Endangered Species Recovery Program

San Joaquin kit fox
Vulpes macrotis mutica

See also the Friends of the San Joaquin kit fox page on Facebook.

Status

U.S.A. Endangered and California Threatened

Life History

The San Joaquin kit fox is a subspecies of the kit fox, the smallest member of the dog family in North America. A kit fox is a small fox with 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.

San Joaquin kit foxes inhabit grasslands and scrublands, many of which have 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.

Kit foxes are active 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 1 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 pupping den. Mating usually takes place between late December and March and the median gestation period is estimated to range from 48 to 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 1 month. After 4 to 5 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 rarely live to 7 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 (Peromyscus spp.), 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 their range, California ground squirrels are the most common prey species. Other prey eaten by kit foxes in this area include 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.

Many factors have contributed to the decline of the San Joaquin kit fox, but the importance of these factors has probably varied over time. By the 1950's, loss, degradation, and fragmentation of habitats in the San Joaquin Valley due to agricultural, industrial, and urban developments were the primary factors in the decline of the San Joaquin kit fox. Since the 1970's, researchers have identified predation, starvation, flooding, and drought as natural mortality factors. Human-induced mortality factors include shooting, trapping, poisoning, electrocution, road kills, and suffocation.

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.

Classification

Order CARNIVORA, Family CANIDAE, Genus Vulpes, Species macrotis

Subspecies

The San Joaquin kit fox, Vulpes macrotis mutica, is one of two recognized subspecies of the kit fox.

Recent Synonyms

None.

Other Common Names

None.

References

Bell, H. M. 1994. Analysis of habitat characteristics of the San Joaquin kit fox in its northern range. M.A. thesis, California State Univ., Hayward, 90pp; Williams, D.F. and K. S. Kilburn. 1992. The conservation and status of the endemic mammals of the San Joaquin faunal region, California. Pp. 329-345, in Endangered and sensitive species of the San Joaquin Valley, California: their biology, management, and conservation (D. F. Williams, S. Byrne, and T.A. Rado, eds.). The California Energy Commission, Sacramento, 386 pp.; State of California, Dept. Fish and Game. 1990. California's Wildlife, Vol. III: Mammals (D.C. Zeiner, W.F. Laudenslayer, Jr., K. Mayer and M. White, eds.). The Resources Agency, Sacramento, 407 pp.; Hall, E. R. 1981. T he mammals of North America. Second ed. John Wiley & Sons, New York, 1:1-600+90; McGrew, J. C. 1979. Vulpes macrotis. Mammal. Species 123:1-6; Jensen, C. C. 1972. San Joaquin kit fox distribution. U.S. Fish and Wildlife Service, Sacramento, CA, Unpubl. Rep., 18 pp; Morrell, S. H. 1972. Life history of the San Joaquin kit fox. California Fish and Game 58:162-174.

Size

Total length (average):
males, 80.5 cm (31.7 in)
females, 76.9 cm (30.3 in)

Weight (average):
males, 2.3 kg (5.0 lbs)
females, 2.1 kg (4.6 lbs)

Identification

The foot pads of kit foxes are small compared to other canids. Tracks of San Joaquin kit foxes average 3.1 cm (1.2 inch) in length and 2.6 cm (1 inch) in width. 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 Valley and are primarily nocturnal. The black-tipped tail and 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. 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.

Authors of Profile

N.L. Brown, C.D. Johnson, P.A. Kelly, and D.F. Williams