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Hibernation

The first frost of the fall occurred on October 27 at my house. This was considerably later than in past years. Since then, we have had several more heavy frosts but the recent warm and sunny days of “Indian Summer” may have pushed the thought of winter from your mind (technically, Indian Summer is a warm and dry period following the first frost). However, the days are getting shorter and the nights longer and colder. No doubt winter is on its way. You probably have been preparing for winter by raking leaves, cleaning the lawnmower, hauling wood, storing the lawn chairs and unpacking the warm coats, hats and gloves.

This time of year always makes me wonder what animals do to survive the long, cold winter. Most people think that many animals are hibernate, but that is not entirely true.

Animals have adapted a variety of strategies to deal with winter, and the serious lack of food that exists during cold months. Birds may migrate. Many of the birds that nest in and around our neighborhoods are flying south for the winter, some of them great distances. Other birds that have spent the summer further north, including robins, blue jays and cardinals, may migrate to northeast Ohio for a “warmer” winter stay.

Most animals remain active for much of the winter. Fox, deer, coyote, rabbit, squirrel, opossum and raccoon tracks can be seen in the snow as they hunt and gather food.

Other animals enter some sort of dormancy state. Dormancy is triggered by photoperiod (shorter periods of daylight) and temperature. Rather than battle the cold and treacherous conditions of winter and lack of food, these animals shut down for a period of time, sometimes many months. There are several strategies that fall under the title of dormancy, including diapause, brumation and hibernation.

Diapause is most common in insects and other arthropods and refers to a period of inactivity triggered by environmental factors. Such factors can be cold temperatures, but may also include drought conditions. Most insects lay eggs in the fall and then die. The eggs survive and hatch in the warming springtime. Others can survive by entering diapause as adults or pupa. Roll over a log and so see some of the organisms that have already entered diapause, including beetles and caterpillars.

Hibernation is a term restricted for endotherms, or warm-blooded animals. These animals enter a deep sleep in which heart rate and body temperature decreases. This process is called torpor. Some animals, including bats, hummingbirds and the beloved black-capped chickadee may enter torpor on a daily basis to deal with cold nights as a means to conserve energy. During winter, the torpor period is extended dramatically. Bats, chipmunks and groundhogs are true hibernators of northeast Ohio winters. Hibernation should not be confused with lethargy. In this case, heart rate decreases but body temperature stays near normal. Most people think bears hibernate. Instead, they enter a state of lethargy during parts of the winter, as do many other mammals.

What do other cold-blooded (ectotherms) animals do in the winter? The strategy for survival is similar. Turtles, snakes, frogs and toads enter a state of dormancy called brumation. This process also involves a decrease in body temperature and heart rate.

For a wonderful book about animals in winter, read Winter World: the ingenuity of animal survival by Bernd Heinrich.

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