Polar bears are apex predators within their harsh Arctic environment. Their survival is intricately linked to a specialized diet, providing the necessary energy and sustenance to thrive in frigid conditions.
The Staple Diet: Seals
The primary food source for polar bears consists of seals, particularly ringed seals and bearded seals. These marine mammals are important due to their substantial blubber layers, which provide the high-fat content polar bears require for energy and insulation against the cold. A polar bear can consume a significant amount of seal blubber in a single sitting, sometimes as much as 45 kg (100 lbs). When hunting is successful and food is plentiful, polar bears often prioritize eating only the blubber and skin, leaving the remaining carcass for scavengers.
Polar bears employ various hunting techniques to capture seals, largely dependent on the presence of sea ice. A common method is “still hunting,” where a bear waits patiently at a seal’s breathing hole in the ice. When a seal surfaces for air, the bear ambushes it, pulling it onto the ice. They also stalk seals resting on the ice, charging when within range. In spring, polar bears target seal birthing lairs, which are snow dens on stable sea ice, breaking through the snow to access the vulnerable pups.
Beyond Seals: Opportunistic Eating
While seals form the bulk of their diet, polar bears are opportunistic feeders and will consume other available food sources. They may scavenge carcasses of larger marine mammals, such as beluga whales or walruses, that wash ashore or become trapped in ice. Although hunting a live walrus is dangerous due to their size and tusks, polar bears occasionally target young, sick, or isolated individuals.
Other supplementary food items include birds, bird eggs, fish, and small land mammals like reindeer or rodents. During periods of extreme scarcity, polar bears have also been observed eating vegetation such as berries, moss, grass, and kelp. However, these alternative foods generally lack the high-fat content found in seals and do not provide sufficient calories for a polar bear’s long-term energy requirements.
Dietary Adaptations and Future Challenges
The polar bear’s diet is intrinsically linked to the Arctic environment, particularly the presence and stability of sea ice. Their physiological adaptations, including a digestive system highly efficient at processing fat, emphasize their specialization for a lipid-rich diet. Changes in sea ice cover directly impact their ability to access their primary seal prey, leading to reduced hunting opportunities.
As sea ice melts earlier and freezes later, polar bears are forced to spend extended periods on land, away from their main food source. During these ice-free periods, bears often lose a significant amount of body mass, averaging about 1 kilogram (2.2 pounds) per day. Studies show that foraging for land-based foods, even when available, does not adequately compensate for the caloric deficit incurred from lost seal hunting. The lower nutritional value of terrestrial resources, which are typically high in protein and low in fat, cannot sustain these large carnivores. This reliance on a specific fat-dense diet highlights the challenges polar bears face in adapting to a rapidly changing Arctic.