For many animals, finding enough food in winter can be difficult, because their main source of food such as insects or green plants is in short supply. Some animals solve this problem by hibernating. Many different kinds of animals hibernate, from mammals and reptiles to amphibians and even some insects. Bears are well known for hibernating, but they only do so if they live in a cold climate. In the UK, only three mammals truly hibernate by sleeping right through the winter. Something you may not know about chipmunks is that they hibernate.
They fall into a deep sleep throughout the season, only waking up occasionally to feed. Unlike some other mammals which hibernate, chipmunks do not put on extra fat to take them through the winter.
They do, however, collect plenty of food, caching it in their burrows before winter comes. This animal has special cheek pouches that they use to carry food, storing it in their burrows. There is usually enough room for them to keep enough food to take them through the entire winter. Chipmunks are quite busy in the months preceding the winter season. Although these little mammals hibernate, they do not spend the entire season in a deep sleep.
They wake up every few days, and at this time, their body temperatures rise to about 94 degrees. This is what is known as an active cycle. Chipmunks eat some of the stored food, urinate and defecate.
Afterward, they lower their body temperatures and go back to hibernating. If you want to know what sounds a chipmunk makes, you can find out in an article I have written here. Ground squirrels retreat into their underground burrows, where they spend the winter in the form of hibernation.
They lower their body temperatures to about one degree higher than that of the temperature outside their burrows. During their hibernation, ground squirrels roll into a ball so that the head is tucked in between the legs and tail on the skull. They also adjust their heartbeat, slowing it down with their breathing rate. Ground squirrels do not hibernate fully and wake up once a week for nourishment. The squirrels can stay awake for up to 20 hours before hibernating once more.
On warmer days, ground squirrels tend to leave the burrow and forage outside for more food. Do you know why animals migrate?
When you think of animals that hibernate, the first thing that may come to mind is bears. There has been a debate as to whether the American black bears hibernate. The phenomenon of hibernation is one reason why the term homeothermy is going out of fashion, to be replaced by endothermy, because maintaining a stable body temperature is the very opposite of what hibernators do. The heartbeat becomes slow and irregular and breathing rate also slows.
Hibernation is an active process, that is, it is a state which animals enter into, not in response to immediate external conditions, but to internal stimuli. Some species are remarkably precise and predictable. For example, the arctic ground squirrel Spermophilus undulatus enters hibernation between 5 and 12 October and emerges between 20 and 22 April, regardless of the weather on those dates. This behaviour is in contrast to other winter states such as torpor or lethargy which are immediate responses to current conditions.
Brown and black bears, for example, are lethargic during very cold periods but are otherwise active in the winter. A feature of hibernation that distinguishes it from other kinds of winter inactivity is that hibernators can arouse themselves spontaneously and are not dependent on external conditions, such as warm temperatures, to do so.
The arctic ground squirrel is described as an obligate hibernator because it hibernates every winter. There are some mammals that are categorised as facultative hibernators , entering hibernation in response to very cold weather and poor food supply. The North American pocket mouse Perognathus californicus is a facultative hibernator. True hibernation only occurs in relatively small mammals, though not all small mammals living in temperate habitats hibernate in winter, as we have seen.
The largest mammal to hibernate is the marmot, which weighs about 5 kg. There are several reasons why larger mammals do not hibernate. Firstly, they would warm up too slowly and therefore use too much energy. Secondly, they have a smaller surface area to volume ratio and so can conserve body heat better than smaller species. Finally, they are better able to carry a thick coat Section 1. Hibernators are mainly found in the orders Rodentia, Chiroptera bats and Insectivora.
Note that although hedgehogs are in the order Insectivora they do not just eat insects! The physiological features that are characteristic of hibernation are not maintained throughout the winter. Rather, the animal wakes up at intervals, its temperature and metabolic rate increasing to near-normal levels Figure The function of this periodic arousal is not wholly clear. Some species, such as the chipmunks genus Tamias eat from stored food reserves during arousal periods, but many others do not.
Most species urinate and defecate, move about and change their position, suggesting that arousal provides an opportunity for various essential physiological processes to be performed and to prevent the animal becoming moribund. Hibernation requires internal energy reserves in the form of adipose tissue and hibernators typically feed intensively prior to winter, building up their fat stores.
Some species, such as the edible dormouse Glis glis , switch to a carbohydrate- and lipid-rich diet, e. Snakes take their cues from their surroundings; when the daylight hours become shorter , they are aware that winter is coming. During brumation, snakes experience periods of wakefulness when they'll travel outside of their resting spot to hydrate. Not all bees hibernate, but bumblebees do. The bumblebee life cycle begins in the spring, when the queen bumblebee emerges from her winter underground hibernation.
The queen lays broods of worker bees first, followed by new queens and male bees. At the end of the cycle, the old queen and worker bees die. The new queens feed heavily, dig underground hibernation spots, and the cycle begins again.
Bats go into a state of torpor when temperatures get cold and they need to conserve energy. Torpor in bats can last from a couple of hours to a month. During this time, the bat's heartbeat can go from to beats per minute down to as few as In order to rewarm themselves from torpor passively, bats sometimes use energy from the sun.
Here's a video showing some of the other animals that hibernate:. Duke Lemur Center. New England Primate Conservancy. Faherty, Sheena L. Genome Biology And Evolution , vol 8, no.
Animal Diversity Web. McAllan, B. Integrative And Comparative Biology , vol 54, no. National Park Service ". Currie, Shannon E.
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