Polar Bear Facts


Photo:daisygilardini.com

Geographic Range

Polar bears have a circumpolar distribution. They range throughout the arctic region surrounding the North Pole. The limits of their range are determined by the ice pack of the Arctic Ocean and the landfast ice of surrounding coastal areas. Bears have been reported as far south as the southern tips of Greenland and Iceland. During the winter, polar bears will range along the southern edge of the ice pack or northern edge of ice formed off the coasts of the continents. Pregnant females will overwinter on the coastlines where denning habitat is available for bearing young. During the summer, bears will remain at the edge of the receding ice pack or on islands and coastal regions that retain landfast ice. Six different populations are recognized as: Wrangel Island and western Alaska, northern Alaska, the Canadian Arctic archipelago, Greenland, Svalbard-Franz Josef Land, and Central Siberia.

Photo:helpsavenature.com

Habitat

Polar bears are considered by many to be marine mammals. The name Ursus maritimus means maritime bear. Their preferred habitat is the pack ice of the Arctic Ocean. The ice edge and pressure ridges where fractures and refreezing occur provide the best hunting ground. Bears will travel as much as 1,000 km north and south, as the ice melts and freezes. During summer bears may remain on islands or coastlines with landfast ice, drift on ice flows, or get stranded on land where they are forced to endure warm weather.

Physical Description

The body of a polar bear is large and stocky, similar to that of a brown bear, except it lacks the shoulder hump. The head is relatively smaller than the heads of other bears and the neck is elongated. At the shoulder a polar bear can measure 1.6 m in height. Adult males weigh between 300-800 kg (660-1760 lbs) and can reach 2.5 m in length from tip of nose to tip of tail. Females are smaller, weighing 150 to 300 kg (330 to 660 lbs) and measuring 1.8 to 2 m in length. The pelage generally has a white appearance, but it can be yellowish in the summer due to oxidation or may even appear brown or gray, depending on the season and light conditions. Polar bear skin is black and the fur is actually clear, lacking in pigment. The white appearance is the result of light being refracted from the clear hair strands. The forepaws are broad and make excellent paddles while swimming. The soles of both hind and fore feet are furred for insulation and traction while walking on ice and snow. Polar bears have a plantigrade gait. Females have four functional mammae.

Photo:polarbearsinternational.org

Reproduction

Polar bears have a sequential polygynous mating system. Male and female breeding pairs remain together for a short time while females are in estrus (3 days).Mating occurs in late winter and early spring, from March to June. Delayed implantation extends gestation to 195 to 265 days. Pregnant females establish a winter den on land dug into the snow usually within 8 km of the coast in October or November. An average of 2 cubs are born in the mother’s den between November and January, litter sizes can range from 1 to 4. She remains in hibernation, nursing her cubs until April. The mortality rate for cubs is estimated to be 10-30%. The average annual rate of reproduction calculated by DeMaster and Stirling (1981) was 0.274 females per adult female.Cubs are born with their eyes closed; they have a good coat of fur and weigh about 600 grams. They will emerge from the den in spring weighing 10 to 15 kg. Mothers provide all parental care of their offspring. The cubs remain with their mother for 2 to 3 years. They will not reach sexual maturity until 5 to 6 years old.

Lifespan/Longevity

In the wild polar bears are estimated to live 25 to 30 years. Annual adult mortality is estimated to be 8 to 16%. In captivity the oldest recorded lifespan was a female that died at the Detroit Zoo in 1991 at 43 years and 10 months old.

Behavior

Polar bears are solitary. The exceptions to this are when a mother is caring for her cubs and when males and females are paired during mating. Bears may also come into competition with one another when a seal kill attracts other bears looking to scavenge. In instances where bears encounter each other, the smaller bear will tend to run away. A female with cubs, however, will charge males that are much larger to protect her young or a kill that they are feeding on. Polar bears are inactive most of the time (66.6%), either sleeping, lying, or waiting (still hunting). The rest of their time is spent traveling (walking and swimming; 29.1%), stalking prey (1.2%), or feeding (2.3%). Polar bears are excellent swimmers, they may range widely in search of food and sightings as far south as Maine, in the United States, have been documented.

Communication and Perception

Like other bear species, polar bears have a keen sense of smell and use their sensitive lips and whiskers to explore objects. They vision and hearing are not exceptionally well developed. Polar bears use a “chuffing” sound as a form of greeting.

Photo:PolarBearFacts.net

Food Habits

Polar bears are carnivores. In the summer, they may consume some vegetation but gain little nutrition from it. Their primary prey are ringed seals (Pusa hispida). They also hunt bearded seals (Erignathus barbatus), harp seals (Pagophilus groenlandicus), hooded seals (Cystophora cristata), walruses (Odobenus rosmarus), sea birds and their eggs, small mammals, fish and scavenge on carrion of seals, walruses, or whales. Bears often leave a kill after consuming only the blubber. The high caloric value of blubber relative to meat is important to bears for maintaining an insulating fat layer and storing energy for times when food is scarce. Polar bears do not store or cache unconsumed meat as other bears do.Polar bears have two hunting strategies. Still-hunting is used predominately. This involves finding a seal’s breathing hole in the ice and waiting for the seal to surface to make the kill. When a bear sees a seal basking out of the water it will use a stalking technique to get close, then make an attempt at catching it. One stalking technique is crouching and staying out of sight while creeping up on the seal. Another technique is to swim through any channels or cracks in the ice until it is close enough to catch the seal. Using this technique a bear may actually dive under the ice and surface through the breathing hole in order the surprise the seal and eliminate its escape route. Feeding usually occurs immediately after the kill has been dragged away from the water. Polar bears consume the skin and blubber first and the rest is often abandoned. Other polar bears or arctic foxes then scavenge these leftovers. After feeding, polar bears will wash themselves by licking and rinsing their fur.

 

Source :animaldiversity.org

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