Spermophilus columbianusColumbian ground squirrel

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Geographic Range

This species is found in the Rocky mountains west of Montana, In Idaho, eastern Washington state, southeast British Columbia and in the mountains of central and eastern Oregon.

Habitat

Columbian ground squirrels are found in alpine and sub-alpine meadows. Their distribution within their range is therefore very discontinous.

Physical Description

It is difficult to characterize these animals by weight, as fat storage for hibernation is a continual process throughout the summer months. The total length of a Columbian ground squirrel ranges from 325-410mm, of which 80-116mm is tail. These ground squirrels have stout bodies with short, dense fur. The nose and face are tawny. The dorsum is a cinamon-buff color with darker brown underfur. The eyes are ringed with a line of pale buff. The legs and venter are buffy, and the tail is black.

  • Range mass
    340 to 812 g
    11.98 to 28.62 oz

Reproduction

Breeding occurs during the early spring after these ground squirrels awake from their winter hibernation. The testes of the males develop during hibernation, and the squirrels are ready to mate shortly after they emerge from their burrows. The females emerge about one week after the males, and they ovulate shortly thereafter. As females approach estrus, their genitals become swollen and emit an odor most attractive to males of the species. Males locate females by this odor. Unmated females return to estrus in two weeks.

The average litter size is 2.7 young, but there is a great deal of variation. Litter size varies with both female size and elevation. Females living at lower elevations give birth to larger litters than conspecifics living at higher elevations. Similarly, larger females bear larger litters than smaller females.

The young are altricial when born. They weigh approximately 6.8-11.4 grams at birth, but they develop quickly. They have hair by 3 days of age, and they are able to walk and climb within 15 days. Juveniles nurse for about 30 days, but they remain near their mothers throughout the first winter of their lives.

Male columbian ground squirrels reach sexual maturity at about three years of age. Females may mate in their second season. Full adult size for both males and females is reached in the third year of life.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual

Behavior

Columbian ground squirrels are moderately social animals. They live in fairly large colonies where related females maintain spatial proximity. Population densities around 61 animals per hectare are common.

Males emigrate from their natal ranges and establish residence among groups of females that are unrelated to them. Females typically remain in the colony in which they were born but occasionally may emigrate to a new area.

These animals are active during the day and retreat into their burrows during the night. Burrows can be elaborately constructed, especially those used for hibernation. In the hibernaculum, a squirrel builds a dome-shaped nest of finely shredded grasses. Drainage holes are often excavated in the floor of the hibernaculum, and these may prevent flooding during the fall and spring. Males cache food within their hibernaculum for use in the early spring. Since males typically emerge from hibernation well before plants start growing, this food cache is very important to their survival. Females, which do not emerge until the first shoots of grass are poking through the soil, do not need such a storage system.

The size of the hibernaculum is related to the size of the animal using it. Young animals excavate smaller chambers to be used for hibernation than do adults. Immature animals often spend their first winter in a hibernaculum close to their mother -- often a separate chamber within the same burrow system. This may account for the relatively high (87%) overwinter survival of juveniles.

These animals are active during the summer days, but their activity level decreased throughout the summer. Males gain wieght very quickly after the mating season ends, and by the time the hottest weather hits in July and August, these males are at risk of overheating in the afternoon sun. Males enter hibernation much earlier than do females, avoiding heat and water stress.

Females enter hibernation later than males, and the timing of entry into hibernation is in part controlled by the timing of parturition. Females cannot gain the weight necessary for hibernation until after they have weaned their litters. Therefore, females giving birth late in the season are among the last to enter into winter sleep.

Communication and Perception

Food Habits

These vegetarians eat flowers, seeds, fruits and bulbs. Among preferred foods are dandelion, timothy, clover and yarrow.

Economic Importance for Humans: Negative

Because Columbian ground squirrels eat many of the same foods that free ranging cattle eat, ranchers are very concerned about the effects these rodents have upon their livestock. In addition, ground squirrels are hosts for spotted fever ticks and may function as natural reserviors for St. Louis encephalitis and Powassan viruses.

Conservation Status

Although not endangered, some conservationists are concerned about the effects of continued poisoning of these squirrels. Because of the negative impact these animals can have on ranching, many ranchers use poison to control poulations. Such actions may have negative effects on brown bear, coyote, marten, badger, mountain lion, and hawks that prey upon these animals.

Other Comments

The physiology of the winter slumber of ground squirrels has been well studied. In fact, these animals spend nearly 70% of the year hibernating! Many changes must occur within an animal's body to allow it to sleep for so many months.

One physiological change is that the body temperature lowers drastically. This helps the animal conserve energy during its long sleep.

When the animals are active, the kidney functions to filter waste from the blood. During hibernation, the function of the kidney is shut down.

There are also some major changes in the blood chemistry of these animals that are related to hibernation.

Contributors

Nancy Shefferly (author), Animal Diversity Web.

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

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

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.

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.

sexual

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

tactile

uses touch to communicate

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.

References

Banfield, A.W.F. 1981. The Mammals of Canada. University of Toronto Press, Toronto and Buffalo.

Elliot, C. and J.T. Flinders. 1991. Mammalian Species No. 372. American Society of Mammalogists.