It was a time when the great ice sheets of the Wisconsin era were melting back into the mountains, and the boreal forests were slowly covering the fresh landscape. The evolution of denning behaviour was a key element in the expansion of black bear range into northern Canada. For this animal, a shorter foraging season simply means a longer denning period. At seven months, the denning period of a Yukon black bear is one of the longest of the species. Mexican black bears spend only a few weeks in the den.
Mountainous terrain tends to reduce the size of each animal's home range.
Black bears need access to different types of habitat for food, water, dens, cover and concealment. Eastern black bears move great distances to meet all of these needs. Yukon bears have only to move to higher or lower elevations to find different types of habitat. The presence of grizzlies in the Yukon affects the distribution and behaviour patterns of our black bears. Grizzlies may kill and eat black bears, and easily win the competition for food where their ranges overlap at river level and the subalpine zone.