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Spermophilus washingtoniWashington ground squirrel

By Laura Merlo

Geographic Range

Spermophilus washingtoni is found in the low elevation Columbia basin of southeastern Washington state east of the Columbia River (Burke, 2001) and northeastern Oregon. In Oregon they occur in Gilliam, Morrow, and Umatilla counties (ASM, 2000). The original range is dramatically reduced because of habitat destruction (Verts and Carraway, 1998). ("American Society of Mammologists; Mammals of Oregon", 2000; "Burke Museum of Natural History and Culture; Washington Ground Squirrel, *Spermophilus washingtoni*", 2004; Verts and Carraway, 1998; Wilson and Ruff, 1999)

Habitat

Native habitats in the low elevation Columbia basin is mainly native bunchgrasses and sagebrush. Grazing, fire, cultivation and irrigation has dramatically altered the habitat of S. washingtoni. Big sagebrush, Artemisia tridentata and bluebunch wheatgrass, Agropyron spicatum once dominated this "shrub-steppe" region. However, the original plant species have mostly been replaced (in non-agricultural areas) by rabbit-brush, Chrysothamnus viscidiflorus and cheat grass, Bromus tectorum (Verts and Carraway, 1998).

These ground squirrels are most abundant in areas with sandy or soft soils that are well-drained and deep, facilitating burrowing, and in areas with abundant grass. ("Burke Museum of Natural History and Culture; Washington Ground Squirrel, *Spermophilus washingtoni*", 2004; Verts and Carraway, 1998; Wilson and Ruff, 1999)

Physical Description

Similar to other ground squirrel species, Spermophilus washingtoni individuals have short legs and small, rounded ears. The tail is short (32-65 mm), the rounded eyes are set high on the head, the postorbital processes are well developed, and the zygomatic arches expand posteriorly. The cheek teeth are high crowned.

Greyish-white spots about 4 mm across mark the smoky-grey base color on their backs. The underside is grayish-white and extends up the sides of the body to a line connecting the shoulder and thighs. There is a white eye-ring. Weight varies seasonally between 120 and 300 grams. Males are slightly larger than females, with total body lengths of males and females ranging from 185 to 245 mm.

Spermophilus washingtoni can be distinguished from other grounds squirrels (S. washingtoni and S. beldingi) in the same area because they are smaller, with smaller ears and a spotted pelage, which the other two species lack. Spermophilus washingtoni have a hind foot of less than 43 mm, whereas the other two species have longer hind foot lengths. (Tomich, 1982; Verts and Carraway, 1998)

  • Sexual Dimorphism
  • male larger
  • Range mass
    120 to 300 g
    4.23 to 10.57 oz
  • Range length
    185 to 245 mm
    7.28 to 9.65 in

Reproduction

Males emerge from hibernation before females and compete for access to females as they emerge. Once mating is completed, there is no further interaction between males and females.

Only one litter per year is produced due to the small amount of time S. washingtoni are active above ground (Verts and Carraway, 1998). Litter size ranges from five to eleven (Verts and Carraway, 1998) and an average of eight embryos was found in a sample of 26 S. washingtoni (Hayssen et al., 1993).

The reproductive season begins in January and sometimes lasts through April. Breeding occurs in late January and early February (Verts and Carraway, 1998). Young are birthed in late February and March in Washington and mostly in March in Oregon (Hayssen et al., 1993).

Spermophilus washingtoni reaches sexual maturity early and first breed as yearlings (Verts and Carraway, 1998).

In 1941, T. Scheffer reported that S. washingtoni are polygamous, but little else has been reported on mating behavior or parental care. (Hayssen, et al., 1993; Tomich, 1982; Verts and Carraway, 1998)

  • Breeding interval
    Breeding occurs once yearly.
  • Breeding season
    Breeding occurs in late January and early February.
  • Range number of offspring
    5 to 11
  • Average weaning age
    1 months
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

The young are birthed underground in burrows and emerge by March (Hayssen et al., 1993). They are altricial and at birth their eyes and ears are closed and no teeth have erupted. However, development is rapid and within 10 days head and body hair is present. After about 15 days the incisors erupt, and the eyes open within 20 days (Tomich, 1982). In late March, when about 1 month old, babies weigh from 22 to 44 grams (Hayssen et al., 1993) and average 38.8 grams (Verts and Carraway, 1998). Weaning takes place in the first month, and after one month no milk curd is found in the stomachs of some captured individuals (Verts and Carraway, 1998). By late April, the average mass is 116 grams (range: 89 - 139 grams). The mass by late May ranges from 147 to 205 grams. The male ranges from 175 to 205 grams and the females ranges from 147 to 193 grams.

Males do not care for young. (Hayssen, et al., 1993; Tomich, 1982; Verts and Carraway, 1998)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • provisioning
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

No information is available on the average lifespan of S. washingtoni.

Behavior

Spermophilus washingtoni is a fossorial species. They construct elaborate subterranean chambers, used year after year and expanded each season. Burrows are closed during periods of inactivity (Hamilton, 1939). Washington ground squirrels may spend up to 8 months of the year in hibernation or aestivation.

The annual cycle consists of successive periods of fattening, torpor, and reproduction. Emergence from winter dormancy resets this cycle. Hibernation begins with the onset of cold weather and aestivation may occur during dry, summer months. (Tomich, 1982)

Spermophilus washingtoni is a colonial species, but little other research is currently available on social behavior (Verts and Carraway, 1998). In areas with good habitat, densities may reach 250 per hectare.

Of the short-tailed ground squirrels, S. washingtoni is sympatric or parapatric with only S. columbianus and S. beldingi (Verts and Carraway, 1998). These squirrels are active during the day. (Hamilton Jr., 1939; Tomich, 1982; Verts and Carraway, 1998; Wilson and Ruff, 1999)

Communication and Perception

Washington ground squirrels probably use a variety of acoustic, visual, tactile, and chemical forms of communication, though little research has been done on this to date. They use the same suite of senses to perceive their environment.

Food Habits

Spermophilus washingtoni feed primarily on grasses until about June when the green of the plants is desiccated. They then feed mostly on seeds of the same grasses (Verts and Carraway, 1998).

Plants eaten include: needle-and-thread grass, Stipa comata, Sandberg grass, Poa sandbergii, cheat grass, Bromus tectorum, globemallow Sphaeralcea, plantain, Plantago, Indian ricegrass, Oryzopsis, tumblemustard Sisymbrium, alfalfa, oats and wheat (Verts and Carraway, 1998). (Verts and Carraway, 1998)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts

Predation

Although S. washingtoni have a large number of predators, their fossorial lifestyle protects them from a high predation rate (Hamilton, 1939).

Most isolated subpopulations are vulnerable to the threat of extinction due to the conversion of rangeland to agricultural land, and due to poisoning and shooting (IUCN, 2000). ("2000 IUCN Red List of Threatened Species", 2000; Hamilton Jr., 1939)

Ecosystem Roles

Washington ground squirrels are important members of the ecosystems in which they live. They are important in influencing the composition of regional plant communities through their grazing and in nutrient cycling through their burrowing activities.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Washington ground squirrels are important parts of healthy Columbian ecosystems.

Economic Importance for Humans: Negative

Spermophilus washingtoni is an agricultural pest. It eats wheat, oats, alfalfa and other agricultural products of the region (ASM, 2000; Verts and Carraway, 1998). (Verts and Carraway, 1998)

  • Negative Impacts
  • crop pest

Conservation Status

According to the IUCN Red list of Threatened Species, the Vulnerable listing of S. washingtoni is due to the increasing fragmentation and loss of its habitat, particularly within the last decade.

The U.S. Fish & Wildlife Services Threatened and Endangered Species System has not yet determined the status of S. washingtoni. It is currently listed as a candidate taxon and is ready for proposal (U.S. F&WS, 2001).

Other Comments

The ground squirrels were formerly under the genus Citellus (Tomich, 1982).

Formerly, this species was split into two subspecies, S. w. washingtoni and S. w. loringi, but in 1948, Dalquest synonymized these into a single group after finding no comparable difference in size (Verts and Carraway, 1998).

S. washingtoni is of the subgenus Spermophilus (Nowak, 1997)

Spermophilus is derived from the vernacular "spermophile," or lover of seeds (Tomich, 1982). (Nowak, 1997; Tomich, 1982; Verts and Carraway, 1998)

Contributors

Laura Merlo (author), University of Michigan-Ann Arbor, Ondrej Podlaha (editor), University of Michigan-Ann Arbor.

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

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

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.

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

folivore

an animal that mainly eats leaves.

fossorial

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

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

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

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.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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

2000. "2000 IUCN Red List of Threatened Species" (On-line). Accessed 01/10/05 at http://www.redlist.org/search/details.php?species=20475.

2000. "American Society of Mammologists; Mammals of Oregon" (On-line). Accessed 01/10/05 at http://www.mammalsociety.org/statelists/ormammals.html.

2004. "Burke Museum of Natural History and Culture; Washington Ground Squirrel, *Spermophilus washingtoni*" (On-line). Accessed 01/10/05 at http://www.washington.edu/burkemuseum/collections/mammalogy/mamwash/spwa.html.

2001. "U.S. Fish & Wildlife Services: Species Information Threatened and Endangered Animals and Plants" (On-line). Accessed 01/10/05 at http://endangered.fws.gov/wildlife.html.

Hall, E., K. Kelson. 1959. *The Mammals of North America, Volume 1*. New York, NY: The Ronald Press Company.

Hamilton Jr., W. 1939. *American Mammals; Their Lives, Habitats, and Economic Relations*. New York, NY: McGraw-Hill Book Company, Inc..

Hayssen, V., A. van Teinhoven, A. van Teinhoven. 1993. *Asdell's Patterns of Mammalian Reproduction*. London, UK: Comstock Publishing Associates, a division of Cornell University Press.

Nowak, R. 1997. "Walker's Mammals of the World Online" (On-line). Accessed 16 November 2001 at http://www.press.jhu.edu/books/walker/rodentia/rodentia.sciuridae.spermophilus.html.

Scheffer, T. 1941. Ground squirrel studies in the Four-Rivers Country, Washington. Journal of Mammology, 22: 270 - 279.

Tomich, P. 1982. *Wild Mammals of North America: Biology, Management, and Economics* "Ground Squirrels (*Spermophilus beecheyi* and Allies)". Baltimore, MD: The Johns Hopkins University Press.

Verts, B., L. Carraway. 1998. *Land Mammals of Oregon*. Berkeley, CA: University of California Press.

Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. Washington: The Smithsonian Institution Press.

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