You'd think the sheer weight of a polar bear would send him plunging through the ice, and the fact is, it can, if the ice is too thin. But for the most part, polar bears traverse and live on ice without breaking through to the frigid water beneath. Weight-bearing adaptations and their instincts help keep them on top of the ice.
Polar Bear Weight
The National Wildlife Federation describes polar bears as the largest carnivorous land mammals on Earth. Most are 7 to 8 feet in length when measured from the tip of the nose to the tip of the relatively short tail. Males can weigh as much as 1,700 pounds; females generally do not weigh more than 1,000 pounds. A polar bear's weight fluctuates throughout the year: up to 50 percent more after their hunting season than when the seal-hunting season began in the spring and summer months -- that's when seal pups emerge from their dens as warmer temperatures melt ice, exposing open water. The bulk of the weight gain is stored as fat to be used for survival in the coming winter months.
Feet Like Snowshoes
Just as humans use webbed snowshoes to stay on the upper crust of snow pack, polar bears employ a natural version of the same solution. Their massive and broad paws -- which measure approximately 12 inches in diameter for adults -- are disproportionately large compared with their bodies, allowing the polar bears to distribute their weight across a larger area, according to fact sheets from Sea World. Bumps called papillae, on the bottoms of their paws, provide additional traction, according to a PBS fact sheet on polar bears.
Even when polar bears get out on ice too thin to support their weight, they'll be able to navigate the cold water they find themselves in. Polar bears are often dubbed "sea bears" due to their highly capable aquatic abilities and their scientific classification -- Ursus maritimus. It's a moniker appropriately earned, as polar bears are strong swimmers, able to swim as fast as 6 miles per hour and up to 60 miles without pausing; they can dive 15 feet and remain submerged for as long as two minutes. Their massive paws work like paddles in the water.
Pounding the Ice
Polar bears wait at the edge of open water when hunting seals, waiting for the opportunity to pounce on what will be a tasty meal. They also use their massive paws to break through thinner ice to surprise and catch seals. In a Daily Mail Online report, the efforts of a mother polar bear to pound on the ice in Norway with her massive front paws was captured by Sue Forbes, a wildlife photographer. The mother bear reared up and thrust her full body weight forward on to the ice because her keen sense of smell detected a den of seals under the ice.
A Pick-Up Line
While male polar bears use scent to detect whether the tracks left behind are those of a female in estrus, human males have been known to use the issue of polar bear weight to gain the attention of human females. The pick-up line -- "How much does a polar bear weigh? Enough to break the ice," followed by an informal introduction such as, "my name is --" may be a lemon, it's a joke that's been around forever. As a pick-up line, the joke's success or lack thereof is detailed on website pages and in a book by Christopher Brya about dating trends.
- PBS: Polar Bear Fact Sheet: Bears of the Last Frontier
- National Wildlife Federation: Polar Bear
- Bear Infosite: Polar Bear
- North American Bear Center: Polar Bear Facts
- Encounters North: Polar Bears - Natural History
- Sea World: Polar Bears
- National Geographic: Plight of the Ice Bear
- Daily Mail Online: Mommy Bears go Hunting
- Jupiterimages/Photos.com/Getty Images