A maximum life span for a wild gray squirrel could be 10 years or even longer, but few live more than two or three years. Grays live in nests and dens. They build leaf nests in trees near good food supplies in both summer and fall, the leaf nests are cooler than tree dens, they're about 12 by 16 inches and are built of twigs, leaves, grass, bark and other plant materials. Tree dens are often in cavities where limbs have broken off or in deserted woodpecker holes, usually 40 to 60 feet off the ground. Resident squirrels gnaw back the outer tree bark that, in time, would otherwise seal off den holes.
Gray squirrels breed in late winter or early spring.
The young are usually raised in tree dens and nursed by their mother for 5-7 weeks. Gray squirrels often bear a second litter in July or August, and small grays seen in autumn are from summer litters. Grays are gregarious and do not seem to demonstrate territoriality. Three or four individuals may feed side by side where food is plentiful. Unlike grays, fox squirrels prefer open, park-like woods with sparse ground cover, usually avoiding mountains and extensive forests.