Polar bear the fourhorn sculpin. With the exception of pregnant females, polar bears are active year-round, although they have a vestigial hibernation induction trigger in their blood. Unlike brown and black bears, polar bears are capable of fasting for up to several months during late summer and early fall, when they cannot hunt for seals because the sea is unfrozen. When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time, as polar bears do not 'hibernate' any time of the year. Being both curious animals and scavengers, polar bears investigate and
Polar bear walrus from the pod. They will even attack adult walruses when their diving holes have frozen over or intercept them before they can get back to the diving hole in the ice. Yet, polar bears will very seldom attack full-grown adult walruses, with the largest male walrus probably invulnerable unless otherwise injured or incapacitated. Since an attack on a walrus tends to be an extremely protracted and exhausting venture, bears have been known to back down from the attack after making the initial injury to the walrus. Polar bears have also been seen to prey on beluga whales ("Delphinapterus leucas")