Hibernation

 Nature Notes by Dr. Frank Lang

Many warm-blooded animals spend much of their time in a state of greatly lowered metabolism called torpor. Hummingbirds, incredibly active during the day, can conserve energy when food is scarce by becoming incredibly inactive at night. A hummer’s temperature may drop from an active high of 104°F to near the ambient temperature, perhaps 50°F. Its basal metabolism reduces by a third. This way, heating calories are not wasted.

Other animals, like mammals, enter a seasonal torpor to avoid unpleasantness. Mammals of hot arid climates may estivate, that is, sleep away the summer. Others may avoid the cold of winter by hibernation. In both cases the animals may slip off into a deep sleep. Breathing may drop to a breath per minute and the heartbeat to four to eight beats per minute. Body temperatures drop, sometimes to just above freezing. Energy conservation is the name of the game.

The game is not without its costs. Animals must add a lot of weight, mostly as brown fat and muscle tissue, to provide enough energy to make it through its seasonal torpor. Metabolism continues, albeit at a much reduced level, and toxic waste products accumulate that must be excreted or detoxified. Energy derived from fat breakdown uses water; dehydration can be a problem. Energy from muscle breakdown adds water. The deep sleep does not allow for urination. Urine formation may be suppressed by pituitary hormones. Special chemical reactions lessen the toxic effects of urea.

Many rodents estivate or hibernate. Some like marmots, our western equivalent of the woodchuck, do both. Marmots eat prodigiously of green stuff until they bulk up to half their body weight in fat. Then they slip away to dens where whole colonies sink into a seven-month slumber, from late September to early May in the mountains, or, east of the mountains, from mid-summer after forage dries up, till early spring.

Black bears, contrary to popular opinion, just sort of hibernate. They often find a den and sleep away the nastiest winter weather, but their sleep is shallow, and their temperature only a few degrees below normal. When disturbed they are quickly roused, and, I suspect, quite grumpy.

I frequently face torpor as certain students in my lectures slip away, not into the deep sleepy state or marmots, but the shallow sleep of bears. Their state must be like that of bears. Their behavior on arousal is much the same.

I frequently experience torpor most Friday afternoons at 3:00 P.M. No matter how dynamic the speaker or how interested I am in the topic, our Friday Afternoon Science Seminars at the University put me down. I have decided this is no reflection on the series’ quality. If you want to attend the science seminars, call or write the School of Science at Southern Oregon University for a schedule of speakers. The public is invited to attend and the series is free. One thing though, don’t rouse the torpid prof. He’s worse than bears!

— Dr. Frank Lang

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