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
Knut (polar bear) 22 March in relation to the necropsy reported there were "significant changes in the brain, which may be regarded as a reason for the sudden death". Animal welfare organizations in Germany initially accused the Berlin Zoo of negligence, claiming that Knut died of stress caused by being forced to share his enclosure with three female polar bears. The zoo denied such claims. Bear curator Heiner Klös stated they "did everything to look after Knut—it's normal for polar bears to live with other polar bears in a zoo, and the idea was that Knut should learn social behavior and other skills