Island foxes (Urocyon littoralis) are listed as federally endangered on four of the six California Channel Islands to which they are endemic. The population on Santa Rosa Island declined by 99% during the 1990s due to golden eagle (Aguila chrysaetos) predation but is now recovering. This drastic population reduction provided an unprecedented opportunity to study home-range size and habitat use at very low levels of intraspecific competition. We used global positioning system (GPS) collars to track 14 adult male foxes from September 2009 through June 2010. On average, the collars operated for 16.5 wk, yielding 364 locations per fox. The 95% minimum convex polygon home ranges averaged 3.39 km2, which is several times larger than reported in previous studies conducted at higher population densities. We used Euclidean distance analysis to assess habitat selection within 95% kernel density isopleth (KDI) home ranges and 50% KDI core areas. The foxes used most of the available vegetation types but exhibited significant selection for valley bottoms and for bare areas and grassland at night. Our results, together with previous studies on island foxes, suggest an inverse relationship between home-range size and population density as has been shown for many other species. However, the pattern is confounded by differences among study areas and methods. We therefore recommend that this study be repeated when the Santa Rosa Island population recovers to its historic density of 4 adult foxes/km2 to better assess density-dependent changes in home-range size and habitat use.
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