Animals living in the freezing Arctic have adapted in several ways to survive. Seals survive the frigid water because of their thick skin, for example. In contrast, sea lions can stay out of the water because they have back flippers to push themselves around on land.
Land mammals living in the Arctic have layers of fur to keep them warm. This thick fur does not keep them warm in the water, however. Here, seals stay warm thanks to a four-inch layer of fatty blubber under their skin. Unlike sea lions, seals have no external ears and cannot walk on land very fast. Therefore, they have a better chance of surviving in the water – albeit cold.
The Arctic tern survives because it lives in the Arctic only during the summer when the sun never completely sets. This means temperatures are warmer. Then, at the end of the summer, this bird makes a 12,000 mile flight to the other end of the world, Antarctica, where daylight remains for months.
It may be hard to imagine living in such cold temperatures; then again, humans aren't made with thick skin or fur.
[Source: The Big Book of Knowledge]