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              Sleeping for survival
In the previous essay we learned how Monarch butterflies make an amazing journey, to a warmer place to survive in winter. Many other animals and birds migrate to warmer places during winter and return back when weather conditions become favorable. This is a cycle that is repeated year after year, for generations.
Some animals do not migrate. They grow thicker coats of fur, and put on an extra layer of fat, to protect themselves from the cold. Example - MOOSE. OR
They sleep through the coldest part of winter. This is called “HIBERNATION”. Hibernators use sleep to protect themselves and preserve their energy when food is scarce. When an animal enters such a deep sleep its body temperature drops, heartbeat and breathing slows down. Its body does not need a lot of energy in this condition. In some parts of the world the weather is worst during summer. It is hot and dry and the food is scarce. Some animals living in those areas react to these conditions by entering a “summer sleep”. This is called “AESTIVATION”. One example of an animal which undergoes such a sleep would be the large toothed Suslik
 
Most hibernating animals prepare for their long winter sleep by eating a lot of food in the fall. Much of this food gets stored in their body in the form of fats. These fats are used by the body while the animal sleeps. There are two different kinds of Hibernators:
1) The Deep Sleepers (true hibernators) - These animals sleep throughout the winter and wake up only with the return of favorable conditions. Animals  like Ground squirrels, Woodchucks, Dormice, Tortoises etc. usually go to sleep in early December and come awake  in early March.
2) The Light Sleepers - like Skunks, Raccoons, Grizzly bears
are animals that mostly sleep during winter, but take some
breaks in their naps.
 
How do all these things happen? How do animals know when to start preparing for Hibernation? And how do they know when to start hibernation? Here are some facts that we know:
 
All animals seem to have some internal body clocks, called “Rhythms of life.” Many animals have very accurate yearly clocks. They start to hibernate, at the same time each year, no matter what the weather is at that time. Some animals get their cues from the changing weather (i.e. the days becoming shorter and temperatures getting colder triggers the process of hibernation and similarly they get their wake up call with the return of the favorable weather.) This cycle keeps on repeating every year. Scientists however are still learning more about hibernation. Much of this phenomenon still remains a mystery.