Polar bears do not hibernate like many other bear species. Unlike other bears that enter deep dormancy, polar bears remain active year-round in the harsh Arctic environment. Their survival strategies are uniquely adapted to their icy habitat and primary food source.
Defining Hibernation
True hibernation involves a significant physiological shutdown. True hibernators experience drastic reductions in metabolic rate, body temperature, and heart rate for weeks or months. This state allows them to conserve energy during periods of extreme cold and food scarcity. Polar bears do not exhibit these profound physiological changes.
The Unique Case of Maternity Dens
Pregnant female polar bears are an exception to year-round activity. They excavate snow dens, known as maternity dens, between October and November. Within these insulated dens, they give birth to their cubs, usually in late December or early January. The den provides a sheltered, warmer environment for the tiny cubs, which are born blind and with sparse fur.
During their three to four months in the maternity den, the mother does not eat, drink, or defecate. She relies entirely on her fat reserves to sustain herself and nurse her cubs. However, unlike true hibernators, her body temperature remains relatively stable, around 36.9°C (98.4°F), and her metabolic rate does not drop to the extreme levels seen in other hibernating species. This period of reduced activity is a reproductive strategy, allowing the cubs to grow large enough to survive the Arctic conditions before emerging onto the sea ice with their mother in spring.
Adaptations for Arctic Survival
Most polar bears, including males and non-pregnant females, remain active throughout the Arctic winter. They possess adaptations that enable them to thrive in extreme cold without hibernation. A thick blubber layer, typically 5 to 10 cm (2 to 3.9 inches) thick, provides insulation and energy reserves, essential for maintaining core body temperature and sustenance.
Their fur coat has two layers: dense underfur for warmth and hollow guard hairs for insulation and water repellency. These adaptations help them retain heat effectively, even in temperatures as low as -40°C (-40°F). Large, wide paws with rough pads and short claws provide excellent traction on ice and snow, acting like snowshoes.
Polar bears primarily hunt seals, which are available year-round in the marine environment. This continuous access to high-fat prey, particularly ringed and bearded seals, allows them to maintain their energy reserves without needing to enter a prolonged state of dormancy due to food scarcity. They often hunt by ambushing seals at breathing holes in the sea ice.