why do polar bears have a thick layer of blubber

Asked by: Audrey Simms, Cirencester
They are incredibly well insulated with a layer of blubber that can be up to 10cm thick covered with another 15cm of fur. Polar bears lose so little heat to their environment that they are almost invisible to thermal imaging cameras. But a recent study at the University of Buffalo found that polar bears have also evolved genes that produce more nitric oxide than other bear species. Nitric oxide is a signalling molecule and one of the mechanisms it controls is whether cells use their available nutrients to produce metabolic energy, or simply convert it into body heat.

Polar bears seem to be able to divert more of their bodyвs resources into generating heat. This relies on them getting enough fuel for this process and adult polar bears have a high calorie diet; they mostly eat seal blubber. A hunt starts with a scent. Polar bears can smell seals up to 20 miles (30 km) away, often by the scent left on their breathing holes. 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.

In the fall, when the ice is softer, seals cut holes in the ice so that they can come up for air when they need to breath. Polar bears find such breathing holes and wait, sometimes for several days, until a seal comes up for a breath. 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. When a polar bear spots a seal coming up for air, it gets down on all fours, delicately putting each paw on the ice to keep silent.

The bear then makes a shallow dive through the hole to grab the seal with its claws. Those sharp, 2 inch claws grip the seal extremely well. Still, seals sometimes get away. Polar bears have been known to get upset when they lose their prey, pounding the ice or throwing blocks of it in a sort of tantrum. When the hunt is successful, a bear will share a kill with others as long as they beg properly: keeping low, circling the kill and occasionally nudging the hunter with their noses.

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