Ursus maritimus
polar bear

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. (DeMaster and Stirling, 1981; Nowak, 1999)

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. (DeMaster and Stirling, 1981; Nowak, 1999; Stirling and McEwan, 1975)

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. (DeMaster and Stirling, 1981; Nowak, 1999)

In the wild polar bears are estimated to live 25 to 30 years. Annual adult mortality is estimated to be 8-16%. In captivity a female was still alive at 45 years in old at the Detroit Zoo in 1999. (DeMaster and Stirling, 1981; Nowak, 1999)

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. (DeMaster and Stirling, 1981; Stirling and McEwan, 1975; Stirling, 1974)

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. (DeMaster and Stirling, 1981)

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. (DeMaster and Stirling, 1981; Stirling and McEwan, 1975)

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. (DeMaster and Stirling, 1981; Nowak, 1999; Ramsey and Stirling, 1988; Stirling, 1974)

Humans and other polar bears are the only predators of Ursus maritimus. Male polar bears may prey on cubs if they come into contact. Females with cubs tend to avoid other bears for this reason. Historically, polar bears have been hunted by the native peoples of the arctic for fur and meat. Commercial and sport hunting of polar bears increased in the 1900s as the price of pelts reached as much as $3000. (DeMaster and Stirling, 1981; Nowak, 1999)

Polar bears are a top carnivore of the arctic. The remains of seal kills left unconsumed by bears are likely an important source of food for younger, less-experienced polar bears and for Artic foxes. (DeMaster and Stirling, 1981; Stirling and McEwan, 1975; Stirling, 1974)

Polar bears are viewed as potentially dangerous to humans. Contact between humans and bears is rare due to the large home range of individual bears and the sparse human population throughout their distribution. Two deaths resulting from polar bear encounters have been reported. (Nowak, 1999)

Polar bear materials have historically been used by native people of the arctic for fur, meat, and medicines. Hunting by those groups is still allowed in the United States, Canada, and Greenland (Denmark). Trophy and commercial hunters have taken bears for pelts that sold for $3000 in the past. (Nowak, 1999)

Polar bear populations were recently considered to be stable or growing. In 1993, the estimated world population was 21,470-28,370 bears. In 1972, the United States Marine Mammal Protection Act prohibited all hunting, except for subsistence, of polar bears in the U.S. In 1973 the United States, Russia, Norway, Canada, and Denmark came to an agreement to protect polar bear habitat, limit hunting, and cooperate on research. The IUCN lists Ursus maritimus as lower risk, but conservation dependent. The species is likely to remain healthy but may become threatened if conservation measures are not maintained and if trends in global warming continue to decrease the extent of their habitat (pack ice) and their prey base. (DeMaster and Stirling, 1981; Hilton-Taylor, 2000; Nowak, 1999)

Polar bears bred with brown bears have produced fertile hybrids (DeMaster and Stirling 1981). In fact, polar bears have been shown to be genetically more closely related to certain brown bear populations than are some brown bear populations to others. This suggests that polar bears have evolved fairly recently from a brown bear ancestor and that brown bear genetic structure is more complicated than previously thought. (DeMaster and Stirling, 1981; Talbot and Shields, 1996)