I know they construct nests in trees but do squirrels hibernate in these or do they find hollow trees to hibernate on and off through out the winter?
Generally Tree squirrels do not hibernate, but several species of ground squirrels do, and they hibernate in burrows like the Richardsons ground squirrel…
Although they are territorial around their nest sites, the burrows of Richardson’s Ground Squirrels are grouped closely together in colonies, and individuals give audible alarm calls when possible predators approach. Recent research has shown that in some cases, ultrasonic alarm calls are given, and are responded to by other members of the colony.
Flickertails hibernate; adult squirrels hibernate as early as July, though in their first year, the young squirrels do not hibernate until September. The males emerge from hibernation in March, and establish territories before the females emerge a couple of weeks later. The young, up to 8 in a litter, are born in April or May. Abandoned burrows are sometimes taken over by other grassland species such as the burrowing owl.
As for tree squirrels…. (Excerpt from Wikipedia.. )
One well-known trait of some species of squirrel is the gathering and storing of nuts for the winter. These squirrels are scatter-hoarders, i.e. they will gather nuts and store them in any accessible hiding place, usually by burying them. Recent research shows that they have excellent memories for the locations of these caches.
These types of squirrels do not hibernate, but instead store food in tree hollows, etc and feed on this during the winter. They usually stay in a den in a tree hollow etc and emerge on warm days to feed on what they can find. Some species in the squirrel family may enter a state of Torpor during periods of inactivity, but are not considered to be truly hibernators.
Any of about 260 species in 50 genera (family Sciuridae) of mostly diurnal rodents found almost worldwide. Many species are arboreal; some are terrestrial. All species have strong hind legs and a hairy tail. They vary widely in colour and form and range in total length from the 4-in. (10-cm) African pygmy squirrel to the giant squirrels of Asia, about 35 in. (90 cm) long. Tree dwellers live in a tree hollow or nest, and most are active year-round. Ground dwellers live in burrows, and many become dormant in winter (hibernate) or summer (estivate). As opposed to some ground squirrels (like white-tailed prairie dog), tree squirrels do not hibernate. They however become very inactive during the winter months to preserve energy. Part of the above retrieved from Answers.comSquirrels live in the same place they did during the summer. Ground squirrels hibernate, but Tree squirrels do not. Tree squirrels can be found in their nests in the trees, with their families, trying to keep warm together. Before the winter months you see them storing food, that’s how they stay alive through the winter.