Wild elephants have a two-hour sleep per day.

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In April 2014, Nadine Gravet [Nadine Gravett] put two elephants to sleep with a tranquilizer and equipped them with tracking devices. These scientific counterparts of fitness bracelets record movements, and researchers can use them to measure how well test subjects sleep. Usually they are worn on the wrist, but in the case of elephant legs this is unacceptable, so Gravet had to implant them in the most mobile parts of the elephant - in the trunks.

The skin in the middle of the trunk is so thick that the elephants did not notice the implants, and scientists recorded the movements of animals for a month. After analyzing the data and studying the five-minute time windows in which there was no movement, Gravet was able to calculate when the elephants are sleeping. She found that on average they sleep only two hours a day - this is the minimum amount of sleep of all animals recorded today.

“Sleep is such a strange behavioral state,” says Paul Manger of the University of Witwatersrand, who led the research. “The main things in life for animals are to eat, to multiply, to do it so that you are not eaten, but in a dream it all stops working. Sleep replaces many survival instincts. We know a lot about him from laboratory animals, but we don’t know about the dream of exotic species. ”
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Munger has been studying animal sleep for nearly twenty years. He began, oddly enough, with the duck-billed platypus , which, as it turned out, has a fast sleep phase - in which dreams occur - it lasts longer than that of any other animals. After this strange topic, Manger continued to study the dreams of dolphins, whales, hippos, echidnas, cats and antelopes.

But most of the research was carried out with animals living in captivity, with a lot of food and few threats. Therefore, they sleep more than their wild relatives. For example, in the 1980s, scientists discovered that three-toed sloths in captivity sleep 16 hours a day - which is why they have the reputation of being slothful. In 2008, other researchers recorded the brain activity of wild sloths, and found that they sleep only for 10 hours . Munger also wanted to bring the science of sleep into the wild. And he began with elephants.

If it is very crude to summarize, then for reasons that are incomprehensible, large mammals sleep less than small ones. Elephants in captivity sleep from 3 to 7 hours a day, but because of their size, they were expected to sleep even less. But to prove it is hard. Elephants can sleep while standing, so it is very difficult to determine whether they are awake or asleep, especially if you follow them through the bushes all night. Sensors of brain activity would give a more accurate answer, but the anatomy of elephants is such that implantation of such sensors would be very risky. So Munger and Gravet stopped at bracelets that track activity. They also put GPS collars on animals to track them.

As Manger suspected, two elephant sleeps only two hours at night, and even in this mode, not in a row, but for 4-5 periods, distributed overnight. Most of the nights they slept standing up; sometimes lay down. They were not picky about where to sleep, and how much they went during the day did not affect how long they slept.

“Under natural conditions, animals show shorter sleep intervals than in laboratories, where there is always food, and there are no predators,” says Isabella Capellini from the University of Hull. "It is very good that we started receiving data on sleep outside the laboratory."

Of course, Gravet and Munger were watching only a couple of elephants, and both were adult females who were at the head of the family — and bearing the duty of leading the herds. It is possible that males, young elephants or females below the rank sleep longer, but at least it is clear that the sleep of the studied females is extremely short.

The gray whale is much more than an elephant, but it sleeps nine hours a day. A dolphin can only sleep with one half of the brain, remaining on the alert for many days in a row - but even with each half, it sleeps at least four hours a day. The next record holder of short sleep, oddly enough, will be a domestic horse, sleeping three hours a day, and behind it is a domestic pony, sleeping a little longer. So far, it looks like the African savanna elephant sleeps the least (the longest brown night-time — the bat, already sleeping 19 hours a day, apparently) sleeps the longest.

What is most surprising, Gravette and Munger found that a few nights a month their elephants did not sleep at all. Why?

Scientists have worked in the national park of Botswana Chobe - one of the few places where lions hunt elephants. Two test elephants stood at the head of the family and were responsible for the cubs, so they could not sleep, standing guard and looking out for lions. Similarly, they could escape from poachers or aggressively behaving under the influence of male hormones . One way or another, the elephants, apparently, did not sleep off after that - at least, they did not sleep longer.

“A surprisingly short period of sleep for wild elephants is the very“ elephant in the room ”that cannot be overlooked for several theories of the functioning of sleep,” says Niels Rattenborg of the Ornithology Institute. Max Planck. Some scientists believe that sleep was the result of evolution as a method of reloading the brain , and preparing it for the day of learning. Others think that sleep provides the ability to clean up toxins accumulated during the day. Some claim that sleep allows animals to consolidate the memories they have created while awake.

But if any of these ideas are true, how do elephants cope with such a short sleep? “Hypotheses about the recovery of the body begin to disappear,” says Munger. “You cannot call them generalized and applicable to the sleep of all mammals.” The idea of ​​consolidating memory works especially badly: this should occur during the fast sleep phase, and Manger's elephants only experienced this phase once every 3-4 days. How do they remember anything at all, not to mention maintaining their apocryphically long-lasting memories?

It is possible that the elephants adapted themselves in a special way so as to go without sleep. Suzana Herculano-Hauzel [Suzana Herculano-Houzel] from the University. Vanderbilt wondered if this adaptation was due to their large size. “They have to eat 17-18 hours a day, and it seems to me that they could survive only if they could learn to sleep a little,” she says. - We know that we cannot do without sleep, but we do not know what determines its duration in different animals. One of the difficulties is getting good sleep data from different animals, and the elephant, as an obvious extreme case, is a very important learning example. ”

Munger agrees that we will be able to understand the nature and evolution of sleep well if we study completely different types of animals - especially in the wild. He plans to continue research, although recently he has problems with free time. “I have a three-year-old child, and personally I had a good night’s sleep, a very long time ago,” he says.