When the raw winds of winter howl outside and the snow begins to pile up, those of us living in colder regions spend most of our time inside where it’s warm, dry, and cozy. Did you know that some animals due something very similar?
Wintertime in north temperate and arctic regions means dangerously low temperatures and very little food. To survive, many animals enter a dormant sleep period called hibernation. As the days get shorter and colder, the animals’ bodies start getting ready for their long winter nap. Their body temperatures drop (close to freezing!), their heartbeats and breathing slow down (only a few breaths per minute), and they eat as much as possible to store up large amounts of body fat (about 40% of their body weight will be lost during hibernation). Specific physical changes differ by species, but this near-death state conserves energy and helps them go without food for a long time.
Some people think that only mammals hibernate, but actually many fishes, amphibians, and reptiles also snooze right through the winter. In other parts of the world, reptiles, amphibians, insects, and snails go through estivation, a long sleep similar to hibernation that helps them survive intense heat and extremely dry conditions.
When wintertime comes, the animals escape to their hideaways. Mice and squirrels build underground nests. Bats pick out a favorite cave. Fish and frogs bury themselves in the bottoms of ponds below the frost line. Some animals---like raccoons, bears, and badgers---enter into their deep sleep without much of a temperature drop at all. This is not true hibernation, so these animals are often called "shallow hibernators." The body temperatures of "true hibernators" stay as close as possible to the temperature of the environment, though their bodies are careful not to go low enough to freeze. Among mammals, there are only three orders of true hibernators: Chiroptera (bats), Insectivora (moles, hedgehogs, etc.), and Rodentia (ground squirrels, hamsters, mice, etc.).
True hibernators wake up periodically to eat and get rid of waste (though some animals recycle part of their waste into protein). But then they go right back to sleep. They must be careful to limit their movements or they’ll use up their stored food and energy. Shallow hibernators are more active. In fact, bears even give birth to cubs during this period.
Before long, the welcoming warmth of spring returns and the hibernating animals slowly begin to awaken. Heartbeats rise rapidly, breathing returns to normal, and hungry tummies urge the creatures to hurry back outside for their first big meal in a long time!
Copyright © 2001 by John W. Schlim Jr.
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