Hibernation Bears hibernate because of a decreased food supply, not, an inablility to stay warm. Dens are used only during winter hibernation. Bears sleep outside, not in dens or caves, from spring through fall. Bears den from October or November to March or April. Males emerge from their dens first each season and females with cubs emerge last.
Body temperature drops only a few degrees during denning.
Unlike rodents, bears can easily be aroused from thier winter sleep. Dens are lined with leaves, spruce or fir boughts, or pine needles. Delayed implantation keeps fertilized eggs from beginning development until around the start of denning season. Cubs are born in January or February. Litter size is usually two, but ranges from one to four cubs.