POLAR BEARS
Polar bears are the world's largest land carnivores. They are larger than tigers, lions and other species of bears. They are also the most carnivorous of all bears, primarily eating seals. Other bears feed primarily on berries, acorns and other plant foods. Polar bears inhabit sea ice and coastal waters in the circumpolar regions of the Arctic. They have been seen all over the Arctic, even near the North Pole itself, but mostly the stay close to areas were there are ice flows from which the bears hunt seals.
There are 20,000 to 25,000 polar bears in 19 populations across the Arctic, with the animal found in Canada, Greenland, Alaska, Norway and Russia. They are listed by the International Union for Conservation of Nature (IUCN) as “vulnerable”.
Polar bears are a relatively new species. They are descendants of brown bears that wandered north and caught seals during ice ages between 500,000 and 200,000 years ago. They likely began by scavenging seal carcasses and later learned to hunt them seals by waiting by their breathing holes and attacking them when they surfaced for air.
Polar bears branched off from brown bears about 250,000 years ago. DNA studies have show that some brown bears are more closely related to polar bears than they are to other brown bears. By 125,000 years ago polar bears had evolved into a separate species with a longer snout and smaller. More -jagged teeth better suited for ripping seals to shreds.
Book: “Lord of the Arctic: A Journey Among the Polar Bears” by Richard C. Davids (Macmillan).
Polar Bear Characteristics
Female polar bears usually weigh half as much as males. Males reach lengths of three meters (95 to 102 inches) and weigh between 350 and 650 kilograms (880-1,300 pounds). Females reach lengths of 2.5 meters and weigh between 175 and 300 kilograms. Their huge paws act like snow shoes on the ice and snow and serve as flippers when they swim. They roam over wide areas and can swim long distances. The bears rely on the marine sea ice environment for their survival, using the ice for hunting and breeding.
Some extremely large males weigh in the neighborhood of 680 kilograms (1,500 pound).A polar bear this size standing on its hind legs would look a large African elephant right in the eye. The next largest terrestrial carnivore is the Kodiak. Great White Sharks are about the same size as polar bears. Killer whales and sperm whales—the world’s largest carnivores—are much larger.
The average life span of a polar bear is 20 years. A polar bear has lived to the age of 38 in captivity and 32 years in the wild. In the wild, the age of a polar bear is determined by its teeth. The tooth as cut and the annual rings are counted like the rings of a tree.☻
Compared to other bears, polar bears have long necks, relatively small heads and a sloping profile. The head of an average-size, 375-kilograms male is half a meter (16 inches) long and a 25 centimeters wide. The paws are about 20 centimeters (8.5 inches) wide. The paws are used as flippers when swimming and as clubs when hunting seals.
Polar bears have a keen sense of smell that can pick up particles per million several kilometers away. They have been clocked running at 35mph and can keep their eyes open and close their nostrils under water and stay submerged for two minutes. Their liver is so high in Vitamin A it is toxic to humans.
Polar hair is clear not white. The scattering of light makes it appear white. On the snow polar bears are white on white. Often the only thing that gives them away is their black nose. Some zoo polar bears become green after algae grows in their hollow hair. To retain heat the bear has dense clear fur that scatters light. Their skin is black which absorbs the sun's rays. Their long snout warms air before it passes to their lungs. To stay warm polar bears even have fur on their feet.
Polar Bear Behavior
Polar bears have been observed sliding down hills, playing in snow banks, and napping with their heads in their paws. They have also been seen playing with tires and putting them around their neck. In Alaska polar bears have been observed punching out the lights on an airstrip one by one.
Polar bears sometimes play with dogs, other times they kill and eat them. They same is true with humans. Polar bears have been observed grieving the dead. Males play fight in October when they gather together to wait for the ice to free up enough to begin hunting. Females carefully watch their cubs if a male approaches. When given a chance, males will eat polar bear cubs.
Polar bear spend most of their time at sea, either in the water or on ice flows. Despite the fact that polar bears have been recorded swimming 100 miles at a stretch in the open sea, they are generally slow and vulnerable in the water.☻
Polar Bears in the Different Seasons
Polar bears stuff themselves with seals from April to early July, when there are ice platforms from which to hunt seals. An impregnated female may increase her body weight by 50 percent or more, building 12.5 centimeters (five inche) layers of fat around her rump and thighs.
Bears need ice floes as a platform to hunt seals. During the summer, when the sea ice has melted, the bears are unable to hunt and sometimes fast the entire summer—eating almost nothing until the sea ice starts to form once again in autumn.
During the summer polar bears can not tolerate long exertions. Scientist can easily track them down on foot as they don’t travel far. It is suspected that the bears have to jump in the water periodically to cool off. In the winter the bears can run and run; scientists had difficulty tracking them even with a snow mobile.☻
In the summer, polar bears sleep, wander around, try to conserve energy in what is sometimes called walking hibernation. Scientist are studying the bears unique metabolism to find treatments for obesity and bone and kidney problems. Males and nonbreeding females go out to sea after the ice freezes over. Pregnant females stay ashore.
Except for nursing or pregnant females polar bears generally do not hibernate in the winter like other bears. Most of the dens that do exist are found in Russia. Females go to their dens. Scientist are not sure where the males and non-breeding females go. During rough Arctic storms, polar bears sometimes build temporary snow shelters. Some bears follow have seasonal migration routes between Norway and Russia.☻
Polar Bear Habitats
Polar Bear Prey and Hunting
Polar bear are the most carnivorous of all bears, primarily eating seals, although in some regions their diet includes kelp, grasses, berries, carrion, sea birds and garbage from nearby settlements. For some unknown reason some polar bears like to feed on antifreeze. ☻
Unlike brown bears that bury their uneaten carcasses to be eaten later, polar bears leave partly eaten carcasses in the ice that are scavenged by foxes, ravens and other bears.
The favorite polar bear prey is seal pups that are born in the spring in little caves hollowed out of snow drifts by their mothers above their breathing holes in the sea ice. The seals are well hidden but the bears can locate the pups with their amazing sense of smell. The polar bears kill the pups with a bite to the head. The 25-kilogram pups are almost half fat.
Polar bear hunt seals mostly from ice flows. They wait for coastal waters to freeze on then live a solitary life of seal hunting. The bears often ignore the meat and gorge themselves on the fat, which they need for energy. Polar bears hunt seals mainly using two methods: by stalking seals from land or underneath ice after they have emerged at breathing holes; or by waiting patiently near the seal's breathing hole and biting its head as it surfaces for air.
Polar bears are so strong they can reach inside a hole in the ice, kill the seal with a single, crushing bite and then pull it out of the water its strong neck and shoulder muscles. Sometimes polar bears break through the ice with their paws to catch seals and fish.
Polar bears have been observed hunting two-ounce voles in the tundra grass and cocking their heads and placing their ears to the round to listen to the animal's squeaking. At the other side of the size spectrum an ecologist told National Geographic that he saw 40 or so beluga whales trapped by ice gathering around a small hole in the ice. It was eight miles to open water, too far for the whales to swim. Twenty five polar bears gathered at one hole and feasted on the whales. Some bears were twice their normal size and had eaten so much they didn’t need t eat for an entire year.
Polar Bears Breeding
In the spring male polar bears fights for mates. Describing one battle. John Eliot wrote in National Geographic, "They faced nose-to-nose, mouths open, they reared up and wrestled with their front legs wrapped around each other. They pummeled hard with their paws but did not draw blood with their claws. Finally one of them lay submissively on his back, punching the bear above with his front paws while rear legs gyrated wildly. After 15 minutes they called time-out."
Pregnant females stay ashore in the winter in dens they have dug in the earth during the summer and autumn. The denning areas often cover more than a thousand square miles and are riddled with dens that bears have used for centuries. The dens are oriented towards the south and east away from the prevailing winds.
The gestation period of a polar bear is 240 days. Females become impregnated in the spring but in a process called delayed implantation the eggs don't begin to develop until the fall. The females give birth to generally two cubs in December or January. While they are in their dens the heart rate of the female bears drops from 60 beats a minute to 30 beats minute. Females often fast for eight months of the year, six of them in her den in the winter and two in the summer when there is no ice to hunt seals. After a mother gives birth and nurses her young she might lose up to 45 percent of her body weight.
Polar Bears Cubs and Their Mothers
Polar bear cubs are born around New Year's Day. They weigh little more than half a kilogram at birth and their fine hair is almost invisible. They open their eyes after around 10 days (compared to 40 days for black bears). Two is the most common litter size. The cubs stay in their den with their mother until April when the cubs weigh about 14 kilograms (30 pounds) and the mother begins hunting seals. The dens are often relatively far inland, a few days walk from the sea.
Polar bear milk is richer than the milk of other bears. It is about 30 percent fat. One scientist tried a bit of polar bear milk said, "Not bad. It tastes like nuts. But its very rich." Cubs need their mothers for warmth and food. If anything happens to their mother, cubs usually die within a few days from exposure, starvation or are eaten by other bears. When threatened mother polar bears leap into the water and their cubs cling to their fur and tail and are pulled to safety.
When mother polar bears emerge from their dens they have fasted and eight months and her hungry cubs may be three months old. Most females keep their young with them for two and a half years. Some wean their cubs a year earlier so they can breed every two years instead of the normal three years.
Nomadic and largely solitary males play no role in childrearing. They can be dangerous and females with cubs usually go out of their way to avoid them. If there are three cubs, the strongest and most persistent one often feeds at the expense of the others. Mothers tend to ignore the rivalry for food. Runts very rarely survive more than a few months.
Polar Bears in Svalbard Islands of Norway
Spitsbergen in Norway’s Svalbard islands is far inside the Arctic circle more than 2,000 kilometers north of Norway’s capital Oslo. Ten per cent of the world’s polar bear population is here. As a 15-year-old midshipman, British naval hero Horatio Nelson fought off a polar bear on Spitsbergen after his musket misfired.
The Barents Sea region has a population of several thousand bears, around half of which use Svalbard islands for their dens to raise cubs. The animals are concentrated in the icier east and the north of the archipelago. The Norwegian Polar Institute says that some bears based in Svalbard follow the sea ice as it retreats north during the summer melting period to continue hunting, while others will remain on land waiting several months for the ice to return. [Source: Neil Syson, The Sun, August 7, 2011]
While the seals are their main source of prey, they are opportunistic hunters who will scavenge from whale carcasses, feed on nesting seabirds and their eggs, and even kill reindeer. Svalbard is one of several places in the Arctic where tourists are given the opportunity to take trips to see polar bears.
Wrangel Island in Russia
Wrangel island is the world’s largest denning ground for polar bears—as many as 400 mothers have been known to land here in winter to raise their young. With climate change making the ice pack much less reliable, polar bears have often sought summertime refuge on the island in recent years as well. Wrangel also supports the largest population of Pacific walruses, and the only snow goose nesting colony in Asia. It is home to snowy owls, muskoxen, arctic foxes, and reindeer as well as massive populations of lemmings and seabirds. And yet, in merciful contrast to the boggy Siberian mainland, there are no mosquitoes. [Source: Hampton Sides, National Geographic, May 2013]
The famous American naturalist John Muir was the first visitor to describe Wrangel Island to the world. After visiting in 1881m he wrote: “This grand wilderness in its untouched freshness” is a “severely solitary” land in the “topmost, frost-killed end of creation.”
Hampton Sides wrote in National Geographic, “Today Wrangel Island is one of the world’s least frequented, most restricted nature reserves—a place that requires several government permits to visit and can be reached only by helicopter during winter or by icebreaker during summer. Rusty barrels are piled everywhere. Weather-scabbed cabins, some of which have been cannibalized for firewood, are built upon a spongy turf of lichen and moss. Disintegrating radar disks lean toward the sea, and a radio antenna’s guy wires sing in the high wind. The windows of a Russian bathhouse are caged and spiked with five-inch nails to keep out the bears. Three hundred yards away an alert young male sniffs with interest. Rodionov eyes him knowingly. “That rascal,” he says with a laugh. “He pay us a visit last night.”
“Wrangel Island was declared a zapovednik—a federally managed nature sanctuary—in 1976, and it remains one of Russia’s coldest, remotest pieces of protected wilderness. The 2,900-square-mile island lying astride the 180th meridian just might be the Galápagos of the far north: Despite the severity of its climate, and in many ways because of it, Wrangel boasts an astonishing abundance of life. Since ancient times Wrangel Island has been felicitously perched on what might be called the ice cusp. Because the island was never completely glaciated during recent ice ages and never completely inundated by seawater during periods of ice retreat, the soils and plants in its interior valleys offer a glimpse of undisturbed Pleistocene tundra unique on the planet. “When you go to Wrangel,” says Mikhail Stishov, a Moscow-based WWF scientist who lived 18 years on the island, “you’re going back hundreds of thousands of years. It’s a place of ancient biodiversity, but it’s also very fragile.”
“Paleontologists believe Wrangel is also the last place where woolly mammoths lived. A dwarf subspecies thrived here as late as 1700 B.C., more than 6,000 years after mammoth populations elsewhere became extinct. Their curved tusks can be found everywhere on the island, lying on the gravel beaches, in streambeds, even leaning against ranger cabins—trophies from another epoch.
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Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, Lonely Planet Guides, Library of Congress, U.S. government, Compton’s Encyclopedia, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Foreign Policy, Wikipedia, BBC, CNN, and various books, websites and other publications.
Last updated May 2016