November 9, 2009
Generally, having white fur is only good if you live in a white environment. The arctic fox, for example, would probably be eaten pretty quickly if it lived in Florida. Likewise, black bears that inherit two copies of a recessive gene for a white coat tend not to live very long, becoming victims of wolves or grizzly bears.
Except on a few small islands in western Canada that lack wolves and grizzly bears. On those islands, 20 to 30 percent of the black bears are white. They are known as “spirit bears” or Kermode bears. Native American tradition from the region says that the spirit bears lived on the ice-covered landscape of times long ago. Scientists, however, have hypothesized that the white color is a more recent mutation that has become prevalent on these islands due to genetic drift.
Whenever the trait developed, it may have given the white bears some sort of advantage. In a new study, published in the Biological Journal of the Linnean Society, biologists from British Columbia started looking at the diet and foraging behavior of the white and black bears. Both types eat the same kind of food, and go after it in the same ways. The difference comes during the autumn salmon run. During the day, the white bears are about 20 percent more efficient in their fishing compared with the black bears. The biologists say that the white fur is less visible in the water during the day and the salmon are less likely to try to evade the white bears. The spirit bears are able to fatten up faster for winter, which translates to better survival.
It’s not all good news for the Kermode bears of western Canada, however. As in many other places along the west coast of North America, the spirit bears’ salmon are on the decline.
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