All members of the squirrel family can run, but most are not exceptionally fast on the ground, particularly in comparison to their enemies, such as hawks or members of the cat family. The terrestrial species rely instead on underground refuges for escape from predators. The tree-climbing forms depend on their agility in the trees, or they retreat to hiding places in nests or tree cavities. Chipmunks will dart into rock crevices or tree holes if danger threatens. The animals spend most of their time in trees, but they will descend to the ground to search for acorns or other nuts, to feed on the shoots of young plants, or to move between trees that are far apart.
Tree squirrels are active primarily during the day and spend their nights asleep in trees.
Most of them build nests of leaves and twigs, usually in the high branches of the tallest trees. Some tree squirrels build temporary nests that may be used for only one night. The animals also usually have several different places to which they can retreat during inclement weather or to avoid detection by predators. The ground-dwelling members of the squirrel family usually live in burrows. Prairie dogs and various ground squirrels live in open prairies.