Which animals hibernate?

The squirrel, a warm-blooded animal, hibernates during the winter.

Both warm and cold-blooded animals hibernate, including some species of squirrels, hedgehogs, frogs, turtles, and even some fish. Most hibernating animals are found in the northern and southernmost areas of the globe – the coldest climates in the world. The range is quite extensive and also includes hamsters, skunks and badgers. Bears, perhaps the most famous of these animals, don’t sleep as deeply as many other animals, so some scientists don’t consider this true hibernation.

warm blooded animals

Some cold-blooded animals, such as the bullfrog, hibernate during the winter.

Many small, warm-blooded animals hibernate during the winter, including many rodents such as the vole, ground squirrel, and marmot. These animals must hibernate for part of the year, and once this process begins, they are extremely difficult to wake up. A hazel vole’s body temperature, for example, drops to just above zero, and its heart beats only a few times a minute. Some of these animals wake up periodically to eat, but others remain in this deep sleep for up to six months. Other warm-blooded animals that hibernate include mouse lemurs and mountain pygmy possums.

Turtles usually hibernate.

Most birds don’t actually hibernate, although the common poor, a species in the family called Nightjars or Nighthawks, do. Found in the southwestern United States and Mexico, this bird can spend weeks or months during the winter in a dormant state. Other birds may enter a state known as torpor, during which metabolism and body temperature decrease, but this usually only lasts for a short time, often overnight. In many cases, hibernation is described as long-term torpor.

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Some hamsters hibernate.

Bears are the most commonly identified animals that sleep during the winter months; however, many scientists do not classify the bear as a true hibernator because it does not undergo the same degree of physiological changes that other hibernating animals do. For example, while a bear’s heartbeat and breathing slow down, its body temperature doesn’t drop much. Along with some bats, bears are also relatively easy to wake up. Most bears give birth to their cubs during the winter and therefore the mother bear must be somewhat conscious during the birthing process to properly care for her cubs.

cold blooded animals

Hedgehogs are animals that hibernate.

Insects, reptiles and other species, including some fish, also hibernate. As they cannot maintain their body temperature in the same way as warm-blooded animals, many cold-blooded animals seek refuge in hollow trees, caves, or underground for protection during the winter. Some swamp creatures – as well as fish – often bury themselves in the mud at the bottom of a lake or pond. Not only does this protect the creature from the elements, it prevents the current from washing the creature downstream and prevents it from becoming a meal for other non-hibernating predators.

Some scientists don’t consider hibernating bears to be true.

Some experts make a distinction between the winter dormancy periods of warm-blooded and cold-blooded animals. Instead of “hibernation”, they refer to it as “brumation” when it occurs in reptiles. The main difference is the power source; mammals eat extra food before hibernating and use stored fat to survive the winter, while reptiles survive on glycogen, an energy storage molecule. For practical purposes, however, the two states are very similar.

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How does hibernation work?

Bats are known to be easily woken up when they go into their winter torpor.

Hibernation allows an animal to slow its life support systems tremendously, often having only one heart beat occur over several minutes. This altered metabolism not only saves energy, it prevents the animal’s body from requiring additional food and water while it sleeps. The animal’s body temperature also drops, and the majority of the warmth is concentrated near and around the vital organs. In some animals, such as the opossum, the young are born while the mother sleeps; the newborns make their way into a pouch on the mother’s underbelly, where they nurse throughout the remainder of the mother’s hibernation period.

Opossums are an example of an animal whose babies are born while the mother sleeps.

In some instances, the weather can turn unusually warm early in the season, bringing the animals out of their hibernating state much earlier than usual. This can often prove to be life-threatening for the animal, because food, such as grasses and berries, are not yet available. In this case, the animals may become starved and malnourished. Such a season can also be life-threatening to newborns as their mother’s milk may dry up due to her lack of nutrition.

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