There are three common tree squirrel species that can be found in the Silicon Valley area. However, only one—the western gray squirrel (Sciurus griseus)—is actually native to the region. The eastern gray squirrel (Sciurus carolinensis) and the fox squirrel (Sciurus niger), both introduced from the eastern United States, are now regular backyard visitors in urban parts of the Bay Area.
Unless you live in the woodland urban interface in the Silicon Valley, spotting a western gray squirrel usually involves heading into nature preserves or parks with stands of oak or mixed evergreen forests.
Western gray squirrel
Western gray squirrels are typically found in forested and woodland areas in the San Francisco Bay Area. These squirrels are slightly larger compared to the eastern gray squirrel.
Western gray squirrels have counter shading, a type of camouflage that helps them blend in against the gray trunks of trees. Their back fur is a gunmetal gray color and the underbelly fur is white. Western grays squirrels have a very long and bushy tail that is mostly gray with streaks of white and black fur.
Like other tree squirrels, the western gray squirrel has hypermobile joints, which means their ankles can rotate 180 degrees. This allows squirrels to descend trees head first. They can also use their rear claws to hold on to the tree trunk in this position, leaving their front paws free to eat.
In the Silicon Valley area, western gray squirrels are typically found din oak woodlands, pine forests, mixed evergreen forests, and other well-wooded areas, where they feed on a mix of acorns, seeds, berries, and fungi.
Eastern gray squirrel
The eastern gray squirrel can easily be mistaken for the western gray because of its name and similar coloration, but there are a few differences. Eastern gray squirrels are smaller than western gray squirrels. The eastern gray also has more color variation: ranging from light gray to nearly black. Like the western gray, the underbelly fur of an eastern gray squirrel is white. The tail of the eastern gray squirrel is significantly shorter and less bushy.
Eastern grays are also more comfortable living close to people, so you’ll commonly spot them in parks and suburban neighborhoods.
Fox squirrel
The fox squirrel is similar in size to the eastern gray squirrel. The back fur typically has a mix of gray and orange, and the underside—from the belly to the feet—often has a distinctly orange or rust tone.
As with the the eastern gray, fox squirrels are common in urban and suburban areas.
Black squirrels
If you see an all-black squirrel, most commonly it’s a melanistic variation of the eastern gray squirrel. Fox squirrels can also have this adaptation. These black squirrels are the result of a variant pigment gene, likely an adaptation to blend in with the darker interior forest conditions of mature forests in the eastern United States.
Eastern gray and fox squirrels are more comfortable around humans
Western gray squirrels are skittish around humans, preferring to remain high in the treetops. If you spot a squirrel busily foraging on the ground and then fleeing to the canopy as soon as you approach, there is a good chance it might be a western gray squirrel. Eastern gray and fox squirrels, on the other hand, easily acclimate to human presence and can be found in abundance in backyards, at bird feeders, and in suburban parks in the area.
