Ammospermophilus harrisiiHarris's antelope squirrel

Geographic Range

Harris antelope squirrels are found below 1,350m elevation in southwestern United States and northwestern Mexico. (Best et al. 1990)

Habitat

The Harris antelope squirrel inhabits arid, sparsely vegetated plains and lower mountain slopes. It prefers rocky hills or rocky soils. (Nowak 1991)

Physical Description

Head and body length is 137-168mm and tail length is 55-95mm. There are no differences in external measurements between the sexes. Harris antelope squirrels have long necks and slender bodies. The tail is short and the ears are small. The body hair is mouse gray in the winter and paler during the summer. Dorsal hairs are short and somewhat coarse, but lay smoothly, giving the animal a glossy appearance. Hairs on the undersurface are coarse and rigid. Winter pelage is longer and softer than summer pelage. There is one white stripe along both sides of the body from shoulder to rump. The undersurface of the tail is mixed black and white. A white ring encircles each eye, giving the Harris antelope squirrel a spectacled appearance. The soles of the feet are heavily haired. The Harris antelope squirrel carries its tail arched over its back. (Best et al. 1990), (Nowak 1991)

  • Average mass
    126 g
    4.44 oz
    AnAge

Reproduction

Although mating can take place from December or January until June, peak reproductive activity occurs from February-March. A vaginal plug is formed after copulation. In females, the beginning of the breeding season is marked by a swelling of the labia, enlargement of the uterus, and opening of the vaginal orifice. In males, spermatogenesis may begin as early as November and lasts until June. The testes regress in size in June and July to less than 10% of the February and March mass. Gestation lasts for about 30 days, and the litter size may range from 5-14. The average litter size is 6.5. Females give birth to only one litter per year. Newborns are naked and the skin is pink and somewhat transparent. The young cannot crawl, and their eyes and ears are closed. After 1 week, the dorsal sides of the head and back are covered with black pigmentation. At 2 weeks, 2 pale stripes appear on the back. These stripes are covered with white hairs in the adult. At 3 weeks, the claws are well-developed and the lower incisors have erupted. At this age, the young still cannot walk without falling over. Between 3 and 4 weeks, the ears open and the young are fully covered with hair. The upper incisors begin to erupt after 4 weeks. At this age, the young are very vocal and frequently utter a trilling noise when disturbed. When trilling, the young generally stand upright and shake all over. Eyes open 29 to 34 days after birth. Running and other movements improve a great deal after the eyes have opened. The young are weaned 7 weeks after birth. The young first emerge from their burrows between 4 and 5 weeks of age. Adult size is attained approximately 217 days after birth. Males reach sexual maturity during their first year. Females are sexually mature at about 10-11 months of age. The vagina does not open until the female is in heat. (Neal 1965), (Best et al. 1990)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
    6.8
    AnAge
  • Average gestation period
    30 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    319 days
    AnAge

Lifespan/Longevity

  • Average lifespan
    Status: captivity
    10.6 years
    AnAge

Behavior

Harris antelope squirrels are diurnal. They have special adaptations that allow them to be active even during the hottest hours of the day. For example, they maintain their body temperature at a level higher than that of any other nonsweating mammal (97-107 degrees F), and they cool themselves through salivation. They are easily seen scampering over rocky slopes in arid canyons and scurrying through the bushy growth on broad, sandy plains. They do not hibernate. Therefore, they store little body fat, and have little fluctuation in body weight throughout the year. They are active above the ground during each month of the year, except in the higher and colder parts of their range. In these areas, they become inactive during the winter, but they do not truly hibernate. Their ability to store food allows for this winter inactivity. They are true ground squirrels, living in burrows that they dig themselves. They have several burrows within their home range of about 6 ha. One or more of these burrows contains a nest, and the others are for retreat or escape. The burrow is usually under a desert shrub, but is sometimes found in the open. The centers of habitation are near rock-bound hills, where safe shelters are easy to find. Harris antelope squirrels are vigorous runners, with sharply delineated periods of activity and rest. They run about the desert floor, stopping frequently to dig things up from the ground. The antelope squirrel commonly sits perfectly erect upon its hind feet. When disturbed, it runs with its tail straight up in the air and utters chipperings as it hurries to a nearby burrow. Before entering the burrow, it often stops, calls, and stamps its forepaws. The alarm call is a trill that does not change with sex, temperature, or season.

Harris antelope squirrels are never found abundantly. They are solitary animals that come together for mating.

The Harris antelope squirrel has two molts during the year. The spring molt occurs in May or June and the winter molt takes place in October. Winter pelage is longer and softer than summer pelage, which consists of coarse, closely spaced hairs. Juveniles first appear above ground in summer pelage.

(Ingles 1965), (Best et al. 1990)

Communication and Perception

Food Habits

The Harris antelope squirrel is omnivorous. It feeds on seeds, fruit, plant stems and roots, some insects, and carrion. It has cheek pouches of considerable capacity. Suitable food supplies are carried in the cheek pouches and stored in burrows, under rocks, or in some other shelter. (Nowak 1991)

Economic Importance for Humans: Negative

Harris antelope squirrels can be a nuisance in irrigated areas because they raid crops and burrow through ditch banks. Some ground squirrels are suspected to be reservoirs of bubonic plague. (Nowak 1991)

Conservation Status

In some parts of its range, the Harris antelope squirrel is losing habitat to agriculture and other human developments. It is considered threatened in the state of California. (Nowak 1991)

Other Comments

The Harris antelope squirrel has also been called Harris's spermophile, marmot squirrel, grey-tailed antelope squirrel, and Yuma antelope ground squirrel. Ammospermophilus is derived from ammos (sand), spermatos (seed), and philos (loving or desiring affinity). The term harrisii honors Edward Harris.

Ammospermophilus harrisii is the most conspicuous small diurnal mammal of the desert plains from Tucson to the Colorado River.

(Best et al. 1990)

Contributors

Amy Shah (author), University of Michigan-Ann Arbor.

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

motile

having the capacity to move from one place to another.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

References

Best, T.L., Titus, A.S., Caesar, K., and Lewis, C.L. 1990. Ammospermophilus harrisii. Mammalian Species 366: 1-7.

Ingles, L.G. 1965. Mammals of the Pacific States: California, Oregon, and Washington. Stanford University Press, Stanford.

Neal, B.J. 1965. Reproductive Habits of Round-Tailed and Harris Antelope Ground Squirrels. Journal of Mammalogy 46: 200-207.

Nowak. 1991. Walker's Mammals of the World, Vol. 2. The Johns Hopkins University Press, Baltimore.