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For many animals hibernations is an instinctual survival technique used during winter months when there is a scarcity of food and colder weather. It is characterized by a lower metabolism, minimal activity, reduced body temperature and restrained breathing. Depending on the animal, hibernation can last mere days or extend to several weeks or months, during which time energy is reserved to burn fat at a very slow rate. There are different types of hibernation or similar behaviors within the animal kingdom.

Hibernation Induction Trigger

There is actually a chemical, opioid, within the blood of hibernating animals that is not present at other times of the year. Opioid reacts in the body much like morphine. For instance, if blood is extracted from a hibernating squirrel, saved and then injected into a squirrel during the springtime, the latter will go into hibernation.

During experiments, researchers were able to extend the life of a pig's heart using the hibernation induction trigger (HIT). This discovery could be of great use in the progress of human organ transplants. It means that the heart (or other organ) could be kept alive outside the body up to three times as long as today. Nasa is researching the possibility of using HIT for astronauts going on a long space trip. With the ability to induce hibernation into a human, he would be able to travel into places in space with little inconvenience or discomfort.


Estivation is similar to hibernation but effects some animals in summer months in areas where it is extremely hot and dry. It is experienced by both land and aquatic animals in order to preserve hydration. Some land snails that are known to estivate may climb up to higher locations in order to avoid the ground heat.

It was unheard of that any primate or tropical mammal estivated until recently. In 2004, animal physiologist, Kathrin Dausmann discovered that the fat-tailed dwarf lemur will estivate for seven months out of the year.

Suspended Animation

A reduction of life processes through external means where involuntary body functions such as breathing and heartbeat are so low that they can only be detected through medical devices. Suspended animation can be entered by means of extreme cold. Cryonics has been developed through the discovery of this medical technique.


Torpor is a term used for a shorter period of time where an animal may slow it's physiological activity. This type of hibernations may be used by birds and some small mammals for a day or less. Many of them going into a torpid state at night when the temperature drops. The animal uses a minimal amount of energy as in regular hibernation. It has just recently been discovered that female crocodiles will go into a torpor while they are laying eggs.

Animal Hibernation

Among animals that hibernate, there are differences in habits and duration. Among the most notorious hibernators is the bear even though they do not go into a "real" hibernation, instead he is actually in a state of "denning." When a bear is in this winter sleep, his metabolism and temperature is working at a lower level. However it is no where as depressed as in smaller mammals. With the lower body temperature of 31 degrees C from his normal 37 degrees C, he can easily be woken up. With a ground squirrel in hibernation, his core temperature may be -2 degrees C.

Animals will consume larger amounts of food before entering hibernation, storing fat deposits that will see them through the winter months. There are even animals that hibernate during gestation, delivering their young shortly after they wake. It has been found that hibernating animals are sometimes wakened by all-terrain vehicles as well as snowmobiles. This can be detrimental to the animal and it may die out from the coldness and lack of food as its body metabolism rises.

Global warming has caused some problems for animals in hibernations. As the earth warms earlier than normal, the animal may wake up and in the confusion not eat, thus starving itself.

It was recently discovered by German scientists that the normally winter hibernating lemur has developed the ability to enter a state of estivation when extremely dry summers have left little to eat. This was reported by doctoral student, Kathrin Dausmann, who along with other researchers implanted sensors into the lemur's abdomens which allowed them to track their body temperatures.

Let's take a look at some different hibernating animals and the differences in their behavior.

* Bats - A bat's primary food source are insects that aren't available during the winter season. Some species of bats will migrate to a warmer climate where insects are available while others hibernate. They go through the normal slowing of heart rate and lowering of temperature, yet these mammals can survive through their five to six month hibernation on just a few grams of fat. There are some bat species that join in dense clusters on cave walls while hibernating.

* Ground Squirrels - These animals will hibernate in their dens for up to five to six of the cold months. The outside temperature will be just a degree or two lower than the hibernating ground squirrel's reaching below freezing at times. Some ground squirrels estivate as those in the Mohave Dessert where they can sleep up to seven months a year when the outside temperature is 98 degrees and above. Males and older squirrels go into estivation/hibernation before females and younger ones as they do not need to store as much fat on their bodies.

* Groundhogs - They are generally known to hibernate from mid October to February or March within their nest chamber. Yet, in warmer climates they may only hibernate for as little as three months. Their chamber is located at the end of a 15 to 25 foot burrow and dug below the frost line. They gorge to their heaviest weight before going into hibernation so that a bit of body fat remains when they wake up. They need that extra fat until the spring food is more abundant.

* Western Diamondback Rattlesnake - As winter approaches these snakes begin hibernation in a den which may just be a crevice in a rock or an old prairie dog burrow which they may share with other snakes. They are found in the southwestern part of the U.S. Mating occurs shortly after the Diamondbacks wake from hibernation.

* Antarctic Cod - This fish puts itself into a dormant hibernation-like state in order to survive the Arctic winter. Although, the Antarctic Cod already had a very slow metabolism and blood proteins which act as an antifreeze, it was only recently discovered that they could further depress their bodily functions to enter a state of hibernation.

* Insects - Cold blooded, insects retain the same temperature as the climate around them and do not do well when the temperature drops below 50 degrees. Although, some insects (flees and lice) survive winter by staying in close contact with warm blooded animals, still others find warm places in our homes, the majority of them that have a longer life span go into hibernation.

Human Hibernation

Seriously injured or ill people could be helped with the discover of human hibernation. Sometimes treatment is delayed and an induced hibernating state could be beneficial until the patient could be attended. Or just the ability to be able to put human organs into a sort of "deep sleep" would improve our ability of organ transplants. A liver can only be used within two hours of removal from the donor. You can imagine how difficult it is to have all the necessary medical procedures in place within that short of time.

Scientists have been studying the ground squirrel in an effort to discover how this creature puts itself to sleep and then wakes back up at the appropriate time. It has already been discovered by a professor of biosciences, Hannah V. Carey, that a ground squirrel's hibernating liver has no significant damage even after 96 hours of cold storage.

The proteins within hibernating ground squirrels and those of summer squirrels have been compared, finding that the hibernating ones contained protein enzymes were linked to two genes. Each of the enzymes carry out two different tasks. One makes usable fat when broken down by fatty acids. The other enzyme helps to conserve glucose. The studies and experiments continue today with the hope of truly understanding the workings of hibernation and extending that knowledge for the betterment of mankind.

More about this author: Karen Ellis

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