7/23/2012 1:17:17 PM

Waiting for Winter

By Dr. Andrew Derocher

The first of our collared females near Churchill swam ashore on July 7th. For perspective, this is a month earlier than the 1980s. Other bears have trickled to land since. On the break-up side of things, it looks like 2012 is fairly similar to other years since 1998.

The downside is that the frequency of the early break-ups is occurring much more often. Because polar bears "remember" good and bad years by either storing or depleting fat stores over several years, a run of bad years can run down a population. This happens because adult females deplete the fat stores needed to either produce cubs when they're pregnant or to produce milk when they have cubs. Based on the aerial survey conducted last summer, recruitment of new polar bears in the Churchill area is well below normal now.

Some of the bears got lucky this year. The last of the ice has lingered off the western coast of Hudson Bay. This atypical break-up means bears in the area can try to catch another seal or two before disembarking for land. An extra seal might make the difference between a mother having enough milk for her cubs to survival the ice-free period or not. We've seen the consequences of mothers running out of milk and it isn't pleasant.

The big question now is: When will the Bay freeze-up? The weather in Churchill has been warmer than normal. A warmer Bay means it takes longer for the ice to form. At the peak of summer, polar bear fans are pulling for a nice cold summer in the Arctic: a bit of a not in my backyard sort of deal. Nonetheless, I think the bears would appreciate a cold summer in their backyard.

Dr. Andrew Derocher is professor of biological sciences at the University of Alberta.

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