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
Brown bears seldom attack humans on sight and usually avoid people. In Russia, it is estimated that one in 1,000 on-foot encounters with brown bears results in an attack. They are, however, unpredictable in temperament, and may attack if they are surprised or feel threatened. Despite the low rate of attack, they appear to be the most dangerous northern carnivoran to humans, attacking more people on average annually than American black bears or northern populations of Asian black bears and Siberian tigers, cougars or gray wolves. Several large carnivorans from tropical regions of Africa and Asia may be more dangerous to humans than brown bears, including other ursids such as the sloth bear and Indian populations of the Asian black bear. Each of the latter species of bear may kill up to 12 people annually in certain Indian districts, about as many in a relatively small area as all of the world's brown bears combined. The high levels of human-directed aggression in these ursine bears is reportedly their evolution with once-large numbers of predatory Bengal tigers (arguably itself the world's most dangerous carnivoran to humans even with its extreme decline in modern times, being statistically much more likely to attack than their northern Siberian cousins) and a very large human population, increasing the risk of surprising and angering a defensive Asian black or sloth bear, the latter species often charging aggressively rather than fleeing if a surprise encounter occurs, as do most other bear species.