Hibernation is defined as a state of inactivity and lowered metabolism. Many mammals in temperate regions hibernate due to the fluctuations of the seasons. During a region’s winter, many animals may hibernate to conserve their energy, and may go on for days, weeks, or months in this state. This duration is affected by many things, differing between species, time that the hibernation starts, and the temperature of the area. While hibernation may seem like it is simply sleeping, the process is fairly arduous, requiring preparation if the animal wishes to survive the deep sleep.
Hibernation is more than just sleep. True hibernation is different than the simple denning,’ the act that bears engage in during winter. True hibernators are usually small mammals; bats, squirrels, and hedgehogs are common mammals that engage in this act. This is because these small mammals lose body heat rapidly. To counter this, they need a high metabolic rate. However, during cold temperatures, they must keep a very large source of food to maintain their body temperature. However, this is impossible during the winter months. Thus, they hibernate.
Animals begin their preparations when the signs of winter begin to appear. The shortening day and arriving cold signify that winter is approaching, and this trigger often begins the preparations for hibernation. Other triggers are internal rhythms, coming around every year at the time that it is necessary. Other creatures display opportunistic hibernation. As soon as conditions begin to deteriorate, regardless of the time of the year, the animal will begin to enter a period of hibernation.
Hibernation preparations start with the collection of fat in the body of the hibernator. During the months leading up to the hibernation, mammals will instinctively search for fattening foods. They will put on more weight than any other time of the year. Finally, when the triggers for hibernation are pulled, the animals quickly take shelter. These triggers are most commonly the reduced temperature, a heavy snowfall, or lack of long periods of sun. These triggers will create chemicals in the body that will cause the animal to become lethargic. At this point, the animal will begin its long slumber.
Under true hibernating conditions, metabolism, heart rate, and temperature must drastically drop, usually to fractions of what they normally function with. Normal body temperature (about 99 degrees Fahrenheit) will drop at least below 50 degrees Fahrenheit. Some species, like the arctic ground squirrel, can have body temperatures below 27 degrees Fahrenheit. Heart rate will drop near five to ten beats per minute. Breathing may even stop for periods of an hour or more. The creatures will curl up in a fetal position for protection and camouflage. The animal may in fact appear dead. However, even with the lowered body metabolism, most mammals will still end up heavily tapping their reserves of body fat. For example, hedgehogs will drop their heart rate and metabolism dramatically during hibernation. However, they still lose anywhere from 30 to 40 percent of their body weight through the winter. The situation is the same for many creatures that hibernate, although the numbers may differ by species.
During hibernation, the animal may be aroused periodically. Scientists propose that slight warming, the need to defecate, or the need to replenish water. Other studies show that animals’ sleep brain waves become absent. They then wake up lethargic and sleepy. Scientists believe that this periodic awakening may be a way to catch up on sleep, interestingly enough.
If all goes well in the hibernation, the animal will wake up. When the time comes, atmospheric triggers will begin the awakening process. The first cue is often the increase in ambient temperature. Since the animals usually lie within secluded areas, it may take a while for them to feel the effects of a warmer temperature, allowing the surrounding area to recover before the animals need food. The time it takes to arouse from hibernation depends on its weight. Small animals will start to warm up faster than larger ones. Vital organs will begin warming first as the creature violently shivers to create the heat required to wake. However, even with their awakening, it may take a few hours, even days for the animals to shake the drowsiness that the hibernation left behind. By the end of that period, the animals will emerge, much leaner and weaker. Bone structure will have been weakened by the lack of movement and lack of nutrients. They will require some time to regain their original weight and stamina.
One of the curious things is the fact that many of the larger animals do not hibernate. Bears appear to hibernate, but do not fulfill some of the requirements, such as periodic waking, or the need to feed or defecate. Some scientists say that this hibernation is very efficient, but lacks the original requirements to be called hibernation. Many other larger temperate animals, such as deer and wolves do not hibernate either. However, there have been cases where animals, and even humans, have succumbed to frigid temperatures, yet still survived the dip into hibernation.’ There was a case where a toddler survived after frigid temperatures nearly stopped her heart, but she made a full recovery soon after. Cases like these have made scientists believe that suspended animation, an induced hibernation, may actually help out human medicine (by preserving people until they can be better treated) and space exploration (by reducing the need for extensive supplies). Whatever the case, it is obvious that nature still has a lot to teach us.