Hibernation

The term hibernation comes from the Latin word hibernare, which means to pass the winter. The term is commonly used for a type of deep winter dormancy in some animals (i.e., mammals, birds, reptiles, and amphibians). A similar type of dormancy that occurs in summer is referred to as estivation. Some insects and snails also exhibit a similar state of dormancy in winter that is often called winter estivation or diapause.

Hibernation (winter dormancy) involves a periodic (seasonal) drastic reduction of the animal's metabolic rate and body temperature for an extended period of time. Generally, in hibernation, the body temperature drops almost to that of the surroundings (the bear being a well-known exception). Basic body processes, like breathing and the rate at which the heart beats, are drastically reduced so that the hibernator appears almost to be in a comatose state. The hibernating animal then lives through the winter on a reserve of body fat and/or externally stored food until it awakens in the spring.

Hibernation is therefore considered to be a fundamental adaptation to the environment since it is essentially an adjustment in the animal to allow its survival during those periods of the year when environmental conditions are so severe that exposure to the elements will be fatal. To survive in these harsh conditions, some animals can temporarily migrate from the hostile environment (e.g., birds). Some animals can remain active but adapt by

• growing thicker fur (e.g., weasels and snowshoe rabbits),
• storing extra food for the coming winter months (e.g., beavers, some squirrels and mice),
• changing their diet to that which is available during the winter (e.g., the red fox normally eats fruit and insects but eats small rodents in the winter),
• using shelters to protect them from the cold.

For others (e.g., reptiles, ground squirrels, and certain bears), migration is impossible and other adaptations are either impossible and/or ineffective as protection. These animals then adapt by means of hibernation.

Hibernation is seen mainly in small animals such as marmots, ground squirrels, chipmunks, dormice, and northern bats whose food supply is very limited or nonexistent in winter. Coldblooded hibernators include such amphibians as frogs and toads and such reptiles as lizards and snakes that pass the winter with body temperatures that are the same as the ambient temperature (i.e., near freezing). More recently, a tropical primate, the f at-tailed dwarf lemur (Cheirogaleus médius), endemic to Madagascar, has also been found to hibernate.

Outside of winter, natural hibernators lacking food and facing other adverse conditions cannot choose to hibernate to survive. Indeed, unless an animal is genetically disposed to hibernation or other states of dormancy, it cannot become dormant at will to escape inhospitable conditions.

[Page 653]Some refer to hibernation as “time migration” since hibernation allows the animals to skip over the entire period of the inhospitable winter season and truly “live” only in the periods of plentiful food and higher temperatures that occur outside of winter. Indeed, to the hibernating animal, time passes unnoticed since it is insensible and unaware during winter and becomes active or “alive” only at the end of hibernation.

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