Hibernation, also known as 'winter sleep', is a state of deep sleep or dormancy that an animal undergoes during the cold months of winter. During this phase, body metabolism and heart rate of the animal go down drastically and the animal practically sleeps for various days to months. There are two types of hibernation, namely 'true' hibernation and torpor, or temporary hibernation. In true hibernation, the animal falls into such a deep sleep that it appears to be dead. The body temperature, breathing, and the heart rate drops down. Torpor is a state of short sleep, where the heart rate and body temperature goes down but the animal is able to move around. There are various types of hibernation and not all animals go into a complete state of hibernation. Adaptations of Hibernating Animals The only reason why certain animals hibernate, is to escape from the harsh weather in winter. Both warm and cold-blooded animals hibernate during winter. Certain species of fish, amphibians, and insects also survive the cold months of winter through the process of hibernation. Before the animals go into hibernation, they use the following adaptation techniques.

• Before the onset of winter, the animal eats a lot of food and stores it in the body in the form of fat. When it undergoes hibernation, the animal uses this fat to survive the chilling days.
• The body temperature drops to match the outside temperature.
• They go into a deep slumber and almost appear to be dead, with their breathing and heart rate slowed down.

It is also important to note that not all animals hibernate in winter. Aestivation or estivation, characterized by lowered metabolic rate and inactivity, is a response to the high heat and arid conditions. North American desert animals like tortoises, crocodiles, frogs, and salamanders go through the aestivation cycle. List of Mammals that Hibernate There are many animals that undergo deep sleep during winter to protect themselves from the freezing temperature. Given below is a list of animals that become dormant during winter as a method of survival. They resume their life activities once the cold, winter months are over. In addition to this, some animals like the hamsters, badgers, skunks, and raccoon do not go into the state of true hibernation but are usually inactive for four to five months or go into torpor. During milder winter months, however, these animals may be active. List of Reptiles, Mollusks and Amphibians that Hibernate Unlike warm-blooded animals, reptiles and other ectothermic creatures cannot create their own body heat and need to get it from the environment. This, along with the food shortages is the reason that they need to go into hibernation. List of Insects that Hibernate Hibernation of the insects in winter is different from mammals. During this phase, they go into a state known as diapause. This is associated with long-term state of suspension of life functions. So insects like the praying mantis bear the brunt of winter as eggs and emerge only when Spring approaches. If they have to bear the winter as adults, many insects alter the chemical composition of their blood, producing an antifreeze-like mixture that prevents them from freezing. Flies, mosquitoes, and beetles are some other insects that hibernate in the cold winter months. List of Birds that Hibernate There are many birds that enter into a state of inactivity or torpor during the cold months. These include birds like swifts, manakins, hummingbirds, and mousebirds. Animals that Hibernate and Migrate Another change adapted by some species of animals is that they go to places with warmer climates and stay there till the winter is over. Their body clocks are timed accordingly and once the climate in their habitat becomes warm, they migrate back. Given below is a list of animals that migrate to other places, to escape the freezing temperature.

• Certain types of birds like geese, ducks, etc.
• Animals like elks, whales, and caribou.
• Insects such as termites, Japanese beetle, moths, and butterflies like Monarch butterflies.

The animal kingdom is full of such mysterious creatures, that adapt themselves to the various climatic and environmental changes. Really intriguing!