Sunday, 1 May 2011

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Polar Bears

What About Polar Bears?

Scientists believe that Ursus maritimus, the "sea bear," evolved about 200,000 years ago from brown bear ancestors. Polar bears are perfectly adapted for survival in the Arctic. The polar bear is the onlybear considered a marine mammal. Although most polar bears are born on land, most of their life is spent at sea. Since they can hunt consistently only from sea ice, they spend most of the year on the ice.

Size Matters

Twice as large as lions or tigers, adult male polar bears are the largest terrestrial carnivores in the world. Adult male polar bears weigh from 400680 kg. Females are considerably smaller and normally weigh 200340 kg. Amazingly, new born polar bear cubs are some of the smallest mammals at birth. Newborns are 3035cmlong and weigh about 450 grams.
Most females choose den sites in snowdrifts along mountain slopes or hills near the sea ice. Others make dens in banks of snow out on the frozen ocean.  After entering their maternity snow dens in November, mother polar bears give birth in early January. Female polar bears usually have two cubs. Although they are born very small, cubs grow rapidly by drinking their mothers’ rich milk. The families remain in their dens until March or early April. What’s really incredible is that mother bears don’t eat the entire time they spend in the maternity den.  They can be in there from four to eight months! When new bear families finally emerge from their dens, mother bears lead their tiny cubs out onto the ice.  There the mothers can hunt for seals and eat for the first time in many months.

An Icy, Watery Wilderness

The five "polar bear nations" where the ice bears are found include the U. S. (Alaska), Canada, Russia, Denmark (Greenland), and Norway. All have polar habitat lying inside the Arctic Circle. Polar bears spend as much time on the ice as they do on land.
Survival in an icy aquatic environment requires several specializedadaptations. One adaption is polar bears’ white fur.  It camouflagesthem when they are out on the ice and in the snow. This makes it easier for them to sneak up on animals they hunt. Another adaptation is fat. To insulate them from the cold, polar bears have a fat layer which is up to 10cm thick. The fat not only protects them from the cold but also adds to the bears’ buoyancy in the water.
Polar bears have special adaptations to help them swim. Adaptations especially for swimming can be found in polar bears’ feet and paws. Polar bears’ forepaws are partially webbed to assist in swimming. The massive size of the forelegs helps as well. Paws measure up to 30cmin diameter. Polar bears have been clocked swimming as fast as9.66km per hour. How far can polar bears swim? No one knows for certain. But it is a long, long way. Researchers have observed them swimming more than 100kms without rest. Another adaptation that helps polar bears while in the water is that they have excellent underwater vision. They can spot food up to 4m away.
Polar bears are also skilled divers. They easily swim from one ice floeto the next. When a polar bear emerges from the water, it shakes water from its fur like a dog. A polar bear also wrings water from its fur by dragging itself across the ice.

A Nose for Seals

Polar bears are the world’s largest land predators. They top the food chain in the Arctic, where they prey primarily on seals. Polar bears are masters of their icy world. They have adapted to hunt seals with great success. Polar bears wander throughout the Arctic in areas where they can hunt seals at open leads. Leads are wide cracks in the pack ice that may be several kilometers long. Seals, whales and ships use these leads to navigate through the ice. Polar bears travel along the icy edge of leads and hunt for seals.
The polar bear’s most common hunting method is called still-hunting. First, using its excellent sense of smell to locate a seal breathing hole, the polar bear crouches near the hole in silence as it waits for a seal to appear. When the seal sticks its nose up into the hole to breathe, the waiting bear smells the seal’s breath, reaches into the hole with its giant forepaw, and drags the seal out onto the ice. The polar bear kills the seal by biting its head to crush its skull. Since still-hunting is the polar bears most common way of hunting, it is important that the sea ice be thick and strong enough to support the polar bear’s and seal’s massive weights. As the sea ice melts and becomes thinner from climate change, polar bears are finding it difficult to get enough to eat. Polar bears are thus in danger of not being able to survive in the wild.
Polar bears also hunt by stalking seals that are resting on the ice.
Polar bears will also eat dead walruses and whales. When these animals are alive, they are too big for the bears to kill.

Polar Bears and People

For several thousands of years, the polar bear has been an important figure in the material, spiritual, and cultural life of Arcticindigenous peoples. Twice as large as lions or tigers, adult male polar bears have been a highly prized target of hunters for thousands of years. Indigenous people have traditionally killed very small numbers of bears and have had limited impact on bear populationsover the years. Hunting of polar bears remains important in indigenous cultures, so they are allowed to hunt a limited number of the bears under international treaties.
Indigenous peoples use almost all parts of the bears they kill. The fur is used to sew pants and, by the Nenets people, to make galoshes-like outer footwear called tobok (toh-bok). The indigenous peoples eat polar bear meat, use the fat to cook, and use the fat as oil to light their lamps.
Polar bears have been prized for their fur, especially in Russia. During the 19th and 20th Centuries polar bear hunting increased to the point where scientists were concerned about the bear’s long-term survival.  Previously, in most years less than 500 bears were killed. In the 1960’s, however, the number of killed bears grew as hunters used snowmobiles and airplanes to hunt down the animals. The largest number of polar bears was killed in 1968. During that year, 1,250 of them were shot.
Recently, in some northern communities like Churchill, Manitoba in Canada polar bears and people have come in conflict as the town has grown in the path of polar bears as they gather waiting for the sea ice to form. Special bear traps have been created to trap bears alive, hold them until the pack ice forms and then release them away from the human community.

Bear-ly Taking the Heat

Unfortunately, polar bears have been in the news a lot the past several years. Climate change is impacting their icy world more than it appears to be impacting most other places on Earth. While a degree warmer seasonal temperature doesn’t bother you and me much, for the polar bear and many of the species with which it shares its frozen habitat, the change can be devastating! Warmingtemperatures melt the pack ice covering the Arctic Ocean. The bears need good covering of pack ice for hunting seals far out from land. If the ice is melted, the polar bears don’t have a good place to hunt and starve from lack of food.
The international organization concerned about species and habitat survival, the International Union for the Conservation of Nature (IUCN), now lists climate change, also referred to as global warming, as the most significant threat to the polar bear. This is primarily because the melting of its sea ice habitat reduces polar bears’ ability to find enough food.
On May 14, 2008, the United States Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act.

Polar Bear FastFACTS

  • Common Name: polar bear
  • Nickname: ice bear, sea bear
  • Scientific Name: Ursus maritimus
  • Classification:
    • Kingdom: Animalia
    • Phylum: Chordata
    • Class: Mammalia
    • Order: Carnivora
    • Family: Ursidae
    • Genus: Ursus
    • Species: U. maritimus
  • Size: Adult male polar bears weigh from 400680 kg. Females are considerably smaller and normally weigh 200340 kg.
  • Lifespan: 20 - 25 years
  • Range: Alaska, Canada, Russia, Greenland and Norway have polar bear populations.
  • Population: 20,000-25,000 polar bears in the world. (Estimate IUCN 2008)
  • Threatsclimate change, hunting by humans
  • Status: Threatened

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