Patterns of island fox habitat use in sand dune habitat on San Clemente Island

Abstract

On San Clemente Island (SCI), the island fox subspecies Urocyon littoralis clementae has been monitored annually since 1988 to track long‐term population trends. Annual density estimates in most habitat types across the island range from 2 to 13 foxes/km2, yet unusually high estimates have repeatedly approached 50 foxes/km2 in a unique sand dune habitat area. Although sand dune habitat is restricted to one small area on the island, these estimates suggest sand dune habitat supports one of the highest population densities of any fox species in the world, and it may support > 5% of the SCI fox population. This finding prompted our investigation to determine if SCI foxes captured in the sand dunes habitat area maintained home ranges within this habitat type. Between January and July 2018, we used global positioning system (GPS) collars to track the movements of 12 island foxes captured in the sand dune habitat area. Contrary to our initial predictions, we found that island foxes captured in the sand dune habitat area do maintain home ranges and core areas centralized in sand dune habitat. All 12 island fox home ranges estimated contained > 50% sand dune habitat in either their 50% or 95% fixed kernel density estimate (KDE) home range, and island foxes were 3.14 times more likely to use active sand dune habitat when compared to the second most abundant habitat type, maritime desert scrub (Adjusted β = 3.14, 95% CI = 3.07–3.12). We also found that island foxes in sand dune habitat maintained much smaller home ranges than reported estimates in other habitat types, with an average 95% KDE home range size of 0.42 km2 (95% CI = 0.20–0.63 km2). Although sand dune habitat comprises just 2% of available habitat on SCI, our research highlights the importance of this unique habitat area for island foxes.