What is hibernation? Hibernation is a state of inactivity in an animal brought about by shorter days, colder temperatures and limited food. Hibernation not only eliminates the need for food gathering in the winter, but also allows an animal to conserve its body energy by slowing down its heart rate and breathing; these are all signs of the consideration of the mercifulness of God. While the average body temperature for a mammal is about 99 F (37 C), a hibernating animal’s temperature drops to around 43oF (6 oC). This is less than half the normal temperature and only 11 degrees above freezing! The lower temperature reduces the amount of energy an animal must use to keep warm.
For example, a hibernating woodchuck’s heart rate slows from 80 beats per minute to 4, and its temperature drops from 98 F (36.6 C) to as low as 38 F (3.3 C). If its body heat falls too low, it will awaken slightly and shiver to warm up a bit. If an animal lives in an area where the winter is mild, it may hibernate only briefly, or not at all.
Why hibernation-why do some animals sleep through the winter?
When the cold temperatures and ice of winter arrive, food becomes scarce for animals in the wild. Hibernation is a survival strategy, given by the Lord of all creatures; it is a technique that can be very successful in environments where food is scarce or just difficult to find during a long, cold winter season. Hibernation not only eliminates the need for food-gathering in the winter, but also lets an animal conserve its body energy by slowing down its heart rate and breathing. During the winter we are unable to see some animals, such as bears, in their usual habitat; they have retired to their dens. Since these kinds of animals have little chance to find food in their regions during that period, dropping into deep hibernation or into a torpid state allows them to use their bodies’ 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.
How do animals know it is time to hibernate?
Although there are some apparent signs that indicate the period of hibernation is approaching, this is still a subject of research. In the weeks before hibernation or dormancy, animals prepare their winter beds.
Hibernating animals have something in their blood called HIT, or Hibernation Inducement Trigger; this works something like a clock. Recent research suggests that it is some kind of opiate, chemically related to morphine. As the days get shorter, the temperature changes, and food becomes scarce, HIT triggers hibernation. How and why it happens is still a mystery waiting to be explored.
Are all “hibernators” the same?
Not exactly. Some animals are classified as “deep hibernators,” such as chipmunks, woodchucks, box turtles, black snakes, garter snakes, and toads. 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 41 F (5 C). Deep hibernation is also called “true hibernation.”
Other animals exhibit a less profound inactive state, called “torpor hibernation”; animals such as deer mice, black bears, skunks, and raccoons are examples of such animals. Torpor may be very short-term (during the cold hours of the night, for example) and involves a drop in the animal’s body temperature of no less than 59 F (15 C). An animal in torpor is also capable of relatively quick arousal. While some animals are given the ability of hibernation to survive, some are given other tools by our God. For example, birds do not hibernate, but most species migrate to warmer regions. Fish do not hibernate, but withdraw to deeper waters and their body processes slow down to the point where their food and oxygen requirements are a tiny fraction of the needs during the summer months. Aquatic insects do not hibernate. Most land insects die, leaving behind them their descendants in the egg, larva or pupa stages. Some insects, though, for instance
certain species of mosquito, hibernate in basements, cisterns and such protected places
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 length of day, in anticipation of 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 the day length decreases. The reliance of these animals upon warmth from their environment to maintain 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 the time that winter conditions become excessively stressful; this means that the animal can possibly 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.
Is hibernation seen only in cold regions?
Unexpectedly, not. While observing nature and learning about the world, one is astounded by the wonderful work of God Almighty. Although it is often viewed as a phenomenon of colder climates, hibernation also occurs in the desert. A classic hibernator is the desert tortoise, which heads underground into burrows with the onset of cold. In a suspended state, it drastically reduces its metabolic rate, digestion, urination, and defecation. Although some move only slightly during winter, others may take advantage of warm days and head out to bask.
Gall moth caterpillars, insects which most of us have never even heard of, typify the second group. They avoid freezing at all costs. Despite what most of us think, water can remain liquid down to -40 F (-40 C), provided that it is free of impurities, so these caterpillars purify what little water is contained in their bodies by emptying their guts of foreign food particles and bacteria.
In addition, they produce an antifreeze, much like that used in cars, but different than that used by freeze-tolerant animals, to lower the temperature at which ice forms. The combination of these two methods allows gall moth caterpillars to survive winter temperatures as low as -36 F (-38 C).
Survival during hibernation
The hibernating animal is quite defenseless when it is in a deep hibernative or even torpid state. They need to prepare a very secure hibernating den (the “hibernaculum”) to protect themselves as they are now an inactive animal. It is interesting that it is possible for an animal to live after six or seven months without eating, drinking, or passing wastes. For example, less than 1 percent of black bears die in their dens. The main threats to their lives are flooding and predators (wolves, dogs, active bears, and humans). Bears do not usually die of starvation in dens. Most deaths from starvation are before or after hibernation and involve primarily cubs and yearlings. Over-wintering black bears do other extraordinary things.For example, snoozing bears are able to gain all the sustenance they need entirely from within their own bodies. Fat tissues break down and supply water and up to 4,000 calories a day; muscle and organ tissues break down and supply protein. Bears’ bodies are somehow able to take urea-a chief component of urine that is produced during tissue breakdown and that, if left to build up, becomes toxic-and use the nitrogen in it to build new protein.
Hibernating bears also have what would seem to be dangerously high cholesterol levels.Because they live off their own fat, their cholesterol levels are more than twice what they are in summer (and more than two times higher than those of most people). But bears evince no signs of hardening of the arteries or the formation of cholesterol gallstones. Research has shown that hibernating bears generate a form of bile acid that, when administered to people, dissolves gallstones, eliminating the need for surgery. Despite being cooped up in a space about the size of a doghouse, hibernating black bears also appear to avoid muscle cramping and degenerative bone loss. How they accomplish this remains a mystery. Even though a hibernating bear drinks no water, it does not become dehydrated. If we can learn how this metabolic feat works we can use the information to help treat people suffering from chronic kidney failure. During this time, the amount of urine entering the kidneys drops by 95%. Disease is uncommon in hibernating animals. Most parasites of bears are adapted to their host’s hibernation cycle and reduce their demands in winter. Medical researchers are studying black bear hibernation to learn how bears cope with conditions that are problematical for people. The findings are aiding studies of human kidney disease, gallstones, obesity, anorexia nervosa, and other problems. Researchers hope that knowledge of bear hibernation may someday even aid space travel. Another mystery goes by the name of delayed implantation.A female will carry a fertilized egg in her womb for many months.The egg is ready to attach itself to the uterine wall and begin developing into a fetus.But it does not do so until the female’s body gives a signal; it is still unknown precisely what this signal is.This adaptation allows bears to time the birth of their cubs, so they’re not born too early or too late. It also gives the mother a way out if food is scarce. If she has not accumulated enough fat by the time she settles into her den to hibernate, the egg will spontaneously abort. Some biologists see this neat trick as a natural mechanism to control the population. Evidence is mounting that hormone-like substances in hibernating bears may control all these physiological tricks.When injected into other species, both those that hibernate and those that do not, these substances engender hibernation-like effects. In conclusion, we can say that what we know about hibernation may not contain even one half of what is to be known. Hibernation is a sign of the Lord’s existence in the world and His ceaseless protection of creatures.We know that hibernators do not decide to hibernate at will; they are put in that position by their All-Merciful Protector. And all of them are doing their job as actors in a great scenario in the World Theater of God.