Did You Know? Polar bears may be the largest land predators on Earth, but they are such agile swimmers, that they are also considered marine mammals. Because of global warming and melting sea ice, even these world-class swimmers are drowning before reaching ice to rest on.

GhostS of the Arctic

In many European languages, polar bears are called “ice bears,” testimony to the fact that they spend their entire life on the ice pack that blankets the Arctic Ocean, hunting for ringed seals, their primary food source.

Polar bears exhibit several physical characteristics that distinguish them from other bears and which enable them to live in their Arctic environment. They have evolved into efficient swimmers — uniquely among bears, they have developed some webbing between their toes. Their necks are longer than other bears, the better for them to keep their heads above water while swimming.

Polar bears are supremely adapted to their Arctic environment, a place where ambient temperatures can plummet below –50 degrees Fahrenheit. They have two layers of fur on top of a layer of blubber that can measure 4 ½ inches thick. Polar bears are so well insulated against the cold that they have more problems from overheating when they exert themselves, such as when they run.

Despite being excellent swimmers, polar bears rarely hunt from the water. Instead, they use the pack ice as a platform for hunting their prey, principally ringed seals. Ringed seals live year-round in the Arctic Ocean, and since they need to come up for air every five to fifteen minutes, they build a series of breathing holes in the ice pack. Polar bears hunt by waiting patiently at a ringed seal’s breathing hole, for hours or even days, until the seal comes up for air.

Polar bears also prey on walruses, belugas, narwhals, bearded seals, hooded seals, harp seals, some seabirds and even reindeer in some areas. Those stranded on land by retreating sea ice — for example, in southern Hudson Bay—will also scavenge on dumps and whale carcasses, and have even been observed consuming sea kelp. When food is unavailable, polar bears enter a hibernation-like of low energy consumption, and can spend several months subsisting on their stored fat.

Polar bears breed in April and May. They have delayed implantation, meaning the eggs stop developing after the first few divisions and remain dormant in the uterus until implantation in mid-September to mid-November, depending on latitude. Cubs are born approximately two months after implantation, in maternity dens which the females build in the snow in late fall after gorging themselves in August and September. The cubs are only 12 to 14 inches long at birth and weigh about one pound. They are blind, have no teeth and are completely dependent on their mother for food. Mother and cubs emerge from the maternity den in March or April, but cubs aren’t on their own just yet. They’ll remain with their mother until they’re about 2 ½ years old, learning how to hunt and survive in the harsh Arctic environment.

One of the most important things a polar bear will learn is how to follow the sea ice to find ringed seals. In summer, when the sea ice retreats to the north, polar bears will travel hundreds of miles to stay with the ice and maintain contact with their prey.

When full grown, males can stand eight to 10 feet tall and weigh in at 500 to 1,700 pounds. Females are smaller, standing six to eight feet tall and weighing in at 200 to 700 pounds. Polar bears have an average life span of 15 to 18 years, although biologists have tagged a few bears that were more than 30 years old.

Approximately 22,000 to 27,000 polar bears roam the circumpolar north. Despite cola commercials depicting polar bears and emperor penguins together, there are no polar bears in Antarctica. Five nations have polar bear populations: the United States (in Alaska), Canada, Russia, Norway and Denmark/Greenland. Scientists have identified 19 distinct populations of polar bears.