Polar Bear Facts

Polar Bear Habitat
http://animals.nationalgeographic.com/animals/mammals/polar-bear/

Physical Characteristics

The Polar Bear is a mammal, weighing in at an average 1400 lbs, with an average height of about seven and a half feet tall (12). The average life span is 25 to 30 years long, barring any drastic changes to their environment (12). Polar bears roam on and swim among the Arctic Sea ice. The morphology of the bears has adapted in various ways to the coldest environment on earth. First, their paws are very large and are webbed. This allows them to swim efficiently in the sea. Secondly, and most importantly, their fur is insulated and covers a layer of fat, which helps keep the animals warm in such cold climates. There is also fur on their paws, aiding with grip strength on the ice and for protection from cold surfaces (3). The color of the bear's fur is white, thus providing camouflage on the snow and ice. Underneath the white fur is black skin. This is a unique adaptation to the environment.  The black skin absorbs the sun's rays and helps warm the animal (3).

Hunting and Food Source

Polar bears are carnivores and skilled hunters. Bearded and ringed seals are their main prey. Typically, the bears frequent areas of shifting or cracked ice. These are areas where seals surface to breathe, roughly every couple of minutes. The bears use their keen sense of smell to find these holes and wait for the seals to surface (12). This type of hunting is called "still-hunting". Seals and other prey resting on the surface of the ice are also subject to attacks by the bears. In order to fulfill their dietary fat needs, polar bears are known to scavenge for animal carcasses, like whales or walruses (3).

Polar Bear Hunting A Seal
http://waterproof-expeditions.com/photo_image_pic__polar_bear_eating_seal_M118G13.html

During late summer and early fall, polar bears are unable to hunt seals because the sea is not frozen. They have a physiological trigger in their blood that allows them to fast for several months (12). When the sea ice is gone in the summer months, polar bears will live off of fat reserves. They can eat other types of food, such as caribou, eggs, birds, and berries, but none of these are an essential part of their diet. The polar bear is unique in that it needs large quantities of fat from marine mammals that live in it's environment. These bears can not obtain adequate energy intake from terrestrial sources (3).

Lifecycle

Polar bears mate during the spring, typically in April and May. The courtship practices take place on the sea ice, in areas of high seal abundance. Once a partner is found, mating can last up to a week (12). It has been discovered that litters of cubs have been found to have different fathers. This suggests that polar bears could have a polygamous mating model (12). Once fertilized, the eggs go into a frozen state until early fall. During this time, the female will eat large amounts of food in order to double her own body mass in anticipation of rearing her cubs in late winter (3).

A Typical Maternity Den Layout
http://www.zworld2.com/MRSZWORLD/polarbearz/cubs_2.htm

In the fall months, when hunting is not possible, the pregnant females will dig a "maternity den" (12). Most dens are made on coastal land away from the sea. A few will be made on the sea ice, if conditions allow for it. In the den, the female will enter a hibernation like state, where her heart rate will slow down and her body temperature will remain the same (3).

During the winter, the cubs are born, usually in the months from December to February. The family will remain in the den until mid-April, during which time the cubs are nursing on the mother's milk. When the cubs emerge from the den, in early spring, they will weigh an average of 30 lbs (12). The family will then spend a week or so outside the den, acclimating the cubs to their new environment. They will then migrate back to the sea ice, where the mother can hunt for seals after nearly eight months of fasting (3).