Notable for its running speed, the Texas Antelope Squirrel has the longest hindlimbs and tail of any antelope squirrel. In the field, the squirrels are noticeable because of the way they carry the tail arched forward over the back. This common inhabitant of the Chihuahua Plateau occurs in rocky habitats in desert mountain ranges, nesting in burrows or in between rocks and crevices, and eating various seeds, berries, and insects. Antelope squirrels do not hibernate--they are active year round.

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This species occupies the Chihuahuan Plateau in Chihuahua, Coahuila, Durango, and Zacatecas, Mexico, and western Texas and south-central New Mexico, United States.

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).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: High intermontane Chihuahuan Plateau from Jaral, Coahuila, near Cinco de Mayo, Zacatecas, and Ciudad Lerdo, Durango, north through western Texas into central New Mexico. Escarpment of Sierra del Carmen-Sierra Madre Occidental acts as barrier at eastern end of range. South to near 25 degrees north latitude, along southern Coahuila-Rio Nazas filter barrier. From 540 to 1830 m in Tran-Pecos Texas; most common at 1050-1650 m (Best 1990).

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.

Average length: 226 mm.

Other Physical Features: endothermic ; bilateral symmetry

Sexual Dimorphism: None

Length:
Average: 226 mm
Range: 220-235 mm

Weight:
Average: 110 g
Range: 99-122 g

Type for Ammospermophilus interpres
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Female; Adult
Preparation: Skin; Skull
Collector(s): V. Bailey
Year Collected: 1889
Locality: El Paso, El Paso County, Texas, United States, North America

Habitat and Ecology

Systems

• Terrestrial

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.

Habitat Regions: temperate

Terrestrial Biomes: desert or dune

Comments: Restricted to rocky associations on and around low-desert mountain ranges. Rocky foothills, cliffs, and canyons in desert and lower woodlands. See Best et al. (1990) for details on vegetation associations in different parts of range. Perches on boulders and in tops of trees and shrubs. Burrows under boulders, ledges, or at base of shrub; also uses crevices as den sites; may use abandoned burrow of other mammal.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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

Primary Diet: herbivore (Frugivore , Granivore )

Comments: Diet includes various seeds, berries, and insects, and green vegetation in spring and early summer; eats seeds of mesquite and creosote-bush, and fruit and seeds of cholla cactus, mountain laurel, and Mexican cactus (Schmidly 1977).

Ecosystem Impact: disperses seeds

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

Ammospermophilus interpres preys on:
Insecta

This list may not be complete but is based on published studies.

Wary and secretive.

Comments: Active throughout the year. Often active during hottest part of day. Probably does not hibernate, or at least not to any great extent.

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.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

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).

Parental Investment: altricial ; female parental care

Breeding begins in February in Texas. Lactating females were present in early March in Coahuila. Litter size is 5-14. One litter per year, or some females may produce a second litter (Schmidly 1977, Best et al. 1990).

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).

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Population

Population Trend

Major Threats

Conservation Actions

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

Comments: Most divergent species in the genus, and probable primitive sister-species to remainder (see Hoffmann et al., in Wilson and Reeder 1993; Thorington and Hoffman, in Wilson and Reeder 2005).