Science of the Seasons: Bearing study

Photo courtesy of Dr. David Wartinbee. A polar bear rests on a gravel bar near Kaktovik during September 2010. Until sea ice reforms in the winter, bears are relegated to shore.waiting for the sea ice to form.

Photo courtesy of Dr. David Wartinbee. A polar bear rests on a gravel bar near Kaktovik during September 2010. Until sea ice reforms in the winter, bears are relegated to shore.
waiting for the sea ice to form.

Polar bears (Ursus maritimus) are an iconic creature that most of us have experienced as cuddly children’s toys or as friendly family groups interacting with penguins in Coca-Cola commercials.

Much of what we commonly see portrayed about polar bears is quite distant from reality. When viewing TV ads, I always want to point out that polar bears and penguins live worlds apart, penguins in the Antarctic and polar bears only in the Arctic. They only meet in fairy tales. I am also bothered by the anthropogenic portrayal of large family units of polar bears because in the real world they are mostly solitary predators who actively avoid contact with their relatives.

Polar bears are found throughout the northern hemisphere Arctic. There are populations in Norway, Russia, Canada, Alaska and Greenland. Most of their lives are spent as ice-pack hunters, looking for seals that have created breathing holes through the ice, or those basking on the ice. When the sea ice melts in the summer, the bears hang out along shore areas. Typically they fast during this onshore time, although they are happy to take carrion or feed on whale carcasses from Native subsistence hunts. They head back out on the pack ice to hunt seals again, as soon as the sea ice starts to reform.

In Alaska villages, like Kaktovik, polar bears are spending more and more time on land due to the earlier and more extensive summer sea ice melting. And the sea ice is reforming later in the fall than it used to, so bears are onshore longer these days. In these situations, they are not usually feeding, so social interactions are less intense.

polar bear males Kaktovik 13-14 Sept 2012I have seen groups of polar bears resting onshore in the fall as they await ice formation and, from my observations, females with young were still wary of males and gave others a wide berth.

These resting bears can be a nuisance in the villages by getting into garbage or breaking into homes. At one point during my visit, a local resident cautioned me not to walk around the end of a particular building, since there was a sow and two cubs just around the corner. The town of Kaktovik has a team of residents who monitor polar bears near town and chase them away from the town center.

Polar bears have thick fur and 4 to 5 inches of fat to keep them comfortable in the Arctic cold. Their fur has outer guard hairs that easily shed water and ice, while an inner layer of shorter, finer hairs provides insulation. The insulation of polar bears is so good that infrared imaging only shows their nose, eyes and the inside surfaces of their legs.

Besides being agile travelers on the ice itself, they are also quite adept at swimming long distances. Their 12-inch-wide front paws work as effective paddles, while the hind legs work as rudders.

During the summer months, as the pack ice melts, polar bears will normally swim from one ice pack to another. In late summer, they normally swim back to the shore to await fall freezing. It is well documented that some adults are able to swim over a hundred miles at a time. With more and more ice melting during summer months, some of these swims back to shore are longer than what young bears can accomplish. There are several reports of monitored bears that have lost their cubs during extra long swims.

Using their highly sensitive olfactory abilities, polar bears can detect prey or food items from great distances. In the spring they can detect ringed seal caves under thick snow and ice. Using a jumping technique with their front feet, they can collapse the lair and seize either the mother or the pup hiding below.

With great stealth, and with their camouflage-white coat, they are sometimes able to capture basking seals. They are also adept at finding seal breathing holes and will wait for a seal to come up for air. It has been estimated that in order to survive the winter months, a polar bear needs to capture one seal each week.

After a successful hunt, polar bears can eat up to 150 pounds at a time. While that may be all there is to a smaller ringed seal, a larger bearded seal might provide several days of feeding. Polar bears usually eat the blubber first. The reason for this behavior is that fats provide far more usable energy than muscle tissue.

Polar bears are opportunistic and will take advantage of whatever food they can find. They will endure the presence of other bears when there is a large source of food, like a whale carcass on a beach. In areas of Western Alaska where walruses haul out, polar bears are known to charge the resting group and feed on those that get trampled and injured by escaping adults.

Pregnant females dig birthing dens in snow and give birth to their young in the spring.  Often these dens are onshore, and many favorite den sites have been identified by researchers. The cubs stay with their mother for two to three years before venturing out on their own. A pair of cubs are the most common, but sows sometimes produce triplets.

Polar bears are dependent on the presence of sea ice and they feed primarily on seals that are also dependent on sea ice. As the sea ice melts away for longer and longer periods of time during the summer months, polar bears in Alaska are facing the impacts. Recent research is showing that Alaska polar bears that are enduring the brunt of the increased ice melt are not is in as good a physical shape as other populations that are not so impacted. It is very likely that the Alaska population of polar bears will dramatically decline in the years to come, and expatriation from Alaska is possible.

This week, through Friday, there is a large conference in Anchorage on the “Response of Arctic Marine Ecosystems to Climatic Change.” Polar bear researchers, as well as those looking at all the other organisms of the Arctic marine environment, will be discussing the monitored and potential changes as the Arctic warms. And indigenous hunters and subsistence villages will present the changes in lifestyle and traditions they are experiencing as the Arctic changes. For more information, visit http://www.alaskaseagrant.org.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus.

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Filed under bears, ecology, science of the seasons

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