Polar bears are apex predators of the Arctic, relying on the ocean and sea ice for survival. They are considered marine mammals, and their diet reflects their specialized existence. Their survival hinges on consuming calorie-rich prey.
Main Food Sources and Hunting
Polar bears primarily prey on seals, a dietary staple providing the high fat content necessary for survival. Ringed seals are the most common prey due to their abundance and manageable size, though polar bears also hunt bearded seals and harp seals. The blubber of these seals helps bears build fat reserves, crucial for enduring periods of food scarcity.
Polar bears employ several hunting techniques to capture seals on the sea ice. They often use “still-hunting,” waiting patiently at a seal’s breathing hole until a seal surfaces. Another strategy involves stalking seals resting on the ice. The bear crawls slowly, freezing when the seal raises its head, then charges from about 6 meters away to pounce. Polar bears also ambush seals at the ice edge or stalk them at birth lairs, snow dens built by seals over breathing holes.
Seasonal and Alternative Prey
While seals constitute the primary diet, polar bears are opportunistic feeders and consume other prey, especially when sea ice is scarce. When seals are less accessible, their diet can include larger marine mammals such as walruses, particularly young or vulnerable adults, and sometimes beluga whales or narwhals. These larger animals provide substantial meat and blubber.
During ice-free seasons, polar bears may also scavenge on carcasses of marine mammals found along the coast, such as bowhead or gray whales that wash ashore. These carcasses can provide significant nutrition for multiple bears. Less commonly, polar bears might consume birds, bird eggs, small mammals like lemmings, or vegetation like berries, grasses, or marine algae. However, these alternative food sources are less calorie-dense, making them insufficient for long-term sustenance.
Physical Traits for Feeding
Polar bears possess adaptations that make them efficient predators. Their powerful jaws are equipped with 34 to 42 teeth, including sharp canines up to 5 cm long for grasping prey and tearing flesh, and pointed molars for shearing meat. A significant gap, called a diastema, between their canines and cheek teeth helps them securely grip seals. Their strong, curved claws provide excellent traction on ice and enable them to pull slippery seals from the water.
An acute sense of smell is an important adaptation, allowing polar bears to detect seals from afar. They can smell a seal on the ice from up to 32 kilometers away and locate a seal’s breathing hole under more than half a meter of snow. This olfactory system guides their hunting strategy, especially when visibility is low. The thick layer of blubber on a polar bear insulates them from the cold and stores energy for periods of fasting.
Environmental Changes Affecting Food
The reduction in sea ice directly impacts the availability of polar bears’ primary food source. Sea ice serves as a hunting platform for seals, and its decline limits bears’ access to this prey. A shorter sea ice season means less time for polar bears to hunt and accumulate the fat reserves needed to survive lean periods.
This forces bears to spend longer periods on land, where access to their preferred high-fat diet is minimal. Increased reliance on less nutritious terrestrial food sources, such as birds or vegetation, does not provide enough calories to sustain their large body size. Studies show that polar bears often lose body mass when forced to forage on land, highlighting the link between sea ice loss and their ability to maintain a sufficient diet. This environmental shift challenges polar bear populations.