Bears hibernate during the winter, usually digging their own dens with their claws. They will often choose the side of a slope where snow collects, providing good insulation. Grizzlies need to eat a lot in the summer in order to survive through a winter of hibernation. If a grizzly does not eat enough before winter, it might not survive through hibernation. The grizzly only defends it's breeding territory, and the mothers fiercely guard their cubs.
Bears live by themselves except during the mating season.
Females have a litter of two cubs every three and a half years. They are born during the hibernation period and do not come out into the world until spring. The mother stays with her cubs for two years. Survival in the lower 48 states depends on the protection of Yellowstone and Glacier National Parks, two main locations of grizzly bears.