Polar bears, large carnivores of the Arctic, are apex predators adapted to an extreme environment. They primarily inhabit the icy expanses characterized by frigid temperatures and seasonal sea ice. Their survival in this harsh habitat is deeply intertwined with a specialized diet that provides substantial energy.
Primary Prey on Sea Ice
Polar bears’ diet heavily depends on marine mammals, particularly seals, hunted from sea ice. Ringed seals are a common and preferred prey due to their abundance and manageable size. Bearded seals also form a significant part of their diet, especially for larger male bears. These seals are rich in fat, an energy-dense food source highly beneficial for polar bears.
The high fat content of seals, particularly their blubber, is crucial. When seals are plentiful, polar bears may consume only the blubber and skin, leaving the rest for scavengers. This energy-rich diet is fundamental to building up the thick layer of fat that insulates polar bears against the intense cold of the Arctic. Other seal species, such as harp, hooded, and ribbon seals, are also hunted when available.
Hunting Methods
Polar bears employ several specialized hunting strategies on sea ice. One common method is “still-hunting,” where a bear waits patiently by a seal’s breathing hole in the ice. When a seal surfaces for air, the bear quickly strikes, pulling it onto the ice. This technique requires considerable patience, as a bear may wait for hours or even days.
Another technique involves stalking seals resting or basking on the ice. The bear uses its white fur for camouflage, slowly approaching with its head and neck lowered. As it gets closer, the bear charges rapidly, aiming to catch the seal before it escapes into the water.
Polar bears also utilize their keen sense of smell, which can detect seals from miles away and even under thick layers of ice, to locate prey or their birth lairs. During spring, polar bears may break into ringed seal birth lairs, which are snow caves built over ice holes, to prey on seal pups.
Seasonal and Opportunistic Foods
When primary seal prey is less accessible, especially during periods of reduced sea ice, polar bears supplement their diet with opportunistic food sources. They may scavenge on marine mammal carcasses that wash ashore, such as whales and walruses. These large carcasses provide a significant, albeit infrequent, food supply for multiple bears.
Beyond marine mammal carrion, polar bears also consume smaller, land-based items. This includes bird eggs and various species of birds, as well as small mammals like lemmings, voles, and other rodents. Some plant matter, such as berries, grasses, moss, and seaweed, may also be eaten. However, these alternative foods are generally less nutritionally valuable and do not provide the same energy density as seals.
Dietary Needs and Survival
The polar bear’s diet is fundamental for its survival in the extremely cold Arctic environment. Their high-fat intake from seals allows them to accumulate a thick layer of blubber, which serves as insulation against the cold and a vital energy reserve. This stored fat is especially important for sustaining them during periods when food is scarce or when they are forced to fast, such as during the summer months when sea ice melts.
Polar bears possess a digestive system uniquely adapted to process a high-fat diet. This specialization enables them to efficiently absorb nutrients from their prey, with studies indicating they can assimilate a high percentage of fat and protein. The ability to store large amounts of fat directly influences their overall health, reproductive success, and capacity to endure the severe Arctic winters. Female polar bears, for instance, must build substantial fat reserves before entering dens to give birth and nurse cubs, relying entirely on these reserves for months.