Factors affecting the spatial distribution of San Joaquin kit foxes

Determining the factors that influence or limit the distribution of endangered species can have important conversation implications. We investigated the spatial distribution of endangered San Joaquin kit foxes (Vulpes macrotis mutica) within a 31,400-ha area of the Naval Petroleum Reserves in California (NPRC) from 1988 to 1995 by relating capture rates of kit foxes to habitat factors, visitation rates of larger predators, and prey counts. Capture rates also were related to habitat factors on a smaller portion (11,500 ha) of NPRC from 1981 to 1995. Kit foxes were relatively evenly distributed in 1981-82, and regression models consequently explained only 6% of the spatial variation in capture rates. Afterwards, the distribution of kit foxes became more restricted, and models explained 36-60% of the variation in rates capture. Capture rates were negatively associated with topographic ruggedness, were lower within a fenced area (limited public access and no livestock grazing; P < 0.001), and were often higher within burned areas (P < 0.001). After 1987, capture rates were usually negatively associated with oil-field development. Visitation rates of coyotes (Canis latrans), a major predator of kit foxes, were higher within the fenced area (P less than or equal to 0.034). Capture rates were negatively correlated (r(132) = -0.22, P = 0.01) with coyote visitation rates during 1992-95. Locations of bobcat (Lynx rufus) captures and visits to scent stations overlapped very little with capture locations of kit foxes. Counts of lagomorphs (a significant prey item) were negatively associated with burning, and between 1992 and 1995, lagomorph counts were positively associated with oil-field development. Capture rates were not correlated with lagomorph counts during 1988-91 (r(77) = -0.09, P = 0.44) or 1992-95 (r(77) = 0.15, P = 0.18). Our findings indicated the relation between kit foxes and the habitat factors studied was somewhat flexible, and the spatial distribution of kit foxes was not determined primarily by prey abundance. Predator density and topographic ruggedness appear to be important underlying factors governing the spatial distribution of kit foxes at NPRC.