What is hibernation?

Hibernation is a state of inactivity in an animal brought about by short day lengths, cold temperatures and limitations of food.

Are all "hibernators" the same?

No. Some animals are classified as "deep hibernators". Deep hibernation is a state in which an animal is inactive for many days or weeks. In deep hibernation the animal's body temperature drops to around five degrees C. Deep hibernation has also been called "true hibernation". Other animals exhibit a less profound inactive state called "torpor". Torpor may be very short-term (the cold hours of the night, for example) and involves the drop of the animal's body temperature to no less that fifteen degrees C. An animal in torpor is also capable of relatively quick arousal.

Why hibernate?

Hibernation is a survival strategy that can be very successful in environments in which food is scarce or just difficult to find during a long, cold winter season. Dropping into deep hibernation or into a torpid state allows the animal to use their body's energy reserves at a slower rate than they would if they were maintaining themselves at their typical basal metabolic rate. Some ecologists refer to hibernation as "time migration". Hibernation allows the animal to skip over the cold, stressful seasons and only expend itself fully in those months of abundant food and moderate climatic conditions. A major disadvantage to hibernation, though, is that the hibernating animal is quite defenseless when it is in a deep hibernative or even torpid state. A very secure hibernating den (the "hibernaculum") is needed to protect the inactive animal.

Do hibernators have to hibernate?

Some hibernators display what is called "predictive dormancy". These animals go into a hibernative state usually in response to the decreasing day lengths which anticipate the approaching winter. "Diapause" in insects is an example of this "hardwired" hibernation response. Some poikilothermic ("cold blooded") animals (like some reptiles and amphibians) also display obligatory hibernative responses as day length decreases. The reliance of these animals upon warmth from their environments for their body heat necessitates that they anticipate the onset of cold conditions and not be caught out of their hibernaculae by potentially lethal cold temperatures.

Other animals enter their hibernative state only after being exposed to adversely cold conditions. These animals display "consequential dormancy". The disadvantage of consequential dormancy is that the organism is exposed to potentially damaging environmental conditions (poikilotherms in particular are especially vulnerable to the stresses of consequential dormancy). If, however, the hibernative response occurs immediately after the cold stress, then damaging exposure is minimized. A major advantage of consequential dormancy is that the animal is capable of activity right up until winter conditions become excessively stressful or possibly can even be active all winter long if the season is particularly mild. This flexibility is especially advantageous for species living in fluctuating, unpredictable environments or in species that are expanding their ranges into either higher or lower latitudes.

What are some Nature Trail animals and their hibernation patterns?

Deep hibernators: chipmunks, woodchucks, box turtles, black snakes, garter snakes, toads.
Torpor hibernators: deer mice, black bears, skunks, raccoons.
Non-hibernators: gray squirrels, shrews, voles, red foxes, wild turkeys.

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