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The Wild Side

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Published on: Jan. 2, 1996

Last revision: Oct. 20, 2010

Hibernating animals gain weight, go into a deep sleep and lower their body temperature and heart rate to conserve energy.

The only "true hibernators" in Missouri include several kinds of bats, woodchucks (or groundhogs), chipmunks, meadow jumping mice, Franklin's ground squirrel and the thirteen-lined ground squirrel. Other animals sleep through the winter but don't lower their body temperature or heart rate as much as true hibernators.

Groundhogs fatten themselves during the late summer months, then slow down, lose energy and get ready to spend the next several months asleep. The groundhog's normal temperature is about 96.8 (close to our own), but in the winter it drops to between 43° and 57° F.

Their heart rate slows from 160 beats per minute to as few as four beats per minute. Breathing drops to as little as one breath per minute. So deep is their sleep it requires several hours for them to awaken. Sometimes a woodchuck will awaken to heed nature's call and move around to keep its muscles from withering away.

Other animals are not true hibernators, but they do have ways of sleeping through the winter. A black bear's heart rate drops from 55 beats per minute to 10 beats per minute, and its body temperature drops from about 96° F to about 88° F. Black bears also grow fat during the fall.

The bear's sleep in the winter is not as deep as that of the groundhog, nor does it get up to pass waste from its system. Its body temperature does not drop much because when black bears sleep in winter the females are pregnant. A female will give birth to a 3-inch, 9-ounce cub and is able to nurse during this period of inactivity. This is one laid back mother!

Grey treefrogs, spring peepers and wood frogs all bury themselves close to the surface of the cold ground. Their bodies may actually freeze solid, but they do not die because of something called glycogen (Gly-kuh-juhn). In the fall they flood their bodies with this natural sugar that acts as an antifreeze.

Several invertebrates also have an antifreeze called glycerol (Gliss-uh-rawl), which is a sugary alcohol. Invertebrates survive the cold by overwintering as an egg, larvae, pupa or adult. These animals often adjust to the cold by supercooling their bodies or producing glycerol.

THIRTEEN-LINED GROUND SQUIRRELS

Thirteen-lined ground squirrels fatten on seeds and insects in preparation for hibernation. They are one of the few true hibernating animals in Missouri. Other animals sleep through the winter, but don't lower their body temperature as much as true hibernators.

Ground squirrels hibernate in a tunnel as much as 20 feet long and deep enough to be beneath the frost line. Seeds carried in cheek pouches may be used to fill food storage chambers. The actual hibernation chamber is often lined with grasses.

Hibernation begins in early fall and ends in late March or early April. For additional information on hibernation, see The Wild Mammals of Missouri by Charles and Elizabeth Schwartz.

HIBERNATION HOT SPOTS

If you had to hibernate through the winter, could you pick a good spot? To test your knowledge let's try an experiment. You will need thermometers, gelatin and film canisters (two per group; half with covers).

Stir one tablespoon of gelatin into 1 cup of hot water, then fill all of the film canisters half full. Go outside and put one canister uncovered on top of the snow, with the other buried under the snow with a lid on top. You can place a thermometer by each of the canisters to check the difference in temperature.

When the gelatin on the surface begins to jell, dig up the buried canister and compare the progress of the two. Which container jelled first? Why? Why might animals stay under the snow?

Check the thermometers. Is there a temperature difference? How much? Where would you want to hibernate if you were a wild animal?

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