It is a crisp, sunny November morning in Churchill, Manitoba, the self-styled "polar bear capital of the world," and the early stages of the annual bear season are in full swing.
The town's moniker is merited: established as a fur trading settlement 1717, it lies directly in the path that a population of polar bears follows from its summer resting areas to the sea ice of Hudson Bay, where the bears spend late fall, winter and early spring feasting primarily on ringed and bearded seals.
In the past, especially as Churchill grew in the mid-twentieth century following the establishment of a military facility, the close proximity of humans and bears inevitably ended poorly for the latter, and polar bears that came into town were commonly shot on sight.
Over the last several decades, however, the community has employed an entirely different approach: residents and visitors alike are taught to be bear-aware; warning signs are posted in areas of high polar bear activity; and a Polar Bear Patrol, operated under the aegis of the Manitoba Department of Conservation, encourages potential problem bears to keep moving rather than loiter in Churchill's streets.
On a recent Monday evening, as the Northern Lights flickered overhead, the air was filled with the sound of cracker shells – explosive warning rounds fired from a shotgun – as the patrol shooed a bear along the beach and away from town.
Today, shooting at bears is done almost entirely with cameras; during polar bear season (which runs roughly for three weeks from late October), the 900 or so residents of Churchill are joined by perhaps ten times that many tourists, who take day trips from the town to the shores of Hudson Bay on Tundra Buggies or even spend a night or two at the Tundra Buggy Lodge, where they can watch bears while enjoying breakfast or evening cocktails.
On a recent morning, buggy passengers and lodge guests watched a group of bears roll in a fresh layer of snow and peer inquisitively at their human visitors. The bears had rounded profiles indicative of rude health, but despite their encouraging appearance, the future for the polar bears of western Hudson Bay is uncertain, threatened by a fate more insidious than the prospect of being shot for wandering too close to human habitation.
Climate change is causing the bay's ice to melt earlier and freeze later, causing bears to spend longer ashore – as much as a month longer in some years. As a consequence, Churchill's polar bears are decreasing in number (from approximately 1,350 three decades ago to roughly 900-1,000 now) and in physical condition. A 2007 study by the United States Geological Survey predicted that the western Hudson Bay population of polar bears could be extirpated by the end of the century.
There have been suggestions that the bears, which are an undeniably intelligent and adaptable species, might be able to adjust to the changes in the environment, but two recent studies have cast doubt on such optimism.
One, led by John Whiteman of the University of Wyoming and published in the journal Science, looked at the proposition that bears that are forced ashore for longer periods might be able to offset the extra period without feeding by significantly decreasing their metabolism by undergoing what is commonly referred to as "walking hibernation": an energy-saving metabolic state similar to that seen in hibernating animals.
Alas, they found that, "although well-adapted to seasonal ice melt, polar bears appear susceptible to deleterious declines in body condition during the lengthening period of summer food deprivation."
A second study, by Karyn Rode of the U.S. Geological Survey and others, examined claims that polar bears could survive sea ice decline by switching to terrestrial food sources, such as caribou and snow geese. Their findings were not encouraging.
"Where consumption of terrestrial foods has been documented, polar bear body condition and survival rates have declined even as land use has increased," they wrote. "Thus far, observed consumption of terrestrial food by polar bears has been insufficient to offset lost ice-based hunting opportunities but can have ecological consequences for other species."
Throughout much of the polar bear's range, the evidence is the same: in the southern Beaufort Sea, for example, a team of researchers led by Jeffrey Bromaghin of the U.S. Geological Survey confirmed that, although other factors may come into play over shorter time periods, over the medium-to-long term, the availability of sea ice is the single biggest determinant in polar bear population health.
Indeed, they concluded, low survival rates of polar bears between 2004 and 2006 related to a decrease in sea ice led to a decline in that area's polar bear population of between 25 and 50 percent. Only two of 80 cubs observed during that period are known to have survived.
"Polar bears are an early warning sign of a dramatically changing climate," Geoff York, Director of Conservation for Polar Bears International, told Discovery News as he looked out from the Tundra Buggy Lodge at a group of bears, huddled in the snow and waiting for the bay to freeze. "The impacts we're seeing in the Arctic will not stay in the Arctic, but will act as positive feedback for warming globally. As go polar bears, so may go many species – including our own – if we fail to heed those warnings."