Diet and interspecific interactions

Asian black bear feeding on berries

Brown bear feeding on infrequent, but predictable, salmon migrationsMost bears have diets of more plant than animal matter and are completely opportunistic omnivores. Some bears will climb trees to obtain mast (edible vegatative or reproductive parts, such as acorns); smaller species that are more able to climb include a greater amount of this in their diets.[31] Such masts can be very important to the diets of these species, and mast failures may result in long-range movements by bears looking for alternative food sources.[32] One exception is the polar bear, which has adopted a diet mainly of marine mammals to survive in the Arctic. The other exception is the giant panda, which has adopted a diet mainly of bamboo. Stable isotope analysis of the extinct giant short-faced bear (Arctodus simus) shows it was also an exclusive meat-eater, probably a scavenger.[33] The sloth bear, though not as specialized as the previous two species, has lost several front teeth usually seen in bears, and developed a long, suctioning tongue to feed on the ants, termites, and other burrowing insects they favour. At certain times of the year, these insects can make up 90% of their diets.[34] All bears will feed on any food source that becomes available, the nature of which varies seasonally. A study of Asiatic black bears in Taiwan found they would consume large numbers of acorns when they were most common, and switch to ungulates at other times of the year.[35]When taking warm-blooded animals, bears will typically take small or young animals, as they are easier to catch. However, both species of black bears and the brown bear can sometimes take large prey, such as ungulates.[35][36] Often, bears will feed on other large animals when they encounter a carcass, whether or not the carcass is claimed by, or is the kill of, another predator. This competition is the main source of interspecies conflict. Bears are able to defend a carcass against some comers. Mother bears also can usually defend their cubs against other predators.[citation needed]The tiger is the only predator known to regularly prey on adult bears, including fully grown adults of brown bears, sloth bears, Asiatic black bears and sun bears[37][38][39][40][41][42] When hunting bears, tigers will position themselves from the leeward side of a rock or fallen tree, waiting for the bear to pass by. When the bear passes, the tiger will spring from an overhead position and grab the bear from under the chin with one forepaw and the throat with the other. The immobilised bear is then killed with a bite to the spinal column. After killing a bear, the tiger will concentrate its feeding on the bear's fat deposits, such as the back, legs and groin.[43][44]