The Ecology of the Introduced Red Fox (Vulpes Vulpes) in the Arid Zone

THE ECOLOGY OF THE INTRODUCED RED FOX (VULPES VULPES) IN THE ARID ZONE.

NICOLA JANE MARLOW

Thesis submitted for the degree of Doctor of Philosophy, University of New South Wales, Australia

January, 1992 UNIVERSilY OF NEW SOU1H WALES Thesis I Project Report Sheet

Abstract 350 words maximum: (PLEASE lYPE]

The ecological r6le of the introduced European red fox (Vulpes vulpes) was investigated by studying the diet, the home range usage, and the population dynamics of foxes in arid N.W. N.S.W.

There has been a coincident decline in the populations of small and medium sized mammals since the introduction of the fox into Australia and this study was initiated to determine the current extent of predation upon native fauna. The dietary composition of foxes was correlated with the field abundances of their prey species and rabbits (Oryctolagus cuniculus) were found to be the most important vertebrate prey species. Dasyurids, ground-dwelling birds, and reptiles, as well as carrion and invertebrates, were all ingested.

When the availability of rabbits was low foxes switched their predatory preferences to dasyurids. A rabbit removal experiment revealed that when rabbits and dasyurids were both unavailable to foxes they predominantly ingested ground dwelling birds and reptiles. Because foxes are able to increase their density out of all proportion to that of their native prey species by ingesting rabbits when they are numerous, they are able to have a profound detrimental impact upon native species by switching to them when rabbits are scarce.

The age structure for the fox population at Fowlers Gap was obtained from shot specimens; the sex ratio was 1:0.92, and the average litter size was 2.33 cubs per vixen. Mean fox density was 0.93 foxes per km2.

Home range analyses were undertaken using the Anderson method of home range analysis. Male foxes were found to have slightly larger weekly home-range areas than females but no seasonal or yearly differences in home-range size between the sexes were found. Mean weekly, seasonal and yearly home-range areas were 130, 160 and 518 (ha) respectively.

Declaration relating to disposition of project report/thesis

I am fully aware of the policy of the University relating to the retention and use of higher degree proj~t reports and theses, namely that the University retains the copies submitted for examination and is free to allow them to be consulted or borrowed. Subject to the provisions of the Copyright Act 1968, the University may issue a project report or thesis in whole or in part, in photostat or microfilm or other copying medium.

I also authorise the publication by University Microfilms of a 350 word abstract in Dissertation Abstracts International (applicable to doctorates only)~~ ~~ ...... ·············· ...... ?...... ··········· .. ··················· ...... ~.1/.. 9'?.: Signature Witness Date

The _U~iversity recognises that there may be excepli~mal ~~cumstances requiring restrictions on copying or conditions on use. Requests for restnction for a penod of up to 2 years must be made m wnting to the Reg~strar. Requests for a longer period of res

I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma of a university or other institute of higher learning, except where due acknowledgement is made in the text.

(Signed) -~~- .. · · · · · · ·

UNIVERSiTY OF N.S.W. 1 5 OCT 1993 LIBRARIES II

TABLE OF CONTENTS PAGE

LIST OF FIGURES VII LIST OF TABLES IX ABSTRACT XI ACKNOWLEDGEMENTS XII

CHAPTER 1: GENERAL INTRODUCTION 1.1 PREAMBLE 1 1. 2 FOX DISTRIBUfiON IN AUSTRALIA 2 1.3 THE IMPACT OF FOXES IN AUSTRALIA 4 1.3.1 Fox predation upon native fauna 4 1.3.2 Status of other Australian vertebrate fauna 14 1.3.3 Other factors that may be responsible for the decline of the mammalian fauna in Australia 15 1.3.3.1 The feral cat (&ill_ catus) 15 1.3.3.2 Changes in fire regime 16 1.3.3.3 Rabbits and other introduced herbivores 16 1.3.3.4 Disease 18 1.4 HOME RANGE AND HABITAT PREFERENCES 18 1.5 GENERAL BIOLOGY 21 1.5.1 Fox diet in other countries 21 1.5.2 World distribution/ taxonomic relationships 22 1.5.3 Other vulpine species 22 1.6 SPECIFIC AIMS OF THIS sruDY 22

CHAPrER 2: GENERAL METHODS 2.1 STUDY AREA 24 2.1.1 General Description 24 2.1.2 Climate 25 2.1.3 The Study Sites 'lJ 2.1.3.1 Warrens 2:} 2.1.3.2 Ram 3) 2.1.3.3 Lambing 3) 2.1.3.4 Mating 31 2.1.3.5 Salt 3 31 Ill

2.1.4 Fauna 31 2.1.4.1 Rabbits 32 2.1.4.2 Dasyurids and rodents 32 2.1.4.3 Macropodids 33 2.1.4.4 Feral cats 33 2.1.4.5 Ground-dwelling birds 33 2.2 CAPrUBE TECHNIQUES 34 2.2.1 The Cannon-Net 34 2.2.2 Snares/Leghold Traps 35 2.2.3 Handling and Collaring Foxes 00 2.3 CENSUS TECHNIQUES 00 2.3.2 Rabbit Abundance Estimations 00 2.3.3 Light Trap 37 2.3.4 Pitfall trapping 37 2.4 STATISTICAL ANALYSES 38

CHAPrER 3: DIET ANALYSES 3.1 INTRODUCTION a:J 3.2 MIITBODS 40 3.2.1 Scat Collection 40 3.2.2 Scat Analysis 40 3.2.3 Field Abundances 42 3.2.4 Analytical Methods 42 3.2.5 Impact of Predation on Native Populations 44 3.3 :RESULTS 44 3.3.1 Overall Dietary Composition 44 3.3.2 Relationships between Species Availability and Dietary Occurrence 45 3.3.3 Yearly, Seasonal and Paddock Interactions 52 3.3.4 Yearly and Seasonal Dietary Interactions 52 3.3 5 Yearly and Paddock Dietary Interactions 52 3.3.6 Seasonal and Paddock Dietary Interactions 54 3.3.7 Impact upon Native Populations 57 3.4 DISCUSSION 58 IV

CHAPfER 4: POPULATION PARAMETERS AND DENSITY 4.1 INTRODUCTION 70 4.2 MEI'HODS 73 4.2.1 Ageing Techniques 74 4.2.2 Placental Scars 74 4.2.3 Sex ratios 75 4.2.4 Life tables 75 4.2.5 Probability Density Estimations 76 4.2.6 Changes in Fox Density with Season, Paddock and Year 71 4.2. 7 Relationships with Prey Species Densities 78 4.3 RESULTS 78 4.3.1 Sex ratios 78 4.3.2 Age structure 79 4.3.3 Fecundity 8> 4.3.4 Life Table 81 4.3.5 Overall Fox Density in the Study Area 81 4.3.6 Fox Density Variations between Paddocks 82 4.3. 7 Seasonal Fox Density Variations 83 4.3.8 Effects of other Environmental Variables 83 4.3.8.1 Food availability 83 4.3.8.2 Lunar phase 84 4.4 DISCUSSION 84

CHAPTER 5: HOME RANGE ANALYSES 5.1INTRODUCTION 5.1.1 Basic Concepts 5.1.2 Home-range Studies in other countries 5.1.3 Home-range Studies in Australia 5.1.4 Dispersal 5.2 METHODS 5.2.1 Hand Tracking 5.2.2 STATION TRACKING 5.2.4 Data Handling 5.2.4.1 Creating and editing plotfiles 5.2.4.2 Fourier transform method V

5.2.4.5 Harmonic mean centres ffi 5.2.4.6 Home-range overlap ffi 5.2.4. 7 Estimating dispersal distances 00 5.3RESULTS 00 5.3.1 Home-range Size 00 5.3.1.1 Sex differences 00 5.3.1.2 Seasonal differences 00 5.3.2 Home-range Use 101 5.3.2.1 Resource preferences 101 5.3.2.2 Home-range Fidelity 102 5.3.2.3 Shifts in activity centres 102 5.3.2.4 Home-range Overlap Between Different Individuals 104 5.3.3 Dispersal Distances 107 5.4 DISCUSSION 108

CHAPrER 6: EFFECfS OF RABBIT REMOVAL 6.1 INTRODUCTION 114 6.2 MEI'HODS 115 6.3 RESULTS 117 6.4 DISCUSSION 12A

CHAPrER 7: FOX CONTROL MEI110DS 7.1 INTRODUCTION 128 7.2 MEI110DS 100 7.2.1 Preparing and Laying Baits 100 7 .2.2 Shooting 131 7.3 RESULTS 131 7 .3.1 Bait Ingestion Rate 131 7 .3.2 Recolonisation Rate 131 7.4 DISCUSSION 132 VI

CHAPI'ER 8: GENERAL DISCUSSION 134

REFERENCES 140

APPENDICES Appendix 1 165 Appendix 2 167 Appendix 3 168 Appendix 4 170 VII

J,Tffi' OF FIGURES

Figure TITLE PAGE Number

1.1 Distribution and spread of red foxes (Vulpes vulpes) in Australia 3

2.1 Topography of Fowlers Gap Station

2.2 The Study area. 28

2.3 The cannon-net. 35

3.1 Overall dietary composition 45

3.2 Seasonal changes in dietary intake 46 3.3 Comparisons of ingestion rates and field abundances for each dietary category. 47

3.4 Comparison of rabbit ingestion rates among paddocks 51

3.5 Dietary composition in relation to season and year 53 3.6 Rabbit ingestion rate in relation to the intake of other dietary categories 55 3.7 Dietary intake and field abundances for each dietary category for Years 1 and 2 61 3.8 Relative field abundance of rabbit in Warrens and Lambing paddocks

3.9 Dietary intake of rabbits and dasyurids with season 3.10 Seasonal variation in diet in Warrens and Lambing paddocks. 65

4.1 Frequency distribution of placental scars 81 VIII

Figure TITLE PAGE Number

4.2 Overall fox density in the study area 83

5.1 A three-dimensional space-use distribution 92

5.2 Weekly, Seasonal and Yearly home-range areas 100

5.3 Seasonal changes in home-range area 101

5.4 Home-range of a fox in relation to habitat features 103 5.5 Comparisons of shifts in Harmonic Mean Centre between male and female foxes 104 5.6 Comparison of shifts in Harmonic Mean Centre between Summer and Winter 107

6.1 Diet in Ram paddock before and after rabbit removal 118

6.2 Ground-dwelling bird ingestion and field abundance 119

6.3 Seasonal change in fox diet before and after rabbit removal 120

6.4 Comparison of fox densities in Warrens, Ram and Lambing paddocks after rabbit removal in Ram paddock 124

7.1 Fox density recovery after removal in July 1989 132 IX

IjlS'f OF TADI·Ri

Table TITLE PAGE Number

1.1 Summary of mammals occurring in dietary analyses in Australia 6

1.2 Summary of dietary analyses in Australia 10

2.1 Summary of Study Site Characteristics.

3.1 Results of Canonical Correlation Analysis comparing species availability and dietary occurrence.

3.2 Results of MANOV A of dietary occurrence testing for Paddock differences. 51

3.3 Results of Canonical Correlation Analysis comparing species availability and dietary occurrence testing for Yearly and Seasonal Effects. Warrens and Lambing Paddocks. 54

3.4 Results of Canonical Correlation Analysis comparing species availability and dietary occurrence testing for Yearly and Paddock Effects. Warrens and Lambing Paddocks. 57

3.5 Results of Canonical Correlation Analysis· comparing species availability and dietary occurrence testing for Seasonal and Paddock Effects. Warrens and Lambing Paddocks. 58

4.1 Rates of barrenness in different localities 72

4.2 Fox densities in Australia 73

4.3a Age structure for male and female foxes at Fowlers Gap 79 X

Table TITLE PAGE Number

4.3b Age structures of fox populations (%)

4.4 Number of placental scars produced in each age class

4.5 Life for red foxes at Fowlers Gap. 82

4.6 Variations in litter sizes with location 86

5.1 Summary of home-range areas

5.2 Degree of home-range overlap between individual foxes. 105

5.3 Dispersal distances of radio-collared cubs at Fowlers Gap 100

6.1 Results of Canonical Correlation Analysis comparing species availability and dietary occurrence in Ram paddock before and after rabbit removal. 121

6.2 Results of Canonical Correlation Analysis comparing species availability and dietary occurrence in Ram paddock before and after rabbit removal. Testing for seasonal effects. 123 XI

ABSTRACf:·

The ecological role of the introduced European red fox (Vulpes vulpes) was investigated by studying the diet, the home range usage, and the population dynamics of foxes in arid N.W. N.S.W.

When the availability of rabbits was low foxes switched their predatory preferences to dasyurids. A rabbit removal experiment revealed that when rabbits and dasyurids were both unavailable to foxes they predominantly ingested ground-dwelling birds and reptiles. Because foxes are able to increase their density out of all proportion to that of their native prey species by ingesting rabbits when they are numerous, they are able to have a profound detrimental impact upon native species by switching to them when rabbits are scarce.

AcJmnwJedeemeng:

I would like to sincerely thank my supervisor Dr. D. B. Croft for his advice and practical help in all aspects of this thesis. Hugh McCarron, Glenn Edwards, Graeme Moss, Debbie Ashworth, Steve and Lynette McLeod, and numerous Earthwatch volunteers all helped with field work and their assistance is greatly appreciated. Many thanks to the staff at Fowlers Gap, and to Professor Terry Dawson, Liz Jeffries, Dominic Fanning, Louise Mazzaroli and Roberto Inzunza for providing support, advice and equipment.

I am indebted to a number of people who gave valuable assistance with various aspects of this work: Dr Brian Coman provided expert consultation and vital equipment; Rossanne Packwood prepared all the teeth for aging and tolerated some very smelly skulls; Judith Marlow kindly measured these same smelly skulls; my mother, Jo Marlow, nobly sorted and typed all the references; and Dr. David Read provided advice about Fowlers Gap in the early stages of the project. Statistical advice was kindly provi4ed by Drs Barry Fox, Mike Macey, and Alex Mazanov.

The project was made possible by financial support from Dr Peter O'Brien (Bureau of Rural resources), the Linnaean Society, the Ethel Mary Read Foundation and a Commonwealth Postgraduate Award. Dr Jack Kinnear is gratefully acknowledged for allowing me to take leave to complete this thesis.

For their support throughout the project, I must also thank Elizabeth May, Dr Tim Clancy, Jaqui and Ian Ralph and Wendy Brown. CHAPTER 1

GENERAL INTRODUCTION

1.1 PREAMBLE

The rate of recent mammalian extinction is greater in Australia than on any other continent (Burbidge and Friend 1990). Various factors have been hypothesised to be responsible for these declines including predation by exotic carnivores, altered fire regimes, habitat destruction, competition from introduced herbivores and disease. The majority of available eVidence indicates that the introduced red fox is largely responsible for these declines. Dietary analyses indicate that the fox preys mainly upon mammalian species and it has been shown that fox predation is responsible for maintaining prey populations at critically low densities (Kinnear et al. 1988). This study was undertaken to examine the ecological role of the red fox in the arid zone, and especially to quantify the current level of fox predation upon the native fauna, even though much of the fauna has long since disappeared. Chapter 1: General Introduction 2

1. 2 FOX DISTRIBUTION IN AUSTRALIA

Foxes were successfully established in Victoria after being released at Ballarat in 1871 (Rolls 1969). They were introduced to provide more suitable hunting opportunities for Australian 'sportsmen' because the native fauna was considered to be of inferior hunting value. Once foxes had become established they expanded their range rapidly. Within ten years of their introduction they had occupied nearly 13,000 km2 in Victoria and had also entered South Australia (Rolls 1969). By 1893 there was a bounty on them in Euroa, Benalla and Shepperton and they had entered N.S.W (Rolls 1969).

Foxes spread quickly through N.S.W. and by 1903 they had been declared noxious in Armidale. Despite a scalp bonus, there was a rapid increase in their numbers about 1911 and by then they had dispersed successfully into southern Queensland. Foxes then extended their range northwards and by 1920 they had been sighted in Longreach which is approximately 320 km south-east of their northern most limit (Rolls 1969) (Fig.1.1). In sheep raising regions the active suppression of dingoes may have enhanced the establishment of foxes (Jarman 1986).

Fox dispersal into Western Australia was also rapid. They were first sighted near Eucla in 1911-12 and by 1915 they had been seen 160 km west of the South Australian border (Gooding, 1955). By 1917 they were 400 km north-west of Kalgoorlie and within another seventeen years they had spread to Derby in the north and also into the far south west. From Derby they continued to move north and the first fox scalps were obtained in the east and north Kimberleys in 1943 (Rolls 1969). King and Smith (1985) summarised the distribution of foxes in Western Australia and they concluded that foxes are found more commonly in coastal areas than in inland areas. They also found that foxes are absent, in general, from the Kimberley area and that they are generally confined to areas south of 19°S. This latitudinal constraint is consistent with fox distribution in Queensland and the Northern Territory (Strong and Low, 1983) and it may be attributable to climatic limitations (King and Smith 1985). Chapter 1: General Introduction 3

1950-52

1931 i------I -- . i929

I 1916 I I ·]9]0 . I I

Fig. 1.1 Distribution and spread of red foxes

Foxes have only recently colonised parts of the arid zone (Burbidge et al. 1988) and Low (1984) reported that foxes do not extend any further north in Central Australia than rabbit populations which suggests that their distribution is limited to a certain extent by the availability of rabbits as a food source. The expansion of the fox across Australia did closely follow the spread of rabbits in most areas. In eastern Australia foxes crossed the Murray River only 13 years after rabbits (Jarman 1986); they reached the New England tableland only a few years later; and they entered Queensland synchronously. Fox dispersal was slightly slower in the far western parts of New South Wales and rabbits preceded foxes over the western end of the Queensland border by 24 years. The distribution of the fox is not inexorably tied with that of the rabbit, however, and foxes are found much further north in Queensland than rabbits are. Foxes are generally absent or at lower densities in areas where dingoes are present. Chapter 1: General Introduction 4

1.3 THE IMPAUf OF FOXES IN AUSTRALIA

1.3.1 Fox predation upon native fauna

Since the arrival of Europeans in Australia, just over 200 years ago, ten species of marsupial and eight species of eutherian have become extinct (Burbidge and Friend 1990). A further twenty species of marsupial are endangered and eight are vulnerable (Burbidge and Friend 1990). Non-flying mammals having a mean adult body weight of between 35 g and 4200 g (the critical weight range (CWR)) and which live(d) in arid areas are the most likely candidates to have been affected by dramatic range declines or to have become extinct (Burbidge and McKenzie 1989).

The fox has been implicated in the demise of much of the native fauna and it has been found to ingest a wide range of mammalian prey (Table 1.1) as well as birds, reptiles and other items (Table 1.2). From as early as 1956 reports about the fox's detrimental effect upon smaller mammals and birds, particularly the 'ground haunting' species, have occurred in the literature (Glauert 1956). Finlayson (1961) claimed that the effect of introduced pests upon the native fauna had been catastrophic and he described how foxes preyed directly upon small groups of marsupials and hunted them out of existence before they could develop protective mechanisms.

Marlow (1958) listed fox predation as the second most probable cause for the decline of many species of indigenous mammal, after the destruction of their habitat. Although he had no direct evidence he felt that there was ample presumptive and indirect evidence to indicate that foxes were of crucial importance in reducing the populations of small and medium sized marsupials. He observed that the foxes' 'extraordinarily catholic' diet enabled them to increase in density out of all proportion to the abundance of any of their prey species and, due to the seasonal prevalence of some of these smaller prey items, this lead to the periodic fluctuation in prey availability which resulted in intense predation upon the longer lived species especially the marsupials. The importance of fox predation was highlighted by the observation that in areas where foxes were absent, such as Tasmania, Kangaroo Island, Chapter 1: General Introduction 5

Flinders island and other off-shore islands, the smaller ground-living marsupials were continuing to survive. Marlow (1958) was also the first author to identify that certain families of mammals were more depleted than others and that the Peramelidae and the Dasyuridae were the two families that suffered the greatest declines and extinctions. He also tabulated extinction rates in different habitats and found that species living in rainforest were least likely to have become extinct, followed by sclerophyll forest, woodland and then 'open country' with 0%, 8%, 13% and 43% of species extinct, respectively.

Mclntosh (1963a) investigated fox predation by examining the contents of 267 fox stomachs from the Canberra region and 111 others from various sites in N.S.W. He found that overall they contained 36% sheep carrion and 38% rabbit as percent of volume occurrence and so he concluded that indigenous mammals were not important in the fox's diet. Similarly, Coman (1973) found that carrion, sheep and mice were the principle prey items when he examined the stomach contents of 1299 foxes in Victoria. However, Coman (1973) felt that small indigenous mammals had populations that were quite low when compared with those of the rabbit and house mouse and that this would explain the secondary importance of native mammals in the diet. He also stated that little was known about the predatory impact of foxes upon 'desirable wildlife' and since low population densities may be characteristic of many small indigenous mammals, he concluded that a low level of predation could not be dismissed as being insignificant. Coman (1973) further suggested that predation by foxes upon smaller native species may be more common in areas of undisturbed habitat, particularly forested areas, where their population densities are proportionally higher than elsewhere. This hypothesis was supported by Brunner et al. (1975) when they examined 1888 seats collected in Sherbrooke forest in Victoria. They identified 24 species of mammal within these seats, and although rabbit had the highest incidence, Pseudocheirus, Trichosurus, Mastacomys fuscus and other mammals that were considered to be uncommon, made up a considerable proportion of the mammalian intake.

The results that Brunner et al. (1975) obtained suggest that the conclusions reached by earlier authors, e. g. Mclntosh (1963a), that ... :::r (11 3' 0 c.. ::s ...... s::

()

- c;· !l

rodents

sps

peregrinus

vulpecu/a

vulpecula

stuartii

fuscus

nasuta

robustus

giganteus

penicillata

eugenii

bicolor apicalis

fuscipes Dasyurids/native

Macropus

fuliginosus

Native

Perameles Wa/labia Antechinus Pseudocheirus Potorous Macropus

Mastocomys 11.1%

Rattus Macropus 14.8% Trichosurus

Bettongia

Trichosurus Macropus

Australia

cuniculus

cuniculus cuniculus

aries

musculus

rauus

Oryctolagus

Ovis

analyses

musculus

musculus aries

Mus

taurus

Introduced

Oryctolagus Bos

Mus Oryctolagus

Oryctolagus

Ovis Mus

Rauus

25.9%

3.7% 44.5%

dietary

S.A.

Vie

NSW

occurring

Ranges

site

S.A.

W.A.

SCATS

W.A.

Study Australia Kempsey, Australia Australia

Warrnambool,

Victoria

Flinders S.W.

S.W.

Arid

mammals

1985

RADIO-TRANSMITTERS

OCCURRENCE

1980

Summary

1981 1917

1978

1956

Wheeler

1.1 1959

1964

1972

authors

1978

LITTER/

LITTER:

Table

Study ANECDOTAL:

Glauert Froggatt

Cogger Dwyer

Seebeck

King

DEN Hornsby Coman

DEN PERCENTAGE Bayly

Christensen

=' ='

0 0

ll) ll)

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......

0 0

~ ~

......

0 0

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0 0

(') (')

0. 0.

0 0

0 0 -

a a

- -

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peregrinus peregrinus

acu/eatus acu/eatus

vulpecula vulpecula

peregrinus peregrinus

crassicaudata crassicaudata

vulpecula vulpecula

apodemoides apodemoides

stuartii stuartii

fuliginosus fuliginosus

vulpecula vulpecula

fuliginosus fuliginosus

sps sps

mitchelli mitchelli

nasuta nasuta

rufogriseus rufogriseus

nasuta nasuta

sp. sp.

species species

bicolor bicolor

fuscipes fuscipes

sps sps

other other

swainsonii swainsonii

lutreolus lutreolus

Trichosurus Trichosurus

Macropus Macropus

Notomys Notomys

8 8

6 6

Sminthopsis Sminthopsis

Tachyglossus Tachyglossus aculeatus

Tachyg/ossus Tachyg/ossus

Ningaui Ningaui

Pseudomys Pseudomys

Antechinus Antechinus

rodent rodent

Antechinus Antechinus

Rauus Rauus

Rallus Rallus

Pseudocheirus Pseudocheirus

Trichosurus Trichosurus

Pseudocheirus Pseudocheirus

A. A.

R. R.

Macropus Macropus

Wallabia Wallabia

Perameles Perameles

19% 19%

1.6% 1.6% 13% 13%

12.3% 12.3%

1.9% 1.9%

1.1% 1.1%

12% 12%

11.2% 11.2%

10% 10%

11% 11%

13% 13%

13% 13% 11.3% 11.3%

1.4% 1.4%

15.6% 15.6%

10% 10%

2% 2%

8% 8% 3% 3%

3% 3%

5% 5%

0.7% 0.7%

0.2% 0.2%

0.9% 0.9%

2% 2%

5.9% 5.9% 6% 6%

4% 4%

Trace Trace

cuniculus cuniculus

musculus musculus

musculus musculus aries aries

catus catus

aries aries

catus catus

musculus musculus

raltus raltus

Oryctolagus Oryctolagus

Mus Mus

Ovis Ovis

Mus Mus

Felis Felis

Ovis Ovis

Oryctolagus Oryctolagus

Felis Felis

Oryctolagus Oryctolagus

Mus Mus

R. R.

1.2% 1.2% I% I%

1.1% 1.1%

28.4% 28.4%

3% 3%

27% 27% 23.0% 23.0%

31.0% 31.0%

27.4% 27.4%

5% 5%

45.4% 45.4%

Vie Vie

S.E. S.E.

Aust Aust

S.E S.E

N.W. N.W.

N.P N.P

N.P. N.P.

1975 1975

1985 1985

cont cont

al. al.

desert desert

al.1984 al.1984

et et

1.1 1.1

et et

Wyperfield Wyperfield

Little Little

b) b)

a) a)

Table Table

Brunner Brunner

Woolley Woolley Triggs Triggs ::s - ::s ::. f1l .. 0

[ .. ;

(')

rodents

rodent

rodents

vulpecu/a

peregrinus

flavipes

aculeatus

ursinus

bicolor

'Possums/gliders'

Macropods

Rodentia

Anlechinus

Dasyurids Peramelids Trichosurus

Possums/gliders

Potoroids

Dasyurids/native

Monotremata

Dasyurid/native

Possums/gliders

Vombatus

Macropodidae

Dasyurids/native

Wa/labia

Peramelidae

Pseudocheirus

Tachyglossus

.I%

19.7%

17.3%

37% 9% 39% 52% 1.0% 30%

34.5% Trace 1.7% Trace

11%

4% 1%

3.2%

9.9%

7% 45% 6%

cuniculus

kids(l6)

rallus

TOIIUS rallus

aries

musculus

taurus

musculus

scrofa

musculus

taurus

hirsutus

Oryctolagus

Ovis Bos

Mus

Sus

Oryctolagus

Orycto/agus

Rattus

Oryctolagus

Rattus

RaiiUS

Oryclolagus

Mus

Bos

12%

2% 5%

Trace 23.6%

4% 3.4%

Trace 17.4% 65.6 Capra

0.4%

Vie

Vie.

S.A.

N.S.W.

Australia

Lofty

Gippsland

Melbourne,

Sth S-W

Bega,

1986

1989

cont

198

1988

1.1

al.1990

Brunner

Triggs

al.

1982

Table

a)1981 b)l984

Lowe

Wallis

Brown

Clark Long

Lunney I» ... ::r

(11

() -

(trace)

peregrinus

vulpecula

ursinus

crassicaudata

rufus

bicolor

vulpecula

chrysogaster

species

Vombatus

Pseudocheirus Trichosurus

Wallabia

Trichosurus

Macropus

Sminthosis

various

1.1% 1.0%

2.5%

2.2%

69%

Trichosurus

Hydromys Trace

0.8%

cuniculus

musculus

aries

aries musculus

hirsutus

musculus

aries

musculus

aries aries

aries

taurus

scrofa

Oryctolagus

Mus

Oryctolagus

Ovis

Ovis Oryctolagus

Mus

kangaroo'

Bos

musculus

Sus

Mus

Ovis

Oryctolagus

Ovis Oryctolagus Ovis

Oryctolagus Ovis Mus

Capra

11%

1.0%

10%

38.8% 19.2% 19.8% 10.4%

35%

26.3% 31.3%

36% 20% 30%

4% 38%

'Grey

Mus 2.7% 4.5% Oryctolagus

42.5%

0.4%

Vie.

A.C.T.

NSW

Vie

N.S.W.

Victoria

N.W.

Frankston,

N.S.W

Menindee, Canberra,

1987

1972

cont

1978

1974

VOLUME:

WEIGHT

OCCURRENCE

ANALYSES

1.1

1963

Degabriele

Stevens

AGE

1971

Hone

Croft

1973

Table

PERCENI'

STOMACH

Martenz

Coman PERCENT

Mclntosh

Coman

Croft

PERCENT

Barker

Ryan ;' 0 ::::. 0. a c 0 ::I

seeds

000)

sect

vertebrates

invertebrates procerus

Other

Rubus

Plan

Cabbages

Various

7.14%

Plants/

eggs

macquarii

sp.

various

Reptiles

Varanid

Various eggs

Fmydura

10.71% 1%

Tiliqua

Various Various

tenuirostris

various

Birds

Bustards/other plover/pee-wee

Various Mallee-fowl

Puffinus Lyre-birds

Mallee-fowl

Various 17%

7.14%

3.7% 2.8%

sps.

cuniculus

Australia

robustus

ctolag

Mammals

'small'

Miniopterus Various

Macropus

Various

14.6%

67%

92.86

32% 4.9%

analyses

Vie.

S.A.

Vie.

S.A.

NSW

S.A.

Ranges

site

dietary

country

SC\TS

Aust

Vie

S.A.

Aust

ders

Lofty

Study

Australia Australia Australia Kempsey, Victoria

Mallee Murray Victoria

Warrnambool, S. Ain

S.W.WA

Renmark, Victoria

Frankston,

S.E

Arid N.W. 73.7% 64.9% Mt

N.P.

N.P

Summary

1985

1973

1976

1983

al.

desert

1917

al.

1971

1956

et 1959

etai.

1981

1.2

eta/.1975

authors

1964 1978 1972

1987

1978 Wheeler

1982

LITTER

Wyperfield

1980 sby

Little

Table

Study ANECDOTAL:

Glauert Cogger Norman

Froggatt Dwyer

Thompson Priddell989 Brunner Seebeck King Lill 1-klrn DEN Booth

Coman

Coman PERONTAGE

Brunner

Bayly

Woolley

Lowe

0 0 ......

n n

::l ::l

s:: s::

:=. :=. 0. 0. 0 0

- ......

sect sect

a a

in in

(16) (16)

1/ 1/

vertebrate vertebrate

insect insect

plant plant

in in

plan plan

inverts/ inverts/

other other

insect insect

plant/ plant/

kids kids

plant plant

other other

Arachneida Arachneida

Lepidoptera Lepidoptera

Insect Insect Cbleopter Cbleopter <}clorana <}clorana

other other

16.7% 16.7%

5% 5%

13% 13%

30.6% 30.6%

57% 57%

28%insect/plant 28%insect/plant

25% 25%

43% 43%

31% 31%

20% 20% 11% 11%

53% 53% 25% 25%

54% 54%

37% 37%

Goat Goat

513% 513%

31.9% 31.9%

idae idae

various various

'other' 'other'

other other

various various

(av) (av)

Various Various

various various

Qckm Qckm

Scincidae Scincidae

Agamidae Agamidae

'snakes' 'snakes'

53% 53%

7.3% 7.3%

11% 11% 3.4% 3.4%

2.4% 2.4%

0.8% 0.8%

5% 5% 4% 4%

4% 4% 2% 2%

3% 3%

diae diae

tibicen tibicen

novaehollandiael4% novaehollandiael4%

reptiles reptiles

and and

novaehollan novaehollan

various various

gal/us gal/us

various various

G. G.

various various

Dromaius Dromaius

(av) (av)

birds birds

Podargusstrigoides Podargusstrigoides

Ojmnorhina Ojmnorhina

Ardea Ardea

10% 10%

19.7% 19.7%

0.6% 0.6%

16% 16%

3.0%varioos 3.0%varioos

6% 6%

3.2% 3.2%

11% 11%

10% 10%

2% 2%

7% 7%

(av) (av)

cuniculus cuniculus

various various

a a

specified specified

86.5% 86.5%

46.4% 46.4%

48.5% 48.5%

66% 66%

59.2% 59.2%

77.0% 77.0% Various Various

92% 92%

not not

65.6% 65.6%

Vie. Vie.

SA SA

NSW NSW

Vie Vie

d d

ACf. ACf.

a, a,

etown etown

N.S.W. N.S.W.

Vie. Vie.

N.S.W. N.S.W.

Vie Vie

eh eh

berr berr

E. E.

Oppslan Oppslan

N. N.

Menindee, Menindee,

Victoria Victoria N.S.W N.S.W

Gm Gm

Bega, Bega,

Frankston, Frankston,

N.W. N.W.

Blan Blan

S-WWA S-WWA

E E S.E. S.E.

1987 1987

19n 19n

1974 1974

84 84

1989 1989

1978 1978

1990 1990

VOLUME: VOLUME:

OCCURRENCE OCCURRENCE

cont cont

ANALYSES ANALYSES

WBGif WBGif

1988 1988

al. al.

a/.19 a/.19

1971 1971

1963 1963

Croft Croft

Hone Hone

'friggs 'friggs

et et

al. al.

1973 1973

1.2 1.2

et et

&IXgabriele &IXgabriele

&Stevens &Stevens

& &

et et

eta/.1981 eta/.1981

tosh tosh

In In

Barker Barker

Ryan Ryan

PffiONfACE PffiONfACE

Coman Coman

Oman Oman

Croft Croft

Table Table

M: M:

Lunney Lunney

Brown Brown

PERCENTAGE PERCENTAGE Oark Oark

PERCENTAGE PERCENTAGE

STOMACH STOMACH

Martenz Martenz

Long Long Triggs Triggs Chapter 1: General Introduction 12 foxes were concluded not to prey upon native mammals to any great extent, may have been influenced by conducting dietary studies in areas where most of the native fauna had already disappeared. Croft and Hone (1978, p89) found that native mammals fonned only a minor part of the fox's diet but they attributed this to the fact that the sample was taken from 'agricultural areas in which small native mammals are less abundant than in natural communities'. Friend (1978, p79) also found that 'the degree of agricultural development appears to affect the results obtained by scat analysis' and some uncommon species such as Sminthopsis leucopus, Cercatetus nanus and Mastacomys fuscus were found in relatively undisturbed areas whereas introduced species were found more commonly in seats that had been collected in more closely settled areas.

The fox has been further implicated in the decline of native fauna in an undisturbed forest area in W.A. (Christensen 1980). Here rabbit baiting was terminated because myxomatosis was considered to be sufficient in controlling rabbits. The 1080 poison that had been used to control rabbits was apparently also causing secondary poisoning in foxes and was thus maintaining their densities at low numbers. Once rabbit poisoning ceased there was a resulting increase in the density of foxes and a corresponding decrease in the densities of the native mammal species, e. g. B. penicillata, Macropus eugenii, Trichosurus uulpecula and M. {uliginosus. Christensen (1980) also stated that during the 1930's and 40s there had been a widespread decline in the medium sized native mammals such as the woylie (B. penicillata), the quokka (Setonix brachyurus), the brush-tailed possum (Trichosurus uulpecula), the tammar wallaby (M. eugenii) and the numbat (Myrmecobius fasciatus) and that these declines closely followed the spread of the fox.

It was not untill981 that Green and Osbourne conducted a comprehensive study in which prey species' occurrences in fox seats were compared to their field abundances. Green and Osbourne ( 1981) undertook their research in an area where sheep and rabbits were uncommon so that they could determine the influence of predation upon native mammals. Their results showed that in the absence of rabbits, small mammals occurred in the diet 'in all months and were Chapter 1: General Introduction 1 3

the winter staple diet'. They recorded Antechinus swainsonii, A. stuartii, Rattus fuscipes and Mastacomys fuscus as prey species.

Although there had been evidence that foxes were ingesting native fauna as prey, there was no information about the effect that predation was having upon the prey species' population dynamics. Kinnear et al (1988) did a controlled fox removal experiment and found that where foxes were removed, rock-wallaby populations (Petrogale lateralis) increased dramatically. They thus showed that fox predation was having a serious detrimental effect upon rock-wallaby populations. Kinnear et al. (1988) conducted this work on rock pile 'islands' in the Westem Australian wheatbelt where rock wallabies had been able to survive at very low densities because they were afforded some protection from fox predation by rock crevices and deep caves. Kinnear et al. (1984) also observed that P. rothschildi occurred at very low densities on Dolphin Island where foxes and cats were present, but that it was abundant upon Rosemary and Enderby Islands where there were no foxes or feral cats. The availability of refugia from fox predation is apparently a significant factor in the survival of P. lateralis and P. rothschildi and presumably this factor that has enabled four out of the five critical weight range species that live in rock-piles in the Pilbara region to remain intact, whereas only one of the seven non-rockpile species remains stable (Burbidge and McKenzie 1989).

Some native mammalian species have been able to maintain relict populations in areas where there is sufficient cover to enable them to avoid fox predation. Seebeck (1978) found that potoroos, for example, were able to avoid capture by foxes because they lived in a habitat that contained a thick understorey of Leptospermum· juniperinium, Acacia verticillata, Cassinia aculeata and various sedges. Christensen (1980) also found that the greatest numbers of native fauna occurred in areas where extensive thickets of Gastrolobium plants grew. These thickets would provide direct cover and protection for the native species, as well as preferentially decreasing fox densities. Gastrolobium plants naturally contain the poison 1080 to which foxes, and other canids, are particularly susceptible. The native mammals, conversely, have a naturally occurring increased tolerance to this poison and so can ingest this Chapter 1: General Introduction 1 4 substance, to a certain extent, with impunity. If foxes ingest mammalian prey that have been eating these plants they are secondarily poisoned by them. Naturally occurring fox control was thus occurring to a limited extent in the areas where Gastrolobium plants grew and this may explain why some of the endangered species were able to retain small populations in these areas (Christensen 1980).

1.3.2 Status of other Australian vertebrate fauna

The decline in the populations of birds and reptiles in Australia is far less pronounced than that of mammals. Only three species (0.7%) of bird (excluding sea-birds, vagrants and exotics) are extinct and only ten (2.4%) species have declined (Burbidge and McKenzie 1989). Of about 400 species of reptiles, none are extinct and only two (0.5%) have declined (Burbidge and McKenzie 1989).

This lack of decline in avian and reptilian species may be the result of foxes not generally prefering these species as prey items. Mclntosh (1963a) found that cold-blooded vertebrates (mainly frogs and skinks) were either not a favoured food or else they were not encountered often by the fox. Birds were also not important and accounted for only 3% of the volume of the diet. The birds that did occur were mainly unidentified passerines, and the ground dwelling species that occurred consisted of nestlings of Anthus australis (the pipit) and Lobibyx novaehollandiae (the spur winged plover). Coman (1973) also found that nestling birds, snakes, skinks and frogs were not major dietary items even though they were reasonably common. Coman stated that although birds were moderately important qualitatively, when they were examined on a percentage volume basis they were relatively unimportant in the diet. Coman concluded that predation upon birds is restricted 'to those situations where they are more abundant and more easily obtainable than other prey'.

Ryan and Croft (1974) also found that although reptiles such as the shingle back, and sand goanna were 'very common in the area', they were not common in the fox's diet. Similarly, birds were not important in the stomach contents of foxes. Chapter 1: General Introduction 1 5

In contrast to the conclusions of these studies Cogger (1959, p75) discusses the predators of goannas in general and says of foxes in particular that 'they appear adept at finding nesting sites and disposing of the eggs'. Similarly, Frith (1962) discusses fox predation upon mallee fowl and says that foxes are not a major threat to adult mallee fowl but they do account for 37% of the eggs. Priddel (1989) also found that juvenile mallee fowl were heavily preyed upon by foxes and that the majority of deaths occurred in the first few days after hatching. These studies show that foxes are able to have at least some predatory impact upon reptilian and avian species and thus concurs with the conclusion of Coman (1973) that foxes will prey upon reptiles and birds if alternative prey is not freely available. Norman (1971) further supports this conclusion by finding that fox predation upon short-tailed shearwaters (Puffinus tenuirostris) was of relatively little importance except upon islands where there was no alternative vertebrate prey.

1.3.3 Other factors that may be responsible for the decline of the mammalian fauna in Australia

1.3.3.1 The feral cat (Felis catus)

It is uncertain when the feral cat was first introduced into Australia but aborigines regard them as always having been present and that they came from the west (Burbidge et al. 1988). Therefore, they were possibly released from shipwrecks that occurred in the 17th century (Burbidge et al. 1988). Because many of the critical weight range mammals persisted well into the 20th century, predation by cats is not considered to be the main factor in the decline of these species (Burbidge and McKenzie 1989). Cats have also been present in the Central deserts for quite some time without having had a significant impact upon the native fauna (Burbidge et al. 1987). Similarly, feral cats are present in Tasmania and on other off-shore islands where populations of some critical weight range species are abundant. Feral cats do ingest native mammals, however, and Jones and Coman (1981) found that they eat Trichosurus vulpecula, Pseudocheirus peregrinus, Petaurus volans, Perameles nasuta, Rattus fuscipes, and an Antechinus species in Victoria. Chapter 1: General Introduction 1 6

1.3.3.2 Changes in fire regime

Since the arrival of Europeans the fire regime in many parts of Australia has been altered. Aborigines no longer light numerous small fires in a variety of seasons which previously produced a 'mosaic' of differently aged areas. Instead there are now infrequent but very intense summer fires that are usually started by lightning. This has lead to a reduction in environmental patchiness upon which many native mammal populations relied but the effects of these changes in vegetation composition upon the native fauna have yet to be fully analysed (Burbidge and McKenzie 1989). Burbidge et al. (1987) concluded that altered fire regimes may be significant in the demise of some mammalian species especially in the northern deserts where foxes did not become established until after the mammals had already declined. Further evidence that altered fire regimes may have been a factor in the decline of native mammals in some areas comes from the fact that extinctions in the deserts of Western Australia, north-western South Australia and the south-western Northern Territory coincided with the departure from the area by Aborigines 20-60 years ago (Burbidge et al. 1988). However, this factor does not account for the decline of many species which still have abundant populations on islands but which have declined on the mainland in the apparent presence of suitable habitat nor does it account for mainly mammalian species declining, especially those of small to medium size (Morton 1990).

Although Bolton and Latz (1978) concluded that changes in fire regime, rather than fox predation, were significant in the decline of western hare wallabies (Lagorchestes hirsutus) in the Tanami Desert, there have been subsequent reports of one fox being responsible for a significant number of deaths of this species in the last free living colony (Johnson unpublished, cited in Morton 1990) and this indicates that predation by foxes is a factor in their decline.

1.3.3.3 Rabbits and other introduced herbivores

Newsome (1971) discusses the competition between stock and native wildlife and reports how the overstocking of western N.S.W,. in Chapter 1: General Introduction 17 combination with severe drought, greatly reduced the carrying capacity of the habitat. He found that the Australian environment had been severely degraded by stock, land clearing, and by the introduction of rabbits which competed with the native fauna for food and shelter He lists Onychogalea frenata, 0. lunata, Lagorchestes hirsutus, L. conspicillatus, Chaeropus ecaudatus and Perameles eremiana as having declined due to the removal of shelter which left them vulnerable to predation by foxes.

According to Christensen (1980), the introduction of rabbits enables the fox to survive in relatively high numbers and to keep the densities of the native fauna at very low levels in most places. He also states that in the absence of rabbits, foxes would almost certainly have reached a natural balance with the native fauna, which would have remained reasonably abundant.

The introduction of the rabbit has been suggested to be one of the most important factors in the decline of small mammal populations (Low 1984). Low (1984) proposed that rabbits provided a new and more abundant food supply for predators which could then feed on native mammals whose populations could not sustain the predators at the increased density. The rabbit also competed directly with small herbivores for shelter and food and Low (1984) believed that it was a major influence in the decrease of bettongs and bandicoots in particular. Wood (1984) describes the phenomenon of rabbits being killed in the hundreds of thousands in western N.S.W. and northern S.A. There was considerable damage to the vegetation by rabbits in these areas with marked decreases in grass and herbage production. Atriplex and Maireana species were most the affected. Wood (1984) describes how Bettongia lesueur and Macrotis lagotis both lived in arid and semi-arid habitats and how they disappeared from large areas once rabbits invaded them. Wood (1984) believed that although rabbits usurped the burrows of these marsupials and competed with them for resources, it was the fox following the spread of the rabbit that was responsible for the final demise of these once widespread species. Chapter 1: General Introduction 1 8

1.3.3.4 Disease

Burbidge and McKenzie (1989) found that there were no data to support the idea that disease had been responsible for the decline in the ranges of Western Australian mammals. They surmised that disease was unlikely to have selectively affected the critical weight range species, particularly those in the more xeric areas ..

1.4 HOME RANGE AND HABITAT PREFERENCES

Variations in the size of fox home ranges (and those of other carnivores) can be attributed to the dispersion and abundance of resources in different areas (e.g. Mech 1970, Kruuk 1972a, Hilton 1978, Bekoff and Wells 1980, Mills 1982, Macdonald 1983, Litvaitis et al. 1986). Thus the area of each habitat that is required to sustain a fox is proportional to its productivity and resource availability. Foxes live in a variety of habitats and the most suitable or preferred habitats can be identified by high densities of foxes (Lloyd 1980a,b). Foxes are provided with greater resource variety in heterogeneous, fragmented or discontinuous habitats (Ables 1969a, Lloyd 1975, Voigt and Macdonald 1984) and so they are generally most numerous there.

Macdonald (1981) showed that certain 'prime', resource-rich, habitats are important to foxes and that home-ranges contained approximately the same amount of this requisite habitat type. The proportion of other non essential habitats within the home range were shown to increase linearly with an increase in home-range size, though they did not determine the overall size of that home range.

Trewhella et al. (1988) summarise the results of many home range analyses for red foxes and highlight the relationship between home-range size and population density. At high densities foxes have smaller home-ranges, though there appears to be a limiting minimum territory size below which home-range areas do not fall. There is an increase in the amount of overlap of neighbouring fox home ranges at high densities (Harris 1980) though Macdonald (1983) found that there was no relationship between territory size and fox family group size. Chapter 1: General Introduction 1 9

Schofield (1960) and Pils and Martin (1978) found that the primary requirements of foxes are food and cover. The suitability of an habitat may be limited by the availability of cover rather than food, though food availability may be important for the reproductive performance of fox populations (Lloyd 1980a,b).

In Europe, the most commonly preferred fox habitat contains rough permanent grassland because this is the optimal habitat for the predominant prey species, Microtus spp. (Lloyd 1980a,b). This grassland, combined with the availability of cover in the form of woodland, thickets or scrub, maintains the highest fox densities. Areas that have a high density of rabbits are also favoured by foxes because here they are assured of a year-round supply of food (Lloyd 1980a,b). Foxes tend to avoid areas that contain flat, open country with few woodlands or very open deciduous woodland. Large arable fields with neat or simple field boundaries and a high water table are also avoided (Lloyd 1980a).

In Britain, high densities of foxes are associated with areas of intensive mixed agriculture and the length of the 'woodland-farmland edge' is an important determinant of fox home range size in rural areas (Macdonald et al. 1981). Foxes have been found to avoid extensive upland areas such as the western Highlands of Scotland, the Lake district, and the Pennine chain (Macdonald et al. 1981). The phenomenon of urban foxes appears to occur more often in Britain than in Europe or North America and a considerable amount of research has been conducted on this topic by Harris (1980), Maurel (1980), Macdonald (1981) and Kolb (1984,1986).

In North America foxes occur in a variety of terrains and vegetation types (Abies 1975). Generally, they prefer a mixture of habitat components, especially the edges of vegetation types. They avoid large, homogeneous tracts of any one habitat type and one of the densest populations of foxes in North America is in southwestern Wisconsin within a patchwork of woodlots, cropland, pasture and stream beds (Richards and Hine 1953 as cited by Abies 1975). Chapter 1: General Introduction 20

Sanderson (1966) stated that home range studies should identify an animal's requirements under all circumstances throughout the year. The advantage of certain resources may be very subtle and the importance of a resource may not be apparent in favourable conditions Lloyd (1980a,b). Food supplies vary in the spatia-temporal pattern of their availability and thus seasonal variations in the use of habitat will occur (Macdonald 1981). Home range analyses should, therefore, be conducted throughout as many seasons and during as many different environmental circumstances as possible.

The social organisation of foxes varies among habitat types and group size may be determined by the abundance of available prey (Macdonald et al. 1981). The degree of home-range overlap between individuals and within populations differs with resource availability and population density. Two basic types of social organisation have been reported for red foxes. The first is usually based upon a mated pair of foxes that do not strongly defend their territories against conspecifics. There is usually a considerable degree of overlap between unrelated individuals and flexible social groupings have been observed. The studies of Storm et al. (1976), Lloyd (1977), Harris (1980) and Keenan ( 1981) identified this type of social organisation.

In contrast, Niewold (1980), Macdonald (1979, 1981) and von Schantz (1984) found that foxes form family groups with a basic social unit comprised of a single male fox and several related vixens. These family groups do not overlap with adjoining families. Macdonald (1979) found that only one of the vixens in the family group actually breeds, and that the other vixens act as helpers in the rearing of the dominant vixens cubs. von Schantz (1984), however, disputes this and suggests instead that the group size increase is due only to a temporary increase in resources. In both these cases, a social class of itinerant males, or else a significantly higher male mortality, would be needed to account for the surplus of males that would be assumed if the usual1:1 sex ratio at birth occurred. Chapter 1: General Introduction 21

1.5 GENERAL BIOLOGY

The red fox is an opportunistic omnivore that has an immense geographical range. Its weight ranges considerably with its distribution and varies from 2.5 to 9.0 kg (Bueler 1974). The body length varies from 50 to 90 cm and its tail measures from 33 to 46 cm. Its height at the shoulder averages 40 cm. Red foxes are monoestrus and up to twelve cubs are born per litter. They are mature at one year. Their scent glands are particularly well developed and they use these and their vocalisations in communication. They have few predators other than dogs and man and they are widely hunted throughout their range for their pelts, to minimise livestock losses and to minimise the incidence of rabies (Bueler 1974).

1.5.1 Fox diet in other countries

The diet of foxes has been studied extensively in other countries and there are numerous reports of the food items ingested by foxes. In general, foxes eat small to medium sized mammals (usually lagomorphs and small rodents), birds, (especially ground-nesting or dwelling species), carrion, invertebrates and plant matter. Additional items include reptiles, fish, frogs, domestic cats, badgers and household garbage (Sequeira 1980). Summaries of the literature can be found in Korschgen (1959), Abies (1975), and Jensen and Sequeira (1978), and more popular accounts are provided by Burrows (1968) and Lloyd (1980a).

Many of the dietary studies are limited in their usefulness because they neglect to estimate the field abundances of the prey species that were prevalent during the study. They are thus inconclusive as to whether the observed dietary composition was due to fox prey preferences or whether it merely reflected the resources that were available to the foxes at that time. Several quantitative studies of diet and field abundance have been undertaken, however, and these include Scott and Klimstra (1955), Lund (1962), Lockie (1964), Goszczynski (1974), Hewson et al. (1975), Forbes and Lance (1976), Richards (1977), Pils and Martin (1978) and Sequeira (1980). Chapter 1: General Introduction 22

1.5.2 World distribution/ taxonomic relationships

The red fox is distributed widely and it occurs across all of Europe, through much of northern Asia, in northern India, and in the northern coastal regions of Africa and the Sudan. It is also found in north America, extending from the circumpolar regions of Canada to central Texas, U.S.A. It has been introduced to Australia and some Pacific islands (Bueler 197 4).

There are approximately 48 subspecies included in this species, which makes it the canid with the largest taxonomic complex and it is also probably the most widely distributed member of the Canidae (Bueler 1974).

1.5.3 Other vulpine species

All vulpine species are opportunistic and generalist foragers which usually hunt alone. They eat a large variety of food items, usually in accordance with availability; although some species have been shown to be have definite prey preferences (Bueler 197 4).

The arid dwelling species of fox are generally light coloured and have large whiskers and ears. The species include V. chama (the cape fox) which is found in Africa, south of Zimbabwe and Angola; V. pallida (the pale fox) of northern Africa extending from Senegal to the Sudan; V. ruppelli (Ruppells fox) which lives in north eastern Africa and the middle East, extending to Afghanistan, V. zerda (the Fennec fox) which extends across the northern parts of Africa and to Saudi Arabia and V. velox (the kit fox) which is confined to the most arid areas in the south-west U.S.A. and northern Mexico (Bueler 1974). These species are all smaller than V. vulpes and V. pallida is the smallest of all foxes (<2kg) (Bueler 1974).

1.6 SPECIFIC AIMS OF THIS STUDY

The main aim of this study was to investigate the ecological role of the red fox in the arid zone. Particular emphasis was placed upon assessing the predation pressure that foxes were exerting on the native Chapter 1: General Introduction 23 mammalian fauna. The extent to which foxes were depleting these populations was assessed to determine whether foxes are continuing to have a detrimental effect upon the native mammals or whether a balance has been achieved between foxes and their prey species. The extent to which foxes prey upon ground-dwelling birds and reptiles was also assessed to establish whether populations of these phyla are being similarly affected by fox predation.

Home range analyses were undertaken to investigate the habitat preferences of foxes and to identify the resources that are most importance to them. This investigation also provided valuable information about their social organisation.

The population dynamics of foxes were studied to determine how mortality and fecundity rates are modified in response to extrinsic environmental factors.

To determine the response of foxes to the removal of their major vertebrate prey species, a rabbit removal experiment was conducted. The subsequent changes in the foxes' diet, home range usage and density were monitored. 24

CHAPTER2

GENERAL METHODS

This chapter describes the study site and summarises the methods that were used throughout this study. More specific techniques are described within the chapters where they are most relevant.

2.1 STUDY AREA

2.1.1 General Description

Fowlers Gap Arid Zone research station is situated approximately 110 km north of Broken Hill, in north-western New South Wales (Lat. 31° 05'S, Long 141° 43'E). It is administered by the University of New South Wales, which was granted the lease 'in perpetuity' by the N.S.W. State Government in 1972. This property covers approximately 39,200 ha and at present it is run as a working sheep station with approximately 7,000 head of stock. The productivity of the land at Fowlers Gap is comparatively low and if it is assessed using sheep stocking rates, then the Conservation land-system (see Chapter 2: General Methods 25 below) can sustain 12.21 dry sheep equivalents per 100 ha (pers. comm W. Tattenal, N.S.W. Soil Conservation Service).

The topography in the study site varies, from the Barrier Ranges at more than 250 m in altitude in the west to the low lying flood plains at 150 m above sea level in the east (Fig. 2.1). The vegetation is semi-arid to arid shrubland (<1 m) which is dominated by the family Chenopodiaceae.

2.1.2 Climate

Fowlers Gap has a climate which is generally dry with hot summers and mild winters (Bell 1973). Detailed climatic records have been kept at Fowlers Gap since 1968 and to obtain estimates of climatic variables before this time, the weather records from other stations in the district, namely White Cliffs, Sturts Meadows, Corona and Broken Hill, were used.

The average annual rainfall at Fowlers Gap is 195 mm with a coefficient of variability of 44%. Rainfall between October and March inclusive, is twenty percent greater than that which falls in winter, but winter rainfall is more reliable than summer rainfall. Rain tends to occur as wet spells ranging from 1 to 6 days. Throughout the year most of the rain is due to local thunderstorms and the wet spells of one day's duration, or less, are responsible for 45% of the summer rainfall and 65% of the winter rainfall. Interspersed between these wet spells are dry spells which may last from a few weeks to many months (Bell 1973).

In summer relative humidities are comparatively low; however, in winter humidities are similar to those recorded in Adelaide and Sydney. The highest mean daily vapour pressure is 12.5 hPa in February and the lowest is 8.0 hPa in August. Comparisons between rainfall and evaporation throughout the year indicate that even under very wet conditions monthly rainfall is never likely to exceed monthly evaporation (Bell 1973).

::s ::s

0 0

[ [

. .

.. ..

~~l ~~l

11 11

.. ..

''i ''i

. .

:·,,. :·,,.

~. ~.

' '

J J

MODEL MODEL

Station Station

Wales Wales

Research Research

ELEVATION ELEVATION

1988 1988

South South

Gap Gap

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Geography Geography

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Fowlers Fowlers

University University

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The The AUSTRALIA AUSTRALIA Chapter 2: General Methods 27

The day-time temperatures in summer usually exceed 30° C with approximately 40 days having maxima above 35° C. In contrast, early morning and night-time temperatures throughout summer are quite mild, and so large differences occur between day and night temperatures.

In winter, conditions during the day are mild to warm and nights and early mornings are relatively cool (Bell 1973). Between April and October temperatures below 0° C occur 7- 10 times per year and are accompanied by heavy frosts in susceptible hollows and gullies. Lighter frosts may also be experienced 10- 20 times per year with accompanying temperatures of 0° C to 2.5° C.

2.1.3 The Study Sites

The majority of the study area was contained within the Conservation land system. This land system is characterised by the presence of scalded flats between the main river flood-outs (Mabbutt et al. 1973). These extensively scalded surfaces are traversed by ill defined, depressed drainage zones within which gilgais are present. The scalds and claypans found within this land system are characterised by having hard bare surfaces with some gravel. Sand accumulations are also found in this land system and these range from sand hummocks around the scalds to elongated low sandy rises in the lower parts of the land system. A small section of the study area occurred upon the Gap Hills land system which was characterised by bands of saltbush, Mitchell grass and stony ground.

The habitat of much of the study site at Fowlers Gap was very patchy in relation to the availability of vertebrate prey. The main variations were due to the dispersion of rabbit warrens, the distribution of soils suitable for the development of crab-holes which would support dasyurid and reptile populations, and the presence of cover that would be suitable for use by ground-dwelling birds. The overall productivity of the area was fairly low and if the carrying capacity for sheep is used as a guide the 12.21 dry sheep equivalents per 100 ha reflects the paucity of resources available to foxes in this area (Tattenall pers. comm. ). 28 Chapter 2: General Methods

I I I I

Fig. 2.2 The Study area. (---Transect lines, o Rabbit warrens, • Tracking towers, -.:::::7 Pitfall traps) Chapter 2: General Methods 29

The study area was divided into five study sites; Ram paddock, Warrens paddock, Lambing paddock, Mating paddock and Salt 3 paddock (Fig.2.2). Although these paddocks are discussed using their paddock names, this was done for ease of reference, rather than because there was a strict delimitation of resources by the paddock boundaries. Foxes were able to move freely from one study site to another.

Each of the study paddocks contained transect lines of various lengths (Fig. 2.2) and these lines were positioned so that the density estimates of foxes and ground-dwelling birds could be readily replicated (see Section 2.3.1). Each line was positioned within the paddock so that no particular habitat type was favoured or avoided (as recommended by Bumham et al. 1980). The exception to this occurred when the transects were positioned in Warrens and Ram paddocks. The transects in these two paddocks were deliberately placed so that they were always within 500 m of an active rabbit warren so that the relationship between fox densities and rabbit abundance could be investigated.

Each of Lambing, Warrens and Ram paddocks contained a set of pitfall traps (See Fig. 2.2 and Section 2.3.4 for details). The sites for these pitfall traps were chosen so as to maximise the capture of dasyurids and rodents by positioning them in the most optimal small mammal habitat available (Morton et al. 1983).

2.1.3.1 Warrens

The Warrens paddock study site is positioned partially upon the Conservation and partially upon the Gap Hills land systems (Fig. 2.2). Only 920 ha of the total Warrens paddock area was used as the study site due to the inaccessibility of most of the paddock. This study site had a relatively high density of rabbits and 38 warren groups were monitored within it. There were 11.5 km of transect lines placed in this study site and all of these were within 500 m of a known rabbit warren (Fig. 2.2). A set of pitfall lines was also established within this paddock. The normal stocking rate for sheep was maintained in this paddock Chapter 2: General Methods 30 and 40 horses and 1000 head of cattle were also run. Kangaroos were present in naturally occurring densities (Table 2.1).

2.1.3.2 Ram

Ram paddock had a high density of rabbits when this project started, with approximately 40 warren groups being present within its 834 ha. It contained 6 km of transect lines. Sheep, cattle and kangaroos were all present in this paddock at normal stocking rates for the duration of the study.

Table 2.1: Summary of Study Site Characteristics. (+=present,-= absent).

Paddock Size Transect Land Characteristics (ha) Length (km) System Rabbit Pitfalls Roos Stock

Warrens 920 11.5 Conservation/ + + + + Gap Hills Ram 834 6.0 Conservation +1- + + + Lambing 595 8.0 Conservation + + + Mating 417 5.5 Conservation + Salt3 618 8.0 Conservation +

In November 1988 all the rabbit warrens in this paddock were 'ripped' as part of an experiment (See Section 7 .2). To enable changes in prey abundances to be monitored before and after this rabbit removal, a set ofpitfalllines was positioned in the northern part of this paddock (Fig. 2.2 and Table 2.1).

2.1.3.3 Lambing

Lambing paddock is approximately 595 ha in area and contained 8 km of transect line (Fig. 2.2). In contrast with Ram paddock, Lambing paddock had a low density of rabbits. However, there were four small and one medium sized warrens on the southern boundary of the paddock. Rabbit density in this area was therefore, initially at least, much higher than elsewhere in the paddock. These five warrens Chapter 2: General Methods 3 1 were ripped in November 1988 as part of the experiment described in Section 7.2.

A set of pitfall lines was positioned in this paddock (See Fig. 2.2 and Section 2.3.4). Lambing paddock was also simultaneously involved in another project in which sheep were present at normal stocking rates and kangaroos were able to move freely into and out of the paddock (Table 2.1).

2.1.3.4 Mating

This paddock covers an area of 417 ha and it contained 5.5 km of transect lines (Fig. 2.2). Only one small rabbit warren was present in this paddock and this was vacant for most of the study. Mating paddock was concurrently involved in another research project for the duration of this study and as a consequence was devoid of any domestic stock. This may have reduced the availability of sheep carrion. Kangaroos, however, were able to move freely in and out of this paddock and so foxes would have had access to any naturally occurring kangaroo carrion (Table 2.1).

2.1.3.5 Salt 3

Salt 3 paddock occupies an area of 618 ha and contained 8 km of transect lines (See Fig. 2.2). This paddock was similar to both Mating and Lambing paddocks in that it had a very low density of rabbits. Only six very small (i.e. <10 burrows) warrens were present within its boundaries. An electric fence surrounds this paddock and this was erected to deliberately exclude kangaroos as part of a concurrent experiment. Sheep, however, were present in this paddock, at standard stocking rates, for the duration of the study (Table 2.1).

2.1.4 Fauna

The indigenous mammalian fauna at Fowlers Gap has suffered a rather drastic decline, especially in the species diversity of smaller marsupials. The native mammalian species that are locally extinct at Fowlers Gap are Myrmecobius fasciatus, Macrotis lagotis, Chaeropus Chapter 2: General Methods 32 ecaudatus, Perameles bougainville, Bettongia penicillata, B. leseur and Lagorchestes leporides. The main decline in these species appears to coincide with the arrival of the the fox, although Chaeropus ecaudatus was probably always rare (Krefft 1886, cited in Marlow 1958). The invasion of rabbits in the 1880's, coupled with severe drought and the overstocking with sheep in the 1890's (Dawson and Russell 1973) could only have enhanced the decline of these species. The mammalian fauna at Fowlers Gap today contains many introduced mammals, in the guise of domestic stock and feral animals, as well as the conspicuous large macropods, plus dasyurids, rodents and microchiropteran bats.

2.1.4.1 Rabbits

Rabbits (Oryctolagus cuniculus) inhabit the red, loamy, sandy soils of the Conservation land system which occupies most of the study area (Fig. 2.2). The distribution of rabbits within the study area was not uniform and some areas supported a high density of rabbits, while others supported considerably fewer. Rabbits were commonly found along drainage channels and around water tanks in the study site and these areas act as refuges during drought (Dawson and Russell 1973). The main breeding season for rabbits in the arid zone is between June and November (Myers 1971).

2.1.4.2 Dasyurids and rodents

There are four species of dasyurid marsupial at Fowlers Gap; Sminthopsis crassicaudata, S. macroura, Planigale tenuirostris and P. gilesi (Read 1987). These species inhabit tussock grassland and low shrubland habitats (Read 1987). S. crassicaudata inhabits low shrubland with clay, sandy or stony substrates (Morton et al. 1983) whereas P. gilesi and P. tenuirostris generally select tussock grassland with densely and deeply cracking soils. P. tenuirostris is also able to exploit habitats with shallow or sparse cracks, that are not commonly exploited by P. gilesi (Read 1987).

The most commonly captured rodent at Fowlers Gap is the ubiquitous introduced house mouse (Mus musculus). This is followed Chapter 2: General Methods 33 in abundance by the native rodent, Leggadina forresti, which prefers tussock grasslands and low shrublands on loam, clay or stony soils (Read 1984). Dawson and Russell (1973) also report the presence of the sandy inland mouse (Pseudomys hermannsburgensis) but this animal has not been caught at Fowlers Gap since the single original specimen was obtained (Dawson pers. comm. ).

2.1.4.3 Macropodids

The red kangaroo (Macropus rufus) and the euro (M. robustus erubescens) are the two most abundant native herbivores at Fowlers Gap. Red kangaroos are most numerous on the plains in the eastern half of the station whereas euros are most numerous in the hilly, high relief areas in the west of the station. The two species of grey kangaroo; the eastern grey (M. giganteus) and the western grey (M. fuliginosus), were also present at Fowlers Gap, although the numbers of these two species, especially the eastern greys,· were low compared to the other two species (McCarron 1990). Foxes are unlikely to prey upon adult kangaroos, however, they probably do have some predatory impact upon young-at-foot.

2.1.4.4 Feral cats

Although feral cats were present at Fowlers Gap, they were not abundant. They were regularly seen during density estimation counts for foxes but were sigriificantly less numerous. Cats are much more closely associated with creek-lines and watercourses than are foxes. One cat that was captured and collared beside the main creek was re trapped two days later approximately seven kilometres away from its initial capture site. All the cats that were shot on Fowlers Gap had their stomachs filled with rabbit remains, although some reptiles had also been eaten.

2.1.4.5 Ground-dwelling birds

The principal species of ground-dwelling birds that are found at Fowlers Gap are the stubble quail, Coturnix pectoralis (Gruiformes: Phasianidae) and the little quail, Turnix velox (Gruiformes: Chapter 2: General Methods 34

Turnicidae). The stubble quail was found throughout the study area and its preferred habitat is saltbush country. When it is flushed it makes a straight flight and then drops suddenly to the ground (Slater 1970), making it very easy to observe even at night. The little quail inhabited similar habitat to the stubble quail and had similar flushing behaviour. The plain wanderer, Pedionomus torquatus, (Gruiformes: Pedionomidae) and Richard's pipit (Anthus novaeseelandiae) were commonly observed during the day but were not knowingly flushed nor counted during the transect counts at night.

2.2 CAPrURE TECHNIQUES

2.2.1 The Cannon-Net

The most successful method of catching foxes at Fowlers Gap was found to be a cannon-net (Wildlife Materials Inc., lll. U.S.A.). This technique involved enticing an animal into a pre-determined area where a net has been attached to 5 projectiles mounted on poles (Fig 2.3). This net was approximately 20 x 20 m and the mesh was approximately 10 cm square. When a fox was within range of the net, the 8 g black powder charges within the cannons were detonated (using a 12 V car battery) and the projectiles were shot forward over the fox's head, carrying the net with them.

Foxes were lured to within range of the net by dragging a kangaroo or goat carcass in a circular path for approximately 5 km and then leaving the carcass at the net site. Alternatively, the net was set up near a water trough where foxes were known to drink, usually at sundown.

At night a night vision scope (Javelin Electronics, L.A. Calif., model NVD20) was used in conjunction with a Sanyo rechargeable torch which was fitted with an infra-red filter (Kodak Wratten gelatine). With this equipment foxes could be seen and identified on even the darkest of nights. Chapter 2: General Methods 35

Fig. 2.3 The cannon-net.

2.2.2 Snares/Leghold Traps

Two types of leg-hold traps were used: treadle snares and modified rabbit traps. The treadle snares rely upon the fox depressing a pressure pad in the centre of the trap, thus releasing a powerful spring

\ which tightened a sturdy snare wire around the fox's leg. These snare I wires were specifically designed to prevent over-tightening and this prevented damage to the fox's leg. Chapter 2: General Methods 36

The modified rabbit traps were specially altered to minimise injury to a fox by welding an extra piece of steel between the jaws so that they would remain approximately 7 mm apart when closed. Each jaw had its teeth removed with an oxy-acetylene cutter and was also padded with a thick layer of rubber to further reduce any possibility of injury to the fox.

2.2.3 Handling and Collaring Foxes

Once caught, foxes were anaesthetised using 1 ml of diazepam ('Valium' 10 mg/ml) and 0.5 ml ketamine hydrochloride (Ketalar). Eyedrops were administered to avoid corneal dehydration. The fox was then sexed, weighed and measured. Standard body measurements were recorded: head and body length, ear length, hind foot length and tail length. Females were examined to determine if they were lactating or if they had enlarged nipples from a previous pregnancy.

. A collar was then placed around the fox's neck and its ear tattooed with an identifying number. Telonics, Titley and DSIR radio collars were used when available (finances permitting). These transmitters all operated at 150-152 Mhz and the transmitter and battery assembly weighed approximately 250 g. 'C-sized' lithium chloride batteries were used and theoretically these lasted for 12 months. If a radio-collar was unavailable for use, a vinyl collar with attached coded reflective symbols was fitted instead so that individual identification of the fox was possible.

2.3 CENSUS TECHNIQUES

2.3.1 Night counts

Night counts were used to estimate the relative densities of foxes and ground-dwelling birds every three months. This technique involved driving along thirty eight kilometres of transect on three consecutive nights. The distance and angle of any fox sighted from the vehicle, using a 100 W spotlight, was recorded. The data were analysed using the methods described in Bumham et al. (1980). An estimated probability density was thus obtained (see section 4.2.1). Chapter 2: General Methods 37

2.3.2 Rabbit Abundance Estimations

The field abundances of rabbits were estimated every three months using the technique of Parer and Wood ( 1986). This involved examining all the burrow entrances present at each of the warrens that were monitored. Each burrow was assessed as to whether or not it was active and this was used as an index of how many rabbits were present in the warren. To further verify this estimation, actual rabbit counts were conducted at ten warrens for three consecutive days each, every three months. Here the number of rabbits observed at the warren surface was recorded for an hour before sundown and then this figure was averaged for the ten warrens and the resulting ratio of rabbits observed to active burrows present was extrapolated to all the other 158 warrens in the study area.

2.3.3 Light Trap

To obtain an estimate of the relative abundance of night flying insects, a light trap was used. This trap comprised a tank of water, 1 m in diameter and 0.45 m deep, above which an ultraviolet light was suspended. As insects were attracted to the light they invariably fell into the water and could not escape. Their chances of escape were further reduced by adding dish washing liquid to the water. Two traps were used, one at the homestead and one in the centre of Mating paddock. Each was employed for ten consecutive days every three months and an insect biomass estimate (kg/trap) was made each morning. These estimates were made just after dawn, so as to minimise the loss of insects from the trap due to opportunistic birds.

2.3.4 Pitfall trapping

Pitfall traps were constructed by digging holes 45 cm deep into the ground and lining each of these with a sheet of galvanised iron. Any small animal that fell into these pits was unable to climb out. Each pit was joined to its neighbour by a small fence or drift line that was approximately 30 cm high and was dug into the ground. This fence was constructed from commercial fly screen wire cut into 45 cm strips. Any small animal that encountered this fence could not cross it, nor Chapter 2: General Methods 38 burrow under it and so it ran along the fence until it unsuspectingly fell into one of the pits.

In this study, 11 pits were placed 10 m apart in three lines at each of three sites. The three pitlines were positioned in a triangular arrangement, the centre pit of each line being located at the mid point of each side of a 300 m equilateral triangle.

Pitfall traps were used to monitor the relative field abundances of small mammals, reptiles and ground-dwelling insects. All sets of pitfall traps were monitored simultaneously for ten consecutive nights every three months.

2.4 STATISTICAL ANALYSES

The statistical methods used in the analyses of data were based upon those discussed in Sokal and Rohlf(1981), Zar (1974) and Siegel (1956). The symbols used are defined in Sokal and Rohlf(1981). Canonical correlations were based on Gittins (1985). Dr. D. B. Croft wrote most of the programs used for univariate and bivariate analyses and these were performed on a range of computers; Apple lie, Amstrad and Bluejem. All multivariate analyses were run on the UNSW's IBM 3090 mainframe computer using SPSSx (SPSS Inc., Il., U.S.A.). 39

CHAPTER3

DIET ANALYSES

3.1 INTRODUCfiON

Various techniques for estimating the relative importance of each of the dietary categories within a scat have been developed. These methods include frequency of occurrence, percentage occurrence, percentage dry weight and volumetric assessment (Scott 1941a). Although Scott (1941a) compared some of these techniques, and found that frequency of occurrence gave the most reliable interpretation of the relative quantities of foods consumed, he later (Scott 1943) concluded that · small-sized foods would have a frequency much in excess of their actual volume, especially if they were eaten regularly and in small amounts. This technique would also tend to disproportionately reduce the relative amounts of associated foods commonly taken in large quantities. Nevertheless various authors have accepted the limitations of this technique and used it anyway e.g. Leopold and Krausman (1986).

Lockie (1959) also found that frequency of occurrence was unlikely to be consistent in its error and so he used the weight of undigested matter instead. In an attempt to overcome the problem of differential Chapter 3: Diet 40 digestibility of the items within the seats, and the influence that this has upon estimating the ingested biomass of each prey item, he calculated various digestibility correction factors. Goszczynski (1974) further tested these factors and found them to be quite accurate for most prey types, especially small rodents and rabbits.

3.2 :METHODS

3.2.1 Scat Collection

Fox seats were collected every three months beginning in October 1986 and finishing in July 1989. Twelve collections were made, with each season being replicated three times. Approximately 100 seats were collected in each sampling period. Seats were collected from the 38 km of transect line that were used for the fox density counts. All the seats were examined closely to ensure that no non-vulpine excrementa were included in the analysis. The seats were tested for the chflracteristic smell that fox seats exude, for the normal greyish-white colour and for their sharp ended 'tail' which is usually composed of hair or grass. Although feral cats were very low in numbers, and dingoes were virtually non-existant in the study area, domesticated work dogs were present and so if there was any serious doubt about the origin of a scat it was not included in the analysis. For the purposes of this analysis a scat is defined to be 'a cohesive intestinal discharge or a limited part thereof (Lund 1962).

3.2.2 Scat Analysis

Seats were stored in 70% alcohol until they were analysed. They were then emptied into a Petri dish and sorted macroscopically into their constituent categories. If necessary, a microscope was used to identify very small fragments. The volume (ml) of each dietary category was then recorded for each scat. The dry weight of each category in relation to its volume was then calculated so that the ingested biomass of each category could be calculated using the digestability estimates.

The identity of all hair found was determined using the techniques described in Brunner and Coman (197 4). Both cuticle scale Chapter 3: Diet 41 patterns and cross-sectional characteristics were used in the identification. For species not listed in Brunner and Coman (197 4), reference slides were prepared using hair known to have come from an individual of that species, e.g. Planigale gilesi.

The remains of feathers found in the seats were identified to Order using the technique of Day (1966). The pattern of barbels along the shaft of the feather is characteristic, although this was found to be commonly lost in heavily digested material.

Reptilian remains were identified by examining the size and shape of the scales. Three categories of scales were used: small scales, large scales and long, narrow scales. The small scales were identified as belonging to Tympanocryptus lineata, which was the only reptile to be caught in the study site that had scales of this size. Similarly, the large scales were attributed to Tiliqua rugosus because this was the only reptile that was observed in the study area that had scales of this siz~. The long, narrow scales were presumed to have come from the bellies of snakes found within the study area, although no attempt was made to identify them more precisely.

Invertebrate remains were readily sorted into Order and Orthoptera and Coleoptera were most commonly encountered. Rarely did any other Order occur. Some seats were found to contain whitish grey, chalk-like material and this was identified as being the remains of a large ingestion of bone (Lund 1962).

An attempt was made in this study to equate the contents of the seats that were collected with the actual ingestion of prey items. Lockie (1959) had previously developed a technique of doing this and this involved weighing the persisting parts of prey items that were fed to captive foxes and estimating correction factors for the digestability of each prey type. The digestibilities of rabbits (33.97), small mammals (18.17), and small birds (20.0) were obtained from Lockie (1959). Carrion digestibility (50.0) was modified from the estimates ofGoszczynski (1974) and invertebrate (10.0) and reptile (18.0) digestibilities were estimated. Chapter 3: Diet 42

3.2.3 Field Abundances

The field abundances of each of the dietary categories were estimated using the methods outlined in Chapter 2. Thus ground dwelling bird densities were obtained using the 'night count' technique described in Section 2.3.1; dasyurid and reptile abundances were estimated using pitfall traps, as described in Section 2.3.4; and invertebrate abundances were estimated using the light trap and pitfall traps (Sections 2.3.3 and 2.3.4). Because ground-dwelling bird sightabilities did not approximate any of the density estimation distributions available, a simple strip width density estimation was used. The number of birds sighted within 20 metres of the vehicle (the maximal distance of birds observed to be flushed by the vehicle) was recorded and as the total distance travelled was known (38 km), it was possible to calculate the relative density of birds per square kilometre.

The field availability of carrion was estimated by calculating ka~garoo and sheep mortality rates. The mortality of sheep was calculated using the stocking records for each paddock. Kangaroo mortality estimates were provided by Dr. G. Edwards based upon data obtained in a concurrent study on red kangaroos (Edwards 1990). No attempt was made to separate kangaroo that was ingested as carrion and that which resulted from fox predation upon young-at-foot even though this may have been substatial.

3.2.4 Analytical Methods

The volume of each dietary category for each scat was stored in a database. The field abundances for each of the categories for each paddock were also entered into the database so that there was a corresponding field abundance entry for every dietary volume entry. The data in the database was then transferred to the IBM 3090 main frame computer where the analyses were performed. Initially the SPSSX AGGREGATE program was run to obtain the overall dietary composition of foxes in the entire study area. The composition within each paddock was then examined to determine whether there was any Chapter 3: Diet 43

dietary variation associated with the availability of rabbits. Regressions were performed between the average occurrences of each food category and its respective field abundance to determine whether each category was being consumed in relation to its availability.

The data were tested to determine whether they were inter related and therefore actually needed to be analysed using multivariate analysis (Norusis 1985). This was done using Bartlett's test of sphericity. The distributions of the variables were then tested for homoscedascity of variance and normality of variance, using both Cochrans C and the Bartlett-Box F tests. Before these analyses were conducted all the data were log-transformed (due to their not having homoscedascity of variance) and converted to z-scores. This last transformation was done because all the field abundances were measured on different scales and this manipulation allowed them to be compared directly.

A canonical correlation was calculated using the MANOVA program within the SPSSX ·statistics package. This analysis was used to identify any interaction effects that occurred between any of the dietary categories and/or one or more of the field abundances. Although none of the distributions for the variables was found to be normally distributed, because 'linear functions of variates are more likely to be normal than are the component variates' (Cooley and Lohnes 1962), the analysis was still performed. Once the overall relationships between the dietary categories and their field abundances had been identified, further analyses were executed wherein year, season and paddock effects and interactions were investigated to determine whether foxes in different areas and during different seasons ate different prey.

Canonical correlation analysis was used for these investigations because it aims to explain as much variance as possible in the dependent variable set (the dietary occurrences) from the independent variable set (the field abundances). It derives a linear combination from the two sets of variables in such a way that the correlation between the two linear combinations is maximised. It thus tries to account for the maximum amount of relationship between two sets of variables (Nie Chapter 3: Diet 44 et al. 1975). The procedure selects the first pair of canonical correlates so that they have the highest intercorrelation possible, given the particular variables involved. Then a second set of canonical variates is selected so as to account for a maximum amount of the relationship between the two sets of variables left unaccounted for by the first canonical correlates. This process is continued until all the variance has been accounted for. Because each successive set of canonical variates accounts for residual variance it produces combinations of variables that are uncorrelated with one another (Norusis 1985).

3.2.5 Impact of Predation on Native Populations

To determine the impact that fox predation was having upon native populations the amount of each dietary category consumed per square kilometre was calculated. This result was compared with the densities of the prey populations and the extent to which foxes controlled the populations was estimated. It was assumed that an ad';llt fox ingests approximately 4 70 g of food per day depending upon its nutritional value (Goszczynski 1974). The number of grams of each category that is ingested per day can be calculated by multiplying this figure by the proportion that each comprises of the total dietary intake. This result was converted to gfkm2 ingested by multiplying by the density of foxes (0.93 km2). The average adult weight of each prey type was obtained and the number of individuals of each prey category that was ingested was calculated. The density of each of the dietary categories per square kilometre was calculated from the density estimations described in Chapter 2.

3.3 RESULTS

3.3.1 Overall Dietary Composition

The overall composition of the fox seats collected at Fowlers Gap was calculated and then these values were corrected for the digestabilities of each dietary category (Fig. 3.1). The latter is a more accurate representation of the actual ingestion rate of each of these categories and it shows that carrion was the most abundant item in the fox's diet followed by rabbits. Chapter 3: Diet 45

Invertebrates, dasyurids and reptiles were also eaten as were ground-dwelling birds. Plant and organic material was eaten in extremely small amounts. These results indicate that vertebrate prey, especially mammals, were the most important items in the foxes' diet. Fluctuations in the rate of ingestion of each of the dietary categories and more specifically the vertebrate prey categories are shown (Figs 3.2a and b respectively). Although more rabbit is ingested in spring and summer than winter and autumn, there is no significant difference in its mean ingestion rate between seasons.

3.3.2 Relationships between Species Availability and Dietary Occurrence

The rate of ingestion and the field abundances of each of the food items throughout the study period were compared (Fig. 3.3a-0. The linear regressions between dietary occurrence and field abundance for each of the food categories revealed that there was very little relationship between the dietary intake of each item and its field abundance. Hence the inter-relationships between the fox's diet and the field abundance of each category were not significant.

• INVERTEBRATES 11 CARRION • RABBITS ~ DASYUAIDS 0 REPTILES • BIRDS ~ PLANT El INORGANIC

UNCORRECTED CORRECTED

Fig. 3.1 Overall dietary composition Chapter 3: Diet 46

The results of the canonical correlation revealed that there was a highly significant inter-relationship between the field abundances of all the dietary categories and the composition of the diet (Hotellings 0.39; F=3.65 Hypoth DF=36, error DF=2006, p< 0.001). The first canonical variate had a correlation coefficient of 0.43, an eigen value of 0.28, and accounted for 70% of the dietary variance. All dietary factors except reptiles and carrion had a significant interaction effect within the diet (Table 3.1).

A) OVERALL DIETARY COMPOSITION WITH SEASON 50

40 w (Jz 30 w 1!1 RABBIT DIET a: a: BIRD DIET ::;) 20 REPTILE DIET (J • (J DASYURID DIET 0 INVERT DIET 10 • c CARRION DIET

0 ,..... CIO CIO CIO CO 01 01 01 CIO CIO CIO CIO CO CIO CO CIO 1- a: z 1- a: z () z a. ::> () z a. ::> 0 <..., < ..., 0 <..., < ...,

B) VERTEBRATE PREY DIETARY OCCURRENCE 40

w 30 (Jz w a: a: 20 1!1 RABBIT DIET ;::) (J BIRD DIET (J REPTILE DIET 0 • 10 0 DASYURID DIET

CIO CO CIO CIO 01 01 C10 C10 CIO CIO CIO CIO z a: z t; z a: < Q. ...,< ..., 0 ..., <{

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The loadings upon the first canonical variate indicated that the presence of rabbits and the absence of dasyurids were the most important factors affecting the composition of the fox's diet (Table 3.1). The field categories that were associated with these dietary influences were the presence of rabbits and the presence of reptiles. Thus rabbits were eaten when the field availability of rabbits was high but dasyurids were not eaten at these times.

The results of the MANOV A investigating the effect of rabbit field abundance upon the diet revealed that there was a significant difference in the ingestion rate of rabbits between the paddocks (Table 3.2). Rabbit field availability also influenced the intake of ground dwelling birds, dasyurids and invertebrates. The differential rabbit ingestion rate for each of the paddocks is illustrated in Fig. 3.4. Chapter 3: Diet 50

Table 3.1: Resulta of Canonical Correlation Analysis comparing species availability and dietary occurrence. (n.s. = not significant)

Eigen Values and Canonical Correlations

Root No. Eigen Percent Cumulative Canonical Value Variance Percentage Correlation

1 0.284 70.13 70.13 0.434 2 0.058 17.39 87.52 0.233 3 0.030 8.94 96.46 0.170 4 0.009 2.80 99.26 0.096 5 0.002 0.72 99.99 0.049 6 0.000 0.01 100.00 0.007

Univariate Regression Analysis of Dependent Variables

Variable R R2 F6,338 p

Rabbit 0.342 0.117 7.467 <0.001 Bird 0.242 0.059 3.514 <0.01 Reptile 0.096 0.009 0.529 n.s. Dasyurid 0.298 0.089 5.501 <0.001 Invertebrate 0.249 0.062 3.722 <0.01 Carrion 0.122 0.015 0.856 n.s.

Correlations between Dependent and Canonical Variables

Variables 1 2 3

Rabbit 0.757 0.105 -0.479 Bird -0.485 0.431 0.088 Reptile 0.099 -0.336 0.038 Dasyurid -0.616 0.252 -0.670 Invertebrate -0.340 -0.838 -0.164 Carrion -0.067 0.129 0.647

Correlations between Independent and Canonical Variables

Variables 1 2 3

Rabbit 0.760 0.552 0.031 Bird 0.152 -0.459 -0.836 Reptile 0.601 -0.692 -0.226 Dasyurid -0.021 0.432 0.143 Invertebrate 0.260 -0.537 -0.783 Carrion 0.307 0.213 -0.757 Chapter 3: Diet 5 1

Table 3.2: Results of MANOVA of dietary occurrence testing for Paddock differences. (n.s. =not significant)

Variable F4,549 p

Rabbit 7.914 <0.001 Bird 2.329 n.s Reptile 0.415 n.s. Dasyurid 3.247 <0.05 Invertebrate 2.008 n.s. Carrion 0.192 n.s.

100

-'#. - 80 ....w 0 LL 0 60 .... 1!1 RAM z WARRENS w ....z • LAMBING 0 0 40 SALT 3 MATING !:: • m m et a: 20

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Fig. 3.4 Comparison of rabbit ingestion rates among paddocks Chapter 3: Diet 52

3.3.3 Yearly, Seasonal and Paddock Interactions

When yearly, seasonal and paddock differences in dietary composition were investigated using a canonical correlation, no significant year by season by paddock interaction effect was found. However, all lower order interactions i.e. season/year (Hotellings 0.115; F=2.09, Hypoth DF=18, Error DF=983, p<0.01), paddock/year (Hotellings 0.259; F=2.39, Hypoth DF=6, Error DF=500, p<0.001) and season/paddock (Hotellings; 0.111, F=2.02, Hypoth DF=18, Error DF=983, p<0.01), were significant.

3.3.4 Yearly and Seasonal Dietary Interactions

Fox dietary composition was examined in relation to season and year (Fig. 3.5a-h). Dasyurids was the only dietary category that contributed significantly to this interaction effect (Table 3.3). An absence of dasyurids in the diet loaded most heavily upon the first canonical variate which accounted for 75% of the dietary variance and which had a canonical correlation of 0.28. Because this was an absence effect, it was reasonable to investigate which items foxes would have been eating when dasyurids were not being eaten. Rabbit was the only category that was ingested in direct inverse proportion to dasyurids and therefore was most likely to be ingested when dasyurids were not being eaten (Figs. 3.6a-e).

3.3 5 Yearly and Paddock Dietary Interactions

The results of the canonical correlation investigating paddock and year dietary effects showed that not all of the dietary categories had a significant influence upon yearly and paddock dietary effects (Table 3.4). Only rabbits, ground-dwelling birds, reptiles and dasyurids were significant. The presence of dasyurids and ground-dwelling birds loaded most heavily upon the first canonical variate and therefore the presence of both of these categories was the most important influence upon dietary intake in different paddocks, in different years. Chapter 3: Diet 53

A) WINTER 1987 E) WINTER 1988

.BIRD• RABBIT • REPTLE F!J OASYURID 0 INVERTEBRATE ·~

B) SPRING 1987 F) SPRING 1988

.BIRD• RABBIT • REPTl.E ~ OASYURIO 0 INVERlEBRATE ·~

C) SUMMER 1987/88 G) SUMMER 1988/89

•am• RABBIT • REPTlE fa OASYURIO 0 INVERTEBRATE ·~

D) AUTUMN 1988 H) AUTUMN 1989

• RABBIT • BIRD • REPTI.E ~ OASYURIO 0 INVERTEBRATE • c:ARflDJ

Fig. 3.5 Dietary composition in relation to season and year Chapter 3: Diet 54

Table 3.3: Results of Canonical Correlation Analysis comparing species availability and dietary occurrence testing for Yearly and Seasonal Effects. Warrens and Lambing Paddocks. (n.s. =not significant)

Eigen Values and Canonical Correlations

Root No. Eigen Percent Cumulative Canonical Value Variance Percentage Correlation

1 0.086 75.07 75.07 0.282 2 0.021 17.87 92.94 0.142 3 0.008 7.06 100.00 0.090

Univariate ANOVA of Dependent Variables

Variable F3,334 p

Rabbit 0.590 n.s. Bird 0.700 n.s. Reptile 1.272 n.s. Dasyurid 4.470 <0.01 Invertebrate 2.522 n.s. Carrion 0.375 n.s.

Correlations between Dependent and Canonical Variables

V~ables 1 2

Rabbit 0.093 -0.403 Bird -0.227 0.300 Reptile 0.011 0.732 Dasyurid -0.650 -0.283 Invertebrate -0.442 -0.228 Carrion -0.036 0.392

3.3.6 Seasonal and Paddock Dietary Interactions

When the interactions between seasonal and paddock dietary interactions were analysed, the results revealed that an absence of dasyurids and reptiles were the most important dietary influences. These were the only two factors that were significant (Table 3.5). Together they accounted for 51% of the dietary variance attributable to season and paddock interactions. Chapter 3: Diet 55

A) 30

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Fig. 3.6 Rabbit ingestion rate in relation to the intake of other dietary categories Chapter 3: Diet 56

D) 30

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Fig. 3.6 cont Chapter 3: Diet 57

Table 3.4: Results of Canonical Correlation Analysis comparing species availability and dietary occurrence testing for Yearly and Paddock Effects. Warrens and Lambing Paddocks. (n.s. = not significant)

Eigen Values and Canonical Correlations

Root No. Eigen Percent Cumulative Canonical Value Variance Percentage Correlation

1 0.147 57.30 57.30 0.360 2 0.055 21.24 78.54 0.229 3 0.027 10.37 88.91 0.162 4 0.017 6.39 95.30 0.128 5 0.011 4.25 99.55 0.104 6 0.001 0.45 100.00 0.034

Univariate AN OVA of Dependent Variables

Variable R R2 F6,338 p

Rabbit 0.202 0.041 2.398 <0.05 Bird 0.273 0.075 4.549 <0.001 Reptile 0.201 0.041 2.380 <0.05 Dasyurid 0.259 0.067 4.051 <0.01 Invertebrate 0.160 0.026 1.478 n.s. Carrion 0.084 0.007 0.400 n.s.

Correb1tions between Dependent and Canonical Variables

Variables 1 2 3

Rabbit -0.392 0.578 0.211 Bird 0.690 -0.090 0.696 Reptile -0.273 -0.720 0.196 Dasyurid 0.656 -0.075 -0.598 Invertebrate -0.174 -0.453 -0.097 Carrion -0.061 0.193 -0.143

3.3.7 Impact upon Native Populations

The daily intake of rabbits, dasyurids, reptiles and ground dwelling birds per adult fox was calculated to be 101.7, 29.15, 25.92, and 14.2 g respectively. These quantities were all multiplied by the density of foxes to convert them to g consumedJkm2. The average weight of individuals of each category was then obtained and so the number of individuals ingested by foxes per square kilometre was calculated. This corresponded to one rabbit and one ground-dwelling bird being eaten every five days and one dasyurid and one reptile being ingested every day per km2. The densities of each of these dietary categories was Chapter 3: Diet 58 calculated to be 120 rabbits/km2, 90 dasyurids/km2, 270 reptiles/km2 and 25 ground-dwelling birds/km2. Foxes thus ingest 73, 402, 128 and 292% respectively, of the rabbit, dasyurid, reptile and ground-dwelling bird populations every year.

Table 3.5: Results of Canonical Correlation Analysis comparing species availability and dietary occurrence testing for Seasonal and Paddock Effects. Warrens and Lambing Paddocks. (n.s. =not significant)

Eigen Values and Canonical Correlations

Root No. Eigen Percent Cumulative Canonical Value Variance Percentage Correlation

1 0.057 51.21 51.21 0.232 2 0.038 34.55 85.77 0.192 3 0.016 14.23 100.00 0.125

Univariate AN OVA of Dependent Variables

Variable F3,334 p

Rabbit 1.382 n.s. Bird 0.033 n.s. ~ptile 4.237 <0.01 Dasyurid 3.952 <0.01 Invertebrate 0.674 n.s. Carrion 1.763 n.s.

Correlations between Dependent and Canonical Variables

Variables 1 2

Rabbit -0.013 0.430 Bird -0.050 -0.024 Reptile -0.504 -0.730 Dasyurid -0.708 0.402 Invertebrate -0.125 0.367 Carrion 0.171 -0.352

3.4 DISCUSSION

When the contents of the seats were corrected for digestibility, carrion was found to be the most abundant item in the diet of foxes. Rabbits were the most important vertebrate prey item, followed by dasyurids, reptiles, and ground-dwelling birds. Invertebrates comprised 10% of the diet and plants and inorganic material were of very little importance. Chapter 3: Diet 59

When the dietary occurrences of each of these items was regressed against its field abundance, there was very little linear relationship between them. However, a canonical correlation showed that there was a highly significant relationship between the field abundances of all the categories and their dietary occurrences.

The canonical correlation indicated that, although carrion was the largest dietary category, it did not have a significant influence on the composition of the diet. Instead, rabbits and dasyurids were the items that most influenced its contents.

The presence of rabbits and the absence of dasyurids (or vice versa) are the most important factors affecting the composition of the fox's diet (Table 3.1). The field category that is most strongly associated with these dietary influences is the presence of rabbits. Rabbits are eaten when the field availability of rabbits is high but dasyurids are not eaten at these times. Because rabbit field abundance is the most important factor influencing the intake of rabbits and dasyurids, the effect of this factor upon the ingestion rate of each of the dietary categories was investigated using a MANOV A. This analysis revealed that there was a significant difference in the ingestion rate of rabbits between paddocks (Fig. 3.4) and that the field availability of rabbits also influenced the intake of dasyurids (Table 3.2).

The results of the yearly and seasonal interaction effect indicate that an absence of dasyurids during certain seasons is an important factor influencing the composition of the foxes' diet. Dasyurids were absent from the diet during the summers of 1987-88 and 1988-9 even though dasyurid field abundances were relatively high at these times (Fig. 3.4d). Rabbit ingestion rates and field abundances were also high in both these seasons (Fig 3.4a) and this suggests that when rabbits are available they are eaten but when they are scarce foxes eat dasyurids, even though dasyurids may themselves be at relatively low densities at this time. Foxes, therefore, prey most heavily upon dasyurids when they are at their lowest density, and are thus at their most vulnerable to the impact of predation. Chapter 3: Diet 60

The yearly and paddock interaction effect was mainly attributable to the presence of dasyurids and ground-dwelling birds. Warrens paddock reveals a relatively low intake of dasyurids in both 1988 and 1989 when compared to Lambing paddock (Fig. 3.7a-f). In 1988 the field abundance of dasyurids in Warrens paddock is similar to that for Lambing paddock and yet the dietary intake is considerably lower. Similarly, in 1989, the field abundance of dasyurids in Warrens paddock is higher than that for Lambing paddock and yet the ingestion of dasyurids occurs at approximately the same level. The main reason for these differences in dietary intake can be explained by other differences within the paddocks. Warrens paddock had a substantial population of rabbits whereas there were relatively few in Lambing paddock (Fig. 3.8). Because dasyurids are eaten in inverse proportion to rabbits (Fig 3.9), it is assumed that foxes prey upon rabbits when they are available, and only eat dasyurids when rabbits are unavailable. Thus dasyurids were probably not eaten in Warrens paddock in 1988 and 1989 because the preferred prey of rabbits was freely available. In contrast, Lambing paddock did not have many rabbits present and so dasyurids and ground-dwelling birds were, as a consequence, more important in the diet there. The reason for the increased ingestion of ground-dwelling birds in Warrens paddock in 1989 is not clear.

The season and paddock interaction effect can be attributed to an absence of dasyurids and reptiles. Dasyurids were scarce in the diet in Warrens paddock in spring and in summer whereas reptiles were very scarce in the diet in Lambing paddock in spring and in Warrens paddock in summer. These relationships are most likely to be due to foxes in Warrens paddock preferentially eating rabbits when they are abundant in spring and summer and thus not ingesting very many dasyurids and reptiles (Fig. 3.10). There were, however, very few rabbits in Lambing paddock and so the absence of reptiles in the diet there in spring must be due to other factors. Invertebrates were heavily preyed upon at this time and these may have been eaten in preference to reptiles. Chapter 3: Diet 6 1

(a) 284.06 312.08 100 w (.) z

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Fig. 3. 7 Dietary intake and field abundances for each dietary category for Years 1 and 2 Chapter 3: Diet 62

(d) 20 w u 16 zc( zQ i 12 c( w • DASYURIO DIET YR 1 ~ 8 0 DASYURIO FIELD YR 1 w a: • OASYURIO DIET YR 2 a: 0 DASYURIO FIELD YR 2 :::»u 4 u 0 0 WARRENS LAMBING

(e) 60 w () z 50 c( 0 z 40 ~ CD c( w- 30 INVERT DIET YR 1 ()z •0 INVERT FIELD YR 1 w INVERT DIET YR 2 a: 20 a: •0 INVERT FIELD YR 2 ~ () 10 (,) 0 0 WARRENS LAMBING

(f) 40 w () z c( 30 z0 ~ Ill c( CARRION w 20 DIET YR 1 (,)- •0 CARRION FIELD YR 1 z w CARRION DIET YR 2 a: •0 CARRION FIELD YR 2 a: 10 ~ (,) () 0 0 WARRENS LAMBING

Fig3.7cont Chapter 3: Diet 63

320 280 w (Jz 240 cC z0 200 ~ CD 160 cC m WARRENS 120 ... LAMBING Gi • CD 80 cC a: 40

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Fig. 3.8 Relative field abundance of rabbit in Warrens and Lambing paddocks

40 w (J z w a: 30 a: ::J (J 0 0 20 m RABBIT a:> cC • DASYURID ...w 10 i3

0 ,.._ 0) CO CO a) CO 0) 0) CO CO CO a) a) a) CO a) 1- 1- z (.) z a: z (.) z a: Cl. ::) Cl. ::) 0 ..,< < .., 0 ..,< < "")

Fig 3.9 Dietary intake of rabbits and dasyurids with season Chapter 3: Diet 64

Of the vertebrate prey species that foxes ingest, the rabbit is by far the most important item. The field availability and rate of ingestion of this species largely determines the rate of predation upon all other species. The rabbit was found to be a preferred prey item and it was ingested even when its field availability was low. In general, rabbits are eaten when they are most numerous, mainly in spring and summer. This may be due to myxomatosis being most prevalent during these seasons (pers. ohs.) and foxes being able to easily catch debilitated rabbits.

Many previous studies have concluded that foxes either do not relish reptiles, e. g. Ryan and Croft 1974 and Baker and Degabriele 1987, or else they do not to ingest many birds (Mclntosh 1963, Baker and Degabriele 1987). The conclusions reached from this study are that foxes will eat any vertebrate prey that is available, depending primarily upon its availability but also upon the foxes' preference for certain items. Ground-dwelling birds and reptiles were both found to be important in the diet of foxes in the arid zone and this may be a reflection of the species composition that is available to foxes in this area.

Rabbits have been found to be the preferred prey species in other analyses of fox diet. In Australia, Mclntosh (1963), Coman (1973), Brunner et al. (1975) Bayly (1978), and Seebeck (1978) have all found that rabbits were the foxes' main prey item and similarly, in overseas studies, Scott and Klimstra (1955), Englund (1965b), Frank (1979), Reynolds (1979) and von Schantz (1980) have all found that rabbits were the preferred prey species.

Other prey species have been found to be the preferred prey item in other dietary studies. Goszczynski ( 197 4) found that small rodents were a constant component of the diet of foxes and they were eaten independently of their population density. Macdonald (1977b) and Lever et al. (1957) found that foxes preferred Microtus (Microtinae) to Clethrionomys and Clethrionomys was preferred to Apodemus l:J" '"1

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(Murinae). Jones and Theberge (1983) found that snow-shoe hares were the foxes' preferred prey item. In Australia, Green and Osboume (1981) analysed the diets of foxes living above the snow-line where there were no rabbits and found that small native mammals formed the main component of the diet. In this case Mastacomys fuse us was preyed upon as heavily as Rattus fuscipes even though it was not as common.

Although the foxes at Fowlers Gap had a preference for rabbits, when the field abundance of rabbits was low, especially in summer 1987-8 and 1988-9, foxes switched their prey preferences to dasyurids, even though the field abundance of these small marsupials was itself low during these times. This pattern of switching from one prey species to another, especially when the field abundance of the preferred species decreases, has been observed by various authors both in Australia (e. g. Mclntosh 1963, Brunner et al. 1975 1976, Croft and Hone 1978, Green and Osboume 1981, Wallis and Brunner 1986 and Catling 1988) and overseas (e. g. Cook and Hamilton 1944, Scott and Klimstra 1955, Goszczynski 197 4, Reynolds 1979 and Yoneda 1982, and Angelstam et al. 1984). The reasons for these switches in prey selection have been attributed to changes in the field availability of the prey item or to changes in the amount of available cover, leading to easier predation.

The degree to which predation affects a prey species depends upon the size of the prey population (Pearson 1966). Predation can only control a population when it is either naturally at a low level or when it has been decreased by some other environmental factor. Murie (1936), Scott (1943), Arnold (1951), Richards and Hine (1953), Korschgen (1959), Lloyd (1980) and Kozena (1988) have all shown that when prey populations are at high densities, fox predation does not have a significant effect. Similarly, in Australia, Newsome et al. (1989) showed that predators (particularly foxes) could control a rabbit population that had been severely decreased by drought but this control is unlikely to last indefinitely because foxes cannot out-breed the rabbit (Pearson 1966). Coman (1973) stated that foxes probably do little to effectively control the overall expansion of the rabbit population even though when rabbit densities are high foxes eat more of them. Similarly, fox predation did not have any significant impact upon M us musculus plagues and it was not until their populations had been Chapter 3: Diet 67 reduced by other factors that foxes were able to have any predatory impact upon their population (Newsome 1969).

Conversely, when predation is effected upon very small or sparsely distributed species, its impact can be intense (Scott and Klimstra 1955, Johnson and Sargeant 1977, Sargeant 1978, Southern et al. 1979, Lloyd 1980, von Schantz 1980, Sargeant et al. 1984, and Kozena 1988). Coman (1973) stated that although the rate ofingestion of some of the less important dietary categories may seem to be relatively unimportant, the actual impact that this degree of predation may be having upon that prey population may not be insignificant. Lloyd (1980) also thought that predation may be significant on some populations in certain circumstances. Scott and Klimstra (1955) studied the relative predatory effects upon several prey species that were all declining in field availability. They found that the dietary occurrence of woodchucks was inversely proportional to their population level whereas predation upon the white-footed mouse and cotton-tails remained the same. Predation upon meadow mice and voles decreased as their populations decreased. Scott and Klimstra's results indicate that as meadow mouse and mole populations declined they reached a comparative level of security against fox predation. In contrast, white-footed mice and cotton tails were preyed upon to the same extent but woodchucks were relatively more available and suffered from predation to an increased extent.

In a similar way fox predation pressure upon dasyurids and ground-dwelling birds was at its greatest even when their population densities were at their lowest. Although the estimates of the amounts of each vertebrate prey that was ingested per square kilometre was very high, the relative degree of predation upon each prey type was revealed. Rabbits only suffered a 73% loss of population every year whereas reptiles lost 128%, ground-dwelling birds 292% and dasyurids 402%. Thus dasyurids suffer more than five times as much from fox predation as rabbits do whereas ground-dwelling birds suffer four times as much and reptiles nearly twice as much. These relative indices of fox 'control' of prey populations do not consider the age or the health of the individuals that were ingested and thus the actual impact upon the populations dynamics can only be surmised. Nevertheless, foxes are Chapter 3: Diet 68 having a much higher impact upon dasyurids and ground-dwelling birds than they are upon reptiles and rabbits. This predation pressure can only be enhanced during times of environmental stress such as drought, and so foxes may be responsible for maintaining the populations of these native species at very low levels.

The availability of suitable cover has been correlated with the survival of several prey species (e. g. Mclntosh 1963, Coman 1973, Christensen 1980, Kinnear et al. 1988). Mclntosh (1963) concluded that the lack of occurrence of small mammals in the diets of foxes in some areas was a reflection of the decrease of these elements in the fauna, particularly the ground-dwelling marsupials. Coman (1973) and Brunner et al. (1975) concluded that more native fauna was taken by foxes in areas of less disturbance because in forested areas there were more native species. Possibly the extent of cover that undisturbed areas provide enables some species may have been able to remain therein and so avoid fox predation. Kinnear et al. (1988) concluded that rock crevices were vital in the survival of rock-wallaby populations because they protected them from fox predation whereas species that did not use this type of protection declined or went extinct.

A further factor that may influence the predatory impact that foxes have upon prey populations is their predilection for surplus killing. Kruuk (1972b) describes this phenomenon and discusses a gull colony where it was expected that the entire population would be exterminated because fox density there was not limited by the number of gulls but instead was reliant upon far more numerous rodent populations. Macdonald (1977b) reported that the foxes he monitored would kill food that they did not particularly relish and which they would then cache. This behaviour was attributed to them putting food aside in case they did not catch anything more palatable and Macdonald (1977b) concluded that because of this behaviour foxes could have a significant predatory impact upon populations that were not significant in their diet. Foxes were known to continue to kill even when they had eaten their fill. Surplus killing was also reported by Petersen (1982) who found that foxes wantonly killed a substantial number of breeding tufted puffins and it was felt that if this behaviour continued a dramatic decline in the puffin population could result. Chapter 3: Diet 69

Fox predation is exacerbated in the arid zone by the fact that foxes are able to increase their density out of all proportion to that of the native species by taking advantage of rabbit availability, especially when conditions are favourable. Foxes are then able to switch their predation pressure from rabbits to other prey species which enables them to maintain their populations even during severe shortages of certain prey species such as during drought. As a consequence there is more predation upon the prey populations than they can withstand. This phenomenon is further enhanced in the arid zone where productivity is low and where the habitat is already marginal for maintaining viable populations of metabolically expensive organisms (Pianka 1986). Any decrease in the carrying capacity of the area would result in more extinctions here than in more mesic habitats (Pianka 1986). Predation pressure may also be enhanced by the presence of rabbits which directly compete with native herbivores for food, or, just as importantly, may destroy the cover that the native fauna requires to avoid falling prey to foxes.

The conclusions that are reached from this analysis of fox dietary intake are that foxes are having a significant predatory impact upon the native prey species at Fowlers Gap. Foxes are able to increase to very high densities by preying upon rabbits which are readily available as a major food source. When drought, seasonal variation or myxomatosis reduces the rabbit density, foxes are then able to have a considerable predatory impact upon the other vertebrate prey species by switching to prey upon these species especially when their densities are low. The impact that foxes are thus able to have upon these species is high even though they may not appear to be particularly important in the composition of the fox's diet. This style of feeding behaviour is one of the main reasons for the foxes' extraordinary success in Australia and it probably accounts for the demise of many native species. CHAPTER4

POPULATION PARAMETERS AND DENSITY

4.1 INTRODUCTION

The age of a fox can be estimated using a variety of techniques and a comprehensive summary of these is given by Harris (1978). Harris (1978) discusses the advantages and limitations of each technique and identifies which techniques are appropriate for determining the actual ages of foxes and which are more appropriate for separating juvenile and adult foxes. Juveniles may be separated from adults by examining the size of the pulp cavity of their canine teeth. This cavity decreases in size with age, as the dentine is deposited, (Harris 1978) and thus if an fox has a pulp cavity greater than 50% of the diameter of the tooth at the gum line, it can be assumed to be a juvenile. If the pulp cavity is less than 20% of the tooth diameter, the fox can be assumed to be at least two years old (Coman 1988).

The timing of the closure of the basicranial sutures has been used to estimate the ages of young foxes (Churcher 1960). The basioccipital/basisphenoid (BO/BS) suture normally closes during the first year (Churcher, 1960) and the presphenoid-basisphenoid (PS/BS) suture then closes during the second year. If this second suture is Chapter 4: Population parameters and density 7 1 found to be open or closing the individual can be considered to be in its second year (Coman 1988).

The technique that has been found to be most reliable in giving an actual age to foxes involves examining the incremental lines that occur in the cementum of a fox's teeth (Jensen and Nielsen 1968, Johnston and Beauregard 1969, Grue and Jensen 1973, Johnston et al. 1989). Cementum is deposited in bands on the roots of the teeth each year, with bands in summer being light coloured and those deposited in winter being dark coloured (Larson & Taber 1980). These layers are deposited so that the ones from earlier years are close to the dentine, whereas those from later years are deposited on the exterior of the root. Determining the number of annuli in the cementum involves counting the number of dark lines (Grue and Jensen 1973). Although the actual physiological processes that determine the rate of deposit of these lines are not fully understood, they have been found to be fairly accurate in determining the actual age of the fox (Grue and Jensen 1973). They are particularly useful because they are unaffected by changes in physiological state such as pregnancy, and they are independent of the sex of the animal and from the specific environmental conditions present when they are formed (Larson and Taber 1980).

A test of the accuracy of this method was undertaken by Grue & Jensen (1973) who examined the annuli in the teeth of 135 foxes of known age. They found that there was some inaccuracy in the interpretation of fox ages using this technique when the animals were between 2 and 3 years of age and this occurred because it was impossible for them to read the number of annuli due to indistinct lines. However, where the number of lines could be delimited clearly, the estimated age was within one year of the known age. Alien (197 4) also investigated the agreement between the number of annuli and the ages of 95 foxes of known age and found 100% agreement between the ages predicted by the annuli and their actual age.

Because foxes are monoestrous, cubs are born at approximately the same time each year. Thus when foxes are shot in winter, their ages are separated by yearly increments. This makes ageing more straightforward because no intermediate age classes are present. Chapter 4: Population parameters and density 72

The number of cubs produced by a fox population each year has been attributed to the number of vixens breeding, rather than to changes in the average litter size of each vixen (Harris 1979, Harris and Smith 1987). Thus the number of vixens that are barren varies with the year. Various authors have reported changing degrees of barrenness in their fox populations (Table 4.1).

Table 4.1: Rates of baiTenness in different localities

Author Location Rate of barrenness

1) Sheldon (1949) New York State 5% 2) Mclntosh (1963b) Canberra, ACT 3% (pseudopregnant) 3) Fairley (1970) Ireland 10% 4) Lloyd (1975) Wales 14to29% 5) Abies (1975) U.S.A. 16% of yearling vixens 6) Ryan (1976) N.S.W 0.01% 7) Harris (1979) London, U.K 52%

High rates of barreness have been attributed to both a lack of available food (Englund 1970) and to high population densities (in the presence of ample food supplies) (Harris 1979). (Macdonald 1980a) suggested that social control of the production of litters of cubs occurs when extremes of conditions prevail.

The density of foxes within an area is difficult to measure accurately. Instead, estimates of fox density are usually made and a variety of techniques have been developed for this purpose. One method of estimating density involves censusing all the cub rearing dens within a certain area (Chirkova 1941, Stubbe 1980, Coman et al. 1991) and from the number of litters of cubs present, the number of adult foxes residing there can be calculated. This method is restricted in its application because all the possible den sites within an area must be known and so it is inappropriate for use over large areas or where there is very thick vegetation. Chapter 4: Population parameters and density 73

Other methods of density estimation include investigating the number of tracks present at scent stations (Scott 1941b), the capture rate of leg hold traps in a standardised trap line (Wood 1959), the trap nights-per -fox method (Parker et al. 1957), changes in the number of foxes killed (Hewson 1984) and estimates from culling statistics (Homolka and Mrlik 1989). Fox densities have also been estimated using bounty records (Sheldon 1950, Scott 1955a, Korschgen 1959 and Phillips 1970). Because many of these techniques are not very reliable and because environmental conditions and habitats vary, it is difficult to make accurate comparisons of fox density between different areas.

Although the fox is widely distributed in Australia, the density of foxes has been studied very little. There are very few estimates of fox abundance and these are usually based upon fairly limited data (Table 4.2).

Table 4.2: Fox densities in Australia

Author Location 'Density'

Marlow 1958 S.E. Australia 2.5 foxes/km2 (calc) King & Smith 1985 W.A. 0.2-1.8 foxes/1000 km King & Wheeler 1985 W.A. 0.8-4. 7 foxes/lOO km Coman (cited in Victoria 1.5 foxeslkm2 Newsome& Coman 1989) Newsome et al. 1989 Yathong N.S.W. 0.5 to 3 predatorslkm2 Coman et al. 1991 Victoria 3.0-3.9 foxesJkm2

4.2 MErHODS

The carcases of foxes that had been shot with a .222 rifle were used to obtain reproductive, mortality and age structure data. These samples were obtained from the properties neighbouring Fowlers Gap in the winter of 1988 and from the actual study site in the winter of 1989. Foxes shot outside the study area were killed for their skins and so no deliberate sex or age bias was applied to the sample. Because young, naive foxes may be more likely to be shot than more experienced foxes (Coman 1988), the age structure of this sample could possibly be biased Chapter 4: Population parameters and density 74

in favour of younger animals. However, because no other method of obtaining population data was available, this system of obtaining specimens was used.

4.2.1 Ageing Techniques

Foxes were initially screened to determine whether they were juveniles or adults. This was done by examining their basicranial sutures and the relative size of the pulp cavity of their canine teeth. Individuals whose pulp cavity was greater than 30% of the tooth diameter were classed as first year animals and unless their BO/BS and PS/BS cranial sutures were closed or closing, their teeth were not examined for cementum annuli (Coman 1988).

Foxes classed as adults by the previous two techniques were aged more exactly by examining the cementum annuli of their canines. Canine teeth were carefully removed from the skulls and a section approximately 1 mm in width was cut from the root apex, approximately 3 mm from the root tip (Coman 1988). Canine teeth were used due to their suitable size even though Harris (1978) states that sections through premolar teeth give more readily interpretable annuli. The tooth section was then hand ground until it was about 20-30 um in width (Frost 1958). Sections were decalcified and stained using the technique described in (Johnston et al. 1989). The sections were then examined for the presence of incremental annuli using an ultraviolet microscope with a 40X objective. No difficulty in interpreting the annuli was experienced during this study, perhaps because all the animals were shot during winter which enhances the identification of the annuli (Harris 1978).

4.2.2 Placental Scars

The fecundity of vixens was estimated by counting the number of placental scars that were present in their uterii. These scars indicate the number of embryos that were implanted in each uterine horn during the vixen's last pregnancy and they are reported to persist until the following oestrous period (Englund 1970, Fairley 1970). Englund (1970) stated that these scars could be graded depending upon whether Chapter 4: Population parameters and density 75 the embryo was carried until full tenn, whether the embryo was resorbed during the pregnancy, or whether a scar was still present from a successful earlier pregnancy. In his specimens the scars varied in colour from almost invisible to completely black. Placental scar counts have been found to slightly underestimate the size of litters (Lindstrom 1981), however, in the absence of any better techniques they were used here nevertheless. In this study the uterii were opened lengthways and the number of scars present in each uterine horn was counted. No noticeable variation in the colour of the scars was observed and so no resorptions were considered to have occurred.

4.2.3 Sex ratios

The sex ratio of the fox population at Fowlers Gap was obtained from shot individuals. Because many of the foxes that were shot on neighbouring properties were not intact, the sex of each of these animals was not known with certainty. A prediction of the probable sex of each individual was, therefore, necessary. This was done by investigating various measurements of fox skulls which were known to have sexual dimorphism. Churcher (1960) successfully used the ratios of the length of the skull by the mastoid width, versus the mandibular length by the zygomatic width to separate males from females in a sample of known gender foxes. These measurements were obtained for all the fox skulls collected, and a discriminate function analysis was conducted to predict the sex of unknown animals from the measurements of animals of known sex.

4.2.4 Life tables

Once the age and sex structure of the population had been established an age specific mortality table for each sex was calculated so that the life expectancy of an individual could be calculated. A hierarchical log linear analysis was then performed to detennine whether there was any relationship between fox mortality and age, sex or year.

An analysis of the age specific fecundity of vixens was then conducted. This involved using a two-way ANOV A to investigate the Chapter 4: Population parameters and density 76 relationship between the number of placental scars that a vixen bore and her age. This analysis enabled any changes in reproductive potential with age to be identified.

4.2.5 Probability Density Estimations

Density estimates were commenced in September 1986 and were conducted every three months, until July 1989. These estimates were made by driving along pre-determined transects and counting all the foxes that were observed with a 100 W spotlight beam. Each count was replicated three times within a sampling period. An additional count was done in November 1988, just after the rabbits were removed from part of the study site (see Chapter 7). Thirteen counts were, therefore, conducted in total.

To ensure that these counts were conducted in conditions that were relatively comparable, efforts were made to do counts on nights when there was no wind, when the sky was clear and within four hours of the sun setting. No counts were done when it was, or had been, raining because even a small amount of rain made the transects impassable. Lunar phase was investigated to determine whether it had any influence upon fox sightability or activity.

Every time an animal was observed during a count its distance from the observer was recorded, as was the angle between it and the line of travel of the vehicle. The distance of an animal from the transect was truncated at 300 m and the angles were measured to the nearest 15°. These two parameters were then used to calculate the perpendicular distance of the animal from the transect.

The technique used to estimate fox densities was based upon the method described by Burnham et al. (1980). Densities are calculated using the formula AD=(nAft0))/2L where AD is the estimated density, n is the number of animals counted, AftO) is the value of Aftx) (the proposed probability density function) when the perpendicular distance (x) of the animal from the transect is zero and L is the total length of the transect line. Chapter 4: Population parameters and density 77

The calculations for these density estimations were done by program TRANSECT (Laake and Burnham 1980 ). This program was run on the U.N.S.W. Vax 111780 mainframe computer.

Various different frequency distribution functions were investigated to determine which was the most suitable for use with the data set. In each case the resulting generated probability density function was compared with the observed data using a chi-squared goodness of fit test. In nearly all cases the Fourier series estimator provided the best fit with the data and so this was used in preference to the other estimators. This estimator was also appropriate because it has good estimation efficiency for small sample sizes and it is model and pooling robust (Burnham et al. 1980).

The estimator of the probability density function at 0 distance for the Fourier estimator series is:

m ftO)= llw* + L "ak i=l where w* is the maximum perpendicular distance observed and

n "ak=21(nw*)[L cos (k 1txi/w*)] i=l where k=1,2,3 ... m and m is the number of expansion terms.

4.2.6 Changes in Fox Density with Season, Paddock and Year

To ensure that statistically meaningful comparisons could be made between fox density estimations for paddocks, seasons and years, sightability curves for each sampling period were compared. A sightability curve usually approximates a monotonically decreasing function with most individuals being seen closest to the observer and decreasing as the distance from the observer increases. Changes in fox sightability can occur due to changes in vegetation height and changes in fox behaviour, due most likely to movement away from an approaching vehicle. A G-test was used to calculate whether there Chapter 4: Population parameters and density 78 were any significant differences between the sightabilities of foxes between any of the sampling periods.

4.2. 7 Relationships with Prey Species Densities

To determine whether fox density was dependent upon the availability of food, fox and prey abundance interactions were investigated. This involved regressing the field abundances of each dietary category against fox density. Linear, exponential, geometric and quadratic regressions were all used. In each of these cases only fox density and the abundance of a single food category were investigated.

To determine whether there were any interactions between the availabilities of the food categories and the density of foxes, a multiple regression was also performed. Fox density was used as the dependent variable and the field abundances of the food items formed the independent variables.

A multiple regression was also performed in which fox density was regressed against the dietary occurrences of each of the dietary categories. This was done to investigate whether fox density in an area could be predicted by, or related to, the dietary intake of foxes in that area. Again fox density formed the dependent variable and the dietary occurrences of the dietary categories formed the independent variables.

In both these multiple regressions the independent variables were log transformed so that they were normally distributed and had homoscedastic variance. These estimates were also converted to z scores because each was measured on a different scale and this conversion enabled meaningful direct comparisons to be made.

4.3 RESULTS

4.3.1 Sex ratios

One hundred and nineteen fox carcasses were collected. The sex of 81 of these was known with certainty. The sex of the other thirty eight individuals was predicted using a discrimination function analysis. Chapter 4: Population parameters and density 79

This analysis had an accuracy rate of 72.73% when it was used to determine the sex of known individuals. It was assumed that the sexes of the unknown individuals would be determined with a comparable level of accuracy.

An estimated sex ratio of 17F:20M (i.e. 1:1.18) for 1988 and of 45F:37M (1:0.83) for 1989 was obtained. A chi-squared test revealed that these were not significantly different from a 1:1 ratio.

4.3.2 Age structure

The age structure of the foxes that were shot at Fowlers Gap is shown in Table. 4 3a. The ages of the animals represented were estimated from skull suture closures and from the number of cementum annuli present in their teeth. The number of individuals in each age class was converted to a percentage of the total population (Table 4.3b). The age structures for fox populations in other areas are also included. The population age distribution for the foxes at Fowlers Gap most closely resembles that of the populations of mid Wales and London (Table 4.3b).

Table 4.3a: Age structure for male and female foxes at Fowlers Gap

Age Males Females Total ( rs)

0-1 76 76 152 1-2 40 32 72 2-3 12 18 30 3-4 3 4 7 4-5 3 2 5 5-6 1 2 3 6-7 2 0 2 7-8 1 0 1 Chapter 4: Population parameters and density 80

Table 4.3b: Age structures of fox population&(%) (Data for West Wales and Mid Wales from Lloyd (1980a); Data for London from Harris (1977); Data for Denmark from Jensen and Nielsen (1968); Data for Ireland from Fairley (1969)). Adapted from Lloyd (1980a).

Age Fowlers West Mid London Denmark Ireland (yrs) Gap Wales Wales

0-1 55.9 43.0 59.0 52.7 75.0 50.0 1-2 26.5 23.0 24.5 27.4 11.0 25.0 2-3 11.0 13.0 10.5 9.5 7.0 13.0 3-4 2.6 11.0 4.5 4.4 3.0 6.0 4-5 1.8 2.5 2.0 3.0 1.0 3.0 5-6 1.1 4.5 0.8 2.4 1.5 1.5 6-7 0.7 0.6 0.3 0.8 7-8 0.4 1.3 0.3 8-9 0.6

4.3.3 Fecundity

Placental scars were found in thirty two vixens and their frequency distribution calculated (Fig. 4.1). The results of the two way ANOV A investigating differences in reproductive productivity for vixens of different ages revealed that there was no significant difference in the number of placental scars produced by vixens of different ages (Table 4.4). When the ages of vixens were pooled into first year, second year and 'older' categories, there was still no significant relationship between age and fecundity.

Table 4.4 Number of placental scars produced in each age class

Age Number of (yrs) placental scars 1-2 0-7 2-3 2-9 3-4 1-5 4-5 3 5-6 4

A total of 85 placental scars were produced by thirty seven vixens. If a 1:1 birth sex ratio is assumed, then 42.5 female cubs were produced by these 37 animals. A ratio of 1.33 female cubs per vixen is thus obtained. If this ratio is extrapolated to the 57 vixens from 1988 and Chapter 4: Population parameters and density 8 1

8 > (,)z 6 w :;:) 0 w 4 a: "" 2

0 0 2 3 4 5 6 7 8 9 PLACENTAL SCARS

Fig. 4.1 Frequency distribution of placental scars

1989, including the individuals that had no reproductive data, then 76 female cubs and 76 male cubs were present in the 0-1 age class for the pooled population. The mean litter size for arid zone foxes is 2.66 cubs.

4.3.4 Life Table

The life table (Table 4.5) was produced from the information obtained on the sex ratio, the age structure and the fecundity rate of the population. When a hierarchical log-linear analysis was performed on this data, comparing sex, age and year effects, it was found that the only significant result was for the age and sex interaction effect CX2=9.59 df=2 p<0.05). The number of males and females found in the second year age category {1-2 years) were found to be significantly different. Thus there were fewer males surviving in this age class than females. However there was no significant difference in the older age/sex classes and so once this decrease in male survivorship had occurred there was no further sex specific mortality.

4.3.5 Overall Fox Density in the Study Area

The mean density of foxes at Fowlers Gap is estimated to be 0.93 foxeslkm-2. This figure is an overall density estimate and is Chapter 4: Population parameters and density 82 irrespective of paddock, season or year effects. No significant differences in fox sightability were found to occur between paddocks and between years but there was a significant difference in sightability between seasons. July 1988 was significantly different from the other seasons (G=17.3; df=9; P< 0.05). When this season was removed from the analysis there were no further significant differences in sightability. Direct comparisons could, therefore, be made between the density estimations in different paddocks and in different sampling periods. Fig. 4.2 summaries the density estimations obtained for all paddocks, seasons and years. A one-way ANOVA of fox density per year, using the five paddock densities as replicates, revealed that there were no significant yearly differences in fox density.

Table 4.5: Life Table for red foxes at Fowlers Gap.

Age Class Frequency Survival Mortality Mortality Survival (l:t) (dx) Rate (qx) Rate (px)

MALES 0 76 1.000 0.474 0.474 0.526 1 40 0.526 0.368 0.700 0.300 2 12 0.158 0.119 0.753 0.247 3 3 0.039 0.000 0.000 1.000 4 3 0.039 0.022 0.564 0.436 >4 4 0.017 0.017 1.000 0.000 FEMALES

0 76 1.000 0.592 0.592 0.408 1 31 0.408 0.184 0.450 0.549 2 17 0.224 0.185 0.826 0.174 3 3 0.039 0.013 0.333 0.667 4 2 0.026 0.013 0.500 0.500 >4 3 0.013 0.013 1.000 0.000

4.3.6 Fox Density Variations between Paddocks

When a one-way ANOV A was used to compare the densities of foxes in the five different paddocks, using the three years as replicates, it was found that there were no significant differences between the paddocks. Because rabbit removal had been conducted in Ram paddock which may have influenced the density of foxes therein (see Chapter 6), this paddock was removed from the analysis. The analysis was rerun and the results obtained were still not significant. Chapter 4: Population parameters and density 83

4.3. 7 Seasonal Fox Density Variations

A one-way AN OVA of fox density per season, using the three year's data as replicates revealed that there was a significant seasonal variation in fox density (F3,39=3.68, P<0.05). Density is at its maximum in summer and at its lowest in winter (Fig. 4.2).

2.5 :&- ~ 2.0 a en - 1.5 -> u;... z 1.0 w Q )( 0.5 0u. 0.0 ...... ,.... CO CO CO CO 0) 0) 0) CO CO CO CO CO CO CO CO CO CO

,.. C') 0) N .., 0 .... N ~ -.... - -CD - -,.. --...... -.... -.... ---......

Fig. 4.2 Overall fox density in the study area

4.3.8 Effects of other Environmental Variables

4.3.8.1 Food availability

The results for the linear regressions between fox density and the field abundances of each dietary category revealed that there was no significant relationship between density and the availability of different prey types. A similar result was obtained for each of the other types of regression, i.e. exponential, geometric and quadratic. There was no relationship between fox density and the abundance of their prey species.

The results of the multiple regression were not significant and thus the availability of food did not explain a significant proportion of Chapter 4: Population parameters and density 84

the variance in fox density. In fact only 39% of the variance in fox density was accounted for by the field abundances of the food categories.

The multiple regression analysis comparing fox density and dietary occurrences of food categories indicated that there was a significant relationship between fox density and their diets (F6,660=2.54; p<0.05). However, because the R2 for this relationship was only 0.02, it was concluded that this significant result was obtained due to the magnitude of the data set rather than to there actually being any significant inter-relationship between these two factors. The results indicate that fox density in an area cannot be predicted by the diet of the foxes within that area.

4.3.8.2 Lunar phase

The number of foxes counted during the different phases of the moon were analysed using a one-way ANOV A. Only three phases of the moon were investigated because no counts were undertaken when the moon was in its first quarter. The results of the ANOVA were not significant and indicate that there were no significant differences in estimations of fox density due to the influence of the lunar cycle.

4.4 DISCUSSION

The age structure for the fox population at Fowlers Gap indicates that mortality is high in age classes 0-1 years and 1-2 years and that it peaks in age class 2-3 years. There is little difference between the longevity of male and female foxes, though males are more likely to die in the 1-2 year age class than females are. This result may be attributable to the more common dispersal behaviour of male foxes which makes them more prone to misadventure and mortality during the time they are seeking a home range of their own. This generally occurs when they are 1-2 years of age In contrast, female cubs tend to disperse less than males and often remain in their natal home range (Harris and Trewhella 1988). Once male cubs have established their own home ranges, their longevity is no different to that of vixens. Although these results were obtained from a shot sample, its use in estimating age specific mortality is vindicated by the fact that the Chapter 4: Population parameters and density 85 greatest relative mortality does not occur in the youngest age class as would be expected if the probability of shooting a fox was inversely proportional to its age and experience.

The observed sex ratios of 1:18 and 1:0.83 are similar to other estimates of fox sex ratios in Australia: e. g. Mclntosh (1963b) who found a ratio of 1:0.85 and Ryan (1976) who found a ratio of 1:0.93. These results indicate that generally there is no deviation from the expected 1:1 sex ratio.

Various studies have indicated that age-specific fecundity for red foxes occurs (e. g. Pearson and Enders 1943, Sheldon 1950, Layne and McKeon 1956a 1956b, Venge 1959, Englund 1970, Harris 1979, Alien 1984). This phenomenon was not, however, observed in this study and the results obtained indicate that from their very first litter, yearling vixens are just as likely to produce the same number of cubs as older vixens. However, from the data collected it is not possible to determine whether the cubs that younger vixens produce have the same likelihood of survival as the cubs of a more experienced vixen and so there may be some other factors affecting cub survival.

The maximum number of placental scars that were observed for any one individual during this study was nine and these were borne by a vixen whose age was estimated to be two years. This observation is not exceptional as records of up to 17 cubs in one litter have been reported (Holcomb 1965). The normal litter size for red foxes is between four and ten cubs (Hamilton 1943).

The rate of resorption of embryos must be taken into consideration when estimating litter sizes from placental scar counts. Layne and McKeon (1956) found that vixens in different years and in different areas had differing levels of embryonic resorption. Foxes in one of their study sites showed no resorption, whereas in their other two study areas the resorption rates were 5.2% and 9.9%. The results of placental scar examinations from other Australian studies indicate that resorption of foetuses is comparatively rare here. Mcintosh (1963b) found only one scar that was possibly caused by resorption and Ryan (1976) found only six out 142 vixens with placental scars in which Chapter 4: Population parameters and density 86 resorption had occurred. Because no lighter coloured scars were observed in any of the placenti that were examined in this study it was concluded that no resorption had occurred and so this factor was not included in the estimation of fecundity.

The mean litter size of2.66 cubs is lower than the 3.7 found by Ryan (1976) for foxes shot in N.S.W generally and the 4.3 recorded by Mclntosh (1963b) for foxes in the Canberra district. Because mean litter size and food availability have been shown to be correlated (e. g. Schofield 1958, Englund 1970, Lindstrom 1980 1983 1989, von Schantz 1980), the low reproductive output of foxes in the arid zone may be a reflection of harsher nutritional and environmental conditions found in this area. This hypothesis is supported by Ryan (1976) who states that the lower litter sizes that he obtained in comparison to Mclntosh's were a reflection of differing environmental conditions in the areas from which the samples were obtained.

Australian foxes generally have smaller litter sizes than foxes found in Britain and North America, though there is some variation in the number of cubs produced in different regions (Table 4.6).

Table 4.6 Variations in litter sizes with location

Study Author Litter size Location

Sheldon (1949) 5.3 New York State Switzenberg(1950) 4.9 Michigan Layne and McKeon (1956b) 4.6 New York Schofield (1958) 4.6 and 5.5 Michigan Englund (1970) 3.1 to6.6 Sweden Fairley (1970) 5.41 Ireland Lloyd (1975) 4.3 Britain Storm et al. (1976) 7.1 Iowa Ryan (1976) 3.7 N.S.W. Pils and Martin (1978) 5.6 Wisconsin Harris (1979) 2.1 to4.7 London Nelson and Chapman (1982) 5.0 Maryland Chapter 4: Population parameters and density 87

Without a comprehensive assessment of the food resources that are available to foxes in each of these areas, and without a knowledge of the environmental extremes and stresses that each fox would face, it is not possible to make any conclusive statements about the reasons for the observed differences in fox litter sizes. Also the different levels of shooting and trapping faced by each population would need to be assessed before any comparisons can be made.

The ratio of adult to sub-adult foxes gives an indication of the level of productivity that the population must maintain to keep the population density relatively stable (Lloyd 1980a). This level of productivity varies with the level of environmental stress and/or man imposed control measures to which the population is subjected. Lloyd (1980a) states that for the three populations that he studied, each of which had a different density and was under differing levels of control, these ratios changed. For the fox population in Pembrokeshire where the population density was high and control was negligible, the ratio of adults to sub-adults was lowest at 1:0.75. The mid-Wales population had a lower density and higher level of control than the Pembrokeshire population and consequently had an adult to sub-adult ratio of 1:1.35. The fox population that Lloyd studied on the Isle of Skye had a low density and was under considerable control pressure. Its adult:sub-adult ratio was 1:2.03. Similarly, Phillips (1970) found that in areas with little control in Iowa the adult to sub-adult ratio was 1:2.56 which was considerably lower than that for areas of high control intensity where it was 1:5.59. The ratios that Phillips presents are probably higher than those quoted by Lloyd because his samples were obtained when there would have been more juveniles in the population.

When the ratio of adult to sub-adult foxes is calculated for the fox population at Fowlers Gap a ratio of 1:1.27 is obtained. The productivity of the fox population is thus comparatively low. This result can be accounted for by the favourable conditions and absence of control during this study which consequently meant that the fox population density did not vary significantly. It can thus be concluded that foxes in the arid zone must sustain a fairly constant but not particularly high level of productivity to maintain their density under favourable conditions. Chapter 4: Population parameters and density 88

This scenario could presumably change quite dramatically if the population was subjected to a severe drought or other ecological adversity.

The density estimates of foxes at Fowlers Gap reveal that there are, on average, 0.93 foxes per square kilometre (one fox every 107.5 ha). This density estimate is low when compared to the results obtained by Coman et al. (1991) (3.9/km2) and Marlow (1958) but the differences in habitat productivity are sufficient to account for this difference. Coman's densities were obtained in prime fox habitat in Victoria and Marlow's estimates were obtained from the more mesic parts of south eastern Australia. Thus the density estimates obtained in this study are consistent with the low productivity and unpredictability of the habitat in the arid zone.

The density estimates that were obtained for September 1987 and July 1989 at Fowlers Gap are lower and higher, respectively, than would be expected if the usual trend for fox density to be highest in summer and lowest in winter was to occur. These observed discrepancies can be explained by the foxes' behaviour during these two periods. In September 1987 the vixens were still probably nursing their cubs and because they were not active, and thus were not counted, the estimate is low. Also, the young would not yet have been recruited and thus the usual spring increase in population density would not yet have occurred. In contrast, the estimate in July 1989 is higher than expected and this may be explained by the fact that this estimate was obtained in the middle of the breeding season when many foxes were particularly active. They were thus more likely to be observed and this influenced the density estimate. In fact, several copulating foxes were observed during this session of counts. It was concluded that at Fowlers Gap, fox density was determined by the availability of food, rather than by social regulation, as reported by Lindstrom (1989) for foxes at high densities.

Although it would be extremely interesting to be able to quantify the factors that caused the decline of the fox population during winter, there is really only circumstantial evidence to suggest the reasons for this decrease. It is most likely that a decrease in the availability of food Chapter 4: Population parameters and density 89

resources in conjunction with the fox's increased metabolic needs to overcome the cold environmental conditions would have led to this decline. Much of this mortality can also be accounted for by the deaths of juvenile foxes that are dispersing and seeking home ranges of their own. The observed low juvenile productivity of the population would suggest that during favourable conditions only sufficient offspring are produced to replace any adults that have died of old age or misadventure and thus the observed decrease in fox density during winter is probably a reflection of the deaths of surplus juveniles that have been born. Their experience in their habitat would be limited and thus they are more likely to perish than the adults are. This hypothesis is supported by the fact that the only radio-collared cub that died starved to death.

Although some of the animals captured or shot in the study site had a small incidence of mange, the population in general was free from this parasite. It was considered to be the cause of death of only one individual. The causes of death of all other individuals were inexplicable, except for one individual that was caught down a rabbit burrow by its radio-collar and starved to death. CHAPTER5

HOME-RANGE ANALYSES

5.1 INTRODUCTION

The aim of this chapter is to describe the home-range use of foxes at Fowlers Gap. The definition of home-range used in this thesis is based upon that ofBurt (1943) and is 'that area which is transversed by an animal in its normal activities of food gathering, mating and caring for young'. To allow comparisons of home-range use between individuals to be made, each home-range estimate includes a time frame and a probability level (see below).

5.1.1 Basic Concepts

Various methods have been devised to determine the perimeters of mammalian home-ranges. The most commonly used is the minimum convex polygon method. However, this technique has several serious drawbacks; however, it is highly sample size dependent, it often includes areas that are not actually visited by the animal under investigation and it provides no information about the relative usage of the different habitats within the home-range (Anderson 1982). Several probabalistic methods of Chapter 5: Home range analyses 9 1 home-range analysis have been developed and these define a utilisation distribution of the data so that a two dimensional relative frequency distribution of an animal's location through time is produced (Van Winkle 1975). Many of these probabalistic methods for determining an animal's home-range (e. g. Calhoun and Casby 1958) rely upon the locational data being normally, as well as symmetrically, distributed. The distributions that are produced 'assume bimodal or even mulitmodal shapes' whilst simultaneously de-emphasising the boundaries of the home-range (Siniff and Jensen 1969). These techniques are inappropriate for the investigation of fox home-range areas and spatia-temporal use of habitat when the underlying home-range area does not approximate a normal distribution (Macdonald et al. 1980, Voigt and Tinline 1980, Dixon and Chapman 1980, Anderson 1982, Harris et al. 1990). Instead, other, non-parametric analyses should be used in an attempt to accurately represent this utilisation distribution.

The Anderson method of home-range estimation was used in this study because it is able to handle large amounts of data generated by radio tracking and because it makes no assumptions about the underlying distribution. This method superimposes a grid onto the distribution of location points and a Fourier transformation series is then used to smooth the resulting frequencies into a probability density function. The Fourier series provides a good estimation efficiency irrespective of the underlying distribution and, therefore, is appropriate for use in estimating space-use distributions in heterogeneous, diverse habitats (Burnham et al.1980) The three dimensional space-use distribution that is produced has troughs representing areas of low activity and peaks representing areas of intense activity (Fig. 5.1). Investigations at any level of probability of home-range use can be undertaken by drawing a plane through the distribution so that the required percentage of the distribution lies beneath the plane. One disadvantage of this technique is that it is slightly biased at high probability levels, especially for small sample sizes (Anderson 1982).

To determine the location of an animal's centre of activity, the Harmonic Mean Centre of the probability density function was calculated. The Harmonic mean centre was used because the arithmetic mean has Chapter 5: Home range analyses 92

Fig. 5.1 A three-dimensional space-use distribution (From Anderson 1982)

several serious limitations: it is not an appropriate measure of central tendency, it is very sensitive to extreme values, and it may not be biologically meaningful (Dixon and Chapman 1980). In contrast, the HMC must lie within the cluster of points of highest frequency of use and it is not greatly influenced by isolated movements within the home-range.

5.1.2 Home-range Studies in other countries

Although many telemetric studies of foxes have been conducted on foxes in other countries it is difficult to make meaningful comparisons between them and to positively identify the reasons for the observed differences in home-range size. Rarely is there sufficient information provided about food availability, population density, and habitat type and productivity (Lloyd 1977a). The number oflocational 'fixes' that were used in the calculation of the home-range area and the time frame over which the investigation was conducted are also commonly omitted. Thus the direct comparison of home-range areas of foxes monitored in different habitats and even different continents is inappropriate and misleading. However, some generalisations are appropriate and these include: larger home-range areas occur in more variable environments than in stable Chapter 5: Home range analyses 93

Table 5.1 Summary of home-range areas (Adapted from Trewhella et al. (1988))

Home-range Location Reference (km2)

0.45 Bristol, UK Harris (1980, 1981) Harris & Trewhella (1988) 1.65 London, UK Page (1981) 0.45 Oxford, UK Voigt & Macdonald (1984) 0.7 West Wales Lloyd (1980a) 4.0 Mid Wales Lloyd (1980a) 1.33 France/Germany Zimen (1984) 0.57 Holland Niewold (1980) 1.2 Niewold (1980) 2.55 Niewold ( 1980) 9.28 Niewold (1980) 4.1 Sweden von Schantz (1981) 6.1 von Schantz (1981) 6.0 Englund (1980a,b) 7.0 East Germany Stubbe (1980) 1.02 U.S.A. Abies (1969) 7.0 Sargeant (1972) 9.6 Storm et al. (1976) 5.98 Pils & Martin (1978) 3.9 Tullar & Berchielli (1980) ones and larger areas occur in habitats of low food diversity when compared with species-rich habitats (Lindstrom et al. 1982). Harris (1980) also states that at high population densities foxes have smaller home ranges than at low population densities. Chapter 5: Home range analyses 94

5.1.3 Home-range Studies in Australia

Coman et al. (1991) used the minimum convex polygon and the Anderson methods to compare the home-range areas used by six foxes; three in semi-urban Bendigo, two in woodland/pasture land and one in heavy bushland in Central Victoria. They found that the home-ranges of the semi-urban foxes were smaller than those of the foxes residing in the woodland/pasture. During the 4-8 nights that each animal was tracked, one breeding pair in the semi-urban area shared an exclusive home-range whereas all other foxes had individually exclusive home-range areas.

5.1.4 Dispersal

A comprehensive summary of the dispersal distances travelled by foxes is given by Trewhella and Harris (1988). They found that dispersal distance was positively correlated with home-range size and negatively correlated with population density. It is assumed that in more heterogeneous habitats, individuals move greater distances as they seek out vacant sites (Murray 1967, as cited by Trewhella and Harris 1988).

Juvenile foxes tend to disperse in autumn (Macdonald and Voigt 1985) and it is believed that, in general, juvenile males disperse earlier, more readily and further than juvenile females (Arnold and Schofield 1956; Phillips et al. 1972; Jensen 1973; Storm et al. 1976; Lloyd 1975,1980a). This is not always the case though, and Englund (1980b) found that there was no difference in dispersal rate between the sexes in the foxes that he studied. The difference in the timing of dispersal between the sexes may be related to the differences in the timing of the onset of reproductive activity in foxes (Phillips et al. 1972).

Trewhella and Harris (1988) investigated the major factors influencing cub dispersal and found that small male cubs from large litters were most likely to disperse, especially if they were born in an area of low fox density which reflected that it was sub-optimal fox habitat. The females that dispersed also came from large litters, although there was no Chapter 5: Home range analyses 95 significant difference in the mean litter size of dispersing and non dispersing females.

5.2 METHODS

5.2.1 Hand Tracking

Radio-collared foxes were hand-tracked approximately once a week for the duration of the study. This involved using a hand-held directional antenna (Telonics, model RA-2A) and a scanner/receiver (Telonics, model nos. TS-1, TR-2E) to locate the signal source from some vantage point. The signal was then followed until its strength indicated that the fox was in very close proximity. Special attention was paid to wind direction and as little noise· as possible was made. If a fox was disturbed whilst being observed, it would leap up and bound away and pursuit would be impossible. Often a very loud signal, heard near a known 'lying up' area, would be recorded as the position of the fox.

The fox's position within the field was identified by using a sighting compass and taking bearings from the animal's position to a known landmark. Windmills and survey markers were found to be reliable reference points. At least two angles for each animal were recorded and the animal's position was then calculated by using a program written by Dr D. B. Croft.

5.2.2 STATION TRACKING

Every six months intensive remote tracking of all radio-collared animals was conducted. This involved taking simultaneous bearings on each animal from two fixed-point stations. Each tracking session comprised two five day 'weeks', during which bearings on all animals were recorded every fifteen minutes, twenty-four hours a day. A single rest day was observed between the two tracking 'weeks'.

Varying numbers of animals were tracked during each session, depending upon signal strengths and reception. A 'bench mark' Chapter 5: Home range analyses 96 transmitter was also 'tracked' during these sessions to guard against errors that may have been introduced into the system by variations in temperature and alterations in antenna position (Heezen and Tester, 1967). Ideally ten animals should have been tracked but due to poor signal quality, problems with transmitter tunings, and movement of foxes out of signal range, the maximum number of animals ever tracked at one time was five. This made simultaneous comparisons of the individual's movements difficult.

In between these six monthly intensive tracking sessions, other, shorter station tracking sessions were conducted. These involved tracking for six consecutive nights for six hours each night. The shifts were alternated so that if a dusk to midnight shift was conducted on one evening then a midnight to dawn shift was conducted the following night and vice versa. Thus three complete 'nights' of tracking data each session were obtained.

The tracking stations were built upon the frames of windmills and were approximately 10 m from the ground. Each tower was fitted with two 4m, 8 element antennas (Telonics, model RA-4B, gain=11.8 dBd), mounted on the ends of a 2m cross-beam. These antennas were attached to a 0.5 m diameter compass rose by way of a 4 m mast. The compass rose was marked with 1° divisions and it was rotated across a fixed pointer. The position of an animal was obtained by finding the null point between the two loudest peaks of the signal. This null point indicated that the antennas were pointing directly at the animal; the 'null' occurred because the signals from the two antennas were being combined 180° out of phase using a two-port null converter (Telonics, model no. TAC-5).

The towers were positioned within the study site so as to minimise the error polygon (Heezen and Tester, 1967), and to maximise the signal quality for the majority of the animals. The positions of the animals were calculated by triangulation and were converted to national grid co ordinates of a topographic map. Chapter 5: Home range analyses 97

5.2.4 Data Handling

5.2.4.1 Creating and editing plotfiles

The tracking data for each animal was divided into weekly, seasonal and, if possible, yearly categories. To increase the sample sizes of the hand tracking data sets, the HMC from each of the day's station tracking sessions was added to these data sets. A minimum of at least thirty data points were used in each home-range area estimation.

The data collected from the tracking towers was more heavily edited than that collected by hand because it was far more prone to inherent error (Lee et al. 1985). If a signal was not of good quality (i.e. a null reading >10°) it was discarded. All data were edited using Samuel and Garton's (1985) bivariate normal utilisation distribution test so that outliers could be identified and discarded. For this editing process all points with a weighted Mahalanobis distance value of less than 0.6 were excluded (Campbell1980 as cited by Samuel and Garton 1985).

Care was taken to minimise the effects of autocorrelation of the data (Swihart and Slade 1985a,b) and so locations were collected from evenly spaced time intervals across the entire tracking period to ensure that a true representation of the fox's movements was obtained.

5.2.4.2 Fourier transform method

The edited data sets were used to generate the three dimensional plots of the animals utilisation distributions using the Anderson (1982) method of home-range estimation. For this purpose the 'core' area of an animals home-range, and thus the area where it concentrated most of its activities, was defined by the smallest area under the utilisation distribution that encompassed 50% of the points (MAP 50). Similarly, the 'total' home-range was the smallest area containing 95% (MAP 95) of the data points. Chapter 5: Home range analyses 98

5.2.4.5 Harmonic mean centres

The HMC for each home-range was calculated using the method described by Jaremovic and Croft (1987). This involves calculating the inverse first areal moment of the data which is at a minimum at the harmonic mean minimum. The location of the minimum inverse first areal moment must be estimated by calculating the IFAM from a reference grid. The size of the grid reference squares was based on the accuracy of the location data and so for all foxes a 50 m grid was used.

Investigations were conducted into the shifts of HMCs with time. Two measures were used; maximum shift and cumulative shift. Maximum shift is the distance between the first and last HMCs for the time period under consideration whereas cumulative shift is the sum of all the intermediate distances between successive HMCs. These two measures provide insight into the movement patterns and relative mobilities of the animals that produce them. Maximum shift indicates by how much the home-range area changes over the total time span under consideration whereas the cumulative shift indicates how the intermediate movements are organized. It can thus be determined whether an animal moves its HMC and thus increases its home-range area or whether it increases its daily movements about that HMC to increase its home-range area. Differences in cumulative shift and maximum shift in HMC for males and females were investigated using t-tests. Similarly, differences in maximum shift and cumulative shift between HMCs on a seasonal basis were studied.

5.2.4.6 Home-range overlap

To enable the extent of home-range overlap to be calculated, home range maps for each animals' MAP 50 and MAP 95 areas were calculated. A program written by Dr D. B. Croft was used to convert these maps into grid files. The grid files must be on the same scale so that the home ranges of different animals can be overlapped. A 64 X 64 grid was used which had boundary limits set on a 4 X 4 km scale. Chapter 5: Home range analyses 99

5.2.4. 7 Estimating dispersal distances

To estimate the dispersal distances of cubs, cubs were captured and collared with Telonics radio collars (Model no: 1B5). The movements of these animals were monitored and their dispersal followed. The distance that they dispersed was calculated to be from the point where they were captured as cubs to the HMC of their independent home-range. Their independent home-range was defined to be established once they had established their own movement patterns within a discrete area.

5.3RESULTS

5.3.1 Home-range Size

The mean home-range area·used by male and female foxes during weekly, seasonal and yearly time intervals was estimated (Fig. 5.2a-c). Both total and core home-range areas for these time intervals are indicated. The raw data used to produce Fig. 5.2 is given in Appendix 2a.

5.3.1.1 Sex differences

The differences in home-range use between male and female foxes for the three time frames were investigated using t-tests. The results of these tests showed that there are no significant differences in the areas used by the two sexes at both the total and core levels of investigation, except male foxes have significantly larger total weekly home-ranges than females (t=2.64, df=17, p <0.05).

5.3.1.2 Seasonal differences

The mean home-range areas were compared between seasons (Fig. 5.3). The raw data used to produce Fig. 5.3 is given in Appendix 2b. The total and core home-range areas obtained for all seasons were compared using an ANOVA. No significant difference in home-range area with season was found. Chapter 5: Home range analyses 100

WEEKLY HOME RANGE - 250 :..• 200 c w a: c 150 w CJ • MALE z 100 c IIFEMALE a: wI ::::E 50 0 X 0 MAP(95) MAP(50)

SEASONAL HOME RANGE 300 -J::• -c w a: c 200 w CJz • MALE c a: IJJ FEMALE w 100 ::::E 0 :::r:

0 MAP(95) MAP(50)

YEARLY HOME RANGE 800 n=2

-J::• c- 600 w a: c w 400 CJ MALE z c •Ill FEMALE a: wI 200 ::::E 0 :::r: 0 MAP(95) MAP(50)

Fig. 5.2 Weekly, Seasonal and Yearly home-range areas Chapter 5: Home range analyses 101

240 :z:c - 200 c:a: w a: c:a: 160 w • MAP95 CJz 120 c:a: 11 MAP 50 a: w 80 :::::E 0:z: 40

0 SUMM:R AUTUMN WINTER SPRING SEASON

Fig. 5.3 Seasonal changes in home-range area

5.3.2 Home-range Use 5.3.2.1 Resource preferences

The majority of home-ranges were located in a mosaic of different habitat types which usually included at least some rabbit warrens, some cracking, crab-holed soil and contained a proportion of habitat that was suitable for ground-dwelling birds.

Certain features of the habitats that foxes preferred were noted. The availability of cover seemed to be very important, although foxes did not require a regular den or resting place. In fact, due to the availability of large 'cotton bushes' (Maireana sp.) and/or large Atriplex plants, foxes had a constant supply of 'resting up' sites. Dens were not always used for rearing cubs and several litters of new born cubs were observed to be sheltered by these large bushes.

The availability of rabbit warrens within a home-range was not found to be a prerequisite for habitat selection and, for example, male 131 Chapter 5: Home range analyses 102 remained within an area which contained no rabbit warrens at all and yet he was able to successfully sire at least two litters of cubs. Some foxes did include rabbit warrens in their home-ranges (Fig. 5.4) and these were used as cover and for rearing cubs. The importance of the water supply can also be observed in Fig. 5.4, with the narrow finger of the home-range indicating the fox's movements to the sheep trough to drink.

5.3.2.2 Home-range Fidelity

There was considerable variation in the fidelity that foxes had towards their home-ranges. For example, the movement patterns of two males were compared and whilst one maintained 56% of his total home range for twelve months, the other male maintained only 12% of his original home-range after only six months. The first male also maintained 6% of his core home-range area whereas the other one retained none of his.

Vixens also showed varying degrees of home-range fidelity. For example vixen 115 maintained 36.1% of her home-range for nine months whereas vixens 133 and 127 only occupied 14.1% and 7.5% of their home ranges, respectively, after nine months.

5.3.2.3 Shifts in activity centres

The results of the t-tests investigating differences between the cumulative shifts in HMCs between males and females revealed that no significant difference occurred between the two sexes. Although these results were not significantly different the standard error for the male's cumulative path was four times greater than that for the females and this indicates that the movement patterns of dog foxes are much more variable than those for vixens (Fig. 5.5).

At-test was also used to investigate the differences in cumulative shift in HMC between summer and winter (Fig. 5.6). There was no significant difference between these seasons although there was four times more variability in shifts in summer than in winter. Chapter 5: Home range analyses 103

HOME RANGE OF FEMALE FOX

I ( -'\Pft~nc>t C11mp &~re• ------;r----- /" ~------'

0 Cn

\ 0

0 1 I , KILOMETRES

- - 0 0

Fig. 5.4 Home-range of a fox in relation to habitat features

o Rabbit warrens Chapter 5: Home range analyses 104

No significant differences in maximum path were observed between male and female foxes (Fig. 5.5) or between summer and winter (Fig. 5.6) but the same high degree of variability that was observed for the cumulative shifts of males and in the summer was repeated.

5.3.2.4 Home-range Overlap Between Different Individuals

The degree to which the home-ranges of different individuals overlapped is shown in Table 5.2. The results of each intensive station tracking session are shown, as well as an overall summary of the total overlap between individuals. There is generally a small overlap between several vixens and one male fox, although only one vixen shares the core home-range of the male at any one time. The social interactions of two males and their vixens were examined in detail (Appendix 3)

12000

10000 -E - 8000 w 0z < 6000 • MALE ...(/) Q 4000 IIFEMALE

2000

0 CUMULATIVE MAXIMUM

SHIFT IN HMC

Fig. 5.5 Comparisons of shifts in Harmonic Mean Centre between male and female foxes Chapter 5: Home range analyses 105

Table 6.2 Degree of home-range overlap between individual foxes.

WINTER 1987

Individual 1 Individual 2 MAP95 MAP 50 M131 F133 64.2 38.3

SUMMER1988

Individual 1 Individual 2 MAP95 MAP 50 M131 F133 28.4 22.0 Ml31 F127 0.0 0.0 M131 F126 13.5 0.0 F127 F126 40.2 6.3

AUTUMN 1988

Individual 1 Individual 2 MAP95 MAP 50 F1087 M131 23.2 7.7 F1087 F127 0.0 0.0 F1087 F126 14.3 0.0 F1087 F115 39.2 0.0

F115 F126 0.0 0.0 F115 F127 0.0 0.0 F115 M131 45.4 6.1

F126 F127 1.4 0.0 F126 M131 0.0 0.0

F127 M131 0.0 0.0

WINTER 1988

Individual 1 Individual 2 MAP95 MAP 50 F126 Fl15 0.0 0.0 F126 F113 0.0 0.0

F115 F113 0.0 0.0

SPRING1988

Individual 1 Individual 2 MAP95 MAP 50 M112 F133 6.0 0.0 M112 F128 0.0 0.0 M112 F127 21.2 16.6 M112 F115 0.0 0.0

F133 F128 0.0 0.0 F133 F127 2.8 0.0 F133 F115 5.7 0.0

F127 F128 0.0 0.0 F127 Fl15 0.0 0.0 Chapter 5: Home range analyses 106

Fl15 F128 0.0 0.0

SUMMER1989

Individual 1 Individual 2 MAP95 MAP 50 M112 Fl13 0.0 0.0 Ml12 F127 10.26 0.0 M112 F128 0.0 0.0 Ml12 F133 26.4 8.0 M112 F133/2 18.6 0.0

F113 F127 0.0 0.0 F113 F128 0.0 0.0 F113 F133 0.0 0.0 F113 F133/2 0.0 0.0

F127 F128 0.0 0.0 F127 F133 10.8 0.0 F127 F133/2 40.2 35.0

F128 F133 0.0 0.0 F128 F133/2

F133 F133/2

OVERALL OVERLAPS M131 (1987) F133 75.5 83.0 M131 (1988) F133 29.6 0.0 M131 F113 0.0 0.0 M131 F115 47.8 8.0 M131 F126 12.8 0.0 M131 F127 5.9 0.0 M131 F128 6.9 0.0

F133 F113 0.0 0.0 F133 F115 30.9 0.0 F133 F126 38.7 0.0 F133 F127 5.8 0.0 F133 F128 4.0 0.0

F126 F113 0.0 0.0 F126 F115 5.9 0.0 F126 F127 21.5 0.0 F126 F128 12.6 0.0

F127 F113 0.0 0.0 F127 F115 5.8 0.0 F127 F128 3.8 0.0

F113 Fll5 0.0 0.0 F113 F128 4.1 0.0

F115 F128 0.0 0.0 Chapter 5: Home range analyses 107

10000

8000 -E w- 6000 0z c • SUM\£R .... 4000 U) 11 WINTER 0 2000

0 CUMULATIVE MAXIMUM

SHIFT IN HMC

Fig. 5.6 Comparison of shifts in Harmonic Mean Centre between Summer and Winter

5.3.3 Dispersal Distances

The dispersals of five female cubs were monitored. The distances that they moved before establishing their own home-ranges are shown in Table 5.3. One fox (1751) died of starvation before establishing her own home-range even though prevailing conditions were comparatively favourable. The mean distance that they dispersed was 3.53 ±0.39 km. Only one male cub was successfully monitored but he did not move away from his natal area and instead remained in an area that was vacated by the death of another radio-collared fox. His movements are not included in the average dispersal distance. All dispersals took place as a single change in position, rather than the foxes moving randomly from one area to another before establishing their home-ranges. Chapter 5: Home range analyses 108

Table 5.8: Dispersal distances of radio-collared cubs at Fowlers Gap

Cub collar number Distance (km)

113 2.75 197 2.88 175 3.13 128 4.13 195 4.75

5.4 DISCUSSION

The home-range areas obtained for the resident foxes at Fowlers Gap were very .variable. Some foxes were faithful to relatively small areas and did not appear to alter their spatial positions markedly, whereas other foxes had no real home-range fidelity and constantly changed their home ranges for the duration of the study.

For those individuals that constantly changed their home-ranges, it was assumed that they were responding to variations in the availability of food and/or other resources. These foxes tended to remain within an area for approximately three months and then move. Because the maximum path of their movements is shorter than the cumulative path, this indicates that the foxes were moving actively about their HMC while simultaneously moving that HMC as they increased their home-range areas. This result suggests that the foxes are constantly changing the spatial position of their short-term home-ranges to take full advantage of any resource surpluses. This method of home-range use would seem to be very useful in an environment which is very variable and where resource distribution is patchy and unpredictable as is the case at Fowlers Gap. Presumably the foxes that did not alter their home-range positions obtained all their resource requirements from these relatively small areas and thus were residing in areas of high resource availability.

/ When the movement patterns of male and female foxes are compared it can be seen that male foxes, on average, tended to move about Chapter 5: Home range analyses 109 more within their home-ranges and to have slightly larger weekly home ranges than the vixens did. This may be a reflection of their social and territorial behaviour rather than being due to differences in metabolic requirements. The high variability of dog-fox movements identified in this study was also observed by Kolb (1984) who found that some dog-foxes in Edinburgh moved through three or four breeding territories in one night whereas others remained within an area of about 50 ha for an entire winter.

The seasonal differences in fox movements are not statistically significant, although it is interesting that home-ranges are slightly larger in summer than in winter. Jones and Theberge (1982) report that foxes in British Columbia established their yearly home-range areas during summer and maintained these throughout the year rather than increasing and decreasing their home-range size in accordance with seasonal requirements. Foxes thus avoided regular territorial disputes and contests. The home-ranges of the foxes at Fowlers Gap may also be larger during summer because they are supporting the cubs of the latest breeding season and thus require extra resources. Laundre and Keller (1984) found that during the pup-rearing season the home-range areas of coyotes were larger than those used during the breeding season.

The resource preferences of foxes were found, by general observation, to coincide with the habitats of their main vertebrate prey items. A similar result was obtained by Jones and Theberge (1982) who related the home-range size and habitat of foxes in the tundra of British Columbia to the spatial distribution of small mammals and artic ground squirrels that were the fox's main prey species. They found that there were significant differences in the selection of different communities, with Salix communities being used most often and Empetrum being used least. These two communities correlated with the highest and lowest densities of microtine rodents, respectively, which were the fox's principal summer prey. Foxes in British Columbia did not, however, select habitats for the abundance of artic ground squirrels, their other summer prey, and this was explained by the fact that the foxes were possibly also selecting their habitats for the presence of suitable cover. Chapter 5: Home range analyses 110

The degree of home-range overlap between foxes (Table 5.2) indicates that there is a small amount of overlap between the total (MAP 95) home range areas of one male and several vixens but that there is only overlap at the core level (MAP 50) of one male and one female. From this result it was concluded that the basic social unit for foxes at Fowlers Gap is that of a mated pair, rather than a family group as has been described by Macdonald (1979a). The small degree of overlap that occurs at the MAP 95 level does not reflect an actual interaction between the foxes as there was temporal separation in its use. Instead it reflects the fluidity of use of home-ranges at Fowlers Gap.

Unlike most other studies of red foxes where a mated pair remained monogamous for life (e. g. Lloyd 1980a), at Fowlers Gap mated pairs did not endure for more than one breeding season. The two male foxes that were monitored changed their consorts every breeding season. It was not the death of a mate that caused a lack of monogamy as has been described by Lloyd (1980a). Macdonald (1979b) has shown that the social organisation of canids in general can be very flexible and that differences in golden jackal (Canis aureus) social behaviour, for example, vary with ecological conditions. Similarly, for badgers, Cresswell and Harris (1988) found that with decreasing density and with increasing unpredictability and heterogeneity of habitat, there is a shift towards a more loosely organised, less territorial, less stable social system. A similar flexibility of monogamy has been observed for the kit fox (V. macrotis). Generally kit foxes are thought to be monogamous and to mate for life but O'Farrell and Gilbertson (1986) found that they use a flexible strategy and some pairs may remain mated for more than one breeding season, while others may change partners frequently. Of the seven mated pairs of kit foxes that Morrell (1972) studied, only one remained bonded the next breeding season. Burrows (1968) observed that the foxes that he studied showed more fidelity to the habitat than they did to individuals. Thus if a male fox had a home range that overlapped one or more vixens he would mate with these individuals. If, however, the home-range positions changed then the male fox would mate with any subsequent vixen that shared his home-range. A similar phenomenon is observed for the foxes at Fowlers Gap and the Chapter 5: Home range analyses 1 1 1

instability of social groups may be a response to the unpredictability of resources and to the heterogeneity of the habitat which lead to changes in home-range position.

Larger groups of foxes may not develop at Fowlers Gap because there are insufficient reliable resources within one home-range area to support a higher density of foxes. Social group size may be determined by the abundance of available prey within habitat patches (Macdonald 1981) and Voigt and Macdonald (1984) suggested that the minimum territory that will support a pair of foxes in Ontario in winter will not support additional adults. Lloyd (1980a) observed that differences between the variable social organisation of the foxes in Wales and the family groups of Macdonald in Oxford were probably due to a minimal food supply being available to the Welsh foxes during winter. Lloyd hypothesised that the diet of foxes in Oxford was enhanced by food resources not available to foxes in west Wales. This may have enabled the population to remain at a stable level throughout the year. Thus because the foxes at Fowlers Gap are constrained by unpredictable and patchy food availabilities they are unable to form larger social groups.

The home-range areas obtained in this study are slightly smaller than those reported by Coman et al.(1991) in the Victorian highlands. In a Victorian 'farmland/ woodland' habitat a male and a female fox had MAP (90) home-range areas of 400 and 330 ha respectively. In comparison the mean seasonal home-range area (MAP 95) for the foxes at Fowlers Gap was 136.5 ha (s.e. 19.37) (range from 17.35 to 421.36 ha; n=29; Appendix 2a). This apparent discrepancy of slightly smaller home-ranges occurring in the resource depauperate habitats at Fowlers Gap, rather than in the resource rich Victorian Highlands, can be explained by the fact that there was considerable overlap in the home-ranges of the foxes in the Victorian study area (Coman et al. 1991), unlike the foxes at Fowlers Gap. Each individual may thus have had a larger home-range area per se but it would have shared that home-range to a greater extent than the foxes at Fowlers Gap would have done. This conclusion is supported by the results obtained by Trewhella et al. (1988) who found that at high densities (such as would be the case in Victoria) the amount of overlap between , Chapter 5: Home range analyses 112 neighbouring fox home-ranges is relatively increased. It can only be assumed that the evolutionary stable strategy used by the foxes at Fowlers Gap results in small but relatively non-overlapping home-ranges occurring, rather than larger areas being used but with a high degree of overlap. This strategy is presumably a response to the previously discussed unpredictability and patchiness of resource availabilities.

Coman et al. (1991) compared the home-range areas that they obtained using the convex minimum polygon method with those obtained using the Anderson technique (MAP 90). They found that as a general guide the non parametric areas were approximately 50% of the convex minimum polygon areas. If this comparison is extrapolated to the home range investigations conducted in North America and Europe, the home range areas that are probably most comparable with those observed in this study are those obtained by von Schantz (1981), Tullar and Berchielli (1980) and Zimen (1984) in Sweden, New York and Germany respectively (Table 5.1).

The dispersal distances for cubs obtained in this study are relatively short when compared with those obtained in studies in other countries and Victoria. However, since dispersal distance is influenced by the population density, home-range size and habitat type of both the area that the fox vacates as well as the new area that it moves into (Lloyd 1980a), there is a great deal of variation in dispersal distance in different areas and in different habitats. Juveniles in a stable population can only replace adults that have died or moved elsewhere, and so dispersal distance is negatively correlated with mortality rate and the fluidity of home-range position. Thus in highly mobile populations and where home-range areas are relatively small (such as at Fowlers Gap), juveniles would not need to disperse very far before they found a vacant site. A sample of male dispersals would probably also considerably increase the average dispersal distance and make it more comparable to other studies.

The dispersals that were observed during this study all took place as simple changes in position, rather than as the more complex patterns of dispersal described by Maurel (1980). This phenomenon may be explained Chapter 5: Home range analyses 1 1 3 by the fact that the dispersal distances observed were relatively short and they were easily undertaken in a single day. The exception to this generalisation was the 'dispersal' of cub 1751. She was tracked to 2.3 km south east of her natal den and then was relocated approximately 2.6 km north west of her natal den. Her carcass was found at this point and her death was attributed to starvation. Her intestines were filled with the sand. It can only be assumed that she was unsuccessful in finding a new home-range, whereas the other cubs that were monitored found a new home-range almost immediately.

The overall conclusions that can be reached from the home-range analyses described in this chapter are that foxes' home-ranges are very fluid and this enables them to move their spatial positions in relation to the food supply. Their social organisation also reflects this unpredictability in resource availability. The fact that foxes are so flexible in their habits is a possible reason why they have been so successful as colonisers. This may also be the reason why they have been able to have such an enormous predatory impact upon native fauna because they are able to prey heavily upon species which may be unable to alter their habitat requirements (see Chapter 3). CHAPTER6

EFFECTS OF RABBIT REMOVAL

6.1 INTRODUCTION

At Fowlers Gap rabbits comprise almost 20% of the foxes' diet (see Chapter 3). Because both foxes and rabbits are introduced species, it is interesting to investigate what foxes would eat in Australia if rabbits were unavailable. Myxomatosis regularly depletes the rabbit population and rabbit removal is carried out spasmodically on many Australian farms with little thought to simultaneous fox control, and so the opportunities for foxes to prey more heavily upon other species when rabbits suddenly become unavailable are ample. Also another rabbit biological control agent is being developed and it is important that the ramifications of such an agent should be known before it is released.

Because foxes are so widely spread within Australia and because many native species occur at fairly low densities, it is important to know the extent of the possible impact that foxes may have upon them, so that if rabbit removal or control is conducted as a general practice it can be done so as to minimise the detrimental consequences that these species would Chapter 6: Rabbit Removal 115 otherwise face. The possibility that rabbits act as a mainstay for foxes during some seasons, thus allowing them to prey more heavily upon native prey species at other times, also warrants investigation.

6.2 :METHODS

This experiment involved dividing the study area into three subsections. The first site, Warrens paddock, had a high density of rabbits which persisted for the duration of the experiment. The second site, Ram paddock, had a high density of rabbits initially but these were removed half way through the experiment so that a before and after removal effect could be obtained. The last site, a combination of Lambing, Mating and Salt 3 paddocks, was naturally devoid of rabbits.

The contents of fox seats collected before and after the removal of rabbits were analysed using the techniques described in Section 3.2.2. These contents were compared using a canonical correlation so that any changes in the diet that occurred due to the removal of rabbits could be identified. For this analysis the contents of seats collected for three sample periods, both before and after rabbit removal, were examined.

The field abundances of each of the dietary categories were monitored in each of the three sites for three sample periods before and after rabbit removal. This was done using the techniques described in Chapter 2. These data were then initially analysed using a two way ANOVA to determine whether there were significant changes in the field abundances of any of these species once rabbits were removed. Because the field abundance estimates for these categories were not normal (See Chapter 3), a Mann-Whitney U test was used to compare the sample pairs.

Fox density estimates were obtained for both before and after the removal of rabbits. Thus any changes in fox density that resulted due to the removal of rabbits could be identified. These density estimates were undertaken during four sample periods before and after rabbit removal to ensure that actual changes in fox densities were being observed (if any), Chapter 6: Rabbit Removal 116 rather than seasonal fluctuations being held responsible for any differences.

To remove the rabbits a 1290 Case FWA tractor was used to 'rip' the rabbit warrens in Ram paddock. The tractor dragged a single tyre J arrette ripper with a maximum penetration of 75 cm through a total of 12 warren groups (37 warrens in total). Because some warrens were covered in fairly heavy vegetation these were initially fumigated using Larvacide. However all the warrens that were fumigated reopened readily, and so it was decided that all warrens would be ripped. Two warrens reopened after being ripped but these were re-ripped and they had not re-opened by the end of the experiment. Some of the destroyed warrens were initially graded after ripping but because this increased the chances of the warren being re-opened, and because it was time consuming and thus expensive, this practice was abandoned.

Ripping was done in November 1988 and attempts were made to ensure that all the rabbits inhabiting a warren were resident at the time of ripping. Unfortunately some rabbits were above ground when the warrens were ripped and because these rabbits were 'easy prey' for foxes, and would have reopened the warrens, several nights were spent shooting them. This process was not completely successful though and so a few rabbits probably remained in the thicker parts of the vegetation. However, because the rabbit population had been drastically reduced by the ripping programme, the number of rabbits remaining was an insignificant proportion of the original population.

Because rabbits are an important dietary item for foxes, there may be a change in fox home-range usage in response to a change in rabbit availability. Thus foxes may seek food in new areas and as a consequence move their home-ranges or at least change their centres of activity. The movements of foxes living in the experimental areas were, therefore, monitored in an attempt to determine whether foxes change their diet, their home-ranges, or a combination of both factors, in response to rabbit removal. Chapter 6: Rabbit Removal 11 7

Possible changes in fox home-range areas were investigated by monitoring the movements of six radio-collared foxes. Two of these foxes lived in each of the three experimental areas and so comparisons between the foxes under different experimental conditions could be made. Variations in home-range overlap and size were used to monitor the changes in fox ranging behaviour. The amount that an individual's home range overlapped its own previous home-range was used as an index of home-range change and these changes were analysed using a two way ANOVA. Similarly, the size of each individuals home-range before and after rabbit removal was analysed using a two way ANOVA. Before these analyses were undertaken the data were tested for normality and homoscedascity using the Bartlett-Box F test. Because the data initially failed this test it was consequently transformed by taking the square root of each datum. The data was then re-tested using the Bartlett-Box F test and found to be normal. The analysis was run using the transformed data.

To ensure that the observed dietary changes that occurred in Ram paddock (if any) were actually due to rabbit removal, analyses of the diets in Warrens and Lambing paddocks were also conducted. The diets of foxes in these two paddocks were examined for three sampling periods before and after rabbit removal. A canonical correlation on this data indicated that no significant change in fox dietary composition occurred in either paddock. Thus no overall change in dietary preferences in the study area occurred during the rabbit removal experiment.

6.3 RESULTS

The average dietary composition in Ram paddock before and after rabbit removal was compared (Fig. 6.1). The amount of rabbit ingested in the three sample periods before rabbit removal averaged 30.36% and this decreased to an average of 19.59% for the three sample periods after rabbit removal. Chapter 6: Rabbit Removal 1 1 8

• RABBIT B BIRD B REPTILE r:zl DASYURID D INVERTEBRATE • CARRION

BEFORE AFTER

Fig. 6.1 Diet in Ram paddock before and after rabbit removal

The results of the canonical correlation comparing fox diets before and after rabbit removal showed that a statistically significant change in diet occurred (p<0.001). An absence of rabbits in the diet was the most significant result (Table 6.1). This factor loaded most heavily upon the first canonical variate which accounted for 75% of the dietary variance. The first canonical variate had a canonical correlation of 0.61 (Table 6.1).

The factor that loaded next most heavily upon the first canonical variate after rabbit removal was the presence of ground-dwelling birds (Table 6.1). Ground-dwelling birds, therefore, became more important in the fox's diet once rabbits were removed. The incidence of birds in the diet increased from 1.8% before rabbit removal to 11.9% after rabbit removal (Fig. 6.1). This change in bird ingestion can be wholely attributed to a change in dietary preference rather than to changes in availability, because ground-dwelling bird field abundance (Fig. 6.2), was taken into consideration in the canonical analysis. Chapter 6: Rabbit Removal 119

30 w CJz c Qz ::::) 20 cCD w -CJ El DIET z w FIELD a: 10 • a: ::::) CJ CJ 0 0 ...... CX) CX) CX) CX) Ol Ol Ol CX) CX) CX) CX) CX) CX) CX) CX) CX) CX) 1- 1- a: z (.) z a: z (.) z a: z Cl. :::> c( Cl. :::> c( Cl. :::> c( ""') 0 ""') c( ""') 0 ""') c( ""')

Fig. 6.2 Ground-dwelling bird ingestion and field abundance (Line indicates rabbit removal).

When the results of the canonical correlation investigating seasonal effects were examined (Table 6.2), they revealed that there was a significant seasonal effect (P<0.001). An absence of rabbits was the dietary category that most influenced seasonal dietary composition.

This absence of rabbits loaded most heavily upon the first canonical variate which accounted for 75% of the dietary variance and which had a canonical correlation of 0.60 (Table 6.2). Again, the category that next loaded most heavily upon the first canonical variate was ground-dwelling birds.

Ground-dwelling bird dietary incidence increased considerably in winter and autumn after rabbit removal i.e. from 5.98% to 19.89% and 3.03% to 35.78% respectively (Fig. 6.3a-e ). However, the increase in summer intake was much smaller (0.0% to 0.31 %). Thus ground-dwelling birds become more important in the fox's diet during winter and autumn but another dietary category must fulfil the fox's dietary requirements during summer. Chapter 6: Rabbit Removal 120

(A) SUMMER 1988 (B) SUMMER 1989

11 RABBITS 11 BIRDS 11 REPTILES f::1!l DASYURIDS 0 INVERTEBRATES 11 CARRION

11 RABBITS 11 BIRDS 11 REPTILES ~ DASYURIDS 0 INVERTEBRATES 11 CARRION

(E) WINTER 1988 (F) WINTER 1989

11 RABBITS 11 BIRDS 11 REPTILES ~ DASYURIDS D INVERTEBRATES 11 CARRION

BEFORE AFTER

Fig. 6.3 Seasonal change in fox diet before and after rabbit removal Chapter 6: Rabbit Removal 121

Table 6.1: Results of Canonical Correlation Analysis comparing species availability and dietary occurrence in Ram paddock before and after rabbit removal. (n.s. =not significant)

Eigen Values and Canonical Correlations

Root No. Eigen Percent Cumulative Canonical Value Variance Percentage Correlation

1 0.566 75.05 75.05 0.601 2 0.106 14.08 89.13 0.310 3 0.056 7.49 96.62 0.231 4 0.025 3.36 99.98 0.157 5 0.000 0.02 100.00 0.011

Univariate Regression Analysis of Dependent Variables

Variable R F5,156 p

Rabbit 0.528 0.279 12.069 <0.001 Bird 0.332 0.110 3.869 <0.01 Reptile 0.223 0.050 1.636 n.s. Dasyurid 0.297 0.088 3.026 <0.05 Invertebrate 0.285 0.081 2.595 <0.05 Carrion 0.237 0.056 1.862 n.s.

Correlations between Dependent and Canonical Variables

Variables 1 2

Rabbit -0.857 -0.313 Bird 0.493 -0.223 Reptile -0.356 0.121 Dasyurid 0.290 -0.528 Invertebrate -0.238 0.707 Carrion 0.290 0.328 Chapter 6: Rabbit Removal 122

Dasyurids and invertebrates are the only other dietary categories that reflect a significant seasonal effect (Fig. 6.3). Although dasyurid incidence in the diet increased this was insufficient to overcome the void left by the removal of rabbits and so invertebrate ingestion was also extended. The incidence of invertebrates in the diet increased from 22.93% to 29.86%.

The results of the two-way ANOVA comparing the change in home range position, before and after rabbit removal, indicated that there was less overlap by an individual upon its previous home-range in the areas in which rabbits were removed. This reveals that foxes changed their home ranges more in areas where rabbits were removed than elsewhere(F16 1=12.42, p

The density of foxes in Ram paddock did not change significantly with the removal of rabbits, but in the control paddocks the densities of foxes changed significantly. There was an increase of foxes in Warrens paddock {p

Table 6.2: Result& of Canonical Correlation Analysis comparing species availability and dietary occurrence in Ram paddock before and after rabbit removal. Testing for seasonal effects. (n.s. = not significant)

Eigen Values and Canonical Correlations

Root No. Eigen Percent Cumulative Canonical Value Variance Percentage Correlation

1 0.475 98.89 98.89 0.568 2 0.005 1.11 100.00 0.073

Univariate ANOVA of Dependent Variables

Variable F2,136 p

Rabbit 12.026 <0.001 Bird 7.276 <0.01 Reptile 2.645 n.s. Dasyurid 3.132 <0.05 Invertebrate 6.258 <0.01 Carrion 0.773 n.s.

Correlations between Dependent and Canonical Variables

Variables 1

Rabbit -0.610 Bird 0.474 Reptile -0.286 Dasyurid 0.301 Invertebrate -0.439 Carrion 0.138 Chapter 6: Rabbit Removal 124

40 ==:.::- 0 30 U)- ...> c;; 20 z w liJ WARRENS c RAM )( 10 LAMBING 0 • u.

0 ,.... ,.... ,.... ,.... ,.... CO CO CO CO 01 01 01 CO CO CO CO CO CO CO CO CO CO CO CO

('f)

}1&. 6.4 Comparison of fox densities in Warrens, Ram and Lambing paddocks after rabbit removal in Ram paddock (Line represents rabbit removal).

6.4 DISCUSSION

The results of the analyses investigating the effects of rabbit removal upon foxes indicate that foxes change their dietary composition, they modify the spatial position of their home-ranges and they decrease slightly in density.

It is not surprising that the amount of rabbit ingested in the experimental area decreased once rabbits were removed from that area. However, the magnitude of the decrease does not totally reflect the decrease in the availability of rabbits and so it indicates that foxes must still have been preferentially seeking rabbits as prey. This preference for rabbits, even at low densities, has been discussed in Chapter 3 and has been observed by several authors e. g. Englund (1965b), Lever et al. (1957) and Lloyd (1980a). Chapter 6: Rabbit Removal 125

Once rabbits were removed from the experimental area, foxes switched their prey preferences to ground-dwelling birds. These birds were ingested at a much higher rate than previously, even though there was no significant increase in their field availability. Similar switches in prey preference have been observed when rabbits have been reduced by myxomatosis in other countries. Lever (1959) compared the diets of foxes after the disease's introduction with that found by Southern and Watson (1941) before its release and found that there was a significant change in dietary composition and that foxes had switched to small rodents. Similarly, Englund (1965b) found that foxes ate more hares, small rodents, game birds and possibly sheep after the introduction of myxomatosis. In Australia, Mcintosh (1963) felt that it was safe to assume that rabbit was eaten preferentially in the pre-myxomatosis diet and that other foods, especially sheep subsequently replaced it.

When the seasonal changes in fox diet were examined after rabbit removal, the absence of rabbit in the diet was again found to be the most significant dietary change. Similarly, ground-dwelling birds were shown to become the next most preferred prey item in winter and spring but in summer their rate of ingestion did not totally offset the decrease in the rate of rabbit ingestion. Instead invertebrates were found to be most important during this season and this may be a reflection of their relative abundance. The rate of ingestion of reptiles was also observed to double during summer despite a decrease in their field abundance, but this result was not statistically significant. Reptiles may, therefore, partially replace rabbits in the diet in summer. The incidence of dasyurids in the diet did not increase significantly after rabbit removal and this contrasts with the conclusions of Chapter 3. However, this result may be explained by the fact that the field abundance of dasyurids in Ram paddock was exceptionally low for the duration of this experiment, and it was concluded that foxes did not switch their preferences to dasyurids because they were simply unavailable. (Dasyurid ingestion rate nevertheless increased to its highest level ever in June 1989.)

Although the foxes that did remain in the rabbit removal area showed no significant increase in their home-ranges areas, there was a Chapter 6: Rabbit Removal 126

significant change in the fidelity that these foxes showed towards their home-ranges. The foxes that were initially residing in the experimental area overlapped their pre-ripping home-ranges to a significantly lesser degree than those that lived outside the experimental area. Presumably, when rabbits became harder to find, foxes changed the spatial position of their home-ranges so that they could take advantage of other more readily available prey resources such as ground-dwelling birds and reptiles.

The density of foxes in the experimental area showed a relative decrease after the removal of rabbits even though there was no absolute reduction within that area. This result would appear to substantiate the conclusions ofLockie (1956) who found that there was a decrease in the number of predators after myxomatosis. Similarly, Sumption and Flowerdew (1985) describe a subsequent prey shortage after myxomatosis occurred in Britain, and how this lead to a reduction of predators. The conclusion that was thus reached in this study was that foxes had moved their home-ranges to take advantage of other available food resources and had switched their feeding preferences to alternative prey species. This conclusion supports those of Chapter 5; namely, the fluidity of fox home range positioning enabled foxes to be able to move their home-ranges in response to changes in prey availability without suffering any decrease in body condition or reproductive success. Lever (1959) similarly found that when myxomatosis had reduced the rabbit population severely, foxes immediately switched to small rodents and he found that the foxes showed no noticeable reduction in weight, condition and breeding. Southern (1956) also discusses how foxes switched to alternative prey and that none of the individuals that he shot was at all emaciated. In Australia, Ratcliffe (1956), found that there was no decrease in fox density after the introduction of myxomatosis, and, in fact, the fox population increased. This result further supports the idea that fox density overall does not become reduced when rabbits are no longer available because foxes are so adept at finding alternative food resources.

Because foxes are so fluid in their home-range positioning and dietary preferences, this would enable them to prey heavily upon the native fauna. The impact that they had upon the native fauna when Chapter 6: Rabbit Removal 127 myxomatosis was first introduced will never be quantified but it can only be presumed to have been considerable. The demise of some species may possibly be attributable to this phenomenon.

From the results presented in this chapter I concluded that rabbit removal should be conducted in conjunction with fox control to ensure that fox prey switching does not occur and thus any detrimental effect upon the native species is minimised. Joint fox and rabbit control measures should be adopted to ensure that native species are simultaneously relieved of competitive pressure from rabbits and predation pressure from foxes. 128

CHAPTER7

FOX CONTROL METHODS

7.1 INTRODUCTION

Various methods of fox control have been developed in Australia in response to fox predation upon lambs (see Appendix 4) and their predation upon native fauna. These methods include shooting, poisoning, trapping, snaring, the digging out or gassing of dens, driving before guns and a scalp bonus system. Each of these methods has limitations and, as yet, no widespread, effective control technique has been developed that will reduce fox populations across Australia.

Shooting has been widely used as a method of controlling foxes in localised areas, especially around lambing time. Shooting for skins can be quite lucrative if the price of furs is high. This method of control is rather limited in its application because it is time consuming and only areas that are relatively near to human habitation are suitable. Its impact as a method of reducing overall fox densities is also questionable. Daylight Chapter 7: Fox Control Methods 129

drives are also limited in their application and are restricted to more accessible areas (Brunner et al. 1980).

Fumigation of dens has been employed as a control technique, and this is most appropriate in summer when juveniles and vixens are still in the dens. Chloropicrin or cyanide gas are usually used as the fumigants (Brunner et al. 1980). This method is also limited in its application because foxes do not always use dens and even where they do it is restricted to relatively accessible and localised areas where fox dens can be readily located.

Mclntosh (1963a) discusses the use of bounty systems to control foxes and concludes that they have apparently no effect on the size of the fox population. They have been implemented in several states including Victoria where they were accounting for 60,000 scalps annually in 1973 (Coman 1973) and in Western Australia where they were initiated in 1928 and then concluded in 1961 (King and Smith 1985). Bounty systems in other countries have similarly been discontinued and Besadny (1966) states how foxes were bountied in ·Wisconsin for over 85 years but then this practice ceased in 1963 because of its ineffectiveness in controlling fox numbers. The use of scalp bonuses to control fox populations is thus of limited value.

Fox baiting, using 1080 baits, has been a very successful way of controlling foxes (Kinnear et al. 1988). It is particularly useful in S.W. W.A. where the native fauna has naturally occurring increased tolerance to 1080 and is therefore less susceptible to the poison (King et al. 1981) The mode of presentation of these baits has been well developed and egg and dried meat baits have been found to be effective in delivering the poison (Kinnear et al. 1988). Several rare and endangered species such as Petrogale lateralis, P. rothschildi, Bettongia penicillata, Macropus eugenii, (Kinnear et al. 1988) and Myrmecobius fasciatus have increased their densities in reserves where foxes have been controlled using this method. Chapter 7: Fox Control Methods 130

Part of this study consisted of an experiment to determine how effective fox baiting may be in controlling foxes in an arid habitat. This involved laying baits and then determining what proportion of the fox population had actually ingested a bait. Apart from establishing the effectiveness of baits in reducing the fox population and thus reducing fox predation, this work has applications in the eventuality of rabies being introduced into Australia. A thorough knowledge of the best baiting regimes for all habitat types would be essential for the containment and elimination of an epizootic if one ever occurred.

7.2 METHODS

To determine whether a fox had ingested a bait or not, all baits were 'labelled' with a biomarker, oxytetracycline. This substance is absorbed into an animal's bones and fluoresces under longwave (360 nm) ultraviolet light. By counting the number of individuals recovered from a population that have ingested the bait and comparing this to the number that have not, it is possible to determine the percentage of the population that would have been affected by a 'real' baiting program.

To ensure that this was a viable technique, two fox-sized dogs (Canis familiaris) were obtained from the dog pound and were given a similar dose of oxytetracycline. They were then kept at the University's animal holding unit for ten weeks until they were destroyed. Their skulls were then examined for the biomarker, which was present.

7.2.1 Preparing and Laying Baits

Chicken heads (n=900) were acquired from a local chicken farm and each was filled with 1 g of 100 mg/g oxytetracycline powder. This powder was forced into the chicken's brain cavity and so a compact and self contained bait resulted. These baits were then partially buried, 100 m apart, for 90 km (including the 38 km of transect lines). This partial burying was aimed at reducing non-target species from taking the baits. A kangaroo carcass was dragged behind the vehicle as the baits were laid, in an attempt to attract foxes to the baits. The position of each bait was Chapter 7: Fox Control Methods 13 1

marked with surveyors tape. It took three days to lay the trails because only the cooler hours of overcast afternoons and evenings were used in an attempt to maximise the attractiveness of the dragged trail. The trails were laid in mid-April 1989.

7.2.2 Shooting

Once the baits were laid, ten weeks were allowed to elapse to ensure that a complete uptake of the biomarker into the fox's bones had occurred. Shooting then commenced and the 90 km of track were thoroughly searched for foxes, until either no more animals were seen, or else they were too far away to be shot.

7.3 RESULTS

7 .3.1 Bait Ingestion Rate

When the 90 km of trail were investigated for untaken baits, only one bait was found to remain. This appears to have been a very successful acceptance rate for the baits. Forty-three foxes were shot in the study site and of these thirty-eight had ingested the biomarker. Thus 88.4% of the population has been reached by the baiting programme.

7 .3.2 Recolonisation Rate

A census of foxes in the study site was conducted before and after the shooting took place. The relative change in fox density was recorded and it showed that the population had recovered to approximately 80% of its original size within three months, due presumably to immigration (See Fig. 7.1). Chapter 7: Fox Control Methods 132

FOX DENSITY 1.4

1.2 -::::& ~ 0 1.0 UJ- >- ...u; 0.8 z w Q

)( 0.6 0 LL 0.4 ~ ~ ~ ~ ~ ~ ~ ~ ~ m ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ v ~ 0 ~ v ~ 0 ~ V ~ 0

Fig. 7.1 Fox density recovery after removal in July 1989

7.4 DISCUSSION

The results from this experiment clearly indicate that most of the fox population in this area would be reached in a 'proper' baiting campaign. Thus if fox density reduction was the object of an exercise, for example to reduce the predatory impact of foxes upon native fauna, then this baiting regime would be very effective. It would, of course, need to be repeated on a regular basis to overcome the effects of immigration and to maintain the desired level of control.

Unfortunately this experiment was limited by the fact that it was not repeated in different seasons, when it may be expected that alternative food availability and thus bait uptake would differ. Thus more repetitions of this experiment need to be conducted to identify the best times of the year for this type of control work to be implemented.

The use of baiting on a state or country-wide scale is obviously very labour intensive and costly. Thus a more effective way of controlling foxes Chapter 7: Fox Control Methods 133 is needed. Thankfully a biological control method for foxes is being developed in Australia. This method involves inducing the fox to immunosterilise itself. This is done by infecting each individual with a contagious virus that has been genetically engineered. The virus will be manipulated so that it contains the DNA sequence of the fox that codes for its own reproductive proteins. Thus when the virus enters the foxes' body and an immune response is raised, the fox raises antibodies to its own reproductive proteins. Antigens from both the sperm and ovum can be targeted, thereby causing the female to produce an immune response to her own ova and the male to similarly produce an immune response to his own sperm. If the ZP3 protein on the ovum is targeted in the female, this also stops fertilization of the ovum because this antigen is vital in the sperm's recognition of the ovum. If both the antigens for the male and female are incorporated into the same virus vector, then infertility will result from all matings because both sexes will be simultaneously targeted. At present, a search is underway to find a suitable virus that will either spread rapidly through the fox population or else is already widespread and which is suitable to be engineered. Once it is found it will be engineered and liberated. A knowledge of the biology of foxes is essential for estimating the spread of this virus through the fox population and research is currently being conducted to determine the contact rate and thus the transmissability of the virus, as well as the dispersal rate of juvenile foxes which would be extremely important in spreading the Immunogen.

A similar technique is presently being developed for rabbit control, using an engineered Myxoma virus. Hopefully both this and the fox virus will be released simultaneously to ensure that fox predation upon native fauna is minimised and so that no increase in rabbit populations will occur with the removal of foxes. Widespread fox control will then, hopefully, ensue and the populations of native fauna will then hopefully increase in density. CHAPTERS

GENERAL DISCUSSION

Red foxes have adapted extremely well to living in Australia and their flexible dietary and social habits have enabled them to thrive here. Although it will never be proved conclusively that foxes are responsible for the Australia-wide decline of small and medium sized mammals, there is certainly sufficient circumstantial evidence to convict them.

The declines in the mammalian populations generally co-incide temporally with the introduction of the fox and its spread across the continent. The absence of declines in areas where the fox has not reached, such as the wet tropics and Tasmania, strongly suggest that the fox is responsible for declines elsewhere. The foxes' absence from off-shore islands where many small and medium sized species are abundant, and its presence where they do not, can only further support this conclusion. Where there is ample cover in the form of either very thick vegetation or rock piles which would reduce fox access, the decline in the fauna is also less marked. The declines also coincide with the dryer, less productive parts of these species' ranges and this is consistent with the fact that any decrease in carrying capacity in these areas (due to predation) would result in proportionally more extinctions (Pianka 1986). Chapter 8: General discussion 135

The introduction of the European rabbit may have been an important factor in the foxes' success because it provided a food resource which enabled foxes to increase in density out of all proportion to the densities of the native fauna. Foxes were then able to switch their prey preferences to the native fauna. This predatory pressure was far greater than the native prey populations could withstand and this lead to the severe decline or extinction of many species. This predatory impact could only have been exacerbated by drought, competition with rabbits for shelter, and the release of myxomatosis.

The rabbit was the preferred vertebrate prey species in this study and it was ingested whenever it was readily available. However, when it was unavailable, foxes switched their prey preferences to dasyurids. The dasyurid population was usually low when this occurred and as a consequence foxes presumably had a serious detrimental impact upon them. Dasyurids must have some level of resilience to predation to have survived to date, perhaps due to their small size they can obtain cover relatively easily but whether they can maintain this level of predation indefinitely is open to debate. The vagaries of the dasyurid fauna further complicate this situation because it is not understood, for example, why P. gilesi was rare during this study and P. tenuirostris was common, whereas only two years earlier the reverse was true. More research into the ecology of these mammals will hopefully resolve some of these questions.

When rabbits and dasyurids were unavailable to foxes, ground dwelling birds and reptiles became the preferred prey species. The potential impact that foxes may have upon birds and reptiles was calculated to be high and whether they can sustain this level of predation pressure, or whether there will be a decline in these species is yet to be revealed.

Various aspects of its biology have enabled the fox to thrive in Australia. In conjunction with its highly flexible dietary habits and its ability to use virtually any food resource available to it, the fox also has very flexible social and reproductive characteristics that enable it to adapt to a wide range of environmental variables. Chapter 8: General discussion 136

The home-range usage of the fox is highly flexible. Foxes are able to move their home-ranges readily so that they can take full advantage of any seasonal or other variation in food or other resource supply. Some foxes use the strategy of living in relatively small areas which are presumably high in reliable resources while others move the position of their home-range constantly to take advantage of any localised resource surpluses. Which of these strategies would be most advantageous during a drought, for example, is yet to be determined. The home range area of foxes was found to be comparatively small when compared with those obtained in other studies but this is partially due to different methods of analysis being used and so direct comparisons are not meaningful. Foxes may also be using different strategies at Fowlers Gap to those employed in other studies. Foxes here have small, flexible home-ranges so that they can take full advantage of locally abundant food resources, rather than having large home-ranges with sparse but relatively evenly spaced resources. The observed fluidity of home-range position has enabled the fox to have a deleterious impact upon the native fauna which, presumably, has been unable to alter its habitat requirements in response to fox predation.

The social behaviour of the foxes at Fowlers Gap also reflects the unpredictability of resources in this low productivity habitat. Instead of relying upon the monogamous mated pair system that has been observed in most other studies, the foxes at Fowlers Gap changed their consorts frequently. Burrows (1968) observed that territorial variations are responsible for the relationships between foxes, rather than individual fidelity. Thus if a male has a territory that encompasses the territory of one or more females he will mate with them but if the territories alter, then he will alter his relationships accordingly and will mate with any new females within his range. Thus at Fowlers Gap where the spatial positions of home-ranges are constantly changing, it is not surprising that changes in fox relationships also occur.

The population dynamics of foxes at Fowlers Gap are also geared towards responding to variations in resource availability. The litter sizes observed during this study were small but presumably would increase considerably if the population was decreased by environmental Chapter 8: General discussion 137 decline or by increased control measures. Fox density was low but this was probably a reflection of the low productivity of the area and the relative paucity of resources available to foxes when compared to other studies. Different methods of density estimation also make direct comparisons between studies difficult. Fox mortality rates most closely resemble those of populations elsewhere which had little control imposed upon them. Because the seasons at Fowlers Gap were relatively favourable during this study, the population was relatively stable and was presumably, at or near, the carrying capacity of the habitat. No major recruitment of juveniles into the population was required and so the litter sizes remained small. Juvenile mortality was not particularly high due to the small litters providing just slightly more individuals than were necessary to replace the adults that had died of old age or misadventure. The dispersal distances of the cubs that survived were relatively short when compared to those observed in other studies. This can be accounted for by the fluidity of the home ranges of the adults which would enable the dispersing juveniles to readily find a home-range of their own.

The other major factors that have been hypothesised to have caused the observed decline in native mammalian species include altered fire regimes, predation by feral cats and competition from introduced herbivores. None of these factors alone could have resulted in such widespread decreases in the native fauna but some of them in conjunction with other factors may account for the declines (Burbidge and McKenzie 1989). The introduction of rabbits, as discussed above, most certainly increased the level of fox predation upon the native fauna by enabling the fox population to increase. Direct competition between rabbits and the native mammals for food and shelter would also have been a significant factor in their demise. Predation by the feral cat may also have had some impact especially after the introduction of the rabbit which would have bouyed up the cat population in a similar way to that of the fox. The native species that have been found to be eaten by cats include Trichosurus vulpecula, Pseudocheirus peregrinus, Petaurus volans, Perameles nasuta, Rattus fuscipes, and Antechinus species (Jones and Coman 1981). However, because the cat had been present in many areas for some time before the major declines in fauna occurred and because it inhabits islands where small and medium sized Chapter 8: General discussion 138 mammals are common, this indicates that it is not generally responsible for the declines elsewhere, though its impact in some areas may be considerable.

Changes in the fire regime of many areas since the relocation of aborigines may have lead to localised declines in the populations of some species but it is unlikely to have resulted in so many different habitat types becoming totally unsuitable for habitation by these species. It also does not account for the reason why island populations of many of these species are abundant (in the absence of foxes) but that in similar habitat nearby on the mainland they are either rare or totally absent. The demise of mosaic burning may have contributed to the decline of some species because the resulting hot fires would remove the cover for many small species over a relatively large area and would thus make them highly vulnerable to predation by foxes.

Many of the native mammalian species that have suffered dramatic declines in their distributions are currently increasing in density in areas where fox control is being under taken e. g. the woylie (Bettongia penicillata), the tammar wallaby (Macropus eugenii), the numbat (Myrmecobius fasciatus), the western mouse (Pseudomys occidentalis), the brush-tailed possum (Trichosurus vulpecula), the brush wallaby (M. irma) and the rock wallabies (Petrogale spp). The control of foxes in these instances is obtained by the repeated laying of 1080 baits. The use of 1080 baiting is limited, however, in its application due to the substantial costs involved. Foxes are difficult mammals to control due to their wide geographical distribution in Australia, due to their flexible use of their home-ranges, their lack of a need to use dens, and their low densities which precludes shooting as a viable, widespread control measure. Thus large tracts of land in Australia are currently devoid of any fox control at all. Luckily foxes appear to readily ingest baits and so their control is possible albeit in relatively small areas. Obviously 1080 baiting as a method of control is only an 'holding' measure and the development of biological control appears to be the most promising method of controlling foxes in the future. This technology is currently being developed. Chapter 8: General discussion 139

The historical impact that foxes have had on the native fauna in Australia can only be infered, but even so there is sufficient circumstantial evidence to convict the fox as a major factor in the decline of many mammalian species. Due to the foxes' amazing adaptability in social, reproductive and dietary behaviour, they are currently able to thrive in Australia and to have a profound detrimental impact upon the native fauna. By switching from one prey type to another they are able to effect considerable predation pressure upon prey species. There is a need for the development of a widespread fox control method and this is currently being undertaken in the form of virally-vectored immunosterilisation When this is achieved, native species will be afforded proper protection from fox predation and they will hopefully return to their previous abundances wherever suitable habitat remains. References:

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APPENDIX 1: Home-range areas (Ha). WEEKLY

MALES MAP(95) MALES MAP (50) 139.67 39.91 119.94 21.76 188.36 41.89 153.98 24.91 311.60 57.66 161.62 2lJl2 1075.17 (x=179.19) 207.15

FEMALES MAP(95) FEMALES MAP(50) 29.64 2.77 165.99 49.08 57.13 8.96 160.78 37.21 44.06 7.31 ~ i.1Q 4 79.52 (i=79.92) 110.03

SEASONAL

MALE MAP (95) MALE MAP(50) 218.57 3.37 333.06 54.81 311.60 57.66 81.28 27.10 243.76 23.38 ~ fiLll 1205.62 (x=200.94) 224.03

FEMALES MAP (95) FEMALES MAP (50). 38.78 3.24 160.78 37.52 21.92 4.70 119.76 21.41 157.77 20.01 78.88 19.27 421.36 159.54 306.72 84.53 64.51 13.13 69.63 14.96 69.91 21.47 97.51 48.65 147.02 31.53 46.13 10.01 140.25 30.54 44.06 7.31 198.38 53.48 128.06 27.05 166

27.92 5.27 38.78 5.30 107.44 39.98 89.96 23.40 176.18 5a.61 2751.71 (x=119.64) 741.97 (x=32.26) YEARLY

MALE MAP (95) MALE MAP(50) 691.86 208.33 642.44 207.36 1334.3 (i=667 .15) 415.69 CX=207.85)

FEMALES MAP (95) FEMALES MAP (50). 818.80 238.37 319.77 73.64 429.36 112.40 337.21 78.49 351.74 93.99 176.35 46.51 849.81 294.57 3283.04 Cx=469.0l) 937.97 Cx=134.0) 167

APPENDIX 2: Variations in home-range area (Ha) with season. MAP(95)

SUMMER AUTUMN WINTER SPRING

218.57 81.28 27.92 140.25 330.60 69.63 38.78 44.06 311.60 69.91 107.44 198.38 38.78 97.51 89.96 128.06 160.78 147.02 176.18 243.76 21.92 ~ ~ 745.51 119.76 511.48 457.63

MAP(50)

SUMMER AUTUMN WINTER SPRING

54.81 23.38 5.27 30.54 57.66 14.96 5.30 7.31 27.10 21.47 39.98 53.48 3.24 48.65 23.40 27.05 37.52 31.53 59.67 fiL1l 4.70 .lQJll 3.a2 176.09 21.41 150.0 136.98 (x=35.22) 20.01 (x=25.0)

APPENDIX 3: Interactions between male and female foxes; two case studies

The interactions between male and female foxes changed considerably with time. Initially male 131 and vixen 133 were a mated pair and, during winter 1987, they shared a core area of 38% of their home ranges and their total home range areas overlapped by 75%. During a fortnight in July 1987, which was the breeding season, the male spent 97% of his time within 100 m of the vixen. In summer 1988 these two animals still maintained similar home ranges. They shared 28% of their total home ranges and 22% of their core home ranges. For the first year that these two animals were tracked they shared 75% of their total home ranges and 83% of their core areas. These two foxes succesfully reared three cubs and oft~n the male was in attendance of the cubs while the vixen was some distance away.

The relationship between male 131 and vixen 133 changed considerably, however, and by autumn 1988 they no longer overlapped at all. Instead male 131 shared his total home range with two new vixens, 126 and 115, though neither of these vixens overlapped each other. Vixen 133 was tracked to a completely different area and produced a litter of cubs with a dog-fox that was not captured. The overlap between vixen 133 in 1987 and vixen 115 in 1988 is 92% and thus vixen 115 moved into vixen 133's home-range once she had vacated it.

The next summer (1988) vixen 126 still remained with male 131 but vixen 115 had been replaced by vixen 128. These two vixens still did not overlap each other. The collar on vixen 128 failed at this time and so the extent of her interaction with male 131 after this time is unknown.

The collar on male 131 failed in winter 1988 and so nothing more of his movements are known until he was finally shot in July 1989, approximately 300 m from where he had last been located in winter 1988. At this time he was in the company of yet another vixen.

The interactions between male 112 and his accompanying vixens were also monitored. In Spring 1988 he overlapped the total home range of vixen 133, the previous consort of male 131, by 6%. He also 169

overlapped another vixen, 127, by 21% at the total home range area level and 17% of the core area. These two vixens overlapped at the total level by 3% but did not share a core area.

In September 1988 vixen 127 produced a litter of five cubs. Male 112 was presumed to be the father of these cubs because these two foxes were often located near each other and no other male was known to frequent the area.

Male 112 maintained his total home range overlaps with vixens 127 and 133 during summer 1989 by 10.3% and 26.4% respectively. He also overlapped one of his and 127's vixen cubs (1332) by 18.6% (MAP 95). These three vixens also overlapped each other. The cub overlapped vixen 133 by 15% (MAP 95) and vixen 127 (her mother) by 42% (MAP 95) and 20% (MAP 50). Vixens 127 and 133 overlapped their total home range areas by 11%. It is surprising that male 112 maintained overlaps with vixens 127 and 133 during this time because he only maintained 12% fidelity to his own home range. In contrast, vixen 133 maintained 34.3% (MAP 95) of her home range and similarly vixen 127 maintained 32.8% (MAP 95) of her home range area.

The foxes at Fowlers Gap were mainly solitary and when they did share a home range area, there was temporal separation of its use. 170

APPENDIX 4: Fox predation upon lambs

Many early investigators of fox diet were interested in predation upon neonatallambs. An excellent summary of this research is given in Rowley (1970). Most of the research into lamb mortality has indicated that foxes are not the major cause of lamb mortality, but some examples of significant fox predation have been reported. Moule (1954) concluded that predators were important in lamb mortality (being responsible for 155 out 453 lamb deaths) but as he did not distinguish between predation by foxes and that of feral pigs it is difficult to estimate the impact that foxes were having upon the lambs he investigated. Crawford and Veitch (1959) found that in Western Australia there is a 'large and thriving fox population [which] ... takes a heavy annual toll of young lambs and poultry'. They did not, however, support this statement with any data. Turner (1965) states that in a western district sheep flock, foxes were directly responsible for 11.8% of all lamb deaths. These lambs were all healthy, robust animals with no utilisation of their fat reserves and which had obtained food. Smith (1964, 1965) also found that predation was significant in some seasons in parts of central Queensland. This was due to young lambs being unable to 'keep up' with their mothers when they went into water and thus they became easy prey. Because many of these lambs would probably have died anyway, whether their deaths can be blamed entirely upon fox predation is debatable. In contrast, McFarlane (1964) attempted to quantify the predatory impact that foxes were having upon lambs and he states that it would appear essential in any examination between potential predators and prey to examine the extent to which the predators reduce the numbers of lambs coming into profit. He therefore attempted to clarify whether a lamb was viable or not. He lists four categories of viability and defines five levels of predation. He concludes that 2.9% of the total lambs examined were the victims of uncomplicated predation whereas a maximum of 9.8% of the lambs were the victims of complicated predation. These figures equal 0.6% and 2.0% of lambs born respectively and thus he concludes that predation was not a major factor in lamb mortality. Alexander et al. (1967) also point out that lamb mortality is difficult to assess objectively because lambs that have died from other causes are often mutilated by predators after death and even starvation is difficult to recognise 1 7 1 without a post-mortem examination. Dennis (1965) felt that predator mutilation afterdeath may mask the real cause of the lambs death and it is usually these cases that farmers record as predation.

The majority of studies of lambing mortality e. g. Alexander et al. (1955,1967), McHugh and Edwards (1958), Dermis (1964,1965,1969), Moore et al.(1966) and Mann (1968) have revealed that foxes were generally unimportant in lamb mortality and instead starvation and mismothering were far more important causes of lamb deaths. However, several authors e. g. Mclntosh (1963), McFarlane (1964), and Moore et al. 1966) have reported instances where 'killer' foxes occurred and where these animals were responsible for killing a large number of lambs. Also, McHugh and Edwards (1958) found that since myxomatosis has reduced the rabbit population, lamb predation has been more of a problem. Thus from the literature it may be concluded that foxes are not usually lamb killers but in some particular flocks foxes may be a problem especially if alternative foods are not available.