There are nine subspecies of A. leucurus in the United States.
(Tomich, 1982)
Perception Channels: tactile ; chemical
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
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
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
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
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 )
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
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.
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.
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:
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
The white-tailed antelope squirrel (Ammospermophilus leucurus) is a diurnal species of ground squirrel, scientifically classified in the order Rodentia and family Sciuridae, found in arid regions of the southwestern United States and the Baja California Peninsula of northwestern Mexico.
The white-tailed antelope squirrel's geographical range extends north to south from southwestern Oregon to New Mexico, and east to west from western Colorado to Baja California, Mexico.[2][3][4]
This species of squirrel has an average home range of 14.9 acres (60,000 m2), and utilizes approximately 4 acres (16,000 m2) in its daily activities.[5] Throughout much of the squirrel's range, especially in Utah, the population density fluctuates greatly, with periods of high density followed by periods of low density.[2][6] Average population density also varies by season, with higher density in autumn relative to late spring.[2][7]
The white-tailed antelope squirrel is commonly spotted in arid habitats throughout the southwestern United States.[2] Throughout this range, Ammospermophilus leucurus is omnivorous, feeding primarily on foliage (10%-60% of its diet), seeds (20%-50%), arthropods, and to a lesser extent, vertebrates (mainly lizards and rodents; predatory behavior by ground squirrels has been noted[8][9][10][11]).[12] In conjunction with being a predator, the white-tailed antelope squirrel is also prey to many larger animals, including raptors, various canids, and snakes.[2][3][4][6] These squirrels are not only preyed upon by large predators, but they also fall victim to many diverse ectoparasites. These include various ticks, fleas, mites, lice, and a couple species of parasitic larvae.[2]
Antelope squirrels are active most during the cooler parts of the daylight hours, avoiding midday as much as possible.[2][13] Although these animals live in hot and arid climates, the white-tailed antelope squirrel is diurnal, meaning heat gain from metabolic activity could be a problem. However, compared to direct exposure of heat from the sun, metabolic heat gain contributes little to the overheating of this species.[2][13] This diurnal activity pattern may be contributed to predation patterns.[14] Selective pressures may have led to this species avoiding nighttime activity due to increased predation by nighttime predators. This behavior is controlled by the squirrels' natural circadian rhythms, and research has shown these rhythms to be highly important in keeping these diurnal activity patterns intact.[14]
White-tailed antelope squirrels' reproductive receptiveness in females and reproductive capability in males peaks in early spring.[15] It only takes the squirrels one year to become sexually mature and begin reproducing; typically, antelope ground squirrels will produce one large litter per year.[15]
Geographical factors, and thus environmental factors, weigh heavily on Ammospermophilus leucurus' reproductive cycle length and average litter size.[16] Specifically, this variation is seen best when comparing the northern and southern extents of the antelope ground squirrels' distribution. In Oregon, which is the northernmost extent of the squirrels' range, reproductive cycles are relatively short, and the average litter size is 9.3. However, in Baja California, the southernmost extent of the squirrels' range, reproductive cycles last half of the year, and the average litter size is 5.9.[16]
{{cite web}}: CS1 maint: archived copy as title (link) The white-tailed antelope squirrel (Ammospermophilus leucurus) is a diurnal species of ground squirrel, scientifically classified in the order Rodentia and family Sciuridae, found in arid regions of the southwestern United States and the Baja California Peninsula of northwestern Mexico.
