Western gray squirrel has a long, bushy and white-edged tail, which helps the animal balance while jumping from tree to tree. The limbs are considerably large. During the winter months, the prominent ears are usually colored in reddish-brown at the back. This rodent is actually the largest tree squirrel, native to Washington. The animal exhibits white under-parts and a salt-and-pepper to steel gray coloration of its back.
The range of this rodent extends across Pacific region of the western U.S. and northern Mexico, from northern Washington State to northern edges of Baja (California). Western grey squirrel typically inhabits woodlands and coniferous forests.
Western gray squirrel is a diurnal animal that is active during the daytime hours. This rodent spends a lot of its active time outside the nest, grooming, exploring the environment, foraging and resting. They usually combine exploring and foraging, whereas grooming takes 3 - 15 minutes, during which most of the time is spent on the head. Excess food is carried to the nest and buried within the individual's territory. When necessary, they can find stored food through the well-developed sense of smell. Each individual has its own territory of 0.5 - 7 hectares on average. Territories of female individuals are considerable smaller that these of males. These rodents don't hibernate. However, during the winter, they generally prefer remaining within their nests. Western gray squirrels are generally solitary and not territorial, except for estrus females. If the squirrel is threatened, it will give out barking sounds, accompanying it by tail-flicking and foot-stamping.
The diet of Western grey squirrel is characterized by its habitat. Populations in coniferous forests generally consume pinecone seeds, whereas those in hardwood forests eat nuts and acorns. Overall, these rodents favor berries, fungus, bark, sap as well as various insects.
Little is known about the mating system of Western gray squirrels. During the breeding period, mating individuals are known to bite and injure each other. Females display highly territorial behavior, engaging in fights and not tolerating one another in their territories. Breeding takes place once a year, from December to June. Gestation period lasts for 43 days, yielding 3 - 5 young per litter. The litter size typically depends on female's age: older females produce larger litters that younger ones. Newborn squirrels are born with closed eyes and ears and lack fur. Weaning takes about 3 months from 7 to 10 weeks old. The age of sexual maturity is 10 - 11 months old.
Since the early 1900s, when Eastern fox squirrels were introduced to Los Angeles area (Southern California), the local Western grey squirrel population has greatly suffered from this aggressive species. A great part of their population has been lost due to various diseases, road accidents as well as habitat degradation. The remaining population had to move into foothills and mountains because of urbanization, wild fires, excessive grazing and degradation of their forest habitat.
According to IUCN, the Western gray squirrel is uncommon but widely distributed and no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.