig density than average reductions in consumptive environmental impacts, except yield. For example, Choquenot et al. (1996) that ‘reduction in yield’ becomes ‘degree of used a measure of year-to-year variation in shift from undisturbed condition’. This estimated lamb predation to construct generic response variable indexes the p robability distributions for predation rates d i ff e rence in the environmental character- expected at given pig densities (Section istic affected by pigs when pigs are absent 4.1.1). They argued that because of the or present at a range of densities. For considerable stochastic variation in pred a t i o n example, changes to plover (P l u v i a l i s s p p . ) rates over and above that due to pig density, nesting success when pigs are absent, and p redicted probabilities provided a more p resent at densities of 0.5, 2.5 and 5 pigs useful basis for developing strategies to per square kilometre will describe the per manage this impact than did pre d i c t e d capita impact of pigs through consumption average predation rates alone. Pre d i c t e d of plover eggs. This relationship will allow p robabilities allow producers to incorporate the increase in plover nesting success caused acceptable degrees of uncertainty into by given reductions in pig densities to be development of appropriate pig management p redicted when pig management strategies strategies. Probabilities of impact can be a re developed. In the same way that the calculated from between-year variation in shape of this function depends upon the the level of impact that is not explained by ratio of pig density to crop availability for obvious sources such as pig density, seasonal agricultural impacts (Figure 9), the shape of conditions, or recent pig control activities. the relationship between consumptive The use of probability functions as a means e n v i ronmental impact and pig density will of better managing the impact of pigs on depend on the degree of competition for agricultural production should be further the available re s o u rc e5. e x p l o re d . Per capita processes affecting destructive impacts of pigs are more difficult to 7.4.2 Estimating environmental c o m p rehend. Impacts associated with impacts g round disturbance through rooting may The environmental impacts of pigs can be persist beyond changes in the density of consumptive (that is, predation on the eggs pigs, complicating the nature of potential of ground-nesting birds or turtles, or per capita relationships. This in turn

5 Extending the example above, if there were sufficient plover eggs to satiate the intake of pigs at 2.5 pigs per square kilometre but not at 5 pigs per square kilometre, the relationship between the inverse of plover nesting success and pig density would be linear up to 2.5 pigs per square kilometre but curvilinear at 5 pigs per square kilometre.

70 Managing Vertebrate Pests: Feral Pigs i n f o rmation on the ecological impact of rooting and factors which influence its temporal and spatial distribution is required for formulating sensible management strategies. Management based on the assumption of a simple linear re l a t i o n s h i p between pig density and the frequency and extent of new rooting is overly simplistic. ‘Basing management on an assumed simple linear relationship between pig density and the amount of new rooting is too Fi g u r e 14: Variation in pig density and the s i m p l i s t i c . ’ extent of new rooting activity predicted for an Although probability of impact has never erupting interactive pig–vegetation system, been used to develop strategies for when rooting activity is negatively corre l a t e d managing the environmental impact of pigs, with vegetation abundance (after Hone 1988a). the approach is probably useful for many of the same reasons it is applicable to the complicates prediction of changes in impact management of agricultural impacts: with changes in pig density thro u g h management. For example, after a warf a r i n • the approach allows uncertainty to be poisoning program had reduced feral pig co n s i d e red when making decisions about density by 94%, Hone (1987) found a 2% management strategies; reduction in the percentage of experimental • measures of risk associated with different plots containing rooting after one month, and strategies can be fully integrated into the a 3% reduction after two months. Longer-t e rm decision process; and evaluation demonstrated a 59% reduction in the area of ground rooted, and a 22% •e ffects of environmental stochasticity on reduction in the number of experimental plots the outcomes of management can be with rooting up to eight months following the explicitly incorporated into decisions about reduction in pig density. Areas of rooting can management strategies. take months or years to re v e g e t a t e , particularly in cooler temperate climates. 7.4.3 Estimating the cost of pig Hone (1987, 1988a) suggested that if the control extent of new rooting was negatively Once a target pig density for a given c o r related with food availability6, the management program is identified, the cost relationship between pig density and the of achieving it will depend on two factors: extent of new rooting as pigs erupt into a new the prevailing rate of population incre a s e e n v i ronment (or back into an enviro n m e n t which will determine the number of pigs wh e re they have previously been control l e d ) , which must be removed; and the cost of would be the inverse of that between pig each removal, which will depend on the density and food supply (Figure 14). In this techniques available for the enviro n m e n t situation the extent of new rooting will be which the population inhabits. related to a range of pig densities, and the e ffect of pig control on subsequent ro o t i n g Choquenot (1993) used a stochastic will be complex at moderate to high pig population model to estimate variation in density. Hone (1987) suggested that more the re q u i red cull of pigs to maintain levels

6 That is, when food availability is high, there is little rooting, and vice versa.

Bureau of Resource Sciences 71 Fi g u r e 15: Generalised relationship between Fi g u r e 16: E ffect of density-dependent cost pig density and cost-per- re m o v a l . recovery on the relationship between pig density and cost-per- removal for a given c o n t rol technique. of control appropriate to given management of the full poisoning program. Per capita strategies for a population in semi-arid cost or unit reduction for outlay can be used w e s t e rn New South Wales (Section 8.8). for trapping programs, depending on how Simpler models (based on a logistic the program is run. population growth) are available to a p p roximate variation in rates of population If pigs which are shot or trapped can be change if information for more complex sold into the commercial harvesting industry, models is unavailable (Caughley 1976). or if re c reational hunters will pay to participate in control programs, the financial ‘If pigs are sold, or if hunters gains obtained can be offset against the cost pay landholders for shooting of control. Because re t u rns of this kind will rights, the financial gains will p robably, though not always, depend on o ffset the costs of pig contr o l . ’ pig density, the most accurate way of using Having identified the level of contro l them in estimates of control costs is to shift re q u i red, Choquenot (1993) used estimates the appropriate cost-per- removal down the of cost-per- removal depending on density y-axis to an amount commensurate with the for shooting from helicopters, and poisoning average re t u rn per pig received (Figure 16). with 1080, to identify the most cost-eff e c t i v e combination of techniques, and the overall 7.5 Use of impact, e x p e n d i t u re re q u i red to achieve the given distribution and level of control. Such estimates7 p redict the cost of removing a pig at a given density density measurements ( F i g u re 15). Prediction of per capita cost is 7.5.1 Introduction a p p ropriate for shooting from the gro u n d or helicopters, where variable costs The management of feral pig impact can be dominate outlay to achieve each kill, and a m o re effective and economical if plans for decision to halt expenditure can be made the program are based not only on at any given density. Prediction of unit sociological aspects, but also on a thorough reduction (pigs killed or reduction in density analysis of the problem as assessed by achieved) for outlay is more appropriate to me a s u res of feral pig impact, distribution and poisoning programs where fixed costs density. This information can be collated for dominate, and expenditure is made in term s interpretation in tables but it is best done on

7 That is, density-dependent cost-per-removal relationships.

72 Managing Vertebrate Pests: Feral Pigs maps on a whole-property, local or regional s o u rces and features which will need to be basis. This approach has two main benefits: identified in planning a feral pig management p rogram. These will include water courses, • it highlights patterns of distribution of tanks, dams, fence lines, lambing paddocks, damage which can reveal underlying refuge habitats for endangered species, causes, best remedies and the most property boundaries, natural boundaries and economical approach to applying feeding and shelter habitat for pigs. management programs; and C o r relations between damage and habitat, • it reveals trends in feral pig damage over w h e re they can be identified, will determ i n e time, and helps to assess the effe c t i v e n e s s w h e re feral pig management needs to be of remedial action. Detection of time-tren d s t a rgeted. A lambing paddock is an obvious re q u i res a monitoring program that is example but conservation problems are less continuous through the management c l e a r. For an endangered animal species program. t h reatened by feral pigs, the species’ re f u g e h a b i t at — which will need to be targeted for A major deficiency in current feral pig pig control if the species is to thrive — may management is the lack of a simple, readily not necessarily be its pre f e r red habitat. In applied system for measuring feral pig density these situations maps can be used to identify and abundance and for re c o rding it in a the distribution of both the refuge and suitable common format for use by land- pre f e r red habitats with efforts to remove feral managers and government agencies. pigs concentrated in both. 7.5.2 Recording information ‘Entering hot spots of pig activity into a GIS will allow After damage, distribution and abundance c o r relations to be identified have been assessed, the information must between these are a s be tabulated. The tabulation should be as and vegetation simple as possible to allow the ready transfer types or endangere d of information into graphs, maps or species habitats.’ databases that will assist interpretation. It is also a way of ensuring that all the re l e v a n t Some Rural Lands Protection Boards in i n f o rmation is documented. New South Wales are developing computer- based mapping systems which display densities derived from property inspections. 7.5.3 Mapping These maps re c o rd changes over time, Maps can be of various types: simple hand including core inputs such as the amount of drawn charts, topographical maps, land poison or other control agents sold to the system or land unit maps, aerial la n d h o l d e r. Global Positioning Systems (GPS) photographs, or sophisticated interactive a re being used to accurately locate activity computerised Geographic Inform a t i o n areas on properties, thus allowing hot spots Systems (GIS). The choice depends on to be easily identified. These activity are a s expertise available, re s o u rces, extent of the can be incorporated into a GIS which will p roblem and the scale of the tre a t m e n t . allow correlations between vegetation types, e n d a n g e red species habitats and feral pig Some landholders or staff of contro l distribution and abundance. agencies have a strong perception of feral pig density and distribution in an area and The primary benefit of mapping is that it may readily map that information. Where , allows a picture to be developed of ho w e v e r, little is known about the distribution manageable control areas. These areas are and abundance of feral pigs in an area, maps decided on the basis of social issues as well a re important for determining and re c o rd i n g as distribution, abundance and impact data. the relationships between variables Plastic overlays re p resenting each of the associated with the distribution of food components involved in the decision-making

Bureau of Resource Sciences 73 process can be used to identify the best area s • type and value of re s o u rces affected by for effective feral pig management. feral pigs; Continuing use of the maps will show • severity of damage; p a t t e rns over time. These patterns can be • p resence of, and damage due to, other c o r related to changes in re s o u rce inputs or pests and other threatening processes; seasonal conditions, permitting a more accurate assessment of the effectiveness of • feasibility of reducing damage in time to control through time. make the effort financially or biologically attractive; 7.5.4 Allocating management • size of the management unit; units • availability of appropriate management The information collated on maps can be used techniques; to identify practical management units. Boundaries in the management unit will be • availability of funds, time, labour and evident from natural and artificial barriers, equipment both for immediate action and apparent changes in the distribution of food for future sustained control; s o u rces, or social units within the local • ability to coordinate management eff o r t ; community. An important difficulty which and must be considered is the mobility of feral pigs. This can negate efforts to control feral • ability to prevent reinvasion by feral pigs. pig damage due to neighbouring feral pigs moving into vacated areas. This influences 7.6 Control techniques the size of the management unit which is in t u rn influenced by the time frame of the 7.6.1 Shooting management program. For example, Shooting has been long established as a protecting a lambing paddock for two months c o n t rol technique for feral pigs. Rolls (1969) will be a much smaller operation than reports that pigs were shot near Mudgee in protecting a large flora reserve to ensure the 1865 and that thousands were shot in the l o n g - t e rm survival of an endangered plant Riverina in the 1880s. species. Until about 1980, shooting was a gro u n d - Although the distribution and abundance based operation undertaken by re c re a t i o n a l of feral pigs in the management area may not hunters and landholders. Since 1980, be known, the size of management units shooting from helicopters has become an based on known figures for density and home i n c reasingly popular form of control, for range for similar areas can be used as a guide. reasons outlined by Korn (1986a). It is, however, critical that this information be used in the context of social groupings within 7.6.2 Shooting from the ground the local rural community. Group control of feral pigs is now a well established process Recreational hunting but its success depends on cohesiveness and The feral pig is commonly taken by shooting a shared common vision (Chapter 9). f rom the ground. Tisdell (1982) estimated that amateur hunters may kill about 15 –2 0 % 7.5.5 Establishing priorities of the feral pig population annually (Section 4 . 4 . 1 ) . Priority for treatment of management units ( c o n t rol areas) will depend on several Landholders factors including: Shooting from the ground by landholders • social groupings within the local rural is generally conducted on an opportunistic community; basis. Occasionally, however, coord i n a t e d

74 Managing Vertebrate Pests: Feral Pigs Shooting from the ground

Advantages D i s a d v a n t a g e s

• Can remove individual pigs in a disease • Rarely effective for damage control outbreak • Can disperse pigs • Species-specific • Costs increase greatly as pig numbers decrease • Inexperienced shooters or use of dogs by hunters may be inhumane • Requires skilled operators • Not long-lasting or effective for large-scale control shooting drives may be conducted. Few data removing residual pigs after densities have a re available on the numbers of feral pigs been reduced by other forms of control. He taken by landholders, although Benson reported a 90% success rate when dogs (1980), in a survey in north-west New South e n c o u n t e red solitary pigs but that the Wales, reported that landholders shot 33% success rate rapidly declined as the gro u p m o re pigs than re c reational hunters. In size of pigs increased. A trial of hunting in Benson’s survey, shooting from the gro u n d jarrah forest in south-west We s t e rn Australia was the control technique which re m o v e d showed that at least one-third of all feral the greatest number of feral pigs. pigs encountered escaped from the dog (Oliver et al. 1992). When groups of pigs Shooting from the ground is generally w e re encountered, usually only one was c o n s i d e red to play an insignificant role in caught. The effectiveness of hunting damage control except where it is depends largely on the skills of the hunter intensively conducted on small populations and dogs. Intensive hunting with dogs might (Masters 1979; Allen 1984; Hone 1984). No cause pigs to disperse (Saunders and Bryant studies have reported on intensive, 1988; Section 3.3.2) which could aff e c t strategically timed shooting programs aimed c o n t rol programs, and be of particular at damage contro l . c o n c e rn in an exotic disease outbreak. The use of dogs to pursue, and hold pigs is Shooting and dogging c o n s i d e red inhumane by the Australian and The use of trained pig dogs to locate and New Zealand Federation of Animal Societies catch feral pigs, which are then shot by the ( A N Z FAS) and also puts the dog at risk of h u n t e r, is popular with re c reational hunters. injury or death (G. Oogjes, ANZFAS, Vic t o r i a , Dogging can have a negative impact on pers. comm. 1996; Section 5.2). sheep enterprises (Tisdell 1982) or native ‘Hunting will not achieve fauna if pig dogs become feral. McIlroy and l a rge-scale reductions in pig S a i l l a rd (1989) studied the efficacy of p o p u l a t i o n s . ’ hunting feral pigs with dogs, and concluded that hunting is generally not effective for l a rge-scale reductions in populations, but 7.6.3 Shooting from helicopters could be useful for obtaining samples of Feral pig control by shooting fro m pigs for monitoring disease during the first helicopters was first conducted in the Moree few days of an exotic disease outbreak, and Rural Lands Protection Board district of also for killing pigs that survive other control n o r t h e rn New South Wales. Its popularity methods. Caley (1993) reported that hunting as a control technique spread to other parts with dogs is an effective technique for of New South Wales and Australia during

Bureau of Resource Sciences 75 Shooting from helicopters

Advantages D i s a d v a n t a g e s

• Ideal for rapid population knockdown over a • Can disperse animals number of properties • Costs increase greatly as pig numbers • Takes up little landholder time decrease • Low costs per pig killed • Annual shoots ineffective for keeping pig • Species-specific numbers low • Allows control in inaccesible terrain • Ineffective in woodland and forest • Unaffected by seasonal conditions the early to mid-1980s. The advantages of 1984; Korn 1986b; Saunders 1993b). Because shooting from helicopters are that it is the technique provides a quick population species-specific, can yield results equal to knockdown, it is seen as a valuable contro l poisoning programs, has a low opportunity tool in an exotic disease emergency. Bayliss cost in terms of time to the landholder (1986) and Saunders and Bryant (1988) because it is efficient, is more than evaluated the use of helicopters in this competitive on a cost-per-pig basis with context whereas Hone (1990c) evaluated other methods of control, permits contro l pig control in the Northern Territory by in marshy country which is difficult to work applying pred a t o r–p rey relationship models. f rom the ground, and is not affected by Saunders (1993b) evaluated the technique seasonal conditions (Korn 1986a). in the southern Macquarie Marshes of New The impacts of shooting from helicopters South Wales over two consecutive years by on feral pig populations have been well applying the index–rem o v al–index method. documented (Hone 1983a; Bryant et al. An estimated 80% population reduction was

Shooting from helicopters allows rapid reduction of feral pig populations over a number of p ro p e r t i e s . Source: NSWAF

76 Managing Vertebrate Pests: Feral Pigs Enterprise substitution

Advantages D i s a d v a n t a g e s

• No expenditure on control programs • Does not protect resources • May have high economic cost • Not feasible in many areas achieved in the first year followed by a 65% instead of lambing ewes. This situation was reduction in the second year, after the reversed in the 1980s following an extensive population had re c o v e red to 77% of its first c o o rdinated control program where feral year level during the intervening 12 months. pig numbers were estimated to have been Although annual campaigns involving reduced to 10% of their previous levels shooting from helicopters are unlikely to ( K o rn 1993). Other landholders running result in long-term reductions of pig lambing ewes switched to running cattle numbers, because the populations generally because of feral pig predation (Hone et al. recover before the next campaign, the 1 9 8 0 ) . technique is strategically useful to pro t e c t susceptible enterprises from short-term 7.6.5 Habitat modification damage. It also gives feral pig control a high This technique is not common (Hone et al. p rofile and has fostered group control of 1980), since it often involves destruction of feral pigs over wide areas. This approach is thick vegetation (Hone 1984). Such a pe rceived to be more effective than prop e r t y practice shows little respect for other benign managers controlling pigs randomly throu g h species using that habitat and supports the space and time because it reduces the effe c t s slash, burn and destroy philosophy of of immigration. Shooting from helicopters is not effective for reducing pigs to very low p revious years. It is not recommended other densities because costs of finding and than in very exceptional circ u m s t a n c e s . shooting remaining pigs increase greatly as The conversion from open bore drains numbers decline (Figure 15). to piped water supply from artesian bore s ‘Shooting from helicopters can in the rangelands might reduce pig habitat p rotect susceptible land fro m and facilitate trapping near point-sourc e s h o r t - t e rm damage, but annual waters, especially in dry times. Replacement shoots do not give long-term of open earth tanks with piped waters might reductions in pig numbers.’ further facilitate pig contro l .

7.6.4 Enterprise substitution 7.6.6 Fencing Enterprise substitution is a control technique Fencing is not a popular control technique of last resort. It was used around the for feral pigs except to protect valuable Macquarie Marshes in the 1970s when enterprises in relatively small areas (McIlro y landholders were forced to run wethers 1993). The insignificance of fencing as a

Habitat modification

Advantages D i s a d v a n t a g e s

• Lack of available water reduces all pest • Often not an effective option used alone numbers • May destroy habitat of conservation value

Bureau of Resource Sciences 77 Fencing

Advantages D i s a d v a n t a g e s

• Effective protection for lambing paddocks or • Can be expensive and requires high level of small high-value resource areas maintenance • More humane than other control methods • Fences will eventually be breached • Not practical for large-scale control fo rm of control is confirmed by three studies designs, with and without electrification, which reported on, among other things, under test conditions. Only one fence landholder use of control techniques p revented total movement of feral pigs (Benson 1980; Appleton 1982; Bryant et al. between paddocks under the test conditions 1984). None of these studies, conducted in and its design is shown in Figure 17. north-west New South Wales and adjoining Electrification significantly reduced the a reas in Queensland, mentioned fencing as f requency of feral pig movement thro u g h a control technique. This is despite the fact fences. Other fence designs have also been that fencing has been shown to pro v i d e developed by New South Wales Agriculture , e ffective protection for lambing ewes in one of which is shown in Figure 18. No north-west New South Wales (Mitchell et al. commonly used ‘exclusion’ fence, electrified 1977; Plant et al. 1978; Pavlov et al. 1981). or not, has been successful in keeping feral pigs out indefinitely. Breaches eventually ‘Fencing is not a popular result due to human erro r, physical damage c o n t rol technique for feral to the fence, electrical failure or lack of pigs except to protect valuable m a i n t e n a n c e . enterprises in small ar e a s . ’ The ineffectiveness of fences in the long- Design of fences is critical for eff e c t i v e l y t e rm, and thus their low adoption as a form restricting the movement of feral pigs. Hone of widespread control, revolves around their and Atkinson (1983) evaluated eight fence maintenance and the fact that if used alone,

F i g u r e 17: Pig fence constructed with 8/80/15 hingejoint and steel posts. This design totally p revented movement of pigs between paddocks under test conditions (after Hone and Atkinson 1 9 8 3 ) .

78 Managing Vertebrate Pests: Feral Pigs Fi g u r e 18: A fully electrified fence with offset trip wires is considered to be highly effective against feral pigs. they merely transfer the problem from one 1983/84; Allen 1984; Bryant et al. 1984; Hone paddock to another or one property to 1984; Bell 1988; Lukins 1989; McIlroy 1993; another (Allen 1984; McIlroy 1993). P. Salleras, C4, Queensland, pers. comm. 1993). The most comprehensive description 7.6.7 Trapping of trapping is that provided by Lukins (1989), who lists the advantages of trapping as: The development of trapping as a contro l technique appears not to have accelerated • trapping does not interf e re with norm a l until the mid-1970s when Giles (1973) pig behaviour (unlike shooting or described various trap designs and outlined dogging); several advantages of trapping over • the number of pigs is known exactly, and poisoning. The increasing popularity of carcases can be removed safely; trapping as a technique is possibly because landholders can see what they get, unlike • it is a flexible technique and can be fitted in poisoning programs, and they can use into routine property activities, making it the trapped pig as a re s o u rce if chillers are economical in terms of labour, materials and number of operators; and in their are a . • traps can be moved or re-used as Trapping, trap types and extent of use necessary. Good trapping makes use of have been widely described over the years opportunities as they arise. (Giles 1977; Benson 1980; Hone et al. 1980; Appleton 1982; Stevens 1983; Ti s d e l l Additional advantages are that:

Bureau of Resource Sciences 79 Trapping is becoming an increasingly popular technique for feral pig management, particular - ly where baiting is not practical. Source: P. Fleming, New South Wales Agriculture

• traps are humane if routinely checked; and the rest of the trap should be designed robustly to cope with the pigs likely to be • dogs are not put at risk as they are with caught. Trap designs are shown in Figure 19 . 1080 poisoning and dogging. A g r i c u l t u re Protection Board (1991b) Landholders often permanently locate traps p rovides additional details of trap designs. in areas of feral pig activity and activate the Hone (1984) lists the important steps in traps when pig signs become evident or on trapping: a strategic basis to protect a susceptible enterprise. Hone et al. (1980) list the following • feeding sites should be placed where feral points to be considered when trapping: pigs are active, for example, water points and pop-holes in fences; • type of trap to use; • initially, feed the pigs with bait such as • number of traps to use; grain (fermented is often attractive), pellets, • w h e re to put traps; vegetables or fruit, meat or carrion; • number of nights each trap is used; • build the trap where feed is being taken, and leave it open and baited, but not set, • type and amount of bait to use; and for one or two nights; • amount and duration of fre e - f e e d i n g . • then set the trap each night; Various trap designs exist and the choice • if the feed is being taken, continue to trap revolves around the experience, knowledge until no more pigs are caught; and re s o u rces available to the trapper. All • leave the trap unset and feed a diff e re n t traps rely on the proper functioning of the bait from that used initially; do o r. This is a key element. Once the trapper is confident that the door works eff e c t i v e l y , • if feral pigs start taking the bait, set the trap

80 Managing Vertebrate Pests: Feral Pigs for several nights; and to be eaten at firetrails in autumn and away f rom firetrails in spring. Saunders et al. • once no bait is taken, start feeding (1993) estimated that 62% of those animals elsewhere before moving the trap. exposed to traps were caught but that this Lukins (1989) elaborates on each of the only re p resented 28% of the entire above points and maintains that trapping is population. If, however, Saunders et al. a flexible technique that can be fitted into (1993) had kept trapping until bait take fell routine property activities. Bait pre f e re n c e s to zero, it may have been more eff e c t i v e . can vary from area to area especially for meat, carrion and grain baits. In relation to Choquenot et al. (1993) tested trapping c a rcase disposal, Lukins states that pigs as a control technique in a central tableland should be shot in the trap, where they may e n v i ronment in New South Wales. They be left as bait for other pigs. In some are a s , reported a 100% population reduction over leaving pig carcases may deter other pigs 16 nights when bait take was used as an f rom entering traps, and in this case they index of feral pig abundance, and an 81% should be removed completely from the reduction when spotlight counts were used a re a . as the index. It is time consuming and expensive to In the wet tropics area of Queensland, construct and maintain traps, there f o re particularly the World Heritage Area where trapping is best used where poisoning is choice of control techniques is more limited, impractical or as a follow-up contro l many people re g a rd trapping as the most m e a s u re after poisoning (Agriculture acceptable technique (McIlroy 1993). P rotection Board 1991b). Results are best if P roblems can be encountered with the a l t e rnative food is in short supply. Once a e n d a n g e red cassowary which sometimes decision is made to trap, interfe rence should enters traps and often cannot be re m o v e d be minimised, particularly shooting or without fatal injury. This aspect is being disturbance by dogs. a d d ressed through cooperative efforts of landholders and the Consultative Committee The key point in the evaluation of for Cassowary Conservation, now the trapping is whether or not feral pigs Community for Coastal and Cassowary encounter the trap. Only if pigs are observed Conservation (C4) (P. Salleras, C4, to approach a trap and then either enter or Queensland, pers. comm. 1993), who have not enter, can a more informed judgement developed a cassowary-proof trip-door be made. Even then the judgement is open m e c h a n i s m . to question because the bait may not be attractive to that pig or some social pres s u re s In a survey of 133 landholders conducted f rom other pigs either inside or outside the in three districts in north-west New South trap may influence behaviour. Wales in 1978 by Benson (1980), trapping was the least used control method (others Trapping success was evaluated in the being poisoning and shooting). Thirty-thre e subalpine environment of Kosciusko of the landholders surveyed used 68 traps National Park by Saunders et al. (1993). They to kill 2600 pigs, an average of 38 pigs per found location of traps and season were trap for the year. This was only 5% of the both important: (a) placement of bait at the total number of pigs killed by all methods t reeline, rather than in timber or out on in the three districts surveyed. There was a clearings, gave the greatest chance of bait bias in the use of traps, with 20 of the 33 being found and accepted irrespective of landholders that used traps coming fro m the presence or absence of other factors; one of the three districts surveyed. (b) the presence of recent pig activity i m p roved the chances of bait being found In a survey of landholders a few years and accepted particularly if bait was placed later in the Waggamba Shire in southern at the treeline; and (c) bait was more likely Queensland, Appleton (1982) found that on

Bureau of Resource Sciences 81 Fi g u r e 19: Feral pig trap designs and specifications (after Lukins 1989).

82 Managing Vertebrate Pests: Feral Pigs Trapping

Advantages D i s a d v a n t a g e s

• Can be incorporated into existing • Must be checked regularly management practices • Labour intensive; best used as follow-up • Pig numbers can be monitored control • Traps can be re-used • Not practical for large-scale control • Landholders can offset trap costs by selling trapped pigs • Does not affect normal pig behaviour • More humane than other methods smaller properties (less than 2100 hectare s ) re q u i red to kill pigs, but, in view of the trapping was the most popular contro l considerable range in intake of poison bait method. An increase in the popularity of by diff e rent sized pigs, 0.05%w/w was trapping on medium-sized pro p e r t i e s preferred. This is the current recommended revolved around switches to cropping and bait loading in New South Wales although the i n c reased machinery use rather than horses, concentration can be reduced to 0.03%w/w and a wariness about losing farm dogs to at the discretion of control officers. 1080 poison. Poisoning was most popular The toxicity of 1080 to feral pigs in on properties larger than 4960 hectares. No Australia was first reported by McIlro y data on the number of pigs trapped were (1983), who established an LD5 0 of 1.04 p rovided for the three control techniques, milligrams per kilogram liveweight following and it is not possible to compare the re s u l t s field work north-west of Bourke in mid- to the New South Wales study by Saunders s u m m e r. In a study, by Sheehan (1984) on et al. (1993). In an earlier study at Narrabri, c a p t u red feral pigs, an oral LD5 0 of 1.03 New South Wales, trapping was found to be milligrams per kilogram and an LD90 of 11.25 the most cost-effective control technique if milligrams per kilogram was established. t h e re were less than 30 feral pigs killed per O’Brien (1988) obtained a LD5 0 of 4.11 year (Turvey 1978; Bryant et al. 1984). milligrams per kilogram for feral pigs kept in enclosures at Trangie. Possible re a s o n s

7.6.8 Poisoning for the dissimilar LD5 0 values obtained are d i ff e rences in the ambient temperature s Poisoning is a control technique that is occurring during the trials and diff e re n t widely accepted throughout rural com- incidences of vomiting by the pigs. For munities. It is perceived as a method which, example, only 20% of the pigs in McIlro y ’ s if properly used, can produce a quick trial vomited, versus 98% in O’Brien’s trial. knockdown of a feral pig population. The D i ff e rences in the length of acclimatisation negative aspects of poisoning are associated by the pigs to the trial conditions and the with its non-specificity and welfare mode of administration of the 1080 (that is, implications (Section 5.2). gastric intubation versus consumption in wheat bait) may also have been partly Sodium monofluoroacetate (1080) responsible, although stress alone does not The first trials on toxicity of 1080 to pigs were appear to affect sensitivity of pigs to 1080 conducted at Moree in north-west New South ( M c I l roy 1983). It is possible that pigs given Wales in 1973 (J. Giles unpublished), using a concentrated aqueous solution of 1080 concentrations from 0.01%w/w to 0.05%w/w may absorb a higher proportion of the in baits. It was found that a minimum ingested dose before vomiting than those concentration of 0.025%w/w in baits was which ingest the 1080 in bait; however, this

Bureau of Resource Sciences 83 has not been tested. al. (1987) examined the toxicity of 1080 to captive feral pigs when administered in Vomiting is a common characteristic of d i ff e rent, but commonly used baits, that is, 1080 poisoning in feral pigs. This has been wheat grain and manufactured pellets. observed in all captive pig trials and vomitus Under the test conditions, it was found that is commonly found around 1080 bait stations wheat produced a significantly higher in the field. O’Brien et al. (1986) reported a mortality than pellets (60% compared with mean of 21 episodes of vomiting for each 28%). When, however, O’Brien and Lukins captive feral pig after 2.1 milligrams of 1080 per kilogram was ingested. This high (1988) investigated the factors influencing incidence of vomiting has four implications: the intake of 1080 by free-ranging feral pigs, they found that pellet bait was ingested in (1) vomitus containing 1080 may cause significantly greater quantities than cere a l secondary poisoning of non-target species (wheat and barley). This would to some close to, and at a distance from, 1080 bait extent counteract the lower toxicity of 1080 stations; loaded pellets identified in captive feral pigs. (2) secondary poisoning of feral pigs may The success of a 1080 poisoning pro g r a m enhance the effectiveness of the revolves around adequate free-feeding with poisoning campaigns; non-toxic bait to attract pigs. Bryant and (3) vomiting may result in sub-lethal dosing Hone (1984) identified problems with fre e - of target animals, decreasing the overall feeding by landholders during the north- mortality and effectiveness of poisoning west pilot feral pig control scheme, the main programs; and one being that it was often terminated before bait-take plateaued. O’Brien and Lukins (4) pigs surviving a sub-lethal dose may (1988), however, question whether this is a develop an aversion to 1080 (or enhanced p roblem, arguing that the plateauing could neophobia to baits), decreasing their just as likely be due to increased bait susceptibility to subsequent poisoning consumption by the same number of pigs. programs (O’Brien et al. 1986). ‘Successful 1080 poisoning Because of concern about these p rograms r e q u i re implications, the effectiveness of meto- adequate initial fr e e - f e e d i n g clopramide (an anti-emetic) in pre v e n t i n g with non-toxic bait vomiting after ingestion of 1080 was assessed. to attract pigs.’ While Rathore (1985) reported complete success with this anti-emetic, Hone and Kleba M c I l roy et al. (1993) found that pigs in (1984) found it ineffective, as all pigs they the hill country of south-east Australia dosed with 1080 vomited, re g a rdless of readily ate fermenting wheat and pellet baits whether they had also been dosed with the t h roughout the year. Trail baiting of pigs is, anti-emetic. O’Brien et al. (1986) tested three h o w e v e r, likely to be more effective during anti-emetics (prochlorperazine, thiethyl- late autumn than at other times of year perazine and metoclopramide) and found because more pigs are likely to be close to that none of them suppressed vomiting in trails then and will more quickly find and pigs which had ingested 1080. They did find eat greater quantities of bait. that metoclopramide decreased the amount Feral pigs are usually off e red 1080 at bait of vomitus produced (and the proportion of stations. If properly constructed, bait stations 1080 ejected) and that although typical levels allow cattle and sheep to be run in the same of 1080 in the vomitus would be hazardous paddock at no risk. In addition, they can be to several non-target species, and peak levels made permanent structures on pro p e r t i e s hazardous to most, they were unlikely to be and activated when necessary. On the other hazardous to other pigs. hand, trail baiting can be used only in As a follow-up to this work, O’Brien et paddocks which contain no domestic stock,

84 Managing Vertebrate Pests: Feral Pigs hence it is little used except where cro p p i n g (SAP — the precursor to CSSP) either alone is extensively practiced. or in conjunction with other poisons. Hone and Pedersen (1980) reported a ‘Although CSSP poison kills 58% reduction in a feral pig population feral pigs it is probably not baited with meat in north-west New South h u m a n e . ’ Wales. A later study by Hone (1983a) in G a rner (1987) and O’Brien and Lukins south-west New South Wales reported a 73% (1990) describe the action of yellow reduction in the same population when pigs phosphorus poisons. Although it is eff e c t i v e w e re baited with pellets laid in trails. This in killing pigs, there are serious doubts about estimate was based on aerial surveys. its humaneness (National Consultative Estimated reductions of 92% and 96% were Committee on Animal We l f a re 1992). No made by spotlight counts and hide counts studies have been conducted on its impact respectively. Bryant and Hone (1984) used on non-target species although there is bait-take as an index in north-west New general concern about them because there South Wales to estimate a population is no control over CSSP application rates. reduction of 92% on grazing properties and Label directions provide crude guidance, 99.4% on farming pro p e r t i e s . but make no allowance for diff e rent sizes M c I l roy (1983) lists several disadvantages of animals on which CSSP is commonly of 1080 as a poison for pigs: used. Phosphorus has an LD5 0 of 5.3 milligrams per kilogram and an LD of 9.3 • survival of some pigs after ingesting very 9 0 high doses; milligrams per kilogram and pigs typically take two to four days to die after intoxication • frequent vomiting of ingested bait which (O’Brien and Lukins 1990). produces a poisoning hazard to non-targe t animals, especially farm dogs; Warfarin • possible development of bait shyness; Wa rfarin, an anticoagulant, is a poison readily accepted by feral pigs. It is very • potential for killing non-target species e ffective providing extended feeding is 8 th rough primary and secondary poisoning ; practiced. Hone and Kleba (1984) achieved and a mortality rate of 92% when penned feral • lack of an antidote to the poison. pigs were fed at 0.08%w/w for two or thre e days or at 0.1%w/w for two days. At these Yellow phosphorus (CSSP) concentrations the pigs took from 5.5 to 9.5 CSSP is a yellow phosphorus-based poison. days to die. Food intake began to drop about It contains 4% active phosphorus and is two days after poisoning started. ma n u f a c t u red and marketed in Queensland. A p p roximately three days after poisoning It is a widely used poison in New South started, feral pigs became lame and lethargi c . Wales and Queensland, its popularity Hone and Mulligan (1982) report that stemming from the fact that landholders can w a rfarin has a latent period of 4–17 days. use it as a take-home poison. That is, they M c I l roy et al. (1989) evaluated warf a r i n can buy it in quantity, store it on their poisoning in Namadgi National Park in the p roperty and use it at a later date. This is Australian Capital Territory by trialing 0.13% m o re convenient than 1080 baits, which w/w soaked wheat, bread and acorns for cannot be stored. The extent of CSSP use is 15 days. They killed 30 of 32 radio-tracked uncertain, but a survey by Benson (1980) pigs (94%), which took an average of 9.7 showed that of 63 landholders using (range 6–15) days to die. Hone (1987) poisons, 28 used Sayers Alport Phosphorus separately estimated an 87–90% re d u c t i o n

8 But see McIlroy (1985, 1986) for further discussion.

Bureau of Resource Sciences 85 Poisoning

Advantages D i s a d v a n t a g e s

• Proven method • Non-target risks • Widely accepted in rural community • Animal welfare implications • Fast and effective initial knockdown • Requires registration • Relatively cheap • May cause vomiting and result in bait-shy pigs or development of resistance • Usually requires prior free-feeding

in pig abundance during the same period, feral pig control, it would need to be based on counts of dung pellets before and re g i s t e red with the National Registration after the poisoning program. Hone and Authority (for agricultural and veterinary Stone (1989) reported a significant decline chemicals) before it could be used rou t i n e l y . in pig abundance over 18 months at sites in T h e re are some welfare concerns associated the Australian Capital Territory where with the slow death caused by anticoagulant w a rfarin was used. At sites with no warfa r i n , poisons. Despite interest in the use of t h e re was no decline in pig abundance. w a rfarin for controlling pigs, no Australian ‘The anticoagulant poison, states or territories have proceeded with w a rfarin, is effective for pig further tests to determine the hazard c o n t rol if extended fre e - w a rfarin poses to other animals. Such tests feeding is conducted first.’ a re necessary before it can be re g i s t e red as a pig poison. Saunders et al. (1990) achieved an estimated 90% reduction in a feral pig 7.6.9 Fertility control population on the central tablelands of New South Wales. This program extended over It is unlikely that chemical contraceptive 57 days, during which non-toxic bait was compounds would be effective or practical o ff e red for the first 14 days. They found for controlling populations of feral pigs for evidence of a decline of warfarin re s i d u e s reasons discussed by Bomford (1990). The with time, which reduced the chance of main potential problems with this appro a c h secondary poisoning. This evidence a re : supports the previous findings of O’Brien • lack of long-acting contraceptive et al. (1987), McIlroy et al. (1989) and compounds (making repeat dosing O’Brien and Lukins (1990). Wa rfarin has an necessary); L D5 0 of 2.9 milligrams per kilogram and an • high costs of delivery by baits (particularly L D9 0 of 6.1 milligrams per kilogram when two consecutive doses, seperated by 24 when repeat dosing is needed); hours, are administered (O’Brien and Lukins • less effect on population size than when 1 9 9 0 ) . an equivalent number of pigs are killed; Choquenot et al. (1990) evaluated and d i ff e rent feeding strategies (ad libitum o v e r • potential effects on non-target species. 14 nights and intermittent distribution over 14 nights). Average reductions calculated The development of immunocontra- f rom helicopter and spotlight counts were ceptive techniques to cause sterility in feral 63% and 35% for the ad libitum a n d pigs, similar to that currently being in t e rmittent strategies respectively. Although re s e a rched for rabbits, foxes and rodents by w a rfarin has been used experimentally for the Cooperative Research Centre for

86 Managing Vertebrate Pests: Feral Pigs Biological Control of Vertebrate Pest 7.6.10 Biological control Populations (Tyndale-Biscoe 1994), may be c o n s i d e red in the future if the curre n t Biological control of feral pigs in Australia re s e a rch projects are successful. It may be might be achieved either by using an possible to package suitable gamete i n t roduced pathogen or by live-vectore d antigens, capable of inducing an immuno- immunocontraception (Section 7.6.9). contraceptive response in pigs, within African swine fever (ASF) and classical biodegradable micro s p h e res that are orally swine fever (CSF), for example (Section 4.3.2), ingested in baits. This would deliver the are two highly contagious viral diseases for immunocontraceptive antigen to the gut, which porcines are the only natural vertebrate leading to an immune response which hosts (Geering and Forman 1987; Geering et would render the animal infertile. If used al. 1995). Mortality rates from acute infections as part of an integrated feral pig of both diseases, passed on by direct contact management program, this technique could and fomites, may reach 90% or even approa c h meet many animal welfare concern s 100% (Geering and Forman 1987; Hone et al. applicable to other control techniques. 1992). Outbreaks of CSF occurred in domestic Although bait-delivered immunocontra- pigs in Australia in 1903, 1927/28, 1942/43 eptives may provide only localised contro l , and in both feral and domestic pigs in 1960/61 they could be useful, if used in conjunction (Keast et al. 1963; Geering et al. 1995). As far with other traditional methods, to contro l as can be determined, the outbreaks were small isolated populations of feral pigs. eradicated, although Littlejohns (1989) R e s e a rch would also be re q u i red to questions whether the causative virus has d e t e rmine the level of sterility that could be been eradicated. Prevalence of CSF virus achieved and the consequent effect on feral strains of low virulence is incre a s i n g , pig populations. No immunocontraceptive particularly in countries where live vaccines re s e a rch for feral pig control is curre n t l y are used and where infected carrier sows have being undertaken, and this type of become an important source of virus spread technology has not yet been developed for (Geering and Forman 1987). This casts doubts the control of any pest species. The main on the usefulness of CSF for control of feral p roblem with such an approach would be pigs in Australia. the high cost of delivering baits, and the The possibility that the CSF virus could consideration that poison baits may pro v i d e persist in feral pig populations above a cheaper and more effective population certain size, of more than 430 pigs for reduction (Bomford 1990). The possibility example (Hone et al. 1992), may lead to exists that suitable technology may one day c o n c e rns that the disease could spread to be developed to allow the spread of domestic pigs. In 1992 there were 2.9 million immunocontraceptives using live org a n i s m s domestic pigs on 5835 farms in Australia as vectors (Section 7.6.10). (Australian Pork Corporation 1993), and

Biological and fertility control

Advantages D i s a d v a n t a g e s

• May assist eradication of small populations • Diseases may spread to domestic pigs and • Some techniques may be humane may have international trade implications • Expensive and may be less effective than lethal controls • No suitable technique currently exists • May not be considered humane

Bureau of Resource Sciences 87 with production worth about $700 million Allen 1991; Williams and Henzell 1992). The annually (B. Ramsay, Pork Council of r a d i o - t e l e m e t e red ‘Judas’ animal joins up Australia, Australian Capital Territory, pers. with, and is used to locate, groups that are comm. 1995), the domestic pig industry is d i fficult to find by other methods. The one of Australia’s most important rural located animals can then be shot fro m industries. The presence of CSF in feral pigs helicopters, trapped or poisoned. The could affect exports of both domestic pig technique is usually used for low density meat (worth over $25 million, mainly to CSF- populations or for survivors of other contro l f ree countries such as Japan, New Zealand campaigns that have become particularly and USA) and ‘Australian Wild Boar’ (Section w a r y . 4.4). Australia supplies 20–30% of the total Little re s e a rch has been done on the use i n t e rnational trade in wild boar meat, worth of this technique for feral pig control. Soule $10 million to $20 million per annum, (1990) considered that the Judas technique depending upon fluctuating market prices (Ramsay 1994). Consequently, the only would not work for feral pigs because they w e re less gregarious than species such as scenario where diseases such as CSF or ASF might be contemplated for biological control feral goats. Choquenot et al. (1993) found of feral pigs in Australia would be to that the presence of oestrous sows in traps eradicate an outbreak of a more financially failed to attract other pigs into the traps, a d i s a s t rous disease, such as foot-and-mouth finding that suggests Judas oestrous sows disease, which had become endemic in feral may also be ineffective. In contrast, Bryan pigs in Australia. (1994) and J. McIlroy (unpublished data) found the technique successful for It might be possible to genetically eradicating small colonies of feral pigs. Both engineer a suitable virus specific to pigs to re s e a rchers found the technique works best include genes for pig proteins capable of with sows captured from the same area as causing an immunological response which the target animals, rather than using males p revents conception or implantation. This or pigs from other areas as Judas animals. has the potential to allow immunocontra- This is presumably because local pigs are ceptives to be delivered to feral pigs at low familiar with the area and are already part cost, which would overcome one of the of the social structure of the targ e t main constraints to using fertility control to p o p u l a t i o n . c o n t rol pest animals (Section 7.6.9). 7.7 Cost of control 7.6.11 Judas pigs The use of radio-telemetered individuals to 7.7.1 Introduction locate animals with which they associate Little information is available on the cost of has been developed as a control technique c o n t rolling feral pigs in a typical farm for strongly social species such as goats enterprise, despite the fact that landholders (Henzell 1987; Taylor and Katahira 1988; a re vitally interested in costs. The only data

Judas pigs

Advantages D i s a d v a n t a g e s

• May make location of sparsely distributed or • Unknown effectiveness wary pigs easier • Requires expensive equipment and skilled • May assist eradication of small colonies operators • May help find survivors of previous control • Only useful for small populations attempts

88 Managing Vertebrate Pests: Feral Pigs accumulated is that associated with res e a rc h from some government or semi-governm e n t projects or control programs that have stron g agency (such as the Rural Lands Pro t e c t i o n g o v e rnment agency involvement. B o a rds in New South Wa l e s ) . One reason for the lack of accurate costs The cost of controlling feral pigs by for pig control on farms is that feral pig shooting from helicopters depends upon co n t rol is not separated from other activities. the following variables: Almost invariably, activities such as checking w a t e r, fences and fence repairs, are • type of terrain — flat, hilly, mountainous; p e rf o rmed concurrently and apportioning • vegetation cover — thick, thin, tall, short, costs on a time basis is difficult. There is continuous, discontinuous; even little information available for on- p roperty expenditure on traps, bait stations, • flying conditions — windy conditions limit and feed (poisoned and unpoisoned). the manoeuvrability of the helicopter; • type of helicopter — the cheapest may 7.7.2 Shooting from helicopters cost $200 per hour and the most The most accurate feral pig control costs are expensive $650 per hour; those for shooting from helicopters. This • pilot experience — positioning of the costing is relatively easy because the cost helicopter in relation to the target is boundaries are clear for the helicopter, c r u c i a l ; ammunition and contracted shooters (if necessary). Individual landholders spend • shooter accuracy — a more accurate little time in arranging helicopter shoots shooter will spend less time killing the because most of the organisation is done by same number of pigs as an inaccurate a few key landholders and re p re s e n t a t i v e s shooter; and

Table 10: Comparative costs of feral pig control methods in diff e rent habitats.

Control method Habitat Cost per pig Cost per hectare Source ($) ($)

Poisoning Slopes, plain 11.40–31.20 – Turvey (1978) scrub Wetland 6.80 1.0 R. Hosie (New South Wales Agriculture, Dubbo, pers. comm. 1986) Dryland 3.25 0.10 R. Hosie (New South Wales Agriculture, Dubbo, pers. comm. 1986) Dryland 3.35 0.30 Korn (1986a)

Trapping Slopes, plain 14.70–20.90 – Turvey (1978) scrub Shooting from Woodland 48.35 0.90 Hone (1983a) helicopters Wetland 9.55 – Bryant et al. (1984) Wetland 5 .00 –15.50 0.25–0.35 Korn (1986a) Dryland 5.65–15.80 0.10–0.15 Korn (1986a) Wetland/ 13.85 1.10 Saunders and Bryant dryland (1988) Wetland/ 7.95 0.40 Hone (1990c) woodland

Bureau of Resource Sciences 89 • feral pig density — at high densities the feral pigs were trapped each year. Above this cost per feral pig is relatively low. As level, poisoning was a better option under density drops, more time is spent the economic circumstances at that time. s e a rching for targets, and costs rise. The cost per pig caught varies widely H o w e v e r, the cost per hectare would depending upon the objective of the prog r a m . d e c rease as less time is spent over each Turvey (1978) reported an on-pro p e r t y h e c t a re . trapping cost of $4.90 to $6.96 per feral pig K o rn (1986a) obtained information on ( a p p roximately equivalent to $14.70–$2 0 . 9 0 costs associated with shooting fro m when converted to 1994–95 values). On the helicopters from 1978 to 1986 for various other hand, Saunders (1988) evaluated the parts of New South Wales and compare d cost of trapping in Kosciusko National Park them to costs of other control techniques in south-east Australia in 1986–87 and ( Table 10). reported it was $104 per feral pig (equivalent to $148 in 1994–95 values). Stone and Tay l o r Saunders (1993b) encountered diff i c u l t y (1984) are quoted as estimating a cost of when attempting to assess the cost- $US103 per pig in Hawaii Volcanoes National e ffectiveness of shooting from helicopters. Park (approximately equivalent to A$240 in Costs per kill varied widely each year, 1994–95 values). despite the fact that there was an obvious reduction in the catch of feral pigs each year. Saunders (1988) proposes a cost structure model for trapping compared with poisoning Caley (1993) obtained a theoretical cost and shooting from helicopters which is shown of shooting from helicopters based on in Table 11. It shows that trapping is reported pred a t or–p rey relationships (Hone consistently the most expensive contro l 1990b). On this basis, Caley concluded that technique. Net costs, however, depend on the benefits of shooting from helicopters whether pigs are sold or not. If so, trapping exceeded the costs for protecting sorg h u m may be more cost-effective than S a u n d e r s and maize crops in the Northern Te r r i t o r y ( 1 9 8 8 ) proposes in his model. f rom feral pig damage. 7.7.4 Poisoning 7.7.3 Trapping Poisoning is consistently reported to be the Turvey (1978) found that trapping in the cheapest form of control, irrespective of Narrabri district of New South Wales was the whether or not the toxin used is 1080, most cost-effective control if fewer than 40 wa rfarin or CSSP. Korn (1986b) lists rep o r t e d

Table 11: Costs for control strategies associated with varying levels of population reduction (after Saunders 1988).

Population reduction (%) Poisoning costs ($) Trapping costs ($) Helicopter costs ($)

0 504 2 521 804 10 1 679 3 190 1 848 30 2 058 4 657 3 249 40 2 292 5 556 4 109 50 2 567 6 620 5 126 60 2 905 7 921 6 369 70 3 340 9 548 7 974 80 3 953 11 966 10 235 90 5 002 16 009 14 100 95 6 050 20 053 17 965 99 7 978 29 443 26 940

90 Managing Vertebrate Pests: Feral Pigs Table 12: Costs ($) per kilometre of fences tested, and their cost efficiencies (after Hone and Atkinson 1983).

Non-electrified Electrified Design Material Cost per Material Cost per number cost kilometre per cost kilometre per ($) pig restrained ($) pig restrained ($) ($)

1 1188 – 1378 115 2 1300 1300 1489 106 3 1104 – 1104 86 4 866 – 866 58 5 1690 242 1880 125 6 1802 201 1991 132 7 1857 310 2047 136 8 2294 143 2484 156

poisoning costs on a per pig basis (range 7.8 Monitoring $ 2 . 10–$10.40, or $3.30–$16.20 when converted to 1994–95 values) which demonstrates that poisoning is at the lower 7.8.1 Introduction end of the control cost scale. Caley (1993), A feral pig management program is not ho w e v e r, estimated that poisoning was more complete unless it contains a monitoring expensive than trapping, fencing or shooting and evaluation component. The compre - f rom helicopters in his study area in the hensiveness of the monitoring component N o r t h e rn Territory. This is in contrast to a will depend on the objective of the prog r a m . study conducted in the Macquarie Marshes, A minimum monitoring component for an in which it was estimated that 15 380 pigs evaluation of lamb predation or cro p w e re killed at a cost of 76 cents ($1.34 in damage would involve monitoring lamb 1 9 94–95 values) per pig (Bryant et al. 1984). losses or crop damage before and after c o n t rol for one lambing or cropping season 7.7.5 Fencing only. Conclusions from such a pro g r a m would, however, be of dubious value given Little information is available on the cost of the potential confounding of enviro n m e n t a l fencing as a control technique. Several or other sources of variation. A more d i ff e rent fences are available as options and c o m p rehensive and definitive monitoring the cost of each on a per kilometre basis is p rogram would involve measurements over listed in Table 12. The cost includes labour. several seasons or years, preferably in are a s Hone and Atkinson (1983) evaluated with diff e rent levels of pig control and eight fence designs and reported that, of the replication, to reduce confounding with non-electrified fences, the most eff e c t i v e other causes of yield reduction. Ideally, was the most expensive. This did not apply monitoring will enable the re l a t i o n s h i p to electric fences, where the cost per between pig density and damage to be k i l o m e t re per pig restrained was dire c t l y d e t e rmined (Section 7.4). co r related to the material cost per kilometre. ‘Monitoring will allow the Caley (1993) reported fencing to be the relationship between pig c o n t rol technique which gave the best density and damage to be b e n e f it–cost ratio, in his study in the d e t e rm i n e d . ’ N o r t h e rn Te r r i t o r y .

Bureau of Resource Sciences 91 7.8.2 Elements of monitoring •rec o rd information in standardised forma t that allows comparisons over time; and Monitoring the results of a management p rogram, and comparing them to the • seek advice of experienced re s e a rc h objectives, enables managers to assess if the professionals. program is efficient and effective or whether it req u i res modification. Financial and physical 7.8.3 Monitoring techniques res o u rces may need to be adjusted accordi n g Assessment of impact is more easily measured to prog ress made within a given timeframe. in an agricultural context than an enviro n - For example, if local eradication is the mental one. The monitoring technique may management objective (Section 8.4.2), it may simply revolve around lamb marking be decided that if by a given time targ e t p e rcentages or crop yields. These two population reduction goals are not met, indicators are easily measured by landholders res o u rces may be better allocated to sustained because they are collected as a normal part of co n t ro l . ma n a g e m e n t . Th e re are two components to monitoring: Monitoring abundance is more difficult and time consuming (Sections 7.2 and 7.3). Indices • operational monitoring — describes the of abundance, rather than absolute abundance process and extent of control, for example, a re the only practical means of measuring number of stations treated per year, the abundance in the field. The technique of money allocated, number of pigs killed, monitoring abundance is generally confined number of pigs killed per unit eff o r t , to res e a rch use because it is, or can be, highly number of pigs remaining, or the cost per labour intensive. unit reduction. The aim is to impro v e efficiency; and Some techniques that can be used to monitor abundance are: • p e rf o rmance monitoring — measures the effect of the management program on the • feral pig signs — that is, sightings of pigs, re s o u rces to be protected. Perf o rm a n c e number of active wallows, extent of roo t i n g , criteria are needed for assessing tracks and droppings (Hone 1988b). This p e rf o rmance. A reduction in feral pig technique is appropriate for use by abundance is not usually adequate as a landholders who are willing to devote time p e rf o rmance indicator. What is req u i red is to monitoring over and above norm a l a measure of the impact of pigs on the property management; valued re s o u rce (agricultural or enviro n - • m a rk–re c a p t u re based on frequency of mental). Consideration of sample design is ca p t u re (Caley 1993); needed if perfo rmance monitoring res u l t s are to be valid. The size, location, security •ca t c h - p e r- u n i t - e ffort (Choquenot et al. 1993). of site tenures, number of replicates, the This technique has the advantage that no initial comparability of plots (including pigs need to be released; and un t reated plots), and how data is collected • bait-take (Bryant and Hone 1984; Saunders can all affect the validity of the res u l t s . et al. 1993). This technique also has some The key elements of a management applicability to landholders who are able monitoring program for feral pigs are outlined: to give the time.

• use methods that are easy and rapid, yet 7.9 Evaluation reliable and repeatable. In general, a better assessment is given by many crude 7.9.1 Introduction assessments over many sites than by a few Feral pig management programs must be precise assessments over relatively few sites; evaluated against established objectives. It is • ensure that sampling is not biased; p referable for these objectives to be set in

92 Managing Vertebrate Pests: Feral Pigs t e rms of damage reduction rather than • Reduced predation levels on lambs. This changes in feral pig numbers. This is because involves keeping accurate rec o rds of lamb reducing pig numbers may not always lead marking percentages before, during and to acceptable levels of reduction in damage after management programs. Other caused by pigs, unless there is evidence to co n c u r rent changes in management should show that there is linear relationship between also be noted because they may also affe c t pig numbers and damage (as in Figure 10 and lamb marking percentages. An objective F i g u re B1, line B). Often in practice, the for a feral pig management program may relationship between pig numbers and be written as follows: To increase the damage is curvilinear (as in Figure 9 and average lamb marking percentage in C Figure B1, line A), so a moderate reduction division of Walgett Rural Lands Protection in pig density may lead to little or no red u c t i o n B o a rd District to 85% by December 30, in damage). Also, some feral pigs (called killer 1994, by implementing a feral pig pigs) have been observed to kill more management strategy; f requently than others (Pavlov and Hone 1982). Therefore, the elimination of a single • Reduced areas of pasture rooting. This is or a few killer pigs may have the same effect more difficult to measure accurately than as reducing a local population of feral pigs lamb marking percentages. It is more by 50% or more. Such circumstances can subjective, being based more on make the assumption of direct relationships p e rception than fact, unless accurate between pig numbers and pig damage sampling methods with random quadrats u n reliable. If, however, measuring damage are used (Hone 1980); and is difficult in practice, it may be necessary to • Another evaluation technique, popular assume that estimates of pig abundance will with res e a rchers assessing changes in feral give an indication of likely levels of pig pig numbers following the use of poison damage. baits, revolves around measuring bait-take ‘Management objectives need (Bryant and Hone 1984; Saunders et al. to be set in terms of damage 1990). reduction rather than changes For cropping enterprises, damage to crop s in feral pig numbers.’ can be accurately assessed by differences in yield between or within cropping paddocks 7.9.2 Evaluating damage over time. Visual assessment can also be used but is subjective and may be very misleading Damage is generally restricted to either if done from the edge of tall cereal cro p s . grazing or cropping enterprises. A feral pig M o re than 20% of a crop may be flattened, management program aimed at grazing yet only be detected from the air (Wilson et enterprises can be evaluated in several ways: al. 1987).

Bureau of Resource Sciences 93 8. Strategic approach to Group action is an essential element of the t h i rd stage which is i m p l e m e n t a t i o n. A l l management at the those in the locality or region who will benefit local and regional from feral pig control, or have a significant level stake in the outcome, should be involved in the coordinated development and imple- mentation of the management plan. This will Summary foster a strong sense of ownership of the plan, This chapter outlines the four stages of a and enhance the probability of successfully strategic management program at the local meeting goals. and regional level. These are: (1) pro b l e m The fourth stage is monitoring and definition; (2) developing a management ev a l u a t i o n . Operational monitoring ensures plan; (3) implementing the plan; and (4) the management plan is executed in the most monitoring and evaluating pro g ress. It also c o s t - e ffective manner. Perf o rmance moni- ad d resses the need for economic frameworks toring assesses the effectiveness of the for assessing the value of alternative contro l management plan in meeting the agricultural s t r a t e g i e s . or conservation outcome objectives established Defining the prob l e m is the first stage of initially. Evaluation of data from both forms strategic management planning. The costs of monitoring enable the continuing and benefits of pig management for red u c i n g refinement of the management plan, where their agricultural impact can both be necessary. m e a s u red in dollars. In some situations in Hypothetical examples of the strategic the semi-arid rangelands, for example, management of feral pigs at the local and su fficient information is available to estimate regional level for conservation and the point where the costs of undertaking pig agricultural production scenarios are management equal the benefits. Although presented. feral pigs are known to cause significant environmental damage, their management is complicated by the need to value intangible 8.1 Economic frameworks concepts such as biodiversity. Economic frameworks are needed to assist The second stage in strategic manage- managers in assessing the relative value of ment planning is the development of a alternative control strategies and the relative management plan. This re q u i res setting benefits compared with other risks that must management objectives which should be managed. Such frameworks re q u i re : include interim and long-term goals, a time definition of the economic problem; data on frame for achieving them and indicators the relative costs and benefits of diffe rent pig for measuring perf o rmance. Developing a management strategies; an under-standing of why the actions of individual land managers management plan also req u i res the selection may not lead to optimal levels of pig control ; of an appropriate management goal. and assessment of the means by which Options for pest control include local g o v e rnments might intervene to overc o m e eradication, strategic management, com- identified market failures. Land managers can m e rcial management, crisis management use such economic frameworks to select the or no management. Strategic management most appropriate pig management strategy of vertebrate pests is based on the concept for their circumstances. of adaptive management, in which the management plan is flexible, re s p o n d i n g Land managers who wish to determ i n e to changes in economic, environmental and the optimal economic strategy for managing pest circumstances. The management plan a problem caused by pigs could use the needs to integrate control techniques into stepwise approach outlined in Appendix B. a systematic pro g r a m . Ideally, land managers could use this

94 Managing Vertebrate Pests: Feral Pigs a p p roach to optimise the control effort, but c o n t rol techniques to protect conservation often budgets are constrained by competing values would also need to be assessed so demands and sub-optimal amounts are that the most cost-effective pig management available. But the process outlined in strategies for meeting community conser- Appendix B is the most sensible way of vation values could be determined. An balancing these competing demands, that example of market failure would be if the is, by contrasting the marginal ratios of community placed a high value on pig d i ff e rent approaches on a common benefit c o n t rol on private land to prevent land m e a s u re, for example, decreasing loss of degradation, but most individual land- biodiversity, or increasing farm income. In holders considered lesser levels of pig such cases, managers have to prioritise c o n t rol were adequate to meet their w h e re control will be conducted. Accurate livestock productivity goals. An assessment i n f o rmation to support many of the of socially equitable means by which decisions needed for this process will almost g o v e rnments could intervene to meet these always be absent and managers will often b roader conservation benefits might then have to make ‘best guess’ estimates. be warranted. This would only be the case, H o w e v e r, the process will give defensible h o w e v e r, if scientific data verified that decisions especially if they are empirically implementing pig control on private land tested by monitoring the outcomes. For would protect conservation values, and that example, sheep graziers will need to the costs of such control would equate with estimate the losses caused by pigs, both the benefits. immediately, through predation on lambs or other livestock, and longer term, thro u g h Animal welfare organisations would also contributing to land degradation and like the suffering caused by harvesting or c o n t rol techniques considered as a cost to consequent losses in future pro d u c t i v i t y . F u t u re losses would need to be discounted the Australian community, and taken into at some appropriate rate. The costs of account in pig management decisions (G. c o n t rol would also need to be assessed, Oogjes, ANZFAS, Victoria, pers. comm. examining diff e rent control strategies to see 1 9 9 4 ) . which are cheapest and most eff e c t i v e . A l t e rnative options and opportunity costs 8.2 Strategic approach would also need to be examined. For The four steps which constitute a strategic example, in some areas where feral pigs are a p p roach to pig management are defining d i fficult to control, and other forms of land the problem, developing a management use are not very profitable, harvesting feral plan, implementing the plan, and monitoring pigs for sale could be an economically viable and evaluating pro g ress (Figure 1). The a l t e rnative to running stock. challenge for local and regional landholders ‘Economic frameworks can and others with a major interest in feral pig assist managers assess the management in the region is to use the value of alternative contr o l i n f o rmation in the preceding chapters, and strategies and their benefits the processes described in this chapter, and relative to other risks that consider how the land is being used, to must also be managed.’ develop a strategic management plan to a d d ress the damage caused by feral pigs. B e f o re economic frameworks could be used to assist meeting conservation goals, This chapter explains how this might be it would be necessary to estimate the achieved, and describes its special feature s economic value the community places on for pigs in agricultural and conservation the conservation of native species and a reas. The process is illustrated for a communities threatened by pigs. The cost hypothetical area centred on the wet tro p i c s and effectiveness of implementing pig World Heritage Area of northern

Bureau of Resource Sciences 95 Queensland, including nearby agricultural in dollars, direct cost–benefit analyses lands. The process is also illustrated for a cannot be used to decide how much to w o o l - g rowing property in the semi-arid spend on their management. Techniques to rangelands. value degradation such as contingent action analysis or cost of restoration are available, 8.3 Defining the problem but their usefulness is not certain (Braysher 1 9 9 3 ) . 8.3.1 Agricultural impacts Pigs affect agricultural enterprises by 8.4 Management plan reducing profitability through decre a s e d yield and/or increased costs (Section 4.1). 8.4.1 Objectives Because both the costs and benefits of pig Agriculture management for reducing agricultural Setting objectives for feral pig management impacts can be measured in dollars, for an agricultural enterprise is complex. An estimating the point where the costs of feral example might be to reduce the level of pig management equal the benefits should, impact on crops and lambs to a level in theory, be straightforward. In reality, the pre d e t e rmined by the value of the enterprise only agricultural systems where enough is and the cost of control. Even where known about all the complex factors s u fficient information exists to conduct involved to estimate this point, are i n f o rmed marginal analyses of diff e rent pig w o o l g rowing enterprises in the semi-arid management options (Appendix B, Step 6; rangelands and grain cropping enterprises Section 8.8.3), valuing reductions in yield in the wet– dry tropics (Section 3.8.2). These will not always be straightforward. For factors include: the relationship between example, although the value of a lamb to a pig density and reduction in yield; the rangelands woolgrowing enterprise can be dynamics of feral pig populations; and the neatly summarised in an economic analysis effect of pig density on the cost-effe c t i v e n e s s by its replacement cost (Section 4.1.1), a of control strategies, such that gre a t e s t grazier cannot replace the generations of benefits are derived from the least costs. selection which may have gone into Until adequate information is available for p roduction of that specific lamb, or the lost other enterprises in other enviro n m e n t s , opportunity to more rapidly increase flock decisions about how much to invest in pig size when the season turns good next management will be based on perc e p t i o n s month. Attempting to value intangibles in of the economic significance of pig damage, and the degree to which this damage is the day-to-day operation of an agricultural reduced by economically feasible and enterprise introduces complexities which practicable pig control. conventional economic analysis cannot encompass. In these situations it may be best to provide producers with as much 8.3.2 Conservation impacts i n f o rmation as is available and let them Pigs are known to disturb the ground by make an informed decision about the rooting, and are believed to reduce the reduction in yield they deem acceptable. abundance of native plants and animals by This will be a particularly valid appro a c h grazing and predation (Section 4.2). w h e re the per capita reduction in yield in Management of the environmental impacts any given season is relatively unpre d i c t a b l e . of pigs is complicated by the need to value Using the relationship between pig density concepts like biodiversity, wilderness, and and per capita probability of reductions in ecosystem sustainability which are less yield allows producers to build an tangible than reductions in yield associated a p p reciation of uncertainty and their own with agricultural impacts. Because these attitude to risk into decisions about how concepts are difficult or impossible to value much pig control to do.

96 Managing Vertebrate Pests: Feral Pigs Conservation • discount rates applicable to expenditure on pig control are negligible (Braysher Because it is difficult to determine the 1993); and e n v i ronmental damage feral pigs cause, and hence to determine the enviro n m e n t a l •t h e re is no risk that pigs will reinvade the benefits of control, the temptation is to focus eradication site. on pig abundance as the ultimate objective Such conditions may be difficult to meet of management. For example, a manage- for agricultural are a s . ment objective might be to reduce feral pig densities to a level where endangered flora Strategic management and fauna populations increase to viable Strategic management is necessary where densities. Unless, however, abundance has local eradication is not an achievable option, a simple, predictable relationship to the level but where it is clear that pig damage will of pig impact (Section 7.4), its value as a re q u i re continuing attention. Three options management outcome is dubious. are possible: sustained management; ta rg e t e d management; or one-off management. 8.4.2 Management options Strategic, sustained management, in which For managing feral pig damage, managers pig numbers are reduced and maintained at have five options, as discussed by Braysher a low level, is the best management option (1993). These are local eradication, strategic when damage can be ameliorated or management (sustained, targeted or one-off) , eliminated by holding the density of pigs co m m e rcial management, crisis management below a threshold above which the damage or no management. is known or believed to be too great for achieving the desired production or Local eradication conservation outcome. In most cases, strategic Local eradication involves the perm a n e n t sustained management involves two steps — removal of the entire feral pig population in an initial knockdown effort aimed at killing a defined area, and maintaining it free of pigs. a very high proportion of the pig population, This option is often unrealistic for feral pigs followed by periodic maintenance control to except in special cases. Examples are on slow or prevent recovery. Reduction in islands where there is no potential for densities of re s o u rce-limited populations recolonisation or small areas where pig-proo f induces an excess of births over natural fences can be erected. For local eradication deaths, and these additional pigs must be to be a viable option, several key conditions removed on some regular basis to maintain must be met (Bomford and O’Brien 1995). the desired density. These are set out in Appendix C. The target density will vary from place to A farm manager may perceive that, place according to a large number of factors, although achieving local eradication is likely including the density–damage re l a t i o n s h i p be extremely costly, the expense will be ( F i g u res 9, 10, 11 and B1), region (for justified by future freedom from pig damage example, semi-arid or temperate), terrain, and from continuing costs of pig contro l . climate, land use, and timing of control. It is This strategy may be a sensible management t h e re f o re a complex option, re q u i r i n g option where : managers to identify res o u rce goals, set targe t • complete local eradication is an attainable pest densities (which re q u i res some goal (Appendix C); understanding of pest–resource dynamics), and kill enough pigs sufficiently often to • feral pigs are known to be causing high ensure the target densities are not exceeded reductions in the yield of a valuable crop; (which req u i res some understanding of pigs’ • the cost of achieving eradication is population dynamics). In most areas, few of a c c e p t a b l e ; these factors are well defined, and all but the

Bureau of Resource Sciences 97 general res o u rce protection goals will change enough to be causing obvious economic or both with time and the area of concern. e n v i ronmental damage. This is called crisis management. There is no clear objective Strategic, t a rgeted management, in which and feral pig numbers rapidly increase to only certain animals or areas are contro l l e d , p re - c o n t rol levels due to immigration and is an appropriate choice when a specific pig natural increase, with considerable waste or group of pigs are causing a problem. For example if a few ‘rogue pigs’ are raiding of re s o u rces and little lasting benefit. s u g a rcane, or if a couple of ‘killer pigs’ have No management developed the habit of killing lambs, the Land managers may perceive that pig control particular individuals involved, rather than the entire local feral pig population, will be p rograms cost more than the gains in the target of control action. p roduction resulting from pig control. This may apply in agricultural areas where pigs An example of strategic, o n e - o ff m a n a g e - a re not abundant or where they aff e c t ment would be building an electric fence p roduction only marginally or sporadically. a round a melon crop to prevent pig W h e re this is so, spending on pig control is d e p redations, although the fence would of not warranted. course re q u i re maintenance. In a conservation area, this option is Commercial management p robably adopted where pigs are not A significant but highly variable pro p o r t i o n c o n s i d e red to be causing significant of feral pigs can be shot by hunters for sale degradation; other sources of degradation (Sections 4.4 and 4.5). The strategic outcome a re perceived to be more important than of encouraging or allowing shooting pigs; and/or available re s o u rces limit depends on whether it is seen as a management action to address other source s c o m m e rcial or re c reational end in itself or of degradation. Managers of conservation as a first step in the strategic management a reas do, however, have a responsibility to of feral pigs as pests. In the former case, it take account of the effect of resident and will only be economic or enjoyable to shoot dispersing pigs on neighbouring pro p e r t i e s , populations above a certain density and pig when assessing the costs and benefits of pig numbers will either be held above that c o n t ro l . th reshold and the natural increase harvested regularly, or as many as possible will be shot 8.4.3 Choice of management goal and the survivors left to breed-up until their numbers again make shooting worth the Integration of several feral pig contro l e ffort. Where feral pigs are shot for strictly techniques is likely to improve eff e c t i v e n e s s c o m m e rcial outcomes, this may help to if the goal is to reduce pig densities to low manage their impact on environmental or numbers. For example, Saunders et al. economic re s o u rces. Commercial shooting (1993) found that 20% of feral pigs will not can only serve this purpose, however, if it enter traps, while Hone and Pedersen (1980) is intense or frequent enough to reduce pig report only a 58% reduction in feral pig densities to the level where damage is abundance after a poisoning program. In reduced. There have been no studies addition, Hone (1983a) showed that a conducted in Australia to determine whether certain proportion of individuals may not c u r rent levels of commercial harvesting of eat poison bait or will eat it and not die. feral pigs are reducing agricultural and Saunders (1993b) found that shooting fro m e n v i ronmental damage (Section 4.5). helicopters may reduce a population by up to 80%. Thus it is probable that in a Crisis management population of feral pigs a combination of All too often managers undertake feral pig techniques will be more successful than any c o n t rol only when populations are larg e technique used alone.

98 Managing Vertebrate Pests: Feral Pigs Timing is important for some techniques. possible, this can have negative results — Poisoning gives better results when food and where either the resource is still at risk from water are scarce as pigs visit water points individual animals which avoid contro l daily. In tableland areas Saunders (1988) techniques, or where the degree of damage found that spring was the best season to trap does not warrant such extreme measure s . and that locating traps near tree-lines was This was shown by earlier eradication policies m o re successful than near water. Shooting, against New Zealand rabbits where huge especially from helicopters, is not affected by sums of money were spent killing rabbits that season. we re not affecting any res o u rce of value (Gibb ‘Integration of several contro l 1967). Another risk is that land managers may techniques is likely to impro v e become disenchanted using a lot of res o u rc e s the effectiveness of feral pig and effort controlling a pest for no apparent m a n a g e m e n t . ’ gain, in terms of achieving the goal of eradication, and consequently give up and Pig management strategies should take cease managing the target animals as pests. account of costs and benefits. Regardless of This can lead to poor resource protection. the nature of the impact management seeks Pragmatists (Caughley 1977; Parkes 1993; to mitigate, its costs can be measured in Bo m f o rd and O’Brien 1995) argue that in cases dollars, albeit with difficulty in some cases. wh e re local eradication is not possible (based Gains may or may not be directly comparable on an honest assessment using the criteria set with costs depending on whether impacts are out in Appendix C) pest management must agricultural or environmental. Consideration be driven by identified re s o u rce pro t e c t i o n of animal welfare issues should be an integral goals. The consequence of this is that the part of any feral animal management plan, n a t u re of the pest’s impact must be including one for feral pigs (Section 5.2). de t e rmined in order to set tolerable densities Some techniques and strategies to manage of pests, however difficult this might be. pests give better outcomes than others, for Usually, an empirical solution is re c o m - example, those techniques where a single mended, which is to manage for some action gives permanent benefits, and those measurable density of pests and observe what strategies that aim to eradicate local pests. happens to the re s o u rce. Whether the T h e re is argument about whether a response in the res o u rce is a consequence of management plan should aim for some ideal the pest management can be tested using outcome or something which is practicable la rge-scale management experiments (Wal t e r s and achievable. and Holling 1990). Managers also need to consider economic issues when selecting the Some people, for example Coman (1993), most appropriate management option argue that for three reasons eradication as a (Section 8.1). management option should not be abandoned just because it is impractical. First, such a goal encourages people to strive for 8.4.4 Performance criteria pe rfection. Second, it avoids changing social P e rf o rmance criteria need to be form u l a t e d or economic perceptions of the goals of pest in terms of the re s o u rce goal (such as tre n d s management. Third, it avoids the need to in lamb production, crop damage or habitat answer the difficult question of how few pests degradation) or some rational index of is few enough to protect some re s o u rc e , t h e s e . which is usually ill-defined and difficult to measure. 8.4.5 Management strategies The countervailing argument is that the ends (protecting res o u rces) are confused with Flexible management the means of achieving them (killing pests). T h e re are some new approaches to In cases where local eradication is not managing complex natural systems. The

Bureau of Resource Sciences 99 management of feral pigs, and other d e s i red outcome for the re s o u rce being vertebrate pests, using best practice p rotected. A key factor in developing a suggested in these guidelines embodies management strategy is an assessment of the many of these new concepts. One such costs and benefits of the combination of a p p roach is adaptive management. As options. This is more easily achieved in a described by Walters and Holling (1990), production scenario, because economic costs this approach is based on the premise that and benefits are more readily quantifiable knowledge of such systems is always than in a conservation scenario. incomplete. Not only is the science incomplete, the system itself is a dynamic Management strategies in one, evolving because of natural variability, agricultural settings the impacts of management and the The option for pig management described p ro g ressive expansion of human activities. above depends on perceptions about the Hence, management actions must be ones value of reduction in yield caused by pigs, that achieve an increasing understanding of and the likely effect of control on the the system as well as the enviro n m e n t a l , magnitude of reductions in yield. Although social and economic goals desired. This has the ‘no control’ option will often be been called ‘learning by doing’. identified as appropriate by producers, a ‘Adaptive management, or significant proportion will adhere to either “learning by doing”, can achieve sustained control or eradication. Managers an increasing understanding of who enthusiastically advocate eradication the system as well as the as the only sensible objective for pig environmental, economic and management mostly rep resent a special case social goals.’ of cost-effective control. They may perc e i v e a tangible benefit from pursuing very low Given the paucity of information, including densities of pigs, and emphasise the scientific theory, about many of the factors magnitude of continuing reduction when that drive natural systems, Danckwerts et al. considering costs; but they are in fact (1992) recommend that managers need to c o n t rolling pigs down to the level where adopt a flexible management approach. That they believe costs equal benefits. is, managers need to learn from their past Similarly, producers who elect to do no successes and mistakes (and those of their pig control usually do so because definite neighbours), and from technical informa t i o n , economic benefits associated with pig and be ready to change management based c o n t rol have not been demonstrated. If, on experience and prevailing conditions. h o w e v e r, producers adopted this A key to the success of the flexible management option when reductions in management approach suggested by yield caused by pigs were economically Danckwerts et al. (1992) is the monitoring of significant, they could forego important t h ree key variables in the system: livestock p roduction opportunities. p roductivity (biological and economic); R e g a rdless of the management option a vegetation changes; and enviro n m e n t a l p roducer adopts, the investment in pig conditions that occur and the management c o n t rol by agricultural producers is, to some responses to these conditions. For feral pigs, d e g ree at least, commensurate with the c rop productivity would also re q u i re p e rceived economic re t u rn on that monitoring where this is a management goal. investment. Improving management These issues are further canvassed in Section decisions by agricultural producers involves 8.6. identifying where these perceptions are T h e re are many ways of managing pigs w rong, and modifying attitudes to pig (Section 7.6), but the challenge is to combine c o n t rol. Improvements in pig management them in an integrated strategy to achieve the decisions by agricultural producers can only

100 Managing Vertebrate Pests: Feral Pigs be made by influencing the perceptions on • best combination of techniques to use, after which their management decisions are the producer makes an informed decision b a s e d . about how much time and money to invest in pig control; Pig management in agricultural settings can be improved by targeting points in the • how to monitor control programs to chain of decisions made by producers which d e t e rmine accuracy of pig abundance lead to identification of a pig control strategy, estimates; and supplying information which may • how to revise pig control programs on the influence the perceptions upon which these basis of information obtained during decisions are based. For example, a control; and rangelands sheep grazier contemplating pig co n t rol will most probably concentrate control • how to predict changes in pig density just before lambing. When that time comes, which have occurred over the intervening the producer will normally consider the costs year. of controlling pigs and the perceived increa s e Extension officers can help pro d u c e r s in lambing they might expect to get fro m develop management strategies which will co n t rol. Some of the factors influencing their re t u rn the best measurable results, by perceptions and subsequent decisions are: i n f o rming them about reliable inform a t i o n • current financial status; on the costs and benefits of diff e rent pig co n t rol strategies, so they do not need to rel y • neighbours’ opinions; solely on subjective perceptions. Better • expected weather until lambing; decisions will be made if the pro c e s s e s described in this chapter are used to move • current and forecast commodity prices; f rom management driven solely by • short- and long-term breeding objectives; p e rceptions, to management with some rational intent and measurable success. This •pe rception of pig abundance and prob a b l e p rocess will work best if it is incorporated trends; and into an effective monitoring and goal setting • attitude to risk. program, and will ret u rn results more rapidly in the context of a group control scheme. Managers will then choose an amount of time and money to spend on pig contro l Given the inadequacy of re s e a rc h which returns to them what they consider is i n f o rmation on the costs and benefits of an acceptable risk of a maximum damage d i ff e rent pig management strategies at the level. Having made that decision, they will local and regional level, computer models as select the combination of techniques they described in Section 3.8.2 can be of believe to be most cost-effective. Some considerable assistance (see also Sections 7.7 graziers will elect to do no pig control, others and 8.8). will expend considerable re s o u rces. After Management strategies in lambing starts, graziers will not think about conservation settings intensive pig control for another eight months. Several issues will impinge upon graziers’ Strategies for managing the enviro n m e n t a l p e rceptions and subsequent decisions. impact of pigs are driven by perceptions in P roviding graziers with the appro p r i a t e much the same way as they are for information at the right time will help them agricultural impacts. As such, the manage- make good decisions on pig management. ment options described above could be used Helpful information includes advice on: to help change perceptions for conservation management. For example, if pigs are • techniques to measure pig abundance; p e rceived to affect the abundance of a local • p robable reduction in predation risk subspecies of plover in a wetland re s e r v e associated with given control efforts; in western New South Wales by pre d a t i o n

Bureau of Resource Sciences 101 on eggs, they will re p resent a potentially Department of Conservation 1994, 1996). important management problem. If an They have established a proc e d u re for ranking i n t roduced aquatic plant is affecting the a reas according to their priority for pest integrity of the wetland reserve, this may be management. seen to take precedence over the perc e i v e d Initially, agencies divide conservation lands impacts of pigs, and most re s o u rc e s available for pest management will be into management units (Section 7.5.4) based d i rected toward control of the intro d u c e d on geographic features such as streams, ridges plant. In this case, because of a re l a t i v e l y or catchments, vegetation type, or limits of low perceived impact, limited re s o u rc e s th reatened animal or plant distribution. Large would dictate a low priority for the areas which are too big to manage as a whole management of pigs on the reserve. If, a re broken into smaller management are a s h o w e v e r, it was established that rather than for ranking. Small reserves pose a diff e re n t just reducing plover density, pig pre d a t i o n p roblem, and are ranked separately, not as had the potential to drive the population to groups of reserves. local extinction, the perception of pigs These management units are then ranked would change, leading to more re s o u rc e s ac c o rding to their conservation value. This is being allocated to the problem and, derived as a primary score, which is p robably, a diff e rent management strategy. developed in two steps. The first scores the Now the status of plovers in relation to pig reserve for its plant or animal values accordi n g c o n t rol activities would become important, to the nature of threatened vegetation or and some sort of plover monitoring prog r a m wildlife. The second scores management units would be likely to drive application of pig ac c o rding to their vulnerability to feral pig or c o n t rol. other pest damage. ‘Conservation managers need to identify areas of high The criteria for ranking plant and animal priority for feral pig values are as follows. Management units have management according to the a high score of six for threatened plants or value of the natural r e s o u rc e s animals of national importance; five for those being aff e c t e d . ’ of exceptional value; four for very highly valuable; three for highly valuable; two for In determining a management strategy for moderately valuable; and one for plants or a conservation area, it is important to animals of potential value. recognise that local eradication of feral pigs is likely to be technically feasible and The criteria for ranking management units economically practical in only a few are a s ac c o rding to their vulnerability to pest damage (Section 8.4.2). In other areas, if feral pigs are has been developed using a score ranging to be managed, sustained management action from a low of one, in which pest damage at for the foreseeable future is req u i red. Due to current levels poses no immediate threat, to the extensive areas involved and the limited a high value of 3.5 where a plant or animal re s o u rces available, this level of control is species within the area is at risk of national unlikely to be possible over the whole area extinction because of feral pest damage. w h e re feral pigs occur. Consequently, The primary score for each management conservation agencies need to identify those unit is then calculated by multiplying the a reas of high priority for management highest plant or animal score by its ac c o rding to the relative worth of the natural vulnerability to feral pig damage. For resources affected by feral pigs. example, a unit may have a plant score of The Department of Conservation in New five, and animal score of four, and a Zealand has considered this issue in several vulnerability weighting of three. The primary National Pest Control Plans, including those s c o re then becomes five (the highest score ) for possums and feral goats (New Zealand times three, giving 15.

102 Managing Vertebrate Pests: Feral Pigs Management units with equally weighted • Sharing costs of contro l — A pro p o r t i o n s c o res can be further ranked if needed by of the land with feral pigs has a clear considering various land attributes (for predominant use, either for conservation example, ecosystem fragility, tenure, size, or for production, and the class of and cultural values) and management criteria beneficiaries of pig control are there f o re (for example, absence of other pests, past also clear — they are either all citizens c o n t rol and accessibility). The New Zealand paying via taxes through govern m e n t Department of Conservation attempted to conservation agencies or they are the apply these secondary considerations in some la n d h o l d e r. However, most of the land with o rder of importance, although only as far as feral pigs in Australia is used for prod u c t i o n was needed to obtain a distinction between but also can have significant conservation the competing management units. Managers and environmental value. The pro b l e m of pests that affect production values might h e re is to fairly apportion the costs of consider comparative cost–benefit analyses control. to prioritise otherwise equal options. Unfair allocation of costs, for example, by Ranking management units in this way is g o v e rnment subsidies to farmers, has adverse effects because it distorts a complex task, but necessary to ensure best landmanagers’ perceptions of all their risks use is made of available re s o u rces. It is and how they manage them, and it is not advisable to convene a panel of experts to sustainable in the long-term if taxpayers assist in the task. Details of this method for are unwilling to meet such costs (Wil l i a m s calculating areas for feral goat and possum 1993). Similarly, expecting farmers to pay c o n t rol in New Zealand were developed by the costs of protecting national conser- Elliot and Ogle (1985), Shaw (1988) and vation values on their land (out of their Parkes (1990). p rofits) will not lead to sustainable outcomes, especially in areas where 8. 4 . 6 Scale of plans p roduction is marginal and risky, and Plans to manage feral pigs must be for businesses often run at losses. defined areas of land and can be at any scale • Unintended effects on neighbours — The — national, state, territory, district, cadastral, second general cause of failure is where or ecological. Because pest management is one landowner’s actions or inactions best driven by communities, small-scale plans impact on another’s. Such external effects (developed within the rules set by of feral pig management occur when g o v e rnments) need to be primary with state, neighbours cannot agree on concerted territory and national plans being the sum of action (an issue further compounded by district or cadastral plans. the dual status of feral pigs as re s o u rc e s and pests). 8.4.7 Market failure Solutions Causes Solutions to these problems re q u i re One of the reasons past and current attempts t r a n s p a rent mechanisms to share costs at to sustain efficient and effective feral pig national, state and local scales. As a first step, c o n t rol at a regional or state level have it would be useful to know what proportion generally failed to deliver optimal outcomes of land with feral pigs has a single class of is because the relationships between those beneficiary — particularly the proportion of who benefit from control and those who pay land that has reserve status and is not used for grazing stock or for cropping. for it have been unclear. Solutions to such market failures depend on the nature of the On land where feral pigs affect both fa i l u re (Bicknell 1993), and in the case of feral market and non-market values, the gains to pigs two general causes have been identified: each beneficiary needs to be considere d

Bureau of Resource Sciences 103 when allocating control costs. A common action carried out eff i c i e n t l y ?’. Perf o rm a n c e solution to sharing costs is for landowners objectives are set to answer the question to pay for the control costs, governments to ‘Did the management action achieve the pay for extension and coordination costs, re s o u rce protection goals used to justify and both to share the cost of monitoring management action?’. That is, were the their relevant goals. In semi-arid rangelands p e rf o rmance criteria met? in Australia, governments have to be care f u l that their share of the costs are not capture d 8.6.1 Operational monitoring by farmers and used to maintain operations on land that should not be used for Operational objectives are developed in the p ro d u c t i o n . management strategy (Section 8.4.5). Thus, re c o rds need to be maintained describing The problem of ensuring concerted action what was done, how many pigs were killed, is discussed in Section 8.7 and Chapter 9. w h e re, by whom, and at what cost. These m e a s u rements need to be taken by the 8.5 Implementation people who do the control as a routine part of their task, and an operational re p o r t Implementation of feral pig management is completed after each operation or annually described in Chapter 9. The value of the for larger group operations. The re p o r t g roup approach to pest management has needs to describe the extent or results of been discussed in detail in the earlier c o n t rol, for example, number of pro p e r t i e s guidelines for managing rabbits (Wi l l i a m s t reated per year, money allocated, total et al. 1995). The group approach re q u i re s number of pigs killed, number of pigs killed local community support, based on an per unit effort, number of pigs re m a i n i n g , understanding of the damage feral pigs or the cost per unit reduction. Mapping cause and how it can be addressed. The some of this information can be helpful. The g roup approach fosters a strong sense of aim is to improve eff i c i e n c y . ownership of the management plan, and successful management which satisfies all relevant players. 8.6.2 Performance monitoring Pe rf o rmance monitoring measures the effe c t 8.6 Monitoring and of management on the re s o u rces to be evaluation p rotected, by comparing the outcome of management against the perf o rm a n c e As described in Section 8.4.5, the key to the criteria (Section 8.4.4). Some perf o rm a n c e success of the flexible management m e a s u res can be taken by the landowners a p p roach is the monitoring of key variables. or pest managers, but others involve Such monitoring enables the continuing complex ecological relationships that are refinement of the control strategy in re l a t i o n better measured by re s e a rchers. Perf o r- to desired reductions in re s o u rce damage. mance monitoring usually re q u i res a long- It is thus important to distinguish between t e rm perspective, and some experimental e fficiency (operational objectives) and and scientific rigour if results are able to be e ffectiveness (perf o rmance objectives) as i n t e r p reted (Section 7.8.2). management can be efficient but ineffe c t u a l . For example, 75% of feral pigs may be killed 8.6.3 Agriculture e fficiently for little cost, but this strategy would fail if the re s o u rce protection goal Good re c o rd keeping will allow changes in req u i red at least a 90% kill. The management pig management to be related to any plan must there f o re have two sorts of subsequent change in yield. Over time, this measurable objectives to be met on time. i n f o rmation will allow a producer to build Operational objectives must be set to answer a picture of what works, what does not, and the question ‘Was the planned management how much of an influence pig management

104 Managing Vertebrate Pests: Feral Pigs has on yield. In developing a feel for plants and animals unique to the region, are e ffective management, the producer must included within a World Heritage Are a always focus on yield. Although pig (WHA). Most of the adjacent lowlands are abundance may help in selecting when and used for production of sugarcane, bananas w h e re control should be implemented, and other tropical fruits. There are several managing the impact of pigs is the object of tourist resorts along the coast only a few the control exerc i s e . hours by road transport from an i n t e rnational airport. Feral pigs occur 8.6.4 Conservation t h roughout the area but are mainly confined to the forests during the wet season and Schemes to monitor the extent of roam more widely, particularly to sugarc a n e degradation due to pigs will help managers c rops, in their search for food during the understand the relationship between pig dry season (May to November). co n t rol activities and impact. These schemes may often need to focus on ultimate rather 8.7.1. Defining the problem than proximate forms of degradation (for example, trends in swan abundance rather Feral pigs are estimated to cause at least $0.5 than trends in nests preyed upon). They will million damage to sugarcane crops in the also provide more information if they are region each year as well as an unmeasure d comparative, contrasting trends in degra- amount of damage to bananas and other dation in areas where pigs are contro l l e d c rops. They are also considered to pose with trends in areas where they are not. substantial threats to WHA values, particularly protection, conservation and rehabilitation of the environment, even 8.7 Example of the strategic though there is little objective inform a t i o n planning process available on their impact. In addition, they centred on the wet may have an actual or potential role as hosts tropics World Heritage or vectors of several important endemic and Area of north exotic diseases and parasites of animals, Queensland including people. Scenario — A typical example of the The main problem with feral pig p roblems of feral pig management in the management in this region is that adjacent wet tropics region of northern Queensland landholders re g a rd the WHA as the sourc e could occur anywhere between To w n s v i l l e of the pigs affecting their crops and mostly and Cooktown. The region covers about expect the authorities responsible for the 1 25000 square kilometres and consists of WHA to control the pigs within the WHA. t h ree major geomorphic areas: a belt of This is generally not practical, given the coastal lowlands; an intermediate Gre a t l a rge size (9000 square kilometres) and Escarpment; and the tablelands of the Gre a t elongated shape of the WHA, its often Divide. Mean annual rainfall varies rugged, steep topography, and the th roughout the region from 1200 millimetres d i fficulties and constraints involved in using on the western edge to over 4000 millimetres c o n t rol techniques for pigs within the WHA, near the coast, with rain falling mainly particularly during the wet season. during December to April (the wet season). The dominant native vegetation consists of 8.7.2 Management plan r a i n f o rest species, which occur largely as a continuous belt along the Great Escarpment, Objectives with outliers on the tablelands and coastal The objective of feral pig management in a lowlands. Most areas of forest, which region including both conservation and re p resent about 80% of the re m a i n i n g agricultural land uses should be to re d u c e r a i n f o rest in Queensland and contain many their impacts within and outside the

Bureau of Resource Sciences 105 conservation area to acceptable levels, and Control strategy to maintain this situation. This will re q u i re studies to quantify the environmental and A combination of techniques may be agricultural impacts of feral pigs in the WHA necessary for effective control of feral pigs and experimental reduction of pig in many areas (Section 8.4.3). Poisoning, populations, through adaptive management, although potentially the most eff e c t i v e to determine threshold densities for technique for the region, is generally not acceptable levels of impact. It will also acceptable in the WHA and sometimes on re q u i re basic re s e a rch, including modelling, adjoining properties, where captured or shot on the likely outcomes of outbreaks of pigs are subsequently used for food. exotic diseases in feral pigs in the re g i o n , Poisoning could be used in certain are a s and greater public education over the risks (for example, margins of the WHA) if more of people being infected by diseases and specific poisons, baits or delivery systems parasites from eating or handling feral pigs. (including free-feeding) were used. Trapping techniques re q u i re extensive fre e - Management units feeding before traps are established, are very labour intensive and are not practical Because of the large size of many conser- for larg e r, more remote areas, but are vation areas, the diversity of values that pigs potentially effective for many small areas or can affect, and the likely costs of control, some local situations, particularly as part of fo rm of ranking system is necessary to decide co o rdinated programs between governm e n t which particular areas should receive priority authorities and landholders. Hunting fro m pig control. This system could include the ground, with or without dogs, is m e a s u res of potential or actual impact on generally considered to be ineffective for biological, agricultural and other values, and sustained control or eradication and may should, at least initially, involve all major a ffect non-target animals such as in t e rest groups concerned. Once these area s cassowaries (Casuarius casuarius), but is are selected, decisions need to be made on a way of life in the region that will not whether local eradication or sustained control readily be stopped by legislation. Aerial of pigs is the appropriate action (Section shooting, previously untried, could be 8.4.3). In deciding this, the following factors c o n s i d e red in specific areas, including the need to be considered: m a rgins of sugarcane farms. Fencing • level of future financial support; (including electric fencing) is probably only c o s t - e ffective around small ecologically • when to conduct control; significant areas or for some instances of e n d a n g e red species protection, but may be •de g ree of population reduction necessary useful to direct feral pigs to areas where to achieve program objectives; and they can be trapped. Biological contro l , • best control methods and strategies. although feasible, is not likely to be available in the near future. Although individual Decision analysis models can help to techniques used alone are thus unlikely to d e t e rmine whether diff e rent management be effective, a carefully selected combination or control techniques are economically of techniques can work. desirable, technically possible, practically feasible, or socially and enviro n m e n t a l l y 8.7.3 Implementation acceptable (Norton and Pech 1988). Norton and Pech also describe pay-off matrices which can be used to determine the Group action outcomes or benefits associated with using The most effective control strategy to use in particular control methods and strategies a region containing both agricultural and for diffe rent types or levels of impact by pigs conservation land uses is to carry out (Appendix B, Step 7). simultaneous control programs against pigs

106 Managing Vertebrate Pests: Feral Pigs inside the margins of the conservation are a a re necessary to help determine thre s h o l d and on adjacent properties (particularly densities and evaluate whether the contro l s u g a rcane farms) during the dry season. p rograms are achieving their goals or not. Priority should be given to areas where pigs If the goals are not being achieved, then a re having significant impacts both within i m p roved strategies and community and outside the conservation area, particularly involvement will be necessary. Monitoring for sustained control or local eradication, and evaluation can also indicate the best during the late dry season when pigs are likely techniques to support, help pro m u l g a t e to be at their lowest numbers and many pigs re s e a rch results, such as new trap designs a re searching for food outside the WHA. A or baits (for example, bananas) and pro v i d e co o rdinated approach, using funds that would m o re motivation and direction to contro l otherwise be spent separately by contro l e fforts. It may also indicate whether further authorities and Cane Boards and farm e r s re s e a rch is re q u i red, such as on the intrinsic during this period could have several benefits rate of increase of pigs after diff e rent levels for both the WHA and adjoining landholders. of population control, including the eff e c t s These include a closer working relationship of environmental factors on this rate. These and recognition of the ‘pig problem’ by all include delays in the onset of the wet season major interest groups, with use of legislation or a poor fruiting year in the rainfore s t s . if necessary to enforce compliance by Such information, along with that on the uncooperative and uninterested landholders. relationship between effort expended on M o re coordinated control between various c o n t rol and the resulting densities obtained, landholders, land management and conser- can be used to evaluate diff e rent methods vation agencies, and, where practicable, and strategies for sustained control or c o m m e rcial harvesters of feral pigs, could eradication in diff e rent are a s . also minimise costs, benefit some landholders with low or negative cash flows, provide a 8.8 Example of costs and means for disease surveillance and result in more cost-effective control compared to the benefits of controlling current, often spasmodic ad hoc efforts. feral pigs in rangelands woolgrowing ‘ C o n t rol programs coor d i n a t e d enterprises between landholders, land management and conservation 8.8.1 Strategic planning process agencies and commerc i a l for a woolgrowing harvesters result in more cost- enterprise e ffective contro l . ’ Lamb predation by feral pigs is perc e i v e d Special control programs may also have to to significantly affect the viability of be undertaken against pigs deeper within the w o o l g rowing enterprises in Australia WHA where they are known to be affecting generally, and in the semi-arid rangelands WHA values. Such programs, which should particularly (O’Brien 1987; Choquenot and be funded solely by the authorities O’Brien 1989). Where levels of pre d a t i o n responsible for the WHA, should be based a re high, loss of lambs re d u c e s : on a priority ranking system (Section 8.4.5). • viability of self-replacing flocks; F u r t h e rm o re, because such programs are likely to involve sustained control, they should • genetic diversity available for selection of have guaranteed continuing financial support. desirable production traits; and • cash-flow from sale of excess lambs. 8.7.4 Monitoring and evaluation Computer simulations of pro d u c t i o n M e a s u rements of impact and indices of pig systems can be used to assess and optimise density before and after control pro g r a m s pig management strategies.

Bureau of Resource Sciences 107 8.8.2 A comparison of four In each of the four case studies described, simulated strategies costs and benefits are summed for each year of simulated control and compared dire c t l y In the first scenario (see following box) four to contrast the economic efficiency of the case studies were constructed and evaluated, di ff e rent management strategies. Two rel a t e d rep resenting four diffe rent strategies for feral elaborations in the way these costs and pig management available to woolgro w e r s benefits are equated and how they might in the semi-arid rangelands. influence decisions about pig control strategies The approach to equating costs and benefits are considered further in the following section: for pig management in agricultural settings the use of marginal analysis to optimise described in Scenario One emphasises the decisions which underlie any control strategy; contrast between the costs of management and identifying points where an enterprise and its benefits in terms of increased yields. manager can intervene with such a decision.

Scenario One S1.1.1 Economic impact The problem for each property relates to Comparison of four pig the potential economic impact of feral pigs control strategies in the due to the costs of control and re d u c t i o n sheep rangelands in lamb production. Costs of control are estimated for the 220 square kilometres of This scenario details four identical p i g - p rone habitat according to the contro l c o m p u t e r-simulated properties consisting techniques selected in each case study. of 45 000 hectares of which 22 000 hectares Costs are the product of the number of pigs is riverine floodplain containing potentially removed and the cost of each removal, the high pig densities. The floodplains also latter varying with pig density, and pasture re p resent the only country with enough availability for poisoning, and with pig forage during droughts (pasture biomass density alone for shooting from helicopters. less than 250 kilograms per hectare) to Outcomes of control are estimated as allow lambing ewes to successfully wean d e c reased lamb predation due to the pig their offspring. Hence, when pasture co n t rol strategy adopted, expressed as both availability exceeds 300 kilograms per a rate of, and as absolute lamb loss. Loss h e c t a re, ewes can be lambed away fro m of lambs by factors other than pig pred a t i o n the floodplains and predation will be is assumed to be a constant 20%. Lambs proportionally reduced. All lambing occurs lost to pig predation affect income in two during spring, and woolgrowers conduct w a y s : pig control during winter. On each prop e r t y a diff e rent pig management strategy is • if predation is extreme the woolgro w e r f o l l o w e d . may have insufficient hoggets to re p l a c e c a s t - f o r-age ewes and have to purc h a s e S1.1 Defining the problem additional sheep; and/or • w o o l g rowers will forego any income For the simulated enterprise, the pro b l e m from the sale of excess lambs which pigs is defined by a series of identical have killed. assumptions made for each property. Each p roperty is stocked at 2.5 hectares per ewe Replacement costs or income fore g o n e giving a total ewe population of 18 000. Of per lamb killed are assumed to be these, 95% (17 100) lamb each year and a p p roximately equal in value at $20 per 21% give birth to twins to give a potential head. Predation rate in any given year is a lamb crop of 20 691. random draw from a probability distri-

108 Managing Vertebrate Pests: Feral Pigs bution associated with prevailing pig S1.2.3 Management strategy density. The estimated predation rate is discounted by 50% when pasture biomass Pig control techniques available to all four is greater than 300 kilograms per hectare wo o l g rowers are shooting from helicopters to account for the ability of graziers to and 1080 poisoning. The manager of conduct lambing away from pig-pro n e Do n t c a re Downs does not req u i re a control a reas in seasons when forage is abundant. strategy, having opted for no control .

Models of each enterprise considered in After considering the available informa t i o n the case studies appraise costs and benefits on shooting from helicopters and poisoning, over 100-years of simulated rainfall. For each the manager on Pragmatic Park decides that case study, costs and benefits are averaged shooting from helicopters once a year should over five runs of the model. hold pigs in check well enough to larg e l y limit their impact. Because it is realised that S1.1.2 Measuring impact the cost-per- removal associated with shooting from helicopters incre a s e s No managers measure the economic dramatically at lower pig densities, the impact of feral pigs on their property. Thus manager adopts a strategy to continue their attitude to control is driven largely by shooting until kill rates drop appre c i a b l y . their perceptions of it. The manager on This means that they will stop shooting at one property, Dontcare Downs, conducts pig densities of between four and five pigs no pig control in the belief that the per square kilometre. They convince some investment aff o rds no net economic gain. neighbours to participate in the shoots, The manager on the second pro p e r t y , reducing the cost of ferrying the helicopter Pragmatic Park considers that pigs at to $500 per year. Because they cannot moderate to high density will impose a evaluate kill rates instantaneously, they significant economic burden on the continue to shoot for three hours after kill enterprise through their effect on lamb rates drop below a threshold of four to five survival. The manager of the third prop e r t y , pigs per square kilometre before calling a Killemall thinks that pigs at even low to halt to the operation. Hence, in years when moderate levels are a high economic pig densities are already below four to five impost. The manager of the final pro p e r t y pigs per square kilometre, total expenditure Doubleup believes any losses due to pigs on shooting from helicopters will be the cost a re unacceptable. of the ferry plus three hours of shooting.

S1.2 Management plan The manager on Killemall conducts a 1080 poisoning program before lambing in winter S1.2.1 Objective w h e rever pasture availability is less than The objective of all four woolgrowers is to 7 50 kilograms per hectare. A fre e - f e e d i n g maximise economic re t u rn s . p rogram is conducted, and if bait con- sumption exceeds 30%, the woolgro w e r p roceeds to a three-day 1080 program. A S1.2.2 Management options th o rough free-feeding program (consisting The woolgrower on Dontcare Downs opts of two 10-kilogram bait trails per square for the no control option. The manager of k i l o m e t re) over the entire 220 square Pragmatic Park chooses cost-eff e c t i v e ki l o m e t res of pig-prone country costs $1199 c o n t rol to restrain feral pigs at moderate per day in time and transport. The duration densities. The woolgrower on Killemall of the free-feeding program depends on the decides on cost-effective control to res t r a i n p e rcentage bait-take ultimately achieved. pigs at a low density, whilst the owner of The cost of the poisoning program is the Doubleup opts to attempt local eradication. same as for free-feeding, with the additional

Bureau of Resource Sciences 109 Table 13: Costs and benefits derived by computer simulation for a no pig contro l strategy on a woolgrowing enterprise.

Parameter Average s.d. c.v.%

Pigs per square kilometre 2.44 3.59 148.05 Cost of control ($) Nil – – Predation rate 0.047 0.052 110.82 Lambs lost 782.93 861.86 110.82 Value of lambs lost ($) 15 658 17 237 110.82

expense of enough poisoned bait to rep l a c e their strategies using the inform a t i o n that consumed during free-feeding. Poisoned provided. They each derive potential costs bait costs $3.93 for 20 kilograms including and benefits over a 100-year period of bags and warning signs. simulated rainfall. The results are summarised in Tables 13–16. The manager on Doubleup conducts a helicopter shoot each winter to reduce pig The results of the computer simulation of density to four to five per square kilometre. the costs and benefits for the no contro l In years where pasture biomass is less than strategy pursued on Dontcare Downs are 750 kilograms per hectare they follow the shown in Table 13. Because no pig control shoot up with a free-feeding program. If more was undertaken, pig numbers varied purel y than 30% of bait is taken during the free - f e e d , ac c o rding to seasonal conditions. Pred a t i o n they pro g ress to a full 1080 poisoning rates varied according to prevailing pig program. Costs for the helicopter shoot and density. poisoning program are as for the other The results suggest that the average en t e r p r i s e s . annual value of lambs lost to pigs is excessive, with the average maximum over S1.3 Implementation the five 100-year runs of the model being $69 294. Clearly the woolgrower pursuing Initially, each woolgrower implements their a no-control strategy would be losing own strategy in isolation from their excessive income through the effects of pig neighbours, although in some cases costs predation, and the perception that control a re share d . would give no net economic gain is incorrect. S1.4 Monitoring and For Tables 13, 14, 15 and 16, standard evaluation deviations (s. d . ) and coefficients of variation After several years, each woolgrower agree s (c . v . %) measure variation between years, to attempt to assess the economic impact of averaged across the five 100-year runs.

Table 14: Costs and benefits derived by computer simulation for a sustained pig control st r a t e g y to restrain pigs at a moderate density on a woolgrowing enterprise.

Parameter Average s.d. c.v.%

Pigs per square kilometre 0.80 1.22 163.93 Cost of control ($) 1547 726 46.91 Predation rate 0.031 0.040 134.81 Lambs lost 509 667 134.81 Value of lambs lost ($) 10 178 13 333 134.81

110 Managing Vertebrate Pests: Feral Pigs Table 15: Costs and benefits derived by computer simulation for a sustained pig contro l strategy to restrain pigs at a low density on a woolgrowing enterprise.

Parameter Average s.d. c.v.%

Pigs per square kilometre 0.18 0.66 645.65 Cost of control ($) 2572 1537 59.7 Predation rate 0.011 0.016 154.58 Lambs lost 178 260 154.58 Value of lambs lost ($) 3556 5201 154.58

The simulated costs and benefits of abundance to very low levels. Again, the pursuing a strategy of sustained control to cost of initial knock-down is very restrain pigs at a moderate density on expensive (average first year costs acro s s Pragmatic Park are summarised in Ta b l e the five runs of the model are $17 361). 1 4 . The costs and benefits derived from the Undertaking an annual helicopter shoot computer simulation of pursuing a pig substantially reduces the value of lambs eradication strategy at Doubleup are shown lost to pigs but leaves pig densities high in Table 16. enough for significant predation to still o c c u r r. Shooting from helicopters is, on The most intensive pig control strategy average, a relatively cheap form of contro l , has marginally increased costs, with no although the cost of reducing pigs to low a p p reciable decrease in the value of lambs levels in the first year of control (average lost to pigs. This is because the cost of a c ross the five runs is $8429) is fairly high. accessing additional pigs when densities have already been substantially re d u c e d The costs and benefits of implementing i n c reases exponentially, whereas the a sustained control strategy to restrain pigs benefits of doing so increase linearly. The at low densities on Killemall are cost of the initial population knock-down summarised in Table 15. is accordingly excessive (average first year costs across the five runs of the model are Poisoning is a considerably more $21 206). expensive control option than is shooting f rom helicopters, but has a more To examine ratios of benefits to costs p ronounced impact on pig density and for the four pig control strategies, the subsequent predation rates. The value of d i ff e rence between the average value of lambs lost to pig predation is considerably lambs lost to pigs in each strategy where reduced by the ability of an intense some control was conducted and that poisoning program to decrease pig wh e re no pig control occurred was divided

Table 16: Costs and benefits derived by computer simulation for a local pig eradication st r a t e g y on a woolgrowing enterprise.

Parameter Average s.d. c.v.%

Pigs per square kilometre 0.15 0.74 512.87 Cost of control ($) 3074 2103 68.54 Predation rate 0.010 0.020 191.07 Lambs lost 174 329 191.07 Value of lambs lost ($) 3470 6578 191.07

Bureau of Resource Sciences 111 by the costs of each strategy. These Table 17: Comparative ratio of benefits to comparisons are shown in Table 17. costs of control strategies. The ratio of benefits to costs is positive Strategy Benefits– costs for all forms of pig control examined. H o w e v e r, the ratio begins to decline when Sustained control 3.54 pig densities are reduced to very low levels (moderate density) (that is, less than 0.18 per square Sustained control 4.71 (low density) k i l o m e t re). The cost of removing pigs to Eradication 3.96 maintain these extremely low densities i n c reases very rapidly (Figure 15), where a s the benefits of doing so increase more s l o w l y .

8.8.3 Optimising costs and emphasises where decisions are made which benefits d e t e rmine the costs and benefits associated with the control strategies, and how these Although most woolgrowers affected by decisions affect the ratio of the marg i n a l feral pigs conduct some form of contro l , benefits of a control program to its marg i n a l lack of reliable information on the costs and costs. The information available to enterprise benefits of control means decisions about managers at the time decisions about pig how much control to do are essentially ad c o n t rol are made is also considered in term s hoc. In Scenario Two (see following box), of the ability of the manager to vary the models are used to simulate the costs and intensity of control and/or vary the decision benefits of the two pig control strategies to proceed to the next phase of the prog r a m . (shooting from helicopters and 1080 poisoning) aimed at restraining pig density at the moderate and low levels considere d M o re commonly, economic inputs and in Scenario One. The purpose is to outcomes for enterprises are considered in demonstrate how such strategies can be a marginal analysis context. This appro a c h optimised to provide the best re t u rns to allows net benefits associated with many w o o l g rowing enterprises from investment f o rms of potential investment in enterprises in pig control. This optimising pro c e s s to be compared.

manager can elect to continue or stop Scenario Two shooting). Assuming the manager elects to Optimising benefits and bring in a helicopter for shooting pigs costs for pig control in the annually, the only decision they must then sheep rangelands make is when to stop shooting. Although this is often decided once a given level of S2.1 Shooting from e x p e n d i t u re is reached (for example, ‘I’ll helicopters spend $6000 on pig shooting this year’), a m o re rational basis for deciding when to Points of a program for shooting feral pigs f rom helicopters at which an enterprise stop the program would be to identify the manager can intervene with a decision point where the marginal costs of which determines the benefits and costs continuing to shoot equate with the of the program are when initiation of the m a rginal benefits of doing so. The only p rogram is first considered (the manager i n f o rmation flowing to the manager which can elect whether or not to undertake the might allow them to identify this point is p rogram); and during the program (the the current cost of killing each pig, which

112 Managing Vertebrate Pests: Feral Pigs Fi g u r e 20: Variation in marginal benefits and costs of simulated programs for shooting fro m helicopters as a function of the target cost-per- removal ($) at which the shooting program is halted. The point Z is the approximate target cost-per- removal at which marginal benefits of c o n t rol equate with its marginal costs.

reflects the prevailing density of the pigs. in increments of $20 per kill (Figure 20). H o w e v e r, because pig density determ i n e s The marginal benefit curve crosses the both the rate (and value) of lamb pred a t i o n m a rginal cost curve (Z ) at a cost per kill and the prevailing cost per kill, it should of about $90. This indicates that, for the be possible to identify the cost per kill at enterprise modelled here, the economically which a shooting program ought be halted optimal strategy is to continue shooting to optimise the ratio of the marg i n a l until kill rate drops such that it costs about benefits and costs of the pro g r a m . $90 to remove each pig. At a charter cost of $300 per hour, a labour cost of $20 per To identify this point for the hour and a fixed ammunition cost of $2 w o o l g rowing enterprise described in per round, this corresponds to about 3.5 Scenario One, the average annual value of pigs per hour. the benefits arising from pig control and the average annual costs associated with The point where marginal benefits the control strategy were estimated, equate with marginal costs will maximise because the cost per kill at which the the total benefit–cost ratio (Figure 21). This shooting program was halted was varied means that adopting the strategy described f rom $100 per kill to $360 per kill. A fixed will maximise the investment made in pig cost of $500 to participate in the pro g r a m c o n t rol to increase the value of the lamb (the cost of sharing the helicopter ferry c rop. If a more complex strategy for c h a rge across four or five enterprises) was shooting from helicopters9 w e re adopted assumed for each year. Marginal benefits the economically optimum frequency or and costs of the control program were t h reshold pasture biomass for initiating a contrasted as cost per kill was incre a s e d p rogram could be identified in the same

9 Where shooting was not conducted each year or was only conducted following years where average pasture biomass exceeded that leading to rapid increases in pig abundance.

Bureau of Resource Sciences 113 Fi g u r e 21: The ratio of benefits and costs of a simulated program for shooting from helicopters as a function of the target cost-per- removal ($) at which the shooting program is halted. The a r row indicates the approximate target cost-per- removal which maximises the ratio.

way that the optimum cost per kill at which and/or the interval since the last contro l to halt an annual program was identified p rogram. Once deciding to initiate a h e re. Because a less frequent pro g r a m p rogram, a manager will commence fre e - would conceivably result in quite diff e re n t feeding, at the conclusion of which they cost and benefit structures, the fre q u e n c y will elect whether or not to proceed to the of initiating a program and the cost per kill poisoning phase of the program, usually at which programs once initiated were on the basis of the amount of fre e - f e e d halted would have to be optimised taken. To simplify the example here, a free - simultaneously. This would re q u i re a feed was conducted on the simulated matrix of potential decision increments or enterprise in any spring where pasture t h resholds to be constructed, and either biomass was less than 750 kilograms per m a rginal benefits and costs or total h e c t a re. The decision as to whether or not be n e f it– cost ratios to be estimated for each to proceed from free-feeding to poisoning possible combination of potential was based on the percentage uptake of d e c i s i o n s . bait trails, which was determined by prevailing pig density and pasture biomass. The threshold percentage of bait trail S2.2 1080 poisoning uptake at which to proceed to poisoning As with shooting from helicopters, there was optimised by estimating average a re several points in a 1080 poisoning b e n e f it– cost ratios in the same way as for p rogram where a manager may intervene the cost per kill at which to halt the with a decision about whether or not to p rogram in the shooting example given continue the program. The first point of above. potential intervention occurs when deciding to initiate the program in the first To cost 1080 programs in the simulation instance. Managers may make this decision models used in this study, it was assumed a c c o rding to their perception of the that a thorough free-feeding pro g r a m number of pigs around, the pre v a i l i n g (consisting of two 10-kilogram bait trails availability of pasture over recent months per square kilometre) over the 220 square

114 Managing Vertebrate Pests: Feral Pigs Fi g u r e 22: The ratio of benefits and costs of a series of simulated 1080 poisoning programs as a function of the threshold percentage of bait trails taken by pigs at which the program pro c e e d s f rom free-feeding to poisoning.

ki l o m e t res of pig-prone habitat costs $1199 suggesting that proceeding to the poisoning per day in time, material and transport. The phase of a program (which will reduce pig duration of the free-feeding phase of the density at least to some degree) makes p rogram depended on the perc e n t a g e economic sense, re g a rdless of what uptake of bait trails ultimately achieved. percentage uptake of bait trails is achieved The cost of the poisoning phase of the during the free-feeding phase. The reason p rogram is the same as for fre e - f e e d i n g for this is that the cost of 1080 poisoning with the additional expense of enough programs is dominated by the cost of free- poison to replace the number of trails feeding, the poisoning phase involving both consumed at the conclusion of fre e - fewer material costs and less time. Hence, feeding. Poisoned bait cost $3.93 for 20 deciding not to proceed with poisoning after kilograms including bags and warn i n g bearing these costs involves high outlay with s i g n s . no benefit. The decision which may have a more profound effect on the b e n e f it– c o s t A plot of b e n e f it–c o s t ratios as a function ratio would be at what frequency or at what of the threshold percentage uptake of bait t h reshold of pasture availability to initiate trails at which to proceed to poisoning such a program in the first instance. Both of (F i g u re 22) is qualitatively diffe rent from that these decisions (the former an incremental for the shooting example. In the 1080 one, the latter a threshold function) could example, the b e n e f it– c o s t ratio declines be optimised in the same way as perce n t a g e steadily from low threshold bait trail uptake, of bait trail uptake.

Comparing the two control cost per kill exceeded $90. In contrast, an strategies annual 1080 poisoning program re t u rned a Using the simplistic assumptions and maximum benefit– cost ratio of around 6 simulations presented in Scenario Two (see when poisoning followed fre e - f e e d i n g box above), shooting from helicopters re g a rdless of bait trail uptake. Although this achieved a maximum benefit–cost ratio of outcome could change substantially when a round 1.5 when shooting halted after the m o re complex optimisation matrices are

Bureau of Resource Sciences 115 c o n s i d e red (that is, when the frequency or poisoning involves more indirect costs. t h reshold conditions for initiation of These include: the need to destock p rograms are considered) it is unlikely that paddocks during poisoning, if trail baiting shooting from helicopters will approach the is used; the danger such programs re p re s e n t a p p a rent economic re t u rns achieved by to people and dogs; and the potential non- 1080 poisoning. Although attempts were t a rget effects of poisoning on wildlife. If made to include realistic estimates of the reasonable estimates of the value of such di rect costs of shooting from helicopters and detrimental aspects of 1080 poisoning were 1080 poisoning in the model described in available, they could be incorporated into Scenario Two, it could be argued that the benefit– cost analyses considered here .

116 Managing Vertebrate Pests: Feral Pigs 9. Implementing a dictate to land manager groups on what to management do if the national interest is at stake. program I m p rovement in current and future management is limited by the lack of knowledge and skills of front-line staff in Summary extension theory and adult education Group action to develop and implement feral principles. This is considered to be a serious pig management is essential for several barrier to the rapid adoption of best practice reasons. It gives those responsible for feral m a n a g e m e n t . animal control, whether private or govern - ment land managers, or others with a key 9.1 The role of extension interest, a sense of ownership of the problem services and its solution. In addition, because individual feral pigs range over areas of up Implementation of the strategic appro a c h to 50 square kilometres, a management to the management of feral pigs, and other program must, by definition, be at least the vertebrate pests, involves land managers size of the maximum average home range adopting several control technologies and for feral pigs in a particular habitat. p rocesses. Traditionally, state and territory extension services have been pivotal in C o o rdination and partnership between assisting the adoption of new technologies g roups of landowners and other major and processes by farmers, and they have a stakeholders is the key element. This key role in the management of vertebrate encourages identification and ownership pests (Appendix A). of the problem and results in gro u p rei n f o rcement, peer pres s u re, and improv e d The role of extension officers in communication, cooperation and eff i - vertebrate pest management is often broa d e r ciency. Effective goal-oriented management than the provision of advice, in that they is the likely outcome. often act as coordinators and facilitators to g roups of land managers and other Factors contributing to success of feral stakeholders in group management pig management groups include enthusiasm schemes. The best methods for this and commitment of land managers and facilitation is a matter of considerable adequate technical and financial re s o u rc e s debate, and raises some important issues. in relation to the size of the problem. The extent to which these res o u rces are available ‘The role of the extension f rom the beneficiaries (generally land- o fficer in vertebrate pest owners) or government is also a factor. management is often bro a d e r Support may be needed to ensure concerted than the provision of action, monitoring and evaluation. It can i n f o rm a t i o n . ’ be beneficial for government agencies to Given the pivotal role of extension supply some field support to initiate o fficers in feral pig management, their implementation processes. It is important training is important, particularly for that government support does not distort operational staff who advise land managers the incentives for beneficiaries to contro l and facilitate the formation of management and pay for management. groups. Agriculture Wes t e rn Australia places C o n t rol agency staff should act as a high priority on extension skills of all field facilitators, ensuring that local land s t a ff. All Agriculture We s t e rn Australia staff managers have strong ownership of the with an advisory role are re q u i red to be p rogram so that they manage their own skilled in advisory techniques, and their p roblems and develop their own solutions. training includes a Technical and Further National and state agencies should only Education (TAFE) course.

Bureau of Resource Sciences 117 In New South Wales, field staff are sciences into their programs. This is a employed by Rural Lands Protection Boards . paradox when many graduates are These staff are re q u i red to undertake a five employed by companies or govern m e n t day residential and practical course in departments to change people’s behaviour. biology, control and legal issues associated Trainers of extension officers need with pest animals. In addition, new staff are knowledge of the theory and practices of encouraged to spend time with experienced extension to complement the technical field operators from neighbouring districts. expertise in biology and ecology. Extension A three-stage legal training program is training should focus on both individual and established to ensure legal evidence is g roup skills, including conflict re s o l u t i o n , c o r rectly collected and presented in court. negotiation, and problem definition. These programs are very practical, with one Technical soundness is essential, but has to stage actually conducted in a Court House. be complemented by skills which perm i t Regional Officers from the Vertebrate Pest f ront-line extension officers to determ i n e C o n t rol Program also conduct re g i o n a l landholder’s views quickly and negotiate meetings, at least annually, and the staff of a round that knowledge. the Boards hold a three-day biennial c o n f e rence, one day of which is devoted to training. 9.2 Around the states The level of involvement of officers of Three contiguous states and territories (New South Wales, Queensland and the Northern the Rural Lands Protection Boards in Territory) probably contain more than of 90% advisory work is described by Grant (1982); of Australia’s feral pigs, and each has similar 44% of Boards from the Eastern Division, concerns about feral pig damage. Currently 70% of Boards from the Central Division and the Northern Territory has no coord i n a t e d 56% of Boards from the We s t e rn Division p rogram for feral pig management (D. reported their officers spend more than half B e rman, CCNT, Northern Territory, pers. their time in advisory roles. Despite this high comm. 1995). Progress in the establishment input to advisory work, the field staff in New of the group approach to developing and South Wales do not receive any training in implementing feral pig management extension techniques, although this is programs has varied between the states. beginning to change as Rural Lands P rotection Board staff are invited to participate in New South Wales Agriculture 9.2.1 New South Wales training courses. A similar situation exists A significant move towards coord i n a t e d in Queensland. g roup control occurred from 1978 onward s When evaluating the pilot scheme to in New South Wales with the formation of manage feral pigs in north-west New South the north-west New South Wales pilot feral Wales, Bryant et al. (1984) stated that, if Rural pig control program. The stated aim of this Land Protection Boards are to stimulate p rogram was to stimulate coord i n a t e d i n t e rest in feral pig control (Benson 1980). c o o rdinated interest in feral pig control by It consisted of 13 Rural Lands Pro t e c t i o n landholders in the future, then it is desirable B o a rds in which 74 groups were formed. A that these officers be more highly trained in total of 739 properties conducted 1298 advisory techniques. A barrier to pro v i d i n g poisoning operations. a p p ropriate training to field staff is that most extension staff trainers within New South The importance of group control has Wales Agriculture and their equivalents from been stressed in extension literature in New other states do not receive formal training South Wales since 1973 (Giles 1973). In 1989, in advisory techniques themselves. Most are New South Wales developed model feral trained as technical scientists by universities pig control plans for Rural Lands Pro t e c t i o n that incorporate little or none of the social B o a rds to adopt.

118 Managing Vertebrate Pests: Feral Pigs The group approach is written into the Coastal and Cassowary Conservation (C4) model state control plan for Rural Lands and have developed cassowary-safe feral P rotection Boards (Circular No. PPB 89/53, pig traps (P. Salleras, C4, Queensland, pers. 13 June 1989) as a strategy of the highest comm. 1993). The Wet Tropics Management o rd e r. Authority has funded the construction of twelve of these traps for use by farm e r s . 9.2.2 Queensland This program provides a model which Cooperative control programs appeared in should be extended to other parts of Queensland shortly after their use in New Queensland. It demonstrates the eff e c t i v e - South Wales. Appleton (1982) reported that, ness of a shared vision, something which f rom 1979 to 1981, 67% of producers on Senge (1992) considers essential for p roperties of 2100 hectares or more in achieving pro g re s s . Waggamba Shire tended to work together to control feral pigs. On properties less than 2100 hectares, only 37% cooperated with 9.2.3 Western Australia neighbours to control feral pigs. We s t e rn Australia, which has a re l a t i v e l y The Queensland Rural Lands Pro t e c t i o n small population of feral pigs compared with B o a rd published a Feral Pig Contro l New South Wales and Queensland, began H a n d b o o k in 1984 and a Pestfact ( t i t l e d an organised control program in 1979–8 0 C o n t rol of Feral Pigs) in 1987. In neither in forested country in the south-west of the was there any mention of coordinated grou p state. This program followed a study which action. Thus, until recently feral pig contro l began in 1977 (Agriculture Protection Board in Queensland was often individually 1 9 8 0 ) . focussed rather than group focussed. T h e re is, however, a new move toward s 9.3 Stakeholders g roup control through a revised policy All those who have the potential to influence requiring pest management plans for individual property management practices d e c l a red animals to be developed for each a re stakeholders. The involvement of local authority area in Queensland. Plans multiple stakeholders will be more likely to are to be jointly developed by local authority result in shared ownership of the pro b l e m and Department of Lands staff with and thus commitment to a successful a p p ropriate input from local stakeholders. outcome. For example, animal welfare It is intended that these local authority pest g roups should be kept informed of, and management plans incorporate at least long- encouraged to provide solutions to, the t e rm and short-term objectives, priorities c o n t rol technology for feral pig manage- for action, and a proposed timeframe for ment. Conservation groups are likely to be achievement of these objectives. In its policy i n t e rested in setting the re s o u rce pro t e c t i o n the Department of Lands has included goals and determining which land is most contingency measures to manage local important for immediate control action. Meat authorities who refuse to participate in the p rocessors need to be involved in the better development or implementation of its pest co o rdination of commercial harvesting. One management plan, or part thereof. means of involving interest groups is to Management in the wet tropics area of include them on a state or regional steering Queensland is more complicated than in the committee along with landowners and w e s t e rn areas because of the restriction on g o v e rnment agencies that have influence c o n t rolling feral pigs in the World Heritage on the planning at the local and re g i o n a l A rea. Landholders work closely with the level. This helps ensure appro p r i a t e Consultative Committee for Cassowary frameworks, and local people must also be Conservation, now the Community for involved in all stages to ensure adoption.

Bureau of Resource Sciences 119 9.4 Identification of goals 9.5 Government involvement The key element in identifying goals for feral pig management is involvement of all the G o v e rnment agencies have a legitimate relevant stakeholders in defining the i n t e rest in feral pig management as p roblem before the goals for action can be legislators, as re p resentatives of the wider developed. A common understanding of the community, and as managers of such are a s problem and the complexity of related issues as national parks. in each local area is essential. As a legislator, it is vital that government Management of feral pigs needs to be seen does not distort the stakeholders’ actions to within the context of wider goals or visions manage pigs by subsidising their management of what individuals want to do with their land of farming risks (Williams 1993). There is, to sustain its production and/or conservation however, a role for government agencies to values, and how they can organise themselves encourage landowners to adopt good to manage the threats that put these wider management practices by pro v i d i n g goals at risk. It is not appropriate in these a p p ropriate incentives, education and guidelines to discuss these wider goals for training, and re s e a rch and development to each local region. That is a task for those support landowners wishing to manage pigs. concerned with developing a land manage- The government might provide a pro g r a m ment strategy for their area. Issues that need manager to coordinate and oversee the plan to be considered include the social, physical, developed by the stakeholders. Governm e n t economic and general biological limits to support for pest management groups can achieving the goals. i n c rease the probability of achieving successful outcomes. Studies indicate that ‘A key element in identifying members of Landcare groups in Australia feel goals for feral pig a need for more expertise (Chamala and management is involving Mortiss 1990) and govern m e n t - f u n d e d a ll stakeholders in defining facilitators or extension officers can provide the pro b l e m . ’ this. Managers of feral pigs need to understand ‘ G o v e rnments are re s p o n s i b l e the scope and nature of the risk posed by for feral pig management as feral pigs, and to have relevant knowledge legislators, as r e p re s e n t a t i v e s of the biology and behaviour of the animals. of the community and as Although this may seem self-evident, owners of national parks and individual landowners often do not see the other lands.’ need for action wider than their own p roperty, or do not perceive pigs as a thre a t , T h e re is a problem with this beneficiary- or are unaware of the biological principles pays philosophy on land where the income that must be applied to succeed in managing f rom production is insufficient to manage feral pigs. the risks. One solution is to commerc i a l l y harvest feral pigs, but this may be The goals or visions of the general inadequate if it is not commerc i a l l y community need to be considered as these profitable to reduce feral pig densities down could be quite diff e rent from those of the to levels where damage reduction goals are individual land managers. The community met. Any support provided by govern m e n t g roups with an interest in managing feral must be justified by the prospect of a net pigs are identified in Chapter 5, but the key social benefit. Where income is insuff i c i e n t stakeholders in this community are those to manage risks and provide a positive owning or managing the land — either as ret u rn on capital and labour employed, then f a rmers, as managers of conservation are a s , the current land-use may not be viable fro m or as traditional Aboriginal landowners. a long-term social perspective.

120 Managing Vertebrate Pests: Feral Pigs G o v e rnment also has a role as landowner The appropriate involvement of other t h rough its management of conservation i n t e rest groups should be encouraged. All areas. Management of feral pigs on state and individuals have a unique perspective on Crown land needs to be integrated with their what is a problem and what impro v e m e n t s management on neighbouring land. That is, a re appropriate. Incorporating these the state should be seen as just another d i ff e rent perspectives does not cre a t e landowner and act as a good neighbour. conflict; rather, conflict arises when people do not allow others to hold a diff e rent view State and national coordination should ( P retty 1994). be restricted in its scope to major policy issues and funding of worthy initiatives ‘ E ffective management of feral associated with feral pig management. As pigs re q u i res a genuine an example, the Vertebrate Pests Committee partnership and cooperative (VPC) should encourage states to adopt action by land managers, policies of multiple use instead of policies g o v e rnment and others who of eradication. The VPC should also act as will benefit.’ a formal coordination body in setting Cooperative action between land national priorities for feral pest management managers is recognised as an essential and lobby government to address these strategy for effective feral pig management, needs by financing initiatives which targ e t and both land managers and contro l priorities. National bodies should not tell agencies are increasingly identifying this as local communities how to manage a key element in reducing the impact of feral p roblems; rather, they should encourage pigs. Group action to develop and and facilitate local communities to manage implement feral pig management is essential their own problems, use local knowledge, for several reasons. Firstly, it gives a sense and develop their own solutions. The of ownership of the problem and its solution exception to this, of course, is if the national to those responsible for feral animal control , i n t e rest is at stake through the threat of whether private or government land exotic disease or loss of export trade income. managers, and to others with a key intere s t . A second rationale behind this approach to 9.6 Partnerships are needed feral pig management revolves around the The crucial step for effective management of l a rge home range of feral pigs. Table 4 feral pigs is to create a genuine partnership shows the home ranges of feral pigs fro m d i ff e rent studies. and cooperative action by land managers, go v e rnment and others who will benefit from Hone et al. (1980) model the effect of the management action or have some other selecting small and large control areas. They stake in the outcome. The risks posed by feral conclude that, where feral pigs are pigs must to some extent be seen as a distributed over large areas, it is essential community problem to be solved by that land managers undertake coord i n a t e d communities out of self-interest or community c o n t rol (Figure 23). Feral pigs have larg e spirit. The problem cannot be solved by the home ranges and will readily move g o v e rnment or the next-door neighbour. considerable distances if continually Although scientists and governments can disturbed or stressed for food and water recognise problems and develop manage- (Sections 3.3.2 and 3.4). A management ment solutions, it is producers who need to p rogram must be at least the size of the implement these solutions. Feral pigs cro s s maximum average home range for feral pigs property boundaries, and landholder action, in the particular area. These control are a s or lack of action, affects neighbours. Theref o re may range from at least 50 square kilometres cooperative action between groups of in western New South Wales, 35 square p roducers and government is needed to ki l o m e t res in the southern highlands of New improve management of feral pigs. South Wales and the Top End of the

Bureau of Resource Sciences 121 N o r t h e rn Territory, down to 11 square Successful formation and maintenance of k i l o m e t res in the central tablelands of New g roups are often difficult tasks re q u i r i n g South Wa l e s . skills in conflict resolution, negotiation, mediation, leadership, chairperson skills, Other advantages of coordinated gro u p team building, planning and evaluation. action are that it: Conflict resolution skills are particularly •m o re effectively uses physical re s o u rc e s important (K. Pines, RLPB, Narrabri; E such as traps, fencing material, bait layers Dekkers, RLPB, Tamworth; M. Mullins, and helicopters; RLPB, Deniliquin; L. Thomas, RLPB, Dubbo, pers. comm. 1994) and facilitation skills of • encourages strong ownership of the extension officers need to be suff i c i e n t l y p roblem by the group as it develops well honed to ensure that the extension cohesiveness; o fficer ‘takes a background role so that the • causes conflicts to surface which can be group owns the problem’ (M. Mullins, RLPB, openly discussed and resolved, thus Deniliquin, pers. comm. 1994). Although contributing to group cohesiveness; such skills are inherent in some people, and a re learnt ‘by doing’ by most people, •p romotes greater interest and aware n e s s p e rf o rmance is often less than optimal. This of the problem and its solutions within the is because the theory and process are not group and local community; well understood. Ultimately, flexibility is • results in peer group pres s u re, thus further paramount because each work situation is contributing to group ownership and d i ff e rent. This results in an extension off i c e r reducing the need for regulatory action to being re q u i red to use whatever works — be implemented; and because no two groups or pest animal are a s a re the same (K. Pines, RLPB, Narrabri, pers. • reduces feral pig impact over a longer comm. 1994). period because it leads to more strategic, long-term management. Feral pig management can only be successful in the long-term if small In a generic sense, Argyris (1970) in Tys o n communities have the zeal and motivation (1989) describes the effective group as for a management program. The impetus having three main abilities: for control should come from the • to gather relevant data; community and not from the pest management authority. The authority should • to make sound, free and inform e d encourage and facilitate group form a t i o n decisions; and but not impose it, otherwise local • to implement those decisions with landholders will not have ownership of the commitment. p roblem or of the proposed solution.

Fi g u r e 23: Selection of control area size relative to the home range of feral pigs. The home ranges a re shown by circles, the control areas by rectangles. More pigs will be killed in B than in A (after Hone et al. 1980).

122 Managing Vertebrate Pests: Feral Pigs Cooperative action is recognised as Kelly (1995). Kelly defines consultation as essential in pest management for many the periodic involvement of the community reasons. As with many other animal pests, in a government-driven activity, and feral pigs can be mobile with large home participation as the continuing partnership ranges. Group schemes allow better between community and government where management of pests that easily cross tenure both parties learn during the pro c e s s . boundaries by providing for bro a d - s c a l e , sy n c h ronised actions to minimise rei n f e s t a t i o n 9.7.1 Social principles of problems. Economies of scale are inherent if participation joint action is taken by landowners, and groups also facilitate peer pressure on those The development of Landcare over the last unconvinced of the need for management. decade has done much to impro v e knowledge of the social dimensions of land 9.7 Facilitation of effective management and the role of group dynamics and communities in ensuring successful groups p rogram outcomes (Campbell 1992; The ultimate aim of implementing feral pig Alexander 1993; Carr 1994). Difficulties can management is to change behaviour and arise when people who need to work facilitate adoption of sustainable land together discover they have diff e rent points management practices. It is recognised that of view, diff e rent interests, diff e rent ideas new approaches in extension are needed and diff e rent approaches to solving to encourage adoption, especially with the p roblems and interacting in social settings. complexities of sustainable land manage- G roup management skills and strategies are ment introduced in the 1990s (Vanclay and needed to overcome these potential L a w rence 1994, Blacket et al. 1995). p roblems (Chamala and Mortiss 1990). Involving all stakeholders in planning the p rogram from the start is essential. Kelly (1995) describes some social principles and techniques for community A common element in most successful consultation and group participation for pest vertebrate pest management has been the management and how these can be used to development of group or district community develop a process to achieve best practice schemes (Ryan 1947; Ratcliffe 1959; Chamala pest management at the local community and Mortiss 1990). The essential features of level (Clarke et al. 1990; Clarke and Filet these schemes include common under- 1 9 9 4 ) .1 0 This ‘participatory problem solving standing of the nature and extent of the model’ provides a cyclical process for p roblem, and identification of clear, share d producers to identify problems, plan actions, goals and objectives. Some govern m e n t trial solutions and evaluate results to support can be beneficial, especially to start i m p rove knowledge and skills. Changes in the schemes (Sections 9.5 and 9.6). management are more likely to occur if all phases of the model are completed. Kelly G roup or community schemes can be (1995) found this participative pro c e s s developed in many ways and the value of motivates land managers and encourages these are the subject of some debate. Var i o u s l o n g - t e rm commitment to action. a p p roaches from passive participation to self-mobilisation which involve people in Kelly emphasises how ‘learning by doing’ developing land management strategies are ( Walters and Holling 1990; Section 8.4.5) described by Pretty (1994). A similar and the principle of flexible management, continuum from top-down to bottom-up which changes according to changing a p p roaches is discussed by Carr (1994) and situations, is important for ensuring the

10 Kelly’s (1995) approach is based on a case study of feral goat management in the mulga lands of south-west Queensland, following a technique developed by the Queensland Department of Primary Industries with cattle producers.

Bureau of Resource Sciences 123 p rocess is relevant to producers’ needs, and often complex changes are needed at a local hence encourages their participation. Also and regional level and that these changes may the opportunity for ‘doing something’ about take time’. Such changes need to be made a problem is often given by landholders as voluntarily by well-informed producers, for an important reason for joining and staying only then will they own the decisions and be with groups (Carr 1994). committed to the process. Encouraging feral pig management This process for developing local best g roups to undertake large-scale experi- practice is new for feral pigs and its long- ments, as described by Walters and Holling t e rm value has yet to be established. (1990), will help to establish cohesion G o v e rnment re s o u rces to support the between group members because people p rocess may enhance the probability of develop a stronger commitment to things s u c c e s s . in which they invest time and money (Lerne r 1994). Kelly (1995) emphasises that it is 9.7.2 Local and regional important for producers to feel ownership coordinated management of the problem as well as the process for solving it. The first report of coordinated control was by J. Giles (unpublished) from the More e ‘Undertaking larg e - s c a l e Rural Lands Protection Board district in 1972. experiments helps feral pig This Board became a leader in coord i n a t e d management groups establish feral pig control, eventually establishing 48 cohesion because they develop active groups of landholders. The gro u p s a strong commitment when initially relied on 1080 poisoning but in latter they invest time and money.’ years have switched to shooting fro m This participative process includes an helicopters (R. Bailey, RLPB, Moree, pers. evaluation step and, by being flexible, can comm. 1994). take account of any relevant social, Surveys by Benson (1980) and Appleton economic or environmental factors. Initial (1982) of early cooperative control prog r a m s reports compiled with landholders pro v i d e in New South Wales and Queensland a benchmark to assess changes in local best c o n f i rmed that land managers perceived the practice during the project. Kelly (1995) lack of coordination amongst themselves as describes a participative partnership a barrier to effective feral pig management. between community and government in A major conclusion of Appleton’s study was which communities with local inform a t i o n the need for pig control authorities to can monitor conditions and undertake action recognise the variables that motivate based on ownership of problems, and p roducers into some form of action and, in g o v e rnments can assist by ensuring the initial stages at least, incorporate this c o h e rence between local, regional and behaviour into a control strategy. The national needs, and providing technical and c o n t rol strategy which comes closest to this re s e a rch information. Government off i c e r s situation is the spasmodic control strategy. need to be involved in the process to Spasmodic control was defined as a understand better the complex social, response on a needs basis, that is e n v i ronmental and economic issues of each landholders should apply control when local situation within which land managers either damage, or feral pig numbers, or both, o p e r a t e . i n c re a s e . Kelly (1995) emphasises the need for The benefits of coordinated control have g o v e rnment facilitators to resist any been demonstrated in north-west New South temptation to attempt to push producers into Wales and reported by Bryant et al. (1984), action at group meetings. She says ‘extension Ko rn and Shands (1983), Korn (1986a,b) and officers and researchers need to realise that K o rn (1993). During the three-year pilot

124 Managing Vertebrate Pests: Feral Pigs scheme to control feral pigs in north-west New • leaders of successful groups should be South Wales, 74 groups were formed. This used to address prospective groups; and was in addition to 48 groups that had been • it is not always necessary to start by formi n g established in the Moree Rural Lands a group where pig densities are highest. P rotection Board district before the pilot scheme started. W h e re Rural Lands Protection Board staff Effective group action depends upon the in New South Wales acted as coord i n a t o r s establishment and maintenance of cohesive of group control programs, they found that groups (Chamala and Mortiss 1990). Proc e s s e s g roup enthusiasm and effectiveness was associated with the formation and main- enhanced by: tenance of effective groups for feral pig control • board staff regularly contacting the group a re described by Korn and Fosdick (1992). by either visiting or telephoning; and The processes target control agency staff: • mailing major decisions of any one group • start with a group of people you feel to all group leaders, if there were several comfortable with and an area of country groups in one district. which is not too large. The group of people selected should be keen, so that a good These findings support other studies in example is set. This first successful grou p g roup dynamics. In the case of feral pig can then act as a role model; c o n t rol in the Macquarie Marshes, it was found that the following elements were • identify an influential landholder from the e s s e n t i a l : g roup and use them to advantage. Such people know the social structure within the • a committed Rural Lands Pro t e c t i o n district: who works well with whom, what B o a rd ; the common needs of the district are and what size is practical for the control area ; • committed staff; • g roup size depends on topography and • good planning; especially on social factors, but it is critical • realistic goals and expectations; that it is a manageable size; • strong leadership; and • existing groups such as bush fire brigades or footrot control groups can be used to •co o rdination and liaison with neighbouring establish a feral pig control group; Rural Lands Protection Boards.

Bureau of Resource Sciences 125 10. Deficiencies in policy makers in state and territory agencies. Cu r rently, few of these staff have any training knowledge and in the principles of adult education, sociology practice or psychology, all of which are important in facilitating a change in behaviour of Summary individuals or groups. The biology and ecology of feral pigs in most major habitats in Australia is reasonably well 10.1 Biology of feral pigs in understood. There is, however, still a scarci t y Australia of information about feral pigs in some parts of tropical Australia, especially in rainfores t s . Deficiency For example, in the wet tropics of north T h e re is a lack of information about the Queensland, there is a perception that feral biology and ecology of feral pigs in some pigs migrate from upland rainforests to the parts of tropical Australia, especially in coastal lowlands (and the sugarcane crops) ra i n f o rests (McIlroy 1993). The most important during the dry season and then ret u rn to the ecological information re q u i red from a f o rests at the onset of the wet season; this, management point of view in these areas is: however, is yet to be proven by research. • the role of habitat and other factors in Two basic problems in determ i n i n g g o v e rning the seasonal distribution, priorities for where to control feral pigs in abundance and movements of pigs; and many areas of Australia are the lack of: (1) • seasonal foods pigs eat at different times objective, quantitative data on the impact of of the year (particularly during wet pigs on the natural environment; and (2) a periods), the availability of and nutrient means to compare costs of enviro n m e n t a l levels in these foods in diffe rent areas, and values affected with agricultural losses caused the effect of this on their rep roduction and by feral pigs. population dynamics, particularly bree d i n g Mo re information is req u i red on the factors frequency and piglet mortality. likely to affect the pro g ress and control of o u t b reaks of exotic diseases amongst feral Developments required pigs in different environments in Australia. One of the key areas of re s e a rch re q u i re d in the wet tropics of north Queensland, is The two major toxins used to control feral to confirm whether the perceived seasonal pigs in Australia are 1080 and CSSP. migration of pigs from upland rainforests to Extensive work has been conducted on the the coastal lowlands (and the sugarc a n e t h reat 1080 poses to non-target species but c rops) during the dry season, and their no studies are known to have been conducted re t u rn to the forests at the onset of the wet on CSSP, despite its longstanding and season does actually occur (Section 3.3.2). widespread use for feral pig control. Factors that may play an important ro l e There are no reliable data on the cost of include: the temporal abundance and controlling feral pigs in normal on-property availability of rainforest fruits and other c o n t rol programs. Because the objective of foods (for example, earthworms) and the national guidelines on vertebrate pest s o u rces of water; weather patterns such as management is to change pest management the effect of cyclones or the duration and actions by land managers, it is essential to timing of the wet and dry seasons; habitat know the current actions in the regions being disturbance; and hunting pre s s u re. targeted for change. R e s e a rch is also re q u i red on the Adoption of the national guidelines will population dynamics of feral pigs in these revolve around behaviour change at various areas, including the effects of environ m e n t a l levels, ranging from land managers up to factors and diff e rent levels of population

126 Managing Vertebrate Pests: Feral Pigs c o n t rol on their intrinsic rate of incre a s e . f rogs, ground-nesting birds and gro u n d - E n v i ronmental factors could include delays feeding or ground-dwelling birds and in the onset of the wet season, or a very mammals. This would include the effects of short wet season, the effect of cyclones, or not only feral pig predation, but also of feral a poor fruiting year in the rainfore s t . pig competition with other animals, such as with cassowaries for rainforest fruits, and Consequences of habitat degradation through selective This information is fundamentally important feeding, trampling and rooting up of the in planning where and when to focus control g round by pigs. The last activities could efforts in the region, and for selecting the best affect plant species composition and density, methods and strategies to control feral pigs. nutrient cycling and erosion, plant succession and the diversity of fauna in the 10.2 Agricultural impact a reas concerned. Other studies could focus on the role feral pigs may play in destro y i n g Deficiency or dispersing native and exotic plant seeds, The major costs of agricultural damage particularly those of rainforest species and caused by feral pigs to landholders have weeds, and the role they may have in the never been reliably estimated. s p read of ro o t rot fungus.

Developments required Other essential information on the e n v i ronmental impact of feral pigs re q u i re d Quantifying these impacts. for management plans is the extent and Consequences intensity of their impact in diff e rent are a s , This information will enable landholders to and the relationship between pig numbers place pig management costs and benefits and levels of impact. within the framework of total pro p e r t y Consequences planning and farm risk management. Ranking will allow comparisons of impacts and control costs for diff e rent areas, which 10.3 Environmental impact will enable land managers to prioritise where Deficiency to control feral pigs in many areas of Australia. If a relationship exists between pig numbers T h e re is a lack of: (1) objective, quantitative (or indices of numbers) and levels of impact, data on the impact of pigs on the natural it can be used to determine threshold pig e n v i ronment; and (2) a means to compare densities for acceptable levels of damage and, costs of environmental values affected with ultimately, the percentage reductions of pig economic losses caused by pigs to numbers or indices req u i red in diffe rent area s a g r i c u l t u re . or circumstances. The objective, then, is to Developments required develop or use appropriate control techniques Some form of ranking encompassing both and strategies that will achieve the required types of impact. This will re q u i re detailed reduction in levels of impact. surveys and studies of the possible, p e rceived and actual ecological impact of 10.4 Impact of diseases and feral pigs. One aim of this re s e a rch should parasites be to identify key threatening processes for valued flora and fauna and both the indire c t Deficiency and direct effects of pigs. Examples may be T h e re is a lack of information on the the impacts of pigs on rare or endangere d parameters and factors likely to affect the plants, particularly succulent species, grou n d p ro g ress and control of outbreaks of exotic o rchids or rainforest palms, and certain diseases amongst feral pigs in diff e re n t species of earthworms, endemic snails and e n v i ronments in Australia for use in exotic

Bureau of Resource Sciences 127 disease contingency planning (Pech and pers. comm. 1992) in the wet tropics of Hone 1988). Queensland (McIlroy 1993) or described by Hone and Stone (1989). Developments required Consequences M o re information is re q u i red on estimates of disease transmission coefficients, the I m p roved exotic disease contingency plans. chances of detection, the rates of spre a d , and the threshold densities of pigs below 10.5 Assessment of non- which diseases will die out. It may be target impact of CSSP possible in some circumstances to extra- polate the req u i red information from studies Deficiency of other viruses in feral pigs or wild boar in T h e re is a lack of information on the thre a t Australia or overseas. the toxin CSSP poses to non-target species Better information on the distribution and and on the relative humaneness of its action abundance of pigs in particular areas or on pigs. regions is also re q u i red. Emphasis should T h e re is a strong perception in scientific be on determining the pattern of distribution and government policy areas that the long- during diff e rent seasons, particularly to t e rm use of CSSP is questionable because identify isolated populations or gaps in pig of animal welfare considerations ( J. Barre t t , distribution, and topographical features that ANCA, Australian Capital Territory, pers. could be used as barriers to the spread of comm. 1994; A. Bryce, SCAW, Australian an exotic disease. Aerial surveys may be a Capital Territory, pers. comm. 1994). This suitable, if expensive, method of obtaining pe rception, however, has persisted for many this information in semi-arid and other years and CSSP is still being widely used. generally open areas, particularly if The reality is that it is probable that its use conducted by helicopter. Bayliss and will continue. Yeomans (1989) found that sightings of feral pigs from a fixed-wing aircraft pro v i d e d Developments required i n s u fficient information on their distribution Evaluation of CSSP’s non-target impacts and and abundance in the Top End of the on the humaneness of its action on pigs. N o r t h e rn Territory, but Wilson et al. (1987) obtained useful information on both Consequences parameters from fixed-wing surveys of Safer use of CSSP for feral pigs and non- grazing, wheat crop, woodland and fore s t t a rget species where this is feasible. habitats in south-east Queensland. Caley (1993) suggests a Geographic Inform a t i o n System could be used to indicate the likely 10.6 ‘Real world’ costs of distribution of pigs in the Northern Ter r i t o r y , ‘feral pig control based on simple criteria such as the pres e n c e of permanent water within ten kilometre s Deficiency and suitable dense cover (for example, along There is a lack of reliable data on the cost of w a t e rcourses). Such a system is not likely controlling feral pigs in normal on-property to be successful in more thickly vegetated co n t rol programs. The only data accumulated a reas, such as the tropical rainforests of a re those associated with re s e a rch pro j e c t s Queensland or eucalypt forests of south- or control programs that have had stro n g east Australia and south-west We s t e rn g o v e rnment or quasi-government agency Australia. In such habitats, gro u n d - b a s e d ownership. These costs are not ‘real’ costs. survey techniques, using indices such as signs of pig activity, may need to be Developments required developed along the lines used by L. Moore Specific data are needed on the costs of (CSIRO Wildlife and Ecology, Queensland, poisoning, shooting, fencing and trapping

128 Managing Vertebrate Pests: Feral Pigs so landholders can compare these costs with Adoption of the national guidelines will the benefits of pig contro l . revolve around behaviour change at various levels, ranging from land managers up to Consequences policy makers in state agencies. Assuming Factual field data would be useful for that state and territory policy makers adopt establishing a benchmark of landholder the principles of these guidelines, the onus behaviour associated with feral pig then falls upon staff to facilitate behavioural management. An objective of the national change in land managers. guidelines on vertebrate pest management is to change land manager behaviour, to Developments required make pest control more cost-eff e c t i v e . R e s o u rces must be allocated to address this deficiency in knowledge and skills by 10.7 Training extension staff of the control agencies in all states and territories. Deficiency Few staff of vertebrate pest management Consequences agencies have training in the principles of adult education, sociology or psychology, L o n g - t e rm changes in the attitudes and which are all important in facilitating a change behaviour of land managers for impro v e d in behaviour in individuals or groups. feral pig management.

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Bureau of Resource Sciences 135 Latham, R.M. (1960) Bounties are Bunk. Lukins, B. (1989) Feral pigs: Trapping in New National Wildlife Federation, Wa s h i n g t o n , South Wal e s . Agfact A9.0.15, 1st Edition, New D . C . South Wales Agriculture. Laun, C.H. (1971) A Guide to the Removal Masters, K. (1979) Feral pigs in the south-west of Bounties. Richard Carson Memorial of Wes t e rn Australia. Final Report to Feral Wildlife Educational Fund. Study No.3. Pig Committee. Agriculture Protection Board and Department of Conservation and Land Laurance, W. F. and Grant, J.D. (1994) Management, Wes t e rn Australia. Photographic identification of grou n d - n e s t p redators in Australian tropical rainfore s t . Masters, K. (1981) The private life of the wild Wildlife Researc h 21: 241–2 4 8 . pig. Department of Agriculture, We s t e rn Australia. Jo u rnal of Agriculture 22: 103–10 5 . Laurance, W.F., Garesche, J. and Payne, C.W. (1993) Avian nest predation in modified McGuckian, N. and McGuckian, R. (1994) and natural habitats in tro p i c a l Innovative Extension Pro g r a m s . C o m e x Queensland: an experimental study. Forum: Best Practice in Communication and Wildlife Researc h 2 0: 7 11–7 2 3 . Extension. Australian Institute of Agricultural Science, Vic t o r i a . Lee, K.E. (1985) E a r t h w o rms. Their Ecology and Relationships with Soils and Land Mc I l roy, J.C. (1983) The sensitivity of Australian U s e . Academic Press, Sydney. animals to 1080 poison. V. The sensitivity of feral pigs, Sus scro f a , to 1080 and its Lembit, M.J. and Fisher, B.S. (1992) The implications for poisoning campaigns. economic implications of an outbreak of Australian Wildlife Research 10: 139–14 8 . foot-and-mouth disease for bro a d a c re M c I l roy, J.C. (1985) Observations on the a g r i c u l t u re. Pp. 83–90 in: M.J. Nunn and sensitivity of some Australian birds and the P.M. Thorn b e r, eds, P roceedings of the feral pig to the org a n o p h o s p h o r u s National Symposium on Foot-and-Mouth insecticide, fenthion ethyl. A u s t r a l i a n Disease, Canberra 8–10 September. Wildlife Research 12: 331–33 5 . Australian Government Publishing Service, C a n b e r r a . M c I l roy, J.C. (1986) The sensitivity of Australian animals to 1080 poison. IX. L e rn e r, S. (1994) Local stewardship: training Comparisons between the major groups of g round for an environmental vanguard . animals and the potential danger non-targe t A l t e rnatives 20: 14–1 9 . species face from 1080-poisoning Letts, G.A. (1962) Early livestock campaigns. Australian Wildlife Researc h i n t roductions of the Top End of the 13: 39–48. N o r t h e rn Territory. Australian Ve t e r i n a r y Mc I l roy, J.C. (1989) Aspects of the ecology of J o u rn a l 38: 282–2 8 7 . feral pigs, Sus scrof a , in the Murchison area , Letts, G.A. (1964) Feral animals in the New Zealand. New Zealand Journal of N o r t h e rn Territory. Australian Ve t e r i n a r y Ec o l o g y 12: 11–22 . J o u rn a l 40: 84–8 8 . Mc I l roy, J.C. (1990) Feral pig. Pp. 358–371 in: Littlejohns, I.R. (1989) A perspective on the C.M. King, ed., The Handbook of New pestiviruses. Australian Veterinary Journa l Zealand Mammals. Ox f o rd University Pres s , 66: 434–4 3 7 . Auckland, New Zealand. Long, J.L. (1988) I n t roduced birds and M c I l roy, J.C. (1993) Feral pig management mammals in We s t e rn Australia. problems in the wet tropics of Queensland A g r i c u l t u re Protection Board of We s t e rn World Heritage Are a . Final consultancy Australia, Technical Series 1, 2nd Edition. report on control of feral pigs (Sus scrof a ) associated with the wet tropics of Queensland World Heritage Area, to We t

136 Managing Vertebrate Pests: Feral Pigs Tropics Management Agency, Cairns . New Zealand Department of Conservation (1994) National Possum Control Plan M c I l roy, J.C. and Saillard, R.J. (1989) The 1993–2002. Department of Conservation, effect of hunting with dogs on the numbers Wellington, New Zealand. and movements of feral pigs, Sus scro f a , and the subsequent success of poisoning New Zealand Department of Conservation e x e rcises in Namadgi National Park, (1996) National Feral Goat Control Plan Australian Capital Territory. A u s t r a l i a n 1993–2002. Department of Conservation, Wildlife Researc h 16: 353–3 6 3 . Wellington, New Zealand (in press). M c I l roy, J.C., Braysher, M. and Saunders, Norton, G.A. and Pech, R.P. (1988) Ver t e b r a t e G.R. (1989) Effectiveness of a warf a r i n - Pest Management in Australia: a Decision poisoning campaign against feral pigs, S u s Analysis/Systems Analysis Approa c h . Pro j e c t s c ro f a , in Namadgi National Park, Report No. 5, Division of Wildlife and Australian Capital Territory. A u s t r a l i a n Ecology, CSIRO, Australia. Wildlife Researc h 1 6: 1 95–2 0 2 . O’Brien, P.H. (1987) Socio-economic and M c I l roy, J.C., Giff o rd, E.J. and Forre s t e r, R.I. biological impact of the feral pig in New (1993) Seasonal patterns in bait South Wales: an overview and altern a t i v e consumption by feral pigs (Sus scro f a) in management plan. Australian Rangeland the hill country of south-eastern Australia. Journal 9: 96–101. Wildlife Researc h 20: 637–6 5 1 . O’Brien, P.H. (1988) The toxicity of sodium Mc I n e rney, J., Small, K.J. and Caley, P. (1995) m o n o f l u o roacetate (compound 1080) to P revalence of Mycobacterium bovis captive feral pigs (Sus scro f a). A u s t r a l i a n infection in feral pigs in the Northern Wildlife Research 15: 163–170. Territory. Australian Veterinary Journ a l O’Brien, P.H. and Lukins, B.S. (1988) Factors 7 2: 4 48–4 5 1 . influencing the intake of sodium McKnight, T. (1976) Friendly vermin: a m o n o f l u o roacetate (compound 1080) by survey of feral livestock in Australia. free-ranging feral pigs. Australian Wildlife University of California Publications in Research 15: 285–291. G e o g r a p h y 2 1: 39–5 5 . O’Brien, P.H. and Lukins, B.S. (1990) Mitchell, J. (1993) Systematic assessment of Comparative dose–response relationships feral pig damage and recommended pig and acceptability of warfarin, brod i f a c o u m c o n t rol methods in the wet tropics Wo r l d and phosphorus to feral pigs. A u s t r a l i a n Heritage Area. Final Report to the We t Wildlife Research 17: 101–112. Tropics Management Agency, Department O’Brien, P.H. and Meek, P. (1992) Feral pig of Lands, Charters Towers, Queensland. management. Final report to the Rural Mitchell, T.D., Kearins, R.D., Marchan, R.S. Industries Research and Development and Plant, J.W. (1977) Electric fences to Corporation, Bureau of Rural Resourc e s , c o n t rol feral pigs. Agricultural Gazette of Canberra. New South Wales 88: October. O’Brien, P.H., Kleba, R.E., Beck, J.A. and Moule, G.R. (1954) Observations on mortality Ba k e r, P.J. (1986) Vomiting by feral pigs after amongst lambs in Queensland. A u s t r a l i a n 1080 intoxication: non-target hazard and Veterinary Journ a l 30: 153–1 7 1 . influence of anti-emetics. Wildlife Society Bulletin 14: 425–432. National Consultative Committee on Animal We l f a re (NCCAW) (1992) Vertebrate Pest C o n t rol and Animal We l f a re . A n i m a l We l f a re Unit, Department of Primary Industry and Energy, Canberra.

Bureau of Resource Sciences 137 O’Brien, P.H., Beck, J.A. and Lukins, B.S. Pavlov, P.M., Kilgour R.J. and Pederson, H. (1987) Residual tissue levels of warf a r i n (1981) Predation by feral pigs on merino and 1080 in poisoned feral pigs. lambs at Nyngan, New South Wa l e s . Unpublished Working Document for the Australian Journal of Experimental 8th Australian Vertebrate Pest Contro l A g r i c u l t u re and Animal Husbandry C o n f e rence, Coolangatta. 2 1: 5 70–5 7 4 . O l i v e r, A.J., Marsack, P.R., Mawson, P. R . , Pavlov, P.M., Hone, J. and Moore, L.A. (1992) Coyle, P.H., Spencer, R.D. and Dean, K.R. Feral pigs, rainforest conservation and (1992) Species management plan for feral exotic disease in north Queensland. p i g s . A g r i c u l t u re Protection Board, Perth, Wildlife Researc h 19: 179–1 9 3 . We s t e rn Australia. Pech, R.P. and Hone, J. (1988) A model of Parkes, J.P. (1990) Pro c e d u res for ranking the dynamics and control of an outbre a k and monitoring feral goat (Capra hirc u s) of foot-and-mouth disease in feral pigs in c o n t rol operations. Forest Researc h Australia. J o u rnal of Applied Ecology Institute Contract Report FWE 90/11, New 2 5: 63–7 7 . Z e a l a n d . Pech, R.P. and McIlroy, J.C. (1990) A model Parkes, J.P. (1993) The ecological dynamics of the velocity of advance of foot-and- of pest–re s o u rce–people systems. N e w mouth disease in feral pigs. J o u rnal of Zealand Journal of Zoology 20: 223–2 3 0 . Applied Ecology 27: 635–6 5 0 . Pav Ecol (1992) Investigation of feral pig Plant, J.W., Marchant R., Mitchell T.D. and populations and control measures: Cape Giles, J.R. (1978) Neonatal lamb losses due Tribulation Section of the wet tro p i c s to feral pig predation. A u s t r a l i a n World Heritage Area. Consultancy re p o r t Veterinary Journ a l 54: 426–4 2 9 . to Wet Tropics Management Authority, P retty, J.N. (1994) Alternative systems of C a i rn s . inquiry for sustainable agriculture . University of Sussex, United Kingdom. Pavlov, P.M. (1980) The diet and general Institute for Development Studies Bulletin ecology of the feral pig in the Girilambone 25: 37–4 6 . district of New South Wales. M.Sc. thesis, Monash University, Melbourn e . P u l l a r, E.M. (1950) The wild (feral) pigs of Australia and their role in the spread of Pavlov, P.M. (1983) Feral pigs. Pp. 494–4 9 5 exotic diseases in Australia. A u s t r a l i a n in: R. Strahan, ed., The Australian Museum Veterinary Journ a l 26: 99–1 0 9 . Complete Book of Australian Mammals. Angus and Robertson, Sydney. P u l l a r, E.M. (1953) The wild (feral) pigs of Australia: their origin, distribution and Pavlov, P.M. (1991) Aspects of the ecology economic importance. Memoirs of the of the feral pig (Sus scro f a) in semi-arid National Museum, M e l b o u rne 18: 7–23. and tropical areas of eastern Australia. Unpublished Ph.D. thesis, Monash R a i n f o rest Conservation Society of University, Melbourn e . Queensland (1986) Tropical rainforests of north Queensland: their conservation Pavlov, P.M. and Hone, J. (1982) The significance: a report to the Australian behaviour of feral pigs, Sus scro f a , i n Heritage Commission. Special Australian flocks of lambing ewes. A u s t r a l i a n Heritage Publication Series, No. 3, Australian Wildlife Researc h 9: 101–1 0 9 . Go v e rnment Publishing Service, Canberra. Ramsay, B.J. (1994) C o m m e rcial Use of Wil d Animals in Australia. B u reau of Resourc e Sciences, Australian Govern m e n t Publishing Service, Canberra.

138 Managing Vertebrate Pests: Feral Pigs Ramsay, B.J. and O’Brien, P.H. (1991) Pest Rose, B. (1995) Land management issues: c o n t rol and commercial use of intro d u c e d attitudes and perceptions amongst animals: what are the issues? A u s t r a l i a n Aboriginal people of central Australia. Vertebrate Pest Control Confere n c e Central Land Council Cross Cultural Land 9: 3 10–3 1 4 . Management Project. Central Land Council, Alice Springs. R a t c l i ffe, F.N. (1959) The hard c o re of the rabbit problem and the role of re s e a rch in Roshier D. (1993) Stability of production of rabbit control. Pp. 70–77 in: The Rabbit c o m m e rcial leases in the chenopod P roblem in Australia. CSIRO, Melbourn e . shrublands. Report to the Australian Wool Research Council. Ra t h o re, A.K. (1985) Use of metoclopramide to prevent 1080-induced emesis in wild Rowley, I. (1970) Lamb predation in Australia: pigs. J o u rnal of Wildlife Management incidence, predisposing conditions and 4 9: 55–5 6 . identification of wounds. CSIRO Wi l d l i f e Research 15: 79–123. R i c h a rds, S.J., McDonald, K.R. and Alford , R.A. (1993). Declines in populations of Ryan, T.K. (1947) Stock Poisoning: Field Australia’s endemic tropic frogs. P a c i f i c Investigations into Mortalities in Stock due Conservation Biology 1: 66–77. to Irritant Poisons and Other Factors. Ridpath, M.G. (1991) Feral mammals and their Associated General Publications, Sydney. en v i ronment. Pp. 169–191 in: C.D. Haynes, Salleras, P. (1995) Conserving cassowaries M.G. Ridpath, M.A.J. Williams and A.A. while controlling feral pigs (landholder Balkema, eds, Monsoonal Australia: perspective). Australian Vertebrate Pest Landscape, Ecology and Man in the Control Conference 10: 133–135. N o r t h e rn Lowlands. R o t t e rd a m , Netherlands. Saunders, G. (1988) The ecology and management of feral pigs in New South Roberts, A., Klomp, N. and Birckhead, J. Wales. Unpublished M.Sc. thesis, Macquarie (1996) Monitoring marine and terre s t r i a l University, Sydney. hunting in an Aboriginal community in north Queensland. Pp. 152–164 in: M. Bomford Saunders, G. (1993a) The demography of feral and J. Caughley, eds, Sustainable Use of pigs (Sus scrof a ) in Kosciusko National Park, Wildlife by Aboriginal Peoples and Torres New South Wales. Wildlife Researc h Strait Islanders. B u reau of Resourc e 20: 559–570. Sciences, Australian Government Printing Saunders, G. (1993b) Observations on the Service, Canberra. e ffectiveness of shooting feral pigs fro m Robertson, W.A.N. (1932) Milestones in the helicopters in western New South Wa l e s . pastoral age of Australia. Pre s i d e n t i a l Wildlife Research 20: 771–776. Ad d ress, Report of the Twenty-First Meeting Saunders, G. and Bryant, H. (1988) The of the Australian and New Zealand evaluation of a feral pig eradication prog r a m Association for the Advancement of Science during a simulated exotic disease outbrea k . 21: 295–325. Australian Wildlife Research 15: 73–81. Robson, J., Harrison, M.W., Wood, R.N., Til s e , Saunders, G. and Kay, B. (1991) Movements M.H., McKay, A.B. and Brodribb, T.R. (1993) of feral pigs (Sus scrofa) at Sunny Corner, Brucellosis: re - e m e rgence and changing New South Wales. Wildlife Researc h epidemiology in Queensland. M e d i c a l 18: 49–61. Journal of Australia 159: 153–158. Rolls, E.C. (1969) They All Ran Wild. Angus and Robertson, Sydney.

Bureau of Resource Sciences 139 Saunders, G.R. and Korn, T.J. (1986) The cost Soule, M.E. (1990) The onslaught of alien and implications of vertebrate pest control species, and other challenges in the coming to livestock industries. P roceedings of the decades. Conservation Biology 4: 233–23 9 . Australian Society of Animal Pro d u c t i o n Standing Committee on Agriculture (1991) 16: 87–91. Feral Livestock Animals: Destruction or Saunders, G., Kay, B. and Parker, B. (1990) Ca p t u re, Handling and Marketing. An i m a l Evaluation of a warfarin poisoning Health Committee, Standing Committee on p rogramme for feral pigs (Sus scro f a) . Ag r i c u l t u re Technical Report No. 34. Australian Wildlife Research 17: 525–533. Statham, M. and Middleton, M. (1987) Feral Saunders, G., Kay, B. and Nicol, H. (1993) pigs on Flinders Island. Papers and Factors affecting bait uptake and trapping P roceedings of the Royal Society of success for feral pigs (Sus scro f a) in Ta s m a n i a 121: 121–1 2 4 . Kosciusko National Park. Wildlife Research 20: 653–66 5 . Stevens, P. (1983) Pigs Run Wil d . De p a r t m e n t of Crown Lands and Survey, Vi c t o r i a , Senge, P.M. (1992) The Fifth Discipline – The Pamphlet No. 83a, Revised May 1983. Art and Practice of the Learn i n g Org a n i s a t i o n . Random House, Milsons Point. Stevenson, W.J. and Hughes, K.L, eds (1988) Brucellosis. Pp. 15–22 in: Synopsis of Shaw, W.B. (1988) Botantical conservation Zoonoses in Australia, 2nd Edition. assessment of Crown lands in the Australian Government Publishing Service, Urewera/Raukumara planning study area . Ca n b e r r a . F o rest Research Institute Report, Rotorua, New Zealand. Stone, C.P. and Tay l o r, D.D. (1984) Status of feral pig management and res e a rch in Hawaii Sheehan, M.W. (1984) Field studies in the use Volcanoes National Park. P ro c e e d i n g s of sodium monofluoroacetate, ‘1080’, in the National Science Conference. Hawaii co n t rol of vertebrate vermin species in inland Volcanoes National Park 5: 106–1 1 7 . south east Queensland. Unpublished M.V.S c . thesis, University of Queensland. Takahashi, S. and Tisdell, C. (1989) The trade S i g n o ret, J.P., Baldwin, B.A., Fraser, D. and in wild pig meat: Australia and Japan. Hafez, E.S.E. (1975) The behaviour of swine. Australian Geographer 20: 88–94 . Pp. 295–329 in: E. Hafez, ed., The Behaviour Ta y l o r, D. and Katahira, L. (1988) Radio- of Domestic Animals. B a i l l i e re Tr i n d a l l , telemetry as an aid in eradicating rem n a n t Lo n d o n . feral goats. Wildlife Society Bulletin S i n c l a i r, A.R.E., Dublin, H. and Born e r, M. 16: 297–2 9 9 . (1985) Population regulation of Sere n g e t i Thompson, R.C.A., Lymbery, A.J., Hobbs, R.P. wildebeest: a test of the food hypothesis. and Elliot, A.D. (1988) Hydatid disease in Oecologia 65: 266–26 8 . urban areas of Wes t e rn Australia: an unusual Smith, M.J. (1990) The role of bounties in pest cycle involving western gray kangaro o s management with specific ref e rence to state (M a c ropus fuliginosus), feral pigs and dingo control programs. Project, Charles Sturt domestic dogs. Australian Ve t e r i n a r y Un i v e r s i t y . Jo u rn a l 65: 188–19 0 . Southwood, T.R.E. and Norton, G. (1973) Tisdell, C.A. (1982) Wild Pigs: Environ m e n t a l Economic aspects of pest management Pest or Economic Resourc e ? P e rg a m o n strategies and decisions. Pp. 168–184 in: P.W. Press, Sydney. G e i e r, L.R. Clark, D.J. Anderson and H.A. Tisdell, C. (1983/84) Feral pigs: wily enemies. Nix, eds, Insects: Studies in Pest Australian Country 27: 66–69. Ma n a g e m e n t . Ecological Society of Australia, Canberra.

140 Managing Vertebrate Pests: Feral Pigs Tisdell, C.A. (1984) Feral pigs threaten native Williams, K., Parer, I., Coman, B., Burley, J. wildlife in Australia. Tigerpaper 11: 13–17. and Braysher, M. (1995) M a n a g i n g Vertebrate Pests: Rabbits. B u reau of Tomlinson, A.R. (1957) Bonuses for vermin R e s o u rce Sciences and Australian c o n t rol. Conference on Ve rmin Contro l . Go v e rnment Publishing Service, Canberra. Ag r i c u l t u re Protection Board, Perth, Wes t e rn Australia. Williams, M.L. and Henzell, R.P. (1992) Operation Pewsey Vale: an exercise in Townsend, S.E. (1981) Some notes on feral co n t rolling an exotic animal disease in feral pigs and their distribution in Vi c t o r i a . goats. Department of Agriculture South Victorian Naturalist 98: 37–41. Australia Technical Paper No. 30. Turvey, R. (1978) Approaches to the selection Wilson, G. and Choquenot, D. (1996) Review of optimal control strategies for feral pigs: of feral pigs and exotic disease co s t - e ffectiveness analysis of present control p re p a redness. Report in preparation for m e a s u res. Unpublished Final Year thesis, Bureau of Resource Sciences, Canberra. University of New England, Armidale. Wilson, G.R., Hill, J.E. and Barnes, A. (1987) Tyndale-Biscoe, C.H. (1994) Vi r u s - v e c t o re d An aerial survey of feral pigs and emus in immunocontraception of feral mammals. s o u t h - e a s t e rn Queensland. A u s t r a l i a n R e p roduction, Fertility and Development Wildlife Research 14: 515–520. 6: 281–287. Wilson, G., Dexter, N., O’Brien, P. and Tyson, T. (1989) Working With Gro u p s. B o m f o rd, M. (1992a) Pest animals in Macmillan Co., Melbourne. Australia – a Survey of Introduced Wi l d Vanclay, F. and Lawrence, G. (1994) Farmer Mammals. Kangaroo Press and Bureau of rationality and the adoption of enviro n - Rural Resources, Canberra. mentally sound practices: a critique of the Wilson, G., McNee, A. and Platts, P. (1992b) assumptions of traditional agricultural Wild Animal Resources: Their Use by extension. E u ropean Journal for Aboriginal Communities. Bureau of Rural Agricultural Education and Extension R e s o u rces, Australian Govern m e n t 1: 59–90. Publishing Service, Canberra. Varley, G.C. and Gradwell, G.R. (1968) Wirth, H.J. (1995) Vertebrate pest control and Population models for the winter moth. animal welfare – the National Consultative London, Symposia of the Royal Entomo- Committee on Animal We l f a re view. logical Society 4: 132–142. Unpublished paper presented and circu l a t e d Walters, C.J. and Holling C.S. (1990) Larg e - at the 10th Australian Vertebrate Pest Control scale management experiments and C o n f e rence, Hobart (not included in learning by doing. Ecology 71: 2060–2068. conference proceedings). Wet Tropics Management Authority (1992) Woodall, P. F. (1983) Distribution and Wet Tropics Plan: Strategic Directions. Wor l d population dynamics of dingoes (C a n i s Heritage Area, Cairns, Queensland. f a m i l i a r i s) and feral pigs (Sus scro f a) in Queensland, 1945–1976. Jo u rnal of Applied Williams, J.M. (1993) The factors and forces Ecology 20: 85–95. shaping rabbit control policies and practices in New Zealand: what lessons for the future? Pp. 42–50 in: B.D. Cooke, ed., Australian Rabbit Control Confere n c e. Anti-rabbit Re s e a rch Foundation of Australia, Adelaide.

Bureau of Resource Sciences 141 Appendix A • incorporation of an evaluation strategy to e n s u re the program is flexible and responsive to external changes such as the Best practice extension in environment or market (Kelly 1995). pest management D e c reasing state government re s o u rc e s limit the ability of extension workers to Quentin Hart and Dana Kelly t a rget individual land managers. Landcare Achieving sustainable land management, g roups provide a partial solution to this including pest management, can be p roblem in that they allow extension facilitated by new approaches to extension. workers to target groups rather than Traditionally, extension has been defined as individuals, and the information diff u s i o n the dissemination of information. In this p rocess within these groups is re l a t i v e l y definition, it is seen as the link between the rapid. The group approach off e red by p roducers of information (re s e a rchers and L a n d c a re can also be used to develop others) and the end-users of the information regional rather than individual management (generally land managers). Researc h e r s , plans for pest management (Chamala and public policy makers and industry tend to Mortiss 1990). refer to res e a rch transfer, technology transfer Extension should not dictate solutions or information diffusion. Bennett (1993) but provide the underlying technical emphasises the need for mutual inter- in f o rmation and decision-making framework dependence and cooperative action com- f rom which land managers can draw their bining these two approaches. If extension is own conclusions. In this way, both to achieve adoption, it must facilitate g o v e rnment and land managers will have a understanding and involve a participatory g reater understanding of the complexity of rather than prescriptive approach. the problems and the possible solutions. Some characteristics and principles Such participatory learning approaches also i n h e rent in innovative extension pro g r a m s p rovide land managers with ownership of a re: the problems and solutions, and this facilitates adoption. • ownership; Involving land managers as co-learn e r s • benchmarking; and co-re s e a rchers has been encouraged in • participatory learning based on principles demonstration projects supported by the of adult learning; Vertebrate Pest Program (VPP) of the Burea u of Resource Sciences. The VPP funded state • equity and respect for everyone’s views and territory government agencies and (Kelly 1995); L a n d c a re groups to determine best practice • p roblem definition with stakeholder pest management for a particular area. The consensus (Ison 1993); projects were generally large-scale field trials involving several properties and comparing • client driven or responsive to the needs of several management strategies. Rather than clients (McGuckian and McGuckian 1994); simply providing land for the re s e a rch, land • consideration of the whole property or managers were integral parts of the pro j e c t s whole agribusiness chain (McGuckian and and helped determine management options McGuckian 1994); which are practical and economically sensible for their particular area. Their • incorporation of processes to cre a t e involvement also facilitated the dissem- learning opportunities that lead to locally ination of project findings to other land meaningful and adaptive changes (Ison managers. One of the roles of extension is 1993), that is, ‘learning by doing’ (Section to maintain the momentum of such pro j e c t s 8.4.5 and Walters and Holling 1990); and once government funding ceases.

142 Managing Vertebrate Pests: Feral Pigs Relevance of information to the land • take a whole-property management manager in a framework of whole-prop e r t y a p p roach by recognising that managers management needs to be considered by have to allocate budgets to deal with many extension workers. Pest damage is a single risks and opportunities and are rarely able and often minor issue amongst a wide range to fund pest control at optimal levels. Given of management considerations a land manager limited budgets, the solution is to use has to contend with. This is particularly true cost–benefit analyses, which are relevant for pests which inflict major but infre q u e n t to the local area, to optimise where, when damage such as mice. Pest management is and how much control is conducted. As peripheral to most land managers’ major part of this, pest damage should be activities, and their motivation relates to curren t quantified and financial situation of land rather than potential damage (Salleras 1995). managers should be taken into account w h e re data are available to do this (see Extension workers and res e a rch workers Appendix B); and ‘must be able to understand the goals and reasons for motivation or otherwise of the • ideally, implement local field trials, and various human stakeholders as well as the f rom these coordinate regional manage- habits and habitat of [the pest animal with] the ment strategies to achieve maximum (and most effective solutions [being] achieved by hopefully long-term) adoption. examining diff e rences in the human Computer technology may provide a dimension rather than concentrating on the partial solution to decreasing re s o u rces for pest’ (Salleras 1995). physical extension. It will enable pest The above assertions by Salleras, a rural management information to be pro v i d e d land manager from Queensland, are prob a b l y e l e c t ronically and readily updated. This a good rep resentation of the attitudes of many i n f o rmation can be linked to decision land managers and provide an insight into support systems to lead landholders step- effective extension methodology. by-step through a process of ‘self- assessment’ so that they may determine the Extension should: best management options based on their • o ffer concise information specific to own on-ground observations. regional needs; H o w e v e r, the potential value of these •offer a framework for making management systems depends entirely on the extent to decisions based on generic inform a t i o n which land managers adopt such combined with local observation; technology. In the foreseeable future adoption rates of best practice pest • o ffer a range of options rather than be management, which are currently low and pre s c r i p t i v e ; vary between localities, will depend on • take account of the availability of pest extension and re s e a rch officers working management tools (for example, Global with land managers to determine what best Positioning Systems and bulldozers for practice is for their situation and becoming w a r ren ripping) within a region so that actively involved in its implementation. recommended control techniques are ap p ro p r i a t e ;

Bureau of Resource Sciences 143 Appendix B much will this increase lambing perce n t a g e s . T h e re may be interactions between pest density and other farm management Economic framework for practices which will need to be taken into feral pig management account. For example the increase in lambing percentage caused by reducing pig (After Bomford and others 1995) densities by 50% may vary with diff e re n t Land managers who wish to determine the levels of availability of shelter for lambs. optimal economic strategy for managing a problem caused by feral pigs could use the Step 4 — Efficacy stepwise approach outlined in this appendix. Estimate the efficacy of each control option. We recognise that managers will have That is, how much will a given effort using incomplete knowledge of the inform a t i o n a particular control option reduce pig necessary to fully complete many of these density. steps. Nonetheless, the exercise of attempting to complete the process, and re c o rding the assumptions and best guess estimates that are Step 5 — Cost–benefit relationships made, may prove a useful aid to decision Use the information from Steps 1–4 to making for feral pig management. estimate costs and benefits of implementing each control option, including options Step 1 — Desired outcomes which combine more than one technique. Costs will be the cost of implementing each Identify desired outcomes and estimate a c o n t rol option, and may include costs of dollar value for each of these. Where monitoring pests and planning. Benefits will outcomes are commodities, such as be the value of the reduction in damage to in c reasing lambing percentages, this should the valued re s o u rce caused by imple- be reasonably easy. Where outcomes are menting control (that is the desire d difficult to measure, such as reduced land outcomes listed under Step 1 above), plus degradation, or intangible, such as increa s e d biodiversity, land managers may be obliged to estimate how much they consider is an acceptable amount to spend to achieve that outcome.

Step 2 — Control options List all control options and how much they would cost to implement. Control options can be diffe rent techniques or combinations of techniques, or diff e rent levels or f requencies of application of techniques (Section 7.6). It is important that the options for control are expressed as activities that a manager can select either to do or not to do. F i g u r e B1: Possible relationships between pig density and the damage they cause. Line Step 3 — Density– damage A is the relationship shown in Figure 9 and relationships line B that shown in Figure 10. Line C might Estimate the relationship between pest occur if, for example, only still-born lambs are density and damage for each re s o u rc e p reyed on by feral pigs at low densities, but if damaged by the pest (Figure B1). For pig density increases, they start to kill healthy example, if pigs are reduced by 50%, how l a m b s .

144 Managing Vertebrate Pests: Feral Pigs any profits (for example, those made from co n t rol. Further increases in control activity selling pigs or from allowing hunters on the do not cause commensurate reductions in property). damage, so at higher levels of contro l beyond this point, costs will exceed savings D i ff e rent pest management options will generate a variety of cost–benefit relation- in reduced damage. An example of margi n a l ships. Estimates of benefits and costs can analysis for shooting feral pigs fro m be discounted back to net present values helicopters is presented in Figure 20. (usually using a discount rate equivalent to The problem for managers is that, because the interest rate the landholder pays on they often do not have good inform a t i o n financing the control operation). This will on the density– damage relationship, it is reduce the value of costs and benefits hard to estimate the optimal control point. accruing in the distant future relative to those Fu r t h e r, even if they can make a good guess, accruing in the near future. it is not usually practical with most control techniques to simply cut off control efforts Step 6 — Marginal analysis. at some pre - d e t e rmined pig density. It is Plot both the incremental change in the cost preferable to have a range of control options of pig control and the incremental change ranked along the x-axis, with their in the cost of damage caused by pigs against associated cost and benefit values for the level of control activity contemplated implementation, so a manager can select ( F i g u re B2). Where the two lines cross is which option is optimal. For example, t h e o retically the optimal level of pest different frequencies of shooting could be put along the x-axis.

Step 7 — Pay-off matrices Construct a table listing all the contro l options and their associated costs and benefits (economists call this a pay-off matrix). For example, Section 8.8.3 c o m p a res the costs and benefits of two c o n t rol strategies — shooting pigs fro m helicopters or poisoning with 1080. Managers may wish to construct diff e re n t matrices for diff e rent conditions, such as d i ff e rent stocking densities, seasonal conditions, or commodity values for wool, lambs or pigs. Managers will also need to consider time-scales when constructing these matrixes — what time span is covered F i g u r e B2: M a rginal analysis plotting both and how will this affect costs and benefits? i n c remental changes in the cost of re d u c i n g pigs to a given density and incre m e n t a l These matrices can then be used to select changes in the cost of damage caused by pigs the option(s) which best meet the managers’ at a given density against level of contro l goals. If the manager is risk averse, the best activity. Where the two lines cross is theore t- options will be those that bring in ically the optimal level of pest control. At higher reasonable re t u rns (benefits in relation to levels of control beyond this point, costs will costs) under the widest range of conditions exceed savings in reduced damage. (that is, in most seasons and with a wide Note: The x-axis units are for control effort (for example, range of commodity prices). If the manager’s dollars spent on control, hours of shooting or trap priority is to maximise profit, the preferred nights) not pig densities. options will be those that are likely to give

Bureau of Resource Sciences 145 the highest re t u rns on investment, even — retaining rural communities; and though there may be some risk of having no returns or even a loss if the seasons and — animal welfare management. prices go badly. • Risk management for spread of disease P a y - o ff matrices can also be used by a land by pigs could also be included in Step 1. manager to compare ret u rns on investment •E ffects of government intervention could in pest control with re t u rns on using the affect value of benefits (in Step 1) or costs money for some other purpose, such as (in Step 2). fencing, new stock watering holes or fertiliser. • C o m m e rcial harvest of feral pigs, as an a l t e rnative to control as a pest, could be Steps 1–7 complete the basic model. The included as a control option in Step 2. model can be made more accurate by adding additional features. Incorporation of such • I n d i rect effects of pest control (for additional features will make the model more example, controlling pigs may lead to an complex, but including at least some of them i n c rease in rabbit numbers) could be may be necessary to make it accurate enough included as interaction effects in Step 3. to be useful. • The form in which benefits come may be One way of improving accuracy may be significant to a manager (Step 5). For to replace single estimates with a range of example, cash ‘bonuses’ from the sale of possible values, and give associated feral pigs may be more attractive as probabilities for each value in the range. immediate cash for spending, than future Managers may also wish to add additional money from increased lambing perc e n - features to the model such as: tages, which may be committed in advance to servicing debts or meeting • Social benefits could be included in Step 1, f a rm running costs. such as: Much of the information needed to follow — off-site effects and good neighbour the steps outlined in this appendix is not relations; available. Some projects funded by the — biodiversity and endangered species Vertebrate Pest Program in BRS aimed to management in agricultural areas; collect some of these data.

146 Managing Vertebrate Pests: Feral Pigs Appendix C that need to be met for eradication to be p referable to long-term feral pig contro l : Criteria for eradication • Feral pigs can be monitored at very low densities. This can be difficult to Eradication is the permanent removal of all achieve, but the rooting behaviour of feral individuals of a species from a defined are a pigs might allow survivors to be detected. within a defined time. • The socio-political environment is T h e re are three essential criteria which s u i t a b l e . For example, if certain gro u p s must be met for eradication to be possible object strongly to the eradication of feral ( B o m f o rd and O’Brien 1995). If all thre e pigs they can directly thwart or politically criteria cannot be met, eradication should influence the pro g r a m . not be attempted: • Discounted cost–benefit analysis • Feral pigs can be killed at a rate faster favours eradication over contr o l . than replacement rate at all densities. Discount rates are used to estimate the As the density declines it becomes value of future benefits against the costs progressively more difficult and costly to of actions in current dollars. This criterion locate and remove the last few animals. is difficult to meet because of the high • Immigration can be prevented. This is initial cost of eradication and because possible for off s h o re islands or small benefits accrue over a long period. At mainland populations which are high discount rates, eradication is unlikely geographically isolated, or where com- to be cost-effective. Eradication has a pletely effective barriers can be ere c t e d l a rge initial outlay but, if it can be and maintained, such as well-maintained achieved, there are no continuing costs pig-proof fences. apart from maintaining the outer • All rep roductive pigs are at risk fr om p rotective boundary. For cost-eff e c t i v e the control technique(s) used. If some eradication, each situation where animals are trap-shy or bait-shy, through eradication is technically feasible should either inherited or learnt behaviour, then be assessed to determine whether this sub-set will not be at risk. discounted eradication costs outweigh discounted benefits. T h e re are three additional criteria identified by Bomford and O’Brien (1995)

Bureau of Resource Sciences 147 ACRONYMS AND ABBREVIATIONS

AHC Animal Health Committee DNR Department of Natural ANCA Australian Nature Resources (Queensland) Conservation Agency ESD Ecologically Sustainable ANZFAS Australian and New Zealand Development Federation of Animal FMD Foot-and-mouth disease Societies FPP Feral Pests Program APB Agriculture Protection GIS Geographic Information Board (Western Australia) System (now AWA) GPS Global Positioning System ASF African Swine Fever NSWAF New South Wales Agriculture AUSVETPLAN Australian Veterinary and Fisheries Emergency Plan RSPCA Royal Society for the AWA Agriculture Western Australia Prevention of Cruelty to BSES Bureau of Sugar Experiment Animals (Australia) Stations SCARM Standing Committee on BTEC Brucellosis and Tuberculosis Agriculture and Resource Eradication Campaign Management BRS Bureau of Resource Sciences SCAW Sub-Committee on Animal Welfare (a sub-committee of CSIRO Commonwealth Scientific SCARM) and Industrial Research Organisation s.d. Standard deviation SRS Sugar Research Stations C4 Consultative Committee for (now BSES) the Conservation of Cassowaries (now the VPC Vertebrate Pests Committee Community for Coastal and VPP Vertebrate Pest Program Cassowary Conservation) WGR Wild Game Resources CSSP Trade name for yellow WEDPP Wildlife and Exotic Diseases phosphorus-based poison Preparedness Program CSF Classical Swine Fever WHA World Heritage Area c.v.% Coefficient of variation WTMA Wet Tropics Management df Degrees of freedom Authority

148 Managing Vertebrate Pests: Feral Pigs GLOSSARY

1080: Sodium monofluoroacetate. An acute Biodiversity: Biological diversity. The natural metabolic poison without antidote. diversity of living things, usually defined at three levels: genetic, species and 95% confidence intervals: The maximum ecosystem. and minimum values either side of an estimate, between which there is a 95% Cadastral plans: Diagrams or maps which probability that the true value will lie. include property boundaries, land tenure, roads and similar information. Ad hoc approach: A reactive appro a c h designed to meet immediate short-term Carrier: Animal infected with (and capable goals (that is, not taking account of broa d e r of spreading) a disease, but showing no issues or the longer term). clinical signs. Ad libitum:Free, without limit (for example, Carrying capacity: Density of an uncon- ad libitum feeding is allowing animals to t rolled population that is in equilibrium eat all they want). with its natural res o u rces and competitors. Age cohorts: Animals born in the same Chiller: Co m m e rcial industry portable free z e r breeding season. for storing game meat. Agouti: Animal fur coloured brown or black Co e f ficient of variation ( c. v . % ): A measure with lighter tips. of variance around a mean: Ambient temperatur e: Tem p e r a t u re of the c.v.% = 100s.d./ x– surrounding air. where s.d. = the standard deviation of the – Anoestrus: N o n - b reeding period, lacking sample and x is the sample mean. oestrus cycles. Cohort: Group of animals born at the same Anticoagulant: Substance that slows or time. prevents blood clotting. Conservation values: Values attributed to Antigen: Substance that triggers an immune maintaining biodiversity, including the reaction. preservation of viable populations of native species and natural communities over their Anti-emetic: Substance that inhibits vomiting. natural range, preservation of wilderness, A r t h r opods: Animals with hard outer and prevention of land degradation. skeleton and jointed legs (includes insects, Consumptive impacts: Impacts due to mites, spiders and crayfish). resources being consumed (for example, Artiodactyls: Animals with an even number pigs eating lambs or crops). of digits (claws). Corm: Bulb-like underground stem. Asymptote: Wh e re a curvilinear line flattens Crepuscular: Active at dawn and dusk. out and approaches a constant value. Curvilinear r e l a t i o n s h i p : Curved line Ba i t : Attractive substance fed to pest animals relationship between two or more that can be used to carry a control agent, variables. such as poison or contraceptive, or to lure them into traps. Demographics: Statistics relating to population dynamics, including birth rates, Bait station: A place for feeding poison bait mortality rates, age and sex ratios. that is usually only accessible to targ e t species.

Bureau of Resource Sciences 149 D e n s i t y - d e p e n d e n c e : W h e re the rate of Extrinsically regulated population: increase of a population is dependent on E n v i ronmental res o u rces limit population its density, so that as numbers incre a s e , size when they are in short supply. rate of increase declines. Farrowing: Giving birth to a litter of pigs. Discount rates: The rate used to calculate Fecundity: The number of fertile eggs the present value of future benefits or costs. produced by an individual female or by a They are calculated using the re v e r s e species. equation to that used to calculate interest rates on invested money. Feral: Domesticated species that has established a wild population. Disease transmission coef f i c i e n t : A measure of the rate at which a disease is Fertility: The ability to produce young. passed from one individual to another. r Finite rate of increase ( e ): (Nt+1) / (Nt) Diurnal: Active during the day. where Nt is population size at time t, and N is population size a unit of time later. Ecosystem: Ecological system formed by t+1 interaction of living things and their Fixed-wing air cr a f t : Ai rcraft with fixed side environment. wings (that is, not a helicopter). Ecotone: Wh e re two or more distinct habitats Fomites: Po rous articles such as clothes and overlap (for example, between forest and some equipment which may carry disease. grassland). Friable: [Soil that is] easily crumbled. Eff i c a c y / e f fectual: Producing desired effe c t . Frugivorous: Fruit eating. Endangered species: Species in danger of Functional r es p o n s e : Relationship between extinction and whose survival is unlikely per capita food intake rate and food if causal threatening processes continue to availability. operate. Gametes: Sex cells (that is, spermatozoa and Endemic: Restricted to a certain region or eggs). country. Generalised r e l a t i o n s h i p : R e l a t i o n s h i p Ephemeral: Short-lived. which describes general features (for Eradication: P e rmanent removal of all example, a computer simulated line individuals from a defined area. between two variables). Exotic: In t roduced from another country (for Genetic engineering: Use of modern genetic example, exotic species). manipulation technology to alter the genes in cell chromosomes so that desire d Exotic disease: Disease which does not characteristics are expressed. occur naturally in a region or country. Geographic information system: Exponential rate of increase ( r): r is log e C o m p u t e r-based system for displaying, of the finite rate of increase of a population overlaying and analysing geographic (that is r = ln(N ) – ln(N ) where N i s t +1 t t i n f o rmation such as vegetation, soils, population size at time t, and N i s t+1 climate, land use and animal distributions. population size a unit of time later). Gestation: Pregnancy. Extrapolation: In t e r p reting data beyond the dimensions within which it was collected Global positioning system: Small device (for example, assuming conclusions drawn that uses satellite signals to accurately from data collected in one region will be locate the user’s position (latitude, relevant elsewhere). longitude and altitude). Gregarious: Living in groups.

150 Managing Vertebrate Pests: Feral Pigs Gross estimates of impact: Estimates of Intrinsic rate of increase ( rm): The intrinsic total damage caused by feral pigs in an rate of increase of a population (rm ) is the area (as contrasted to per capita impact). natural logarithm of the rate at which the Home range: Area that an animal (or group population will grow in a given environ- of animals) ranges over during normal daily ment when res o u rces are not limiting (that activities. is, the population’s maximum rate of increase). Immunity: An organism’s resistance, natural or acquired, to illness caused by infection Intrinsically regulated population: by micro-organisms or their products. Behavioural or genetic factors cause populations to self regulate their size. Immunocontraceptive: Substance that triggers an immune reaction that causes Keratin: H a rd, nitrogenous substance that sterility in treated animals, acting as a f o rms basis of horns, claws, nails, etc. contraceptive. Plaques or shields up to three centimetres thick can develop on shoulders and Indices of feral pig abundance: Field signs anterior flanks of male feral pigs. that can give a relative measure of pig abundance (for example, abundance of Killer pig: Pig that has developed a habit of fresh droppings, tracks, fresh rooting). killing lambs. Indigenous people of Australia: Ab o r i g i n a l Land degradation: Soil erosion by wind and peoples and Torres Strait Islanders. water; soil salination, acidification or structural decline; loss of soil fertility; Ingested: Taken orally. s t ream and lake pollution, infestation by Instantaneous rate of incr ea s e : Rate at pest plants and animals; loss of biodiversity. which a population is increasing at a given Latent period: Time lag between an action stage of logistic or exponential population and a response. g rowth. Its value will lie between the maximum rate of increase (when LD 50 : Dose (per kilogram of body weight) population density is low) and zero (when that will, on average, kill 50% of tre a t e d population density is at carrying capacity). animals.

Intangibles: That which cannot be LD 90 : Dose (per kilogram of body weight) numerically quantified (for example, that that will, on average, kill 90% of tre a t e d for which it is difficult to estimate a money animals. value). Life table: Schedule of age-specific mortality Interactive computer system: When a (that is, a frequency distribution table computer user can input data and get an p resenting data on age, survival and immediate response without having to mortality rates for a population) write a program and run a job (for example, Limiting factor: Factor which places some wo rd processing spell-check packages are limitation on the density of a population interactive). (for example, an environmental resource I n t e rf e r ence competition: C o m p e t i t i o n that limits population growth because it is between species where one suppre s s e s in short supply). another’s rate of increase by interf e r i n g Linear r el a t i o n s h i p : Straight line rel a t i o n s h i p with its ability to procure or use a limiting between two or more variables. re s o u rce, o r w h e re one species limits another’s use of a limiting res o u rce, not by Lipids: Fats and oils. prior consumptive use, but thro u g h p reventing access (for example, thro u g h behavioural aggression and exclusion).

Bureau of Resource Sciences 151 Ma r ginal benefits: The shift in benefit values Numerical r es p o n s e : Relationship between that occur as incremental changes are made the rate of change of a population and in the factor(s) which affect level of benefits factor(s) which affect this rate of change (for example, changes to pig damage that (for example, effect of diff e rent levels of occur as pig density is reduced). a consumable re s o u rce, such as pasture Marginal costs: The shift in cost values that biomass, on the rate of increase of a occur as incremental changes are made in population). the factor(s) which affect level of costs (for Oestrus: The sexual heat of female animals. example, changes in the cost of finding Om n i v o r ous: Eating both plants and animals. and removing an extra pig that occur as pig density is reduced). Opportunistic feeding: Taking advantage Ma r k – re c a p t u r e: Technique of live catching, of new foods. tagging, releasing and then re c a p t u r i n g Origin of a graph: Point where the horizontal animals, and using a formula to estimate (x) and vertical (y) axes cross. population size from the proportion of Parturition: Birth. recaptured animals that are tagged. Pasture biomass: Weight of above-ground Market failur e: When commodity prices set by natural supply and demand have pasture available per unit area of ground, undesirable social or enviro n m e n t a l usually expressed as kilograms per hectare consequences (for example, unsustainable (either wet or dry weight). use of natural re s o u rces or development Per capita: Per head of population (for of social inequities). example, food consumption per pig is per capita food consumption). Maximum rate of increase ( rm) : T h e maximum rate of increase of a population Pe r i c a r p : Soft fleshy tissue surrounding seeds (rm ) is the natural logarithm of the rate at in a fruit. which the population will grow in a given e n v i ronment when re s o u rces are not P o l y o e s t r ous: Having a succession of limiting (that is, the population’s intrinsic oestrous periods in one sexual season or rate of increase). year. Melioidosis: Bacterial disease causing Population: Group of animals of a particular pneumonia and septicaemia. species occupying an area where they are subject to the same broad set of 0. 7 5 Metabolic body weight: (Body weight) . en v i ronmental or management conditions. Mi c ro s p h e r es: M i c roscopic particles of a Post partum: Following birth. substance that are coated with a prot e c t i v e layer to delay breakdown in the gut or Pr obability function: Predicted prob a b i l i t i e s bloodstream. of an event for a range of values (for example, probabilities of pig damage for Negative corr el a t i o n : When one variable a range of seasonal conditions or for a d e c reases proportionately as another range of control strategies). increases. Pr oximal limiting factor: E n v i ro n m e n t a l Neophobia: Fear or avoidance of new things. factor that directly limits population size. Net pr od u c t i o n : Final production after all Re g r ession equation: An equation which losses and have been subtracted from the describes the relationship between two or gross production. more variables. Nocturnal: Active at night. Rooting: Pigs using their snouts to dig up the ground and surface vegetation.

152 Managing Vertebrate Pests: Feral Pigs Ruminant: Animal whose stomach is divided Sustained contr ol : Continued control in the into four segments, one of which longer term. re g u rgitates undigested food for further Th e rm o r egulation: Ability to regulate body chewing (chewing cud). te m p e r a t u re . Sensitivity analysis: P rocess for testing Th r eshold density for disease: Mi n i m u m simulation models to see whether making density of susceptible animals at which a changes to parameters or input data disease will persist in a population. significantly alters the model’s output. Transect: A rectangular plot in which data Simulation model: Computer model that collection occurs. rep resents a real system, into which data or parameters can be entered to obtain an Trap night: One trap set for one night (for estimate of what would happen in the rea l example, if three traps were set for two system under these conditions. nights each, this would be six trap nights). Sp e c i e s : Group of interbreeding individuals Udder scor es : Sc o re based on palpation of not breeding with another such group and a ewe’s udder, which indicates whether she which has characteristics which distinguish cu r rently maintains viable lambs. it from other grou p s . Ultrasound scanning: Use of low-freq u e n c y Species specific: A ffecting only the targ e t sound to investigate the internal structure sp e c i e s . of an animal (used for counting foetuses). St a n d a r d error ( s. e . ): The standard error of Ungulate: Hoofed animal such as horse, goat, a mean value (s . e .) is a measure of the sheep, pig and antelope. variability of measurements around the Variance ( s2 ): The variance of a sample is a – – mean. The interval (x ± 2 s. e . (w h e re x is random variable which gives an estimate the sample mean) will contain the true of the distribution of measurem e n t s : mean in 95% of large random samples. This interval thus constitutes the 95% confidence limits: wh e re x = value of each measurement from √ – i s. e. (x– )= s. d . / n 1–i ; x = sample mean; and n = sample w h e re s . d . = standard deviation and n = si z e . sample size. Vector: Carrier for spreading disease or S t a n d a r d deviation ( s . d .) : The standard biological control agent (for example, deviation (s. d . ) of a sample is an estimate mosquitos are a vector for myxomatosis). of its variability, and is calculated from the Vesicular diseases: Diseases caused by sq u a re root of the variance (s 2 ): viruses that cause blisters on the skin or ho o v e s . w/w: Weight per weight (for example, wh e re x = value of each measurement from kilograms of 1080 per kilogram pig body – i 1– i ; x = sample mean; and n = sample weight). Usually expressed as a perce n t a g e . si z e . Wild boar: Feral pig (Sus scrof a ). Australian Stochastic: Incorporating some degree of feral pigs share many characteristics with natural variation. the Eurasian wild boar. Subspecies: G roup of individuals within a Wil d e r ness: Land that has been essentially species, having certain characteristics which unmodified since European settlement. distinguish them from other members of x- a x i s : The horizontal axis on a graph. the species, and forming a breeding grou p . y- a x i s : The vertical axis on a graph. Sustainability: Continuing in present form and at current level in the longer term.

Bureau of Resource Sciences 153 Index Aujeszky’s disease, 26, 45 Australian and New Zealand Federation of Animal Societies, 51, 54, 75 Australian Capital Territory 1 environmental impact, 41 1080 exotic disease, 46, 59 aerial survey, 62 ground surveys, 63 control with, 80, 83, 85, 109, 124 legislation, 59 costs of control, 40, 72, 90, 112, 114 occurrence of pigs, 13, 16 non-target implications, 83, 84 population dynamics, 24, 30 state use, 58 warfarin use, 59, 85 Australian Capital Territory Parks and A Conservation Service, 59, 60 Australian Nature Conservation Agency, 10 Aboriginal peoples, 11, 12 AUSVETPLAN, 46 commercial harvesting, 58 landowners, 120 Acacia, 20 B adaptive management, 9, 100, 106 bait, 57, 59, 63, 64, 80, 81, 83, 84, 85, 86, 87, Adelaide River, 16, 24 92, 93, 98, 106, 109, 114, 115, 122, 147 aerial bait stations, 84, 89 photographs, 73 bananas, 20, 22, 34, 38, 40, 42, 105, 107 shooting, 106, see also shooting from barley, 36, 84 helicopters Bathurst Island, 14 surveys, 62, 85, 128 beetles, 21, 43 African swine fever, 26, 45, 87 benefit, see cost–benefit agricultural impact, 34, 37, 39, 50, 62, 64, bounties, 55 66, 70, 71, 96, 101, 106, 127, see also control, 48, 50, 90, 94, 97, 98, 100, 101, economic impact, lambs predation 103, 106, 107, 108–112, 110, 121, 124 Agriculture and Related Resources -cost ratio, 111, see cost–benefit Protection Act 1976, 58, 60 maps, 73 Agriculture Western Australia, 60, 117 plans, 73 Alectura lathama, see brush-turkey best practice management, 9, 100, 123, 124, Ampelocissus, 21 142 amphipods, 43 biodiversity, see biological diversity Animal and Plant Control (Agricultural biological control, 87, 106 Production and other Purposes) Act biological diversity, 95, 96, 144, 146 1986, 59, 60 birds, 21, 127 Animal and Plant Control Commission, 60 ground-nesting, 21, 43, 70, 127 animal welfare bounties, 31, 32, 50, 55, 56 considerations, 48, 51, 99, 119 bracken, 20, 22, 39, 42 costs, 95, 146 breeding CSSP, 51, 85, 128 conditions, 21, 25, 126 fertility control, 87 cross-, 11 Anseranas semipalmata, see magpie goose briar, 20 anticoagulant, 85, 86 brolga, 43 aquatic life, 20, 41, 102 Brucella suis, see brucellosis Arnhem Land, 14, 15, 52 brucellosis, 26, 43, 44 Arthropodium milleflorum, 20 brucellosis and tuberculosis eradication arthropods, 21, 43 campaign, 44 Ascarops strongylina, 26 Bruny Island, 11 Asteraceae, 21 brush-turkey, 43

154 Managing Vertebrate Pests: Feral Pigs Bubalus bubalis, see buffalo Wildlife and Exotic Disease Preparedness buffalo, 14, 30, 31, 44 Program, 53 Bureau of Resource Sciences competition, 70 Vertebrate Pest Program, 1, 7, 142 from buffalo, 30 Bureau of Sugar Experiment Stations, 37 inter-pig, 66 bush peanuts, 20 with livestock, 34, 39 with other animals, 43, 127 C conservation areas, 41, 50, 73, 98, 102, 105, 106, 121 cadastral plans, 103 ranking, 102, 106 Cane Boards, 107 costs, 103 canecutter’s disease, 44 economic frameworks, 95 carpal glands, 24 impacts, 96, see environmental impact carrying capacity, 31, 47 management plan, 97, 101, 105 cassowary, 43, 81, 106, 127 National Strategy for the Conservation of -safe traps, 81, 119 Australia’s Biological Diversity, 7, 9 Casuarius casuarius, see cassowary opinions, 53 Catchment and Land Protection Act 1994, role of harvesting, 50 58, 60 Conservation Commission of the Northern catchments, 14, 42, 102 Territory, 60 cattle, 18, 44, 45, 46, 77, 84 contingency plans, 46 centipedes, 43 Cooperative Research Centre for Biological Cervidae, 27 Control of Vertebrate Pest Populations, 87 chillers, 49, 54, 79 Coprosma, 20 classical swine fever, 26, 45, 47, 87 cost–benefit, 108–114 clovers, 20, 39 analyses, 37, 96, 103, 110, 145 Coburg Peninsula, 12 ratios, 56, 91, 96, 99, 112 coconut trees, 20 crocodile, freshwater, 43 Code of Practice Crocodylus johnstoni, see crocodile, Feral Livestock Animals, 51 freshwater commercial use, 33, 47 Crown land, 14, 57, 121 harvesting, 120, 146 crustaceans, 21 accreditation, 50 CSSP, 85 bounties, 56 animal welfare, 51, 85, 128 conflicts, 53 costs of control, 40, 90 impact on density, 50 lethal dose, 85 operations, 48 cull processors, 119 by hunters, 48 State policy, 57, 58 exotic disease control, 46, 47 management, 97, 98 rate for stable density, 50, 71 position of SCARM, 48, 54 Cunnamulla, 13 position of welfare, 54 cycads, 20 Commonwealth Government Cyperus rotundus, 20 AUSVETPLAN, 46 cysts contingency plans, 2, 46 bladder worm, 26 Ecologically Sustainable Development, 9 hydatid, 26 Environment Statement, 9 funding, 53 involvement in pest management, 7, 9 D Landcare, 7, 9, 59, 120, 123, 142 National Strategy for the Conservation of Darling Ranges, 12, 14 Australia’s Biological Diversity, 7, 9 Darling River, 12, 13

Bureau of Resource Sciences/Australian Nature Conservation Agency 155 deer, 18, 27, 44 rates, 97, 145, 147 defining the problem, 4, 7, 94, 96, 105, 108 diseases, 25, 26, 43, 47, 53, 127 degradation, 98 biological control, 87 by feral pigs, 41, 95, 105, 127 endemic, 26, 43 pasture quality, 39 exotic, 26, 27, 44 demonstration projects, 9, 142 quarantine regulations, 46 Density, 16, 30, 31, 34, 43, 47, 97, 98, 147 repercussions, 45 achieving target, 71 Wildlife and Exotic Disease Preparedness buffalo, 31 Program, 53 cost-per-removal, 72, 90, 108, 112, 113 dock, 21 –damage relationship, 91, 97, 144 dogs dependence and independence, 27, 66 animal welfare, 51, 75 dingo, 31 costs of control, 40 effect of reduction, 37, 71 fence, 27 environmental impact, 62, 70 hunting with, 48, 75, 106 estimates of, 63, 86 non-target implications, 80, 83, 116 estimating reduction in yield, 66, 68 predation, 26 factors influencing, 26, 28, 29, 31 Douglas River, 47 harvest, 50, 58, 98 Douglas–Daly area, 16, 24 lamb predation, 35, 67, 108 drought, 15 measurements, 72, 107 effect on lambing, 108 plover predation, 70, 102 market ramifications, 50 target, 97 population dynamics, 24, 25, 26, 30 threshold dung cost per kill, 64 estimate of density, 63, 86 damage, 97, 106, 127 exotic disease, 46, 47, 128 E dental formula, 20 Earthworms, 21, 23, 28, 41, 43, 126, 127 Department of Conservation (New Echinococcus granulosus, see hydatid cysts Zealand), 102, 103 Ecologically Sustainable Development Department of Conservation and Natural Strategy, 7, 9 Resources, 58, 60 economic Department of Environment and Land frameworks, 94, 144–146 Management, 60 harvest, 50, 54, 98, 113 Department of Lands, 57, 60, 119 impact, 33, 36, 37, 57, 108 Department of Primary Industries, 123 ecosystem, 96, 103 Department of Primary Industry and Elaeocarpus spp., see bush peanuts Fisheries, 60 electric fences, see fences dieback disease, 42, 58, see also rootrot Eleocharis spp., 20 fungus endangered species diet, see also food effect of pigs, 42, 127 density, 28 non-target implications, 81 requirements, 21, 22, 43 protection, 73, 74, 97, 106 dingo enterprise substitution, 77 bounties, 31, 32 Environment Statement, 9 cohabitation, 31 predation, 26, 28, 30, 31 environmental impact, 7, 33, 41, 53, 59, 71, Dioscorea, 21 101, 127 discount assessment, 52, 62, 64, 70 future losses, 95 management, 96 predation rates, 109 eradication, 34

156 Managing Vertebrate Pests: Feral Pigs as a management option, 92, 97, 99, 106 damage by pigs, 37, 69 brucellosis and tuberculosis eradication design, 78, 79, 91 campaign, 44 dingo/wild dog, 27 conservation areas, 53, 102 electric, 67, 78, 91, 98 criteria for, 147 Feral Pests Program, 10 effect of bounties, 50 fertility control, 86 exercises, 47 Ficus variegata, see figs local, 97, 109 figs, 20, 42 of exotic disease, 46, 47 fish, 21 RLPB policy, 53, 58 fixed-wing counts, 62, 128 simulated strategy, 109 Flinders Island, 12, 13, 14, 16, 42, 56 costs, 111 floodplains, 14, 20, 23, 47, 108 versus commercialisation, 53 food, 20, see also diet estimate breeding, 25, 26 control costs, 40, 108 competition, 43 crop losses, 36, 37, 38, 105 effect on density, 15 density, 62, 64, 85, 86 habitat, 24, 30, 42, 73, 121 gross, 33, 66, 70 movements, 22 habitat abundance, 16, 30 nutrient levels, 21 per capita, 33, 37, 40, 66, 68, 70 population dynamics, 27, 29, 30, 31, 32, rate of increase, 29, 30 126 total density, 16 rooting, 71 Eucalyptus marginata, see jarrah foot-and-mouth disease, 25, 44, 53, 58, 88 evaluation, 91, 92, 93, 94, 104, 107, 110, forbs, 20, 22, 28 122, 124, 142, see also monitoring foxes exercises fertility control, 86 eradication, 47 free-feeding, 64, 80, 84, 106, 109, 114, 115 exotic disease outbreak, 57, 58 frogs, 21, 28, 43, 127 exotic funding diseases, 25, 27, 44, 105, 121 extension, 40, 55, 121, 142 outbreaks, 45, 46, 47, 53, 57, 58, 75, 76, feral pig control, 52, 57, 59, 107, 119 106, 127, 128 feral pig research, 53, 55 plants, 42, 127 Vertebrate Pest Program, 10, 142, 146 extension, 101, 104, 117, 118, 122, 123, 129, fungi, 21, 43, see also rootrot fungus 142, 143 funding, 40, 55 G Game Management Australia Pty Ltd, 48 F game meat, 5 Family Asteraceae, 21 for export, 48 Family Cervidae, 27 processors, 48 Family Hippopotamidae, 18 Geographic Information System, 73, 128 Family Suidae, 11 geranium, 21 Family Tayassuidae, 18 Geranium solanderi, see geranium farmers, 35, 52, 53, 55, 103, 104, 107, 117, Global Positioning System, 73, 143 119, 120, see also graziers, woolgrowers goat, 18, 44, 88, 102, 103 Farmers’ Federation, National, 54 Government Fasciola hepatica, see liverfluke Commonwealth fecundity, 25, see also breeding Environment Statement, 9 fence involvement, 7, 9 as a control tool, 77 expenditure, 40, 52, 55, 57, 104, 142 cost, 91, 128 legislation, 57

Bureau of Resource Sciences/Australian Nature Conservation Agency 157 role, 9, 10, 51, 89, 94, 104, 120, 124, 142 implementation graziers, 34, 35, 55, 95, 101, 109, see also management programs, 62, 94, 104, 106 farmers, woolgrowers simulated strategy, 108–112 grazing pressure, 39, 40 strategic approach, 117 gross estimates, 33, 66, 70 index group size, 23, 47, 75, 125 abundance, 31, 64, 70, 81, 85, 99 Grus rubicundus, see brolga food availability, 30 guavas, 42 protein content, 28 -removal-index, 76 H invertebrates, 23, 41, 43 Ipomoea, 21 habitat, 20, 47, 73, 126 abundance estimates, 16, 30, 62, 63, 128 control costs, 89, 108, 115 J degradation, 41, 127 jarrah, 58, 75 modifiation, 77 Judas pigs, 88 suitability, 18 Juncus spp., 20 Haematopinus suis, see pig lice hardjo, 44 K Hawaii, 42, 90 Hawaii Volcanoes National Park, 90 K (carrying capacity), 31, see also carrying helicopters, 90, 122 capacity shooting from, 64, 74, 75, 77, 88, 98, kangaroo, 30, 51, 52, 62 108–112, 109, 124 Kangaroo Island, 12, 13, 56 animal welfare, 51 kidney worm, 26 costs, 40, 72, 89, 90, 112–114 kill rate, 64, 109, 113 survey, 62, 64, 86, 128 Kosciusko National Park, 16, 20, 24, 25, 26, Helmholtzia spp., see lilies 81, 90 helminths, 26, 45 Hippopotamidae, 18 L hippopotamus, 18 Lachlan River, 13 hog cholera, see classical swine fever lactation home range, 15, 23, 24, 74, 121, 122, 123 requirements, 21, 29, 32 size, 24 lagoons, 14, 41 hunting, 48, 54, 58, 74, 106 lambs, 34, 96, 98, 144 animal welfare, 52, 75 predation, 34, 35, 36, 43, 52, 64, 67, 68, disease, 44, 46 107, 108 dispersal, 23, 25, 75 determining cause of death, 65 with dogs, 75 monitoring, 91, 92 hydatid cysts, 26 protection, 67, 69, 74, 78, 101, 109 Hyostrongylus rubidus, see red stomach value, 108, 110, 111 worm land degradation, 95, 144 Landcare, 7, 9, 59, 120, 123, 142 I LD50, LD90 immigration, 77, 98, 147, see also 1080, 83 recolonisation, reinvasion CSSP, 85 immunocontraceptive, 86, 87, 88 warfarin, 86 impact, 40, 42, 43, 50, 57, 64, 66, 72, 92, 96, legislation, 57, 60, 106, 107 105, 106, 109, 127, see also agricultural, legumes, 20, 21, 28 economic and environmental impact Leptospira spp., see leptospirosis

158 Managing Vertebrate Pests: Feral Pigs leptospirosis, 26, 43, 44 medics, native, 20, 22 lice, see pig lice Megapodius reinwardt, see scrubfowl lignum, 20, 23 Melaleuca spp., see paperbark lilies, 20 melioidosis, 26, 43 liverfluke, 26 Melville Island, 12, 14 Liverpool River, 15 Metastrongylus spp., see lungworms lizards, 43 mice, 21, 143 local eradication, see eradication Mimosa pigra, 20 lucerne, 20 Minister for Agriculture, 53, 57 lungworms, 26 monitoring, 91, 94, 95, 100, 104, 107, 110, lychees, 34, 38 see also evaluation abundance, 64, 92 M costs, 104, 144 disease, 75 Macquarie Marshes, 16, 20, 27, 52, 76, 77, estimates, 62 91, 125 operational, 92, 104 Macquarie River, 13 performance, 92, 104 Macracanthorhyncus hirudinaceus, see programs, 73, 91, 92, 102, 105 thorny-headed worm techniques, 92 Macrozamia spp., 20, 21 Moree, 13, 83 magpie goose, 43 Rural Lands Protection Board, 53 maintenance district, 75, 124, 125 control, 97 mortality, 26, 27, 28, 30, 31, 32, 45, 84, 85, fence, 78, 79, 98 87, 126 feral pig populations, 50, 54 Mossman–Herbert River, 37 groups, 122, 125 Moyle River, 14 maize, 20, 36, 37, 66, 90 Muehlenbeckia cunninghamii, see lignum management Murray Irrigation Area, 40 animal welfare, 51, 52 Murray Valley encephalitis, 26, 44 best practice, 142 muster, 59, 60 commercial, 54, 57, 58 Mycobacterium spp., see tuberculosis conflicts, 53 costs, 71 current, 56 N foot-and-mouth disease outbreaks, 46, 47 Namadgi National Park, 16, 19, 24, 30, 42, groups, 53, 57, 117, 123 46, 47, 59, 85 history, 55 nardoo, 20 objectives, 92 National Consultative Committee on options, 35, 46 Animal Welfare, 51, 85 plans, 53, 57, 62, 70, 73, 91, 119, 121 national contingency plan, 46 strategic, 94–116 National Farmers’ Federation, 54 units, 74 national guidelines, 1, 7, 129 mange mite, 26 mangoes, 20, 34, 38 National Landcare Program, 7, see also maps, 73, 74, 104 Landcare market failure, 94, 95, 103 national parks, 53 mark–recapture, 27, 28, 30, 63, 92 government role, 40, 59, 120 Marsilea drummondii, see nardoo National Parks and Wildlife Act 1970, 59, 60 Mary River, 16, 24 National Parks and Wildlife Service, 57 Measuring impact National Pest Control Plans, New Zealand, simulated strategy, 109 102 Medicago spp., see medics, native national plans, 103, 121

Bureau of Resource Sciences/Australian Nature Conservation Agency 159 National Registration Authority, 86 oestrus, 25 National Strategy for the Conservation of operational Australia’s Biological Diversity, 7, 9 monitoring, 92, 94, 104 native objectives, 104 fauna, 43, 48, 51, 53, 75, 95, 96 report, 104 flora, 21, 42, 53, 59, 95, 96, 105, 127 staff, 117 medics, 20, 22 opportunistic pasture, 39 approach to management, 52 Nature Conservation Act 1980, 60 feeding habits, 20 neophobia, 84 hunting, 59, 74 New South Wales, 25, 26, 27, 39, 44, 52, 56, surveillance scheme, 46 67, 72, 75, 101, 118 orchards, 22 commercial industry, 48, 54 fruit, 20 control, 52, 73, 75, 76, 78, 81, 83, 85, 121 Order Artiodactyla, 18 costs, 90 Oxalis spp., 21 economic impact, 36, 37, 40 foot-and-mouth disease implications, 46 P group action, 118, 124, 125 palms, 20, 42, 127 habitats, 16, 20, 23, 63 pandanus, 20 home ranges, 24 paperbark, 16, 20 legislation, 52, 57 Papua New Guinea, 11, 45 occurrence of pigs, 12, 13, 29, 55 parasites, 25, 26, 43, 45, 106 New South Wales Agriculture, 53, 57, 60, endemic, 26, 43, 105 118 exotic, 26, 44, 105 New Zealand, 11, 42, 88, 99 Parks and Conservation Service, ACT, 59, 60 Department of Conservation, 102, 103 Paroo River, 16, 29 diseases, 45 parvovirus, 26, 44 National Pest Control Plans, 102 Paspalum paspaloides, 20 occurrence of pigs, 11, 15 pasture, 22, 34, 93 population data, 18, 22 availability, 29, 39, 109, 115 Northern Territory, 27, 41, 56, 128 biomass, 29, 39, 40, 108, 113 breeding, 25 effect of pigs, 39, 59 commercial industry, 48 pathogen, 26, 58, 87 control, 62, 63, 76, 118 pawpaw, 34, 38 costs, 40, 90, 91 pay-off matrices, 106, 145 diseases, 44, 47, 58 peanuts, 20 eradication exercise, 47 peccaries, 18 estimates of damage, 37 per capita estimates, 33, 37, 40, 66, 67, 68, habitats, 16, 20, 23 70 home range, 24, 122 performance legislation, 58 criteria, 99, 104 occurrence of pigs, 12, 13, 14, 24, 25 monitoring, 92, 94, 104 Noxious Animal Inspectors, 57 objectives, 104 noxious declaration, 52 Persoonia, 20 nutrient, 42, 127 Phragmites spp., 20 levels, 21 Physocephalus sexalatus, see stomach research, 126 worm requirements, 22 Phytophthora cinnamomi, see dieback disease O pig lice, 26 oats, 20, 36 pineapple, 38

160 Managing Vertebrate Pests: Feral Pigs plover, 70, 101 Pseudomonas pseudomallei, see Poa spp., 20 melioidosis poison, see 1080, CSSP or warfarin Psidium guajava, see guavas poisoning, 79, 81, 83–86, 93, 99, 106, Pteridium esculentum, see bracken 108–112, 124 pumpkins, 20, 38 animal welfare, 51 costs, 40, 72, 89, 90, 114, 115, 128 Q government role, 57, 59 quarantine, 45 history, 12 Queensland, 28, 42, 43, 96, 123, 126, 128 programs, 29, 30, 62, 64, 71, 76, 81, 98, bounties, 55 118 commercial industry, 48, 50 State use, 58, 59 control, 53, 62, 64, 78, 81, 85, 105–107 policy, 121, 128, 129, 142 diseases, 44, 57 foot-and-mouth disease, 46 economic impact, 36, 37, 38, 40 National Farmer’s Federation, 54 eradication exercise, 47 Northern Territory government, 58 group action, 119, 124 NSW Agriculture, 57 habitats, 20, 22, 41 QLD Department of Lands, 57, 119 history, 11, 12 RLPB, 53, 58 legislation, 57 pomona, 44 occurrence of pigs, 13, 16 population population dynamics, 31, 32 control, 51, 53, 56, 58, 59, 71, 75, 76, 85, training, 118 86, 90, 97, 98, 119 Queensland Sugar Research Stations, 37 diseases, 87 dynamics, 15, 16, 19, 24, 26–32, 126 eradication, 97, 147 R estimates, 62 Rabbit Destruction Act 1919, 60 foot-and-mouth disease, 46, 47 rabbits, 21, 25, 43, 104 harvesting, 48, 58, 75 control, 40, 86, 99 percent killed by hunters, 48, 74 rabies, 45 rate of increase, 50 radio- porcine brucellosis, 44 collared, 67 porcine parvovirus, 26, 44 tracking, 85, 88 Port Essington, 12 rainforest, 20, 22, 37, 41, 42, 43, 64, 105, Portugal, 11, 45 107, 126, 128 Portulaca oleracea, 20 ranking areas for pest management, 102, possums, 102, 103 106, 107, 127 potatoes, 20, 39 rate of predation, 31, 41, 43, 58, 70, 77 decline, 29, 30, 32 dingoes and dogs, 26, 28, 30 dispersal, 15 frogs, 43 foot-and-mouth disease spread, 46 lamb, 34, 35, 36, 52, 67, 70, 107 increase, 26, 29, 30, 50 simulated strategy, 108–112 mortality, 27, 31, 32, 45, 85, 87 monitoring, 91 predation, 35, 36, 67, 70, 108–112 plover, 70, 101 reproduction, 25 worm, 42 rats, 43, 45, see also rodents predator–prey relationships, 76, 90 razorback, 18 problem definition, 94, 118, 142, see also recolonisation, 30, 97, see also immigration, defining the problem reinvasion protein, 21, 22, 28, 31, 43, 88 recreational requirements, 21, 26, 32 harvesting, 50, 54, 58, 74, 98

Bureau of Resource Sciences/Australian Nature Conservation Agency 161 shooters, 48, 59, 72, 74, 75 costs, 89, 112–114, 115 red stomach worm, 26 from the ground, 74 reinvasion, 74, see also immigration, government role, 59 recolonisation recreational, 48 research, 40, 53, 55, 89, 107, 126 with dogs, 75 abundance estimates, 62, 92 siltation, 41 biological control, 86, 87 Simmondsia paradoxa, 26 exotic disease, 47, 53, 106 snails, 21, 43, 127 survey methods, 62 snakes, 43 rice, 37, 40 Society Islands, 11 Riverina, 12, 52, 74 Sodium monofluoroacetate, see 1080 rodents, 43, 44, 86, see also mice, rats Solanum ellipticum, see forbs rooting, 11, 71 sorghum, 20, 36, 37, 66, 90 as population index, 63, 64, 71, 92, 93, 99, South Australia, 28 147 legislation, 59 impact, 37, 39, 41, 70, 71, 96, 127 occurrence of pigs, 13, 56 rootrot fungus, 42, 127, see also dieback Southern Game Meat, 49 disease sparganosis, 26, 44 Roper River, 14 Spirometra erinacei, see sparganosis Rubus rubiginosa, see briar Standing Committee on Agriculture and Rumex spp., see dock Resource Management, 1, 7, 48, 51, 54 rural state reserves, 40 areas, 13, 48 Stephranus dentatus, see kidney worm community, 52, 54, 56, 74, 83 Stock Act 1932, 59, 60 industry, 88 Stock Diseases Act 1923, 60 lease areas, 59 Stock Diseases Act 1994, 60 Rural Lands Protection Act 1985, 57, 60 stomach worm, 26 Rural Lands Protection Act 1989, 57, 60 Strzelecki National Park, 14, 42 Rural Lands Protection Board, 52, 53, 57, Sub-committee on Animal Welfare, 51 60, 73, 89, 118, 125 sugarcane, 20, 22, 34, 37, 38, 42, 43, 66, 69, Moree, 53, 75, 124, 125 98, 105, 106, 107, 126 Queensland, 119 Suidae, 11 Walgett, 93 survival, see mortality swamps, 14, 16, 20, 23, 41, 42, 43, 44 S Sarcoptes scabei, see mange mite T Scale of plans, 103 Taenia hydatigena, see cysts of bladder scent markers, 24 worm Schefflera actinophylla, see umbrella trees tarassovi, 44 Scirpus spp., 20 Tasmania, 45 screw-worm fly, 26, 45 legislation, 59 scrubfowl, 43 occurrence of pigs, 11, 13, 14, 16 Setaria sphacelata, 20 Tayassuidae, 18 sheep, 18, 30, 44, 45 teeth, 20 production, 34, 35, 39, 52, 75, 84, 95, 101, territorial behaviour, 24 108 Territory Parks and Wildlife Conservation shellfish, 21 Act 1988, 58, 60 shooting, 59, 74, 81, 98, 99, 145 Territory Wildlife Regulations 1987, 60 costs, 40, 49, 64, 72, 77, 128 thermoregulation, 24 from helicopters, 75, 106, 108–112, 124 thistles, 21 animal welfare, 51 thorny-headed worm, 26

162 Managing Vertebrate Pests: Feral Pigs threshold density, 46, 47, 64, 97, 106, 107, contamination, 34, 37, 42, 44, 69 128 counts, 63 Tonga Islands, 11 occurrence of pigs, 13, 20, 22, 23, 24, 41, toxins, see 1080, CSSP, warfarin and 99, 121 poisoning water buffalo, see buffalo trail baiting, 84, 116 watermelons, 20, 38 training, 117, 118, 120, 129 weeds, 39, 41, 127 Trangie, 83 Weil’s disease, 44 transect counts, 41, 62, 64 welfare, see animal welfare trapping, 54, 63, 69, 77, 79– 83, 98, 99, 106 Western Australia, 56, 75, 128 animal welfare, 51 diseases, 44 cassowary-safe, 119 expenditure, 40 costs, 40, 89, 90, 128 group action, 119 government role, 58, 59 habitats, 16 programs, 37, 64, 72, 106 legislation, 58 trichinellosis, see trichinosis occurrence of pigs, 12, 13, 14, 24 trichinosis, 26, 45 Wet Tropics Management Authority, 119 trunk-fruiting figs, see figs Wet Tropics Plan: Strategic Directions, 53 tuberculosis, 26, 43, 44 wheat, 16, 20, 22, 37, 62, 128 eradication, 44 bait, 83, 84, 85 turtles, 21, 41, 43, 70 industry, 36 tusks, 18, 20, 24, 43 white-tailed rats, 43 Typha spp., 20 wild boar, 11, 18, 45, 47, 48, 49, 88, 128 Wild Game Resources, 49 U Wildlife and Exotic Disease Preparedness Program, 53 umbrella trees, 42 woodlands, 2, 14, 20, 41, 47, 63 Uromys caudimaculatus, see white-tailed woolgrowers, 108, 109, 112 rats World Heritage Area, 41, 81, 95, 105–107, 119 V worms, 26, 44, 45, see also earthworms Vertebrate Pest Control Program, 118 predation, 42 Vertebrate Pest Program, 1, 7, 9, 142, 146 Vertebrate Pests Committee, 1, 7, 9, 56, 121 Y vesicular diseases, 26, 45 yams, 21 Victoria, 40 Yantabulla, 16, 27, 28, 29 legislation, 58 occurrence of pigs, 13, 55, 56 Victoria River, 14 viral diseases, 44, 45, 87

W Walgett, 13 Rural Lands Protection Board, 93 warfarin, 85 control with, 59, 71 costs of control, 90 lethal dose, 86 water

Bureau of Resource Sciences/Australian Nature Conservation Agency 163