REPRODUCTION AND SPACING PATTERNS OF KIT FOXES RELATIVE TO CHANGING PREY AVAILABILITY

The occurrence of drought and a corresponding decline in the availability of the primary prey of San joaquin kit foxes (Vulpes macrotis mutica) during 1990 and early 1991 provided a unique opportunity to document the effect of changing food resources on kit fox productivity and spacing patterns. Thus, we studied reproduction and spacing patterns of 38 kit foxes on a 110-km2 study area of the Carrizo Plain Natural Area, California from December 1988 through November 1991. The primary effect of prey scarcity on kit foxes was to decrease reproductive success; none of 9 collared females reproduced in 1990. Home ranges of members of the same social group overlapped extensively (xBAR = 70.0 +/- 3.0 [SE] %, n = 20), whereas those of foxes in adjacent social groups overlapped only slightly (xBAR = 14.0 +/- 2.0%, n = 73). Individual home ranges averaged 11.6 +/- 0.9 km2 (n = 21) and did not change in size for foxes monitored among years (P = 0.31). Overlap between home ranges of adjacent, same-sex foxes decreased (P = 0.02) during prey scarcity. Foxes apparently maintained relatively exclusive home ranges of sufficient size to sustain their own body mass and condition during periods of prey scarcity. The maintenance of large and relatively non-overlapping home ranges in kit foxes may be an adaptation to drought-induced periods of prey scarcity that are episodic and temporary in this region of the country.