Spacecog

Aha. Ground squirrels hibernate, tree squirrels live in trees and don't hibernate and their home is called a nest and is either made in a tree-hollow or from leaves and has an escape route in case of attack.

And tree squirrels are not "true hibernators". Maybe because although they hide from the cold in their snug wee nests they don't have the same fat-burning and sleep patterns as the gophers. <-- a made up explanation, deckchair rating:

plausible to most non-botanists

Also interesting to note is that much as their saskatchewan cousins do hibernate in winter, so desert ground squirrels go into torpor marky paws mode to escape the summer, and that this analogous summer process is called:

estivation