Polar Bears
Polar bears could be called "ice bears" because they spend most of their lives wandering on Arctic sea ice in search of seals. Unlike grizzly bears, they spend little time on land.
Polar
bears and grizzly bears: distant cousins
Scientists believe that polar bears evolved from grizzly bears between 70,000 and 150,000 years ago. The bears became supremely adapted to life on sea ice: their fur is white with water repellent guard hairs and dense under-fur. The white fur helps to camouflage polar bears as they stalk seals resting on the edges of ice shelves.
Polar bears' relatively short furry snout and small ears are less likely to get cold than the longer noses and ears of grizzlies. These northern-most bears have big paddle-like feet with short, curved claws that are suitable for both swimming and walking on ice and snow, and are much less effective at digging than long grizzly claws. Grizzly teeth and polar bear teeth are also different: polar bear molars better suited for chewing meat while grizzly molars are flattened for grinding vegetation. Large male polar bears have weighed over 1,400 lbs and measured over 9 feet from nose to tail. By contrast, male grizzlies in the Lower 48 can weigh up to 800 lbs and measure up to 7 feet.
Polar
bears wander the ice searching for seals
As predators, polar bears are specialists; that is to say, most of their diet comes from their primary prey, ringed seals and other "ice seals." Polar bears don't just specialize in a particular kind of prey, they also specialize in the way they hunt their prey. Arctic ice seals are most vulnerable when they swim up to breathing holes in the ice, and when females give birth and nurture their pups in snow caves. Polar bears can detect the smell of a seal from far away, and will follow the scent, quietly stalking their prey. When they sense a seal in a snow cave, they break through the snow to devour it—unless it slips away. Because they specialize in hunting ice seals and other marine mammals, polar bears are completely dependent upon the yearly formation of new sea-ice for survival. Female polar bears have been known to travel over a 230,000 square mile area in one year to search for prey!
Shrinking ice mass means fewer polar bears
Scientists are noticing that less sea ice is freezing because our climate is warming. Not only is there less ice, the ice is forming later in the fall and winter. The ice shrinkage and late formation also means that polar bears are likely to swim longer distances to hunt or find mates. While polar bears are great swimmers, they cannot survive very long journeys, especially if storms bring high wind and waves. Following one major storm in the Alaska Beaufort Sea, scientists in a small plane observed four dead polar bears floating in open water. Currently, all evidence points to the probability of continued Arctic warming and decreasing Arctic sea ice cover in the 21st century.
Polar
and grizzly bears intersect more often as the climate warms
Polar bear ranges and grizzly bear ranges overlap in parts of northern Canada and northern Alaska. While waiting for ice to form later in the fall, polar bears appear to be spending more time on land, and this increases the likelihood they will encounter grizzly bears. While grizzly and polar bears have bred and produced offspring in zoos, this crossbreeding was unknown in the wild…until recently. In 2006, a sport hunter in Canada killed a hybrid bear that was later genetically tested. The testing confirmed that the 6-year old male bear came from a breeding of a polar bear female and a grizzly bear male. The hybrid bear had thick white fur like a polar bear, but it also had the long claws, humped back and dished face of a grizzly.
Omnivorous grizzly bears have an advantage over their polar bear cousins. With the help of conservation leaders, grizzly territory and habitat will be protected and they will likely survive even as the planet warms.
Polar Bear Statistics
Polar Bear Distribution Map
U.S. Fish and Wildlife Service Safety Guidelines: Polar Bears and Humans (2.1 MB PDF)