Urocitellus townsendii, Townsend's ground squirrel
Howard, Janet L. 1996. Urocitellus townsendii, Townsend's ground squirrel. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/species-reviews/urto
| Abbreviation | Common Name | Scientific Name | Classification | Status |
|---|---|---|---|---|
| Animals | ||||
| URTO | Townsend's ground squirrel | Urocitellus townsendii | Life Form: Animals/Mammal Kingdom: Animalia Class: Mammal Order: Rodentia Family: Sciuridae Genus: Spermophilus | Fed. Protected: No Nativity: Native Invasiveness: Noninvasive |
Taxonomy
The scientific name of the Townsend's ground squirrel is Urocitellus townsendii (Bachman). It is in the family Sciuridae [29]. Six subspecies are recognized [9,29]:
- Urocitellus townsendii artemesiae (Merriam), sagebrush or least Idaho ground squirrel
- Urocitellus townsendii canus (Merriam), gray ground squirrel
- Urocitellus townsendii idahoensis (Merriam), Snake Valley or Payette ground squirrel
- Urocitellus townsendii nancyae (Nadler), Townsend's ground squirrel
- Urocitellus townsendii townsendii (Bachman), Townsend's ground squirrel
- Urocitellus townsendii vigilis (Merriam), Malheur ground squirrel
Synonyms
- Spermophilus townsendii Bachman [9,14]
- Spermophilus townsendiiartemesiae (Merriam)
- Spermophilus townsendii canus Merriam
- Spermophilus townsendii idahoensis (Merriam)
- Spermophilus townsendii nancyae Nadler
- Spermophilus townsendii townsendii Bachman
- Spermophilus townsendii vigilis (Merriam) [9]
Other Common Names
None
General Distribution
The Townsend's ground squirrel is distributed in the Great Basin and on 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]:
- Urocitellus townsendii artemesiae - south-central Idaho
- Urocitellus townsendii - eastern Oregon; northeastern corner of California; northwestern corner of Nevada
- Urocitellus townsendii idahoensis - southwestern Idaho
- Urocitellus townsendii nancyae - south-central Washington
- Urocitellus townsendii townsendii - south-central Washington
- Urocitellus townsendii vigilis - Snake River Canyon bottomlands of east-central Oregon and west-central Idaho
States and Provinces
- United States: CA ID NV OR UT WA
Plant Communities
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 listed in Table A1 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 (Achnatherum thurberiana), and lowest in shadscale-Indian ricegrass (Oryzopsis hymenoides)-needle-and-thread grass (Hesperostipa 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].
Biological Characteristics
Townsend's ground squirrel at the entrance of a burrow, Yakima County, Washington. (CC BY-NC 4.0)
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].
Development and Reproduction
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].
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.), American crows (Corvus corax), badgers (Taxidea taxus), coyotes (Canis latrans), long-tailed weasels (Mustela frenata), western rattlesnakes (Crotalus viridis), and gopher snakes (Pituophis melanoleucus) [1,12,25,27].
Habitat
Diet
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 important 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 cannibalism of unweaned young has been observed in the Townsend's ground squirrel [3].
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 squirrel colony in Hanford, Washington.
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].
Fire-caused Mortality
Wildfire normally occurs in summer or fall in Townsend's ground squirrel habitats, after grasses have cured. Since Townsend's ground squirrels are aestivating in their burrows at that time, wildfire probably has no direct effect on them [11,28].
Fire Effects on Habitat
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 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, partially burned, and burned-rehabilitated 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-and-seeded, 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-rehabilitated 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]:
| Treatment | Number of Burrows |
|---|---|
| Burned | 9 |
| Partially burned | 19 |
| Burned-rehabilitated | 7 |
| Control | 29 |
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 ground squirrel numbers increased after fire in a big sagebrush-bluebunch wheatgrass (Pseudoroegneria spicata) community in southeastern Washington. A wildfire occurred 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]:
| Year | Survey Month | Number of Townsend's ground squirrels |
|---|---|---|
| 1973 - prefire | March | 13 |
| April | 20 | |
| May | 18 | |
| 1974 - postfire | March | 10 |
| April | 33 | |
| May | 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].
Fire Regimes
For fire regime information, search FEIS for this species by entering the species name on the Advanced Search page and selecting “Fire Regime” as the publication type.
Fire Management Considerations
No entry.
Federal Status
None
Other Status
No entry.
Other Management Information
Grazing effects: Effects of cattle grazing on Townsend'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].
Table A1— Forest and range ecosystems, Bureau of Land Management (BLM) physiographic regions, Kuchler plant associations, Society for American Foresters (SAF) forest cover types, and Society for Rangeland Management (SRM) rangeland cover types in which this species occurs.
Forest and Range Ecosystems (Garrison et al. 1977)
- FRES29 Sagebrush
- FRES30 Desert shrub
BLM Physiographic Regions (Bernard and Brown 1977)
- 5 Columbia Plateau
- 6 Upper Basin and Range
- 7 Lower Basin and Range
Kuchler Plant Associations (Kuchler 1964)
- K038 Great Basin sagebrush
- K055 Sagebrush steppe
- K056 Wheatgrass-needlegrass shrubsteppe
- K040 Saltbush-greasewood
SAF Cover Types (Eyre 1980)
- None
SRM Rangeland Cover Types (Shiflet 1994)
- 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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