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Scott Wilson

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Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept. of Fish and Game

San Joaquin Kit Fox

Vulpes macrotis mutica

Listed as Endangered by the Federal Government and listed as Threatened by the State of California


Life History

The San Joaquin kit fox is one of the eight recognized subspecies of kit fox. It resembles a small lanky dog with disproportionately large ears; total length is about 32 inches, including a 12 inch black-tipped tail. Coloration of the kit fox ranges from light buff to grayish along the back and tail; gray, rust, or yellowish along the sides; and white along the belly (O'Farrell 1983).

San Joaquin kit foxes are nocturnal, using dens that have been excavated in loose soil (O'Farrell 1983); individual animals may utilize from three to 24 separate dens (Morrell 1972). The entrances of any one den may range from one to 36 extending into several individual tunnels and chambers reaching depths of up to ten feet (O'Farrell 1987). Man-made structures such as culverts and pipes may also be utilized as dens (O'Farrell 1983) in those areas with a shortage of dens. Typically, den entrances are higher than wide and are sufficiently small to prevent access by large carnivores such as coyotes. Dimensions of the entrances are generally about eight to ten inches in height and less than eight inches in width (O'Farrell 1987) but may be as small as four inches in width. Burrows of other animals, particularly California ground squirrels (Spermophilus beecheyi) are opportunistically enlarged and utilized as den sites by San Joaquin kit foxes (Balestreri 1981). Although occupied dens may show freshly excavated soil, scats, and prey remains (O'Farrell 1987), such obvious signs are frequently absent (Hall 1983).

Individual San Joaquin kit foxes have an average home range of one to two square miles (Knapp 1978; Morrell 1972). Courtship and mating occur in December and January and the pups are typically born in February and March, dispersing at around five months of age (Morrell 1972; O'Farrell 1983). Survival rates of kit fox pups are low; about 75 percent die before the age of eight months (O'Farrell 1984).

The San Joaquin kit fox was historically distributed over a large portion of central California, extending roughly from southeastern Contra Costa County south along the eastern flanks of the Interior Coast Range to the southern San Joaquin Valley, including major portions of western Kern County and Tulare County. San Joaquin kit fox were also distributed through adjacent valleys, foothills, and plains, including portions of San Luis Obispo County, Monterey County, and the Santa Clara Valley on the western side of the Interior Coast Range (Morrell 1975).

Findings and Conclusions

Mortality for this species has been documented from attacks by coyotes, golden eagle, road kills, conversion of habitat, shooting, drowning, entombment, pneumonia, and starvation (Berry et al. 1987, Briden et al. 1987, O'Farrell et al. 1986, Knapp 1978, Morrell 1975). Additionally, the use of rodenticides has resulted in secondary mortality, since kit foxes are vulnerable to poisoning through consumption of poisoned rodents (USFWS 1985b).

Habitat conversion for agricultural and a variety of urban uses has been the principal cause of significant kit fox population declines and the reason for both state and federal listing of this species.

Although the Stanislaus River lies just outside of the San Joaquin kit fox's historic and presently known range, suitable habitat can be found along the Stanislaus River with some areas only 10 miles from kit fox's present range boundary.

The nearest sighting occurred in 1972, near LaGrange (Bell pers. comm.) but recent surveys carried out in the Oakdale area found only red fox, gray fox, feral dog, and bobcat (BioSystems 1994) any of which could prohibit or result in the decline of San Joaquin kit fox use in the area.

San Joaquin kit fox could potentially occur in grassland habitats adjacent to the Stanislaus River and any project impacting these adjacent grasslands could potentially impact the species. Further surveys would be required.