Western Gray Squirrel

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iWestern Gray Squirrel

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Sciuridae
Genus:	Sciurus
Species:	S. griseus

Binomial name

Sciurus griseus
Ord, 1818

The Western Gray Squirrel (Sciurus griseus) is a tree squirrel found along the western coast of the United States and Canada.

At various times and places, this species has also been known as the silver-gray squirrel, the California gray squirrel, the Oregon gray squirrel, the Columbian gray squirrel, the banner-tail, and simply as the gray squirrel. There are three geographical subspecies: Sciurus griseus griseus (central Washington to the western Sierra Nevada in central California); S. g. nigripes (from south of San Francisco Bay to San Luis Obispo County, California; and S. g. anthonyi, which ranges from San Luis Obispo to south-central California).

The Western Gray Squirrel was first described by George Ord in 1818 based on notes taken by Lewis and Clark at The Dalles in Wasco County, Oregon.

Compared with the Eastern Gray Squirrel S. carolinensis (which has been introduced into its range), it is a shy animal. Weights vary from about 400 g to nearly 1 kg, and length (including tail) from 45 to 60 cm. It is the largest native tree squirrel in the western coastal United States. Western Gray Squirrels exhibit a form of coloration known as counter shading. The dorsal fur is a silver gunmetal gray, with pure white on the underside; there may be black flecks in the tail. Ears are large but without tufts. The ears turn reddish-brown at the back in the winter. The tail is long and typically very bushy. Tree squirrels undergo a complete head-to-tail molt in the spring and a rump-to-head mold in the fall. Tail hair is replaced only in the spring.

Western Gray Squirrels mate over an extended period ranging from December through June. Young are born after approximate 44 day gestation period. Juveniles emerge from nests between March and mid-August. Litter sizes range from 1 to 5.

Western Gray Squirrels are forest dwellers, and can be found at elevations up to at least 2000 m. They are strictly diurnal, and feed mainly on seeds and nuts, particularly pine seeds and acorns, though they will also take berries, fungus and other soft food. Pine nuts and acorns are considered critical foods because they are very high in oil and moderately high in carbohydrates, which helps increase the development of body fat. They feed mostly in trees and on the ground. They are scatter-hoarders making numerous caches of food when it is abundant, and thus contribute to the seed dispersion of their food trees. They do not hibernate, but become less active during the winter.

There are two stick nest types made by the Western Gray Squirrel. The first is a large, round, covered shelter nest for winter use and rearing young, and the second is a broad platform for seasonal or temporary use. Both types are built with sticks and twigs and are lined with leaves, moss, lichens and shredded bark. The nest may measure 43 - 91 cm (17 to 36 inches) in length and up to 46 cm (18 inches) in height. It is usually built within the top third of the tree.

The Western Gray Squirrel was listed as a threatened species in Washington state in 1993. Populations of the western gray squirrel have not recovered from past reductions. They are being threatened with habitat loss, road-kill mortality and disease. Habitat has been lost due to urbanization and catastrophic wild fires. Previous areas of forest have been degraded by fire suppression and overgrazing, allowing the invasion of Scot's Broom. Notoedric mange, a disease caused by mites, becomes epidemic in western gray squirrel populations and is a major source of mortality. Other species of Eastern Gray Squirrels, fox squirrels, California ground squirrels and wild turkeys are expanding and may compete with the Western Gray.