370 Xerospermophilus spilosomaabout two to three weeks). Mating takes place when the fe-
males appear. After a gestation of 28 days, a litter of fi ve to
eight young is born in a burrow; the young emerge 3–4
weeks later, and are weaned after an additional three weeks.
Home range sizes are relatively large for both males (1.02–
4.86 ha) and females (0.50–1.55 ha). Adult males immerge in
July and August, followed closely by adult females; juveniles
often remain active until late September. X. spilosoma adults
are aggressive during the breeding season but become more
tolerant of conspecifi cs outside of that time period. Burrow
densities and populations are typically low, probably refl ec-
tive of resource availability and the low levels of sociality in
this species. Burrows seem to be relatively simple, and they
penetrate to about 1 m belowground. Spotted ground squir-
rels will feed on leaves, shoots, fl owers, and the seeds of
grasses, forbs, small shrubs, and cacti; they will also con-
sume insects and small vertebrates. Most of their active
time aboveground consists of foraging and feeding. Over-
winter food caches are not common. Their predators are
primarily mustelids, canids, raptors, and snakes. X. spilo-
soma is seldom hunted or trapped, but it is sometimes re-
moved by shooting or poisoning. This species can persist in
overgrazed grasslands.
general references: Fitzgerald and Streubel 1978; Li-
voreil and Baudoin 1996; Livoreil et al. 1993; Mandier and
Gouat 1996; Millán-Peña 1998; Stangl and Goetze 1991.
Xerospermophilus tereticaudus
(Baird, 1858)
Round-Tailed Ground Squirrel
description: Round-tailed ground squirrels have a pale
gray to pinkish buff to tawny dorsum, with the sides, the
feet, and the venter white to pale buff. The cheeks are white
to pale clay. The short round tail has a black tip; the tail is
the color of the dorsum above, and drab to buff to cinnamon
below.
size: Both sexes—HB 204–278 mm; T 60–112 mm; Mass 110–
170 g.
distribution: X. tereticaudus is found in the deserts of
southeastern California, southern Nevada, and western
Arizona (USA), and northeast Baja California and Sonora
(México).
geographic variation: Four subspecies are recognized.
X. t. tereticaudus—southern Nevada and southeastern Cali-
fornia (USA), and northeastern Baja California (México).
See description above.
X. t. apricus—isolated in the Valle de la Trinidad, at higher
elevations between mountain ranges, in northern Baja
California (México). This form is slightly darker and
browner.
X. t. chlorus—Coachella Valley, in southern California (USA).
This subspecies has a drabber and less pink dorsum.
X. t. neglectus—southern and western Arizona (USA), and
northwestern Sonora (México). This is a darker and
shorter-tailed form.conservation: IUCN status—least concern. Population
trend—stable. X. t. chlorus is a subspecies of special concern
in California (USA).habitat: Round-tailed ground squirrels occur in sandy low
fl at deserts, commonly in communities dominated by mes-
quite (Prosopis) and creosote bush (Larrea). This species can
also be found in urban areas, cemeteries, and parks.natural history: X. tereticaudus is diurnal. Round-tailed
ground squirrels can stay active year-round in some loca-
tions, but they typically enter torpor in burrows. Torpor
lasts for four to six months in the case of adult females (Sep-
tember–March), and for seven to nine months for adult
males (May–January) in some areas. Males emerge fi rst and,
in some populations, defend territories; females follow two
to four weeks later, and breeding occurs soon after their