White-tailed Antelope Squirrels can often be seen in western and southwestern deserts, especially in shrubby areas with rocky soil. They do not hibernate, but in cold winter weather several may huddle together in a burrow to keep warm. They breed from February to June, producing litters of 5-14 offspring. The young begin to appear aboveground when they are about six or seven weeks old, and nurse for about two months. Adults eat both plant matter and insects.

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Extends from south-eastern Oregon and south-western Idaho east to western Colorado and north-western New Mexico (United States), and south through Baja California and Baja California Sur (Mexico). It also occurs on the islands of San Marcos and Espiritu Santo (Gulf of California).

White-tailed antelope squirrels are found in northwestern New Mexico, western Colorado, southeastern Oregon, northern Arizona, southwestern Idaho, Utah, southern Nevada, southern California, and as far south as the southern Baja California peninsula. Of all Ammospermophilus, white-tailed antelope squirrels are the most widespread in North America; their general range is the Great Basin to Baja California.

(Belk and Smith, 1991; Tomich, 1982)

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: Southwestern North America: southeastern Oregon, southwestern Idaho, Nevada, most of Utah, western Colorado, northwestern New Mexico, northern Arizona, eastern and southern California, and Baja California (including Isla San Marcos) (Belk and Smith 1991).

Ammospermophilus leucurus appear quite similar to other antelope ground squirrels. They have slightly longer legs and small, rounded ears. White-tailed antelope squirrels are whitish on their ventral surface. Their backs are brown to gray in color with two white stripes from the shoulder to the hind end. The outer surfaces of all legs are somewhat more reddish in color. The underside of their tails are pure white and they have a subterminal black band on the tail.

They range in total length from 188 to 239 mm and in tail length from 42 to 87 mm. They weigh from 96 to 117 grams.

The hair of the tail molts in the fall and the rest of the hair molts once in spring and then again in fall. White-tailed antelope squirrels have cheek pouches that they can carry food in. They also have ten mammae, slightly more than other ground squirrels, which typically have four to seven.

(Nowak, 1999; Belk and Smith, 1991; Tomich, 1982)

Range mass: 96 to 117 g.

Average mass: 105 g.

Range length: 188 to 239 mm.

Average length: 211 mm.

Other Physical Features: endothermic ; bilateral symmetry

Average basal metabolic rate: 0.511 W.

Length: 24 cm

Weight: 156 grams

Sexual Dimorphism: None

Length:
Average: 211 mm
Range: 188-239 mm

Weight:
Average: 105 g
Range: 96-117 g

Type for Ammospermophilus insularis
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Female; Adult
Preparation: Skin; Skull
Collector(s): E. Nelson & E. Goldman
Year Collected: 1906
Locality: Espiritu Santo Island, Gulf of California, Baja California Sur, Mexico, North America

Habitat and Ecology

Systems

• Terrestrial

White-tailed antelope squirrels live in deserts and foothills. These areas are sandy, gravelly or rocky, provided the soil can be burrowed in to escape from extreme heat and predators. Ammospermophilus leucurus will use burrows of other rodents, such as kangaroo rats, for shelter and will make numerous burrows of its own within its home range. Common habitats include desert succulent shrub, riparian, and wash areas. Ammospermophilus leucurus also occurs in chaparral and grassland.

(Johnson and Harris, 2001; Belk and Smith, 1991)

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune ; chaparral

Comments: Low dry desert and foothills; shrubby areas with sandy to rocky soil. Alkali sink; shrublands with sagebrush, greasewood, shadscale, creosotebush, or sometimes juniper; Sonoran and lower Transition life zones. Burrows may be under a shrub (usually) or in the open; often uses abandoned burrows of kangaroo rats; may use multiple burrows over a period of a few weeks. Young are born in underground burrows.

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.

Recorded home ranges 1.4 to 9.4 hectares (Allred and Beck 1963, Bradley 1967), mean 6.7 hectares in southern Nevada (Allred and Beck 1963). Bradley (1968) determined that 13 of 15 individuals successfully homed from a 1.6-km displacement. Karasov (1981) found that daily movements in California averaged about 1 km; the longest daily movement was 2.6 km by a male in April.

During the year, different food sources make up the bulk of the diet. During the spring, greens are widely available, so they consitute the bulk of the diet, or approximately 60%. In the fall, when greens are not readily available, they only comprise about 20% of the diet. Seeds and fruits are the most important food source in the fall, making up about 60% of the diet, and are not as important in the spring, making up about 20% of the diet. Invertebrates, mainly insects, make up the rest of their diet during the year. Compared to other antelope squirrels, A. leucurus was found to be more carnivorous. The use of efficient kidneys keeps water loss low, but they must have some succulent plants or free water in their diet in order to survive. Foraging by A. leucurus occurs in trees and shrubs or on the ground. White-tailed antelope squirrels have cheek pouches in which they can store food until they return to their burrows, where they will hoard the food, or put it into a cache, as do other squirrels.

Common foods eaten include: seeds, green vegetation, including grasses, mesquite, acacia, yucca, ephedra Mormon tea, Joshua tree, evening primrose, storksbill, blackbrush and opuntia cactus, fruits, invertebrates, carrion.

(Johnson and Harris, 2001; Belk and Smith, 1991; Tomich, 1982)

Animal Foods: carrion ; insects

Plant Foods: leaves; seeds, grains, and nuts; fruit

Foraging Behavior: stores or caches food

Primary Diet: omnivore

Comments: Omnivore; eats green vegetation, seeds, insects, and carrion; sometimes may prey on small live vertebrates. Diet changes seasonally with availability of various foods. Cannot survive indefinitely without free water. Stores food, may forage in trees or shrubs.

White-tailed antelope squirrels store seeds in food caches, possibly resulting in the dispersal and germination of seeds.

(Belk and Smith, 1991)

Ecosystem Impact: disperses seeds

These animals are eaten primarily by diurnal, desert-dwelling predators, some of which are listed here.

They animals tend to run away from predators instead of seeking shelter. When they are running away, they very seldom look back. This species has slightly longer feet than other antelope squirrel species, which enable them to run faster. They can also escape into their burrow if there is an opening nearby. (Johnson and Harris, 2001; Belk and Smith, 1991)

Known Predators:

• hawks (Accipitridae)
• owls (Strigiformes)
• kit foxes (Vulpes velox)
• bobcats (Lynx rufus)
• coyotes (Canis latrans)
• weasels (Mustelinae)
• snakes (Serpentes)
• badgers (Taxidea taxus)

Ammospermophilus leucurus is prey of:
Strigiformes
Serpentes
Accipitridae
Mustela
Vulpes
Taxidea taxus
Lynx rufus
Canis latrans

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

Ammospermophilus leucurus preys on:
Insecta

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

Primarily solitary. Does not maintain exclusive territory; forms dominance hierarchies. In southern Nevada, density ranged from 0.06/ha (late spring) to 0.35/ha (fall). In Utah, population density varies widely among years.

Comments: Active throughout the year. Not known to hibernate or estivate (Larrison and Johnson 1981). Active throughout the day, but may rest in shaded areas or in burrow during the hottest part of the day in summer. In winter, often basks in sun. May become torpid (as a last resort) if exposed to cold temperatures.

Average lifespan is not known, but one white-tailed antelope squirrel lived five years and ten months in captivity. The average lifespan for other members of this genus is typically one year.

(Nowak, 1999)

Average lifespan

Status: captivity: 5.8 years.

Maximum longevity: 11.2 years (captivity)

Males and females are sexually mature by the end of their first year. The breeding season for A. leucurus is in spring, between February and June. Usually females have one litter per year with between five and fourteen babies per litter. Litter size seems to depend on the quantity of green vegetation available to the mother. The young weigh about three or four grams at birth. Sometimes a female will have two litters in one year. Gestation time is probably between thirty and thirty-five days.

(Johnson and Harris, 2001; Nowak, 1999; Belk and Smith, 1991)

Breeding season: February through June

Range number of offspring: 5 to 14.

Average number of offspring: 8 or 9.

Range gestation period: 30 to 35 days.

Range weaning age: 65 (low) days.

Average age at sexual or reproductive maturity (female): 1 years.

Average age at sexual or reproductive maturity (male): 1 years.

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

Average birth mass: 3.21 g.

Average number of offspring: 8.

Average age at sexual or reproductive maturity (male)

Sex: male: 365 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 365 days.

Ammospermophilus leucurus build nests for the young near the center of the burrow. Nests are made from dry plant materials and animal fur. When the young are born, they are helpless and without adult fur; their eyes and ears are closed. Young come out of the burrow about one or two weeks before weaning, at approximately 2 months of age.

(Johnson and Harris, 2001; Belk and Smith, 1991)

Parental Investment: altricial ; female parental care

In southern Nevada, breeds February-June with February-March peak. In southern California, mating occurs mostly during first two weeks of March. Gestation lasts 30-35 days in Nevada and California. Litter size is 5-14 (average 8); probably one litter per year, possibly sometimes two in some areas (Burt and Grossenheider 1964). In southern California, young first appear on the surface in mid-May, 1-2 weeks before weaning at age 8 weeks (Kenagy and Bartholomew 1985).

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 12
Species With Barcodes: 1

These animals are abundant in suitable habitat throughout their range.

US Migratory Bird Act: no special status

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Comments: Apparently little affected by construction of campgrounds and roads (see Belk and Smith 1991).

Conservation Actions

White-tailed antelope squirrels can become bothersome to farmers. This rarely happens because A. leucurus lives in deserts where there are very few farms. However, in some areas they occasionally cause trouble by burrowing on farmland and eating crops.

(Nowak, 1999)

Negative Impacts: crop pest

White-tailed antelope squirrels make good research subjects because they can be easily studied.

(Nowak, 1999)

Positive Impacts: research and education