by D Garcelon · 2011 · Cited by 1 — While numerous island foxes were captured, no feral cats were trapped. IWS continued wildlife fact sheet. abcbirds/cats/NFWF.pdf. Coonan, T.J.
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MSRP Seabird Restoration Program Œ San Nicolas Island, California Annual Report on Island Fox Ca re and Monitoring Provided in Support of the San Nicolas Island Seabird Restoration ProgramŒ2010 Prepared by: David Garcelon Institute for Wildlife Studies P.O. Box 1104 Arcata, CA 95518 November 2011
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INTRODUCTION In 2009, the Montrose Settlements Restorati on Program (MSRP), in cooperation with the U.S. Navy, initiated a project to protect seabirds and other native wildlife on San Nicolas Island (SNI) through the removal of feral cats ( Felis catus ). Feral cats kill millions of birds and small mammals each year (Warner 1985, ABC 2004), can severely impact island bird populations (Merton 1977, Moors and Atkinson 1984, Dowding and Murphy 2001) and have been responsible for the extinction of at least 33 bird species worldwide (Lever 1985). The removal of feral cats from SNI was initiated to help restore seabird populations, reduce impacts on native species such as the island night lizard (Xantusia riversiana ) and reduce competition for resources w ith species such as the island fox (Urocyon littoralis) (USFWS 2009). After release of the draft Environmental Imp act Statement (USFWS 2008), the U.S. Fish and Wildlife Service and the U.S. Navy entered into dialog with animal protection groups regarding the feral cat remova l project, including discussion regarding whether lethal removal would be used as the main removal method. The Institute for Wildlife Studies (IWS) was contracted by MSRP to work with the largest of the anim al protection groups, the Humane Society of the United States (HSUS) , in their effort to evaluate if using live-capture box traps would be an effective means of capturing the cats. HSUS staff visited the island to test out methods of live capturing feral cats using box traps and a variety of enticements. While numerous is land foxes were captured, no feral cats were trapped. IWS continued testing methods suggested by HSUS for trapping cats in box traps over a 4-month period, and then compared that captur e success with a brief capture effort using padded leg-hold traps (Garcelon 2009). Results from this investigation found that capture success for feral cats was significantl y higher in leg-hold traps compared to box traps, suggesting that feral cats may be wary of entering box traps. Considering the much greater efficiency of using leg-hold traps to capture feral cats on SNI, and the fact that no cats were injured during the leg-hold trap testing, that method was adopted for conducting the bulk of the subsequent feral cat removal effort. Trapping effort began in June 2009 by Island Conservation (IC), the organization contracted to conduct the removal of the feral cats. IWS was contracted to provide support for the project by caring for any foxes that might become injured in traps during the project, and to evaluate impacts of the leg-hold trapping effort on the fox population overall. After it was later determined that all cats that could be captured would be transported live to an HSUS holding facility, IWS also was tasked with caring for the cats until they could be transferred off of the island (Garcelon 2010). The large majority of the leg- hold trapping component of the feral cat removal project on SNI had been completed by the end of 2009 (Hanson et al. 2010, 2011). During 2009, IWS had 99 fox patients admitted to the m obile clinic, of which 73 had conditions associated with having been captured in a leg-hold trap (Garcelon 2010). As it was unknown how much additional trapping effort w ould be required in 2010 to complete the cat removal effort, IWS was asked to mainta in the mobile fox hos pital on SNI to handle foxes that may become injured in the process of capturing feral cats. Furthermore, there
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were still patients in the hospital at the end of 2009 that had been injured during trapping that had occurred in that year (Garcelon 2010), and those individuals needed continued care. In addition to the veterinary care of injured foxes, IWS was tasked with evaluating the status of the fox population on the island during and after the leg-hold trapping was conducted, and to determine if their were any chronic physical problems associated with foxes that had been caught in these trap s. These objectives were accomplished concurrently through capture-mark-recapture efforts both on mini-grids set up in each major habitat type on the island, and by exam ining foxes captured during annual trapping on the long-term monitoring grids established by the Navy. This report covers the fox care and population monitoring that was conducted in 2010 METHODS Estimating Change in Fox Density on the Island The Navy has monitored foxes on three establ ished trapping grids annually since 2000. This has been the principal means of tracking trends in density, survival and reproduction in the island fox population. Because these grids encompass a relatively small portion of island (18%; Garcelon and Hudgens 2011), and do not include all of the available habitat types present on the island, they cannot be used to detect changes in fox demography on a habitat-specific or a spatially comprehensive basis. In an effort to assess potential changes in fox density across SNI on a habi tat-specific basis, we established 26 mini- grids that were configured in a 2 X 6 a rrangement with 250 m spacing between traps and operated for four days. This approach follows the recommendations by Spencer et al. (2006) for island fox monitoring, and that used by the National Park Service for monitoring island foxes on San Miguel and Santa Rosa islands (Coonan 2010). The mini-grids were placed within each of the following habitat types: coreopsis forest, grassland, coastal dune and coastal scrub. We placed additional grids in what was classified as fiBarrenfl areas, which constituted habitat that was primarily void of vegetation and was dominated by rocky exposed soils. To the degree possible, the grids were oriented such that all of the traps were encompassed within one habitat type, although this was not always possible due to the irregular nature of some habitat patches (Figure 1). To avoid capturing foxes on more than one grid at a time when trapping multiple grids concurrently, we scheduled trapping such that grids directly adjacent to each other we not operated at the same time. We determined the density of foxes on each mini-grid using Program DENSITY (Efford 2004). This spatially-explicit method for density estimation uses a probability model for capture data that explicitly incorporates the spatial component of the sampling process (i.e., the location of each capture) with in a maximum likelihood framework. That probability model is comprised of 2 submodels: 1 for the distribution of animals exposed
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to the sampling grid and 1 for the detecti on process. The detection submodel describes the probability of detection of an animal, gi ven the location of its home range in relation to the sample sites. The form of the dete ction submodel and associated parameters is dependent on the chosen detection function. Additional types of variation in the detection process (e.g., time variation, behavioral res ponse, and individual heterogeneity) can be modeled similar to closed population models. Because this method is likelihood based, AICc (Akaike Information Criterion, correct ed) can be used for model selection and model averaging. We ran competing models and selected the model with the lowest AICc weight. RESULTS Foxes Presented to IWS by IC During 2010 Six foxes were brought to IWS between 1/11/10 and 1/15/10. Two of the foxes (E720E and 41534) had injuries or conditions not related to the day they were captured and were just brought in for examination. Another f ox (0683B) was found to be coughing while in the trap, but no abnormalities were found and th e fox did not exhibit the behavior again while held in the clinic. One AC2 female fox (95A3A) had a possible di slocation of a metatarsal and was held 5 days for cage rest. An AC2 male fox was found to have some laxity in its carpus joint and was held 2 days for cage rest. The last fox (3003F), an AC1 male, was found with the trap chain wrapped around its capture leg. Th e fox was treated for swelling and held over for 25 days for observation and recuperation. We completed treatment and rehabilitation of two foxes captured in leg-hold traps in 2009, and these animals were released in 2010. One was an AC4 male originally admitted with a metatarsal fracture on 7 August 2009, who was released on 18 February 2010. The second was an AC4 male that was admitted on 1 November 2009 with hyperthermia and some soft ti ssue injuries. This animal wa s released on 20 February 2010. Animals recovering from fractures or long -term stays at the clinic were place in outdoor pens to retain their strength prior to release (Figure 2). Figure 2. Set of 4 outdoor pens were used to allow fox patients to exercise prior to rele ase.
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Mitigation Foxes Treated and Feral Cats Cared for in 2010 In addition to the six foxes brought in by IC in January, we admitted another 11 foxes to the clinic during 2010 as mitigation cases. These were individuals that were not associated with the leg-hold trapping effort , but were discovered with injuries either through other trapping efforts conducted by IWS or by island residents. The injuries ranged from very serious (fractures caused by car collision) to relatively minor puncture wounds (Table 1). These patients represented a total of 487 patient-days in the clinic associated with their treatment and rehabilita tion (Table 1). Including the patients held over from 2009 and the foxes brought in by IC for evaluation or care, there were a total of 610 patient-days in the clinic in 2010. No feral cats were trapped in 2010, therefore IWS received no cats to care for during that period. Table1. Fox patients handled at mobile veterinary clin ic in 2010 that were cla ssified as mitigation cases (i.e., not associated w ith leg-hold trapping). Date Date No. Days Fox ID Sex Age AdmittedReleased at Clinic Injury or Illness 27336 M 4 1/14/101/15/101Old fracture on metatarsals 6193E M 4 8/11/092/18/10191Fractured radius 64653 F 3 2/2/102/20/1018Possible kidney infection 3423F M 2 7/3/107/7/104Inf ected puncture above eye 07A59 M 2 9/5/109/6/101Mouth jammed in wire trap 15135 M 2 6/29/1010/19/10112Pelvic fracture, hip dislocation 67565 F 4 10/20/1010/22/1012Significant trauma to left front foot 50469 M 0 9/30/1010/28/10228Infected puncture above eye 1930B F 4 10/15/1011/1/1017Fractured tail B4759 F 0 7/27/1011/1/1097Partially severed foot B7C70 M 4 10/16/1011/1/1016Abrasions & punctures on legs 1Fox was euthanized due to extent of injury. 2Developed spinal fracture upon re lease and was later euthanized. Follow-up Monitoring of the Fox Population We conducted trapping efforts across SNI, both as follow-up to the feral cat removal effort and as part of the Navy sponsored annual island fox monitoring. As part of the annual fox monitoring on the three established trapping grids, we captured 112 foxes during 888 trap nights (Garcelon and Hudgens 2011). During that effort we were able to reassess 69 foxes that had been previously captured in leg-hold traps. The assessment involved testing the mobility of each of the leg joints and palpating for healed fractures above and below the joints. In addition, we also set up a number of fimin i-gridsfl across the island in 2010 to both examine foxes previously caught in leg-hol d traps and to have a broader sampling methodology from which to assess changes in the fox population that might have occurred due to feral cat removal effort (see be low). During this effort we captured a total of 192 (155 adults, 37 pups) individual foxes 367 times during 1248 trap nights (29.4%
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Table 2. Capture results for mini-grids trapped on Sa n Nicolas Island in 2010 and dens ity estimates produced using program DENSITY. Where more than one grid within a habi tat type is listed, the best fit model required individual estimates for each grid. ML DensityDensityDensityDensityDetection Habitat/GridNo. GridsNo. Indiv.Total Captures Foxes/km 2SELower 95% CIUpper 95% CIProb. (g0) Barren 416 281.910.81 0.86 4.220.20 Grassland 427 471.890.66 0.793.670.129 Scrub 765 9610.282.00 7.0514.990.049 Dune – A 110 235.541.84 2.9310.461.000 Dune – B 114 1718.729.20 7.5246.600.102 Dune – C 118 4211.833.02 7.2319.350.578 Dune – D 121 3614.414.14 8.3025.020.245 Dune – E 16 172.991.35 1.29 6.940.999 Coreopsis523 303.09251.8668 1.03719.22120.07089 Coreopsis – D124 3110.47816.7861 1.149395.52870.03631 DISCUSSION Fox Patients Due to the fact that IC only operated leg-hold traps for a 5-day period in January 2010, there was only a short period when foxes were exposed to these traps and had any opportunity to become injured. However, IW S maintained the clinic in operation until it was determined by the U.S. Fish and Wildlife Service that the likelihood was low of any further leg-hold trapping occurring. During the period between when IC ceased leg-hold trapping, and when the operation of the clinic was shut down on 1 November 2010, we were able to continue providing care to foxes that had been admitted as mitigation cases. The last of the foxes that were being held for care and rehabilitation were released on 1 November 2010. From the start of the pr oject in June 2009 through October 2010, the clinic took in a total of 116 island fox patients for examination and/or veterinary care. In addition, we provided health checks and care for 52 adult cats and 10 kittens that were born to three adults cats at our facility. All of the cats were successfully transported off of SNI and received by the HSUS for transport to their holding facility. Population Monitoring Using Mini-Grids The only comparison we can make for fox de nsity estimates on San Nicolas Island are the results obtained from the annual grid trapping that has occurred on the island since 2000. There some problems associated with dire ct comparison to those data, as the larger grids (48-50 traps each) used for that monitoring encompass more than one habitat type (Garcelon and Hudgens 2011). Fox densities found on the Grassland and Barren habitat mini-grids were encompassed within the 95% confidence intervals for the density estimates found on the a primarily grassland grid (Skyline) trapped during the Navy™s annual fox monitoring. In 2009 the density estimate was 3.53 ( 95% CI = 1.9 Œ 6.5 foxes/km2) and in 2010 was 3.3 (95% CI = 1.9 Œ 5.7 foxes/km2) (Garcelon and Hudgens 2011). The Scrub habitat mini-grids are similar to the predominant habitat on the a nnually trapped Tuft™s grid, and the estimated density on our mini-grids fell within the 95% CI for Tuft™s grid for the 2008-2010 period
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(Garcelon and Hudgens 2011). The Dune habitat mini-grids are similar to the Redeye annual trapping grid, but not all of that grid is comprised of dune habitat. Three of the higher density Dune mini-grids (B, C, D) fell within the 95% CI of Redeye grid for the 2008-2010 period. There were no previous data to compare fox densities specifically within Coreopsis habitat. Based on five of the six grids sampled in that habitat, the quality of that habitat for foxes would appear to be higher than either Barren or Grassland, but is considerably lower than densities in Scrub or Dune habitat. The one exception was the Coreopsis-D mini-grid, which is adjacent to Nictown, th e location on the island with the greatest human occupation. We believe the density found on this mini-grid was abnormally high due to the foxes being fed by residents in Nictown and then occupying suitable habitat nearby. As the mini-grid approach appears to be approximating the densities obtained on the larger annual trapping grids, and give the added benefits of providing great spatial representation of the island and habitat-specific density information, we believe it will be a good method of detecting changes that may ta ke place in the island fox population that might be associated with the removal of feral cats from the island. LITERATURE CITED American Bird Conservancy (ABC). 2004. Do mestic cat predation on birds and other wildlife fact sheet. http://abcbirds.org/cats/NFWF.pdf Coonan, T.J. 2010. Island fox recovery program 2009 annual report. National Park Service, Channel Islands National Park, Ventura, CA. 33 pp. Dowding, J. E. and E. C. Murphy. 2001. The impact of predation by introduced mammals on endemic shorebird in New Z ealand: A conservation perspective. Biological Conservation. 99:47Œ64. Efford, M.G., D.K. Dawson and C.S. Robbins. 2004. DENSITY: software for analyzing capture-recapture data from passive detector arrays. Animal Biodiversity and Conservation 27.1: 217-228. Garcelon, D. K. 2009. Report on testing of methods to remove feral cats from padded leg-hold traps, San Nicolas Island, Califor nia. Unpublished report by the Institute for Wildlfie Studies, Arcata, CA. 6 pp. Garcelon, D.K. 2010. Annual report on is land fox care and monitoring provided in support of the San Nicolas Island seabird restoration programŒ2009. Unpublished report to the Montrose Settleme nts Restoration Program. 16 pp.
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Garcelon, D. K. and B. R. Hudgens. 2011. Island fox monitoring and demography on San Nicolas IslandŒ2010. Unpublished report prepared by the Institute for Wildlife Studies, Arcata, California. 28 pp. Hanson, C.C., Will, D.J., Bonham, J.E., and B. S. Keitt. 2010. The removal of feral cats from San Nicolas Island, California to Protect Native and Endemic Species: 2009 Annual Report. Unpublished report, Island Conservation, Santa Cruz, CA. 19 pp. Hanson, C.C., and Bonham, J.E., 2010. The re moval of feral cats from San Nicolas Island, California, to Protect Native and Endemic Species: 2010 Annual Report. Unpublished report, Island Conservation, Santa Cruz, CA. 21 pp. Lever, C. 1985. Naturalized mammals of the world. Longman, London; New York. Merton, D. V. 1977. Controlling introduced pr edators and competitors on islands. Pp. 121Œ128 In S. Temple (ed.). Endangered birds: Management techniques for preserving threatened species. University of Wisconsin Press. Moors, P. J. and I. A. E. Atkinson. 1984. Predation on seabirds by introduced animals and factors affecting its severity. Pp. 667-690 In J. P Croxall, P.G. H. Evans and R. W. Schreiber (eds.). Status and Conservation of the Worlds Seab irds. International Council for Bird Protection Technical Publication No. 2. Cambridge. Spencer, W., E. Rubin, J. Stallcup, V. Bakke r, B. Cohen, S. Morrison and R. Shaw. 2006. Framework monitoring plan for the San Clemente Island Fox. Conservation Biology Institute, Corvallis, OR. 88 pp + Appendices. U.S. Fish and Wildlife Service (USFWS). 2008. Draft Environmental Assessment for the restoration of San Nicolas Island™s seabirds and protection of other native fauna by dradicating feral cats. Repor t on behalf of the Montrose Natural Resources Trustee Council and U.S. Navy. 81 pages. U.S. Fish and Wildlife Service (USFWS). 2009. Final Environmental Assessment for the restoration of San Nicolas Island™s Seabirds and protection of other native fauna by removing feral cats. Report on behalf of the Montrose Natural Resources Trustee Council and U.S. Navy. 79 pages. Warner, R. E. 1985. Demography and moveme nts of free-ranging domestic cats in rural Illinois. Journal Wildlife Management. 49:340Œ346.
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