The Polar bear is not only the largest species of bear in the world, it is the largest living carnivore. The species is sexually dimorphic, with the male being considerably larger than the female. Males can weigh up to 700 kg (1,540 lbs) while females may reach half that, but body weight varies significantly throughout the year (especially among females that can double their body weight from the spring to the late summer).
The polar bear has a circumpolar distribution, but is largely restricted to areas that have sea ice during a significant part of the year. They live in Alaska, Canada, Greenland, the Russian Arctic, the Norwegian Arctic (including the Svalbard Archipelago), and on sea ice surrounding the North Pole. There are some 20 different populations of polar bears in the Arctic, which total about 25,000 bears. Individual bears roam over large areas, and populations are therefore well connected.
Polar bears are typically off-white in color, but vary through shades of white to yellow. Their specialized fur is a very efficient insulation that consists of air-filled hairs which are reminiscent of tiny fiber optics. These individual hairs transmit light through their shafts directly to the surface of the skin, which is nearly black and acts as a heat absorbent. In fact, it seems as though polar bears have a more difficult time keeping cool enough than staying warm enough.
Adult males can be distinguished from females on the basis of their larger size, and more powerful necks that look wider than their heads. Compared to other bears polar bears have: a long narrow head; a head that is relatively small compared to the body; small, heavily furred ears; claws that are short and strong; canine teeth that are long; and cheek teeth that are sharper. These features have been selected for in polar bears as a consequence of their almost purely carnivorous way of life. Like all bears, they are massive animals that walk flatfooted, not on their toes like most other mammals. They have big heads, powerful limbs, and very short tails, which often cannot be seen through the thick fur.
Polar bears are largely solitary, except for mothers with their young and brief periods of male/female pairings during the mating season. The female bears usually breed every two or three years, and the cubs stay with the mother for at least a year, but sometimes as much as two. Polar bears mate in April or May, and males track the smell of females over many kilometres. Females in Svalbard usually mate for the first time when they are five years old, but males reach sexual maturity somewhat later and do not reach full body size until they are 8-10 years old. A large male can mate with several females within the same season, attending each for some days or weeks. Polar bears have delayed implantation; the egg does not begin to develop beyond some few initial steps before the Autumn (September-October), although the female mates in the Spring. Only pregnant females will den during the winter (usually for about four months)…all other polar bears are active throughout the winter, even during the months with 24 hour darkness. However, non-denning bears often dig day-beds in the snow during severe weather and will rest for a day or two at a time. Females give birth around New Year, while they are in their winter asleep. The cubs are very small (approximately half a kilo or one pound) when they are born. Most frequently polar bears have two cubs in a litter, but litter size ranges from one to three. Polar bear milk is rich in fat, and the nursing cubs grow quickly in the security of the den. They weigh about 10 kg (22 lbs) when the family leaves their winter home in late March or early April. Juveniles follow their mother until the age of 2.5 years, at which time the mother is ready to mate again. Survival of juveniles is low, with only about one out of three reaching the age of two years. Adults, however, have high survival rate and typically live 15-25 years.
In Svalbard, some bears have small home ranges of a few hundred square kilometers where they hunt on the sea ice in the Spring. However, during the short Summer these bears must wait on land until the sea surface starts to freeze again. The western part of Spitsbergen has relatively low densities of bears most of the year, while higher densities are found along the east coast and also in the fjordland in the north. Many bears specialize in hunting near glacier fronts in the fjords in the Spring, because ringed seal tend to concentrate their lairs there.
Polar bears are powerful swimmers and are able to spend several days at a time in the water, and travel very long distances at sea. For this reason, they are often considered true marine mammals. Their favorite prey species are ice-living seals, so they spend much of their time on the sea ice. In Svalbard, they prey mainly on ringed seals, bearded seals, and harp seals. However, polar bears are opportunistic feeders and will eat almost everything edible that they encounter, including carrion. Some bears specialize on eating bird eggs in the summer and will even try to hunt sea birds on steep cliffs. Dead whales that have washed up on shore can attract large numbers of scavenging bears.
Polar bear hunting was banned in Svalbard in 1973, after a century of intensive exploitation, and their population has now recovered significantly. However, some bears are still killed each year in Svalbard in defense of people or property…encounters between bears and humans have become more common in recent years because of increased human traffic within the archipelago.
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