The polar bear has a white fur, a color that is the result of millennia of evolution and adaptation to blend in and keep its warmth. A peculiarity of the fur of polar bears is the structure of the hair. The fur may appear white, but it is actually formed of transparent, hollow, straw-like hairs.
The polar bear's skin is dark, but the high reflectivity of these hollow tubes makes everything appear white. Thanks to this phenomenon, bears can sometimes appear a different color, with a tinge of green. From the analyzes conducted on the specimens at the San Diego Zoo, the outer surfaces of the polar bear hair appeared clean and smooth.
The coloration was clearly attributable to the presence of algae within the hairs, particularly in the hollow medulla of many of the larger and stiffer hairs of the outer coat. Within some hairs the hollow spaces were partly occupied by masses of small greenish algal cells.
What happened at the San Diego Zoo
At the San Diego zoo, such as Cologne, Germany, and Nagoya, Japan, some bears' fur turned green without a plausible explanation. The researchers then explained that the coloration, particularly evident on the sides, legs and along the rump of the animals, depended on some algae present not on the surface of the fur but inside the individual hairs, deposited following some dives in the lakes of the park.
The polar bear lives in the Arctic and its habitat is included in 6 countries: Canada (Manitoba, Newfoundland, Northwest Territories, Nunavut, Ontario, Québec, Yukon), USA (Alaska), Russia (Krasnoyarsk, Magadan, Northwestern Federal District, Western Siberia, Yakutia), Greenland, Norway (Svalbard), Iceland.
The current polar bear population is estimated at 20-25,000, 60% of which are in Canada. As evidence of this, a polar bear is depicted on the Canadian 2 dollar coin. The most famous hunting method of polar bears is that used for seals: the plantigrade hears the sound of the prey under the ice, lurks near a crack and, as soon as the prey comes out to breathe, kills it with a violent paw.
Only the males have such powerful musculature and the size to attack belugas and narwhals, both up to five and a half meters long, easily over 1000 kg in weight and the latter with the long tusk typical of males. Once the prey has been identified, often a young or a female narwhal, the white bear enters the water and nimbly attacks the cetacean in the delicate points, such as the fins and the belly, avoiding the deadly blows.