Spermophilus townsendii

The Townsend's ground squirrel is distributed in the Great Basin and the
Columbia Plateau. Its range includes south-central Washington, eastern
Oregon, southern Idaho, western Utah, most of Nevada, and extreme
eastern California [25]. Distribution of subspecies is [9]:

Spermophilus townsendii artemesiae - south-central Idaho
S. t. canus - eastern Oregon; northeastern corner of California;
northwestern corner of Nevada
S. t. idahoensis - southwestern Idaho
S. t. mollis - eastern California; southeastern Oregon; southern Idaho;
western Utah; Nevada; most widely distributed subspecies
S. t. nancyae - south-central Washington
S. t. townsendii - south-central Washington
S. t. vigilis - Snake River Canyon bottomlands of east-central Oregon
and west-central Idaho

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range

CA ID NV OR UT WA

This species is restricted to the Yakima River Valley of Washington in the United States, west of the Yakima River and in the Horse Heaven Hills to the south of the valley (Hafner et al 1998). The entire area of the species' range appears to be less than 7,000 km².

More info for the terms: cover, shrubs

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].

More info for the term: density

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].

More info for the terms: cover, density, mesic

Townsend's ground squirrels typically inhabit arid grasslands and
shrub-grasslands. Malheur ground squirrels, however, inhabit the
relatively mesic and fertile Snake River Valley [25]. Plant communities
in which Townsend's ground squirrels occur that have not been previously
listed include crested wheatgrass (Agropyron cristatum), big sagebrush
(Artemisia tridentata)-crested wheatgrass [15], and rabbitbrush
(Chrysothamnus spp.)-, shadscale (Atriplex confertifolia)-, and
winterfat (Kraschenninikovia lanata)-bunchgrasslands [21].

Yensen and others [28] found that on the Snake River Birds of Prey Study
Area (SRBPSA) of southeastern Idaho, density of active Townsend's ground
squirrel burrows was highest on winterfat-Sandberg bluegrass (Poa
secunda), intermediate in big sagebrush-Thurber needlegrass (Stipa
thurberiana), and lowest in shadscale-Indian ricegrass (Oryzopsis
hymenoides)-needle-and-thread grass (Stipa comata) communities. Burrow
densities were highly variable in mixed exotic annual communities, and
negatively correlated with cheatgrass (Bromus tectorum) communities.
Another study on the SRBPSA showed that Townsend's ground squirrel
density generally increased with increasing native grass cover.
Populations were unstable when native grass cover was extremely high,
however [16].

REFERENCES :
NO-ENTRY

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This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

More info for the term: shrub

104 Antelope bitterbrush-bluebunch wheatgrass
105 Antelope bitterbrush-Idaho fescue
314 Big sagebrush-bluebunch wheatgrass
315 Big sagebrush-Idaho fescue
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
414 Salt desert shrub
422 Riparian
501 Saltbush-greasewood

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

K038 Great Basin sagebrush
K055 Sagebrush steppe
K056 Wheatgrass-needlegrass shrubsteppe
K040 Saltbush-greasewood

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

FRES29 Sagebrush
FRES30 Desert shrub

Habitat and Ecology

Systems

• Terrestrial

More info for the terms: aestivation, shrubs

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].

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].

More info for the terms: cover, density, fire frequency, frequency, long-term effects, shrub, shrubs, wildfire

Due to the arid climate, postfire recovery of vegetation in Townsend's
ground squirrel habitats is slow. In the short term, fire usually
reduces abundance of Townsend's ground squirrels because less forage is
available on burned sites, and because predation increases with reduced
escape cover [8]. Studies on the long-term effects of fire on
Townsend's ground squirrels have only been conducted in communities
invaded by exotic annuals. In these communities, frequent fire has
harmed the Townsend's ground squirrel. Occasional fire in other
Townsend's ground squirrel habitats probably benefits the species in the
long term by reducing shrub density and providing a nutrient pulse to
grasses and other Townsend's ground squirrel forage.

Examples: A year following a July 1985 wildfire on the SRBPSA, more
than twice as many active Townsend's ground squirrel holes were found on
unburned control plots than on burned, partially burned, and
burned-rehabilitated plots. Burned-rehabilited plots had been
drill-seeded to crested wheatgrass, yellow sweet clover (Melilotus
officinalis), and fourwing saltbush (Atriplex canescens) the fall and
spring after fire. In the first postfire summer, the burned, paritally
burned, and burned-rehabilited sites were dominated by cheatgrass,
whereas the unburned control sites were dominated by fourwing saltbush.
Cheatgrass cover was 26 percent on burned, 9 percent on partially
burned, 14 percent on burned-rehabilitaed, and 5 percent on control
sites. Winterfat, an important food source for Townsend's ground
squirrels on the SRBPSA, had 7 percent cover on control sites, less than
1 percent cover on burned sites, and was absent on partially burned and
burned-rehabiliated sites. Bottlebrush squirreltail (Elymus elymoides)
and Sandberg bluegrass, which, along with winterfat, presumably
comprised the bulk of the Townsend's ground squirrel diet prior to
cheatgrass invasion, were present only on partially burned and control
sites. At postfire year 1, numbers of active Townsend's ground squirrel
burrows were [8]:

B P R C
---------------------------------------------------------
burrows 9 19 7 29
---------------------------------------------------------
B=burned
P=partially burned
R=burned-rehabilitated
C=control

Groves and Steenhof [8] speculated that Townsend's ground squirrel
numbers may have been reduced in the cheatgrass-dominated areas by
impeded movement through the thick stands of cheatgrass, which affected
breeding and population size, increased predation due to loss of shrub
cover, and changed available food resources.

Fire in wet years: Townsend's ground squirrel populations may show a
short-term increase when fire is followed by above-average
precipitation. Townsend's gound squirrel numbers increased after fire
in a big sagebrush-bluebunch wheatgrass (Psuedoroegneria spicata)
community in southeastern Washington. A wildfire occured in August
1973, when Townsend's ground squirrels were belowground and dormant,
burning 10,000 acres (4,000 ha). Townsend's ground squirrels had been
trapped prior to the fire, from March to May of 1973, for census. They
were trapped on the same site from March to May of 1974. Precipitation
from October to May was 4.8 inches (120 mm) in 1973 and 13.2 inches (330
mm) in 1974. Townsend's ground squirrel numbers were [11]:

Prefire Postfire
------- --------
Mar Apr May Mar Apr May
------------------------------------------------------------------------
Townsend's ground squirrels 13 20 18 10 33 28
------------------------------------------------------------------------

Where fires are frequent in Townsend's ground squirrel habitats, the
species may decline. As fire frequency has increased in shrub steppe of
the Great Basin and Columbia Plateau, shrubs have been lost and
cheatgrass and other annuals have become dominant. With short fire
return intervals, annuals are able invade large blocks of land. The
effects on Townsend's ground squirrel will probably be increased
vulnerability to predation and to annual climatic fluctuations, with
attendant unpredictability of forage [21]. With fewer bunchgrasses and
forbs, exotic annual communities have lower plant species diversity and
thus less nutritional variety for Townsend's ground squirrels. Although
Townsend's ground squirrel numbers will increase during years when
exotic annual production is high, unreliable production will probably
result in high-amplitude population fluctuations of Townsend's ground
squirrels [28].

More info for the term: litter

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].

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 2000
  Data Deficient
• 1996
  Data Deficient

Population

Population Trend

Major Threats

More info for the term: density

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

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