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All text below courtsey World Wildlife Fund Canada.
Polar bears are one of the world's largest carnivores. Males can weigh up to 800 kilograms (almost 2,000 pounds) and measure three metres in length (nearly ten feet long). Male bears can be twice the size of females. Their coat is thick, made up of hairs that conserve heat, and varies in colour from white to creamy yellow, even light brown in summer. Under this dense coat is black skin, good for absorbing the rays of the Arctic sun. Their claws are shorter, and more solid than that of their grizzly bear cousins, better suited for walking on ice or climbing steep banks. Polar bears have sharp, jagged back (or molar) teeth, and canines that are larger and sharper than grizzly teeth. Their tails and ears are stubby and compactly fitted to their body-less surface area means less heat loss. But that doesn't apply to their feet! Polar bears have huge feet. When swimming, their feet act like oars, and when crossing thin ice, the huge paws function like snowshoes. Such feet spread out the bear's weight and keep this massive animal from breaking through ice cover that would crack under a human's feet. The pads of these remarkably well-adapted appendages are covered with soft, tiny growths called papillae, which increase friction between paw and ice, reducing the chance of a slip.1 Habitat Living mainly in Arctic seas on offshore pack ice and along coasts and on islands, there are estimated to be about 21,500 to 25,000 polar bears in the world. About 40 per cent live in Canada, from Labrador to Yukon and from Ellesmere Island to James Bay. They share this habitat with the Inuit, and with narwhal, beluga whales, Arctic foxes, ringed seals, and in the summer, millions of migratory birds. Polar bears prefer to live on the sea ice all year round, to give them a base from which to hunt seals. When the edge of the ice moves north in summer, bears will travel many miles to stay on the ice, near the seals. Any bears stranded on land would have to wait until freeze-up in the fall to get back on the ice. The southern-most population of polar bears, living near Churchill, Manitoba on Hudson Bay, can't follow retreating ice. They spend their summers on land, living off body fat stored from eating well the winter before. When the pack ice gathers again as temperatures drop in the fall, the bears leave the land to resume life on the sea. As levels of climate-warming greenhouse gases in the atmosphere rise, this causes increases in Arctic and global temperatures. As a result, the sea ice melts earlier and forms later. The bears are left with less and less time to hunt for food. As their habitat shrinks away, these populations of bears face a grave threat to their survival. At the current rate of climate warming, experts predict that polar bears may be extinct in Southern Hudson Bay by the year 2050. Behaviour Polar bears have influenced Arctic seal populations, and the seals have influenced the polar bears. Most of the bears' interesting body adaptations make it a better Arctic hunter, and some learned behaviours accomplish that, too. On thin ice, a polar bear relies on its snowshoe feet to distribute its weight as it searches the ice for prey. When the ice gets thinner still, the bear will resort to crawling on its knees and elbows to make it across. Similarly, there have been reports of polar bears covering their black noses with a giant paw so their camouflage against the snow will be complete as they stalk seals. Some bears are great travelers. Even mothers with cubs can move 30 kilometres a day for several days. Others stick around where food sources are abundant, following the pack ice in coastal areas, but never venturing far. They move slowly, plodding across the ice so they don't overheat. Their skin, fat layer and coat are meant to keep heat in - and sometimes work too well. In warmer times of the year especially, the bears will swim to reduce body heat. Polar bears are also great swimmers. They won't hesitate to swim across a bay and they'll swim for hours at a time in the summer. Their streamlined bodies are well adapted for swimming. Their body fat helps them float and they use their large forepaws to paddle and sometimes use their hind legs as rudders. Family Polar bears are solitary animals. They may gather in groups where food is abundant, but then separate. Male and female polar bears avoid each other except for the mating season in the spring. After mating, the female has only a few short months to stock up the large fat deposits she will need for herself and her new cubs. The female enters the maternity den in the fall, a warm, single-room shelter she digs into a snowdrift or peat bank. Polar bears have one to three cubs, weighing less than a kilogram when born (1 to 1 1Ú2 pounds). They fatten up to 10 to 15 kilograms (25-30 pounds) by the time their mother breaks out of the den to rejoin the Arctic world. Cubs usually stay with their mother for about two years before striking out on their own. Diet Polar bears prefer to eat seals. They will also catch and eat some fish, seabirds or whales, and aren't too proud to make a meal of a dead animal they might find in their travels. Seals are caught most commonly at seal breathing holes in the ice. The bears remain motionless and absolutely silent, lying on their stomach and chest with their chin on the ice, waiting patiently for the seals to appear. This is called the "still-hunt", for obvious reasons. Near human settlements, the bears are drawn to garbage dumps as a food source. This happens with the bears near Churchill, Manitoba and innovative ways to discourage this behaviour have been developed. These include polar bear "jails" where the captured bears are confined until freeze up, or relocating the bears far away from the dumps. These methods reduce the number of nuisance bears, possibly saving the life of a bear that could become a threat as it becomes too accustomed to humans. Polar Bears and Climate Change2 Deep core tests of Arctic ice packs have shown that levels of greenhouse gases in the atmosphere are higher now than at any time in the past 420,000 years. The result is a rapid increase in global temperature that has shocking implications. The Arctic sea ice pack is 14 per cent smaller than it was just 20 years ago - a disastrous situation for the polar bears who depend on the ice to access their food source. The polar bear is a marine mammal. It depends on the sea for its very existence, hunting seals from pack ice and coming ashore only as the ice disappears every summer. The ebb and flow of the polar ice determines the bears' fate, and as climate warming reduces the extent of the pack ice, the polar bear loses out Ñ loses hunting time, loses weight Ñ and the number of polar bears declines. This top predator is significant in the make up of the Arctic ecosystem, and what affects the polar bear affects all Arctic species. All Arctic wildlife and the Inuit people who live on this land are negatively affected by environmental changes. WWF plays a major role in supporting research and is leading action globally to address the major threats from POPs and climate change. Work must continue to identify causes, address and reverse the effects of climate change and chemical pollution in our planet's last great-inhabited wilderness. 1Description from http://www.wwf.ca/en/PolarBearCentral/ 2Adapted from http://www.wwf.ca/en/PolarBearCentral/LearnAboutPolarBears/default.asp |
