San Joaquin Kit Fox

Vulpes macrotis mutica

Description

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 in (81.2 cm), which include a 12 in (30.4 cm) black-tipped tail. It has large ears that are set close together, slim body with long slender legs, narrow nose, and long, bushy tail tapering slightly toward the tip. The tail is usually carried low and straight. The color and texture of the fur of kit foxes varies seasonally and geographically. Buff, tan, and yellowish gray are the most common colors. There are two distinct coats during the year: a tan summer coat and a silver gray winter coat. The undersides vary from light buff to white, with the shoulders, lower sides, flanks, and chest varying from buff to a rust color. The ears are dark on their inner (back) sides and the tail is black tipped.

The footpads of kit foxes are small compared to other canids. The amount of fur and the size, shape, and arrangement of the pads distinguish kit fox tracks from those of other canids and domestic cats.

The gray fox, red fox, and coyote are other canids that live within the same habitat and are primarily nocturnal. The black-tipped tail and the coat color usually distinguish kit foxes from red foxes, with their white-tipped tails. It is not unusual for gray foxes and young coyotes to be misidentified as kit foxes. In the winter, the fur of the kit fox is thicker and has more gray color. Both the kit fox and gray fox have black-tipped tails, but gray foxes also have a distinctive black stripe or "crest" running along the top of the tail. Both the gray fox and coyote are larger than the kit fox, and many times an adult coyote will be in the same area as the younger pups.

Behavior

Kit foxes are active all year round and are primarily nocturnal. Dens are used for housing and protection. One fox may use several dens, particularly during the summer months. Females may change natal and pupping dens one or two times per month. Kit foxes construct their own dens, but they can also enlarge or modify burrows constructed by other animals, such as ground squirrels, badgers, and coyotes. They also den in human-made structures, such as culverts, abandoned pipes, and banks in roadbeds. Most dens, especially natal and pupping dens, have at least two entrances.

Although kit foxes may not breed their first year, they are able to reproduce when they are one year old. Adult pairs remain together year round but may not share the same den. During September and October, the females begin to ready the natal or pup-ping den. Mating usually takes place between late December and March and the median gestation period is estimated to range from 48-52 days. Litters are born between February and late March and consist of two to six pups. While the female is lactating, the male provides most of the food for her and the pups. The pups emerge from the den for the first time when they are slightly older than one month. After four to five months, usually in August or September, the young begin dispersing. Occasionally, a young female remains with the adult female for several more months, and sometimes offspring of both sexes will remain with their parents through the year to help raise the next litter. Similar to other predators, reproductive success of kit foxes is related to the abundance of their prey. Decreases in prey abundance caused by circumstances such as drought and too much rainfall result in decreases of reproductive success of kit foxes. In captivity, kit foxes have been known to live as long as 10 years, but in the wild they rarely live to seven years of age.

There are geographical, seasonal, and annual variations in the diet of San Joaquin kit foxes based upon temporal and spatial variation in abundance of potential prey. In the southern portion of their range, at least one-third of their diet is comprised of kangaroo rats, pocket mice, white-footed mice, and other nocturnal rodents. Ground squirrels, black-tailed hares, San Joaquin antelope squirrels, cottontails, ground-nesting birds, insects, and vegetation, particularly grasses, also are eaten. In the central portion of their range, their prey consists of white-footed mice, insects, California ground squirrels, kangaroo rats, San Joaquin antelope squirrels, black-tailed hares, and chukar (an introduced bird species). In the northern part of the kit fox's range, California ground squirrels are the most common prey species. Other prey eaten by kit foxes in this area includes cottontails, black-tailed hares, pocket mice, and kangaroo rats. Although kit foxes are considered to be primarily nocturnal, they are commonly seen during the day in the late spring and early summer.

Habitat

San Joaquin kit foxes inhabit grassland or scrub-land, much of which has been extensively modified. Types of modified habitats include those with oil exploration and extraction equipment and wind turbines, and agricultural mosaics of row crops, irrigated pastures, orchards, vineyards, and grazed annual grasslands. Oak woodland, alkali sink scrubland, and vernal pool and alkali meadow communities also provide habitat for kit foxes. Dens are scarce in areas with shallow soils because of the proximity to bedrock, high water tables, or impenetrable hardpan layers. However, kit foxes will occupy soils with high clay content, such as in the Altamont Pass area in Alameda County, where they modify burrows dug by other animals.

In the southernmost portion of the range, the kit fox is commonly associated with valley sink scrub, valley saltbush scrub, upper Sonoran subshrub scrub, and annual grassland. Kit foxes also inhabit grazed grasslands, petroleum fields, and urban areas; and they survive adjacent to tilled or fallow fields. Agriculture dominates this region where kit foxes inhabit grazed, nonirrigated grasslands, but also live next to and forage in tilled or fallow fields, irrigated row crops, orchards, and vineyards. In the northern portion of their range, kit foxes also are commonly are associated with annual grassland and valley oak woodland.

Distribution

Prior to 1930, kit foxes inhabited most of the San Joaquin Valley from southern Kern County north to eastern Contra Costa County and eastern Stanislaus County. Although no reason was given for the decline, it was believed that by 1930 the kit fox range had been reduced by more than half, with the largest remaining portion being in the western and southern portions of the valley.

Although no extensive survey has been conducted of the historical range, kit foxes are thought to inhabit suitable habitat on the San Joaquin Valley floor and in the surrounding foothills of the coastal ranges, Sierra Nevada, and Tehachapi Mountains. Kit foxes have been found on all the larger, scattered islands of natural land on the valley floor in Kern, Tulare, Kings, Fresno, Madera, San Benito, Merced, Stanislaus, San Joaquin, Alameda, and Contra Costa counties. They also occur in the interior basins and ranges in Monterey, San Benito, San Luis Obispo, and, possibly, Santa Clara counties; and in the upper Cuyama River watershed in northern Ventura and Santa Barbara counties and southeastern San Luis Obispo County.

Threats

Kit foxes are subject to predation or competitive exclusion by other species, such as the coyote, non-native red foxes, domestic dog, bobcat, and large raptors. Coyotes are known to kill kit foxes, though an experimental coyote-control program at the Elk Hills Naval Petroleum Reserves in California did not result in an increase in survival rate for kit foxes, nor did coyote-induced mortality decrease. The extent to which gray and kit foxes compete for resources is unknown. The need for similar den sites and prey species probably place non-native red foxes in direct competition with the much smaller kit fox. Non-native red foxes are expanding their geographic range in central California, and competition with or predation on kit foxes may be a factor in the apparent decline of kit foxes in the Santa Clara Valley, and perhaps elsewhere in the northwestern segment of their range. Coyotes aggressively dominate encounters with red foxes and will pursue and kill both red and gray foxes, as well as kit foxes. Coyotes may reduce the negative impacts of red foxes on kit foxes by limiting red fox abundance and distribution, but details of interactions between the two species and the extent to which coyotes might slow or prevent the invasion of red foxes into kit fox habitats are unknown.

Loss and degradation of habitat by agricultural and industrial developments and urbanization continue, decreasing carrying capacity of remaining habitat and threatening kit foxes. Livestock grazing is not thought to be detrimental to kit foxes, but may alter the numbers of different prey species, depending on the intensity of the grazing. Livestock grazing may benefit kit foxes in some areas, but grazing that destroys shrub cover and reduces prey abundance may be detrimental.

Petroleum field development in the southern half of the San Joaquin Valley affects kit foxes by causing habitat loss due to grading and construction for roads, well pads, tank settings, pipelines, and settling ponds. Habitat degradation derives from increased noise, ground vibrations, venting of toxic and noxious gases, and release of petroleum products and wastewater. Traffic-related mortality is also a factor for kit foxes living in oil fields. The cumulative and long-term effects of these activities on kit fox populations are not fully known, but recent studies indicate that areas of moderate oil development may provide good habitat for kit foxes, as long as suitable mitigation policies are observed. The impacts of oil activities at the Elk Hills Naval Petroleum Reserves in California on kit fox population density, reproduction, dispersal, and mortality appeared to be similar in developed and undeveloped areas of the Reserve.

Other developments within the kit fox's range include cities and towns, aqueducts, irrigation canals, surface mining, road networks, nonpetroleum industrial projects, power lines, and wind farms. These developments negatively impact kit fox habitat, but kit foxes may survive within or adjacent to them given adequate prey base and den sites.

The use of pesticides and rodenticides also pose threats to kit foxes. Pest control practices have impacted kit foxes in the past, directly, secondarily, or indirectly by reducing prey. In 1925, near Buena Vista Lake, Kern County, seven kit foxes were found dead within a distance of 1 mi (1.6 km), having been killed by strychnine-poisoned baits put out for coyotes. It was suspected that hundreds of kit foxes were similarly destroyed in a single season. In 1975 in Contra Costa County, the ground squirrel was thought to have been eliminated countywide after extensive rodent eradication programs. In 1992, two kit foxes at Camp Roberts died as a result of secondary poisoning from rodenticides. The federal government began controlling the use of rodenticides in 1972 with a ban of Compound 1080 on federal lands.

Conservation and Recovery

Research has been conducted with respect to dispersal, mortality, movements, home range, and habitat enhancement of kit foxes, and on relocation, supplemental feeding, and coyote control as means of enhancing recovery of the kit fox population on the Naval Petroleum Reserves in California.

Conserving a number of populations, some much more significant than others because of their large sizes or strategic locations, is necessary for recovery. The areas these populations inhabit need to encompass as much of the environmental variability of the historical range as possible. This will ensure that maximal genetic diversity is conserved to respond to varying environmental conditions, and that one environmental event does not negatively impact all existing populations. Connections need to be established, maintained, and promoted between populations to counteract negative consequences of inbreeding, and random catastrophic events such as droughts.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

References

Morrell, S. H. 1972. "The Life History of the San Joaquin Kit Fox." California Fish and Game, no. 58: 162-174.

U. S. Fish and Wildlife Service. 1983. "San Joaquin Kit Fox Recovery Plan." U.S. Fish and Wildlife Service, Portland.