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 predators, whereas Antarctic seals all have dark fur at birth. Brown bears tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens. Wolves are rarely encountered by polar bears, though there are two records of Arctic wolf ("Canis lupus arctos") packs killing polar bear cubs. Adult polar bears are occasionally vulnerable to predation by orcas ("Orcinus orca") while swimming, but they are rarely reported as taken and bears are likely to avoid entering the water if possible if they detect an orca pod in the area. The melting sea