Tours bear witness to Earth's sentinel species (1/5ページ)

There's something vaguely disturbing about the George Hamilton tan sported by the flight attendant on the Convair 580 prop that's buzzing into the Great White North. Ditto, the declaration from the Churchill office worker that she's wearing flip-flops in mid-October. And the researcher who shows up at the local bakery in his shirtsleeves.

This is, after all, winter's eve in the Canadian Sub-Arctic, when the vast waters of Hudson Bay solidify, and the world's southernmost population of polar bears ventures back out onto the ice for a blissful seven months of gorging on the ringed seals that dwell below its crust.

The so-called bear season in October and November is also the time when 7,500 visitors converge on this Arctic outpost of 1,100 hearty souls to witness the annual migration of the magnificent white behemoths.

Interest in the tours is keen, in part, because of bleak predictions that global warming could cause the world's polar bear population to shrink by two-thirds in the next 50 years. As the bears' primary hunting grounds, polar ice is crucial to their survival. But after a 20-year warming trend, Hudson Bay is melting an average of three weeks earlier, scientists say. And it's freezing later, which keeps the bears land-bound longer. On terra firma from July to November, they grow hungry and skinny in their "walking hibernation" until their return to the ice to bulk up over the winter and spring.

The Western Hudson Bay population, the most studied group of bears, dropped from 1,140 to 950 in the past decade. The average weight of females is down from 583 pounds to 418 pounds, which has negative reproductive consequences. Moreover, the mortality rate for bears between birth and age 5 is up 50 percent because of the shortened hunting time on the ice, says Robert Buchanan, president of Polar Bears International, a group that supports research and education.

"There's a difference between weather and climate, but I've never experienced it this warm for this long in all the years I've been coming here," says Buchanan, a 20-year bear-season resident of Churchill. "Is it disturbing? Yes. Polar bears are the sentinel species for global climate change. They're the canary in the coal mine."