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Ammospermophilus interpresTexas antelope squirrel

By Gabriel Tamaska

Geographic Range

Ammospermophilius interpres occurs on the Chihuahauan plateau of the southwestern United States (Best, 1999), mainly Texas and New Mexico, and in north-central Mexico. It is distinct from A. leucurus, which lives in Oregon, California, and New Mexico (Walker, 1983; Davis, 1960; LTER; Best, 1999).

Habitat

A. interpres are characteristic of sparsely vegetated areas. They seems to prefer lowland areas like valleys or low hills and have been seen perched on boulders or short junipers. They are seen primarily in rocky areas and less often in flat sandy areas (Walker, 1983; Davis, 1960; Best, 1999). They dig multi-chambered dens, and they use rock crevices and abandoned dens of other animals as their dens. They normally locate these dens in a cut bank or at the base of a large object such as a bush or a rock. Often the den has more than one entrance. The nest inside the den is lined with bits of fir and feathers, dried grass, and any other soft material the squirrel finds (Davis, 1960; Best, 1999). Canyons and rocks seem to be important in determining their range (Best, 1999).

  • Range elevation
    540 to 1830 km
    335.54 to 1137.11 mi

Physical Description

A. interpres average 226 mm in length with males weighing between 94 and 121 g. and females between 84 and 115 g (Davis, 1960; Best 1999). The coat is course in texture with light gray-brown to red brown coloring and a white stripe on each side extending from the shoulder to the base of the tail. The stripes are surrounded by darker portions of the main coat color. The eyes are outlined by white fur. The legs have reddish fur (Best, 1999). The tail has three black bands on the dorsal side. Near the body it is black, but the distal two thirds is grey (Best, 1999). The under parts including the tail are white in the summer and gray in the winter. A. interpres generally holds its tail over its back, exposing the contrasting white ventral fur. It has small external ears and ten mammae (Walker, 1983; Davis, 1960; LTER; Best, 1999).

  • Range mass
    84 to 121 g
    2.96 to 4.26 oz
  • Average length
    226 mm
    8.90 in

Reproduction

Breeding generally starts in February, continuing through June (LTER). After a gestation period of about 29 days a litter of five to fourteen is born. Occasionally a female will rear two litters in a year, but little is known about the reproductive cycle of A. interpres (Walker 1983, Davis 1960; Best, 1999).

  • Breeding season
    February - June
  • Range number of offspring
    5 to 14
  • Average gestation period
    29 days
  • Average weaning age
    1 months

The young remain in the mother's nest about a month until they are a quarter grown, then start venturing out and eating solid food. They do not hibernate, so they need not store extra fat during their early development (Davis 1960, LTER; Best, 1999).

Behavior

A. interpres is strongly diurnal, even venturing out in the heat of the day when other animals sleep. When active A. interpres occasionally retreats to a shady place and stretches out on the ground, dispersing its excess body heat in the cool rocks (Davis, 1960). They are extremely nimble, and spend most of their time on the ground, though they have been seen perching on large objects (Walker, 1983; Davis, 1960; Best, 1999). When agitated they flick their tails (Davis, 1960; Best, 1999). They do not hibernate, though individuals in the northern range may become inactive during the winter (Walker, 1983; Davis, 1960).

Communication and Perception

Food Habits

A. interpres has a largely vegetarian diet consisting of fruit and seeds from various plants, as well as insects. It has been found to collect food using its cheek pouches and store it in the den and under rocks (Davis, 1960; Best, 1999). In the spring individuals eat a large number of succulents and other vegetation (Best, 1999). A study of a related species, A. leucurus found that species to be omnivorous, eating arthropods and some vertebrates, depending on the season (Bradley, 1968). Another study has shown that succulents are important in the diet of A. leucurus, in order to maintain body moisture in the arid climates inhabitated by that species (Hudson, 1962).

Common foods eaten include: yucca, juniper, salt grass, prickly pear fruits, cholla fruits, mesquite, sotol, creosote bush and insects.

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

In its range A. interpres is so common that it is an important food source for many predators, including humans (Best, 1999).

Ecosystem Roles

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Negative

In some areas A. interpres can become a nuisance by raiding crops, but is controlled by various poisoning methods (Walker, 1983; BISON).

  • Negative Impacts
  • crop pest

Conservation Status

In some cases different species of antelope ground squirrels are being displaced by farms and settlements, which alter their habitat, forcing them to shift their range to non-traditional areas (BISON). Global warming could also be playing a role in the shifting ranges (Cameron, 2001).

Other Comments

Much of the information available about antelope ground squirrels is about a species other than A. interpres. Davis (1960) and Best (1999) were the best sources.

Contributors

Gabriel Tamaska (author), University of Michigan-Ann Arbor, Ondrej Podlaha (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

female parental care

parental care is carried out by females

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

seasonal breeding

breeding is confined to a particular season

sexual

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

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

"Biota information system of New Mexico BISON" (On-line). Accessed November 5, 2001 at http://www.cnr.vt.edu/fishex/nmex_main/species/050765.htm.

1998. "Sevilleta LTER data" (On-line). Accessed November 5, 2001 at http://sevilleta.unm.edu/data/species/mammal/sevilleta/profile/texas-antelope-squirrel.html.

Best, T. 1999. Texas Antelope Ground Squirrel. Pp. 404-405 in D Wilson, S Ruff, eds. The Smithsonian Book of North American Mammals. Washington [D.C.]: Smithsonian Institution Press in association with the American Society of Mammalogists.

Bradley, W. 1968. Food habits of the antelope ground squirrel in southern Nevada. Journal of Mammalogy, 49: 14-21.

Cameron, G., D. Scheel. 2001. Getting Warmer: effects of global climate change on rodent distribution. Journal of Mammalogy, 82: 652-680.

Davis, W. 1960. The mammals of Texas (Texas antelope squirrel). Austin Texas: the Information-Education Division, Game and Fish Commission.

Hudson, J. 1962. The role of water in the biology of the antelope ground squirrel *Citellus leucurus*. University of California Publications Zoology, 64: 1-56.

Walker, ., F. Warnic, S. Hamlet, K. Lange, M. Davis. 1983. Antelope ground squirrels. Pp. 596-597 in J Paradiso, ed. Mammals of the World. Baltimore, Maryland: Johns Hopkins University Press.

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