Thursday, April 05, 2007

A Long Winter Sleep Means Survival For Many Animals

Hibernation is a kind of sleep that allows an animal to live for months without eating or drinking.

During hibernation, an animal's metabolic rate is greatly reduced. The animal's breathing and heart rates are much slower, and its body temperature is dramatically lower. By hibernating, an animal can avoid low temperatures and food shortages that often occur during winter.

Thanks to Punxsutawney Phil, a lot of us know that groundhogs hibernate for much of the winter. Many people know that bears also hibernate. Other hibernating animals in Virginia include chipmunks, jumping mice and bats. All these animals are mammals. They use milk to feed their young, and they have hair.

Hibernators also include a lot of animals that aren't mammals. For example, many snakes and lizards live in climates that are too cold for them to stay warm and active during the winter. To survive, they seek shelter and hibernate in burrows, inside rotten logs, or under tree bark.

Other animals seek shelter in fresh water during the winter. Before the onset of cold weather, many frogs and turtles move to the bottom of lakes and ponds. There, they burrow under rocks, logs or fallen leaves. They may even bury themselves in mud.

While hibernating, frogs and turtles are able to obtain enough oxygen without breathing air, because they can absorb oxygen through their skin.

Amazingly, because of water's special properties, these animals don't freeze to death. Water reaches its greatest density at about 39 degrees Fahrenheit. So, water at that temperature sinks to the bottom of ponds and lakes. When water is warmer or colder than 39 degrees, it is less dense, and it rises from the bottom. As a result, if the lake or pond is deeper than the frost line, temperatures at the bottom do not go below about 39 degrees, and the animals do not freeze.

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Source : Richmond Times Dispatch

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