In summer, bears feed opportunistically on caribou calves and adults as prey and carrion, and on other species. In late summer, bears move up river valleys feeding on berries, ground squirrels, and roots, and gradually move to higher elevation den sites for the winter. In these northern areas where the plant growing season is very short, winters are severe, and other food sources such as fish are relatively scarce, bears develop more slowly. Thus females do not produce young until they are six to 12 years old, and cubs remain with their mothers for up to five years. Average litter sizes are also smaller than in more southern areas.
Natural mortality is generally low in grizzly bears, except for cubs.
Up to half of all cubs that die are killed by other bears. Wolves are widely distributed throughout Alaska and much of Canada. They are the largest wild members of the dog family, and adult males often weigh more than 100 pounds. They have a highly developed social structure which is manifested in the pack which is made up largely of family members. Within the pack, breeding is confined to the dominant male and the dominant female.