San Joaquin kit fox home range, habitat use, and movements in urban Bakersfield

Habitat destruction and fragmentation has led to the decline of the federally endangered and state threatened San Joaquin kit fox (Vulpes macrotis mutica). Kit foxes in the San Joaquin Valley occur in and adjacent to several urban areas. The urban kit fox population in Bakersfield has the potential to contribute to recovery efforts, however, little is known about habitat use in the urban environment. Habitat use in the urban landscape was examined in 28 radiocollared adult kit foxes between 1 May 1997 and 15 January 1998. The area of the urban environment needed to meet kit foxes' ecological requirements varied among the sexes and fluctuated throughout the year. Mean home range size was 1.72 km2 (100% minimum convex polygon estimate) and mean concentrated use area (core area; 50% fixed kernel estimate) size was 0.16 km2. Females had a greater median number of core areas than did males, but core area size did not differ between the sexes. Mean home range size was significantly larger during the dispersal season than during the pair formation and breeding seasons. Home range size was greater for males than females during the breeding season. To assess the extent to which kit foxes were concentrated around limited resources, the percentage of overlap between adjacent kit foxes' home ranges and core areas was determined. Mean home range overlap was greater than 71% for family group members and less than 16% for unrelated individuals, which was less than that reported for the nearby rural population. Overlap of adjacent kit foxes' core areas indicated that kit foxes were concentrated around key urban habitat patches. Core area overlap was greater for members of the same family group than core area overlap of neighboring males and females or neighboring males. To determine which attributes of the urban environment were used by kit foxes and may support the population over time, habitats used disproportionately were compared to what was available in home ranges and the urban landscape. Kit foxes used open and sump (water catchment basins) habitats more than their availability in both the home range area and study area. There was more open and sump habitat in home ranges than in the study area. Kit fox core areas contained a disproportionately high amount of sumps that had food and den sites and restricted public access. Sump and open habitats were more suitable for denning and consequently, were used more than their availability in the study area. Kit foxes primarily used subterranean dens but also used pipes and other man-made structures. Dens were located farther from roads than expected and in habitat patches that were larger than the median habitat patch in the study area. To identify which urban habitats kit foxes used for resting, foraging, and traveling, kit fox movements and travel paths through adjacent habitat patches were examined. Kit foxes moved an average speed of 1.33 km/h. Minimum speed for females was greatest from approximately 0330 - 0730 h and for males was greatest from approximately 1830 - 2230 h. Kit foxes used sump and open habitats for resting. Kit foxes also foraged in these habitats, as well as in transition and commercial habitats. Habitats used for traveling included manicured open and open habitats, in which total distance traveled per movement session was longest. Overall median speed was greatest in residential habitat. Kit foxes were observed crossing roads and using culverts and bridges to move under roads. Demographic characteristics and weights of the kit foxes that were captured were used to assess habitat quality. Two of the 28 radiocollared kit foxes died during 6,036 days of active radiotransmitters. Radiocollared kit foxes had 15 litters, comprised of 2.8 + 0.45 (range = 1 – 7) pups. Urban kit fox weight was similar to that for rural kit foxes. The availability of sump and open habitats appeared to shape the distribution and abundance of the urban population. Therefore, retaining sump and open habitats throughout Bakersfield may promote the continued existence of the urban kit fox population.