The World of Polar Bears
A. Food preferences and resources
- Polar bears feed mainly on ringed seals and bearded seals. Depending upon their location, they also eat harp and hooded seals and scavenge on carcasses of beluga whales, walruses, narwhals, and bowhead whales.
- On occasion, polar bears kill young walruses and beluga whales.
- When other food is unavailable, polar bears eat reindeer, small rodents, seabirds, ducks, fish, eggs, vegetation (including kelp), berries, and human garbage.
B. Food intake
- A polar bear’s stomach can hold an estimated 15% to 20% of its body weight. It can assimilate 84% of the protein and 97% of the fat it eats (Stirling, 1988).
- Polar bears need an average of 2 kg (4.4 lb.) of fat per day to survive. A ringed seal weighing 55 kg (121 lb.) could provide up to eight days of energy for a polar bear (Stirling, 1988).
C. Methods of collecting and eating food
- Still hunting.
a. Still hunting is the most common method of hunting year-round.
b. The polar bear remains motionless beside a breathing hole or lead edge waiting for a seal to surface. When a seal surfaces, the polar bear bites onto the head or upper body, then flips the entire seal onto the ice.
c. Still hunting usually takes less than one hour, but polar bears will wait much longer.
- Stalking on land.
a. Stalking is a hunting method used in summer when seals haul out on sea ice.
b. Once spotted, the seal is slowly and steadily stalked by the polar bear. At 15 to 30 m (49.98 ft.) away, the polar bear suddenly charges the seal. With its claws or teeth, the polar bear grabs the seal before the seal can leave the ice.
- Aquatic stalk.
a. The aquatic stalk is a method also used in summer when seals haul out on sea ice.
b. The polar bear swims toward a hauled-out seal. Once the polar bear reaches the ice edge, the bear quickly emerges from the water and grabs the seal with its claws or teeth.
- Stalking birth lairs.
a. Stalking ringed seals at their birth lairs is a hunting method polar bears use in spring, when ringed seals give birth to their pups.
b. Ringed seal birth lairs are caves built under snow drifts next to a hole in the ice. The snow drifts are on stable sea ice attached to land.
c. Once a polar bear identifies a birth lair, it slowly and quietly positions itself next to the lair. If a polar bear smells or hears a seal in the lair, it slowly raises up on its hind legs and crashes down with its front paws to break through the lair roof.
d. To break the roof’s hard surface, several tries are sometimes needed, which may allow the seal to escape into the water.
e. This method is most commonly used by polar bear females with cubs under one year old.
(1) Mother seals and pups have the high fat content needed for hungry polar bear mothers and their growing cubs.
(2) Male polar bears that may attack young polar bear cubs don’t normally hunt seals in birth lairs.
(3) Birth lairs are usually on sea ice attached to land, allowing young cubs (who have little protective blubber) to avoid crossing water.
a. Once a seal is captured, a polar bear bites it several times on the head and neck before dragging it several meters from the water to feed.
b. The skin and fat are eaten first, followed by the meat.
c. Polar bears often stop to wash during feeding, using water nearby or rubbing in the snow.
d. Polar bears don’t always eat the entire kill. Carcass remains are scavenged by other bears, arctic foxes, and gulls.
A. Daily activity cycle Polar bears are most active the first third of the day and least active the final third of the day. In the Canadian Arctic, adult female polar bears with cubs hunt about 19% of their time during the spring ...
Adaptations for an Aquatic Environment
A. Swimming Polar bears are strong swimmers; they swim across bays or wide leads without hesitation. They can swim for several hours at a time over long distances. They’ve been tracked swimming continuously for 100 km (62 mi ...