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November 19, 2017  |  Login

Polar Bear
Ursus maritimus

 
 
 
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What Are They Like?

The polar bear is the largest species of bear, the largest land carnivore in the world, and the top predator in the food chain of the Arctic. Only Alaska’s Kodiak brown bears come close to the polar bear in size. While born on land, polar bears are a true marine mammal, spending most of their life on sea ice. Males stand from 8 -11 feet (2.4-3.35 meters) tall. They generally weigh between 500-1,000 pounds (227-453.5 kilograms), but may weigh as much as 1,400 pounds (635 kilograms). Females usually stand 8 feet (2.4 meters) tall and weigh between 400-700 pounds (181.4-317.5 kilograms). The polar bear has a longer, narrower head and smaller ears than other bears. Polar bears have huge feet, with fur-covered paws. Strong, long-distance swimmers, they use their front feet as paddles and their back feet as a rudder. Polar bears also have about a four-inch layer of extra fat on their bodies to keep warm in subzero temperatures.

Where Do They Live?

Polar bears live only in the Northern Hemisphere, and can be found in all the ice-bound waters of the circumpolar Arctic—in the U.S. waters of the Arctic Ocean off Alaska, in Canada from the northern arctic islands south to Hudson’s Bay, and off the coasts of Greenland, Norway and Russia. Polar bears are completely dependent on sea ice to live. Ice provides a platform for hunting and feeding, for seeking mates and breeding, for movement to maternity denning areas on land, and for long-distance movements.

 
Did You Know?
Polar bears’ fur coats, which cover everything except their nose, have no white pigment. They appear white because the individual hairs of their coats are clear, hollow tubes that reflect light when the sun shines on them.

How Are Babies Made?

Female polar bears reach reproductive age at between four and five years, and males at about six. Most polar bears mate in April and May, when they congregate in the best seal hunting areas. Females are pregnant for four months and often double their body weight during gestation, giving birth to usually two cubs in December or January. The cubs are blind, hairless, and only about the same size as a full-grown squirrel, weighing about 2 pounds (0.9 kilograms). Cubs stay with their mothers for about two0and-a-half years, so female polar bears typically only breed every three years. A female polar bear will only produce five litters in her lifetime, an unusually slow reproductive rate for a mammal.

What Do They Eat?

Ringed seals and bearded seals are the polar bear’s primary source of food. They have also been known to prey on walruses. Polar bears usually eat only the skin and blubber of their prey, and leave the rest of the meat for other arctic animals to eat, providing a crucial food supply.

 
Did You Know?
Polar bears can swim up to 60 miles (96.6 kilometers) in one day.

What Do They Do?

Polar bears are marine mammals, which means they are born on land but spend the majority of their lives at sea. They can walk across significant distances on land, but are most agile in the sea. They can swim at speeds of up to six miles per hour, and have been known to dive 10 to 15 feet (3-4.6 meters) below the water surface. A polar bear may stalk a seal by waiting quietly for it to emerge from its blow hole or “atluk,” an opening seals make in the ice allowing them to breathe or climb out of the water to rest. A polar bear can smell a seal that is swimming beneath three feet of ice—and can pull a seal out of a six-inch hole in the ice. The polar bear will often have to wait for hours for a seal to emerge. Because the bear’s coat is camouflaged against the whiteness of the ice and snow, the seal may not see the bear until it’s too late.

How Concerned Should We Be?

The International Union for the Conservation of Nature (IUCN) lists the Polar Bear as “vulnerable.” Melting ice caps and rising sea levels caused by global warming pose the biggest threat for polar bears, as the habitat they rely on has melted and shrunk. Because of melting ice from rising temperatures, the season when polar bears can hunt the ice seals on which they rely has become dramatically shorter, causing many bears to die of starvation.  Although global warming is the bears’ chief enemy, both legal and illegal hunting also pose a threat. Human trophy hunters kill over 500 polar bears a year in Canada, where trophy hunting is legal. Besides commercial hunting, polar bears are threatened by air and water pollution, and by oil and gas drilling in the icy waters of their home. There is no way for a polar bear to survive if its fur is fouled by an oil spill, and no proven way to clean up oil in icy arctic waters.

What's Being Done?

The U.S. has banned all importing of polar bear trophies, and has petitioned the Convention on Illegal Trade in Endangered Species (CITES) to ban all trade in polar bear fur and body parts throughout the world. In May of 2008, polar bears were listed as “threatened” under the Endangered Species Act (ESA). In October 2009, the U.S. Fish and Wildlife Service proposed that an area of more than 200,000 square miles be designated as “critical habitat” for polar bears under the ESA. About 93% of the proposed critical habitat is sea ice; the remainder is barrier islands and land along the coastlines of the Beaufort and Chukchi Seas where polar bears are known to den and bear their young. The Endangered Species Act prohibits “destruction or adverse modification” of designated critical habitat, meaning that activities like oil and gas development and burning the fossil fuels that cause global warming could be regulated more strictly to protect the polar bear.

 

Mother Polar Bear and Cubs Emerging from Den

 
 
 
 
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