Squirrels take refuge in dens and nests in the wintertime. Like humans and many other mammals, squirrels need protection from the harsh winds and elements of winter. Their wintertime shelters vary in size and composition depending on location, but all contain overhead roofs and warm linings to keep out the cold.
While many squirrels take up shelter in nests during spring and summer months, they sleep in dens during the winter. Dens and burrows offer more protection than nests, which are primarily used for raising young. Squirrels, like birds, typically build nests to accommodate parents and offspring: essentially, nests act like homes for immediate family. During the winter months, however, they change their social habits by congregating in large communities.
As groups, squirrels stake out territories and find prime locations for nesting. Winter dens may take the form of tree cavities or shelters previously occupied by other mammals such as foxes. Sometimes, however, squirrels must construct dens, which they accomplish using twigs, small branches and other organic materials such as leaves and stems. Squirrels generally build sturdy winter residences: the dens and drays they construct may withstand significant winds and storms and may remain in place for several years after construction.