Urocitellus columbianus 355of ground squirrels, adults enter hibernation fi rst, some-
times as early as mid-July but usually by August. Adults
emerge in early March. No precise data on the length of ges-
tation and lactation are available. An annual litter appears in
late April or early May, estimated to vary between 5 and 10
individuals. Numerous birds of prey, carnivorous mam-
mals, and snakes are either assumed or observed to prey on
U. canus. Little else is known about the ecology of this spe-
cies. Populations of Merriam’s ground squirrels are highly
fragmented and appear to be declining, as a result of their
elimination as pests by the farming community.
general references: F. R. Cole and Wilson 2009; Helgen
et al. 2009; Yensen and Hammerson 2008; Yensen and Sher-
man 2003.
Urocitellus columbianus (Ord, 1815)
Columbian Ground Squirrel
description: Noted for its large and robust size and its
dense pelage, the Columbian ground squirrel is also distin-
guished by the cinnamon buff color of its dorsal pelage. The
tail is dark above and lighter below. The neck is light gray,
the eye ring is a pale buff , and the sides are light gray or buff.
size: Female—HB 247.8 mm; T 84.3 mm; Mass 441.4 g.
Male—HB 258.0 mm; T 101.3 mm; Mass 490.1 g.
Sex not stated—HB 269.5 mm; T 98.0 mm; Mass 576.0 g.
distribution: The Columbian ground squirrel is found
across southeastern British Columbia and the southwestern
edge of Alberta (Canada) southward to eastern Washington,
northeastern Oregon, central Idaho, and western Montana
(USA). Models of climate change suggest that alterations in
vegetation will most likely result in a reduction in the geo-
graphic range of U. columbianus in the future.geographic variation: Two subspecies are recognized.U. c. columbianus—most of the species’ range, except in
northeastern Oregon. See description above.
U. c. rufi caudus—northeastern Oregon (USA). This subspecies
is distinguished from U. c. columbianus by its more tawny
throat and face, darker legs and feet, and broader skull.conservation: IUCN status—least concern. Population
trend—stable.habitat: The Columbian ground squirrel occupies open
habitats, sometimes in association with open forest stands,
but usually in meadows of the Hudsonian, Canadian, and
upper transition life zones. This species frequently occurs
in wet alpine and subalpine meadows, where fl ooding is
sometimes common. U. columbianus is also found on agricul-
tural fi elds and rangelands.natural history: The diet of the Columbian ground
squirrel consists primarily of fl owers, bulbs, fruits, and
seeds. This species competes with cattle and sheep for for-
age and is therefore the subject of strict control eff orts in
some parts of its range. U. columbianus hibernates for approxi-
mately 8.5 months and is only active during the remaining
3.5 months. The animals periodically arouse from torpor,
depending on the ambient temperature. Males emerge from
hibernation in full reproductive condition, and females en-
ter estrus within a few days of emergence. Breeding con-
tinues for about 21 days thereafter. However, females that
did not successfully breed during this three-week period
have been observed to reenter estrus and breed a few weeks
later. Yearling females will sometimes forego reproduction
because of low body mass at the time of emergence from
their fi rst hibernation. Primary factors infl uencing age at
fi rst reproduction appear to be body mass, environmental
conditions, and whether the mother is present through the
fi rst 2 years of life. Lower reproduction in older females ap-
pears to be related to senescence. The timing of the breed-
ing season varies more at higher elevations. In general, it
appears that several life-history traits, physiology, and the
overall body mass of an animal all show considerable phe-
notypic plasticity across elevations, whereas structural size