254 Ammospermophilus leucurusA. l. tersus—extreme northwestern Arizona (USA). This
form is similar in size to A. l. leucurus, but the color is
darker.
conservation: IUCN status—least concern. Population
trend—stable.
habitat: White-tailed antelope ground squirrels are found
in sandy and rocky desert habitats, ranging from low-eleva-
tion valley fl oors up to pinyon–juniper (Pinus, Juniperus) for-
ests, often among shrubs and cacti.
natural history: This squirrel is diurnal, active year-
round, and does not estivate or store fat, even in the high
temperatures that accompany desert life. White-tailed ante-
lope ground squirrels require free water in their arid habi-
tats. They exhibit behavioral thermoregulation by reducing
their activity in the heat of the day, and their sparsely haired
tail appears to be eff ective for dissipating heat. A. leucurus
lives in shallow (< 1 m) burrows spread throughout a 3–8 ha
home range, probably this widespread both for escape and
for heat avoidance. Burrows contain a nest chamber that is
provisioned with bedding. Nearly all adults more than 1
year old breed each year, from February–June in the north
and March–September in the south; usually a single litter of
5–14 young (average = 8) is produced each year after a gesta-
tion of 30–35 days. There is a latitudinal gradient in litter
size, with northern populations in Oregon averaging 9.3
young /litter and southern populations in Baja Ca lifornia av-
eraging 5.8 young/litter. The young emerge at 50–60 days
and are weaned soon afterward. Juveniles disperse from
their natal area. Adults live a solitary life, with dominance
rank well established between neighbors. Naso-oral sniff -
ing and contact appear to be a major means of maintaining
a rigid dominance hierarchy among neighbors. Aggression
can lead to lunging and side-to-side displays, chases, tooth
chattering, and boxing and other physical combat. White-
tailed antelope ground squirrels feed heavily on green veg-
etation, cactus, yucca, and assorted seeds, but they will also
eat insects or scavenge vertebrate carcasses. As one of the
few diurnal rodents in the desert, A. leucurus appears to
minimize its interaction with other species. Densities are
rather low, but its relative body size means that A. leucurus
accounts for the majority of rodent biomass in many desert
ecosystems. Two alarm vocalizations are given—shrill rapid
“chitters” and high-pitched trills—that appear to be adapta-
tions to open environments. Their predators include foxes,
coyotes (Canis latrans), procyonids, small felids, raptors, and
snakes. White-tailed antelope squirrels are not hunted or
trapped, due to their small size. However, in some areas it
will visit cultivated crops, orchards, and gardens.
general references: Belk and Smith 1991; Karasov 1983;
O’Farrell and Clark 1984; Whorley and Kenagy 2007.Ammospermophilus nelsoni
(Merriam, 1893)
Nelson’s Antelope Squirreldescription: Nelson’s antelope squirrels have a buff to tan
dorsum with a suff usion of yellow; and a single thin white
stripe on each side, parallel to the spine. The venter is white
to cream. The tail is buff gray on the dorsal surface and
creamy white underneath.size: Female—HB 238 mm (230–256 mm); T 72 mm (67–
78 mm); Mass 154.5 g (141.8–179 g).
Male—HB 249 mm (234–267 mm); T 73.1 mm (66–78 mm).distribution: A. nelsoni is found in the San Joaquin Valley
of southern California (USA).geographic variation: None.conservation: IUCN status—endangered. Population
trend—decreasing.habitat: Nelson’s antelope squirrels are found in dry fl at or
rolling terrain with slopes less than 10°–14°—sparse shrub-
lands and sparse grasslands—on alluvial and loamy soils,