Urocitellus armatus 349Urocitellus armatus Kennicott, 1863
Uinta Ground Squirrel
description: The Uinta ground squirrel can be identifi ed
by its brown to black tail that is mostly black on top, pale on
the edges, and gray on the underside.
size: Female—HB 216.7 mm; T 69.2 mm; Mass 347.3 g.
Male—HB 223.5 mm; T 71.8 mm; Mass 394.9 g.
Sex not stated—HB 225.0 mm; T 65.0 mm; Mass 344.6 g.
distribution: This species’ range extends from southeast
Idaho and southern Montana to western Wyoming and
southcentral Utah (USA).
geographic variation: None.
conservation: IUCN status—least concern. Population
trend—no information.
habitat: The Uinta ground squirrel occupies large open
areas, often near timberline. Found in high valleys, this spe-
cies inhabits dry meadows and agricultural and pasture
lands. In western Wyoming, U. armatus is also reported to
occur in shrub-steppe communities consisting of sagebrush
(Artemisia) and rabbitbrush (Chrysothamnus). The shrubs may
be used for shading.natural history: U. armatus is herbivorous, with grasses
comprising the majority of its diet; however, strong sea-
sonal variation is reported. Immediately following emer-
gence, 90 percent of the animal’s diet consists of grass leaves,
but this food component later drops when the leaves of
forbs and grass seeds are added. Sagebrush (Artemisia) leaves,
earthworms, and roots are also consumed. The mean daily
energy budget of the Uinta ground squirrel is 45 kcal/day,
and its metabolic rate is 500–570 ml O2/hour at 10°C. This
species’ arousal from hibernation and emergence from the
burrow vary with conditions. One study reported emer-
gence around the beginning of April, in which adult males
emerged fi rst, adult females followed, and then yearlings ap-
peared. All individuals begin hibernation before 1 Septem-
ber, but they may immerge as early as late July. Adults tend
to enter hibernation before juveniles. Males exhibit territo-
rial behavior soon after emergence, scent-marking the ground
by rubbing their cheeks on it. Female distribution, however,
often causes males to shift their territory. Breeding occurs
within 30 days of emergence. Aggression between males—
which includes fi ghting, biting, and some vocalizations—is
common during the breeding season. Females are in estrus
for less than one day, usually two to three days after emer-
gence from the burrow; mating occurs within the burrow.
Yearling males usually do not mate, whereas yearling fe-
males can mate but may experience reproductive failure.
The Uinta ground squirrel produces only one litter per year,
following a gestation of 23–26 days. Litter sizes range from
four to six, usually less than the initial number of embryos.
The young are born around 1 May and typically emerge
about 22 days later. After mating, females become aggres-
sive and intolerant until their young are weaned. These
squirrels have been observed to engage in cannibalism as
well as in infanticide.
The Uinta ground squirrel’s vocalizations, of which six
are reported, are involved in agonistic behavior, and alarm
calls are used to warn of predators. Ground predators, other
than snakes, elicit a “churr” call, whereas aerial predators
engender a distinctly diff erent “chirp” call. Survival rates
are reported to be directly related to body mass, which al-
lows an animal to remain alive during hibernation. As a re-Urocitellus Obolenskij, 1927
This genus contains 12 species of ground squirrels.