Arctic birds and mammals are specialized for life in the extreme environment they call home. Insulation against cold is a key factor in their survival. Indeed, it has been shown that the skin temperature of large Arctic mammals is only a few degrees lower than their deep-body temperature, even when the air is as cold as -40°C! In fact, there can be a difference of more than 51.6°C between skin and air temperatures, demonstrating the efficiency of the animals’ fur as an insulator.
For example, the musk ox has a dense layer of wool next to the body, covered and protected by an outer layer of long fur. By comparison, the caribou or reindeer has a coat that consists of long, hollow hairs to trap air. The hairs of the polar bear’s coat are transparent, and allow light to reach the skin beneath, which is black and absorbs its heat. The fur then traps the heat, and little escapes.
Other animals, like the walrus, rely almost entirely on thick reserves of blubber to insulate them from the harsh environment.
Bird feathers are also good insulators! The plumage of resident Arctic birds tends to be denser than that of the migrating bird species. Birds can reduce heat loss by fluffing their feathers. When it becomes very cold, they can pull their legs up under their bodies and tuck their heads under the feathers on their back, turtle style.