SPACE USE AND DEN VISITATION BY THE ISLAND SPOTTED SKUNK (SPILOGALE GRACILIS AMPHIALA) AND ISLAND FOX (UROCYON LITTORALIS)

On the California Channel Islands, wildlife researchers have hypothesized that the island fox (Urocyon littoralis) competes with the smaller-bodied island spotted skunk (Spilogale gracilis amphiala). Recent declines in spotted skunk captures have raised concerns about the status of the spotted skunk population on Santa Cruz Island and the potential role of foxes in the decline. From 2018 to 2019, we used global positioning system and very-high-frequency radio collars to assess patterns of space use by foxes and spotted skunks and deployed remote cameras to determine the potential for interaction between the two species at spotted skunk den sites. Spotted skunk home ranges were approximately five times larger than previously reported (range = 55-299 ha), and temporal patterns of space use differed between spotted skunks and foxes, with spotted skunks utilizing only 32% of their 6-month home range during a week, while foxes moved more widely over short time periods, covering 60% of their seasonal home range during 1 week. In spite of overall larger seasonal home ranges, the number of vegetation types used by spotted skunks (mean = 4) was smaller than that used by foxes (mean = 7) living in the same area, consistent with the narrow niche hypothesized for spotted skunks. More broadly, selection for vegetation types varied among individuals, within species, and across locations on the island. Based on camera trapping at spotted skunk den sites, we found a positive relationship between spotted skunk visitation rate and slope at den sites but no relationship with vegetation cover, suggesting more heavily used dens were in areas of steeper slope. Photographic evidence of a fox attempting to dig an adult spotted skunk from its den suggested predation at den sites could be a factor in spotted skunk mortality.