NATURAL AREAS ECOLOGICAL DAMAGE AND ECONOMIC COSTS SURVEY REPORT SUBMITTED TO: All Interested Survey Respondents PREPARED BY: Rick A. Sweitzer and Blake E. McCann Department of Biology, University of North Dakota Grand Forks, ND 58202 e-mail: [email protected] July 2007 Sweitzer & McCann • Wild Pig Natural Areas Survey Report TABLE OF CONTENTS BACKGROUND AND INTRODUCTION ...........................................................................1 METHODS .............................................................................................................................5 RESULTS ...............................................................................................................................7 Wild Pig Presence and Issues .......................................................................................7 Resource Damages and Visitor Interactions.................................................................10 Habitat Protection and Management to Control Wild Pig Populations ........................12 Economic Costs of Managing Natural Areas with Wild Pigs.......................................16 DISCUSSION........................................................................................................................18 Presence and Trends for Wild Pigs in Natural Areas ...................................................18 Resource Damage and Visitor Interactions with Wild Pigs..........................................19 Economic Costs Incurred from Wild Pig Damage and Removal Efforts .....................20 Natural Areas Using Lethal Control to Reduce Wild Pig Populations.........................22 Lethal Control Options ........................................................................................23 Non-lethal Control Options .................................................................................26 MANAGEMENT IMPLICATIONS .....................................................................................27 RECOMMENDATIONS.......................................................................................................28 Course of Action for Mangers Facing Feral Pig Damage.............................................28 Non-lethal Damage Control – Fence Design................................................................29 Trapping and Trap Design ............................................................................................30 Dispatching Trapped Animals .............................................................................33 Shooting Free-ranging Wild Pigs..................................................................................34 ACKNOWLEDGMENTS .....................................................................................................36 LITERATURE CITED ..........................................................................................................36 i Sweitzer & McCann • Wild Pig Natural Areas Survey Report NATURAL AREAS ECOLOGICAL DAMAGE AND ECONOMIC COSTS SURVEY REPORT Abstract: Wild pigs (Sus scrofa) are a large ungulate native to Eurasia and North Africa which are now widely distributed as non-indigenous species in many areas, including California. Because of their adaptability to new environments, reproductive capabilities and foraging behaviors, wild pigs cause numerous damages to natural areas and wildlife throughout the state. To assess these damages we developed and distributed a survey to managers of all identifiable natural areas in California. Our objective was to identify ecological and monetary costs associated with managing natural areas within the current range of wild pigs. Surveys were mailed to 333 representatives of natural areas across California between mid December 2006 and early January 2007, and by July 2007 we had received information on 573 individual natural areas. Survey results indicated that wild pigs were present at 137 natural area units. Managers of most of these natural areas reported moderate to high concern regarding presence of wild pigs related to rooting and other disturbances in grassland, oak woodland areas and riparian habitats. Many visitors to natural areas with wild pigs commented to managers on rooting damage and negative interactions with wild pigs while hiking or camping, while others asked about hunting access. Some adjacent landowners wanted managers of natural areas with wild pigs to reduce pig numbers, whereas other nearby landowners were less bothered and likely benefited by enhanced hunting on their properties. A significant subset of the 137 natural areas with wild pigs reported using some combination of lethal and non-lethal methods to reduce damages from wild pigs. A key trend identified from the survey was that increased numbers of natural areas developed management programs to reduce wild pig damages in recent years compared to in the past. The overall minimum economic costs to all natural area management entities that reported wild pig-related management costs were $11,300,132 over the last 3 years and $18,672,023 overall. However, this was a conservative estimate because the majority of expenditures were associated with exclusion or removal of wild pigs, and not representative of damages incurred to the natural resources themselves. There is a need for reliable methods of assigning monetarily value to undisturbed natural areas and native plants and animals to provide a consistent economic presentation of actual resource damage caused by wild pigs. Non-lethal control methods, such as caging around seedlings, small-scale exclusionary fencing around sensitive habitats, and perimeter fencing, can provide protection to resources from wild pigs or be used to aid in lethal control efforts. Lethal techniques ranging from trapping/shooting programs to aerial shooting and “Judas” animals were used for wild pig removal by managers of natural areas, representing all of the current primary options for wild pig population reduction. Detailed descriptions of how these different techniques can be applied are provided. Management of wild pigs in California will continue to be difficult and controversial in the future. Consensus will need to be reached on how to effectively manage a large, widespread population of wild pigs as a game species while achieving a more appropriate balance with the need to preserve and maintain California’s unique and diverse natural resources. ii Sweitzer & McCann • Wild Pig Natural Areas Survey Report BACKGROUND AND INTRODUCTION Feral pigs (Sus scrofa) are a large ungulate native to Eurasia and North Africa which are now widely distributed as wild animals in many areas, including California. Feral pigs (designated “wild pigs” in California) were initially established in coastal regions during the Spanish colonial period and remained regionally localized around original points of introduction for hundreds of years. However, significant range expansion has occurred since the 1950s by a combination of numerous additional releases of domestic and wild swine and natural dispersal from points of introduction (Figure 1; Waithman et al. 1999). The current distribution of wild pigs encompasses areas in parts of 47 of California’s 58 counties (Figure 2). Figure 1. Estimated distribution of wild pigs in different counties in California during (a) 1965-67, (b) 1983-85, (c) 1992-94, and (d) in 2006-07 (current range). Distributions for the first three time periods were estimated from Annual Hunter Game Take Survey records (Waithman et al. 1999), whereas the current range was determined from from mapped positions of wild pigs that were killed by hunters (reported on wild pig tags) or removed under Depredation Permits. 1 Sweitzer & McCann • Wild Pig Natural Areas Survey Report Figure 2. Estimated current distribution of wild pigs in California at the level of the county. Wild pigs are present in appreciable numbers in 47 of 58 counties in the state (small numbers may be present in 2-3 other counties). The distribution map was based on the mapped positions of wild pigs that were either killed by hunters (locations reported on wild pig tags) or removed on Depredation Permits during the period from 2004-06. A basic wildlife habitat model (Mayer and Laudenslayer 1988) and our recent research indicates that wild pigs are most abundant in oak-dominated habitats in Central and North Coast regions of California, but they are expanding elsewhere. The distribution of wild pigs is closely associated with portions of six major floristic provinces/ecoregions where the combined presence of 8 native oak species and annual grasslands (hereafter oak woodlands) provide cover and forage (Figure 3). California’s oak woodlands provide watershed protection, public recreation and habitat and forage for over 3500 species of vertebrates and invertebrates (Garrison 1996, Pavlik et al. 1991). Regionally, this habitat type is of important conservation concern because of pressure from agricultural and urban development, recent spread of disease (Kelly and McPherson 2001), and limited or negligible regeneration in several key species (Bartolome et al. 1987). On a larger scale California’s oak woodlands are recognized as unique in North America (Rutledge et al. 2001) and one of the Earth’s 25 biodiversity hotspots (Myers et al. 2000). For these reasons, and because of the damaging effects of their presence and activities, biologists and managers of many natural areas are concerned for the presence of nonnative wild pigs in California oak woodlands. 2 Sweitzer & McCann