Despite outward appearances, a polar bear actually has black skin. They only appear white because of highly reflective, translucent fur around 2.5 to 5 cm (1-2 inches) thick. The fur, along with an insulating layer of fat, helps keep them warm in frigid Arctic conditions. To keep from slipping on the ice a polar bear's foot is covered with small, soft bumps that create friction.

Polar bears rely on marine fat, or blubber, to stay alive. Their main source: seals, which they hunt on sea ice in the winter months to store energy for summer and fall, when food can be scarce. They can put away as much as 45 kilograms (100 pounds) in one meal. But with sea ice now melting earlier and forming later in the year, bears are spending longer periods without food.

Food scarcity can cause birth rates to drop in unhealthy bears and cubs can die from a lack of fat on nursing mothers. Most females give birth once every three years, digging their dens in early winter and waiting for the snow to cover the entrance before giving birth — largely to a litter of one or two cubs. The mother and her young leave the den and head toward the sea ice in March or April.

A cub will spend the first two to three years of its life with its mother. During this time the mother will be fiercely protective. Eventually though, she will chase them away or abandon them, leaving them to fend for themselves. Besides brief encounters during mating season, polar bears will then spend most of their lives alone — although they may occasionally share a large kill with other bears.

Unlike other bear species, polar bears don't hibernate. With the exception of pregnancy, when a female polar bear remains in her den until her cubs are large enough to survive outside, they stay active all winter while food is plentiful. But they're happy to take a nap whenever a snowstorm hits. They can even remain in one place for hours while the snow piles up around them.

Polar bears are native to the Arctic and can be found in Russia, the US, Norway, Greenland and Canada, which is home to around two-thirds of the global population. They spend much of their time on the ice hunting and breeding. But as the world warms the northern ice cap retreats, threatening their habitat.

With loss of their ice habitat, polar bears are increasingly coming in contact with humans. People in settlements around Canada's Hudson Bay may run into the bears, typically young adults — inexperienced hunters — and mothers with cubs at dump sites, where they scavenge for food. In Churchill, Manitoba, authorities have built a jail where nearly 30 polar bears can be held before being relocated.

Today there are roughly 22,000 - 31,000 polar bears left in the wild, and the population is considered vulnerable. In addition to habitat loss, the bears are also threatened by unsustainable hunting and industrial development, which includes offshore oil and natural gas exploration. Some estimates suggest polar bear numbers will decline by more than 30% in the next 30 years.