Mammal Species of the World
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- Original description: Phipps, C.J., 1774. A voyage towards the North Pole, p., 185. J. Nourse, London, 253 pp.
Description of Ursus maritimus
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.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); arctic ocean (Native )
Other Geographic Terms: holarctic
- DeMaster, D., I. Stirling. 1981. *Ursus maritimus*. Mammalian Species, 145: 1-7.
- Nowak, R. 1999. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.
The species is found in Canada (Manitoba, Newfoundland, Labrador, Nunavut, Northwest Territories, Quebec, Yukon Territory, Ontario), Greenland/Denmark, Norway (including Svalbard), Russian Federation (North European Russia, Siberia, Chukotka, Sakha (Yakutia), Krasnoyarsk), United States (Alaska). Also, vagrants occasionally reach Iceland.
- UNESCO-IOC Register of Marine Organisms
U.S.A. (AK), Canada, Russia, Denmark (Greenland), Norway
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.
Range mass: 150 to 800 kg.
Range length: 180 to 250 cm.
Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Size in North America
Range: 2,300-2,600 mm males; 1,900-2,100 mm females
Range: "400-600 kg males; 175-300 kg females (350-500 kg when pregnant) "
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.
Range elevation: 0 (low) m.
Average elevation: 0 m.
Habitat Regions: polar ; terrestrial ; saltwater or marine
Terrestrial Biomes: tundra ; icecap
Aquatic Biomes: coastal
- Stirling, I., E. McEwan. 1975. The caloric value of whole ringed seals (*Phoca hispida*) in relation to polar bear (*Ursus maritimus*) ecology and hunting behavior. Canadian Journal of Zoology, 53: 1021-1027.
Habitat and Ecology
Seasonally, in the summer open water season in the Canadian arctic islands and Svalbard, and in recent years during the fall in northern Alaska and Russian Chukotka, polar bears may be found on land in higher densities.
Breeding occurs in March to May, implantation is delayed until autumn, and birth is generally thought to occur from late November to mid-January. Although some cubs are born in earth dens, most births occur in snow dens that may be occupied between 5-6 months during the maternal event. In Alaska the maternal dens are located on the offshore sea ice. Only pregnant female polar bears den for this protracted period of time, during which time they rely on fat stores for energy and sustenance. The average litter size is less than two. Cubs are dependent upon mothers until after the start of their third year of life. Age of first reproduction is normally 5-6 years for females. These factors contribute to the low reproductive potential for the species.
Water temperature and chemistry ranges based on 10 samples.
Depth range (m): 0 - 0
Temperature range (°C): 0.297 - 0.745
Nitrate (umol/L): 0.703 - 2.388
Salinity (PPS): 32.124 - 32.916
Oxygen (ml/l): 7.926 - 8.105
Phosphate (umol/l): 0.529 - 0.576
Silicate (umol/l): 1.929 - 4.631
Temperature range (°C): 0.297 - 0.745
Nitrate (umol/L): 0.703 - 2.388
Salinity (PPS): 32.124 - 32.916
Oxygen (ml/l): 7.926 - 8.105
Phosphate (umol/l): 0.529 - 0.576
Silicate (umol/l): 1.929 - 4.631
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
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.
Animal Foods: birds; mammals; fish; eggs; carrion
Plant Foods: leaves
Primary Diet: carnivore (Eats terrestrial vertebrates)
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.
Ecosystem Impact: keystone species
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.
Anti-predator Adaptations: cryptic
This list may not be complete but is based on published studies.
Known prey organisms
Based on studies in:
Norway: Spitsbergen (Coastal)
This list may not be complete but is based on published studies.
- Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
- V. S. Summerhayes and C. S. Elton, Contributions to the ecology of Spitsbergen and Bear Island, J. Ecol. 11:214-286, from p. 232 (1923).
Life History and Behavior
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.
Communication Channels: tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
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.
Status: wild: 25 to 30 years.
Status: wild: 30.0 years.
Status: captivity: 38.2 years.
Status: wild: 25.0 years.
Lifespan, longevity, and ageing
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 System: polygynous
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.
Breeding interval: Females breed yearly.
Breeding season: Breeding occurs from March to June.
Range number of offspring: 1 to 4.
Average number of offspring: 2.
Range gestation period: 195 to 265 days.
Range weaning age: 24 to 36 months.
Range age at sexual or reproductive maturity (female): 3.5 (low) years.
Average age at sexual or reproductive maturity (female): 5-6 years.
Range age at sexual or reproductive maturity (male): 3.5 (low) years.
Average age at sexual or reproductive maturity (male): 5-6 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous ; delayed implantation
Average birth mass: 665 g.
Average number of offspring: 2.
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.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); extended period of juvenile learning
- DeMaster, D., I. Stirling. 1981. *Ursus maritimus*. Mammalian Species, 145: 1-7.
- Nowak, R. 1999. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.
- Ramsey, M., I. Stirling. 1988. Reproductive biology and ecology of female polar bears (*Ursus maritimus*). Journal of Zoology, 214: 601-634.
- Stirling, I., E. McEwan. 1975. The caloric value of whole ringed seals (*Phoca hispida*) in relation to polar bear (*Ursus maritimus*) ecology and hunting behavior. Canadian Journal of Zoology, 53: 1021-1027.
Evolution and Systematics
Hair of polar bear insulates it from cold because it has low emissivity in infrared.
"Polar bears are masters at conserving energy. During their eight-month fast, breeding females can lose as much as 45 percent of their weight. So heat retention is important, to avoid spending too much energy to keep warm. The bears' fur is dense, made of clear hairs that scatter light, creating a white effect. Underneath the fur lies black skin that absorbs the sun's rays…polar bears are nearly invisible in the far infrared, the frequency range in which bodies radiate heat. Researchers from Berkeley's Department of Mechanical Engineering, led by professors Boris Rubinsky and Ralph Greif, found that the conventional explanation, that the bears are so well-insulated that their surfaces are the same temperature as the snow, is correct but incomplete: the hair's emissivity in the infrared is also nearly equal to that of snow and that this low emissivity could help to insulate the bears by lowering the amount of infrared heat that the bears radiate away." (Courtesy of the Biomimicry Guild)
Learn more about this functional adaptation.
- Preciado JA; Rubinsky B; Otten D; Nelson B; Martin MC; Greif R. 2002. Radiative properties of polar bear hair. Proceedings of the ASME International Mechanical Engineering Congress and Exposition. BED-53: 1-2.
The paws of polar bears grip ice well due to the rough surface of their pads.
"A polar bear spends the winter living on sea ice—ice formed when the ocean freezes. But the bear has no trouble keeping its footing on slippery ground. Its paws are perfect for getting around on a slick, cold surface. Rough pads give it a nonslip grip, and thick fur between the pads keeps the bear’s feet warm. It uses the sharp, curved claws on its front paws like hooks to climb onto the ice from the water. Polar bears' claws also help them dig in the ice when they hunt seals." (Kranking 2001)
Learn more about this functional adaptation.
- Kathy Kranking. 2001. Bear Necessities: How Polar Bears Survive the Deep Freeze. National Geographic Kids Magazine [Internet], Accessed 9/24/2007.
Molecular Biology and Genetics
Barcode data: Ursus maritimus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
-- end --
Download FASTA File
Statistics of barcoding coverage: Ursus maritimus
Public Records: 29
Specimens with Barcodes: 32
Species With Barcodes: 1
Polar bear populations were recently considered to be stable or growing in some areas. In 1993, the estimated world population was 21,470 to 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. Polar bear populations are currently threatened by trends in global warming, which continues to decrease the extent of their habitat (pack ice) and their prey base. In 2008 the U.S. Fish and Wildlife Service listed polar bears as threatened. The IUCN lists Ursus maritimus as vulnerable.
US Federal List: threatened
CITES: appendix ii
IUCN Red List of Threatened Species: vulnerable
- Hilton-Taylor, C. 2000. "The 2000 IUCN Red List of Threatened Species" (On-line). Accessed Dec 5, 2001 at http://www.redlist.org/search/details.php?species=22823.
IUCN Red List Assessment
Red List Category
Red List Criteria
Polar bears rely almost entirely on the marine sea ice environment for their survival so that large scale changes in their habitat will impact the population (Derocher et al. 2004). Global climate change posses a substantial threat to the habitat of polar bears. Recent modeling of the trends for sea ice extent, thickness and timing of coverage predicts dramatic reductions in sea ice coverage over the next 50-100 years (Hassol 2004). Sea ice has declined considerably over the past half century. Additional declines of roughly 10-50% of annual sea ice are predicted by 2100. The summer sea ice is projected to decrease by 50-100% during the same period. In addition the quality of the remaining ice will decline. This change may also have a negative effect on the population size (Derocher et al. 2004). The effects of sea ice change are likely to show large differences and variability by geographic location and periods of time, although the long term trends clearly reveal substantial global reductions of the extent of ice coverage in the Arctic and the annual time frames when ice is present.
While all bear species have shown adaptability in coping with their surroundings and environment, polar bears are highly specialized for life in the Arctic marine environment. Polar bears exhibit low reproductive rates with long generational spans. These factors make facultative adaptation by polar bears to significantly reduced ice coverage scenarios unlikely. Polar bears did adapt to warmer climate periods of the past. Due to their long generation time and the current greater speed of global warming, it seems unlikely that polar bear will be able to adapt to the current warming trend in the Arctic. If climatic trends continue polar bears may become extirpated from most of their range within 100 years.
There is little doubt that polar bears will have a lesser AOO, EOO and habitat quality in the future. However, no direct relation exists between these measures and the abundance of polar bears. While some have speculated that polar bears might become extinct within 100 years from now, which would indicate a population decrease of >50% in 45 years based on a precautionary approach due to data uncertainty. A more realistic evaluation of the risk involved in the assessment makes it fair to suspect population reduction of >30%.
Other population stress factors that may also operate to impact recruitment or survival include toxic contaminants, shipping, recreational viewing, oil and gas exploration and development. In addition to this comes a potential risk of over-harvest due to increased quotas, excessive quotas or no quotas in Canada and Greenland and poaching in Russia.
This assessment was reviewed by all the participants at the 14th Working Meeting of the IUCN SSC Polar Bear Specialist Group held in Seattle, Washington, USA during June 20-24, 2005.
- 2006Vulnerable(IUCN 2006)
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
- 1982Vulnerable(Thornback and Jenkins 1982)
Date Listed: 05/15/2008
Lead Region: Alaska Region (Region 7)
Where Listed: Entire
Population location: Entire
Listing status: T
For most current information and documents related to the conservation status and management of Ursus maritimus , see its USFWS Species Profile
The increasing changes in the sea ice that affect access to prey will have a negative effect on the bears. With less food, polar bears will fail to reproduce more often and give birth to smaller young that have higher mortality rates.
Polar bears may be forced on shore for extended periods and rely on fat reserves deposited the previous spring for survival. In such a situation they will be increasingly vulnerable to hunting if not regulated. If these periods become excessively long, mortality will increase. Sea ice is also used for access to den areas and if ice patterns change, existing den areas may be unreachable. Warmer temperatures and higher winds may reduce ice thickness and increase ice drift. Because polar bears must walk against the moving ice (like walking the wrong way on an escalator) increased ice movements will increase energy use and reduce growth and reproduction.
Polar bears are the apex predator and are exposed to high levels of pollutants that are magnified with each step higher in the food web. A key characteristic of the pollutants is that they tend to persist in the environment and resist degradation. Many of the organochlorine pollutants are lipophilic or "fat loving" and bond tightly to fat molecules. Polar bears are particularly vulnerable to organochlorines because they eat a fat rich diet. Ringed, bearded, and harp seals comprise the main food of polar bears and the blubber layer is preferentially eaten by the bears and subsequently, the intake of pollutants is high.
Certain areas of the Arctic, such as northeastern Greenland, the Barents Sea and the Kara Sea, have higher levels of pollutants. Based on studies in other species, it is reasonable to believe that the pollutant load of polar bears in some areas are negatively affecting the immune system, hormone regulation, growth patterns, reproduction, and survival rates of polar bears. Recent studies have suggested that the immune system is weaker in polar bears with higher levels of PCBs. A major concern with polar bears pertains to their reproductive system. There are suggestions that species with delayed implantation are more vulnerable to the effects of pollution through endocrine (hormone) disruption. Further, female polar bears are food deprived during gestation their pollution loads increase because as they use their fat stores, where pollutants are stored, for energy. Because the cubs are nursed on fat rich milk, the cubs are exposed to very high pollution loads from their mother.
Oil development in the Arctic poses a wide range of threats to polar bears ranging from oil spills to increased human-bear interactions. It is probable that an oil spill in sea ice habitat would result in oil being concentrated in leads and between ice floes resulting in both polar bears and their main prey (ringed and bearded seals) being directly exposed to oil. Another concern is that seals covered in oil may be a major source of oil to polar bears. Other studies suggest that polar bears are sensitive to disturbance at maternity den sites. Disturbance could occur both when a pregnant female is selecting a den site and during the winter-spring after the cubs are born. If exploration or development occurred sufficiently close to a den, the mother may abandon the den prematurely or abandon her offspring.
Over-harvest is an ongoing concern for some polar bear populations: particularly in areas where there is no information on population size (e.g., Québec, east Greenland, and the Chukchi Sea) and no quotas. It is important that population estimates and projections are based on substantiated scientific data. An additional concern is that population inventory programs occur relatively infrequently in some areas so if the harvest rate is above the sustainable level, the population may be reduced before the next inventory is made. Recent development of co-management agreements and greater involvement of local people and hunters is improving the management of polar bears in some areas.
The principle use of polar bears in the circumpolar arctic is for subsistence purposes. These include consumption of meat; use of hides in the construction of clothing such as mittens, boots (mukluks), fur ruffs for parkas, and fur pants; and small scale creation of items of handicraft. The US (Alaska), Canada and Greenland manage a subsistence harvest. Norway and Russia prohibit harvest of polar bears. In Russia during the early 1990s an unsanctioned harvest of polar bears began following dissolution of the Soviet Union. Levels of harvest are not quantified.
In Canada a portion of the annual harvest is by sports hunters employing native guides utilizing traditional harvest methods such as dog-teams. The harvest levels are regulated and based on principles of sustainable resource management. Greenland introduced a quota system which came into force on January 1, 2006 and plans to start sport hunting in the near future.
A small number of orphaned cubs are placed in zoos and public display facilities.
Research activities: live capture and release of polar bears.
Public viewing and photography are another form of utilization and occur locally at Churchill, Canada, and other remote areas, at specific locals in Svalbard, Norway, and to a limited extent in location on the north coast of Alaska.
Coordinated research is ongoing, management actions reviewed for consistency, and legislation to effect bilateral management for internationally shared populations such as between the US-Russia is being pursued. Additional cooperative management agreements between Canada and Greenland are desirable and currently being developed.
Additional details of the Global Status and Management of Polar Bears are contained in the IUCN "Status Survey and Conservation Action Plan: Bears" (Servheen et al. 1999).
It is listed on CITES Appendix II.
Relevance to Humans and Ecosystems
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.
Negative Impacts: injures humans (bites or stings)
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.
Positive Impacts: food ; ecotourism ; source of medicine or drug ; research and education
The polar bear (Ursus maritimus) is a carnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is a large bear, approximately the same size as the omnivorous Kodiak bear (Ursus arctos middendorffi). A boar (adult male) weighs around 350–700 kg (770–1,540 lb), while a sow (adult female) is about half that size. Although it is the sister species of the brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet. Although most polar bears are born on land, they spend most of their time at sea. Their scientific name means "maritime bear", and derives from this fact. Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present.
The polar bear is classified as a vulnerable species, with eight of the nineteen polar bear subpopulations in decline. For decades, large scale hunting raised international concern for the future of the species but populations rebounded after controls and quotas began to take effect. For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and polar bears remain important in their cultures.
- 1 Naming and etymology
- 2 Taxonomy and evolution
- 3 Population and distribution
- 4 Habitat
- 5 Biology and behavior
- 6 Dietary flexibility
- 7 Hunting
- 8 Conservation status, efforts and controversies
- 9 In culture
- 10 See also
- 11 Notes
- 12 References
- 13 External links
Naming and etymology
Constantine John Phipps was the first to describe the polar bear as a distinct species in 1774. He chose the scientific name Ursus maritimus, the Latin for 'maritime bear', due to the animal's native habitat. The Inuit refer to the animal as nanook (transliterated as nanuq in the Inupiat language). The Yupik also refer to the bear as nanuuk in Siberian Yupik. The bear is umka in the Chukchi language. In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, the white bear), though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear"). In French, the polar bear is referred to as ours blanc ("white bear") or ours polaire ("polar bear"). In the Norwegian-administered Svalbard archipelago, the polar bear is referred to as Isbjørn ("ice bear").
The polar bear was previously considered to be in its own genus, Thalarctos. However, evidence of hybrids between polar bears and brown bears, and of the recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed.
Taxonomy and evolution
The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. The Ursinae subfamily originated approximately 4.2 million years ago. The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004. Fossils show that between ten to twenty thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene or from the eastern part of Siberia, (from Kamchatka and the Kolym Peninsula).
The evidence from DNA analysis is more complex. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago. Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears, meaning that the polar bear would not be a true species according to some species concepts. The mtDNA of Irish brown bears is particularly close to polar bears. A comparison of the nuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603,000 years ago, although the latest research is based on analysis of the complete genomes (rather than just the mitochondria or partial nuclear genomes) of polar, brown and black bears, and establishes the divergence of polar and brown bears at 4–5 million years ago.
However, the two species have mated intermittently for all that time, most likely coming into contact with each other during warming periods, when polar bears were driven onto land and brown bears migrated northward. Most brown bears have about 2 percent genetic material from polar bears, but one population residing in the Alexander Archipelago has between 5 percent and 10 percent polar bear genes, indicating more frequent and recent mating. Polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids, rather than indicating that they have only recently diverged, the new evidence suggests more frequent mating has continued over a longer period of time, and thus the two bears remain genetically similar. However, because neither species can survive long in the other's ecological niche, and because they have different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.
When the polar bear was originally documented, two subspecies were identified: Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter Simon Pallas in 1776. This distinction has since been invalidated. One fossil subspecies has been identified. Ursus maritimus tyrannus — descended from Ursus arctos — became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.
Population and distribution
The polar bear is found in the Arctic Circle and adjacent land masses as far south as Newfoundland Island. Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore. While they are rare north of 88°, there is evidence that they range all the way across the Arctic, and as far south as James Bay in Canada. Their southernmost range is near the boundary between the subarctic and humid continental climate zones. They can occasionally drift widely with the sea ice, and there have been anecdotal sightings as far south as Berlevåg on the Norwegian mainland and the Kuril Islands in the Sea of Okhotsk. It is difficult to estimate a global population of polar bears as much of the range has been poorly studied; however, biologists use a working estimate of about 20,000 to 25,000 polar bears worldwide.
There are 19 generally recognized, discrete subpopulations. The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated. The thirteen North American subpopulations range from the Beaufort Sea south to Hudson Bay and east to Baffin Bay in western Greenland and account for about 70% of the global population. The Eurasian population is broken up into the eastern Greenland, Barents Sea, Kara Sea, Laptev Sea, and Chukchi Sea subpopulations, though there is considerable uncertainty about the structure of these populations due to limited mark and recapture data.
The range includes the territory of five nations: Denmark (Greenland), Norway (Svalbard), Russia, the United States (Alaska) and Canada. These five nations are the signatories of the International Agreement on the Conservation of Polar Bears, which mandates cooperation on research and conservations efforts throughout the polar bear's range.
Modern methods of tracking polar bear populations have been implemented only since the mid-1980s, and are expensive to perform consistently over a large area. The most accurate counts require flying a helicopter in the Arctic climate to find polar bears, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear. In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. Scientists have responded by noting that hungry bears may be congregating around human settlements, leading to the illusion that populations are higher than they actually are. The Polar Bear Specialist Group of the IUCN takes the position that "estimates of subpopulation size or sustainable harvest levels should not be made solely on the basis of traditional ecological knowledge without supporting scientific studies."
The polar bear is a marine mammal because it spends many months of the year at sea. However, it is the only living "marine mammal" with powerful, large limbs and feet that allow them to cover miles on foot and run on land. Its preferred habitat is the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic. The polar bear tends to frequent areas where sea ice meets water, such as polynyas and leads (temporary stretches of open water in Arctic ice), to hunt the seals that make up most of its diet. Polar bears are therefore found primarily along the perimeter of the polar ice pack, rather than in the Polar Basin close to the North Pole where the density of seals is low.
Annual ice contains areas of water that appear and disappear throughout the year as the weather changes. Seals migrate in response to these changes, and polar bears must follow their prey. In Hudson Bay, James Bay, and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up. In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.
Biology and behavior
The only other bear of a similar size to the polar bear is the Kodiak bear, which is a subspecies of brown bear. Adult male polar bears weigh 350–700 kg (770–1,540 lb) and measure 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length. The Guinness Book of World Records listed the average male as having a body mass of 385 to 410 kg (849 to 904 lb) and a shoulder height of 133 cm (4 ft 4 in), slightly smaller than the average cited for male Kodiak bears. Around the Beaufort Sea, however, mature males reportedly average 450 kg (1,000 lb). Adult females are roughly half the size of males and normally weigh 150–250 kg (330–550 lb), measuring 1.8–2.4 metres (5 ft 11 in–7 ft 10 in) in length. Elsewhere, a slightly larger estimated average weight of 260 kg (570 lb) was claimed for adult females. When pregnant, however, females can weigh as much as 500 kg (1,100 lb). The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds such as elephant seals. The largest polar bear on record, reportedly weighing 1,002 kg (2,209 lb), was a male shot at Kotzebue Sound in northwestern Alaska in 1960. This specimen, when mounted, stood 3.39 m (11 ft 1 in) tall on its hindlegs. The shoulder height of an adult polar bear is 122 to 160 cm (4 ft 0 in to 5 ft 3 in). While all bears are short-tailed, the polar bear's tail is relatively the shortest amongst living bears, ranging from 7 to 13 cm (2.8 to 5.1 in) in length.
Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose. As predicted by Allen's rule for a northerly animal, the legs are stocky and the ears and tail are small. However, the feet are very large to distribute load when walking on snow or thin ice and to provide propulsion when swimming; they may measure 30 cm (12 in) across in an adult. The pads of the paws are covered with small, soft papillae (dermal bumps) which provide traction on the ice. The polar bear's claws are short and stocky compared to those of the brown bear, perhaps to serve the former's need to grip heavy prey and ice. The claws are deeply scooped on the underside to assist in digging in the ice of the natural habitat. Research of injury patterns in polar bear forelimbs found injuries to the right forelimb to be more frequent than those to the left, suggesting, perhaps, right-handedness. Unlike the brown bear, polar bears in captivity are rarely overweight or particularly large, possibly as a reaction to the warm conditions of most zoos.
The 42 teeth of a polar bear reflect its highly carnivorous diet. The cheek teeth are smaller and more jagged than in the brown bear, and the canines are larger and sharper. The dental formula is 220.127.116.11
Polar bears are superbly insulated by up to 10 cm (4 in) of blubber, their hide and their fur; they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography. Polar bear fur consists of a layer of dense underfur and an outer layer of guard hairs, which appear white to tan but are actually transparent. The guard hair is 5–15 cm (2–6 in) over most of the body. Polar bears gradually moult from May to August, but, unlike other Arctic mammals, they do not shed their coat for a darker shade to camouflage themselves in the summer conditions. The hollow guard hairs of a polar bear coat were once thought to act as fiber-optic tubes to conduct light to its black skin, where it could be absorbed; however, this theory was disproven by recent studies.
The white coat usually yellows with age. When kept in captivity in warm, humid conditions, the fur may turn a pale shade of green due to algae growing inside the guard hairs. Males have significantly longer hairs on their forelegs, which increase in length until the bear reaches 14 years of age. The male's ornamental foreleg hair is thought to attract females, serving a similar function to the lion's mane.
The polar bear has an extremely well developed sense of smell, being able to detect seals nearly 1.6 km (1 mi) away and buried under 1 m (3 ft) of snow. Its hearing is about as acute as that of a human, and its vision is also good at long distances.
The polar bear is an excellent swimmer and often will swim for days. One bear swam continuously for 9 days in the frigid Bering Sea for 400 mi (687 km) to reach ice far from land. She then traveled another 1,100 mi (1,800 km)  With its body fat providing buoyancy, the bear swims in a dog paddle fashion using its large forepaws for propulsion. Polar bears can swim 10 km/h (6 mph). When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 5.6 km/h (3.5 mph). When sprinting, they can reach up to 40 km/h (25 mph).
Hunting and diet
The polar bear is the most carnivorous member of the bear family, and throughout most of its range, its diet primarily consists of ringed (Pusa hispida) and bearded seals (Erignathus barbatus). The Arctic is home to millions of seals, which become prey when they surface in holes in the ice in order to breathe, or when they haul out on the ice to rest. Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water.
The polar bear's most common hunting method is called still-hunting: The bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear. The bear may lay in wait for several hours. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear kills the seal by biting its head to crush its skull. The polar bear also hunts by stalking seals resting on the ice: Upon spotting a seal, it walks to within 90 m (100 yd), and then crouches. If the seal does not notice, the bear creeps to within 9 to 12 m (30 to 40 ft) of the seal and then suddenly rushes forth to attack. A third hunting method is to raid the birth lairs that female seals create in the snow.
A widespread legend tells that polar bears cover their black noses with their paws when hunting. This behavior, if it happens, is rare – although the story exists in native oral history and in accounts by early Arctic explorers, there is no record of an eyewitness account of the behavior in recent decades.
Mature bears tend to eat only the calorie-rich skin and blubber of the seal, which are highly digestible, whereas younger bears consume the protein-rich red meat. Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs. For subadult bears which are independent of their mother but have not yet gained enough experience and body size to successfully hunt seals, scavenging the carcasses from other bears' kills is an important source of nutrition. Subadults may also be forced to accept a half-eaten carcass if they kill a seal but cannot defend it from larger polar bears. After feeding, polar bears wash themselves with water or snow.
The polar bear is perhaps unequaled by any other living land predator in its enormous physical power. However, its primary prey species, the ringed seal, is much smaller than itself, and many of the seals hunted are pups rather than adults. Ringed seals are born weighing 5.4 kg (12 lb) and grown to an estimated average weight of only 60 kg (130 lb). They also in places prey heavily upon the harp seal (Pusa groenlandica) or the harbor seal. The bearded seal, on the other hand, can be nearly the same size as the bear itself, averaging 270 kg (600 lb). Adult male bearded seals, at 350 to 500 kg (770 to 1,100 lb) are believed to be too large for a female bear to overtake, and so are potential prey only for mature male bears. Enormously powerful large males also occasionally attempt to hunt and kill even larger prey items. It can kill an adult walrus (Odobenus rosmarus), although this is rarely attempted. At up to 2,000 kg (4,400 lb) and a typical adult mass range of 600 to 1,500 kg (1,300 to 3,300 lb), a walrus can be more than twice the bear's weight, and has up to 1-metre (3 ft)-long ivory tusks that can be used as formidable weapons. Most attacks on walruses occur when the bear charges a group and either targets the slower moving walruses, usually either young or infirm ones, or a walrus that is injured in the rush of walruses trying to escape. They will also attack even adult walruses when their diving holes have frozen over or intercept them before they can get back to the diving hole in the ice. Yet, polar bears very seldom attack full-grown adult walruses, with the largest male walrus probably invulnerable unless otherwise injured or incapacitated. Since an attack on a walrus tends to be an extremely protracted and exhausting venture, bears have been known to back down from the attack after making the initial injury to the walrus. Polar bears have also been seen to prey on beluga whales (Delphinapterus leucas) and narwhals (Monodon monoceros), by swiping at them at breathing holes. The whales are of similar size to the walrus and nearly as difficult for the bear to subdue. Most terrestrial animals in the Arctic can outrun the polar bear on land as polar bears overheat quickly, and most marine animals the bear encounters can outswim it. In some areas, the polar bear's diet is supplemented by walrus calves and by the carcasses of dead adult walruses or whales, whose blubber is readily devoured even when rotten. Polar bears sometimes like to go fishing where they swim underwater to catch fish like the arctic charr or the Fourhorn sculpin.
With the exception of pregnant females, polar bears are active year-round, although they have a vestigial hibernation induction trigger in their blood. Unlike brown and black bears, polar bears are capable of fasting for up to several months during late summer and early fall, when they cannot hunt for seals because the sea is unfrozen. When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time. Being both curious animals and scavengers, polar bears investigate and consume garbage where they come into contact with humans. Polar bears may attempt to consume almost anything they can find, including hazardous substances such as styrofoam, plastic, car batteries, ethylene glycol, hydraulic fluid, and motor oil. The dump in Churchill, Manitoba was closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba.
Although seal predation is the primary and an indispensable way of life for most polar bears, when alternatives are present they are quite flexible. Polar bears will consume a wide variety of other wild foods, including muskox (Ovibos moschatus), reindeer (Rangifer tarandus),. birds, eggs, rodents, crabs, other crustaceans and other polar bears. They may also eat plants,. including berries, roots, and kelp, however none of these are a significant part of their diet, except that beachcast marine mammal carcasses are an exception. When stalking land animals, such as muskox, reindeer. and even willow ptarmigan (Lagopus lagopus), polar bears appear to make use of vegetative cover and wind direction to bring them as close to their prey as possible before attacking. Polar bears have been observed to hunt the small Svalbard reindeer (R. t. platyrhynchus), which weigh only 40 to 60 kg (90 to 130 lb) as adults, as well as the Barren-ground caribou (R. t. groenlandicus), which is about twice as heavy as that. Adult muskox, which can weigh 450 kg (1,000 lb) or more, are a more formidable quarry. Although ungulates are not typical prey, the killing of one during the summer months can greatly increase the odds of survival during that lean period. Like the brown bear, most ungulate prey of polar bears is likely to be young, sickly or injured specimens rather than healthy adults. The polar bear's biology is specialized to require large amounts of fat from marine mammals, and it cannot derive sufficient caloric intake from terrestrial food.
In their southern range, especially near Hudson Bay and James Bay Canada polar bears live all summer without sea ice. Here their food ecology shows their dietary flexibility. They still manage to consume some seals, but they are food-deprived in summer as only marine mammal carcasses are an important alternative without sea ice, especially carcasses of the bowhead whale. These alternatives may reduce the rate of weight loss of bears when on land. One scientist found that 71% of the Hudson Bay bears had fed on seaweed (marine algae) and that about half were feeding on birds  like sea ducks, especially the oldsquaw (53%), common eider, long-tailed duck or dovekieby swimming underwater to catch them. They were also diving to feed on blue mussels and other underwater food sources like the green sea urchin. 24% had eaten moss recently, 19% had consumed grass, 34% had eaten black crowberry and about half had consumed willows. This study illustrates the polar bear's dietary flexibility but it does not represent its life history elsewhere. Most polar bears elsewhere will never have access to these alternatives, except for the marine mammal carcasses that are important wherever they occur.
Unlike grizzly bears, polar bears are not territorial. Although stereotyped as being voraciously aggressive, they are normally cautious in confrontations, and often choose to escape rather than fight. Satiated polar bears rarely attack humans unless severely provoked. However, due to their lack of prior human interaction, hungry polar bears are extremely unpredictable, fearless towards people and are known to kill and sometimes eat humans. Many attacks by brown bears are the result of surprising the animal, which is not the case with the polar bear. Polar bears are stealth hunters, and the victim is often unaware of the bear's presence until the attack is underway. Whereas brown bears often maul a person and then leave, polar bear attacks are more likely to be predatory and are almost always fatal. However, due to the very small human population around the Arctic, such attacks are rare. Michio Hoshino, a Japanese wildlife photographer, was once pursued briefly by a hungry male polar bear in northern Alaska. According to Hoshino, the bear started running but Hoshino made it to his truck. The bear was able to reach the truck and tore one of the doors off the truck before Hoshino was able to drive off.
In general, adult polar bears live solitary lives. Yet, they have often been seen playing together for hours at a time and even sleeping in an embrace, and polar bear zoologist Nikita Ovsianikov has described adult males as having "well-developed friendships." Cubs are especially playful as well. Among young males in particular, play-fighting may be a means of practicing for serious competition during mating seasons later in life. Polar bears have a wide range of vocalisations, including bellows, roars, growls, chuffs and purrs.
In 1992, a photographer near Churchill took a now widely circulated set of photographs of a polar bear playing with a Canadian Eskimo Dog (Canis lupus familiaris) a tenth of its size. The pair wrestled harmlessly together each afternoon for ten days in a row for no apparent reason, although the bear may have been trying to demonstrate its friendliness in the hope of sharing the kennel's food. This kind of social interaction is uncommon; it is far more typical for polar bears to behave aggressively towards dogs, however dogs are the bears closest relative as in the bear dog.
Reproduction and lifecycle
Courtship and mating take place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas. A male may follow the tracks of a breeding female for 100 km (60 mi) or more, and after finding her engage in intense fighting with other males over mating rights, fights which often result in scars and broken teeth. Polar bears have a generally polygynous mating system; recent genetic testing of mothers and cubs, however, has uncovered cases of litters in which cubs have different fathers. Partners stay together and mate repeatedly for an entire week; the mating ritual induces ovulation in the female.
After mating, the fertilized egg remains in a suspended state until August or September. During these four months, the pregnant female eats prodigious amounts of food, gaining at least 200 kg (440 lb) and often more than doubling her body weight.
Maternity denning and early life
When the ice floes break up in the fall, ending the possibility of hunting, each pregnant female digs a maternity den consisting of a narrow entrance tunnel leading to one to three chambers. Most maternity dens are in snowdrifts, but may also be made underground in permafrost if it is not sufficiently cold yet for snow. In most subpopulations, maternity dens are situated on land a few kilometers from the coast, and the individuals in a subpopulation tend to reuse the same denning areas each year. The polar bears that do not den on land make their dens on the sea ice. In the den, she enters a dormant state similar to hibernation. This hibernation-like state does not consist of continuous sleeping; however, the bear's heart rate slows from 46 to 27 beats per minute. Her body temperature does not decrease during this period as it would for a typical mammal in hibernation.
Between November and February, cubs are born blind, covered with a light down fur, and weighing less than 0.9 kg (2.0 lb), but in captivity they might be delivered in the earlier months. The earliest recorded birth of polar bears in captivity was on 11 October 2011 in the Toronto Zoo. On average, each litter has two cubs. The family remains in the den until mid-February to mid-April, with the mother maintaining her fast while nursing her cubs on a fat-rich milk. By the time the mother breaks open the entrance to the den, her cubs weigh about 10 to 15 kilograms (22 to 33 lb). For about 12 to 15 days, the family spends time outside the den while remaining in its vicinity, the mother grazing on vegetation while the cubs become used to walking and playing. Then they begin the long walk from the denning area to the sea ice, where the mother can once again catch seals. Depending on the timing of ice-floe breakup in the fall, she may have fasted for up to eight months.
Cubs may fall prey to wolvesor to starvation. Female polar bears are noted for both their affection towards their offspring, and their valiance in protecting them. One case of adoption of a wild cub has been confirmed by genetic testing. Adult male bears occasionally kill and eat polar bear cubs, for reasons that are unclear. As of 2006, in Alaska, 42% of cubs now reach 12 months of age, down from 65% 15 years ago. In most areas, cubs are weaned at two and a half years of age, when the mother chases them away or abandons them. The western coast of Hudson Bay is unusual in that its female polar bears sometimes wean their cubs at only one and a half years. This was the case for 40% of cubs there in the early 1980s; however by the 1990s, fewer than 20% of cubs were weaned this young. After the mother leaves, sibling cubs sometimes travel and share food together for weeks or months.
Females begin to breed at the age of four years in most areas, and five years in the Beaufort Sea area. Males usually reach sexual maturity at six years; however, as competition for females is fierce, many do not breed until the age of eight or ten. A study in Hudson Bay indicated that both the reproductive success and the maternal weight of females peaked in their mid-teens.
Polar bears appear to be less affected by infectious diseases and parasites than most terrestrial mammals. Polar bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism, although infections are usually not fatal. Only one case of a polar bear with rabies has been documented, even though polar bears frequently interact with Arctic foxes, which often carry rabies. Bacterial Leptospirosis and Morbillivirus have been recorded. Polar bears sometimes have problems with various skin diseases which may be caused by mites or other parasites.
Polar bears rarely live beyond 25 years. The oldest wild bears on record died at age 32, whereas the oldest captive was a female who died in 1991, age 43. The causes of death in wild adult polar bears are poorly understood, as carcasses are rarely found in the species's frigid habitat. In the wild, old polar bears eventually become too weak to catch food, and gradually starve to death. Polar bears injured in fights or accidents may either die from their injuries or become unable to hunt effectively, leading to starvation.
The polar bear is the apex predator within its range. Several animal species, particularly Arctic Foxes (Vulpes lagopus) and Glaucous Gulls (Larus hyperboreus), routinely scavenge polar bear kills.
The relationship between ringed seals and polar bears is so close that the abundance of ringed seals in some areas appears to regulate the density of polar bears, while polar bear predation in turn regulates density and reproductive success of ringed seals. The evolutionary pressure of polar bear predation on seals probably accounts for some significant differences between Arctic and Antarctic seals. Compared to the Antarctic, where there is no major surface predator, Arctic seals use more breathing holes per individual, appear more restless when hauled out on the ice, and rarely defecate on the ice. The baby fur of most Arctic seal species is white, presumably to provide camouflage from predators, whereas Antarctic seals all have dark fur at birth.
Polar bears rarely enter conflict with other predators, though recent brown bear encroachments into polar bear territories have led to antagonistic encounters. Brown bears tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens. Wolves are rarely encountered by polar bears, though there are two records of Arctic wolf (Canis lupus arctos) packs killing polar bear cubs. A rather unlikely killer of a grown polar bear has reportedly included a wolverine (Gulo gulo), anecedotely reported to have suffocated a bear with a bite to the throat during a conflict over food. Polar bears are sometimes the host of arctic mites such as Alaskozetes antarcticus.
Long distance swimmer
Researchers tracked 52 sows in the southern Beaufort Sea off Alaska with GPS system collars; no boars were involved in the study due to males' necks being too thick for the GPS-equipped collars. Fifty long-distance swims were recorded; the longest at 354 kilometres (220 mi), with an average of 155 kilometres (96 mi). The length of these swims ranged from most of a day to ten days. Ten of the sows had a cub swim with them and after a year six cubs survived. The study did not determine if the others lost their cubs before, during, or some time after their long swims. Researchers do not know whether or not this is a new behavior; before polar ice shrinkage, they opined that there was probably neither the need nor opportunity to swim such long distances.
Polar bears have long provided important raw materials for Arctic peoples, including the Inuit, Yupik, Chukchi, Nenets, Russian Pomors and others. Hunters commonly used teams of dogs to distract the bear, allowing the hunter to spear the bear or shoot it with arrows at closer range. Almost all parts of captured animals had a use. The fur was used in particular to sew trousers and, by the Nenets, to make galoshes-like outer footwear called tobok; the meat is edible, despite some risk of trichinosis; the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber; sinews were used as thread for sewing clothes; the gallbladder and sometimes heart were dried and powdered for medicinal purposes; the large canine teeth were highly valued as talismans. Only the liver was not used, as its high concentration of vitamin A is poisonous. Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning. Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat.
History of commercial harvest
In Russia, polar bear furs were already being commercially traded in the 14th century, though it was of low value compared to Arctic Fox or even reindeer fur. The growth of the human population in the Eurasian Arctic in the 16th and 17th century, together with the advent of firearms and increasing trade, dramatically increased the harvest of polar bears. However, since polar bear fur has always played a marginal commercial role, data on the historical harvest is fragmentary. It is known, for example, that already in the winter of 1784/1785 Russian Pomors on Spitsbergen harvested 150 polar bears in Magdalenefjorden. In the early 20th century, Norwegian hunters were harvesting 300 bears a year at the same location. Estimates of total historical harvest suggest that from the beginning of the 18th century, roughly 400 to 500 animals were being harvested annually in northern Eurasia, reaching a peak of 1,300 to 1,500 animals in the early 20th century, and falling off as the numbers began dwindling.
In the first half of the 20th century, mechanized and overpoweringly efficient methods of hunting and trapping came into use in North America as well. Polar bears were chased from snowmobiles, icebreakers, and airplanes, the latter practice described in a 1965 New York Times editorial as being "about as sporting as machine gunning a cow." The numbers taken grew rapidly in the 1960s, peaking around 1968 with a global total of 1,250 bears that year.
Concerns over the future survival of the species led to the development of national regulations on polar bear hunting, beginning in the mid-1950s. The Soviet Union banned all hunting in 1956. Canada began imposing hunting quotas in 1968. Norway passed a series of increasingly strict regulations from 1965 to 1973, and has completely banned hunting since then. The United States began regulating hunting in 1971 and adopted the Marine Mammal Protection Act in 1972. In 1973, the International Agreement on the Conservation of Polar Bears was signed by all five nations whose territory is inhabited by polar bears: Canada, Denmark, Norway, the Soviet Union, and the United States. Member countries agreed to place restrictions on recreational and commercial hunting, ban hunting from aircraft and icebreakers, and conduct further research. The treaty allows hunting "by local people using traditional methods". Norway is the only country of the five in which all harvest of polar bears is banned. The agreement was a rare case of international cooperation during the Cold War. Biologist Ian Stirling commented, "For many years, the conservation of polar bears was the only subject in the entire Arctic that nations from both sides of the Iron Curtain could agree upon sufficiently to sign an agreement. Such was the intensity of human fascination with this magnificent predator, the only marine bear."
Agreements have been made between countries to co-manage their shared polar bear subpopulations. After several years of negotiations, Russia and the United States signed an agreement in October 2000 to jointly set quotas for indigenous subsistence hunting in Alaska and Chukotka. The treaty was ratified in October 2007.
The Soviet Union banned the harvest of polar bears in 1956, however poaching continued and is believed to pose a serious threat to the polar bear population. In recent years, polar bears have approached coastal villages in Chukotka more frequently due to the shrinking of the sea ice, endangering humans and raising concerns that illegal hunting would become even more prevalent. In 2007, the Russian government made subsistence hunting legal for Chukotka natives only, a move supported by Russia's most prominent bear researchers and the World Wide Fund for Nature as a means to curb poaching.
In Greenland, hunting restrictions were first introduced in 1994 and expanded by executive order in 2005. Until 2005 Greenland placed no limit on hunting by indigenous people. However, in 2006 it imposed a limit of 150, while also allowed recreational hunting for the first time. Other provisions included year-round protection of cubs and mothers, restrictions on weapons used, and various administrative requirements to catalogue kills.
About 500 bears are killed per year by humans across Canada, a rate believed by scientists to be unsustainable for some areas, notably Baffin Bay. Canada has allowed sport hunters accompanied by local guides and dog-sled teams since 1970, but the practice was not common until the 1980s. The guiding of sport hunters provides meaningful employment and an important source of income for native communities in which economic opportunities are few. Sport hunting can bring CDN$20,000 to $35,000 per bear into northern communities, which until recently has been mostly from American hunters.
The territory of Nunavut accounts for the location 80% of annual kills in Canada. In 2005, the government of Nunavut increased the quota from 400 to 518 bears, despite protests from some scientific groups. In two areas where harvest levels have been increased based on increased sightings, science-based studies have indicated declining populations, and a third area is considered data-deficient. While most of that quota is hunted by the indigenous Inuit people, a growing share is sold to recreational hunters. (0.8% in the 1970s, 7.1% in the 1980s, and 14.6% in the 1990s) Nunavut polar bear biologist, Mitchell Taylor, who was formerly responsible for polar bear conservation in the territory, insists that bear numbers are being sustained under current hunting limits. In 2010, the 2005 increase was partially reversed. Government of Nunavut officials announced that the polar bear quota for the Baffin Bay region would be gradually reduced from 105 per year to 65 by the year 2013. The Government of the Northwest Territories maintain their own quota of 72 to 103 bears within the Inuvialuit communities of which some are set aside for sports hunters. Environment Canada also banned the export from Canada of fur, claws, skulls and other products from polar bears harvested in Baffin Bay as of 1 January 2010.
Because of the way polar bear hunting quotas are managed in Canada, attempts to discourage sport hunting would actually increase the number of bears killed in the short term. Canada allocates a certain number of permits each year to sport and subsistence hunting, and those that are not used for sport hunting are re-allocated to Native subsistence hunting. Whereas Native communities kill all the polar bears they are permitted to take each year, only half of sport hunters with permits actually manage to kill a polar bear. If a sport hunter does not kill a polar bear before his or her permit expires, the permit cannot be transferred to another hunter.
The Marine Mammal Protection Act of 1972 afforded polar bears some protection in the United States. It banned hunting (except by indigenous substinence hunters), banned importing of polar bear parts (except polar bear pelts taken legally in Canada), and banned the harassment of polar bears. On 15 May 2008, the United States department of Interior listed the polar bear as a threatened species under the Endangered Species Act and banned all importing of polar bear trophies. Importing products made from polar bears had been prohibited from 1972 to 1994 under the Marine Mammal Protection Act, and restricted between 1994 and 2008. Under those restrictions, permits from the United States Fish and Wildlife Service (FWS) were required to import sport-hunted polar bear trophies taken in hunting expeditions in Canada. The permit process required that the bear be taken from an area with quotas based on sound management principles. Since 1994, more than 800 sport-hunted polar bear trophies have been imported into the U.S.
Conservation status, efforts and controversies
Estimates of the status of the global population of polar bears vary widely. As of 2008, the World Conservation Union (IUCN) reports that the global population of polar bears is 20,000 to 25,000, and is declining. In 2006, the IUCN upgraded the polar bear from a species of least concern to a vulnerable species. It cited a "suspected population reduction of >30% within three generations (45 years)". However, a report published in July 2013, estimates that the global population of polar bears increased by an average of almost 4,200 bears since 2001. Risks to the polar bear include climate change, pollution in the form of toxic contaminants, conflicts with shipping, stresses from recreational polar-bear watching, and oil and gas exploration and development. The IUCN also cited a "potential risk of over-harvest" through legal and illegal hunting.
According to the World Wildlife Fund, the polar bear is important as an indicator of arctic ecosystem health. Polar bears are studied to gain understanding of what is happening throughout the Arctic, because at-risk polar bears are often a sign of something wrong with the arctic marine ecosystem.
The IUCN, Arctic Climate Impact Assessment, United States Geological Survey and many leading polar bear biologists have expressed grave concerns about the impact of climate change, including the belief that the current warming trend imperils the survival of the species.
The key danger posed by climate change is malnutrition or starvation due to habitat loss. Polar bears hunt seals from a platform of sea ice. Rising temperatures cause the sea ice to melt earlier in the year, driving the bears to shore before they have built sufficient fat reserves to survive the period of scarce food in the late summer and early fall. Reduction in sea-ice cover also forces bears to swim longer distances, which further depletes their energy stores and occasionally leads to drowning. Thinner sea ice tends to deform more easily, which appears to make it more difficult for polar bears to access seals. Insufficient nourishment leads to lower reproductive rates in adult females and lower survival rates in cubs and juvenile bears, in addition to poorer body condition in bears of all ages.
In addition to creating nutritional stress, a warming climate is expected to affect various other aspects of polar bear life: Changes in sea ice affect the ability of pregnant females to build suitable maternity dens. As the distance increases between the pack ice and the coast, females must swim longer distances to reach favored denning areas on land. Thawing of permafrost would affect the bears who traditionally den underground, and warm winters could result in den roofs collapsing or having reduced insulative value. For the polar bears that currently den on multi-year ice, increased ice mobility may result in longer distances for mothers and young cubs to walk when they return to seal-hunting areas in the spring. Disease-causing bacteria and parasites would flourish more readily in a warmer climate.
Problematic interactions between polar bears and humans, such as foraging by bears in garbage dumps, have historically been more prevalent in years when ice-floe breakup occurred early and local polar bears were relatively thin. Increased human-bear interactions, including fatal attacks on humans, are likely to increase as the sea ice shrinks and hungry bears try to find food on land.
The effects of climate change are most profound in the southern part of the polar bear's range, and this is indeed where significant degradation of local populations has been observed. The Western Hudson Bay subpopulation, in a southern part of the range, also happens to be one of the best-studied polar bear subpopulations. This subpopulation feeds heavily on ringed seals in late spring, when newly weaned and easily hunted seal pups are abundant. The late spring hunting season ends for polar bears when the ice begins to melt and break up, and they fast or eat little during the summer until the sea freezes again.
Due to warming air temperatures, ice-floe breakup in western Hudson Bay is currently occurring three weeks earlier than it did 30 years ago, reducing the duration of the polar bear feeding season. The body condition of polar bears has declined during this period; the average weight of lone (and likely pregnant) female polar bears was approximately 290 kg (640 lb) in 1980 and 230 kg (510 lb) in 2004. Between 1987 and 2004, the Western Hudson Bay population declined by 22%.
In Alaska, the effects of sea ice shrinkage have contributed to higher mortality rates in polar bear cubs, and have led to changes in the denning locations of pregnant females. In recent years, polar bears in the Arctic have undertaken longer than usual swims to find prey, resulting in four recorded drownings in the unusually large ice pack regression of 2005.
Polar bears accumulate high levels of persistent organic pollutants such as polychlorinated biphenyl (PCBs) and chlorinated pesticides. Due to their position at the top of the food pyramid, with a diet heavy in blubber in which halocarbons concentrate, their bodies are among the most contaminated of Arctic mammals. Halocarbons are known to be toxic to other animals, because they mimic hormone chemistry, and biomarkers such as immunoglobulin G and retinol suggest similar effects on polar bears. PCBs have received the most study, and they have been associated with birth defects and immune system deficiency.
The most notorious of these chemicals, such as PCBs and DDT, have been internationally banned. Their concentrations in polar bear tissues continued to rise for decades after the ban as these chemicals spread through the food chain. But the trend seems to have abated, with tissue concentrations of PCBs declining between studies performed from 1989 to 1993 and studies performed from 1996 to 2002.
Oil and gas development
Oil and gas development in polar bear habitat can affect the bears in a variety of ways. An oil spill in the Arctic would most likely concentrate in the areas where polar bears and their prey are also concentrated, such as sea ice leads. Because polar bears rely partly on their fur for insulation and soiling of the fur by oil reduces its insulative value, oil spills put bears at risk of dying from hypothermia. Polar bears exposed to oil spill conditions have been observed to lick the oil from their fur, leading to fatal kidney failure. Maternity dens, used by pregnant females and by females with infants, can also be disturbed by nearby oil exploration and development. Disturbance of these sensitive sites may trigger the mother to abandon her den prematurely, or abandon her litter altogether.
The U.S. Geological Survey predicts two-thirds of the world's polar bears will disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by climate change. The bears would disappear from Europe, Asia, and Alaska, and be depleted from the Arctic archipelago of Canada and areas off the northern Greenland coast. By 2080, they would disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic archipelago.
Predictions vary on the extent to which polar bears could adapt to climate change by switching to terrestrial food sources. Mitchell Taylor, who was director of Wildlife Research for the Government of Nunavut, wrote to the U.S. Fish and Wildlife Service arguing that local studies are insufficient evidence for global protection at this time. The letter stated, "At present, the polar bear is one of the best managed of the large Arctic mammals. If all Arctic nations continue to abide by the terms and intent of the Polar Bear Agreement, the future of polar bears is secure ... Clearly polar bears can adapt to climate change. They have evolved and persisted for thousands of years in a period characterized by fluctuating climate." Ken Taylor, deputy commissioner for the Alaska Department of Fish and Game, has said, "I wouldn't be surprised if polar bears learned to feed on spawning salmon like grizzly bears."
However, many scientists consider these theories to be naive; it is noted that black and brown bears at high latitudes are smaller than elsewhere, because of the scarcity of terrestrial food resources. An additional risk to the species is that if individuals spend more time on land, they will hybridize with brown or grizzly bears. The IUCN wrote:
Polar bears exhibit low reproductive rates with long generational spans. These factors make facultative adaptation by polar bears to significantly reduced ice coverage scenarios unlikely. Polar bears did adapt to warmer climate periods of the past. Due to their long generation time and the current greater speed of climate change, it seems unlikely that polar bear will be able to adapt to the current warming trend in the Arctic. If climatic trends continue polar bears may become extirpated from most of their range within 100 years.
Controversy over species protection
Warnings about the future of the polar bear are often contrasted with the fact that worldwide population estimates have increased over the past 50 years and are relatively stable today. Some estimates of the global population are around 5,000 to 10,000 in the early 1970s; other estimates were 20,000 to 40,000 during the 1980s. Current estimates put the global population at between 20,000 and 25,000.
There are several reasons for the apparent discordance between past and projected population trends: estimates from the 1950s and 1960s were based on stories from explorers and hunters rather than on scientific surveys. Second, controls of harvesting were introduced that allowed this previously overhunted species to recover. Third, the recent effects of climate change have affected sea ice abundance in different areas to varying degrees. Finally, the prediction methods used to predict the decline in the future population of bears excluded key forecasting principles and included questionable assumptions.
Debate over the listing of the polar bear under endangered species legislation has put conservation groups and Canada's Inuit at opposing positions; the Nunavut government and many northern residents have condemned the U.S. initiative to list the polar bear under the Endangered Species Act. Many Inuit believe the polar bear population is increasing, and restrictions on sport-hunting are likely to lead to a loss of income to their communities.
U.S. endangered species legislation
On 14 May 2008 the U.S. Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act, citing the melting of Arctic sea ice as the primary threat to the polar bear. While listing the polar bear as a threatened species, the Interior Department added a seldom-used stipulation to allow oil and gas exploration and development to proceed in areas inhabited by polar bears, provided companies continue to comply with the existing restrictions of the Marine Mammal Protection Act. The main new protection for polar bears under the terms of the listing is that hunters will no longer be able to import trophies from the hunting of polar bears in Canada.
The ruling followed several years of controversy. On 17 February 2005 the Center for Biological Diversity filed a petition asking that the polar bear be listed under the Endangered Species Act. An agreement was reached and filed in Federal district court on 5 June 2006. On 9 January 2007, the United States Fish and Wildlife Service proposed to list the polar bear as a threatened species. A final decision was required by law by 9 January 2008, at which time the agency said it needed another month. On 7 March 2008, the inspector general of the U.S. Department of the Interior began a preliminary investigation into why the decision had been delayed for nearly two months. The investigation is in response to a letter signed by six environmental groups that United States Fish and Wildlife Director Dale Hall violated the agency's scientific code of conduct by delaying the decision unnecessarily, allowing the government to proceed with an auction for oil and gas leases in the Alaska's Chukchi Sea, an area of key habitat for polar bears. The auction took place in early February 2008. An editorial in The New York Times said that "these two moves are almost certainly, and cynically, related." Hall denied any political interference in the decision and said that the delay was needed to make sure the decision was in a form easily understood. On 28 April 2008, a Federal court ruled that a decision on the listing must be made by 15 May 2008; the decision came on 14 May to make the polar bear a protected species.
Upon listing the polar bear under the Endangered species act, the Department of the Interior immediately issued a statement that the listing could not be used to regulate greenhouse gas emissions, although some policy analysts believe that the Endangered Species Act can be used to restrict the issuing of federal permits for projects that would threaten the polar bear by increasing greenhouse gas emissions. Environmental groups have pledged to go to court to have the Endangered Species Act interpreted in such a way. On 8 May 2009, the new administration of Barack Obama announced that it would continue the policy. On 4 August 2008, the state of Alaska sued U.S. Interior Secretary Dirk Kempthorne, seeking to reverse the listing of the polar bear as a threatened species out of concern that the listing would adversely affect oil and gas development in the state. Alaska Governor Sarah Palin said that the listing was not based on the best scientific and commercial data available, a view rejected by polar bear experts. In March 2013, a United States Appeals Court ruling upheld the "threatened" status of the polar bear against a challenge led by the State of Alaska.
Canadian endangered species legislation
In Canada, the Committee on the Status of Endangered Wildlife in Canada recommended in April 2008 that the polar bear be assessed as a species of special concern under the federal Species at Risk Act (SARA). A listing would mandate that a management plan be written within five years, a timeline criticized by the World Wide Fund for Nature as being too long to prevent significant habitat loss from climate change.
For the indigenous peoples of the Arctic, polar bears have long played an important cultural and material role. Polar bear remains have been found at hunting sites dating to 2,500 to 3,000 years ago and 1,500 year old cave paintings of polar bears have been found in the Chukchi Peninsula. Indeed, it has been suggested that Arctic peoples' skills in seal hunting and igloo construction has been in part acquired from the polar bears themselves.
The Inuit and Alaska Natives have many folk tales featuring the bears including legends in which bears are humans when inside their own houses and put on bear hides when going outside, and stories of how the constellation which is said to resemble a great bear surrounded by dogs came into being. These legends reveal a deep respect for the polar bear, which is portrayed as both spiritually powerful and closely akin to humans. The human-like posture of bears when standing and sitting, and the resemblance of a skinned bear carcass to the human body, have probably contributed to the belief that the spirits of humans and bears were interchangeable. Eskimo legends tell of humans learning to hunt from the polar bear.
Among the Chukchi and Yupik of eastern Siberia, there was a longstanding shamanistic ritual of "thanksgiving" to the hunted polar bear. After killing the animal, its head and skin were removed and cleaned and brought into the home, a feast was held in the hunting camp in its honor. In order to appease the spirit of the bear, there were traditional song and drum music and the skull would be ceremonially fed and offered a pipe. Only once the spirit was appeased would the skull be separated from the skin, taken beyond the bounds of the homestead, and placed in the ground, facing north. Many of these traditions have faded somewhat in time, especially in light of the total hunting ban in the Soviet Union (and now Russia) since 1955.
The Nenets of north-central Siberia placed particular value on the talismanic power of the prominent canine teeth. They were traded in the villages of the lower Yenisei and Khatanga rivers to the forest-dwelling peoples further south, who would sew them into their hats as protection against brown bears. It was believed that the "little nephew" (the brown bear) would not dare to attack a man wearing the tooth of its powerful "big uncle" (the polar bear). The skulls of killed polar bears were buried at specific sacred sites and altars, called sedyangi, were constructed out of the skulls. Several such sites have been preserved on the Yamal Peninsula.
Symbols and mascots
Their distinctive appearance and their association with the Arctic have made polar bears popular icons, especially in those areas where they are native. The Canadian Toonie (two-dollar coin) features the image of a polar bear and both the Northwest Territories and Nunavut license plates in Canada are in the shape of a polar bear. The polar bear is the mascot of Bowdoin College in Maine and the University of Alaska Fairbanks (see also Alaska Nanooks) and was chosen as mascot for the 1988 Winter Olympics held in Calgary.
Companies such as Coca-Cola, Polar Beverages, Nelvana, Bundaberg Rum or Good Humor-Breyers have used images of the polar bear in advertising, while Fox's Glacier Mints have featured a polar bear named Peppy as the brand mascot since 1922.
Polar bears are also popular in fiction, particularly in books aimed at children or teenagers. For example, The Polar Bear Son is adapted from a traditional Inuit tale. Polar bears feature prominently in East (also released as North Child) by Edith Pattou, The Bear by Raymond Briggs (adapted into an animated short in 1998), and Chris d'Lacey's The Fire Within series. The panserbjørne of Philip Pullman's fantasy trilogy His Dark Materials are sapient, dignified polar bears who exhibit anthropomorphic qualities, and feature prominently in the 2007 film adaptation of The Golden Compass. The television series Lost features polar bears living on the tropical island setting.
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