About Polar Bear

Range and Habitat
Polar bears live in the arctic circle in Greenland, Canada, and adjacent ice sheets. They live mostly on the shorelines. They do not venture to far north as the permanent pack ice is too thick for the seals to break through, so the bears will not have any food.
Polar bears migrate frequently within their home range, as the availability of sea ice changes. They use the sea ice as a platform for hunting seals. During the winter months, they tend to move further south, as far south as the Labrador Sea and the Bering Sea in Canada. Occasionally, they will be set adrift on ice floes as far as Iceland, Newfoundland in Canada, and even Hokkaido in Japan!
Physical Appearance
The polar bear is the largest bear in the world. They are also the largest land carnivore. Adult males weigh from 880 - 1320 lb (400 - 600 kg) and can exceed 1760 lb (800 kg). Females are half the size of the males, and weigh from 440 - 660 lb (200 - 300 kg). Females can weigh up to 1100 lb (500 kg) in the winter months before dormancy due to stored fat on the body. Adult males are between 95 - 105 in (240 - 260 cm) in length from nose to tail, and females are 75 - 85 in (190 - 210 cm) in length. Males reach their full size at 9-10 years old.

Polar bears are instantly recognized by their stark white coat, which is sometimes stained light yellow. Polar bears have black skin, which can be seen on their nose, paw pads, lips and around the eyes. This allows them to absorb sunlight and keep them warm. Their double-dense coat also keeps them warm and dry, even when they are swimming in the cold arctic waters. In addition, the hairs are like optical fiber: hollow. This allows the hair to reflect light down to the black skin, where it is absorbed. A thick layer of fat adds further to the insulation. In fact, they are so well insulated that they can overheat, and are often seen sprawled out on ice sheets to cool down.

Polar bear's bodies are very elongated, and their muzzle and head is longer and more wedge-shaped. Their ears are much smaller than the other bears species, to conserve heat. They have a very short, stubby tail, just like all bears. They posses very large canine teeth, and their carnassials (shearing teeth) are highly developed. Their long, brown claws are non-retractable. The soles of their feet have a suction-cup like surface, so they have a good grip on the slippery ice. Also, their feet are much larger in proportion to their body than other bears. Like all bears, the polar bear is plantigrade, which means that it walks with its entire foot like a person, rather than on its toes like dogs and cats, which are digitigrade. They can also stand up in their hind legs for extended periods of time, which makes them look rather human. Their eyesight and hearing are similar to a humans, but its their sense of smell that is the most highly developed. They can smell a seal under the ice.

Polar bears also have the ability to store incredible amounts of fat on their body to be used later. They can survive on these fat stores alone for months at a time when food is scarce. When they go into dormancy, they do not urinate, and do not need to drink because they can create water from metabolism of fats and recycle their body wastes without using their kidneys. Also, while they are living on their fat reserves, their body only metabolizes the fat, and not lean body mass, unlike a starving human.

Diet

Polar bears are the most carnivorous of all the bears and feed entirely on seals, in particular ringed and bearded seals. They even have preyed on young walruses, belugas, and narwhals. They will eat carrion readily, and sometimes feed on kelp that washes up.

They often wait at seals breathing holes for a seal to surface and then grab it. They may wait for hours at a time for the seals to emerge, and sometimes they break into the ice to grab the seal in the water. During the spring and summer months, they swim underwater and catch seals that way. Though polar bears spend half their time hunting, they are successful less than 2% of the time.

Reproduction and Life Cycle

Polar bears are solitary animals, coming together only to mate. The male does not help in the rearing of the young. Males often fight viciously over females during the breeding season, and cause extensive injuries to themselves. Females breed only once every three years. Mating season is from March to May. The pair stays together for only a few days during the breeding season, and during this time they copulate many times. Female bears are induced ovulators, meaning they have to be stimulated several times in order to ovulate, so this is why they must mate so often. Also, like other mammals in the order carnivora, the male bears have a special bony structure in their penis called a "baculum". This structure serves to stimulate the female into ovulating, as well as prolonging copulation by widening to lock the two mating bears in a copulatory "tie". This tie may last for 10 - 30 minutes. However, the fertilized egg is not implanted in the uterus until September.

The cubs are born between late November to January, in a den dug by the mother in the snowdrifts. The majority of litters consist of two cubs; however, sometimes one to three are born in a litter. At birth, the cubs weigh from 1 lb 3 oz to 1 lb 6 oz (600 - 700 g). Bears, unlike any other mammal, are born very small, much smaller than mammals of a similar size. In fact, when they are born, their weight is 10% of that of a mammal of similar size. The reason bears are born so small is because their mother fasts (does not eat) during the gestation period (pregnancy) with her young, unlike any other mammal which continues to eat while pregnant with her young. The mother bear's body proteins actually break down to provide glucose in order to nourish the young while they are still inside her. And since the baby bears obtain very little nutrients while still inside the mother, they are born premature. To make up for the lack of nutrients during gestation, the milk of bears is more rich in nutrients than other carnivores. Because the milk is so rich in fats and nutrients, young bear cubs do not need to drink as much milk as other carnivore cubs. In fact, polar bear milk is the richest milk in the bear family. Cubs remain with their mothers for two and a half years. During this time they are taught how to hunt. Physical maturity is attained at 5-6 years for females and 10-11 years for males. They can live for up to 36 years in captivity.