Spermophilus townsendii

Geographic Range

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 nearctic
  • native native

Habitat

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.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune

• Other Habitat Features
• suburban suburban
• agricultural agricultural

Physical Description

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.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

Townsend's ground squirrels produce one litter per year and the species is polygynous.

• Mating System
• polygynous 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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous 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 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

Lifespan/Longevity

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.

Behavior

Townsend's ground squirrels are primarily active during the day, especially in early morning. By contrast, they avoid long periods of activity in the heat of the day, or on windy days. Their activities include climbing to survey surroundings and find food, and crossing rivers.

Townsend's ground squirrels live together in large groups, and each individual in the group has an individual burrow. The burrow becomes more complex the longer it is occupied, and the burrows of older individuals have more tunnels, nests, and entrances. The sex ratio of adults and yearlings favors females, while the juvenile sex ratio favors males. After reaching adulthood, males tend to leave their birth population and immigrate to new populations. The squirrels hibernate in groups during winter. Males awaken in late January, shortly before females. Females have considerably higher overwinter survival rates than males. Populations tend to drop during drought years, but are at their lowest in years after a drought.

• Key Behaviors
• terricolous
• fossorial fossorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• hibernation hibernation
• territorial territorial
• social social
• colonial colonial
• dominance hierarchies dominance hierarchies

Home Range

Individual populations can occupy a territory approximately as large as a hectare. Populations consist of a stable adult population, along with transient males and females.

Communication and Perception

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 visual
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• ultrasound ultrasound
• chemical chemical

Food Habits

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.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • lignivore

• Animal Foods
• insects

• Plant Foods
• leaves
• roots and tubers
• wood, bark, or stems

• Foraging Behavior
• stores or caches food stores or caches food

Predation

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 melanoleucus ). They are also eaten by Piute Indians.

• Anti-predator Adaptations
• aposematic aposematic
• cryptic cryptic

Ecosystem Roles

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

Economic Importance for Humans: Positive

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 food

Economic Importance for Humans: Negative

Townsend's ground squirrels have been observed to cause agricultural damage, and have been subject to control programs.

• Negative Impacts
• crop pest

Conservation Status

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.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Ethan Fifield (author), University of Alaska Fairbanks, Laura Prugh (editor), University of Washington, Catherine Kent (editor), Special Projects.

References

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Bossard, R. 2006. Mammal and Flea Relationships in the Great Basin Desert: from H. J. Egoscue's Collections. Journal of Parasitology , 9 (2): 260-266.

Hafner, D., E. Yensen, G. Kirkland, Jr.. 1998. "Status Survey and Conservation Action Plan: North American Rodents" (On-line pdf). IUCN Red List of Threatened Species. Accessed December 11, 2012 at http://data.iucn.org/dbtw-wpd/edocs/1998-039.pdf .

Hall, E. 1946. Mammals of Nevada . Berkeley, CA: University of California Press.

Johnson, V. 2000. "Townsend’s Ground Squirrel" (On-line). California Wildlife Habitat Relationships System. Accessed December 08, 2012 at http://www.sibr.com/mammals/M069.html .

Mateo, J. 2007. Ecological and hormonal correlates of antipredator behavior in adult Belding’s ground squirrels (Spermophilus beldingi). Behavioral Ecology and Sociobiology , 62 (1): 37-49.

Rickart, E. 1988. Population Structure of the Piute Ground Squirrel (Spermophilus mollis). The Southwestern Naturalist , 33 (1): 91-96.

Rickart, E. 1987. "Spermophilus townsendi. Mammalian Species No. 268" (On-line pdf). Accessed December 11, 2012 at http://www.science.smith.edu/msi/pdf/i0076-3519-268-01-0001.pdf .

Smith, G., D. Johnson. 1985. Demography of a Townsend Ground Squirrel Population in Southwestern Idaho. Journal of Ecology , 66 (1): 171-178.

Van Horne, B., R. Schooley, P. Sharpe. 1998. Influence of Habitat, Sex, Age, and Drought on the Diet of Townsend’s Ground Squirrels. Journal of Mammology , 79 (2): 521-537.

Wilber, P., H. Shapiro. 1997. An artificial life approach to host-parasite interactions. Journal of Ecological Modeling , 101 (1): 113-122.

Yensen, E., G. Hammerson. 2008. "Spermophilus townsendii (Townsend's Ground Squirrel)" (On-line). IUCN Red List of Threatened Species. Accessed December 11, 2012 at http://www.iucnredlist.org/details/20476/0 .