Townsend's ground squirrels communicate with each other using calls of varying pitch and complexity. Calls can be single or multiple-note, and the ground squirrels emit calls of higher pitch when underground. The purpose of these calls is unclear, though it has been hypothesized that they are used to confuse predators. Alarm calls sometimes vary between species.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; ultrasound ; chemical
Townsend's ground squirrels are listed as vulnerable by the IUCN Red List because less than ten percent of their habitat remains, its extent of occurrence is less than 6,700 square kilometers, and its available habitat continues to decrease in both size and quality. Populations of are highly fragmented and isolated, and no estimates of population density are available. In addition, Townsend's ground squirrels are subject to pest control in some areas, due to the damage that they do to crops.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Townsend's ground squirrels have been observed to cause agricultural damage, and have been subject to control programs.
Negative Impacts: crop pest
Piute Indians use Townsend's ground squirrels as a food source, and it has been hypothesized that they may have introduced the species to some areas of its current range.
Positive Impacts: food
Townsend's ground squirrels are hosts to several parasites, primarily intestinal. Parasites include several species of fleas, including Meringis shannoni, Opisthocrosis washingtonensis, and Thrassis petiolatus. Intestinal parasites include many species of eimerians: Eimeria adaensis, Eimeria beecheyi, Eimeria bilamellata, Eimeria callospermophili, Eimeria lateralis, Eimeria morainensis, Eimeria pseudospermophili. Parasitic helminths include Hymenolepis citelli, Pterygodermatites colaradensis, Spirura infundibuliformes, and Syphacia citelli.
Ecosystem Impact: disperses seeds
Commensal/Parasitic Species:
Townsend's ground squirrels subsist primarily on an herbivorous diet, inlcuding Sandberg's bluegrass (Poa secunda), winterfat (Krascheninnikovia lanata), big sagebrush (Artemisia tridentata), Russian thistle (Salsola tragus>), tansymustard (Descurainia pinnata), and cheatgrass (Bromus tectorum). Diet is similar between males and females, but varies based on habitat and age. Sandberg's bluegrass is a common food item in most habitats, with winterfat becoming a larger part of the diet in habitats where winterfat is represented more heavily among the vegetation cover. In addition to plants, small amounts of insects also factor into their diet.
Animal Foods: insects
Plant Foods: leaves; roots and tubers; wood, bark, or stems
Foraging Behavior: stores or caches food
Primary Diet: herbivore (Folivore , Lignivore)
The current range of Townsend's ground squirrels includes the Yakima River Valley in Washington, the Horse Heaven Hills to its south, and land to the west of the Yakima River. Their range is estimated at 7,000 square kilometers. Townsend's ground squirrels once occupied ranges throughout Nevada, eastern Oregon, southern Idaho, south-central Washington, and extreme eastern California. Within this range, different geographic barriers separated the species into subspecies. S. t. idahoensis and S. t. vigilis were separated by the Snake River. The Yakina River separated S. t. townsendii from S. t. nancyae. Spermophilius townsendii townsendii also existed separately from another subspecies, S. t. canus, south of the Columbia River, where their known ranges were separated by over 100 kilometers. Other subspecies occurred in shared ranges. The ranges of S. t. idahoensis and S. t. artemesiae overlapped, as do those of S. t. artemesiae and S. t. vigilis.
The shrinking range of Townsend's ground squirrels can be attributed both to decreasing populations of the species and to the taxonomic division of the species into several species. Piute ground squirrels (Spermophilus mollis) and Merriam's ground squirrels (Spermophilus canus) were at one point considered subspecies of Townsend's ground squirrels, but have been recognized as separate species.
Biogeographic Regions: nearctic (Native )
Townsend's ground squirrels primarily inhabit the Upper Sonoran Life Zone, which ranges from approximately 1,000 meters to 2,100 meters in elevation. Within this zone, they can be found in arid desert habitats, including communities of sagebrush, greasewood, and shadescale. They prefer well-drained soils, and their habitats of choice include abandoned farmland, canals, and railroad embankments. Their habitat selection can be restricted by competition with other species within the Spermophilus genus; when its range overlaps with Belding's ground squirrels (S. beldingi) or Uinta ground squirrels (S. armatus), their realized niche tends to be the most arid areas of its preferred habitats. The exception is subspecies S. t. vigilis, which is found in a limited area of relatively fertile river valley bottomland.
Range elevation: 1000 to 2100 m.
Average depth: 1.46 m.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: desert or dune
Other Habitat Features: suburban ; agricultural
Longevity may be similar to that of Piute ground squirrels (Spermophilius mollis) which lives in similar environments and was at one point believed to be a subspecies of Spermophilus townsendii. Piute ground squirrels live for a maximum of 5 years. In general, females are more likely to live to 5 years than males, which usually don't live longer than 3 years.
Range lifespan
Status: wild: 5 (high) years.
Average lifespan
Status: wild: 3 years.
Townsend's ground squirrels have pale, smoke-grey dorsal coloration, with creamy white underneath. Both dorsal and ventral coloration are washed with pinkish buff. Variations occur within subspecies. Spermophilius townsendii mollis from the Escalante desert of southern Utah are significantly redder than northern populations. A very pale color morph has also been found in western Nevada. Townsend's ground squirrels typically measure 167 to 271 mm long and weigh 82 to 325 g.
Skulls of Townsend's ground squirrels can be distinguished by a broad braincase; widely expanded zygomata; a stout rostrum with parallel sides; slender, decurved postorbital processes; a long auditory meatus; moderately-inflated auditory bullae; and hypsodont cheekteeth. The dental formula of Spermophilus townsendii is I1/1, C0/0, P2/1, M3/3.
Range mass: 82 to 325 g.
Range length: 167 to 271 mm.
Range basal metabolic rate: .62 to 1.10 cm3.O2/g/hr.
Average basal metabolic rate: .86 cm3.O2/g/hr.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Townsend's ground squirrels likely use camouflage, burrows, and warning signals to avoid predators. They are hunted by badgers (Taxidea taxus), coyotes (Canis latrans), long-tailed weasels (Mustela frenata), prairie falcons (Falco mexicanus), red-tailed hawks (Buteo jamaicencis), rough-legged buzzards (Buteo lagopus), ferruginous hawks (Buteo regalis), Swainson's hawks (Buteo swainsoni), ravens (Corvus corax), prairie rattlesnakes (Crotalus viridus), and northern pine snakes (Pituophis catenifer sayi). They are also eaten by Piute Indians.
Known Predators:
Anti-predator Adaptations: aposematic ; cryptic
Townsend's ground squirrels produce one litter per year and the species is polygynous.
Mating System: polygynous
Townsend's ground squirrels breed once a year, shortly after females awaken from hibernation in late winter. Adult females reproduce more than yearlings. Females give birth between February and April after a gestation time of 23 days. Average litter sizes range between 7 and 10 offspring that weigh 2.2 to 4.9 g at birth. Young are weaned in an average of 35 days and independent a year after birth. Females are sexually mature in 1 year, and males may take 2 years to reach sexual maturity. As in other species of Spermophilus, infanticide has been observed among Townsend's ground squirrels. Victims are typically offspring who have not yet been weaned.
Breeding interval: Townsend's ground squirrels produce one litter per year, soon after they awaken in late winter.
Breeding season: The breeding season for Townsend's ground squirrels is late winter through early spring, or January to March.
Range number of offspring: 7 to 10.
Average gestation period: 23 days.
Average weaning age: 35 days.
Average time to independence: 1 years.
Average age at sexual or reproductive maturity (female): 1 years.
Range age at sexual or reproductive maturity (male): 1 to 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Female Townsend's ground squirrels provide most of the care for their young until they reach independence at one year, nursing their offspring and providing food.
Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
Townsend's ground squirrel (Urocitellus townsendii) is a species of rodent in the family Sciuridae. It is found in high desert shrublands in several areas of the United States.
Townsend's ground squirrel is found 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.[2] The subspecies are distributed as follows:[3]
Townsend's ground squirrels typically inhabit arid grasslands and shrub-grasslands. Malheur ground squirrels, however, inhabit the relatively mesic and fertile Snake River Plain.[2] Plant communities in which Townsend's ground squirrels occur include crested wheatgrass (Agropyron cristatum), big sagebrush (Artemisia tridentata) wheatgrass,[4] rabbitbrush (Chrysothamnus spp.), shadscale (Atriplex confertifolia), and winterfat (Kraschenninikovia lanata) grasslands.[5]
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.[6][7]
Although Townsend's ground squirrels occur in arid environments, within those environments they are most common around desert springs and irrigated fields.[8] They also occupy ridgetops, hillsides, and valley bottoms,[2] canal and railroad embankments, and old fields.[9] As a burrowing species, Townsend's ground squirrels select sites with deep, friable, well-drained soils.[2][5] In southeastern Idaho, 68% of Townsend's ground squirrel burrows were in sand, 28% in silt, and 4% in clay.[10]
Smith and Johnson reported a mean home range of 1,357 square meters for 14 Snake Valley ground squirrels.[11] 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.[11] Densities of 296 to 331 individuals per hectare have been reported for Piute ground squirrels.[12]
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.[12][13] It is shorter in wet years, when green forage is available later in summer, than in dry years.[11][12]
Females breed as yearlings. Most males also breed as yearlings, although male Snake Valley ground squirrels breed at 2 years of age.[11][13] Most breeding occurs in late January or early February,[11] just after dormancy ends. Piute ground squirrels breed from mid-February to early March, somewhat later than other subspecies.[13][14] Gestation is about 24 days.[12] One litter is produced per year, with 6 to 10 pups per litter.[2] 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.[2]
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.[2] 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.[7] 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.[10]
Townsend's ground squirrels have been observed climbing shrubs while foraging, apparently for cover and to spot palatable vegetation.[2]
Townsend's ground squirrels consume mainly green vegetation and some seeds and insects.[15][16] Green grasses are apparently a staple from late winter until just prior to grass senescence and Townsend ground squirrel estivation, when seeds become the primary diet item. Seeds are an important source of calories just prior to estivation.[14] Where present, winterfat is browsed heavily,[17] 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.[16] 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.[18] 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.[7]
Adult cannibalism of unweaned young has been observed in the Townsend's ground squirrel.[19]
Townsend's ground squirrels are the primary prey of ferruginous hawks (Buteo regalis) in the Great Basin and Columbia Plateau.[4] They are also a major and often primary diet item of prairie falcons (Falco mexicanus).[5][20] 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.[5] 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).[2][11][12][21]
This article incorporates public domain material from Spermophilus townsendii. United States Department of Agriculture.
Townsend's ground squirrel (Urocitellus townsendii) is a species of rodent in the family Sciuridae. It is found in high desert shrublands in several areas of the United States.
