The Great White Bear
For most of the year, Churchill, Manitoba is your standard, picturesque tundra town. Located on the western edge of Hudson Bay, Churchill was once a critical hub of the Hudson Bay Company, an English fur trading empire. Now it is a big seaport for exporting central-Canadian grains to the Atlantic. But for six weeks every year, it is the polar bear capital of the world.
Polar bears are seal specialists. They spend all winter and spring patrolling the edges of the sea ice for the breathing holes of unwary ringed seals. During the bountiful seal season, bears will almost double their body weight. The seal season ends as the ice on the Hudson Bay breaks up around mid-July. Then the bears surf southward on ice floes, pushed by the north winds until they run aground at the southern end of the Bay. For the next four months, the bears wander around in a state of “walking hibernation,” eating practically nothing for about four months while daydreaming about seals and waiting for the sea ice to re-form.
The bears know that solid ice means seal hunting, so they trek up the coastline to the place where they know the ice will form first. Churchill is this place. Four different major rivers flow into the Hudson Bay here. This freshwater lowers the salinity of the seawater around Churchill, allowing it to freeze much more readily than elsewhere. Come mid-November, a nice, thick layer of ice extends into the bay from Churchill, weeks before the rest of the bay begins to freeze. The bears want to be in position for the big day when the ice becomes thick enough to hunt on, so 600 to 1,000 bears arrive at Churchill weeks in advance.
There are no seals around before freeze-up, and mating season isn't until May, so the bears take advantage of the downtime by socializing. Polar bears roam over hundreds, even thousands of square miles over the course of the year, so this is a great opportunity for males to see who else is in the neighborhood. Two evenly-matched males will size each other up with a sparring match. Though they look brutal, and sometimes draw blood, these matches only serve to assess the strength of their competition come mating season. Fights during mating season are terribly vicious and very dangerous for both contenders, so friendly sparring matches right now help males avoid injury in the spring.
At first glance, this makes little evolutionary sense. Females should hibernate during the off-season, and give birth in time to take advantage of the whole hunting season. Why don't they? Here's my guess:
Polar bears and grizzlies are very closely related. Fossil and genetic records indicate that polar bears may have diverged from grizzlies as recently as 200,000 years ago. Polar bear hibernation is timed almost exactly the same as grizzly hibernation, and grizzly hibernation makes perfect sense. Grizzlies hibernate over the dead of winter, a nice strategy to budget energy during a time of food scarcity on land. The fact that polar bears' hibernation schedule is decoupled from their maritime food calendar is evolutionary baggage from their grizzly ancestors. Males and non-pregnant females have done away with hibernation entirely, suggesting that it is not evolutionary advantageous for them. Thus, we are right in the middle of a "half-finished" adaptive trajectory. If we fast-forwarded through time, I imagine we would see pregnant females hibernating much earlier in the season, or not at all.
One cannot discuss polar bears without discussing global climate change. Most skeptics have an attitude of "I'll believe it when I see it." Truly, any one storm, one bad winter, or one unprecedented heat wave cannot be blamed on climate change. Anecdotes are not data, and single events considered independently cannot support a scientific theory. That is why storms like Hurricane Sandy and this year's crippling droughts in the west cannot be paraded around by scientists as the silver bullet equivalent of conclusive evidence. Meanwhile, skeptics refuse to consider all the statistically rock-solid trend graphs that scientists constantly release, mostly because of a cultural distrust of science and ignorance of the scientific method. This is quite a bind: Skeptics want convincing, but refuse to be convinced with science.
(Un)fortunately, climate change has become such a reality that we no longer need graphs and figures to do the convincing. Instead, dumbfounding and obvious changes in natural processes reveal sobering truths. We can look at some ecosystems and immediately notice that something is seriously out-of-whack. Regular readers of this blog will remember the relationship between the pine bark beetle, whitebark pine trees, and Clark's Nutcrackers. That is one great example of how warming temperatures have clearly resulted in the collapse of a normally self-regulating balance.
The polar bears of Churchill are another example. The sea ice around Churchill freezes later and later each fall and thaws earlier and earlier in the spring, to the point that our company's Churchill tour calendar is 2 weeks earlier than 12 years ago. Fewer cubs are seen in Churchill because fewer females can put on enough body weight in the shortened hunting season to become pregnant. The Hudson Bay polar bears are predicted to be the first population to go extinct by 2050, due to a seal hunting season shortened by 7-9 weeks, 75% pregnancy failure due to low female weights, and dwindling sea ice. Every time the average extent of arctic sea ice is measured, it is the lowest ever recorded. In my lifetime, the polar bear season in Churchill will probably cease to exist. Out-of-whack indeed.
Churchill lies at the heart of one of the most significant fur trade hubs in the planet's history, and the polar bears continue to rendezvous here every year, getting ready for the coming hunting season, not unlike the trappers of not-too-long ago. May they continue to do so.