Hibernation is one of the most interesting and yet one of the most misunderstood aspects of nature. Oh sure, just about everyone grasps the general concept of hibernation but not many really understand it. So at this time of year when the weather is turning cold and snowy it the perfect time to spend a few minutes to look at hibernation.

Let’s first look at what is hibernation then look at some animals that hibernate. The act of hibernation only occurs in warm blooded animals. It is a period of time where the entire metabolic system is repressed or depressed. It is characterized by lowering the body core temperature, slowing the metabolism of food, decreasing respiration, and lowering the heart rate. The over all effect of this is to conserver the body’s stored energy (fat) so it will last the entire period of hibernation.

The key to any successful hibernator is the amount of body fat it has upon entering hibernation. The fat is the fuel that will sustain them all winter. If the animal doesn’t have enough fat it will simply run out of fuel before spring and will die. Accumulating this fat during fall is extremely important requiring the most hibernating animal to be constantly feeding during every waking hour of the day.

All mammals (which include humans) maintain a constant body core temperature usually in the high 90’s degree F. Even a slight deviation of just a couple degrees either higher or lower dramatically affects the animal. Think about yourself for example. On average you have a body core temperature of 98.6 F. With just a 2 degree rise in temperature you will be running a low grade fever. A rise of 4 degrees and you are burning up with a high grade temperature and chances are you will be very ill. Conversely if your temperature dropped 4 or 5 degrees you would be hypo-thermic and you would be nearly unconscious from the cold. Now consider that a bat or a bear may drop their body core temperature 10 or more degrees and you can start to see how amazing hibernation can be.

Looking at respiration, we breathe about 10-12 times a minute. During hibernation respirations drop to only 1 or 2 times a minute. Heart rates that run near 100 beats per minute in many animals drops to only 20 or 30 beats thus slowing down the flow of blood to the entire body including the vital organs such as the liver, kidneys and brain. Under any other circumstance reduced blood to these organs would result in major organ failure.

Some mammals that are considered true hibernators include many species of bat. Some bats will migrate to warmer climates during winter while others move to caves where they will hibernate. In fact many bat species will be so cold and inactive that they are covered with a layer of frost during winter. In northern states hibernating bats may be down and out for 6 or 7 months. This is where having enough fat stored is extremely important.

Woodchucks are also a true hibernator. These plump short-legged critters feed non-stop during fall and enter their winter den with a layer of fat so thick they look like furry pigs hence their other common name whistle-pig. Once a woodchuck enters hibernation it is out for the entire winter.

There is another small furry critter that hibernates but they are not true hibernators. The Eastern Chipmunk gathers food in the fall and caches a stockpile of nuts and seeds underground in its burrow. During winter the chipmunk will hibernate but it’s not a true hibernation because they periodically wake up to feed and build up their fat reserves before going back into hibernation.

Just about everyone knows about bears hibernating. But bears are also not true hibernators. The average person envisions hibernating bears in their den completely unconscious, laying there with their tongues hanging out, totally oblivious to the world around them. Well actually when a bear is hibernating its heart rate, respiration, and all other bodily functions are greatly reduced but they are still awake. Female bears give birth to young during hibernation remaining awake enough to care for their young.

Other critters such as raccoons and skunks don’t hibernate but rather take a break during the coldest parts of the winter. They will hold up in a den and just sleep for up to 6 weeks. So if you are like me and you feel like hibernating, remember the first thing to do is put on a nice layer of fat. Until next time

Stan Tekiela is an author/naturalist and wildlife photographer who travels the US to study and photograph wildlife. He can be contacted via his web page at www.naturesmart.com