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Ammospermophilus leucuruswhite-tailed antelope squirrel

By Jennifer Nixon

Geographic Range

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)

Habitat

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)

Physical Description

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
    3.38 to 4.12 oz
  • Average mass
    105 g
    3.70 oz
  • Range length
    188 to 239 mm
    7.40 to 9.41 in
  • Average length
    211 mm
    8.31 in
  • Average basal metabolic rate
    0.511 W
    AnAge

Reproduction

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
  • Average number of offspring
    8
    AnAge
  • 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 (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    1 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

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)

Lifespan/Longevity

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)

Behavior

White-tailed antelope squirrels are diurnal and active throughout the year. In order to stay cool, A. leucurus are most active in the morning and late afternoon and are not active during the hottest part of the day. When they forage, they will stop in the shade in order to avoid heat from the sun. They will also lay flat in a burrow with their stomach against the cooler ground to cool off. Most of the year they live alone in burrows, females occupy burrows with their young of the year. In the winter, several individuals will live together in a burrow and huddle together at night in order to conserve heat. Ammospermophilus leucurus form dominance heirarchies when they encounter other individuals, but there is no evidence of territoriality. Home ranges are usually about six hectares.

(Johnson and Harris, 2001; Nowak, 1999; Belk and Smith, 1991; Tomich, 1982)

Communication and Perception

Food Habits

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)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit

Predation

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)

Ecosystem Roles

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

Economic Importance for Humans: Positive

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

(Nowak, 1999)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

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

Conservation Status

These animals are abundant in suitable habitat throughout their range.

Other Comments

There are nine subspecies of A. leucurus in the United States.

(Tomich, 1982)

Contributors

Jennifer Nixon (author), University of Northern Iowa, Jim Demastes (editor), University of Northern Iowa.

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.

carrion

flesh of dead animals.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

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.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

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

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

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).

terrestrial

Living on the ground.

viviparous

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

References

Belk, M., H. Smith. April 12, 1991. *Ammospermophilus leucurus*. Mammalian Species: Special Publication of the American Society of Mammalogists, 368: 1-8.

Johnson, V., J. Harris. "California Wildlife Habitat Relationships System" (On-line). Accessed October 22, 2001 at http://www.dfg.ca.gov/whdab/cwhr/M067.html.

Nowak, R. 1999. Walker's Mammals of the World 6th Edition. Baltimore and London: Johns Hopkins University Press.

Tomich, P. 1982. Ground Squirrels. Pp. 192-194, 196, 201 in J Chapman, G Feldhamer, eds. Wild Mammals of North America: Biology, Management Economics. Baltimore and London: Johns Hopkins University Press.

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