San Joaquin Antelope Squirrel (Ammospermophilus nelsoni)
San Joaquin Antelope Squirrel (Ammospermophilus nelsoni)
General Distribution
Historically, San Joaquin antelope squirrel occurred in the southern and western portions of the San
Joaquin Valley and adjacent upland habitats (Williams and others 1988) from western Merced County
south to Kern and San Luis Obispo Counties. Its historical range included portions of the Carrizo and
Elkhorn Plains in San Luis Obispo County, Cuyama Valley in San Luis Obispo and Santa Barbara
Counties, and Elk Hills in Kern County (Williams and others 1988).
Currently, San Joaquin antelope squirrel occupies only about 20 percent of its original range. It occurs
in the San Joaquin Valley and on slopes and ridgetops in the foothills along the western edge of the
valley, in the Cuyama and Panoche Valleys, and on the Carrizo and Elkhorn Plains (Best and others
1990).
San Joaquin antelope squirrel's range approaches, and potentially extends onto, the Los Padres National
Forest along the upper margins of the Cuyama Valley. This species has not been documented on
National Forest System lands in southern California (Stephenson and Calcarone 1999). Systematics
San Joaquin antelope squirrel is one of five species in the genus Ammospermophilus. The other four
species of antelope squirrels are A. harrisii, A. insularis, A. interpres, and A. leucurus (Best and
others 1990). Members of this genus are found in desert arid steppe habitats in the southwestern United
States and northern Mexico (U.S. Fish and Wildlife Service 1998). Habitat Requirements
San Joaquin antelope squirrels inhabit arid grassland, shrubland, and alkali sink habitats, and are often
found in association with saltbush (Atriplex sp.) and Mormon tea (Ephedra sp.). Present populations
occur at elevations of approximately 100-3,600 feet (30-1097 meters) (Best and others 1990). Low-density
populations of San Joaquin antelope squirrel have been found in alkaline soil areas dominated by
iodine bush (Allenrolfea occidentalis) and spiny saltbush (Atriplex spinifera) (California Department of
Fish and Game 1994). Habitat features such as scattered shrubs and arroyo banks are probably
important determinants of antelope squirrel distribution (Williams 1980). Hawbecker (1953) reported
that San Joaquin antelope squirrel does not occur in areas where the annual rainfall exceeds 9 inches
(22.9 centimeters). Reproduction
The breeding season of San Joaquin antelope squirrel begins in late winter and lasts through early
spring. Gestation lasts 26 days and litter sizes average 8.9 young (Best and others 1990). Young are
born between March and April and are observed aboveground at about 30 days of age. Weaning ends in
late May (U.S. Fish and Wildlife Service 1998). Daily/Seasonal Activity
San Joaquin antelope ground squirrels are primarily diurnal and generally active aboveground during
spring and summer when air temperatures are 68-86 ° F (20-30 ° C) (California Department of Fish and
Game 1994, Williams and others 1997). Survival in this species depends on the year and the season.
In general, the highest mortality occurs
during the summer months, when summer heat forces individuals to forage at dawn and dusk when
predators are also foraging (Best and others 1990). A mortality rate of 70 percent for young-of-the-year
and 50-60 percent for adults was recorded at the Elkhorn Plain Ecological Reserve (Williams and others
1988). Diet and Foraging
San Joaquin antelope squirrels feed on insects, seeds of grasses and forbs, green vegetation, and
occasionally small vertebrates (Best and others 1990). The amount and type of food consumed depends
on season and availability (Williams and others 1997). From mid-May to mid-December insects are the
predominant food items. From mid-December to mid-May green vegetation constitutes the majority of
the diet. Small vertebrates and seeds of perennial shrubs, annual grasses, and forbs are consumed
throughout the year and comprise approximately 5-20 percent of the diet (Best and others 1990). Territoriality/Home Range
Home range size for both sexes averages 11 acres (4.4 hectares) (Best and others 1990). Predator-Prey Relations
Common predators of San Joaquin antelope squirrel include badger (Taxidea taxus), coyote (Canis
latrans), kit fox (Vulpes macrotis), snakes, hawks, and owls (Best and others 1990). Literature Cited
Best, T.L.; Titus, A.S.; Lewis, C.L.; Caesar, K. 1990. Ammospermophilus nelsoni. Mammalian Species?367: 1-7. Published by the American Society of Mammalogists.
California Department of Fish and Game. 1994. 1992 annual report on the status of California state
listed threatened and endangered animals and plants. Sacramento, CA.
Hawbecker, A.C. 1953. Environment of the Nelson antelope ground squirrel. Journal of Mammalogy
34: 324-334.
Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment:
Habitat and species conservation issues. General Technical Report GTR-PSW-172. Albany, CA: Pacific
Southwest Research Station, Forest Service, U.S. Department of Agriculture.
U.S. Fish and Wildlife Service. 1998. Recovery plan for upland species of the San Joaquin Valley,
California. Portland OR.
Williams, D.F. 1980. Distribution and population status of the San Joaquin antelope squirrel and giant
kangaroo rat. Nongame Wildlife Investigation Final Report. E-W-4. Sacramento, CA: California
Department of Fish and Game.
Williams, D.F.; Tordoff, W., III; Harris, J.H. 1988. San Joaquin antelope squirrel (Ammospermophilus
nelsoni) study – 1988. Final Report. Contract No. 7398. Sacramento, CA: California Department of Fish
and Game, Endangered Wildlife Program.
Williams, D.F.; Cypher, E.A.; Kelly, P.A.; Norvell, N.; Johnson, C.D.; Colliver, G.W.; Miller, K.
J. 1997. Draft recovery plan for upland species of the San Joaquin Valley, California. Prepared for U.S.
Fish and Wildlife Service. Portland, OR.
Zeiner, D.C.; Laudenslayer, W.F., Jr.; Mayer, K.E., eds. 1990. California's wildlife. Volume
III: Mammals. Sacramento, CA: California Statewide Wildlife Habitat Relationships System, California
Department of Fish and Game.
Information gathered from California DFG - California Interagency Wildlife Task Group
