Townsend's Ground Squirrel
Encyclopedia
The Townsend's ground squirrel (Urocitellus townsendii) is a species of rodent
in the Sciuridae family. It is found in high desert shrublands in several areas of the United States
.
and the Columbia Plateau
. Its range includes south-central Washington, eastern Oregon
, southern Idaho
, western Utah
, most of Nevada
, and extreme eastern California
. The subspecies are distributed as follows:
Townsend's ground squirrels typically inhabit arid grassland
s and shrub-grasslands. Malheur ground squirrels, however, inhabit the
relatively mesic and fertile Snake River Plain
. Plant communities in which Townsend's ground squirrels occur include crested wheatgrass (Agropyron cristatum
), big sagebrush (Artemisia tridentata
) wheatgrass, rabbitbrush (Chrysothamnus
spp.), shadscale (Atriplex confertifolia), and winterfat (Kraschenninikovia lanata) grasslands .
In southeastern Idaho, the density of Townsend's ground squirrel burrows is highest on winterfat-Sandberg bluegrass (Poa secunda
), intermediate in big sagebrush-Thurber needlegrass (Stipa thurberiana), and lowest in shadscale-Indian ricegrass (Oryzopsis hymenoides) and thread grass (Stipa comata) . Burrow densities were highly variable in mixed exotic annual communities, and negatively correlated with cheatgrass (Bromus tectorum) . They increase with increasing native grass cover, but the populations are unstable when native grass cover is overly high.
As a burrowing species, Townsend's ground squirrels select sites with deep, friable, well-drained soils . In southeastern Idaho, 68% of Townsend's ground squirrel burrows were in sand, 28% in silt, and 4% in clay .
Smith and Johnson reported a mean home range of 1,357 square meters 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 . Densities of 296 to 331 individuals per hectare have been reported for Piute ground squirrel
s .
Females breed as yearlings. Most males also breed as yearlings, although male Snake Valley ground squirrels breed at 2 years of age . Most breeding occurs in late January or early February , just after dormancy ends. Piute ground squirrels breed from mid-February to early March, somewhat later than other subspecies . Gestation is about 24 days . One litter is produced per year, with 6 to 10 pups per litter . 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 .
Townsend's ground squirrels have been observed climbing shrubs while foraging, apparently for cover and to spot palatable vegetation .
, when seeds become the primary diet item. Seeds are an important source of calories just prior to estivation. Where
present, winterfat is browsed heavily, 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 is 49% Sandberg bluegrass, 11% western yarrow (Achillea millefolium var. occidentalis), 8% pinnate tansymustard
(Descurania pinnata) seed, 31% other plant species (mostly forbs), and 1% insects . On a big sagebrush-crested
wheatgrass community in southeastern Idaho, 80% of Townsend's ground squirrels trapped in June had consumed crested wheatgrass, and Townsend's ground squirrels became dormant after the crested wheatgrass senesced . 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.
Adult cannibalism of unweaned young has been observed in the Townsend's ground squirrel .
(Buteo regalis) in the Great Basin and Columbia Plateau . They are
also a major and often primary diet item of prairie falcons (Falco mexicanus) . The Townsend's ground squirrel has been rated one of the two most important prey species in southeastern Idaho because of its importance to ferruginous hawks and prairie falcons. 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) .
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
in the Sciuridae family. It is found in high desert shrublands in several areas of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
Distribution
The Townsend's ground squirrel is found in the Great BasinGreat Basin
The Great Basin is the largest area of contiguous endorheic watersheds in North America and is noted for its arid conditions and Basin and Range topography that varies from the North American low point at Badwater Basin to the highest point of the contiguous United States, less than away at the...
and the Columbia Plateau
Columbia Plateau
The Columbia Plateau is a geologic and geographic region that lies across parts of the U.S. states of Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade Range and the Rocky Mountains, cut through by the Columbia River...
. Its range includes south-central Washington, eastern Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, southern Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, western Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, most of Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
, and extreme eastern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. The subspecies are distributed as follows:
- Spermophilus townsendii artemesiae – south-central Idaho
- S. t. canus (Merriam's ground squirrelMerriam's Ground SquirrelMerriam's ground squirrel is a species of rodent in the family Sciuridae. It occurs in the states of Idaho, Nevada, and Oregon in the United States.-Description:...
) – eastern Oregon; northeastern corner of California; northwestern corner of Nevada - S. t. idahoensis – southwestern Idaho
- S. t. mollis (Piute ground squirrelPiute Ground SquirrelThe Piute ground squirrel is a species of rodent in the family Sciuridae. It is endemic to the United States....
) – 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
Townsend's ground squirrels typically inhabit arid grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
s and shrub-grasslands. Malheur ground squirrels, however, inhabit the
relatively mesic and fertile Snake River Plain
Snake River Plain
The Snake River Plain is a geologic feature located primarily within the state of Idaho in the United States of America. It stretches about westward from northwest of the state of Wyoming to the Idaho-Oregon border. The plain is a wide flat bow-shaped depression, and covers about a quarter of Idaho...
. Plant communities in which Townsend's ground squirrels occur include crested wheatgrass (Agropyron cristatum
Agropyron cristatum
Agropyron cristatum is a species in the Poaceae family. This plant is often used as forage and erosion control...
), big sagebrush (Artemisia tridentata
Artemisia tridentata
Artemisia tridentata is a shrub or small tree from the family Asteraceae. Some botanists treat it in the segregate genus Seriphidium, as S. tridentatum W. A. Weber, but this is not widely followed...
) wheatgrass, rabbitbrush (Chrysothamnus
Chrysothamnus
Chrysothamnus is a member of the plant family Asteraceae. It is a semi-deciduous shrub, sometimes also called sagebrush. The native distribution is in the arid western United States and northern Mexico...
spp.), shadscale (Atriplex confertifolia), and winterfat (Kraschenninikovia lanata) grasslands .
In southeastern Idaho, the density of Townsend's ground squirrel burrows is highest on winterfat-Sandberg bluegrass (Poa secunda
Poa secunda
Poa secunda is a widespread species of grass native to North America. It is highly resistant to drought conditions, and provides excellent fodder.-External links:**...
), intermediate in big sagebrush-Thurber needlegrass (Stipa thurberiana), and lowest in shadscale-Indian ricegrass (Oryzopsis hymenoides) and thread grass (Stipa comata) . Burrow densities were highly variable in mixed exotic annual communities, and negatively correlated with cheatgrass (Bromus tectorum) . They increase with increasing native grass cover, but the populations are unstable when native grass cover is overly high.
Preferred habitat
Although Townsend's ground squirrels occur in arid environments, within those environments they are most common around desert springs and irrigated fields . They also occupy ridgetops, hillsides, and valley bottoms , canal and railroad embankments, and old fields .As a burrowing species, Townsend's ground squirrels select sites with deep, friable, well-drained soils . In southeastern Idaho, 68% of Townsend's ground squirrel burrows were in sand, 28% in silt, and 4% in clay .
Smith and Johnson reported a mean home range of 1,357 square meters 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 . Densities of 296 to 331 individuals per hectare have been reported for Piute ground squirrel
Piute Ground Squirrel
The Piute ground squirrel is a species of rodent in the family Sciuridae. It is endemic to the United States....
s .
Timing of major life events
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 . It is shorter in wet years, when green forage is available later in summer, than in dry years .Females breed as yearlings. Most males also breed as yearlings, although male Snake Valley ground squirrels breed at 2 years of age . Most breeding occurs in late January or early February , just after dormancy ends. Piute ground squirrels breed from mid-February to early March, somewhat later than other subspecies . Gestation is about 24 days . One litter is produced per year, with 6 to 10 pups per litter . 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 .
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 . 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. 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.Townsend's ground squirrels have been observed climbing shrubs while foraging, apparently for cover and to spot palatable vegetation .
Food habits
Townsend's ground squirrels consume mainly green vegetation and some seeds and insects . Green grasses are apparently a staple from late winter until just prior to grass senescence and Townsend ground squirrel estivationEstivation
Aestivation is a state of animal dormancy, characterized by inactivity and a lowered metabolic rate, that is entered in response to high temperatures and arid conditions...
, when seeds become the primary diet item. Seeds are an important source of calories just prior to estivation. Where
present, winterfat is browsed heavily, 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 is 49% Sandberg bluegrass, 11% western yarrow (Achillea millefolium var. occidentalis), 8% pinnate tansymustard
(Descurania pinnata) seed, 31% other plant species (mostly forbs), and 1% insects . On a big sagebrush-crested
wheatgrass community in southeastern Idaho, 80% of Townsend's ground squirrels trapped in June had consumed crested wheatgrass, and Townsend's ground squirrels became dormant after the crested wheatgrass senesced . 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.
Adult cannibalism of unweaned young has been observed in the Townsend's ground squirrel .
Predators
Townsend's ground squirrels are the primary prey of ferruginous hawks(Buteo regalis) in the Great Basin and Columbia Plateau . They are
also a major and often primary diet item of prairie falcons (Falco mexicanus) . The Townsend's ground squirrel has been rated one of the two most important prey species in southeastern Idaho because of its importance to ferruginous hawks and prairie falcons. 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) .