Polar bears, apex predators of the Arctic, possess a highly specialized diet intricately linked to the marine ecosystem. This dietary specialization allows them to thrive in an extreme environment where few other large mammals can endure.
The Primary Feast: Seals
The polar bear’s diet consists predominantly of seals, particularly ringed and bearded seals. These marine mammals provide the high fat content polar bears require for insulation and energy storage in the frigid Arctic. Polar bears efficiently metabolize fat, converting seal blubber into energy for survival and warmth.
Seal blubber is particularly rich in calories, making it an ideal food source. A polar bear can consume up to 45 kilograms (100 pounds) of seal blubber in a single feeding. When hunting conditions are favorable, they may prioritize eating only the blubber and skin, leaving the remaining carcass for scavengers like Arctic foxes. This preference maximizes caloric intake, essential given their high energy demands.
Masters of the Hunt: Hunting Techniques
Polar bears employ several hunting strategies to capture their seal prey. One common method is “still-hunting,” where a bear waits motionless by a seal’s breathing hole in the ice, sometimes for hours. When a seal surfaces for air, the bear swiftly lunges to capture it. This technique is energy-efficient and effective in areas with numerous seal breathing holes.
Another strategy involves “stalking and pouncing” on seals resting on sea ice. The bear slowly approaches a hauled-out seal, using available cover, then charges rapidly to secure its prey. Polar bears also utilize “aquatic stalking,” swimming stealthily underwater toward seals resting on ice floes before emerging to ambush them. Their keen sense of smell, capable of detecting seals from afar, aids in locating prey.
Beyond Seals: Opportunistic and Seasonal Foods
While seals are the primary food source, polar bears are opportunistic feeders and will consume other items, especially when seals are scarce or during certain seasons. They may scavenge on the carcasses of larger marine mammals, such as whales or walruses, that wash ashore. These provide substantial amounts of meat and blubber, offering an important caloric supplement.
During periods when sea ice is limited, typically in the summer, polar bears may spend more time on land and diversify their diet. This can include preying on birds, bird eggs, and small mammals like rodents. Occasionally, they may also hunt larger land animals such as reindeer or consume vegetation like berries and kelp. However, these alternative food sources generally do not provide the high-fat content found in seals, making them less sufficient for meeting the bears’ long-term energy requirements.
The Changing Menu: Climate Impact on Diet
Environmental shifts, particularly the reduction of Arctic sea ice, are influencing the polar bear’s traditional diet. As sea ice melts earlier in spring and forms later in autumn, polar bears have less time and opportunity to hunt their primary seal prey from the ice platform. This forces them to spend extended periods on land, away from their main food source.
Increased time on land leads to greater reliance on less nutritious, land-based food sources. While polar bears have been observed consuming items like berries, grass, bird eggs, and even refuse from human settlements, these foods are not calorically dense enough to sustain their large body size and high energy needs. Studies indicate that polar bears forced onto land often lose significant body mass, highlighting the insufficiency of these alternative diets. The changing availability of sea ice directly impacts their ability to access the fatty seals essential for their survival.