People who are not at all happy about the approaching cold dark time, probably, do not mind falling into sleep until spring, as bears or marmots do. But it turns out that in nature everything is not so simple. Here are a few facts about hibernation that you probably didn't know.
What is hibernation?
Everyone has heard of bears sleeping in their den in winter. But in fact, clubfoot and other wintering species do not sleep at all during the cold season. Hibernation (as hibernation is scientifically called) is an extended form of torpor, a condition in which the metabolism is reduced to less than 5% of the norm.
"Most physiological functions in this state are extremely slowed down or completely stopped," says Marina Blanco of the Lemur Center in Durham, North Carolina, who studies the dwarf Madagascar lemurs (Cheirogaleus spp.), The only primates that hibernate on a regular schedule.
For example, when lemurs are hibernating, their heart rate drops from 300 beats per minute to 6. And instead of breathing every second, they can spend up to 10 minutes without taking a single breath. Their brain activity becomes imperceptible, which is very different from sleep, when the brain is still performing unconscious functions.
Why do animals hibernate?
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“Simply put, hibernation is a way to conserve energy,” explains Kelly Drew, a neuropharmacologist at the University of Alaska at Fairbanks who studies brain chemistry in wintering Arctic ground squirrels (Spermophilus parryii).
Although hibernation is most commonly seen as a seasonal behavior, it can be associated with weather events. For example, there are tropical species that can hibernate to survive the heat. But temperature isn't the only possible factor. Some species hibernate in response to lack of food. For example, the Australian echidna can do this after a fire and stay that way until food resources are restored.
Recent research has also identified a third reason. This is protection. “When you hibernate, you don't smell, make noise, make no movement, so it's very difficult for a predator to spot you,” says Thomas Roof, professor of physiology at the University of Veterinary Medicine in Vienna. His work showed that the mortality of small mammals is five times higher during active periods than during hibernation.
What happens to an animal in hibernation?
To slow down their metabolism, animals cool their bodies by an average of 5–10 ° C, and Arctic ground squirrels even below the freezing point. Research has shown that cooling is likely regulated by brain adenosine levels.
However, species are not in their coma for the entire hibernation period. About 80% of their energy is spent on periodic awakening and warming up. “Why this happens is one of nature's greatest mysteries,” says Roof. Some scientists believe that in this way they support their immune system to fight disease.
Unfortunately, these awakenings are threatening the existence of species in the face of climate change. Due to the increase in ambient temperature, animals during periods of awakening remain active longer than usual, depleting their energy reserves.
What animals hibernate?
One bird and many amphibians, reptiles and insects exhibit states similar to hibernation. There is also one fish that slows down its metabolism in winter, becoming 20 times less active - this is Antarctic cod.
And, of course, mammals. While bears may be the first to come to mind, they are an exceptional case. Most hibernating mammals are much smaller, with an average weight of only 70 grams. This is because small bodies have a high surface area to volume ratio, which makes them more susceptible to heat loss. They need much more seasonal energy savings to keep them warm in cold weather than large animals.
Who is hibernating the longest?
The obvious candidate for the prize for the longest hibernation is the dormouse (Glis glis). These rodents can remain dormant for more than 11 months. To sustain this “pause,” they must double or even triple their body weight while active.
Another contender for the victory is a large brown bat (lat. Eptesicus fuscus), which "hibernated" in the refrigerator for 344 days as part of the experiment. True, such a record cost her her life.