BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Spermophilus townsendii | Townsend's Ground Squirrel 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Aestivation - Townsend's ground squirrels become dormant in late spring
or early summer, after grasses cure.  They emerge from dormancy in late
winter.  Dormancy lasts 7.5 to 9 continuous months [1,24].  The
aestivation period is shorter wet years, when green forage is available
later in summer, than in dry years [1,27].

Breeding - Females breed as yearlings.  Most males also breed as
yearlings, although male Snake Valley ground squirrels breed at 2 years
of age [24,27].  Most breeding occurs in late January or early February
[27], just after dormancy ends.  Piute ground squirrels breed from
mid-February to early March, somewhat later than other subspecies
[23,24].

Gestation - about 24 days [1]

Litter size - One litter is produced per year, with 6 to 10 pups per
litter [25].

Development - Pups are born hairless and with eyes closed.  Early
postnatal development of Townsend's ground squirrels is relatively slow
compared to development of other Spermophilus species.  Pups open their
eyes at 19 to 22 days of age, and are weaned shortly thereafter [25].


PREFERRED HABITAT : 
Although Townsend's ground squirrels occur in arid environments, within
those environments they are most common around desert springs and
irrigated fields [10].  They also occupy ridgetops, hillsides, and
valley bottoms [25], canal and railroad embankments, and old fields [5].
As a burrowing species, Townsend's ground squirrels select sites with
deep, friable, well-drained soils [21,25].  In southeastern Idaho, 68
percent of Townsend's ground squirrel burrows were in sand, 28 percent
in silt, and 4 percent in clay [19].

Home range and density:  Smith and Johnson [27] reported a mean home
range of 1,357 square meters (+/- 189.7 sq m) for 14 Snake Valley ground
squirrels.  Townsend's ground squirrel density can fluctuate greatly
from year to year.  Estimated population density of Snake Valley ground
squirrels ranged from 3 to 32 individuals per hectare [27].  Densities
of 296 to 331 individuals per hectare have been reported for Piute
ground squirrels [1].


COVER REQUIREMENTS : 
Townsend's ground squirrels occupy open habitats and use burrows for
shelter, protection from predators, and food storage.  Burrows are often
grouped into colonies, but some Townsend's ground squirrels are solitary
[25].  Except when mothers have pups, there is only one Townsend's
ground squirrel per burrow.  Burrows have one to many openings and may
have numerous auxiliary burrows in addition to the "home" or nest
burrow [28].  Burrow dimensions of Townsend's ground squirrels in
southeastern Idaho ranged from 2.6 to 3.8 inches (6.5-9.6 cm)
horizontally and from 1.7 to 2.5 inches (4.3-6.3 cm) vertically [19].

Townsend's ground squirrels have been observed climbing shrubs while
foraging, apparently for cover and to spot palatable vegetation [25].


FOOD HABITS : 
Townsend's ground squirrels consume mainly green vegetation and some
seeds and insects [4,13].  Dietary studies on the Townsend's ground
squirrel are few, but green grasses are apparently a staple from late
winter until just prior to grass senescence and Townsend ground squirrel
aestivation, when seeds become the primary diet item.  Seeds are an
imortant source of calories just prior to aestivation [23].  Where
present, winterfat is browsed heavily [8], but only light browsing of
other shrubs has been reported.  From March through May on the Arid Land
Ecology Reserve in eastern Washington, the Townsend's ground squirrel
diet was 49 percent Sandberg bluegrass, 11 percent western yarrow
(Achillea millefolium var. occidentalis), 8 percent pinnate tansymustard
(Descurania pinnata) seed, 31 percent other plant species (mostly
forbs), and 1 percent insects [13].  On a big sagebrush-crested
wheatgrass community in southeastern Idaho, 80 percent of Townsend's
ground squirrels trapped in June had consumed crested wheatgrass, and
Townsend's ground squirrels became dormant after the crested wheatgrass
senesced [17].

Cheatgrass (Bromus tectorum) is an important food item in some years.
As an annual with wide year-to-year swings in productivity, however, it
is not a reliable food source.  Yensen and others [28] found that on the
SRBPSA, Townsend's ground squirrel burrow densities declined over a
7-year period in areas dominated by cheatgrass or other exotic annuals.

Adult cannabalism of unweaned young has been observed in the Townsend's
ground squirrel [3].


PREDATORS : 
Townsend's ground squirrels are the primary prey of ferruginous hawks
(Buteo regalis) in the Great Basin and Columbia Plateau [15].  They are
also a major and often primary diet item of prairie falcons (Falco
mexicanus) [21,22].  The Townsend's ground squirrel has been rated one
of the two most important prey species on the SRBPSA because of its
importance to ferruginous hawks and prairie falcons.  (The other
important prey species is the black-tailed jackrabbit [Lepus
californicus]) [21].  Other important predators of Townsend's ground
squirrels include other hawks (Accipiter and Buteo spp.) and falcons
(Falco spp.), common crows (Corvus corax), badgers (Taxidea taxus),
coyotes (Canis latrans), long-tailed weasels (Mestrela frenata), western
rattlesnakes (Crotalus viridis), and gopher snakes (Pituophis
melanoleucus) [1,12,25,27].


MANAGEMENT CONSIDERATIONS : 
Grazing effects:  Effects of cattle grazing on Towsend's ground
squirrels vary.  In a small mammal population study on riparian sites in
Nevada, Townsend's ground squirrels were trapped only in areas where
cattle had been excluded [20].  In sagebrush steppe in southeastern
Idaho, however, Townsend's ground squirrel density did not significantly
vary between ungrazed sites and sites grazed by cattle [16].

Census:  Because a given burrow may have one to many entrances, trapping
is a more reliable method of Townsend's ground squirrel census than
counting burrow entrances [16].

Predator-prey relationships:  In areas where exotic annuals are
increasing, Townsend's ground squirrel predators will probably face an
increasingly unstable prey base [28].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Spermophilus townsendii | Townsend's Ground Squirrel