Brown bear
Interspecific predatory relationships

Adult bears are generally immune to predatory attacks except from large Siberian (Amur) tigers and other bears. Following a decrease of ungulate populations from 1944 to 1959, 32 cases of Siberian tigers attacking both Ussuri brown bears (Ursus arctos lasiotus) and Ussuri black bears (U. thibetanus ussuricus) were recorded in the Russian Far East, and hair of bears were found in several tiger scat samples. Tigers attack black bears less often than brown bears, since the brown bears live in more open habitats and are not able to climb trees. In the same time period, four cases of brown bears killing female tigers and young cubs were reported, both in disputes over prey and in self-defense. In rare cases, when Amur tigers prey on brown bears, they usually target young and sub-adult bears, besides small female adults taken outside their dens, generally when lethargic from hibernation. Predation by tigers on denned brown bears was not detected during a study carried between 1993 and 2002. Ussuri brown bears, along with the smaller black bears constitute 2.1% of the Siberian tiger's annual diet, of which 1.4% are brown bears.

Brown bears regularly intimidate wolves to drive them away from their kills. In Yellowstone National Park, bears pirate wolf kills so often, Yellowstone's Wolf Project director Doug Smith wrote, "It's not a matter of if the bears will come calling after a kill, but when." Despite the high animosity between the two species, most confrontations at kill sites or large carcasses end without bloodshed on either side. Though conflict over carcasses is common, on rare occasions, the two predators tolerate each other on the same kill. To date, there is a single recorded case of fully-grown wolves being killed by a grizzly bear. Given the opportunity, however, both species will prey on the other's cubs. In some areas, grizzly bears regularly displace cougars from their kills. Cougars kill small bear cubs on rare occasions, but there was one report of a bear killing a cougar of unknown age and condition between 1993 and 1996.

Brown bears usually dominate other bear species in areas where they coexist. Due to their smaller size, American black bears are at a competitive disadvantage to grizzly bears in open, unforested areas. Although displacement of black bears by grizzly bears has been documented, actual interspecific killing of black bears by grizzlies has only occasionally been reported. Confrontation is mostly avoided due to the black bear's diurnal habits and preference for heavily forested areas, as opposed to the grizzly's largely nocturnal habits and preference for open spaces. Brown bears may also kill Asian black bears, though the latter species probably largely avoids conflicts with the brown bear, due to similar habits and habitat preferences to the American black species. As of the 21st century, there has been an increase in interactions between brown bears and polar bears, theorized to be caused by climate change. Brown and grizzly bears have been seen moving increasingly northward into territories formerly claimed by polar bears. They tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens.
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