Santa Cruz Island Reserve

15 Jul, 04 AM - 01 May, 08 AM

Summary: Santa Cruz Island is home to two insular, endemic carnivores: the island spotted skunk (Spilogale gracilis amphiala) and the island fox (Urocyon littoralis). There is great potential for these two protected species to have negative effects on one another through competition, disease transmission, and/or predation; yet, such interactions have not been studied. Thus, developing a comprehensive management strategy requires an understanding of the ecology of the two species, both independently and in their interactions. The autoecology of the island fox has been well studied; therefore, the proprosed research will focus on the ecology of the island spotted skunk and its interactions with the island fox through analysis of diet, habitat use, and spatial patterns. Background: Islands are typically lacking in mammals, particularly mammalian carnivores, due to their poor over-water dispersal abilities, low carrying capacities, and large body sizes (Brown and Gibson 1983, Alcover and McMinn 1994). Therefore, Santa Cruz Island is unusual in supporting two insular, endemic carnivores: the island spotted skunk (Spilogale gracilis amphiala) and the island fox (Urocyon littoralis). The island spotted skunk is a unique subspecies of western spotted skunk and a ?Species of Special Concern? in California, located only on two of the northern Channel Islands (Santa Cruz, Santa Rosa). The island fox, a diminutive relative of the mainland gray fox, is listed as "Threatened? in California, and a petition for protection under the U.S. Endangered Species Act is currently under review. Both the National Park Service (NPS)and The Nature Conservancy (TNC) have accorded high priority to the conservation of these endemic species and have worked closely together in managing their populations. However, the two species may negatively impact each other through competition, disease transmission, or even predation (Crooks and Van Vuren 1995). Until 1993, island foxes were relatively common on Santa Cruz Island and easy to trap. Consequently, they have been fairly well studied and their general ecology is well known (Crooks and Van Vuren 1995, Roemer et al. 2001b). In contrast, island spotted skunks were known to be very rare and difficult to trap, resulting in a paucity of knowledge about them (Laughrin 1980, Crooks and Van Vuren 1995). Between 1993 and 1999, the island fox population on the island declined by nearly 90%, most likely due to predation by a novel predator, the golden eagle, and to disease (Crooks et al. 2001, Roemer et al. 2001a). This recent catastrophic decline has led to the establishment of a captive breeding program and the petition for federal listing. Over this same time period, the island spotted skunk population on the island has increased dramatically, presumably due to release from competitive pressure (Crooks and Van Vuren 2000, Roemer et al. 2002). The current abundance of island spotted skunks provides an unprecedented opportunity to learn about their ecology and the nature of their interactions with the island fox. This information is vital for the conservation of both of these insular, endemic carnivores. The need for research is urgent because if recovery efforts for the island fox population are successful, the island skunk could soon return to its former rarity. Consequently, we propose to begin an intensive, nine-month field study this summer. Objectives: A) Describe skunk ecology by determining home range size and overlap, habitat use, and diet within two areas of intensive study. B) Examine possible negative relationships between island foxes and island spotted skunks in three ways: 1) by investigating patterns of spatial movements and avoidance between foxes and skunks; 2) by determining fox and skunk densities at multiple areas around the island; and 3) by examining skunk behavior in an area devoid of foxes both before and after the release of juvenile foxes. Methods: 1) The ecology of island spotted skunks will be intensively studied within two primary study sites with similar habitats. The exact sites on Santa Cruz Island have yet to be determined. Trapping will be conducted to radiocollar 30-40 skunks. During handling, we will also take basic measurements (e.g., weight), hair samples, and potentially blood samples. Exact procedures will be determined following several weeks of training with the IWS trapping crew in July. Once the animals are collared, radiotelemetry will be used to determine habitat use, home range size, and daily activity patterns and scats will be collected for dietary analysis. When possible, information on mortalities, litter size, and pup survival will also be collected. 2) Within the two areas of intensive study, patterns of spatial movement and avoidance of both foxes and skunk will be measured. We will collar thirty to forty skunks, as well as any foxes not previously collared by TNC. Then,in collaboration with the Institute for Wildlife Studies, we will monitor locations and movements of both foxes and skunks in our two study areas. Using established methods (Minta 1992), the spatial data will then be analyzed to assess whether skunks preferentially avoid, attract, or move randomly with respect to foxes and vice versa. Interspecific avoidance would suggest direct interference competition between the foxes and skunks. The degree of spatial overlap between foxes and skunks will also indicate the potential for disease transmission. 3) Fox and skunk densities will be estimated using mark-recapture techniques at 10-12 sites around the island. An inverse relationship between fox and skunk densities would suggest avoidance by one or both species due to interspecific competition. 4) If a release of juvenile foxes from the captive breeding program is planned during the period of the study, and it is consistent with the management plan to release them into an area devoid of foxes, then the impact of fox reintroduction on local skunks could be measured experimentally. All of the skunks in the reintroduction area would be collared and monitored via radiotelemetry and scats would be collected for several weeks before and after the fox releases to determine any subsequent shifts in daily activity patterns, habitat preferance, diet, etc. Significance to Island Conservation: This research on Santa Cruz Island will accomplish two main objectives. First, we will establish a basic knowledge of island spotted skunk ecology (especially diet, home range size, and habitat use). The current abundance of skunks provides a unique opportunity to remedy the lack of prior research resulting from their former rarity. Understanding the autoecology of species is crucial to developing proper management strategies. Second, we will seek to identify the basis of competition and potential for disease transmission between island spotted skunks and island foxes. Understanding the ecological interactions between these two rare species would greatly improve the chances that they can be managed cohesively in a manner that would not protect one to the detriment of the other. Conservation of these two valuable species can be best achieved by the successful integration of the needs of both species into a comprehensive management plan. Required Resources: During my research on the island, I will require a private room in the field station, a jeep or truck, and one pick-up/drop-off from the boat dock. Literature Cited: Alcover, J. A., and M. McMinn. 1994. Predators of vertebrates on islands. Bioscience 44:12-18. Brown, J. H., and A. C. Gibson. 1983. Biogeography. Mosby, St. Louis, MO. Crooks, K. R., C. A. Scott, and D. Van Vuren. 2001. Exotic disease and an insular endemic carnivore, the island fox. Biological Conservation 98:55-60. Crooks, K. R., and D. Van Vuren. 1995. Resource utilization by two insular endemic mammalian carnivores, the island fox and island sptted skunk. Oecologia 104:301-307. Crooks, K. R., and D. Van Vuren. 2000. Update on the status of the island spotted skunk. Pages 298-299 in D. R. Browne, K. L. Mitchell, and H. W. Chaney, editors. Proceedings of the fifth California Islands Symposium. U.S. Department of the Interior, Minerals Management Service, Camarillo, CA. Laughrin, L. 1980. Populations and status of the island fox. Pages 745-749 in D. M. Power, editor. The California Islands: proceeding of a multidisciplinary symposium. Santa Barbara Museum of Natural History, Santa Barbara, CA. Minta, S. C. 1992. Animal spatial and temporal interactions. Ecological Applications 2:178-188. Roemer, G. W., T. J. Coonan, D. K. Garcelon, J. Bascompte, and L. Laughrin. 2001a. Feral pigs facilitate hyperpredation by golden eagles and indirectly cause the decline of the island fox. Animal Conservation 4:307-318. Roemer, G. W., C. J. Donlan, and F. Courchamp. 2002. Golden eagles, feral pigs, and insular carnivores: How exotic species turn native predators into prey. PNAS 99:791-796. Roemer, G. W., D. A. Smith, D. K. Garcelon, and R. K. Wayne. 2001b. The behavioural ecology of the island fox (Urocyon littoralis). Journal of the Zoological Society of London 255:1-14.

Visit #1559 @Santa Cruz Island Reserve

Approved

Under Project # 1004 | Research

University of California Davis - Wildlife, Fish, and Conservation Biology

graduate_student - University of California, Davis

Reservation Members(s)

Krista Jones Jul 15, 2003 - May 1, 2004 (292 days)

Reserve Resources(s) | Create Invoice

Jeep 1 Jul 15, 2003 - May 1, 2004
Private Room 1 Jul 15, 2003 - May 1, 2004