In Search of Grizzly Bear Dens

2/8/2012 3:52:28 PM

In Search of Grizzly Bear Dens

On a tundra lit by a full moon and the crystalline stars of the big dipper, a pair of biologists listen intently to a radio signal emitted by a collared grizzly bear. They're trying to pinpoint the location of a hibernating female grizzly with two yearling cubs hidden in their den for the winter.

April Cheuvront and Dick Shideler

Yes—we've switched gears for the day as Dick Shideler, an Alaska Department of Fish and Game biologist, looks for grizzly bear dens.

Grizzly bears and polar bears are related on an evolutionary scale. Polar bears evolved from grizzly bears around some 140,000 years ago. Although there are many similarities amongst the bears, there are striking differences. The most noticeable are hair color and the fact that grizzly bears are omnivores, whereas polar bears rely on a carnivorous diet for survival. Their denning behavior is also dramatically different.

All grizzly bears, male and female, enter dens during the winter months due to the scarcity of food at that time. Most den up between the months of September and November and emerge during the early spring months of April and May. Grizzly bears in Arctic Alaska dig an earthen den on a slope of land. As winter arrives, snow covers the den, drifting up to five meters deep.

In contrast, only pregnant female polar bears enter dens. They give birth and care for their cubs until the cubs are able to survive the arctic environment. Female polar bears in Arctic Alaska dig their dens in snow banks—instead of in the ground like grizzlies.

Unlike polar bears, grizzly bears enter a state of hibernation in which their metabolism slows down along with their heart rate, breathing rate, and nutritional requirements. Until they emerge in spring, they don't leave the den but occasionally move around inside shivering, shaking, and making small movements to keep their body temperature at a certain level.

Using the FLIR

Today we check on two grizzly bear dens. We track one bear under the moonlight by following the signal from its radio collar. We then record the GPS coordinates of the den and mark the location with an inukshuk. Radio collars work well on grizzly bears of either sex, but are difficult to keep on male polar bears because of their long, pointed neck. However, the radio collars work on female polar bears so most of the information gained from tracking polar bears comes from females.

An inukshuk

We use the FLIR camera to see if it can detect the grizzly den. Unfortunately, the FLIR camera isn't able to pick up a heat signal—the bear is hidden under too much snow and soil for the FLIR to pick up any heat.

Along the way across oil fields and ice roads, we spot some foxes. The count is fourteen red foxes to two arctic foxes. The arctic fox often trails behind polar bears acting as a scavenger, living off the remains of their seal kills. Tomorrow we are off to Pingok Island and polar bears.

Arctic fox

Temperature: 0 F

Wind speed: 1.6 mph

Photos courtesy of April Cheuvront.

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