Why Do Animals Hibernate?
The first case of hibernation was documented by Edmund Yaeger where he noticed the state of extended torpor of a bird approaching hibernation in the Condor Magazine. He wrote a lot of nature books and bagged the title of the “Dean of the California Deserts.”
The term hibernation is gotten from the Latin word hibernatus or hibernationem. Hibernation is a term used to describe the condition of an animal (or plant) that spends the winter being dormant. It functions to conserve energy when sufficient food isn’t available.
Hibernation is an extended form of torpor. Depending on the species, hibernation may last days, weeks and sometimes months; this period of time depends on the species of animals, their body condition and their ambient temperature. For example, looking at the dwarf lemurs, they are the only primates known to hibernate for an extended period of time- approximately 7 months.
During this time, the heart rate of a lemur drops from about 180 beats per minute to as low as eight beats per minute. Its body temperature also drops and becomes driven by the ambient temperature of the environment.
The process of hibernation is a way for creatures to survive the cold, dark winters without having to forage for food or migrate to somewhere warmer.
Apart from hibernation, there are other changes some animals undergo like aestivation and torpor.
Torpor
Animals that undergo torpor have a decreased body temperature and they also possess a non-physiological state of inactivity. Torpor enables animals to survive long periods of reduced food availability.
Animals like lungfish, hummingbirds, mice all undergo torpor.
Aestivation
Can also be spelt estivation, which is similar to hibernation. This process takes place in the summer, rather than during winter.
Terrestrial and aquatic animals undergo aestivation.
Examples of Animals That Hibernate
- Chipmunks
These animals weigh less than a pound, and their body temperature drops drastically during winter. They sleep heavily and wake up occasionally for food and would not be seen until springtime when they come out to play.
2. Bats.
These animals possess rubber-like looking wings and are black in colour (except on few occasions). But not all bats hibernate; some live in warmer climates or they choose to head towards the warmer regions when the food status begins dropping.
They fall into a deep sleep for as long as six months which makes them true hibernators.
3. Box turtles
These animals crawl into their shells when they are ready to hibernate, and they do this between Mid-September and Mid-October. Once they go into that mode, you don’t get to see them fully back to life for a period of 3–4 months. At intervals, they come out for water and then hastily go back to their shelves.
4. Bumblebees
Well, well, well. Who would have thought these honey-making machines actually hibernate? I didn’t think so either. One big difference between bumblebees and honeybees is that bumblebees are bigger and fuzzy with short wings and they are also pollinators.
During fall, the bees die leaving the queen bumblebee to hibernate and get ready to begin her new colony during springtime. The queen doesn’t eat when hibernating because she’s full of pollen and she’s plump enough to go to sleep and stays healthy for the entire period of hibernation.
5. Fat-tailed lemurs
This is the only primate in the world known to hibernate for a long period of time. They can last up to six months and are defined by periods of torpor (severely decreased metabolism, heart rate and body temperature. They also have interbout arousals which are characterised by metabolically active periods of rewarming. These arousals occur every 6–12 days during hibernation. They accumulate fat in their tails by gorging on food during the wet seasons — when flowers and fruits are in abundance — in preparation for the dry season when there will be scarcity.
When preparing for torpor, a fat-tailed dwarf lemur can increase its body weight by 75g (which is about 40%). It begins in Madagascar as early as March when they retreat to their hollow tree trunk which serves as a shelter. And they sometimes don’t emerge until the beginning of the wet, hot season in November.
6. Bears
Bears are always the first animals that come to mind when hibernation is talked about; but did you know that bears are not true hibernators? I’ll get to that in a minute.
Bears fall into a deep sleep called torpor, which decreases their heart and breathing rates. Bears can turn their urine into protein through a urea recycling process (they can sleep for more than 90 days without them drinking, passing waste and eating).
7. Poorwill
They are known as the first known hibernating birds. When other animals are migrating or entering brief states of torpor (hummingbirds), poorwills can be in a torpid state for some months. During this process, their breathing becomes reduced, they get a low temperature and a reduced heart rate.
Conclusion
When we talk of true hibernators, we talk of animals that can reduce their heart rate and body temperature drastically when they fall asleep. They only fully awake every few weeks to eat little amounts of their stored food and to also pass out waste. In summary, animals that are true hibernators don’t sleep all through the entire winter.
