The polar bear is the largest species in the family Ursidae with its body, neck and head being much longer, on average, than those of other bears (Kodiak bears, a subspecies of brown bears, have been known to grow larger than polar bears). The polar bear is completely covered with fur, with the exception of its nose and the pads of its feet. The coat can vary from pure white to a creamy yellow depending on the time of year and the angle of light. The males weigh between 350kg to over 650kg, they have a slight hump above their shoulders and a conical neck and head making tracking collars essentially impossible to attach. Females are typically smaller, weighing between 150kg and 250kg although this can double when they are pregnant. Females also tend to have a more pronounced distinction between their head and neck.
Food and Feeding
Polar bears large size can be attributed to their high fat diet which consists mainly of ringed seals, but also bearded, harp, harbour and hooded seals and young walrus. Large males have also been known to capture beluga whales. Polar bears depend on sea ice to hunt these marine mammals and in subpopulations where bears spend more time onshore due to the ice free season, they supplement their diet. For example, polar bears may eat seabirds, eggs, and carcasses of stranded marine mammals, fish, mussels, crabs, grasses, seaweed, mosses and sedges if they come upon them, but they do not generally hunt or look for these foods. Throughout the species range, polar bears also go through annual fasting times where they live off of their fat reserves. This occurs during the ice free seasons when they have a very limited access to seals and sea ice from which to hunt from.
Polar bears are skilled hunters. They use their powerful jaws and paws to capture seals and drag them out of the water. In the spring, female polar bears usually consume the entire seal with the exception of larger bones of the skeleton and flippers. Single mature males are more likely to feed only on the fat of a seal, and leave the rest on the ice. These remains are an important source of food for younger bears, who often scavenge these kills after the larger males have left.
Polar bears are well-known for their excellent swimming ability. During their travels, they swim across bays and wide leads without trouble, and during the summer they have been known to swim great distances in open water. Unlike black bears and grizzly bears, polar bears do not hibernate. However, pregnant polar bears enter dens during the winter to give birth. All polar bears may dig temporary dens to escape cold or stormy weather. If a polar bear does not feed for about 10 days, its body changes into a hibernation-like state with a lowered metabolic rate and body temperature.
Polar bears are found at high latitudes in the five polar bear range states: Canada, Greenland, Norway (Svalbard area), the Russian Federation, and the United States of America (Alaska). In Canada, they have been seen as far as 88º north and as far south as the Gulf of the St. Lawrence.
Within which subpopulation polar bears live dictates the amount of time annually they spend on the sea ice. Polar bears in the more northern subpopulations can spend the majority of the year on the sea ice while those in the more southern parts of the range (e.g. Hudson Bay) spend greater time onshore during the ice free season. Polar bears are generally found close to the coastline, but some animals may travel many kilometers inland to den or simply to cross islands and get to other hunting areas. The seasons, availability of food, good denning sites, sea-ice conditions, and breeding season are all factors that affect where polar bears may be found.
Males and females mate in the spring but the fertilized egg remains undeveloped until autumn when it implants itself and begins to grow. This reproductive adaptation is known as ‘delayed implantation’. The female will excavate a den and, in early January, give birth to a litter of cubs. Twins are common, but often a single cub is born in first pregnancies. Litters of three and even four have been recorded. The first few weeks following birth are spent in the den, feeding, sleeping and gaining weight and strength. In early spring, the cubs leave the den with their mother and begin the journey to the sea-ice. The mother hunts and although the cubs begin to eat fat and meat, they continue to nurse until they are almost two years old. Cubs will stay with their mother until they are two and a half years old. Polar bear average life expectancy is between 12-20 years, but it is not uncommon to find adults that live between 20 to 35 years in the wild. Some captive polar bears are known to have lived even longer.