Published 10 Jan 2017
Polar bear or Ursus maritimus, sympathetic white Teddy bear and formidable predators, is one of the most remarkable animals in the world. Among North America’s largest land carnivores, polar bears are taller than grizzlies and can weigh more than 1,500 pounds. Their claws are needle sharp for traction on the ice and for subduing seals, their canines longer than those of grizzlies and ideally suited to tearing apart flesh. Polar bears are strong enough to pull a beluga whale out of the water, patient enough to wait hours above a seal’s blowhole, and canny enough to hide their black nose with a paw as they stalk an unwitting seal. They are capable of killing humans and have done so often.
Like sharks, they are attuned so perfectly to their environment that we humans can only be clumsy and ineffective interlopers in their world. Moreover, even to most animals, a description of life on the Arctic’s frozen seas sounds pretty grim. Not only is it dark for much of the year, bur icy winds, subzero temperatures, and fierce blizzards are the rule. For the polar bear, however, that environment is a happy home. In fact, of all the Earth’s bears, only the polar bear lives exclusively in the Arctic region, justly earning such nicknames as the sea bear, the ice bear, and lord of the Arctic.
Because its polar bear’s life is so intimately connected to oceanic environments, scientists consider Ursus maritimus a marine mammal and place it in a group that includes whales, sea otters, and walruses. Exactly how the polar bear adapted to the sea ice is something of a mystery, though in scientific circles it is generally accepted that it evolved from the grizzly bear line. This might have happened during the mid-Pleistocene period 200,000 to 250,000 years ago (Struzik, 39), when a population of grizzly bears became isolated by an advancing ice sheet. Secluded in an environment filled with seals and no other predatory competitors, these opportunistic feeders discovered a wide-open niche and evolved into the modern polar bear.
As generations of sea bears adapted to their new environment and life as pure carnivores, their bodies went through dramatic change. Teeth became sharper for shearing of hide and flesh; claws became shorter, sharper, and strongly curved, to permit a better grip on ice and prey (). Most noticeably, their fur became a creamy white, to better blend with ice and snow. Polar bears also have black skin, and blubber, a thick layer of fat below the skin that provides insulation for their bodies and allows them to withstand arctic temperatures.
Now North America’s largest land carnivore, adult males average around 1,000 pounds but may weigh up to 1,700 pounds and, standing on hind legs, reach more than 11 feet tall. Adult females, though considerably smaller, may reach 700 pounds. Evolutionary changes also are evident in other aspects. For instance, most female polar bears have four nipples instead of the grizzly’s six, which makes it more difficult for them to deal with triplet (Struzik, 42).
Throughout the species’ range, including U.S. habitat in Alaska, polar bear populations are considered to be healthy and stable. Yet these symbols of wilderness and raw animal power require vast, undeveloped landscapes to thrive. That need, plus the species’ low reproduction rate and relatively small numbers, makes polar bears vulnerable to human intrusion and industrial development – challenges that could have tremendous impact on these giant creatures’ future. Today, an estimated 22,000 to 28,000 polar bears are scattered throughout fire Northern Hemisphere’s region of ice-covered seas, occupying lands and waters of Canada, Greenland, Norway, Russia, and the United States (Seaworld, 2005).
However, until the 1960s, scientists believed that polar bears were circumpolar nomads that wandered randomly through the Arctic. Close monitoring in recent decades has radically altered that view. Polar bears, it turns out, have a seasonal fidelity to certain regions. At any given season, an inpidual bear is likely to be found in the same area, from one year to the next. Thus, instead of one huge population, scientists now pide polar bears into 16 subpopulations.
Polar bears in all these subpopulations prefer to remain on sea ice because that is where they find their primary prey – seals. An adult seal can provide could provide up to eight days of energy for a polar bear (Seaworld, 2005). Ringed seals are a special favorite, hunted in snow-covered lairs or while basking on ice besides breathing holes. Occasionally, though, polar bears will move onto land in search of food, but primarily to den. Unlike grizzly and black bears, most polar bears do not spend their winters in hibernation, because ringed seals provide a reliable year-round supply of food. However, any polar bear may build a temporary den to escape extreme cold or Arctic storms. According to scientific evidence available, only pregnant females normally den for extended periods.
Although polar bears prefer to occupy particular territory, large populations of bears inhabit on drifting sea ice. For instance, study conducted by Mette Mauritzen from Norwegian Polar Institute used information from satellite telemetry, satellite images and atmospheric pressure readings to examine how the active movements of 74 female polar bears living on the Barents Sea compare with the movement of the ice (Torr and Hickey, 19). Scientists found that polar bears do undergo an annual migration with drifting ice (Torr and Hickey, 19). However, it does not represent any significant threat to animals, because as Russian bear expert Nikita Ovsyanikov points out, “polar bears don’t drown. They have been observed swimming as far as 100 kilometers without a rest” (Stock, 20).
Pregnant polar bears leave the sea ice in the autumn or early winter and search for denning sites in the bank and bluff habitats of the North Slope. When they find a suitable snowbank, they excavate a snow cave and settle in for the winter. Subsequent winter storms cover them and provide the substrate that allows them to expand their space as needed. Settled in their dens, hibernating females give birth in December or January, usually to a pair of cubs. The newborns weigh only 1 to 1.5 pounds at birth, have such fine hair they appear naked, and cannot see (Seaworld, 2005). Protected from winter’s severity and nursing on milk that is 46 percent fat, the cubs grow quickly and weigh 25 to 30 pounds when they emerge in spring.
But months will pass before they are developed enough to survive the rigors of an Arctic winter on their own. Conservationists and some scientists fear that if the coastal plain were opened to oil and gas exploration, seismic testing would endanger the Arctic refuge’s denning families. Past seismic work on Alaska’s wildlife refuges has caused hibernating grizzly bears to abandon dens. Given what’s known about denning bears, if a mother and cubs were chased from their den in mid-winter, the cubs would almost certainly die.
According to scientists, other dangers to the populations of polar bears include ingestion of contaminants associated with oil development, as well as oil spills that could directly harm, either polar bears or the marine food upon which they depend. Another, though still largely undefined, threat to polar bear populations is pollutants, because many of them transported through the atmosphere. For instance, scientist Derocher has found the highest PCB levels in Svalbard’s polar bears, with as much as 80 parts of the chemical per million parts of body tissue (Cone, 72). Interestingly, polar bears in Svalbard carry 12 times more of the chemical contaminant in their bodies than do male bears in Alaska (Cone, 72).
Indeed, these chemical contaminants in polar bears generally increase from west to east, from the Chukchi and Bering seas across Alaska and Canada and then to Greenland and Norway. This particular pattern makes sense if one considers prevailing wind directions from the North America to Europe. According to scientific evidence available, biological changes in the animals’ hormone and immune systems are linked to the levels of toxic contaminants in their bodies.
However, the problem of global warming imposes even greater challenges on the populations of polar bears. Polar bears inhabiting southern areas of the Arctic Circle are stranded each summer as the melting of ice packs starts. Moreover, being separated from their principal prey of ringed seals, the bears endure a summer-long last until the ice returns in November. According to explanations given by Arctic ecosystems expert Derocher, “The climate predictions coming out are showing massive changes in sea-ice distribution…You don’t have to be a polar scientist to see that if you take away all the sea ice you don’t have polar bears anymore” (Cristol, 6).
Indeed, over the last 35 years, Arctic ice has thinned from an average of 3.1 meters to 1.8 meters (Cristol, 6). As a consequence of the climatic shifts, polar bears are eating less, thus building up less fat reserves and have fewer chances to survive during hard seasons. Moreover, it diminished cubs’ birth rate as well as their survival rate because they do not have enough fat too.
According to Cristol, some scientists have even predicted the Arctic Ocean could be entirely ice-free by 2050 (Cristol, 6). If these global warming forecasts are correct, they may be a harbinger of what is to come throughout the circumpolar region as the Earth’s climate continues to heat up. Long-term temperature increases will mean a diminished ice pack that, in turn, will affect the survival of ringed seals, polar bears, and other northern species in unknown ways. It may not happen in our lifetimes, but there may come a day when polar bears, the world’s most remarkable animal, no longer walk the shores of Arctic parklands. As always, that future depends on actions taken in the present.
- Cone, Marla “Bear Trouble”, Smithsonian, 00377333, Apr 2003, 34(1)
- Torr, G., Hickey, G., “Polar Drift”,Nature Australia, 13242598, Spring 2004, 28(2)
- Stock, Peter “Polar opposites”,Report / Newsmagazine (National Edition), 14888084, 1/20/2003, 30(2)
- Cristol Hope. “As Arctic ice melts, polar bears may starve,”The Futurist.Washington: Jul/Aug 2003, 37(4)
- Struzik, Ed, “GRIZZLIES ON ICE”,Canadian Geographic, 07062168, Nov/Dec2003, 123(6)
- Seaworld, Polar Bears. A SeaWorld Education Department Resource, 2005