San Francisco State University
Department of Geography
Geography 316:  Biogeography   In progress 11/14/00

The Biogeography of the San Joaquin Kit Fox (Vulpes macrotis mutica)
by Kathryn Entriken, student in Geography 316, Fall 2000

Kit Fox Figure 1. Photo of San Joaquin kit fox
(Photo B. Moose Peterson in Bell, Heather.2000.)

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Vulpes
Species: Vulpes macrotis

Description of Species:
The kit fox gets its name from its size because baby foxes are called kits.  An adult San Joaquin kit fox averages only about 20 inches long and weighs about as much as a common house cat, around 5lbs, about 25 percent smaller than the more common red fox. They have a slim body with long slender legs, narrow nose, and long, bushy tail tapering slightly toward the tip. They have a pale, thick fur coat that insulates it against both the heat of the day and the chill of the night (Grambo, 1995).  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 and chest varying from buff to a rust color (Brown et al., 1997). The ears are dark on their inner (back) sides and the tail is black-tipped (Brown et al., 1997). They have very large ears, which some scientists suggest are nature’s way of helping the fox dissipate heat (Holing, 1987). It is also thought that the ears may help them to focus on tiny noises in the night, such as insects or mice. They have heavily pigmented eyes, which provide protection from the fierce desert sun (Grambo, 1995). They have hair on the soles of their feet, which may protect their feet from hot sand as well as give them increased traction.

Kit Fox Figure 2. Foot prints of the San Joaquin kit fox
(Southwest Wildlife, 2000)

A nocturnal hunter, the kit fox preys on rabbits and kangaroo rats that thrive in untouched saltbush and brome grass habitat. It also eats insects, mice, voles, birds, and cactus fruits. Its varied diet gives the kit fox all the moisture it requires, freeing it from the need to find a source of drinking water; an important adaptation to its desert home (Grambo, 1995). But its food supply vanishes when the land is converted to intensive agriculture.  According to O’Farrell (1997), a wildlife biologist, kit foxes can’t live in areas that are being tilled twice a year and sprayed with herbicides and pesticides. He says that farming destroys their burrows and eliminates their food supply. This is causing the kit foxes to move into more urban areas and their numbers to dwindle.

Natural History:
Mating for the kit fox occurs sometime between December and January. They have a gestation period of about fifty days. A female kit fox may give birth to four or five young in a litter each weighing around 1.4 ounces, but no more than five percent live long enough to reach sexual maturity at 22 months.  According to researchers, such high mortality is typical for a carnivore of this kind (Holing, 1987). While the mother is nursing, she rarely leaves the den, depending on her mate to bring her food (Grambo, 1995). Kit foxes use their underground dens throughout the year, perhaps partly to avoid coyotes. Where natural dens have been destroyed, kit foxes improvise, using well casings, culverts and abandoned pipelines (Grambo, 1995). Though it is often said to be monogamous and to mate for life, biologists have noted some incidents of polygamy.  Kit fox pups first venture outside the den when they are about one month old. Two or three months later, they begin hunting with their parents (Grambo, 1995).  Like other species of fox, the young foxes leave to seek out new territories when autumn comes.

  Kit fox Figure 3. Photo of the San Joaquin kit fox. (Grambo, 1995)

Following the extinction of dinosaurs and many other Mesozoic forms there became a wide array of ecological niches open for the rapid expansion and diversification of mammals. There are three major subgroups of living mammals: the egg-laying mammals, the pouched mammals, or marsupials and the placental mammals (Jurmain et al., 1997). The San Joaquin kit fox belongs to the placental subgroup. The carnivores have undergone a succession of radiations. Early carnivores are often placed in the order Creodonta; the first of these were the arctocyonids of the Paleocene, which were replaced in the Eocene by mesonychids, hyaenodonts, and oxyaenids (Futuyma, 1986). Most of these became extinct at the end of the Eocene, being replaced by modern carnivores such as weasels (Mustelidae), cats (Felidae), and dogs (Canidae), all of which began to diversify in the late Eocene or Oligocene (Futuyma, 1986).  The earth’s temperature had been falling throughout the Miocene and areas of woodland were being replaced by grasslands. Herbivorous mammals had to adapt to a differing diet, with less emphasis on leaves, and were also faced with less cover in which to hide from potential predators. The generalist and adaptable lifestyle of canids, which enables them to be omnivorous in their feeding habits, was probably a further factor which assisted their spread through Eurasia at this stage. The success of their colonization of Eurasia can be gauged by the fact that canids had spread right across into Europe by the early Pleistocene, some three million years ago. Remains of carious wolves, as well as a dhole, raccoon dog and Vulpes foxes have all been found here in strata from this era. The red fox (Vulpes vulpes) was established at an early stage. In turn, it gave rise to the corsac fox (V. corsac),  and then both Ruppell’s fox (V. rueppelli) and the swift fox (V. velox), which in turn gave rise to the kit fox (V. macrotis).

Kit Fox Figure 4. Two possible interpretations of the relationship of the families of carnivores.
Numbers on the left indicate millions of years ago. (Ewer, 1973).

The San Joaquin kit fox is found in the arid to semi-arid regions of western North America.  It was once a common predator in the semi-arid Central Valley of California, ranging through a territory more than 400 miles long and up to 100 miles wide.   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 (Brown et al., 1997). Kit foxes have also 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 (Brown et al., 1997). They can also occur in the interior basins and ranges in Monterey, San Luis Obispo, and, possibly, Santa Clara counties; also in the upper Cuyama River watershed in northern Ventura and Santa Barbara counties and southeastern San Luis Obispo County (Brown et al., 1997). Beginning in the early 1900s, however, an elaborate series of water projects helped transform the valley from fox paradise to  an agricultural breadbasket. Today less than 7 percent of all undeveloped lands in the southern part of the Central Valley remain untilled. Not surprisingly, the kit fox population has been seriously affected. Wildlife biologists believe fewer than 7,000 survive in the state today, down from more than 10,000 just 50 years ago (Holing, 1987). As a result, the San Joaquin kit fox is classified as endangered under the federal Endangered Species Act and as a threatened under California law (Holing, 1987).

Map of Distribution:

Kit Fox Figure 5. Map of the Distribution of the San Joaquin kit fox. (Townsend, 2000)

Other interesting issues:
Primary threats to the kit fox are loss, degradation, and fragmentation of habitat due to agricultural, industrial and urban development.  Pesticide use, predator control programs, and illegal shooting and trapping may make up the secondary threats. Competition from other predators, particularly coyotes also has been identified as a potential threat to kit foxes (Cypher, 1998).  Their natural predators are coyotes and eagles, though it has been found that coyotes kill the foxes, but don’t eat them, perhaps out of a sense of competition for prey. The eastern red fox, a larger animal introduced to California at the turn of the century for fur farming and now abundant is also a predator for the kit fox (Holing, 1987).

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        Vol. 35 Dec1996/Jan1997, pgs. 52-57. Published by the National Wildlife
Bell, Heather. 2000, Nov. 28. San Joaquin Kit Fox. Online. Available: (photo taken with permission by Moose B. Paterson
Brown, N. L., C.D. Johnson, P.A. Kelly and D.F. Williams. 1997, Feb. 1. San Joaquin Kit
        Fox. Online. Available:
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        undeveloped  and oil-developed areas.”
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        Between coyotes and San Joaquin kit foxes” in Journal of Mammalogy, 79(1):204-214.
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        Inc. pgs. 341-342.
Grambo, Rebecca L. 1995. The World of the Fox. Canada: Greystone Books.
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    Vol. 25 Apr/May 1987, pgs. 14-17.  Published by the National Wildlife Federation.
Jurmain, Robert, Lynn Kilgore, Harry Nelson, and Wenda Trevathan. 1997. Introduction
        To Physical Anthropology, Seventh Edition. Belmont, California: West/Wadsworth Publishing.
Southwest Wildlife. 2000. Kit Fox. Online.    
Townsend, Sue. 2000. San Joaquin Kit Fox Distribution: Defining the Northern Range.
        Online. Available:
Warrick, Gregory D. And Brian L. Cypher. 1999. “Variation in body mass
        of San Joaquin kit foxes.” in Journal of Mammalogy, 80(3):972-979.

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