Polar Bear

## Description

The Polar bear (Ursus maritimus) is a hypercarnivorous bear found within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear species, as well as the largest extant land carnivore. Although it is the sister species of the Brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting seals, which make up most of its diet. Although most Polar bears are born on land, they spend most of their time on the sea ice. Their scientific name means "maritime bear" and derives from this fact. Because of their dependence on sea ice, Polar bears are classified as marine mammals. For thousands of years, the Polar bear has been a key figure in the material, spiritual, and cultural life of circumpolar peoples, and these bears remain important in their cultures. Historically, the Polar bear has also been known as the "white bear". It is sometimes referred to as the "nanook", based on the Inuit term nanuq.

## Appearance

Polar bears are one of few large mammals that have been able to adapt well to life on the ice. Their fur consists of a layer of dense underfur and an outer layer of guard hairs, which appear white to tan but are actually transparent. The white coat usually yellows with age. The feet of these massive animals are very large to distribute load when walking on snow or thin ice and to provide propulsion when swimming; they may measure 30 cm (12 in) across in an adult. The pads of the paws are covered with small, soft papillae (dermal bumps), which provide traction on the ice. The claws are deeply scooped on the underside to assist in digging into the ice of the natural habitat.

## Distribution

Polar bears are found in the Arctic Circle and adjacent land masses as far south as Newfoundland. While they are rare north of 88°, there is evidence that they range all the way across the Arctic, and as far south as James Bay in Canada. Their range includes the territory of five nations: Denmark (Greenland), Norway (Svalbard), Russia, the United States (Alaska), and Canada. Polar bears prefer to live on the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic. Polar bears frequent the areas where sea ice meets water, such as polynyas and leads (temporary stretches of open water in Arctic ice), to hunt the seals that make up most of their diet.

## Behavior

Polar bears live a solitary life. They may come into competition with each other when there is the chance to scavenge when a seal is killed. In such cases, the smaller bear usually runs away. Polar bears can dive underwater to catch their prey, keeping their eyes open while holding their breath for as much as 2 minutes. They are inactive for a good part of the time, lying, sleeping, or waiting (still hunting). The rest of the time is usually spent traveling, either walking or swimming, feeding or stalking prey. They may travel far in search of food. Polar bears are usually quiet but do communicate with various sounds and vocalizations. Females communicate with their young with moans and chuffs, and the distress calls of both cubs and subadults consist of bleats. Cubs may hum while nursing. When nervous, bears produce huffs, chuffs, and snorts while hisses, growls, and roars are signs of aggression. Chemical communication can also be important: bears leave behind their scent in their tracks which allow individuals to keep track of one another in the vast Arctic wilderness.

## Diet

Most of what Polar bears eat is the blubber and skids of Ringed seals. They often leave the rest of the carcass, which becomes an important food source for other animals. They also eat birds, fish, berries, reindeer and sometimes walrus. Carcasses of walruses, seals and even whales can provide a regular source of food for Polar bears. They sometimes break into underground seal dens to hunt the pups inside them.

## Reproduction

Polar bears are polygynous and do not form pairs. Courtship and mating take place on the sea ice in April and May, when they congregate in the best seal hunting areas. A male may follow the tracks of a breeding female for 100 km (60 mi) or more, and after finding her engage in intense fighting with other males over mating rights; fights often result in scars and broken teeth. After mating, the fertilized egg remains in a suspended state until August or September. When the ice floes are at their minimum in the fall, ending the possibility of hunting, each pregnant female digs a maternity den consisting of a narrow entrance tunnel leading to one to three chambers. In the den, she enters a dormant state similar to hibernation. Between November and February, cubs are born blind, covered with light down fur, and weighing less than 0.9 kg (2.0 lb). On average, each litter has 2 cubs. The family remains in the den until mid-February to mid-April, nursing her cubs on fat-rich milk. By the time the mother breaks open the entrance to the den, her cubs weigh about 10 to 15 kg (22 to 33 lb). For about 12 to 15 days, the family spends time outside the den while remaining in its vicinity; the grazes on vegetation while the cubs become used to walking and playing. Then they begin the long walk from the denning area to the sea ice, where the mother can once again catch seals. The younf usually remain with their mother for 2 to 3 years. Females begin to breed at the age of 4years in most areas, and 5 years in the area of the Beaufort Sea. Males usually reach reproductive maturity at 6 years; however, as competition for females is fierce, many do not breed until the age of 8 or 10.

## Population

### Threats

Polar bears are still hunted for fur and meat by the Arctic's native peoples. They are also threatened by drilling for gas and oil, increased shipping activity, and pollution from industrial chemicals. But the major threat is climate change and global warming causing the sea ice to melt earlier in the year and forcing the bears to shore before they have built sufficient fat reserves to survive the period of scarce food. It is suggested that Polar bears could be extinct in the wild within the next 30 years.

### Number

According to IUCN, as of 2010, between 22,000-31,000 Polar bears are estimated to be roaming near to the North Pole, most being in northern Canada. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List.

### Ecological niche

Polar bears are the top Arctic carnivores. The remains of seals left by the bears are likely to be an important food source for younger, less experienced bears and Arctic foxes.

## Fun Facts

Polar bears are marine mammals because they spend many months of the year at sea. However, they are the only living marine mammals with powerful, large limbs and feet that allow them to cover kilometers on foot and run on land.

A Polar bear's fur is hollow and reflects light, so it is not actually white. Their fur is also water repellent and oily. The bears can shake themselves dry after a swim.

Polar bears have an extremely well-developed sense of smell, being able to detect seals nearly 1.6 km (1 mi) away and buried under 1 m (3 ft) of snow. Their hearing is about as acute as that of a human, and their vision is also good at long distances.

Polar bears are excellent swimmers and often will swim for days. With their body fat providing buoyancy, the bears swim in a dog paddle fashion using their large forepaws for propulsion. Polar bears can swim at 10 km/h (6 mph). When walking, they tend to have a lumbering gait and maintain an average speed of around 5.6 km/h (3.5 mph). When sprinting, they can reach up to 40 km/h (25 mph)!

Female Polar bears prefer to construct their dens using "old snow" from previous years instead of freshly fallen snow.

Female Polar bears are known to be very good mothers and may adopt other cubs.

A Polar bear is strong enough to kill an animal by giving it one blow with its paw.

When curled up, a bear may put a paw over its muzzle to help conserve heat.