Polar Bear

## Baby, it's cold outside!

Perhaps no other animal symbolizes the frozen tundra regions of the Earth as do polar bears. They live on ice and snow, but that’s not a problem - these bears have some cool ways to stay warm!

### Hair

An outer coat of long guard hairs that stick together when wet protects a dense, thick undercoat of fur. Even though polar bears look white, their hair is really made of clear, hollow tubes filled with air. Scarring or residue on the fur can cause the “white” fur to appear to human eyes as cream colored, yellow, or even pink in the Arctic light.

### Fat

Fat acts as a nutritional reserve and energy storage when food can’t be found and may provide the ability to generate heat to help insulate polar bears from the freezing air and cold water. This fat may also help the bears float in the water. It is 2 to 4 inches (5 to 10 centimeters) thick.

### Shelter

Unlike brown bears and black bears, polar bears do not hibernate, and only pregnant females' over-winter in dens. While in the den, the pregnant female’s activity level decreases and her metabolism slows down. During this period, she gives birth and nurses her cubs. Sometimes, when weather conditions are particularly rough, other bears may dig temporary shelters where they spend several days at a time.

## Who's the biggest?

The polar bear is the newest of the eight bear species, and scientists believe that the polar bear evolved about 200,000 years ago from brown bear ancestors. Both polar bears and brown bears are big and are the largest land carnivores. But most experts agree that polar bears are the longest bears, as males may measure over 10 feet (3 meters) when standing on their hind legs.

## At home on the ice

Polar bears spend their days hunting and sleeping after a good meal. For some, these meals need to last them during the upcoming months when the Arctic ice has melted, and they are forced to spend their days on land waiting for the fall cold to once again form the very important ice. When not hunting, polar bears are resting, perhaps as much as 20 hours a day. Polar bears are great bed makers, building nest-like beds in seaweed piled up on the coast, digging deep caves of snow into the bluffs, or resting in a shallow snow bed and letting the blowing snow cover them, making for a snug day den.

## Sea bears

Polar bears live throughout the Arctic in areas where they can hunt seals in wide cracks in the sea ice or at breathing holes. The taxonomic name for polar bears is *Ursus maritimus*, which means "sea bear," a fitting name for these champion swimmers. They have been known to swim more than 60 miles (about 100 kilometers) without rest in search of food, using their broad front feet for paddling and their back legs like rudders to steer. Unfortunately, due to loss of ice, the bears are now having to swim longer distances, as much as a few hundred miles, which takes a toll on their energy and fat storage.

## What's on the menu?

Polar bears have no natural enemies. Strong, ferocious, intelligent, and patient hunters, they top the food chain in the Arctic, where they dine primarily on seals. The bears can remain motionless for hours above a seal's breathing hole in the ice, just waiting for a seal to pop up. The polar bear's nose is so powerful it can smell a seal on the ice 20 miles (32 kilometers) away, sniff out a seal's den that has been covered with snow, and even find a seal's air hole in the ice up to 1 mile (1.6 kilometers) away. No wonder many people call them "noses with legs!"

Stiff fur on the sole of each foot keeps the bear from slipping on the ice. It also muffles the sound of the bear’s approach when sneaking up on a sleeping seal. It costs a polar bear twice as much energy as most other mammals to move about in its Arctic environment. This helps explain their preference for resting frequently and hunting for seals using ambush techniques rather than stalking their prey.

The ringed seal is the polar bear’s main prey, as it is the most numerous seals in the Arctic. Polar bears typically kill and eat every four to five days. These bears eat just about anything if they have the opportunity, but it is important to remember that they need access to the high-calorie diet that seals provide. While they will eat walrus, caribou, beached whales, grass, and seaweed, none of these have been shown to provide adequate and reliable nutrition for wild polar bears.

Polar bears at the San Diego Zoo get a special ground-meat diet made for zoo carnivores, dog kibble, trout and other fish, as well as root vegetables and lettuce as treats. Cow femur bones and thawed rabbits are added once or twice per week. Polar bears get very little nutrition or calories from vegetables, so these items are offered as treats, and the whole carrots keep their teeth clean.

## Snow can be fun!

Polar bears are highly intelligent and playful. In the wild, two or more bears sometimes form "friendships" that last for weeks or even years. These bears wrestle as a form of play and may also feed and travel together. Individual polar bears have been observed sliding repeatedly downhill or across ice for no apparent reason other than just for the fun of it!

## Den mothers and cubs

Breeding season for polar bears goes from about March to mid-July. A pregnant female digs a maternity den, usually into a snowbank, in October or November. The den is often no bigger than a telephone booth, but it can be about 40 degrees warmer in there. The female gives birth to one to three cubs, usually twins, in December or January.

For such a big animal, they sure start out small! Cubs weigh about 1 pound (0.45 kilograms) when born and are hairless and have their eyes closed at birth. They depend on the mother to keep them warm and fed. Milk from polar bear mothers is 35 percent fat, the richest milk of any bear species. This helps the cubs grow quickly, and by April they weigh more than 20 pounds (9 kilograms) and start exploring with their mother outside the den. At about two years of age, they are ready to be on their own.