Sciurus griseuswestern gray squirrel

Geographic Range

Sciurus griseus lives on the west coast of the United States. S. griseus can be found in Washington, Oregon, California, and in a very small part of Nevada.


Western grey squirrels are found in woodlands and coniferous forests. They can be found at elevations up to 2500 meters.

Physical Description

The western grey squirrel ranges from about 18 inches to 24 inches in total length with the body and the tail. Their weight varies from 350 to 950 grams.

Sciurus griseus has silver grey fur on its back and a white underside. It has a long bushy tail which is the same silver grey color. Their tail may also have black in it. S. griseus has large ears without tufts.

The western grey squirrel sheds its fur once in the late spring and again in early fall. The fur on the tail is only shed during the spring molting.

Sciurus griseus lives to be between 7 and 8 years old in the wild.

  • Range mass
    350 to 950 g
    12.33 to 33.48 oz


Sexual maturity of Sciurus griseus is reached at 10 to 11 months. When S. griseus is approximately one year old it will begin breeding. When a female is in estrus the vulva becomes pink and enlarged. When a male is sexually active the scrotum turns black from its original pinkish gray color. Breeding takes place once a year in the late spring. There are betwee 3 and 5 young per litter. Younger females generally have smaller litters than older females. The gestation period averages 43 days. Young are born without hair and with closed eyes and ears. The head and feet of young are large compared to the rest of the body. They are weaned at approximately 10 weeks.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
  • Average gestation period
    44 days
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    319 days


Western grey squirrels live in hollow trees or in nests they build called dreys. These are made of sticks and lined and insulated with softer materials such as moss.

Sciurus griseus is diurnal. While out of the nest S. griseus spends its time grooming, exploring, gathering food, and resting. Grooming can last from 3 to 15 minutes, with most of the time being spent on the head area. Western grey squirrels have a home range size of 0.5 to 7 hectares. Males generally have a larger home range than females. While exploring Sciurus griseus gathers food. Food they don't eat or take back to the nest is buried around their home range. The buried food is called a cache and is later found by their good sense of smell. Caches are usually used in the colder months when food is scarce.

Western grey squirrels do not hibernate but much less time is spent outside during the colder winter months.

Sciurus griseus is non-territorial except when the female is in estrus.

When threatened western grey squirrels make barking sounds while flicking their tails and stamping their feet.

Communication and Perception

Food Habits

Western grey squirrel's main source of food depends largely upon local habitat characteristics. Those that live in coniferous forests feed primarily on seeds of pinecones. Those that live in hardwood forests feed largely on nuts and acorns. Sciurus griseus is also known to eat berries, fungus, bark, sap, and insects. It opens hard seeds and nuts using its incisors.

Western grey squirrels will feed on the ground as well as in trees.

Economic Importance for Humans: Positive

Sciurus griseus can be hunted and used for food. Western grey squirrels also help disperse and plant trees by burying seeds in their caches which remain uncollected.

Economic Importance for Humans: Negative

Some people consider squirrels to be a nuisance.

Conservation Status

Western grey squirrels are a United States species of concern, but are not currently listed as threatened or endangered under the U.S. Endangered Species Act. In late 2002 the Washington subspecies, S. griseus griseus was proposed for listing as an endangered species. In Washington they are considered threatened at the state level, in Oregon they are considered a state sensitive species.


Sara Crane (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.



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.


uses smells or other chemicals to communicate


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.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


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.


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


uses touch to communicate


Carraway, L., B. Verts. December 2, 1994. Mammalian Species. The American Society of Mammalogists.

Halloran, P. March 16, 1999. Accessed November 15, 1999 at

Nowalk, R. 1999. Walkers' Mammals of the World Volume II. Baltimore: Johns Hopkins University Press.