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Written by: Nancy Moncrief
Monday January 12, 2015

Hibernation is a kind of sleep that allows animals to live for months without eating or drinking.  We often associate hibernation with mammals such as groundhogs and bears, but other animals are hibernators, too.

During hibernation, an animal’s metabolic rate is greatly reduced, its breathing and heart rate 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.

For example, many snakes and lizards live in climates that are too cold for them to stay warm and active during the winter.  In order to survive, they seek shelter and hibernate in underground 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 they are 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 4 degrees Celsius (39 degrees Fahrenheit).  So water at that temperature sinks to the bottom of ponds and lakes.  When water is warmer or colder than 4 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 4 degrees Celsius, and the animals do not freeze.

Lithobates pipiens (Northern Leopard Frog) avoids freezing in winter by burrowing into mud on the bottom of lakes and ponds   James Harding (photographer; copyright holder; identification), Michigan State University.


Tags: Biology, Dr. Nancy Moncrief, Mammal of the Month, Research and Collections