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 ice in the Arctic may be causing an increase of orcas in the Arctic sea, which may increase the risk of predation on polar bears but also may benefit the bears by providing more whale carcasses that they can scavenge. The remains of polar bears have found in the stomachs of large Greenland sharks ("Somniosus microcephalus"), although it certainly cannot be ruled out that the bears were merely scavenged by this slow-moving, unusual shark. A rather unlikely killer of a grown polar bear has reportedly included a wolverine ("Gulo gulo"), anecedotely reported to have suffocated a bear in a zoo