At night, squirrels conclude their activities by retreating to nests, which are primarily built in trees. Like birds, most squirrels build nests to serve as homes, which they use for raising young and resting. Many construct their dwellings on tree branches, although some take up shelter in tree cavities located high in tree trunks.
Some squirrels, like owls and larger birds, take shelter in tree cavities or dens when night falls. Several species, such as gray, fox and red squirrels, are most likely to rest in this manner. These squirrels may make their dwellings comfortable by adding soft bedding material, such as leaves and moss. Squirrels may build temporary nests in tree branches during the warmer months in spring and summer and reserve dens for winter hibernation. Short-term seasonal nests, called drays, allow squirrels to sleep and raise their young. These sleeping quarters, like dens, are often fortified with leaves and twigs and are located towards the trunk part of larger trees. While nearly all squirrels hibernate during the winter, only those that live in hot locales estivate, or hibernate, during the summer. Instead of nesting in trees, however, squirrels dig burrows beneath the surface of the Earth to escape the scorching summer rays.