Asian black bear
Asiatic black bears are diurnal, though they become nocturnal near human habitations. They may live in family groups consisting of two adults and two successive litters of young. They will walk in a procession of largest to smallest. They are good climbers of rocks and trees, and will climb to feed, rest, sun, elude enemies and hibernate. Some older bears may become too heavy to climb. Half of their life is spent in trees and they are one of the largest arboreal mammals. In the Ussuri territory in the Russian Far East, black bears can spend up to 15% of their time in trees. Asiatic black bears break branches and twigs to place under themselves when feeding on trees, thus causing many trees in their home ranges to have nest-like structures on their tops. Asiatic black bears will rest for short periods in nests on trees standing fifteen feet or higher. Asiatic black bears do not hibernate over most of their range. They may hibernate in their colder, northern ranges, though some bears will simply move to lower elevations. Nearly all pregnant sows hibernate. Black bears prepare their dens for hibernation in mid-October, and will sleep from November until March. Their dens can either be dug out hollow trees (sixty feet above ground), caves or holes in the ground, hollow logs, or steep, mountainous and sunny slopes. They may also den in abandoned brown bear dens. Asiatic black bears tend to den at lower elevations and on less steep slopes than brown bears. Female black bears emerge from dens later than do males, and female black bears with cubs emerge later than barren females. Asiatic black bears tend to be less mobile than brown bears. With sufficient food, Asian black bears can remain in an area of roughly 1–2 sq km, and sometimes even as little as 0.5–1 sq km.
Brown bear
The brown bear has lost 98% of its habitat in the lower 48 states. About 95% of the brown bear population in the United States is in Alaska, though in the lower 48 states, they are repopulating gradually but steadily along the Rockies and the western Great Plains. The Alaskan population is estimated at 32,000 individuals. The largest populations of brown bears in the lower 48 states are found in the 23,300-km2 Greater Yellowstone Ecosystem and the 24,800-km2 Northern Continental Divide Ecosystem. The Greater Yellowstone Ecosystem of northwest Wyoming is estimated to hold about 674–839 grizzly bears, followed slightly the Northern Continental Divide Ecosystem of northwest Montana with about 765 animals, the Cabinet-Yaak Ecosystem of northwest Montana and northeast Idaho with about 42–65 bears of the species, the Selkirk Ecosystem of northeast Washington and northwest Idaho with only about 40–50 animals and even less the North Cascades Ecosystem of northcentral Washington with about 5–10 grizzlies.
These five ecosystems combine for a total of a maximum 1,729 wild grizzlies still persisting in the contiguous United States. Unfortunately, these populations are isolated from each other, inhibiting any genetic flow between ecosystems and creating low genetic diversity in remaining populations which can have negative long-time effects. This isolation poses one of the greatest threats to the future survival of the grizzly bear in the contiguous United States. Although there is no record of their existence in the United States east of the Rocky Mountain and Great Plains regions (except for a relict population in the Ungava Peninsula which survived until the dawn of the 20th century) in human history, fossil records from Kentucky do in fact show that grizzly bears once roamed in eastern North America.