Some scavenging also occurs. Brown bear populations concentrate along most of the major streams and rivers within the park. Although brown bears range through all habitat types, they are most commonly found in open alpine or tundra habitats. Brown bears gain weight rapidly during the late summer and fall and are waddling in fat just prior to denning. At this time most mature males weigh between 500 and 900 pounds with extremely large individuals weighing as much as 1,400 pounds.
Females weigh one half to three quarters as much.
There is an average of one brown bear for each 100 square miles of habitat in the Arctic. Black bears, which are more common in the southern forested regions, have similar food habitats and behavior. Black bears are creatures of opportunity with it comes to matters of food. Upon emergence from hibernation in the spring, freshly sprouted green vegetation is the main food item, but blacks will readily take anything they encounter. Things such as winterkilled animals are readily eaten, but carrion is apparently taken only if little else is available.