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
Grizzly–polar bear hybrid hollowness, which blends the traits of both polar bears and grizzlies. In cross section, the hair of polar bears is hollow, while the hair of grizzlies is either solid or has small hollow regions. This varies according to which part of the grizzly the hair is located. In the hybrid male, the paw hair was solid, but the dark back hair was somewhat hollow, albeit with "smaller empty regions than found in polar bear hair". The hair of the female hybrid, "contains a range of hollow regions". The hybrids demonstrated behavior more similar to polar bears than grizzlies. They stomped