Polar bears live in some of the coldest temperatures in the world and swim in icy, glacier-filled waters. To deal with these extreme temperatures, they have developed many ways of dealing with the extreme cold. In fact, they are almost too well adapted to their environment.
First, polar bears have a lot of pigment-free fur. This means the fur is not actually white, it just scatters all the light that reflects off the fur. Each strand of fur is transparent, which means the light can pass through it, and has a hollow core. A polar bear’s coat consists first a shaggy outer layer that sticks together to become waterproof. It also traps air and body heat next to the fine inner layer that also protects the bear’s body from cold. Its coat easily sheds water once the bear gets out of the ocean.
Next, right under the skin is a layer of blubber, or fat, which can be up to 4.5 inches or 11 cm thick. This blubber insulates the polar bear’s body against the cold. It can also provide nutrition when food is scarce.
A lot of heat loss comes from areas of the body that do not have much fur, or that have many blood vessels close to the surface of the body. A polar bear has very small ears and a small tail, which limits the amount of heat loss through these body parts. However, polar bears have large, very effective noses. When it gets too cold, a bear will cover up its nose with a large, furry paw.
When it gets very cold, polar bears will do what humans do—go inside. They will dig out a cave in the snow and curl up inside it. Although polar bears do not hibernate, they will sometimes go to sleep in their snow cave. Their body’s metabolism slows down and keeps them warmer than if they were moving. This period of inactivity is called “winter sleep.”
Bears are so well adapted to their frigid environment that they are very likely to overheat if they move around too much or too quickly. They tend to move slowly and rest often so they do not get too hot. Even when the temperatures are very cold, polar bears will need to take a swim to cool off.
A polar bear’s unique coat, thick layer of blubber, small ears and tail, and ability to dig a cave and go into winter sleep all help it cope with the freezing temperatures in the north. These characteristics of polar bears make them so well adapted to the cold that polar bears can often be seen swimming in ice-filled water to cool off. Truly, the polar bear has adapted well to its environment.
Resources: http://www.seaworld.org/infobooks/polarbears/pbadaptations.html
http://www.polarbearsinternational.org/bear-facts/polar-bear-fur/
http://www.loc.gov/rr/scitech/mysteries/polarbear.html
