Polar bears
Polar bears, scientifically known as Ursus maritimus, are the largest bear species and the largest carnivorous land animals, predominantly found in the Arctic region. They are exceptional apex predators, primarily hunting seals, which they stalk on the sea ice, using their white fur for camouflage. Polar bears are well-adapted to their harsh environment, with thick blubber and fur providing insulation against extreme cold, and large paws that aid in swimming as well as walking on thin ice.
Typically solitary animals, polar bears have a gestation period of about eight months, giving birth to one to three cubs in snow dens. While they primarily consume marine mammals, they may also eat vegetation when on land. However, polar bears face significant threats from climate change, as the melting sea ice impacts their hunting grounds. Conservation efforts have been implemented, particularly since the population declined in the 1960s due to hunting. As of recent estimates, their populations range between 20,000 to 40,000, although some subpopulations are in decline, highlighting the ongoing challenges they face in a rapidly changing environment.
Polar bears
Polar Bear Facts
Classification:
- Kingdom: Animalia
- Subkingdom: Bilateria
- Phylum: Chordata
- Subphylum: Vertebrata
- Class: Mammalia
- Subclass: Theria
- Infraclass: Eutheria
- Order: Carnivora
- Suborder: Caniformia
- Family: Ursidae
- Genus and species:Ursus maritimus
- Geographical location: Northern marine areas of Alaska, Canada, Greenland, Norway’s Svalbard Archipelago, and Russia
- Habitat: The sea ice and adjacent land areas of the circumpolar Arctic
- Gestational period: About eight months
- Life span: Up to thirty-two years in the wild, over forty years in captivity
- Special anatomy: Fur, hide, and blubber providing effective insulation from the extreme arctic cold; white fur providing camouflage against the backdrop of ice and snow and greatly aiding in stalking seals; large paws used for paddling in water and that act like snowshoes on thin ice; pads of the feet covered with small, soft papillae that improve traction on ice; small ears and tail to reduce heat loss and a large body mass to conserve heat
Protected from cold by a thick fur coat and a layer of blubber, the polar bear hunts seals in open areas in the Arctic sea ice. A strong swimmer, the polar bear uses its large front paws as paddles. Its white fur blends in with the ice and snow as it stalks or still-hunts seals. Ringed seals are the polar bear’s primary food, but it also consumes bearded seals, and occasionally walruses, belugas, narwhals, musk oxen, and carrion (dead terrestrial and marine mammals). Although largely carnivorous, when on land the polar bear may eat grasses, kelp, berries, and lichens. Males and nonpregnant females do not make dens or hibernate, but spend the winter hunting on the sea ice.
The polar bear evolved from the terrestrial brown bear about 100,000 to 200,000 years ago. In captivity, polar bears and brown bears have interbred and produced fertile offspring. This shows a high degree of genetic relatedness. In nature, however, these two species are geographically isolated from one another and would rarely meet.
Swimming in icy water among the ice floes of the Arctic, quietly stalking a resting seal, then killing it with a crushing blow of its forepaw, the polar bear is an impressive example of an animal’s ability to adapt to and live in one of the harshest environments on earth.
Physical Characteristics of Polar Bears
Male polar bears are up to five feet high at the shoulder while on all fours and up to ten feet long. When standing on its hind legs, a male can be eleven feet tall. Adult males are generally much bigger than females: 1,100 to 1,770 pounds for males, 330 to 770 pounds for females. Like other bears, polar bears are plantigrade.
Mating takes place in late March to late May. This is the only time that the male is with the female. Other than family groups of females with their cubs, polar bears are solitary. Pregnant females dig snow or earth dens in which they will give birth to one to three cubs in late November to early January. The mother’s milk is very rich, with an average fat content of 33 percent. The cubs, which weigh 1 to 1.5 pounds at birth, grow quickly and weigh 22 to 33 pounds when they emerge from the den with their mother in late February to early May. Polar bear cubs usually leave their mother at 2.5 years of age, at which time the mother is ready to breed again. Therefore, the female usually gives birth every third year.
Conservation
By the 1960s, polar bear populations were in serious decline due to sport hunting and public support for the conservation of polar bears increased. In 1967, the five “polar bear nations” (the United States, Canada, Denmark, Norway, and the Soviet Union) limited hunting to the Inuit people. By 2001, polar bears had recovered, and there were twenty thousand to forty thousand in the world. In 2014, there were nineteen recognized subpopulations of polar bear worldwide, of which three were declining, six were stable, one was increasing, and nine had insufficient data to draw conclusions.
A 1999 study by longtime polar bear biologist Ian Stirling and his colleagues showed that polar bears at Hudson Bay were 10 percent thinner and had 10 percent fewer cubs than they did twenty years prior. In 1999, the ice on Hudson Bay melted three weeks earlier than it did twenty-five years earlier. Polar bears must wait for ice to form each fall to hunt ringed seals, their main food source. Hudson Bay polar bears fast six to eight months each year and then hunt seals intensively during the ice season. The three-week reduction of hunting time has not yet resulted in significant decline of the polar bear population, but is expected to do so if the global warming trend continues, which also threatens significant habitat loss due to the melting of sea ice.
Principal Terms
blubber: thick layer of fat under the skin
carnivorous: eating meat
geographically isolated: living in different habitats
plantigrade: walking on the entire foot, not just the toes
terrestrial: living on land
Bibliography
Atwood, Todd C., et al. "Forecasting the Relative Influence of Environmental and Anthropogenic Stressors on Polar Bears." Ecosphere 7.6 (2016): 1–22. Web. 5 Oct. 2016.
Derocher, Andrew E. Polar Bears: A Complete Guide to Their Biology and Behavior. Baltimore: John Hopkins UP, 2012. Print.
Lynch, Wayne. Bears: Monarchs of the Northern Wilderness. Seattle: The Mountaineers, 1993. Print.
Matthews, Downs. Polar Bear. San Francisco: Chronicle, 1993. Print.
Stirling, Ian. Polar Bears. Ann Arbor: U of Michigan P, 1988. Print.
"Summary of Polar Bear Population Status per 2014." Polar Bear Specialist Group. IUCN/SSC PBSG, 24 Jan. 2015. Web. 4 Oct. 2016.
Stirling, Ian, Nicholas J. Lunn, and John Iacozza. “Long Term Trends in Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climate Change.” Arctic 52.3 (1999): 294–306. Print.