Why?
Polar bears do not hibernate like grizzly bears, but pregnant polar bears will enter dens in the autumn, after gorging heavily at the end of the summer and prior to giving birth. Dens usually consist of a snow tunnel, or earth if it is not yet snowing, with one to three chambers and inside she will live alone, her heart beat slowed to a similar state of hibernation, yet with a high enough temperature to care for her cubs.
Polar bears give birth in November and December time to one to three blind cubs weighing just two pounds and covered in downy fur. She will nurse them, living off her fat reserves, until it is time to leave the den in February or March when her little ones are capable of trekking with her. At this time, they head out to hunt on the coast together. By denning, the mother is avoiding predators such as wolves or male polar bears, allowing her cubs to grow to a reasonable size before facing the harsh realities of the natural world. In March she will break open the front of the den, allowing her cubs outside for the first time. They’ll spend up to two weeks around the den, grazing and giving the cubs some time to practice using their legs and play fighting whilst she grazes on the vegetation, the first thing she will have eaten in months. After this, they head out to hunt on the coast.
This area of the Hudson Bay provides excellent, reliable snow and good access back to the floe edge for hunting in the summer. The polar bears return here year after year and in March each year, they leave their dens, cubs in tow.
