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This article is about the animal. For other uses, see Polar bear (disambiguation).

Polar Bear
Conservation status

Vulnerable  (IUCN 3.1)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Genus: Ursus
Species: U. maritimus
Binomial name
Ursus maritimus
Phipps, 1774
Polar bear range

The polar bear (Ursus maritimus), also known as the white bear, northern bear, sea bear, or nanuq in some Inuit languages, is a species of bear that is native to the Arctic and the apex predator within its range. Its thick blubber and fur insulate it against the cold, and its translucent fur, which appears white or cream-colored, camouflages it from its prey. The bear has a short tail and small ears that help reduce heat loss, as well as a relatively small head and long, tapered body to streamline it for swimming. The polar bear is a semi-aquatic marine mammal that depends mainly upon the pack ice and the marine food web for survival. It has uniquely adapted for life on a combination of land, sea, and ice and is now dependent on this combination.

Scientists now believe that the projected decreases in the polar sea ice due to global warming will have a significant negative impact or even lead to extinction of this species within this century. Population reductions of up to 20% have been recorded in recent years, the average weight of the bears has been declining significantly, and cub survival rates have plunged.

Physical description

Size and weight

Polar bears rank with the Kodiak bear as among the largest living carnivores, and male polar bears may weigh twice as much as a Siberian tiger. There is great sexual dimorphism, with some males reaching more than twice the size of the females. Most adult males weigh 300-600 kg (660-1320 lb) and measure 2.4-2.6 m (7.9-8.5 ft) in length. Adult females are roughly half the size of males and normally weigh 150-300 kg (330-660 lb), measuring 1.9-2.1 m (6.25-7 ft). At birth, cubs weigh only 600-700 g or about a pound and a half.

The largest polar bear on record was shot in Kotzebue Sound, Alaska, in 1960. According to Guinness World Records 2006, this bear weighed an estimated 580 kg (1960 lb) and was 3.38 m (11 ft 11 in) tall when mounted.

Recent data, however, suggest that polar bear weights are declining, an indication of the current pressure on the bears. A 2004 National Geographic Society study showed that polar bears that year weighed, on average, fifteen percent less than they did in the 1970s. In 2007 the females in Hudson Bay averaged only 230 kg, down from near 300 kg in 1980.

Fur and skin

A Polar Bear resting.

A polar bear's fur is translucent despite its apparent white hue, providing good camouflage and insulation. It may appear yellowish brown as they age. Its black skin has evolved to radiate heat out to its layer of thick fur, which helps keep the animal warm in the coldest weather. The bear has a black nose. Stiff hairs on the soles of its paws provide insulation and traction on ice.

Unlike other Arctic mammals, polar bears do not shed their coat for a darker shade in the summer. It was once conjectured that the hollow hairs of a polar bear coat acted as fiber-optic tubes to conduct light to its black skin, where it could be absorbed - a theory disproved by recent studies. The thick undercoat does, however, insulate the bears: they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography; only their breath and muzzles can be easily seen. These bears often sprawl upon the ice to cool off; on land, they may dig for the cooler permafrost layer beneath. Growing through the undercoat is a relatively sparse covering of hollow guard hairs about six inches long. These guard hairs are stiff, shiny and erect, and stop the undercoat from matting when wet. Water is easily shaken off before it can freeze. The bear also rolls in snow to shed moisture from the coat.

Evolution

Speciation

The raccoon and bear families are believed to have diverged about 30 million years ago. The spectacled bear split from other bears around 13 million years ago. The six distinct ursine species originated some 6 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear roughly 200 thousand years ago; fossils show that between 10 and 20 thousand years ago the polar bear's molar teeth changed significantly from those of the brown bear.

Polar bears have, however, bred with brown bears to produce fertile grizzly–polar bear hybrids, suggesting that the two are close relatives. But neither species can survive long in the other's niche, and with distinctly different morphology, metabolism, social and feeding behaviors, and other phenotypic characters, the two bears are generally classified as separate species.

In a widely cited paper published in 1996, a comparison of the DNA of various brown bear populations showed that the brown bears of Alaska's ABC islands shared a more recent common ancestor with polar bears than with any other brown bear population in the world. Also to see how the bear species once split yet are still connected, polar bears still have HIT (hibernation induction trigger) in their blood, but do not now utilize this to hibernate as the brown bear does. They may occasionally enter a dormant state referred to as "denning" (pregnant females in particular), though their body temperature does not decrease during this period as it would for a typical mammal in hibernation.

Subspecies and populations

Many sources list no polar bear subspecies, while others list two - Ursus maritimus maritimus and Ursus maritimus marinus. The number of populations varies depending upon who is counting. The IUCN/SSC Polar Bear Specialist Group (PBSG), the pre-eminent international scientific body for research and management of polar bears, recognizes twenty populations, or stocks, worldwide. Other scientists recognize six distinct populations.

  1. Chukchi Sea population on Wrangell Island and western Alaska
  2. Northern and northwestern Alaska and northwestern Canada (the Beaufort Sea population)
  3. Canadian Arctic archipelago
  4. Greenland
  5. Spitzbergen-Franz Josef Land
  6. Central Siberia

Natural range

Though it spends time on land and ice, the polar bear is regarded as a marine mammal due to its intimate relationship with the sea. The circumpolar species is found in and around the Arctic Ocean, its southern range limited by pack ice. Their southernmost point is James Bay in Canada. While their numbers thin north of 88 degrees, there is evidence of polar bears all the way across the Arctic. Population estimates are just over 20,000.

The main population centers are:

Their range is limited by the availability of that sea ice they use as a platform for hunting seals, the mainstay of their diet. The destruction of its habitat on the Arctic ice threatens the bear's survival as a species; it may become functionally extinct within the century. Signs of this have already been observed at the southern edges of its range.

Polar bear sow and two cubs on Beaufort Sea coast, Alaska

Hunting, diet and feeding

The polar bear is the most carnivorous member of the bear family, and the one that is most likely to prey on humans as food. It feeds mainly on seals, especially ringed seals that poke holes in the ice to breathe, but will eat anything it can kill: birds, rodents, shellfish, crabs, beluga whales, young walruses, occasionally musk oxen or reindeer, and very occasionally other polar bears. Still, reindeer and musk oxen can easily outrun a polar bear, and polar bears overheat quickly: thus the polar bear subsists almost entirely on live seals and walrus calves, or on the carcasses of dead adult walruses or whales. They are enormously powerful predators, but they rarely kill adult walruses, which are twice the polar bear's weight. Orcas, humans, and larger bears of their own species are the only predators of polar bears.

As a carnivore which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A, which is stored in their livers; in the past, humans have been poisoned by eating the livers of polar bears. Though mostly carnivorous, they sometimes eat berries, roots, and kelp in the late summer.

Polar bears are crafty hunters and will wait by the breathing holes of the seals in the ice and wait for them to surface. Sometimes they crawl up to sleeping seals, stopping if the seal wakes, then resuming and finally leaping and catching them. Adult bears mainly eat the skin and blubber and leave the organs and muscle. This reduces the need for water as less urea is produced than from a high protein diet. In the winter, when water is hard to find, this helps save energy as well since they need to ingest less snow. They have lowest cholesterol levels when eating many seals, likely because of the plentiful omega-3 fatty acids in the seal blubber. Their cholesterol rises during fasting. Lactating females and young and growing bears will eat entire carcasses. Typically the normal adult bear will eat a seal every five days or so when their prey is most plentiful.

Polar bears are excellent swimmers and have been seen in open Arctic waters as far as 60 miles from land. In some cases they spend half their time on ice floes. Their 12 cm (5 in) layer of fat adds buoyancy in addition to insulating them from the cold. Recently, 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 at the Toronto Zoo

Polar bears are enormous, aggressive, curious, and extremely dangerous to humans. Wild polar bears, unlike most other bears, are barely habituated to people and will quickly size up any animal they encounter as potential prey. A polar bear should never be approached and if one is spotted, it is best to retreat slowly on foot to an indoor location, or leave in a vehicle.

Like other bear species, they have developed a liking for garbage as a result of human encroachment; the dump in Churchill, Manitoba is frequently scavenged by polar bears, who have been observed eating, among other things, grease and motor oil..

Breeding

Mother with cub at Svalbard

The polygamous polar bears mate in the spring (March to May); pairing only lasts for the actual mating with few permanent bonds observed. Testosterone levels increase in the spring for the males and the testicles increase in size. Once fertilized the females ova undergoes a delayed implantation, which takes hold in September or October. The gestation period is between 195 and 265 days (about 8 months) with the cubs born soon after the ova implant in early winter (November to December). The mother digs a two-chambered cave in deep snow for the birth in October after a period of heavily feeding. Usually, two cubs are born, less often one or three; litters of four cubs have been recorded. Like other Ursus bears, the new cubs are tiny, typically 30 cm long and weighing 700 g (a pound and a half), compared to their sometimes 300 kg (660 lb) mothers. The helpless and blind cubs open their eyes after about a month, emerge from the den at about 10 kg (22 lb), are able to walk at 1.5 months, and start eating solid food at 4-5 months. They remain with their mother, learning to hunt and protect themselves against adult males, which sometimes cannibalize cubs. Females nurse their young for up to two and a half years on milk that contains approximately 33% fat, higher than that of any other species of bear and comparable to that of other marine mammals. The bears farther north tend to stay longer with their young, with weather conditions and age of the female affect this time as well. Sexual maturity is reached at 3-4 years. Adult polar bears are known to live over 30 years in captivity with average around 25. In the wild this is likely much shorter. Polar bears do not hibernate, though lactating females go into dormancy during denning. The female can control urea cycling so she can endure a long fast during this time; they often go without eating for a period of nine months and rely on stored body fat (also known as blubber) to keep themselves and their cubs alive. Once the cubs mature they go their separate ways.

The 2004 National Geographic study found no cases of cubs being born as triplets, a common event in the 1970s, and that only one in twenty cubs were weaned at eighteen months, as opposed to half of cubs three decades earlier.

In Alaska, the United States Geological Survey reports that 42 percent of cubs now reach 12 months of age, down from 65 percent 15 years ago. In other words, less than two of every three cubs that survived 15 years ago are now making it past their first year.

Conservation status

The population of 20,000-25,000 polar bears has been shrinking. On the west coast of Hudson Bay in Canada, for example, there were an estimated 1200 polar bears in 1987, and 950 in 2007.

In February 2005 the environmental group, Center for Biological Diversity, with support from American senator Joe Lieberman, petitioned the United States Fish and Wildlife Service (FWS), part of the Department of the Interior to use the Endangered Species Act and list the bears as a threatened species.

Under United States law the FWS was required to respond to the petition within 90 days, but in October 2005 after no reply had be received the Center for Biological Diversity threatened to sue the United States Government. On 14 December 2006 the Center for Biological Diversity along with Greenpeace and the Natural Resources Defense Council filed a lawsuit in California.

On December 27, 2006, the United States Department of the Interior in agreement with the three groups proposed that polar bears be added to the endangered species list, the first change of this type to be attributed to global warming. It will take up to a year to make the final determination.

The World Conservation Union had already given polar bears threatened status in May 2006.

The March 6, 2007 issue of the Canadian newspaper the National Post ran a cover article that showed the population of polar bears is actually surging, contrary to what global warming alarmists have reported.

Threats natural and unnatural

The most immediate and topically recognized threat to the polar bear is the drastic changes taking place in their natural habitat, which is literally melting away due to global warming.The United States Geological Survey, for example, in November 2006, stated that the loss of sea ice in the Alaskan portion of the Beaufort Sea has lead to a higher death rate for polar bear cubs.

The Harvard University Gazette said:

  • A 1999 study of polar bears on Hudson Bay showed that rising temperatures are thinning the pack ice from which the bears hunt, driving them to shore weeks before they've caught enough food to get them through hibernation.

The BBC reported:

  • Climate change is threatening polar bears with starvation by shortening their hunting season, according to a study by scientists from the Canadian Wildlife Service.

There is also some concern over pollution in addition to the normal natural problems the bears might face. Reduced cub survival has been reported in connection with PCBs, as well as reports of organochlorines affecting the endocrine system and immune systems with lower immunoglobulin G seen with increasing PCB levels. The lipophilic PCBs are considered a serious threat to marine mammals generally and to their food web, quickly concentrating into fat and blubber. These and related compounds are known in mammals (including humans) to cause such things as abortion, still births, alteration of the menstrual cycle, poor growth and survival of young, carcinogenicity, immunotoxicity, and even outright lethality. Other classes of organohalogens have been found in polar bears, such as PCDDs, PCDFs, TCPMe and TCPMeOH. Hermaphroditic polar bears have now been observed in less pristine areas. While some countries now ban some of these substances, they are still produced in others, and still end up all over the entire planet including the formerly pristine arctic. Even after the use of these chemicals is stopped, they continue to accumulate up the food chain, including in marine mammals and humans, for some time to come.

The bears sometimes have problems with various skin diseases with dermatitis caused sometimes by mites or other parasites. The bears are especially susceptible to Trichinella, a parasitic roundworm they contract by eating infected seals. Sometimes excess heavy metals have been observed, as well as ethylene glycol (antifreeze) poisoning. Bears exposed to oil and petroleum products lose the insulative integrity of their coats, forcing metabolic rates to dramatically increase to maintain body heat in their challenging environment. Bacterial Leptospirosis, rabies and morbillivirus have been recorded. Interestingly, the bears are thought by some to be more resistant than other carnivores to viral disease. The pollutant effect on the bears' immune systems, however, may end up decreasing their ability to cope with the naturally present immunological threats it encounters, and in such a challenging habitat even minor weaknesses can lead to serious problems and quick death.

Entertainment and commerce

Polar bears have been made both controversial and famous for their distinctive white fur and their habitat. Companies like Coca-Cola, Polar Beverages, Nelvana, Bundaberg Rum and Good Humor-Breyers have used images of this bear in logos. The first has consistently displayed the bears as thriving near penguins, though the animals naturally live in opposite hemispheres. The Canadian 2-dollar coin (right) features the image of a polar bear. The panserbjørne of the fantasy trilogy His Dark Materials are polar bears with human-level intelligence.

The TV series Lost has featured polar bears on a mysterious tropical island.

Trivia

  • In February 2004, two polar bears in the Singapore Zoo turned green due to algae growth. A zoo spokesman said that the algae had formed as a result of Singapore's hot and humid conditions. The bears were washed in a peroxide blonde solution to restore their expected colour. A similar algae grew in the hair of three polar bears at San Diego Zoo in the summer of 1980. They were cured by washing the algae away in a salt solution. This is very common in all zoos in warm areas.
  • In July 2005, during an extremely hot and humid summer in Chicago, several polar bears in the Brookfield Zoo turned green as a result of algae growing in their hollow guard hair tubes. The staff let the harmless algae run its course, and did not subject the bears to chlorine or bleach treatment.
  • In April 2003, the American submarine Connecticut (SSN 22) poked its sail and rudder through an area of polar ice between Alaska and the North Pole. A large (700-800 lb) polar bear was seen approaching the sub and loitering for about 40 minutes around the subs rear rudder. It took a bite out of the rudder and, finding it inedible, stayed around the area of broken ice near the rudder for a time, apparently thinking a seal might use it as an air hole. The bear finally left when he heard the noise of an approaching helicopter. Photos of the polar bear at the submarines rudder were taken from the periscope camera and distributed to the media.

Gallery

References

Cited references

  1. ^ Template:IUCN2006 Database entry includes a lengthy justification of why this species is listed as vulnerable.
  2. http://animaldiversity.ummz.umich.edu/site/accounts/information/Ursus_maritimus.html
  3. "Polar bear 'extinct within 100 years'". BBC. Retrieved 2006-02-01.
  4. SeaWorld
  5. U.S. Fish and Wildlife Service
  6. Guinness World Records, Guinness World Records 2006, Guinness (August 15, 2005), ISBN 1-904994-02-4
  7. ^ T. Appenzeller and D. R. Dimick, "The Heat is On," National Geographic 206 (2004): 2-75. cited in Flannery, Tim (2005). The Weather Makers. Toronto, Ontario: HarperCollins. pp. 101–103. ISBN 0-00-200751-7.
  8. NZZ Online, Eisbären müssen fasten
  9. Is Polar Bear Hair Fiber Optic?, Daniel W. Koon, Applied Optics LP, vol. 37, Issue 15, pp.3198-3200, 1998.
  10. ^ "Natural history". Center for Biological Diversity. 2005-02-15. Retrieved 2006-07-28. {{cite web}}: Check date values in: |date= (help)
  11. Gunderson, A. 2002. "Ursus maritimus" (On-line), Animal Diversity Web. Accessed July 28 2006 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Ursus_maritimus.html.
  12. Report of wild hybrid bear
  13. Lisette P. Waits, Sandra L. Talbot, R.H. Ward and G. F. Shields (1998). "Mitochondrial DNA Phylogeography of the North American Brown Bear and Implications for Conservation". Conservation Biology. pp. 408–417. {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  14. Stirling 1988, Polar Bears...& also... Bruce et al.,1990 in Pharmacol. Biochem. Behav., 35: 705-711.
  15. "Wildfacts - Polar bear". BBC. Retrieved 2006-07-28.
  16. http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=622083
  17. http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=622084
  18. "Polar Bear FAQ". Polar Bears International. Retrieved 2006-07-28.
  19. US Environmental Protection Agency
  20. "Bear Facts". Polar Bears International. Retrieved 2006-07-28.
  21. "Global warming has U.S. rethinking polar bear status". CBC Canada. 2006-02-08. Retrieved 2007-01-08. {{cite news}}: Check date values in: |date= (help)
  22. Polar bears and climate change.
    • "Endangered Species Act Listing Process for Polar Bears Underway". Center for Biological Diversity. Retrieved 2006-07-28.
    • Barber, D.G., Iacozza, J. Historical analysis of sea ice conditions in M'Clintock Channel and the Gulf of Boothia, Nunavut : implications for ringed seal and polar bear habitat. Arctic 57(1) Mar. 2004, p. 1-14
    • Stirling, I., Lunn, N.J. Iacozza, J., Elliott, C., Obbard, M. Polar bear distribution and abundance on the southwestern Hudson Bay coast during open water season, in relation to population trends and annual ice patterns. Arctic 57(1) Mar. 2004, p. 15-26
    • Stirling, I. Parkinson, C.L. Possible effects of climate warming on selected populations of polar bears (Ursus maritimus) in the Canadian Arctic. Arctic 59(3) Sept. 2006, p. 261-275
  23. http://www.fws.gov/home/feature/2006/polarbear.pdf
  24. http://www.visitandlearn.co.uk/factfiles06/diet3.asp
  25. Iredale, Will (2005-12-18). "Polar bears drown as ice shelf melts". The Sunday Times. Retrieved 2006-07-28. {{cite news}}: Check date values in: |date= (help)
  26. Ed Struzik. "Nanook: In the tracks of the great wanderer" (1987). Equinox 6 (1): 18–30.
  27. http://www.nzz.ch/2007/02/04/ws/articleEVLOF.html
  28. http://www.nzz.ch/2007/02/04/ws/articleEVLOF.html
  29. ^ "Time to protect polar bears from warming?". MSNBC. Retrieved 2006-02-01.
  30. "Activists sue U.S. to protect polar bears". MSNBC. Retrieved 2006-02-01.
  31. "U.S. weighs listing polar bear as threatened species". REUTERS. Retrieved 2006-02-01.
  32. "Release of the 2006 IUCN Red List of Threatened Species reveals ongoing decline of the status of plants and animals". World Conservation Union. Retrieved 2006-02-01.
  33. http://www.feed24.com/go?item_id=36284429&q_orig=2040%20ice-free
  34. http://www.usatoday.com/weather/resources/coldscience/2004-11-08-arctic-warming_x.htm
  35. "Polar bear survival rate falls as climate warms: study". REUTERS. Retrieved 2006-02-01.
  36. (Alvin Powell) March 22, 2001
  37. "Global warming could starve polar bears". BBC. Retrieved 2006-03-01.
  38. http://www.bbc.co.uk/nature/animals/features/144index.shtml
  39. http://www.pwrc.usgs.gov/bioeco/polarbear.htm
  40. http://www.ngo.grida.no/wwfap/polarbears/risk/toxic.html
  41. http://www.seaworld.org/animal-info/info-books/polar-bear/longevity.htm
  42. "Grizzly-Polar Bear Hybrid Found -- But What Does It Mean?". news.nationalgeographic.com. May 16, 2006. Retrieved 2006-11-01. {{cite news}}: Check date values in: |date= (help)
  43. "Bear Attacks Sub". www.strategypage.com. April 27, 2003. Retrieved 2007-1-15. {{cite news}}: Check date values in: |accessdate= and |date= (help)
  44. Zoological Society of Manitoba

General references

  • Bears of the World, Terry Domico, Photographs by Terry Domico and Mark Newman, Facts on File, Inc, 1988, hardcover, ISBN 0-8160-1536-8
  • Arctic Dreams, Barry Lopez, Macmillan 1986, hardcover, ISBN 0-333-42244-9
  • Marine Mammal Medicine, Leslie Dierauf & Frances Gulland, CRC Press 2001, ISBN 0-8493-0839-9

See also

External links

Global Warming Issues

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