Bear Facts
Polar Bear Fur
Despite what our eyes tell us, a polar bear's fur is not white. Each hair shaft is pigment-free and transparent with a hollow core. Polar bears look white because the hollow core scatters and reflects visible light, much like ice and snow does.
When photographed with film sensitive to ultraviolet light, polar bears appear black. Because of this, some scientists speculated that the polar bear's hollow hairs serve as fiber optic guides that conduct light to their black skin. The widely repeated theory was disproved in 1988 by Daniel W. Koon, a physicist at St. Lawrence University in Canton, New York.
Koon and a graduate assistant, Reid Hutchins, obtained polar bear hair from the Seneca Park Zoo in Rochester, New York. Their experiments showed that a one-fifth inch strand of polar bear hair was able to conduct less than a thousandth of a percent of the applied ultraviolet light. The high loss rate proved that the polar bear's black skin is not absorbing meaningful amounts of ultraviolet light. Instead, Koon believes the ultraviolet light is absorbed by the keratin making up the hair.
Because the polar bear's fur lacks pigment, it appears white when clean and in sunlight, especially just after the molt period, which typically begins in late April or May and is complete by late summer. Before the molt period, the polar bear's fur can appear yellowish due to oil from prey.
Occasionally, polar bears in a zoo environment will turn green due to colonies of algae growing in their hollow hair shafts. This happened to three polar bears at the San Diego Zoo in 1979. Although the algae in no way harmed the animals, zoo veterinarian Phillip Robinson restored the bears' white fur by killing the algae with a salt solution.
The polar bear's thick fur includes a dense undercoat topped by guard hairs of various length. In addition to its insulating fur, the bear's blubber layer can measure 4.5 inches thick. These insulating factors keep the bears so cozy that they experience almost no heat loss. In fact, the insulation is so effective that adult males quickly quickly overheat when they run.
Because polar bears give off no detectable heat, they do not show up in infrared photographs. (Infrared film measures heat.) When a scientist attempted to photograph a bear with such film, he produced a print with a single spot—the puff of air caused by the animal's breath.
When photographed with film sensitive to ultraviolet light, polar bears appear black. Because of this, some scientists speculated that the polar bear's hollow hairs serve as fiber optic guides that conduct light to their black skin. The widely repeated theory was disproved in 1988 by Daniel W. Koon, a physicist at St. Lawrence University in Canton, New York.
Koon and a graduate assistant, Reid Hutchins, obtained polar bear hair from the Seneca Park Zoo in Rochester, New York. Their experiments showed that a one-fifth inch strand of polar bear hair was able to conduct less than a thousandth of a percent of the applied ultraviolet light. The high loss rate proved that the polar bear's black skin is not absorbing meaningful amounts of ultraviolet light. Instead, Koon believes the ultraviolet light is absorbed by the keratin making up the hair.
Because the polar bear's fur lacks pigment, it appears white when clean and in sunlight, especially just after the molt period, which typically begins in late April or May and is complete by late summer. Before the molt period, the polar bear's fur can appear yellowish due to oil from prey.
Occasionally, polar bears in a zoo environment will turn green due to colonies of algae growing in their hollow hair shafts. This happened to three polar bears at the San Diego Zoo in 1979. Although the algae in no way harmed the animals, zoo veterinarian Phillip Robinson restored the bears' white fur by killing the algae with a salt solution.
The polar bear's thick fur includes a dense undercoat topped by guard hairs of various length. In addition to its insulating fur, the bear's blubber layer can measure 4.5 inches thick. These insulating factors keep the bears so cozy that they experience almost no heat loss. In fact, the insulation is so effective that adult males quickly quickly overheat when they run.
Because polar bears give off no detectable heat, they do not show up in infrared photographs. (Infrared film measures heat.) When a scientist attempted to photograph a bear with such film, he produced a print with a single spot—the puff of air caused by the animal's breath.
Page 1 of 1