There’s no mistaking this large, specialized top predator padding along the snow with a small white cub following close behind. Polar bears Ursus maritimus are one of the best-known species on the planet, though few people will ever have the chance to see them in their Arctic home. Polar bears loom large on the tundra, with some males reaching 10 feet tall when standing upright. This charismatic animal is classified as a threatened species.
Despite the long, harsh winter, polar bears do not hibernate. But females do build dens to give birth and “hole up” with their newborn cubs. During this time, their bodily functions slow down in a process scientists call “winter sleep,” but the bears can be easily awakened. Polar bears possess adaptations for an almost exclusively carnivorous diet, a semi-aquatic lifestyle, and the largest home range of any terrestrial mammal.
Big Hairy Deal
Living on the freezing Arctic tundra has led to some great adaptations for polar bears. A thick layer (two to four inches) of blubber helps insulate the animal against the cold, acts as a nutritional reserve when food cannot be found, and makes them more buoyant in the water. Their fur consists of a dense, thick undercoat protected by an outer coat of long guard hairs that stick together when wet, forming a waterproof barrier to keep the cold water off their skin. Their hair is made of clear, hollow tubes filled with air, and their skin is black, which better absorbs solar warmth. With feet the size of frying pans and coarse fur between its footpads, the bear is able to maintain traction on the ice.
Seal of Approval
Life in the unforgiving climate of the Arctic requires a high-calorie diet, and ringed seals are rich in fat. Polar bears rely on Arctic sea ice as a platform from which to hunt these animals. On average, the bears require 47 seals each year to maintain enough fat to get through the summer months when they cannot hunt. Polar bears lie in wait at the seals’ breathing holes for hours or even days, remaining still as snow until the seals come up for a breath. In a flash, they grab the seal, drag it onto the ice, and devour it. They can eat 40 pounds of food in one sitting! The bears must wait for the sea to freeze before they can begin hunting in the autumn. Climate change affects when the sea freezes—as the freeze comes later and later, the bears go hungry for longer and longer. Polar bears face losing about 2.2 pounds of body weight daily for several months each year.