While many bears hibernate, polar bears do not truly enter a deep, prolonged winter sleep. Their behavior differs significantly from other bears, as they generally remain active throughout the coldest months. This distinction is key to understanding how they survive in the Arctic.
Understanding Hibernation and Polar Bears
True hibernation involves profound physiological changes: a significant drop in body temperature, a drastically slowed metabolic rate, and a reduced heart rate. Animals in this state typically do not eat, drink, or excrete for extended periods, relying on stored fat. Polar bears do not exhibit these extreme shutdowns; their metabolism and body temperature remain relatively high. Instead, “denning” or “winter lethargy” better describes the reduced activity some polar bears engage in.
The Maternity Denning Period
The closest polar bears come to a prolonged inactive state is during the maternity denning period, exclusively for pregnant females. These mothers enter dens to give birth and protect their vulnerable cubs from harsh Arctic conditions. Cubs are born tiny, blind, and with little fur, making the insulated den a necessary nursery.
Pregnant females dig dens into snowdrifts, usually from October or November. They remain there for three to four months, giving birth to one to three cubs around December or January. During this time, the mother does not eat, drink, or excrete, relying on fat reserves to sustain herself and nurse cubs.
While her heart rate and metabolism slow, her body temperature does not drop drastically, as a high temperature is needed for pregnancy and nursing. This fasting can lead to a significant loss of body mass, sometimes up to 43%. The family emerges in March or April, when cubs are larger and better equipped to survive.
What Other Polar Bears Do in Winter
Unlike pregnant females, most other polar bears remain active throughout the Arctic winter. Male and non-pregnant females continue to roam the sea ice, their primary hunting ground. Extensive sea ice provides the best opportunities for hunting seals, their main food source.
These bears actively hunt by waiting at seal breathing holes or stalking prey. Their survival depends on accumulating sufficient fat reserves to sustain them through scarcer food periods.
Despite extreme cold, these polar bears maintain a constant body temperature, continuously expending energy to navigate and find food. While they may seek temporary shelter in snow pits to conserve warmth, they do not enter a prolonged state of dormancy.