Polar Bears International

More Dens, More Bears

10/4/2011 8:36:06 PM

More Dens, More Bears

Polar bear along shore
The distribution of polar bears along the coast varies from year to year, depending on where the bears came off the ice.

From September 29 to October 1, we continued our aerial count of the Southern Hudson Bay polar bears by surveying the section of the coast from the mouth of the Sutton River to Cape Henrietta Maria, the section from the Sutton to the mouth of the Winisk River, and the section from the mouth of the Winisk to the mouth of the Shagamu River, plus all the inland transects in each sector. 

The distribution of polar bears along the Hudson Bay coast of Ontario varies among years. It depends on where the last ice remained offshore in summer, since many bears remain on the ice as long as possible before swimming ashore. 

In 2011 residual ice was off the eastern part of the Ontario coast towards Cape Henrietta Maria, so we saw many bears in this sector. In addition, there was suitable residual ice off the coast between the Winisk River and the Shagamu River in summer, and we saw 101 bears along our coastal transect in this area.

In addition to flying our survey transects, we checked the maternity den locations of three GPS-collared bears that used the dens in winter of 2010/11. Each den was essentially a large pit dug into the peat layer in a stand of black spruce. Such dens would provide little overhead protection for the female and young cubs, but the spruce stand would provide considerable protection from winds and would act to trap and accumulate snow that might form a drift over the denned female. 

 Polar bear den under a spruce tree
This maternity den twas simply a pit dug into the peat in a dense spruce stand. We know the bear had her cubs there because we found her collar in the den: it was scheduled to drop off on December 1, 2010. Also, there were a few small cub-sized scats on the den's floor!

Such dens are almost impossible to discover from the air because the spruce stands are so dense and they point out the bias that can exist if we rely on other sources of information, such as aerial surveys to reveal potential den locations. Dens that can be seen readily from the air are dug into the side of palsas, or into river banks and lake shores, but they may give a biased view of the habitat important to denning females since other den types can't be seen readily from the air.

A few years ago, we established a network of three remote weather stations across the Hudson Bay Lowlands to provide trend data over the next decades in light of climate warming. Each year some maintenance is required for these stations, so we've also been visiting them to replace components and ensure they are operating correctly and transmitting data properly to the satellite network.

From the field in Ontario's Hudson Bay lowlands with Dr. Martyn Obbard, Research Scientist, Ontario Ministry of Natural Resources (OMNR); Kevin Middel, Analytical Biologist, OMNR and M.Sc. student, Trent University; Brandon Laforest, Ph.D. student, York University, and Doug Holtby, Helicopter Pilot, OMNR.

Den photo ©Martyn Obbard.

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