Inside a Polar Bear Den

10/2/2011 1:20:41 PM

Inside a Polar Bear Den

On Tuesday September 27th, we left the Attawapiskat Airport bright and early on another day with clear skies ideal for aerial survey work. Starting near the Swan River we flew the rest of our inland transects all the way to Hook Point. Again, we saw few bears on the inland transects. 

In addition to the aerial survey work, we visited the dens used last winter by two of our GPS-collared bears to give birth to cubs. The first den (below) was about 60 kilometers inland from the James Bay coast. It was a shallow excavated den dug near the top of a steep bank in the side of a glacial moraine. The substrate was gravel, giving the den the appearance of a very large black bear den.

 Polar bear den in Southern Hudbson Bay
Polar bears show great flexibility when choosing den sites. While bears farther north dig snow dens in which to give birth, more southerly populations dig into peat banks, permafrost, or gravel, like this one.

The second den (below) was about 45 kilometers inland from the James Bay coast and was a shallow excavated den dug into the face of a palsa (elevated permafrost feature). The bear's claw marks were still visible in the frozen peat of the back of the den! 

Polar bear den dug in permafrost
A polar bear den dug into a palsa, or elevated permafrost mound. Note the claw marks in the peat moss at the back.

These two dens are typical of the den sites used by pregnant bears in this population, making their den site choice quite different from that of other polar bear populations, including the neighboring Western Hudson Bay bears, which often den in the frozen peat banks of lakes. Bears farther north dig snow dens.

All in all, we had another great day in the field (though when seeing no bears on the long inland transects, I found myself wishing that Red Bull was a sponsor of the research!). We were particularly pleased to find the two maternity dens—the GPS collars are proving to give highly accurate location information. The polar bear is listed as a Threatened Species in Ontario and such detailed habitat preference information will be useful to the recovery planning process.

We arrived in Peawanuck about 7:45 p.m. to find our old friend J-M Kelley, one of OMNR's aircraft maintenance engineers, waiting for us at the staff house. For many years, J-M has ensured that the helicopters we use in our fall polar bear field work are well maintained and keep us safe.  It was good to see his smiling face on our arrival.

On September 28th, we first flew a coastal survey from the mouth of the Brant River around Cape Henrietta Maria, including some offshore islands and sand spits, to Hook Point on James Bay. We saw 71 bears on this survey, including many family groups. Seeing large numbers of bears in this area is normal since it seems to be an area where the ice forms early in the late fall, enabling the bears to get back to hunting seals. After we completed the coastal survey, we completed a number of inland transects in the vicinity of Cape Henrietta Maria, bringing the total number of bears sighted to 92.

Later, we were able to find the maternity den used last winter by another of our GPS-collared females. This den was simply a surface nest in the center of a large clump of high willows on a small island in the middle of the Brant River about 25 kilometers inland from the Hudson Bay coast.  Southern Hudson Bay females show considerable flexibility in den site choice!

So far, we've had excellent weather for our field work—clear skies and warm temperatures.  A cold front is due to pass through overnight so we'll see what tomorrow brings.

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.

Photos ©Martyn Obbard.

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