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Spermophilus townsendiiTownsend's ground squirrel

By Ethan Fifield

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. (Baker, et al., 2003; Hafner, et al., 1998; Rickart, 1987)

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. (Baker, et al., 2003; Hafner, et al., 1998; Rickart, 1987)

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. (Rickart, 1987)

  • Range elevation
    1000 to 2100 m
    3280.84 to 6889.76 ft
  • Average depth
    1.46 m
    4.79 ft

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. (Rickart, 1987)

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. (Rickart, 1987)

  • Sexual Dimorphism
  • male larger
  • Range mass
    82 to 325 g
    2.89 to 11.45 oz
  • Range length
    167 to 271 mm
    6.57 to 10.67 in
  • Range basal metabolic rate
    .62 to 1.10 cm3.O2/g/hr
  • Average basal metabolic rate
    .86 cm3.O2/g/hr

Reproduction

Townsend's ground squirrels produce one litter per year and the species is polygynous. (Johnson, 2000)

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. (Hall, 1946; Johnson, 2000; Rickart, 1987)

  • 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

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

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. (Rickart, 1988)

  • Range lifespan
    Status: wild
    5 (high) years
  • Average lifespan
    Status: wild
    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. (Rickart, 1987; Smith and Johnson, 1985)

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. (Rickart, 1987; Smith and Johnson, 1985)

  • Average territory size
    .01 km^2

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. (Hafner, et al., 1998; Smith and Johnson, 1985)

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. (Rickart, 1987)

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. (Smith and Johnson, 1985; Van Horne, et al., 1998)

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

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. (Mateo, 2007)

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. (Bossard, 2006; Wilber and Shapiro, 1997)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species
  • eimerians (Eimeria adaensis)
  • eimerians (Eimeria beecheyi)
  • eimerians (Eimeria bilamellata)
  • eimerians (Eimeria callospermophili)
  • eimerians (Eimeria lateralis)
  • eimerians (Eimeria morainensis)
  • eimerians (Eimeria pseudospermophili)
  • helminths (Hymenolepis citelli)
  • helminths (Pterygodermatites colaradensis)
  • helminths (Spirura infundibuliformes)
  • helminths (Syphacia citelli)
  • fleas (Meringis shannoni)
  • fleas (Opisthocrosis washingtonensis)
  • fleas (Thrassis petiolatus)

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. (Rickart, 1987)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Townsend's ground squirrels have been observed to cause agricultural damage, and have been subject to control programs. (Rickart, 1987)

  • 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. (Yensen and Hammerson, 2008)

Contributors

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

herbivore

An animal that eats mainly plants or parts of plants.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Baker, R., L. Bradley, R. Bradley, J. Dragoo, M. Engstrom, R. Hoffman, C. Jones, F. Reid, D. Rice, C. Jones. 2003. Revised Checklist of North American Mammals North of Mexico, 2003. Occasional Papers: Museum of Texas Tech University, 229: 23. Accessed December 11, 2012 at http://www.nsrl.ttu.edu/publications/opapers/ops/op229.pdf.

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.

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