What is hibernation? And how is it different from aestivation?

The word ‘hibernation’ originated from the Latin word ‘hibernus’ which means ‘of winter’. Hibernation is the process that certain animals and birds retreat from their surroundings and lie dormant in a very deep sleep for a prolonged period of time, during the cold winter season. While in this phase, the hibernating animals reduce their body functions to a minimum and their body temperature and heartbeats drop to a very low level. They store barely enough food that can help them survive the period and their growth process is almost nonexistent during this phase.
Hibernating animals are found in all classes of organisms, from insects to mammals. Rabbits, rodents, raccoons, skunks, squirrels and bats are some of the popular hibernators. Some mammals, like polar bear, even hibernate during gestation period. The young ones are born during or after the hibernation.
Hibernation is an enigma that has been puzzling the zoologists for a long time. The experts consider it to be a way of nature helping the creatures pass the cold months of winter during which the food supplies are very meager. The animals, before their long slumber, eat a large quantity of food to store up energy in their bodies. Some of the animals even eat such an amount that their body weight almost doubles. During the hibernation, certain animals may wake up periodically for a very brief time, only to eat and get rid of waste; and they go back to sleep instantly. They have to be very careful to limit their movements, so as to reduce the energy loss. The hibernators are classified into two types: Obligate and Facultative. The former are traditional hibernators while the latter ones only hibernate due to lack of food and unbearable cold.
The retreat of a hibernating animal is called a hibernacula. They find the perfect place often after a long period of search. They have to make sure the place is both warm and comfortable and safe from the predators. It takes from twelve hours to a day for the animals to enter hibernation. Their bodily functions gradually reduce during this period. From this point they are very much incapable of protecting themselves. This is one of the disadvantages of the hibernation and underscores the need of a protected retreat.
Even though hibernation is normally associated with winter, some animals also spend the hot summer months in a state equivalent to hibernation. This process is known as Aestivation. It is most common among the animals living in deserts. Lizards, garden snail and lungfish are examples of aestivating creatures. Then there are organisms like earthworms, who are both hibernators and aestivators.
Hibernation has been one of the major wonders in the animal world and continues to be so. The scientists call it sometimes ‘time migration’ because of the organisms’ escape from the natural biological clock.
Additional reading:
Hibernation (Wikipedia)
Aestivation (Wikipedia)

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