Threatened and Endangered Species - Status Reports
Date Published: July 1993
Number of Pages: 50
The western gray squirrel (Sciurus griseus) ranges from north-central Washington to southern California including parts of the California coast. It once occurred throughout Washington's oak-conifer forests but is now less widely distributed. Remnant populations exist in southern Puget Sound, Klickitat, Okanogan, and possibly Yakima counties.
There is a close correlation between the distributions of Oregon white oak and the western gray squirrel in Washington. This co-occurrence is not surprising since oak mast is a critical winter food item for this squirrel. Other food items in order of significance are underground fungi, green conifer cones and seeds, other mast, and green vegetation. Western gray squirrels inhabit three vegetation types in three regions of Washington: the Oregon white oak-Douglas-fir woodlands of the southern Puget Trough, the white oak-ponderosa pine woodlands of the Columbia River Gorge, and the grand fir-Douglas-fir zone in Chelan and Okanogan counties. Western gray squirrels need a variety of mast-producing trees and shrubs for food, cover, and nesting sites. Quality habitat includes a moderately-closed tree canopy for arboreal travel, several mast-bearing trees species, large-sized trees for nests and mast production, and proximity to water. Most western grays build round stick nests in large conifers.
The western gray squirrel has an intermediate reproductive rate, producing one litter of two to five young between March and June each year. Their life span in the wild is about 8- 10 years.
Prehistoric climate change caused a reduction in oak woodlands and a probable decline in the gray squirrel population. Recent population declines are attributed to a combination of factors: habitat loss and conversion, fluctuating food supplies, disease, interspecific competition, road kills, and illegal shooting. There are no signs of population recovery. The recent reduction and fragmentation of suitable habitat is a result of fire suppression, logging, over-grazing, and residential development. Current regulations are not adequate to protect the habitat and restore western gray squirrel populations.
This combination of adverse factors places the western gray squirrel in danger of extirpation throughout most of its range in Washington. The Columbia River Gorge may harbor the last viable local population of this species in the state.
It is recommended that the western gray squirrel be designated as a threatened species in Washington.
Washington Department of Wildlife. 1993. Status of the western gray squirrel (Sciurus griseus) in Washington. Unpubl. Rep. Wash. Dept. Wildl., Olympia.