Biology Reference
In-Depth Information
edged with stiff hairs to make them even wider, act as great paddles to propel the owner easily through
its aquatic environment.
Not surprisingly, polar bears subsist almost entirely on meat, for plant materials are scarce in this
great bear's habitat. Berries and other plant foods are consumed when available, but the seal is the polar
bear's main food supply. Such things as nesting birds and their eggs, as well as stranded whales, sup-
plement the bear's diet.
Polar bears can be incredibly patient hunters, waiting for hours beside a seal's breathing hole to dis-
patch the seal when it comes up for air. They will also stalk seals on the ice by doing what one scientist
terms “otter travel,” in reference to the otter's rather humpy land gait, which tends to emphasize the
height of the hindquarters. In this mode, the bear flattens its head and front quarters against the ice,
tucks its front paws beneath it, and propels itself slowly toward the seal with its hind feet and slightly
elevated rump. The sight of this huge beast creeping forward in such a strange position must indeed be
an astonishing one!
In addition to their other remarkable aquatic skills, polar bears can also dive to a depth of up to fif-
teen feet. They sometimes use this ability to pursue an escaping seal, or to swim underwater to reach a
seal basking on an ice floe: at the edge of the floe, the bear hurls itself out of the water to seize its prey.
The coastal brown bear is the world's largest bear, right? Not so fast—some knowledgeable scientists
aren't so sure. They think that the polar bear at least equals the brown bear in size, and may occasionally
exceed 1,600 pounds. Understandably, reliable polar bear weights are hard to come by; given the re-
moteness of most polar bears, weighing them, alive or dead, can be a daunting proposition. For the
present, then, we can think of the brown and polar bears as Their Ursine Majesties, sitting atop thrones
of equal height as the planet's largest land carnivores.
Almost everyone knows that polar bears are white—but almost everyone is wrong! The polar bear's
white appearance is part of an astounding twin adaptation that allows the bear to survive and function in
a land of almost unimaginable cold. The first adaptation is in the bear's long outer hairs. The center of
each hair conducts light, much like a fiberoptic strand. Some of this light filters through the translucent
outer part of the hair, making it
appear
white, although it doesn't have pigment to make it truly white.
The second adaptation is black skin, which readily absorbs the heat from the sunlight filtering down
through the centers of the hairs. These adaptations are highly unusual, although not unique, for arctic
foxes and seal pups also share them.
These adaptations combine to give the polar bear the best of two worlds, as it were. Without the
white-appearing coat's camouflage, it would be extremely difficult for the great predator to stalk and
kill its prey in a largely white world. Also, lacking the black skin underneath to absorb the heat of the
Arctic sun during that part of the year when it's visible, the bear would require a great deal more en-
ergy to keep itself warm. Working in tandem, these wonderful adaptations help ensure the polar bear's
success in its forbidding environment.
Although polar bears have been known to attack people, and certainly should be considered danger-
ous, scientists believe that they're far less aggressive and temperamental than inland grizzlies. They're
