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.

Western gray squirrels eat berries, nuts, a variety of seeds, and the eggs of small birds.

[5] Western gray squirrels reach sexual maturity at 10 to 11 months, and at approximately one year of age, will begin breeding.

The kits are relatively slow in development, and will not leave the nest for six months or more, another species disadvantage when in competition with other, more-rapidly fledging squirrels.

They generally forage in the morning and late afternoon for acorns, pine nuts, new tree buds, and fruits.

When on alert, they will spread their tails lavishly, creating an umbrella effect that shields them and possibly provides cover from overhead predators.

Western gray squirrels are prey for hawks, eagles, bobcats, cougars, coyotes, raccoons, cats, dogs and humans.

Squirrel nests are called dreys and can be seen in trees, built from sticks and leaves wrapped with long strands of grass.

Young or traveling squirrels will also "sleep rough" when weather permits, balanced spread-eagled on a tree limb high above the forest floor.

The western gray squirrel has many predators, including red-tailed hawks (Buteo jamaicensis), great horned owls (Bubo virginianus), eagles (Accipitridae), bobcats (Lynx rufus), coyotes (Canis latrans), cougars (Puma concolor), domestic cats (Felis catus) and domestic dogs (Canis familiaris).

[7] In Washington State, the western gray squirrel was listed as a threatened species in 1993, and was reclassified as endangered in November 2023.

Notoedric mange, a disease caused by mites, becomes epidemic in western gray squirrel populations and is a major source of mortality.

Local rehabilitation experts recount that fox squirrels were released in urban regions of Los Angeles throughout the 20th century.

These aggressive cousins drove the more reclusive western gray squirrels back into the mountains, where competition was not so strong.