TOPIC :- Animal Hibernation – Its Causes and Function 

What is Hibernation?

Hibernation as the term denotes is a state of inactivity and metabolic depression in endotherms.Hibernation refers to a period of heterothermy  that is characterized by low body temperature, slow breathing and heart rate and low metabolic rate. The calculative changes that occur during hibernation include a) 50% to 100% drop in breathing rates.

b) Heart rates between 3 to 10 beats per minutes are Typical.

c) Metabolism drops to 2% of the previous rate. 

Some animals undergo extreme changes during hibernation. As for example, the body temperature of arctic ground squirrel goes below freezing. Because of this heat stress, it loses bone density, brain tissue and even teeth. Many hibernators do not eat or drink at all. Therefore they do not urinate. The urea is broken down into amino acids and recycled in the body.

Hibernation is not Sleep

Sometimes hibernation is referred to as deep sleep, but this is completely inaccurate. During sleeping the brain remains in a resting stage for a wide period. Body temperature, breathing rates, heart rates vary but not to a greater degree. But Hibernation is more of a suspended animation. During hibernation, the brain never rests but remains in an active stage, but with suppressed activity. In general, animals rising from hibernation shows signs of sleep deprivation and often have to sleep for days to be rested.

Types of Hibernators

Basically,There are two types of hibernators present: the obligate hibernators and the facultative hibernators.

The obligate hibernators are animals that naturally and annually enters hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of Ground Squirrels, rodents, European hedgehog, etc. 

 Unlike obligate hibernators, Facultative hibernators only enter hibernation when there is cold stress, food scarcity or both. A good example of facultative hibernators includes black-tailed Prairie Dog.

What is aestivation?

  Aestivation derived from the Latin word “Aestas” meaning summer is a state of animal dormancy similar to hibernation characterised by inactivity and lowest metabolic rate in conditions of high temperature or desert conditions. Invertebrates and vertebrates are known to enter this state to avoid damage from high temperatures and risk of desiccation.

Causes of Hibernation

Hibernation is an adaption that helps many animals conserve energy by remaining inactive, slowing down their metabolic activity and reducing their body temperature for days, weeks or even months. In general, animals hibernate to survive for a greater period when foods are scarce. Hibernating animals eat a lot of food before hibernation and then survive off the energy stored in their fat. Hibernating animals uses 70 to 100 times less calorie than when active, allowing them to survive till food is plentiful.

List of Hibernating Animals

Name of the Animals Hibernating conditions

1. Wood Frogs Hibernate inside logs or burrows, under rocks or leaf piles. During winter season they stop breathing , heart stops and ice crystals form in their blood. During warm condition they defrost, their lungs and heart go back into action.

2. Deer Mice Have Light Hibernation( short Torpor) period. During cold weather, they show light hibernation from morning to late afternoon and spend the night searching for food.

3. Common Poorwills

Only species of bird that goes into hibernation.  Hibernates when the temperature gets cold, really hot or when food is scarce. If necessary, they can hibernate while incubating their eggs.

4. Ground Squirrels Most types of ground squirrel hibernate, and some do for nine months a year. They have light hibernation during the other times of the year.

5. Hamsters Have light hibernation. Hamsters usually torpor few days to a week at one time when the weather is cold.

6. Skunks Skunks also have a light hibernation during the cold winter months. During their period of Hibernation, they occasionally wake up in search of food.

7. Bats Undergoes true hibernation i.e., they are in such a deep sleep that appear to be dead.

During Hibernation a bat’s heart rate slows down from 400 to 25 beats per minute and its breathing continues slowly. 

8. Bears Bears are true hibernators. Instead of hibernating bears goes into a torpor (light hibernation). During their hibernation period they don’t eat or drink for about six months on average, and they rarely urinate.

9. Hedgehogs Hedgehogs hibernate anywhere for a few weeks to six months depending on the weather conditions. It also undergoes aestivation when the weather is extremely hot.

10. Prairie Dogs Prairie dogs are not actual dogs, but they are rodents. Depending on the species of prairie dogs and the area it lives in, it either hibernates or goes into light hibernation.

Functions of Hibernation in Animals

Hibernation allows a broad range of animals to exhibit seasonal dormancy which might increase survival and cosequently associated with relatively slow life histories.

Hibernators shows approximately 15% higher annual survival rate than non- hibernating species. Hibernation are mainly controlled by endocrine systems. Glands in the body control the hormone secretion which in turn controls the physiological behaviour of hibernation. The parts involved are  Thyroid and Pituitary.

When a mammal enters hibernation, it becomes somewhat like cold blooded  animals whose body temperature varies depending on the temperature surrounding it. However, there is a starting temperature known as the set point. When the mammal body temperature reaches the set point, the metabolic activity starts thereby burning the reserve fat present. This reserve fat generates energy.

Hibernating conditions in humans.

Current researches are going on to find out on how to induce hibernation in humans. The ability to hibernate can be useful for a number of reasons, as for eg, saving a life of seriously injured people by putting them into the state of hibernation.