Toward fall, roots and moths clustering in rocky, high-elevation areas are added. Hibernation Bears hibernate because of a decreased food supply, no an inability to stay warm. Dens are used during winter hibernation . Bears sleep outside in day beds from spring through fall. May. 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 be easily aroused from their winter sleep. Grizzly bears usually excavate their own dens, while black bears more often locate a natural cavity, such as a rock crevice or hollow tree. Dens are often lined with leaves, grass, spruce or fir boughs, or pine needles. Delayed implantation keeps fertilized eggs from beginning development into embryos until around the start of denning season. If female bears do not attain sufficient body fat or weight , their embryos will not develop.