Polar Bears vs. Black Bears

Mira Unverzagt and Jason Lee
Ecology – Biology 408
December 8, 2000

The polar bear is a mighty hunter of seals. The most carnivorous of the bears, it is also the most patient. They will sit near a seal blowhole for hours, waiting, until the animal surfaces. When it does, it is all over for the seal. One powerful blow from a forepaw brings a swift meal for the bear.

Adult male polar bears weight from 775 to more then 1,500 pounds. Females are considerably smaller, normally weighing 330 to 550 pounds. Polar bears range throughout the Arctic in areas where they can hunt seals at open leads. The five "polar bear nations" where the ice bears are found include the United States, Canada, Russia, Denmark, and Norway.

Like many other bear species, the ears of the polar bear are round. They are, however, smaller and closer to the head. This, along with the overall shape of the animal helps to make it a formidable swimmer. The paws are large and slightly webbed which also help him swim as well.

The conditions of the polar north are harsh, with temperatures well below freezing. In order to survive, the polar bear has to be an expert survivalist. The skin of the bear is black to draw every bit of possible heat from the sunlight. The hairs of the pelt appear to be white, but are actually pigment-free and translucent which transmit light down to the skin. A thick layer of blubber, approximately 4.5 inches thick, provides polar bears with such excellent insulation that their body temperature and metabolic rate remain the same even at freezing temperatures. A polar bear’s body temperature is 98.6 degrees Fahrenheit, which is average for many mammals.

On severely cold days with fierce winds, polar bears dig out a shelter in a snow bank and curl up in a tight ball to wait out the storm. They also curl up to retain their body heat. The polar bear’s compact ears and small tail also help prevent heat loss. Polar bears also have two layers of fur for further protection from the cold. Polar bears actually have more problems overheating then they do with cold. Even in very cold weather, they quickly overheat when they try to run.

Polar bears can run quite swiftly, but are most agile in the sea. They are excellent swimmers, and can reach speeds of up to 6-mph n the water. They are good divers as well. When being pursued by hunters in open water, polar bears have been known to escape by plunging 10 to 15 feet below the surface and resurfacing a good distance away. They also have been seen swimming up to 100 miles away from ice or land.

Polar bears communicate with each other through a combination of body language and vocalizations. A deep growl serves as a warning to other bears. Growls are frequently employed to defend a food source. To beg food from another bear a polar bear will approach slowly, circle around the carcass, and then meekly offer a nose-to-nose greeting. Bears who observe proper manners are frequently allowed to share a kill. When a polar bear wants to play, he communicates this to another bear by wagging his head from side to side.

The American black bear (Ursus americanus) inhabits wooded and mountainous areas throughout most of North America, from Alaska to Florida, Canada to Mexico. They tend to wander great distances, some adult males having lifetime ranges of 500 to 620 square miles. The distances wandered by the black bears vary greatly depending on the amount of food and type of food available from area to area.

The black bear is approximately 5 feet long and varies in weight from 125 to 600 pounds. It has small eyes, rounded ears, a long snout, a large body, and a short tail. The shaggy hair varies in color from white through chocolate brown, cinnamon brown, and blonde to black, but most black bears are indeed black or a darker shade of brown.

While black bears are capable of standing and walking on their hind legs, their usual posture is on all fours. Each paw of the black bear has five very strong retractable claws used for tearing, digging, and climbing. One blow from a powerful front paw is enough to kill an adult deer.

Black bears have a wide and varied diet. They can and will eat almost anything. They are most fond of honey, nuts and berries, and small vegetation. Given the opportunity, black bears will feed on small animals and even humans if the bear is scared in to defense.

During hibernation, black bears body temperatures usually do not fall below 88 degrees Fahrenheit, which makes it easier for them to wake up. They normally hibernate during the winter season and always create a den to hibernate in. One amazing fact about the hibernation of black bears is that they can go for up to 7 months without food during hibernation.

While there are several differences between the two species of bears, black and polar, there are also obvious similarities between the two. The major reason for the great number of similarities between the two species is the fact that it is believed that polar bears actually evolved from black bear ancestors over 200,000 years ago. The major source of the differences between the two species is due to the fact that the polar bears migrated and evolved to adapt to very cold temperatures.