Wildlife: Groundhogs, jumping mice only mammals to truly hibernate

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Hibernation seems the perfect way to deal with extreme winter weather. Protected by thick layers of fat in a cozy den below the frost line, hibernators are oblivious to subzero temperatures, wind, snow and ice.

Hibernation, however, is a broad, imprecise term. Though many mammals sleep through at least portions of winter, only a few truly hibernate. Hibernators go dormant in the fall and do not wake until they emerge in the spring. Furthermore, hibernators' body temperature, heart rate and respiration rate plunge. In Pennsylvania, the list of true hibernators is short: groundhogs and two species of jumping mice.

When groundhogs disappear underground for the winter, they plug the entrance to the burrow to maintain a stable environment. Curled up in the sleeping chamber, their body temperature drops about 57 degrees to 44 degrees. Breathing slows and the heart rate drops from about 100 beats per minute to about four beats per minute. In March, groundhogs awaken and emerge as lean eating machines.

Meadow and woodland jumping mice behave similarly. Because they are so much smaller (they weigh less than an ounce), surviving in winter can be a challenge. Some years, more than half die in the hibernaculum.

Black bears and chipmunks also sleep through much of winter, but they don't qualify as true hibernators. Bears fatten up in the fall and sleep deeply, but their respiration, heart rate and body temperature do not fall significantly. Furthermore, sows give birth to cubs in late January. And if disturbed during their deep winter sleep, bears can arouse themselves in just a few minutes.

Chipmunks escape winter's fury underground, but they don't rely on a layer of fat to survive. During their fall foraging frenzy, they collect and cache as much as a bushel of seeds and nuts in their burrows. They wake periodically during winter and eat the stored food. On warm winter days they sometimes emerge and search for food.

Squirrels, raccoons, skunks, opossums and foxes remain active all winter long, but during extremely cold weather, they can curl up in a hollow log or den tree, or burrow for days.

Biologist, author, and broadcaster Scott Shalaway can be heard 8-10 a.m. Saturdays on 1370 WVLY-AM (Wheeling) and online at www.wvly.net. He can be reached at www.drshalaway.com, sshalaway@aol.com and 2222 Fish Ridge Road, Cameron, WV 26033.

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