Quck answer
Hibernation is a state of reduced metabolic activity that some animals enter to conserve energy during the winter months or when food is scarce. During hibernation, an animal’s body temperature drops and its breathing and heart rate slow down. This allows the animal to survive on stored body fat until conditions improve. Hibernation is triggered by changes in daylight and temperature, and different animals have different hibernation patterns. Some hibernate for months at a time, while others only hibernate for short periods. Scientists are studying hibernation to learn more about metabolic processes and how they might be applied to human medicine, such as in the treatment of obesity and diabetes.
Animal Facts
A hazel dormouse hibernating in a burrow.
Bon Elsdale/The Image Bank/Getty Images
Every living creature on Earth burns energy in various ways such as physical activities, pumping blood, digesting food, and even thinking. For warm-blooded animals, a significant amount of energy is required to maintain body temperature. Eating provides the energy required to fuel these processes. However, what happens when food becomes scarce during winter? How do animals survive with limited energy sources?
There are various winter survival strategies in the animal kingdom, and one of the most fascinating is hibernation. Some animals go into a state of “suspended animation” where their heart and breathing rates slow down, and their body temperature drops significantly, sometimes even below freezing point. They stop eating and excreting to conserve energy.
Animals either hibernate or migrate to warmer regions based on their evolution. Smaller animals are more likely to hibernate since migrating requires a lot of energy relative to their body size. Larger animals are less likely to hibernate due to the additional energy required to maintain body warmth.
Hibernation is more diverse than what people may think. While most animals hibernate in dens during winter, some animals hibernate in summer, and certain fish can hibernate in mucus envelopes if their lake dries up. Additionally, some birds and bats enter a daily hibernation period called torpor.
On the next page, we’ll discuss the differences between hibernation and sleep and learn about animals in zoos.
The Sleeping Goldfish
You may have owned a hibernating animal without realizing it. Domesticated goldfish in outdoor ponds hibernate during winter and float at the bottom of the pond below the ice in a state of reduced metabolic activity. The greatest threat to them is the accumulation of ammonia in the water from their waste and decaying plant matter.
How Is Hibernation Different From Sleep?
Early spring sun wakes up a hibernating black bear.
Mark Raycroft/Minden Pictures/ Getty Images
Biologists have differing opinions on how to classify hibernation. A common definition of hibernation is a long-term state where body temperature drops significantly, metabolism slows down drastically, and the animal goes into a comalike condition that takes time to recover from. By this definition, bears don’t hibernate since their body temperature drops only slightly, and they wake up relatively easily. However, not everyone accepts this narrow definition. For this article, we’ll use the term hibernation to describe any long-term reduction in body temperature (hypothermia) and metabolism during winter months.
During the summer, when an animal enters a hibernation-like state, it is referred to as estivation, which is less common than hibernation. In reptiles, hibernation is also known as brumation, but it differs from mammalian hibernation because reptiles are cold-blooded and require a warm enough place to spend the winter as they cannot control their own body temperature. Torpor is another term used to describe reduced temperature and metabolism functions, but it is commonly used to describe short-term periods of reduced temperature that occur for a few hours daily. The poorwill is the only bird species that hibernates for up to 100 days by dropping its body temperature up to 60 degrees Fahrenheit and living off 10 grams of stored body fat.
Hibernation is not just a long nap. Animals undergoing hibernation undergo significant physiological changes, including a drop in body temperature up to 63 degrees F. In contrast, sleep is mostly a mental change with slight physiological changes compared to hibernation. Zoo animals may not hibernate due to living in different environments from their natural habitat and may be fed every day and provided with warm sleeping areas. However, some zoos intentionally trigger hibernation in certain species to replicate natural life cycles.
Different animal species hibernate at different times and have various ways of knowing when to hibernate. Temperature most closely regulates hibernation, with animals preparing to hibernate when it gets cold outside. When it warms up, they wake up. Food supplies and photoperiod also trigger hibernation in some species.
Many animals enter hibernation at the same time each year, guided by an internal biological “calendar”. Circannual rhythms control hibernation, which all animals, including humans, are affected by. Some animals prepare a den or hibernacula and line it with insulating material, while others build nests out of paper. Food storage is also essential for successful hibernation. The endocrine system controls hibernation, with glands altering hormone levels to control various physiological aspects. When an animal enters hibernation, its body temperature varies depending on the temperature around it but has a minimum set point. Metabolism burns fat reserves to generate energy to heat things back up above the set point. Several other changes occur during hibernation.
During hibernation, the heart rate of animals can drop significantly, with some experiencing a reduction of up to 97.5% from their usual levels. Breathing rate can also decrease by 50-100%, with some animals even stopping breathing completely. Consciousness is greatly diminished, and many hibernating animals are unaware of their surroundings and difficult to wake up. Body fat is burned off to maintain minimal levels of body functions, providing energy for several months. Waste is also recycled during hibernation, with urea being broken down into amino acids. Hibernating animals also use brown fat to stay warm, which is oxidized directly by cell mitochondria, producing heat without shivering.
Estivation is similar to hibernation, but it occurs in hot weather, with animals burrowing into the ground to reduce metabolic activity. Lungfish can survive without water for up to three years using a special form of estivation that involves secreting mucus to create a sack that holds moisture.
Many bird species, such as the black-capped chickadee, use daily torpor to survive colder months. Daily torpor is a short-term hibernation that lasts for a few hours and reduces body temperature by a few degrees, saving calories from being burned off overnight.
Hummingbirds have a high metabolic rate and use daily torpor to conserve energy, even in the tropics. Hummingbird torpor is more profound than other birds and can exceed 50 percent body temperature reduction.
Scientists have used hydrogen sulfide to induce a hibernation-like state in mice and believe that humans also have the ability to survive in a state of hibernation. This could help stabilize accident victims, slow the progress of a disease, and make radiation therapy for cancer more effective by reducing healthy cells’ dependence on oxygen.
Hibernation is a long-term state in which body temperature significantly decreases, metabolism slows drastically, and the animal enters a coma-like condition. Breathing and heart rate slow down, and body temperature drops, in some cases even below freezing. Hibernating animals undergo physiological changes, and waking them up midwinter can be lethal.
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More Great Links
- NOVA Online: Secrets of Hibernation
Sources
The following sources are listed in the bibliography: Laura Austgen’s article on Brown Adipose Tissue from Colorado State University, Bernd Heinrich’s book Winter World, the Open University’s resource on hibernation and torpor in animals, Clive Roots’ book Hibernation, and Jun Yan’s study on the differential gene expression in Brown Adipose Tissue of hibernating Arctic Ground Squirrels using mouse microarrays. The sources are presented in an unordered list format.
FAQ
1. What is hibernation?
Hibernation is a state of inactivity that animals enter to conserve energy during harsh environmental conditions, such as winter. During hibernation, an animal’s metabolic rate slows down, their body temperature drops, and they enter a state of torpor, which is similar to deep sleep.
2. How do animals prepare for hibernation?
Animals that hibernate prepare for their long sleep by consuming large amounts of food to build up fat reserves. This fat is used as a source of energy during the hibernation period when food is scarce. Some animals also build nests or burrows to protect themselves from the elements.
3. Why do animals hibernate?
Animals hibernate to conserve energy during times of extreme environmental conditions when food is scarce. By slowing down their metabolism and entering a state of torpor, they can survive for extended periods without food or water.
4. What animals hibernate?
Many different types of animals hibernate, including bears, bats, groundhogs, hedgehogs, and some species of rodents. Even some species of frogs and turtles have been known to enter a state of torpor during extreme environmental conditions.
5. How long do animals hibernate?
The length of time an animal hibernates depends on the species and environmental conditions. Some animals hibernate for just a few weeks, while others can hibernate for several months. Some species can even enter a state of torpor multiple times throughout the year.
6. Can animals wake up during hibernation?
Yes, animals can wake up during hibernation if they are disturbed or if environmental conditions change. However, waking up too often can deplete their energy reserves and make it difficult for them to survive until spring.
7. How do animals survive without food or water during hibernation?
Animals that hibernate survive without food or water by slowing down their metabolism and entering a state of torpor. This reduces their energy needs and allows them to conserve energy until food is available again.
8. Can humans hibernate?
No, humans cannot hibernate. While humans can enter a state of torpor under extreme conditions, our metabolism and body temperature do not slow down enough to qualify as true hibernation.
9. How do scientists study hibernation?
Scientists study hibernation by monitoring the physiological changes that occur in hibernating animals, including changes in body temperature, heart rate, and breathing. They also study the genes and proteins that are involved in the hibernation process to better understand how it works.
10. Can hibernation be induced in animals?
Yes, hibernation can be induced in animals using drugs or other methods. This is useful for studying the hibernation process and developing new medical treatments for conditions such as stroke and heart attack.
11. What are the potential benefits of hibernation for humans?
The potential benefits of hibernation for humans include reducing the metabolic demands of critical care patients, preserving organs for transplantation, and enabling long-term space travel. However, further research is needed to fully understand and harness the benefits of hibernation for humans.
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