During hibernation, an animal's heart rate, breathing rate and body temperature drop, allowing it to conserve energy while entering a dormant or torpid state. This survival process lets animals enter a period of inactivity during the winter months so they can avoid harsh weather conditions and diminished food availability. Read on to learn about some of the animals that are able to hibernate and how they do it.
Hedgehogs build a nest, curl up into a ball, and appear to be dead during the coldest two or three months of the year. Brain activity slows to a bare minimum, and the animal's heart rate drops from nearly 200 beats a minute to only 20. A breath every few minutes is all the hedgehog needs during hibernation. It lives off fat reserves built up during late fall and early winter. A hedgehog wakes up one-third smaller than before going into hibernation. (Source)
BEES AND WASPS
Most bees, wasps and their kin hibernate in one way or another. Many species have only one survivor per colony every year: the queen. When the males and workers die off in the fall, the queen finds a safe, warm place to hide until the following spring. Small, protected holes in the ground or under leaf litter are two prime hibernation spots fit for the queen. In many cases, the hibernation lasts for most of the year — six to eight months. (Source)
Groundhogs, aka woodchucks, undergo a severe change as they relax into a hibernation state. Their heart rate slows from between 80 and 100 beats per minute to around four or five beats per minute. With reduced nutritional needs while hibernating, groundhogs survive off the fat layer they build up in the summer and fall, and nothing else. A groundhog's body stays barely above the ambient temperature in the burrow, falling from 98 degrees Fahrenheit to as low as 38 degrees. (Source)
Aquatic frogs, such as the leopard (Lithobates pipiens), pig (Lithobates grylio) and bullfrog (Lithobates catesbeiana), hibernate underwater. As the temperatures drop, the metabolism of the frogs drops as well, lowering their food and oxygen demands. The frogs move to the bottom of the lake or pond, and essentially go to sleep. They are able to supply their lowered oxygen requirements by absorbing oxygen directly from the water through their skin. (Source)
A chipmunk's ability to slow its heart rate down to conserve energy allows it to hibernate. Normally pumping at around 350 beats per minute, its heart pumps only about 15 times per minute during hibernation. Respiration rates slow from 60 breaths per minute to 20 breaths per minute. Awake and active, a chipmunk might have a body temperature of between 96 and 106 degrees Fahrenheit, but it can drop to as low as 42 degrees when the animal hibernates. (Source)
Hibernation can last as long as eight months for bears living in northern habitats, where winters are longer and harsher than other areas. During the hibernation stage, bears' heart rates slow to between eight and 21 beats per minute. They don't eat, drink or relieve themselves during this time. Bears form fecal plugs — made of intestinal cells, hair and bedding material — during this time to help prevent defecation. (Source)
Hibernation is mostly a natural reaction that allows turtles to survive temperatures and food scarcity that could otherwise kill them. Most Asian, European and North American turtles hibernate. Usually it's in response to the climate changes that signal winter. Some of the turtles who heed nature's urging to sleep in the winter include bog turtles, Eastern box turtles, snapping turtles, painted turtles and wood turtles.
Some squirrels inhabit areas with such extreme winter climates that hibernation is the only way they can survive. Arctic ground squirrels (Spermophilus parryii) living near the Arctic Circle can hibernate for up to eight months. To survive under such difficult conditions, Arctic ground squirrels have developed their own method for hibernating. During their winter sleep, these squirrels allow their body temperatures to drop lower than any other living mammal — sometimes below 32 degrees Fahrenheit. (Source)
A temperature drop is enough to cause a snake’s metabolism to slow down to the point where it doesn’t need to eat over the course of the winter. Though solitary, snakes hibernate in communal dens. In one instance, more than 8,000 garter snakes were discovered hibernating together in Canada, although its more common to find only a few dozen together at once. (Source)
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Bats are relatively small mammals with high metabolic rates. They hibernate because maintaining a constant livable body temperature in cold weather would require them to burn more energy than they can generate, since the insects that bats consume are not readily available in the winter. Hibernating during winter slows metabolism, heart rate and breathing. Bat hibernation is not strictly seasonal; they hibernate for short periods of time year-round whenever the temperature is low or food is scarce. (Source)