Tree squirrels don't hibernate during the winter, but many species mate, hunker down in their winter nests and live off of food storage during the cold months. These winter nests are distinct from summer nests, and are located underground or in abandoned buildings.
Many species of squirrels spend the winter months reproducing. According to the Washington Department of Fish and Wildlife, mating occurs any time from early winter to late spring, with many species reproducing twice a year. If the litter is a winter one, the young stay with the mother until spring.
During the summer, squirrels spend their time stashing food in secret locations. Using their sense of smell, they dig up this food during the winter when food is scarce. They rely on this food and their fat stores to survive the cold.
The Eastern Gray Squirrel, one of the most common species in North America, usually live in American beech, American elm, white oak and red maple trees because of the profusion of nuts and seeds they get from these trees. They feed largely on acorns, walnuts, beechnuts, hickory nuts, tree buds and blossoms, bark, seeds, fruit, such as apples and grapes, grasses, insects and even bird eggs.