The use of volunteer hunting as a control method for feral pig populations on O ahu, Hawai i

Transcription

1 Burt, M.D.; C. Miller, and D. Souza. The use of volunteer hunting as a control method for feral pig populations on O ahu, Hawai i Island invasives: eradication and management The use of volunteer hunting as a control method for feral pig populations on O ahu, Hawai i M. D. Burt¹, ², C. Miller 3, and D. Souza¹, ² ¹Pacific Cooperative Studies Unit, Botany Department, University of Hawai i Manoa, 3190 Maile Way, St. John Hall #408, Honolulu, HI 96822, USA. <mburt@hawaii.edu>. ²Department of the Army USAG-HI, Directorate of Public Works, Environmental Division, Natural Resources, (IMPC-HI-PWE), 947 Wright Avenue, Wheeler Army Airfield Schofield Barracks, HI 96857; 3 Department of Land and Natural Resources, Division of Forestry and Wildlife, Natural Area Reserve System, 2135 Makiki Heights Drive, Honolulu, HI Abstract The O ahu Army Natural Resources Program and the State of Hawai i Department of Land and Natural Resources Division of Forestry and Wildlife Natural Areas Reserve System initiated feral pig eradication within fenced management units using volunteer hunters with hunting dogs and a staff escort. This method successfully removed a large percentage of the animals trapped within these units. This control method bridges the divide between the hunting community and programmes aimed at the conservation of natural ecosystems. The aim is to build a rapport and educate hunters about the biological resources and restoration work that the agencies are trying to accomplish. This outreach reduces potential conflicts and vandalism while encouraging new conservation partnerships. Since 1997, about 688 ha of endangered species habitat in 17 management units ranging in size from 10 to 175 ha have been fenced on O ahu. Pigs have been eliminated from three units (93 ha) and reduced to low densities in two units (242 ha) using volunteer hunters. Planning for each hunt utilises information gathered from various aspects of the programme to ensure strategic and systematic coverage. Results of scouting, fence inspections, game cameras, and GPS dog collar tracks from previous hunts are considered in planning hunt strategy. Keywords: eradication, fencing, Natural Area Reserve, Sus scrofa INTRODUCTION Feral pigs (Sus scrofa) have become a problem following their introduction to such diverse locations as Australia, the Galapagos Islands, New Zealand, Seychelles and the United States, where their direct and indirect ecological impacts are well documented (Spatz and Mueller-Dumbois 1975; Springer 1977; Singer et al 1984; Kroll 1985; Loope et al. 1988; Aplet et al. 1991; Vtorov 1993; Atkinson et al 1998; Atkinson and Atkinson 2000; Sweitzer and Van Vuren 2002). The control and eradication of feral pigs has been attempted worldwide for many years (Barret and Stone 1983; Veitch and Bell 1990; Katahira et al. 1993; Caley and Ottley 1995; Lombardo and Faulkner 2000; Cruz et al. 2005; McCann and Garcelon 2008) often using dogs to trail, bail and/or catch the animals (Barret and Stone 1983; Katahira et al. 1993; Caley and Ottley 1995; Lombardo and Faulkner 2000; Cruz et al. 2005; McCann and Garcelon 2008). Here, we report on the effectiveness of volunteer hunters with dogs as the initial tool to eradicate feral pigs from fenced habitats on the island of O ahu, Hawai`i, USA. Secondary tools, not recorded in detail in this paper, are snaring and possibly trapping. These mainland island fenced habitats, or Management Units (MUs), are designed to protect endangered species of native plants (Table 1) as stable populations through management of the taxa and their habitat. Typically, these MUs are fenced areas from which ungulates and other threats are removed or controlled. We have compiled the results from five MUs where the O`ahu Army Natural Resources Program (OANRP) and the State of Hawai`i Department of Land and Natural Resources Natural Areas Reserve System (NARS) utilised volunteer hunters with dogs under the direction of a staff escort as the primary management tool to initiate the removal of pigs. METHODS Study Area This study was conducted on O ahu Island, Hawai`i, USA, in five separate MUs ranging in size from 10 to 175 ha and referred to as: Ēkahanui, Kapuna/Keawapilau, Mākaha Subunit I, Ōpae ula, and Palikea (Fig. 1, Table 1). Fencing Two types of fencing materials were used depending on terrain (Fig 2): 1) 82 or 107 cm tall hogwire mesh, cost US$269/100 m; and 2) 1.1m high welded livestock panel, cost US$1247/100 m. The more expensive panels were Fig. 1 O ahu in the Hawaiian Islands with Management Units (MUs) highlighted. Pages In: Veitch, C. R.; Clout, M. N. and Towns, D. R. (eds.) Island invasives: eradication and management. IUCN, 402 Gland, Switzerland.

2 Burt et al.: Volunteer hunting for pig control Table 1 Description of each Management Unit (MU) including the number of listed threatened and endangered species. Management Unit Elevation (m) Area (ha) Dominant native plant species Listed species Ōpae ula, Ko olau Mountains Metrosideros polymorpha, M. rugosa, Cheirodendron trigynum, and C. platyphyllum 11 Mākaha Subunit I, Acacia koa, M. polymorpha, Diospyros sp., and Dicranopteris linearis 16 Palikea, A. koa, M. polymorpha, and D. linearis. 7 Ēkahanui, A. koa and M. polymorpha 24 Kapuna/Keawapilau, A. koa, M. polymorpha, and D. linearis 13 rigid, easily transported along the cleared lines, and were cut and manipulated to fit the landscape. The taller fencing was used where there was a threat of entry by feral goats (Capra hircus). The fence was typically either anchored into the ground or buried along its length to prevent pigs from digging underneath. In areas with high pig traffic outside the MU, or with very loose soils, a length of hogwire mesh was connected along the outside of the fence as a skirt partly up the fence and partly on the ground (Fig. 3). This was connected with hog-rings along the base of the fence from the second or third horizontal wire down to the bottom and positioned so that the smallest holes of the skirt mesh overlapped the smallest holes of the fence mesh. The skirting was then anchored tight to the ground. This helped slow erosion caused by foot traffic (human and ungulate) along steep sections of fence, and stopped pigs creating entrances. Hunting with dogs This technique involves hunters walking through an area while allowing their dogs to search for pig scent. Any pigs located are chased by the dogs and caught or bailed until hunters arrive and dispatch the animal with a knife or firearm. This technique is particularly effective for pigs that are shy of other removal techniques and in areas that contain small remnant populations. Elsewhere, contract or staff hunters were used in conjunction with other removal techniques since public hunting alone is often unsuccessful with eradication. However, in accessible areas, public hunting could be effective for the initial reduction (Barret and Stone 1983; Anderson and Stone 1993). Volunteer hunters and staff escorts ranged from groups of two to six people and the number of dogs ranged from Fig 2 Details of hog-wire mesh and livestock panels. Fig. 3 The skirt of hogwire mesh added to a fence of the same material. 403

3 Island invasives: eradication and management four to 21. Most of the hunters came from communities close to the MU and had personal ties to the area. They were both sport and subsistence hunters with varying skill levels and experience. Various dog breeds were used. Hound mixes were utilised for their ability to follow scent trails. The catch dogs were usually of some bull terrier mix. The quality of the dogs used varied from very experienced and well trained, to young first-year dogs at early stages of training. Monitoring A Garmin (Olathe, KS) Astro 220 Global Positioning System (GPS) unit and two DC 30 GPS dog tracking collars were utilised to monitor dog movements on all hunts at Kapuna/Keawapilau. The GPS collars communicate with a handheld GPS unit via Very High Frequency (VHF) radio signals. A topographic map on a 66 mm colour display (updated every 5 sec.) on the GPS unit showed the location dogs, the distance and path a dog had taken, and whether or not the dog was moving. The spatial data collected by the unit was then downloaded and converted into GIS shapefiles using ARCMAP (ESRI Redlands. CA) and the Minnesota Department of Natural Resource free DNR Garmin Application. These shapefiles were used for future hunting plans to ensure coverage of previously unchecked locations. Two Moultrie (Alabama) Game Spy 4.0 wildlife game cameras were used sporadically and throughout the Kapuna/Keawapilau MU. Triggered by motion or infrared sensors, they provided digital photos or videos of passing wildlife 24 hours a day. RESULTS Details of each MU, fences, hunting effort, and results are given in Table 2. Ōpae ula To make this MU pig proof, skirting was applied around the whole unit. There are two stream crossings, one is at a waterfall and the second utilises a Hypalon (chlorosulfonated polyethylene synthetic rubber) sheet to block access for pigs and still allow water to pass unimpeded. When the fence was completed, the amount of pig sign indicated that there was only one small pig left within the unit. Snares were installed by qualified staff members, but were removed after one year without catching any animals. Then hunters were flown in by helicopter. They split up into two groups and spent two days covering the unit. The sign indicated that the one remaining pig had pushed out under the Hypalon during the hunt. Mākaha Subunit I Skirting was applied in the steepest and most pig prone areas. Once the fence was completed, hunts with and without staff escorts were conducted over a 20-month period. Animals caught ranged in weight from 4.54 to kg with a mean of kg. Eight males, five females (one of which had eight embryos), and 14 infants (sex not determined) were removed. This eradicated pigs from the MU. Palikea Skirting was applied in the steepest and most pig prone areas. An kg male pig was caught during the first hunt but none in the second, although a single pig was known to be present. This last pig was later caught in a snare. Ēkahanui This MU is comprised of two subunits, the first being completed in 2001 and the second in Skirting was applied in the steepest and most pig prone areas. Hunts with staff escorts began in November 2008, prior to the final completion of the fence. Three males, four females, five infants (sex not determined) and four unknowns (data not collected) were removed but no weights were recorded. The hunting was limited to three months. Snares were deployed and two more sows were captured. One animal is left within the MU. Kapuna/Keawapilau The Kapuna/Keawapilau MU is comprised of three subunits (I, III, IV). Subunits I and III are small and are considered free of pigs. Subunit IV is larger and was the focus of pig eradication through public hunting. Skirting was applied in the steepest and most pig prone areas. NARS staff escorted the public hunts, which commenced soon after the completion of fences in August All except three animals were taken by dogs and hunters; two were shot by staff and one was trapped. Animal weights ranged from 2.27 to kg with a mean of kg. Nineteen were females, six were males, and one was undocumented. Ungulate control is continuing with public assistance. During the hunts at Kapuna/Keawapilau, GPS collars provided real-time spatial data of dog locations. Images recovered from game cameras aided in assessing animal presence vs. absence and helped with identifying targeted individuals (i.e. one large boar, which was brushing off dogs and evading capture). DISCUSSION Across all five MUs, 60 volunteer hunters participated in 117 hunts. Beyond hunting opportunities for the public, this Table 2 Details of each Management Unit (MU) and hunting effort. MU Size (ha) Year Length (m) Fence Type No of Hunts No of Hunters Hunter No of Hours Pigs Hunter hrs/ha hrs/pig Person Ōpae ula Hog-wire Mākaha Subunit I Hog-wire & Panel Palikea Hog-wire & Panel Ēkahanui Hog-wire & Panel Kapuna/Keawapilau Hog-wire & Panel

4 Burt et al.: Volunteer hunting for pig control pig eradication method also created a working relationship between federal and state conservation organisations and a core group of pig hunters. Hunters within the community spread the word about management work we were accomplishing and also acted as eyes and ears in the field. In MUs that were accessible, hunters reported damage to the fences such as tree falls and blow-outs between our fence inspections. They also reported possible issues with other hunter groups that needed our resolution. We have thus been able to gain knowledge from their expertise and get a better understanding of the hunting community. Volunteer hunter programmes required many different stakeholders. As an example, in Mākaha, we partnered with the City and County of Honolulu Board of Water Supply (landowner), Mauna Olu Estates (site access), Ka ala Farms (non-profit community organisation), and State of Hawai i Department of Land and Natural Resources. Community meetings were held to inform the public of the fence project and gain support by local hunters. Four good faith hunts were conducted prior to the completion of the fence. A total of seven community hunters and four staff escorts participated for a total of 76 person hours, removing two pigs. Although a modest effort, this showed all those involved that such an operation could be successful and could reach a common goal. These early efforts led to a pig eradication programme in Mākaha that was led by volunteer hunters. Once the eradication effort was complete and trust was gained we were able to extend the hunts outside the MU in order to keep pressure off the fence. Our data do not allow predictions of the duration and cost of volunteer hunters and dogs, an optimum number of dogs or hunters, or the efficiency of the technique. To offset costs, we limited the time and season of some hunting campaigns before applying other management techniques. This may give the hunters a sense of purpose to complete the eradication before the set date and focus effort on the animals such as piglets and pregnant/lactating females that may be more susceptible to hunting pressure. Any time limitation would be highly dependent on the principal management agency and its mission and mandates. Keeping hunters focused on eradication was sometimes challenging. In Ēkahanui, Kapuna/Keawapilau and Mākaha we started with groups of hunters that were interested in conducting the campaign but as time went on, and catch rates diminished, that interest dwindled. We were left with a few groups of hunters that really understood what we were trying to do and why, wanted to help, and were determined to see successful conclusions of eradication campaigns. Because each of the current and future MUs have unique characteristics, dog and hunter numbers may need to be modified to match each site. The breeds or numbers of dogs did not seem to be as important as their general disposition, physical conditioning and amount of hunting experience. The match of hunters and dogs to the MU also had an impact on the success of hunts. Hunters with previous experience in the area have valuable knowledge about pig movement patterns and effective hunt strategies. Limiting our search for hunters to those that have experience in these MUs should increase efficiency. Hunting with dogs will not work for every MU. Cliffs and steep environments pose safety hazards for dogs and hunters, and the cost of ferrying hunters, dogs and staff by helicopter can become too high. Reliable access and safe workable environments are keys to the use of dogs and hunters. Tools, such as GPS dog collars and game cameras, made hunts safer, more efficient, and more effective. Knowing the location of dogs with the GPS collars reduced the time to reach pigs that were bailed or caught. Pigs were dispatched faster, thus resulting in more successful catches, fewer injuries to dogs, and less suffering by the pigs. The collars will be standard practice from now on. The GPS dog collar data also showed us pig movement patterns. Using the GPS receiver, we could observe routes that dogs took while chasing pigs, thus indicating where the pigs were running. With this information, interception zones such as major trail crossings, clearings, and ridgeline saddles were revealed. Hunts then involved pre-positioned gunners (staff or hunters with firearms) or individual hunters with 1-2 dogs at interception zones prior to releasing the main dog pack. For example, a pack of dogs taken into a gulch with a consistent water source encountered a pig that eluded capture. The pre-positioned gunner was able to shoot the pig which had outdistanced the dogs by approximately 100 m. It is very likely that this pig would otherwise have eluded capture. Information gathered from the cameras, combined with observations made during hunts and other field activities, was used to inform public hunters of animal movement patterns, active zones vs. inactive zones, and to choose hunt strategies. An in-house hunting dog programme or contract hunters could more effectively capture pigs per unit hunt effort. However, the frequency and timing of completion of MU fences and seasonal nature of the hunting do not warrant the costs associated with running an in-house hunting dog programme. The use of outside contractors for hunting also risks alienation of the local hunting community. Feral pig populations continue to threaten conservation areas in Hawai i, so having multiple control techniques will increase the efficiency of our ungulate control programmes. The use of volunteer hunters with dogs has produced positive results but is at a relatively early stage of development. We will continue to nurture relations with hunters through mutual trust, respect, and understanding. Good communication and strong relationships between conservation programmes and the hunting community are fundamental to the preservation of biological resources and the restoration work that the agencies are trying to accomplish. There has been some damage to fences by people, but we believe that potential conflicts and persistent vandalism can be averted with education and collaboration. ACKNOWLEDGEMENTS We are grateful to the State of Hawai i Department of Land and Natural Resources and the Army Garrison, Hawai i via the Pacific International Center for High Technology Research, for their sponsorship of this study and associated endangered species conservation and restoration efforts. We would like to thank all of the staff and public hunters who have participated throughout the years; (Staff) George Akau, Dan Forman, Josiah Jury, Justin Luafalemana, Simoi Luafalemana, Nalani Mailhue, Kahale Pali, Robert Romualdo, Dan Sailor, Darin Shiu, William Weaver, Matt Wickey, (Public Hunters) Aiwohi Jr., Aiwohi Sr., Chris Burner, Kasey Cabison, Robert Cardus, Walter Cardus, Chad, Corey, Correia, Curtis, David, Richard Delima, Frannie Drammundo, Matt Elvina, Mark Elvina, Marcus Eslit, Gary Fernandez, Flores, Greg, James Jr., Jr. Boy, John, Cyrus Kanakaole, Kawika, Kelly, 405

5 Island invasives: eradication and management Lane, Lopaka, Wendell Lucas, Frank Mahuka, Albert Mandac, Mano, Ronald Masilio, Nainoa, Nick, Roman Paris, Earl Perez, Joey Perez, Mike Perez, Pila, Quentin, Russell, Shanda, Shine, Soliz, Tripp, and the many others we have failed to mention. We would also like to thank the editors of this manuscript for the helpful insights (Dr. James Jacobi, Kapua Kawelo, Michelle Mansker, Joby Rohrer, Dr. Clifford Smith, Talbert Takahama and Dr. Eric VanderWerf) and Krista Winger for her exceptional work on the maps for this manuscript. Veitch, C.R. and Bell, B.D Eradication of introduced animals from the islands of New Zealand. In: Towns, D.R.; Daugherty, C.H. and Atkinson, I.A.E. (eds.). Ecological Restoration of New Zealand Islands, pp Department of Conservation, Wellington, New Zealand. Vtorov, I.P Feral pig removal: effects on soil microarthropods in a Hawaiian rain forest. Journal of Wildlife Management. 57(4): REFERENCES Anderson, S.J. and Stone, C. P Snaring to control feral pigs Sus scrofa in a remote Hawaiian rain forest. Biological Conservation 63: Aplet, G. H.; Anderson S. J. and Stone, C. P Association between feral pig disturbance and the composition of some alien plant assemblages in Hawaii Volcanoes National Park. Vegetation 95: Atkinson, C. T.; Lease, J. K.; Shema, N. P.; Dusek,R. J. and Drake, B. M Habitat management and vector control: Prospects for managing avian disease in Hawaiian forest birds. Wildlife Disease Association Conference, 9-13 August Madison, WI. Atkinson, I.A.E. and Atkinson, T.J Land vertebrates as invasive species on islands served by the South Pacific Regional Environment Programme. In: Invasive Species in the Pacific: A Technical Review and Draft Regional Strategy, pp South Pacific Regional Environment Programme, Samoa. Barrett, R. H. and Stone C. P Hunting as a control method for wild pigs in Hawaii Volcanoes National Park. A report for Resource Management, Hawaii Volcanoes National Park. Volcano, HI. Caley, P. and Ottley, B The effectiveness of hunting dogs for removing feral pigs (Sus scrofa). Wildlife Research 22: Cruz, F.; Donlan, C. J.; Campbell, K. and Carrion, V Conservation action in the Galapagos: feral pig (Sus scrofa) eradication from Santiago Island. Biological Conservation 121: Katahira, L. K.; Finnegan P. M. and Stone, C. P Eradicating feral pigs in montane mesic habitat at Hawaii Volcanoes National Park. Wildlife Society Bulletin 21(3): Kroll, J. C Interspecific competition between feral hogs and whitetailed deer in the Post Oak Savanna region of Texas. Federal Aid Project W-109-R-8 Job. No. 44, Final Perf. Rep. 404 pp. Lombardo, C.A. and K.R. Faulkner Eradication of feral pigs (Sus scrofa) from Santa Rosa Island, Channel Islands National Park, California. In: Brown, D.R.; Mitchell, K.L. and Chaney, H.W. (eds.). Proceedings of the Fifth California Islands Symposium, pp OCS Study MSS U.S. Department of the Interior, Mineral Management Services Pacific OCS Region, Washington, D.C. Loope, L. L.; Hamann, O. and Stone, C. P Comparative conservation biology of oceanic archipelagos: Hawaii and the Galápagos. BioScience 38(4) : McCann, B. E. and Garcelon, D. K Eradication of feral pigs from Pinnacles National Monument. Journal of Wildlife Management 72(6): Singer, F. J.; Swank, W. T. and Clebsch, E. E. C Effects of wild pig rooting in a deciduous forest. Journal of Wildlife Management. 8(2): Spatz, G. O. and Mueller-Dumbois, D Succession patterns after pig digging in grassland communities on Mauna Loa, Hawaii. Phytocoenologia 3(2/3): Springer, M.D Ecological and economic aspects of wild hogs in Texas. In: Wood, G.W. (ed.). Research and management of wild hog populations: Proceedings of a symposium, pp Belle W. Baruch Forest Science Institute, Clemson University, Georgetown, SC. Sweitzer, R.A. and Van Vuren, D Rooting and foraging effects of wild pigs on tree regeneration and acorn survival in California s oak woodland ecosystems. In: Standiford, R.B.; McCreary, D. and Purcell, K.L. (technical coordinators). Proceedings of the fifth symposium on oak woodlands: oaks in California s changing landscape, pp Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. 406