Hobbies And Interests
Thermoregulation Adaptations
Polar bears inhabit large portions of the Arctic Circle, where winter temperatures may plummet to minus 50 degrees. The bears display a number of adaptations for dealing with such frigid environments. They sport a layer of fat called blubber under their skin that may be more than 4 inches thick. Blubber may account for up to 40 percent of the bear's total weight. Polar bear fur consists of two insulating layers: air-trapping underfur and longer guard hairs. The hollow fur may help funnel solar radiation down to the black hide, effectively colored to absorb heat energy. The scattering of visible light and absorption of ultraviolet light in the bear's hair gives it its distinctive white or yellowish hue.
Overheating
So well-insulated are polar bears that they easily overheat, especially if exerting themselves for a prolonged period or if exposed to high summer temperatures of 70 degrees or more. They excel at conserving energy. Their usual mode of locomotion is a steady, majestic but unhurried stride across sea-ice and snowfields. Networks of blood vessels track close to the bear's skin, allowing them to transfer out heat. Polar bears often retreat to water on hot days -- an activity pattern easily observed in zoological parks.
Denning
Polar bears do not hole up in dens during winter in the same manner as most populations of brown bear and American black bear, which hibernate not because of cold temperatures but because of scarcity of food. Pregnant female polar bears excavate snow dens in winter to give birth, but males and non-pregnant females spend the season hunting on the sea-ice. Polar bears may engage in a kind of "walking hibernation" in the late summer and early fall, which across much of their range is the time of least access to prey, Ian Stirling wrote in his book, "Polar Bears." Their physiological condition then, measured by blood chemistry, can resemble that of a hibernating American black bear, suggesting polar bears adopt an energy-conserving mode when food is scarce.
Climate Change
As of the early 21st century, polar bears are playing an important role in investigations of widespread climate change. As global temperatures warm, sea ice in the Arctic may last for less and less duration, and retreat significantly. Such changes could be disastrous for the bear, which relies on the frozen ice to hunt. Warming temperatures might also promote the collapse of winter maternity dens.