Denali in Winter

Where Have All the Grizzlies Gone?

In mid-winter, gone are many of Denali's highest-profile animals: grizzlies and ground squirrels, marmots and beavers, golden eagles and gulls. Birds leave on migratory journeys, bears and rodents hide in hibernation.

A dominant presence in summer, grizzly bears go underground in September and October and remain there until May. Pregnant females are the first to den and, in the company of their newborn cubs, the last to leave their winter shelters in spring. Amazingly, pregnant bears give birth during this cycle of extended fasting and then nurse their cubs for several months while still in hibernation. Bears tend to build their dens around the time of the first heavy snowfalls in fall or winter. Denali's grizzlies have been observed digging dens as early as August, in response to six-inch snowfalls. Grizzlies don't need to defecate, urinate, eat, or drink during their months-long dormancy, and their body temperature and metabolic rates drop only slightly. By winter's end they may lose 25 to 50 percent of their body fat; but for healthy bears, the loss is all, or nearly all, fat.

The hibernation mechanisms of rodents are vastly different from bears. Arctic ground squirrels, for example, enter a deathlike torpor in which body temperatures drop to near freezing (or even below) and bodily functions dramatically slow down. They rouse themselves periodically throughout the winter, bringing body temperature and heart rates back to normal, perhaps to eliminate body wastes. Marmots too go into a deep dormancy that is periodically broken. Beavers, though hidden, remain active through the winter inside mud-smeared "winterized" lodges, surviving on willows harvested in fall and now safely stored beneath pond ice.

The absence of bears, ground squirrels, birds, and other wildlife is striking, says kennel manager Gary Koy, who sees Denali's winter landscape as much as anyone: "It's remarkable how little wildlife you encounter out there. From Sable Pass to Wonder Lake (45 miles), it's unusual to see more than a few fox or ptarmigan. There's a real sense of being in a subarctic desert—which of course it is. It brings home just how tough it is to make a living out there in winter, and how many species have either left or gone into hibernation as an adaptation."

Published: 28 Apr 2002 | Last Updated: 8 Nov 2010
Details mentioned in this article were accurate at the time of publication


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