Wild elephants have enough two hours of sleep per day

I get up already!

In April 2014 Nadine Gravet [Nadine Gravett] lulled by using tranquilizer two elephants and equipped them with tracking devices. These scientific counterparts to fitness bracelets record movements, and researchers can use them to measure how well 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 moving parts of the elephants - 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 recorded in animals today.

“Sleep is such an odd behavioral state,” says Paul Manger of the University of Witwatersrand, who led the study. “The main things in life for animals - to eat, multiply, to make sure that you are not eaten - but in a dream all this 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.”

Manger has been studying animal sleep for almost twenty years. He began, oddly enough, with the platypus , in which, as it turned out, the fastest phase of sleep - in which there are dreams - lasts longer than 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 went with the use of animals living in captivity, which have a lot of food and few threats. Therefore, they sleep more than their wild relatives. For example, in the 1980s, scientists discovered that three-fingered sloths in captivity sleep 16 hours a day - which is why they have a reputation for sloths. In 2008, other researchers recorded the brain activity of wild sloths, and found that they only sleep for 10 hours. Manger also wanted to bring the science of sleep into the wild. And he began with elephants.

If very crudely generalized, then, for reasons that are not yet understood, large mammals sleep less than small ones. Captive elephants sleep 3 to 7 hours a day, but because of their size, they were expected to sleep even less. But it’s hard to prove it. Elephants can sleep while standing, so it’s very difficult to determine if they are awake or sleeping, 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 the implantation of such sensors would be very risky. So Manger and Gravet settled on bracelets that track activity. They also placed GPS collars on animals to track them.

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

"In vivo animals showed shorter sleep intervals than in the laboratory, where there is always food and no predators," - says Isabella Kapelini [Isabella Capellini] from the University of Hull. “It is very good that we began to receive data on sleep outside the laboratory.”

Of course, Gravet and Manger watched just a couple of elephants, and both were adult females, who were at the head of the family - and carrying the responsibility of leading herds. It is possible that males, young elephants, or females of lower rank sleep longer, but at least it is clear that the studied females have an extremely short sleep.

A gray whale is much larger than an elephant, but it sleeps nine hours a day. A dolphin can sleep only one half of the brain, staying alert for many days in a row - but even each half sleeps at least four hours a day. The next record for short sleep, strangely enough, will be a domestic horse, sleeping three hours a day, followed by a domestic pony, sleeping a little longer. So far, everything looks like that the African savannah sleeps less than everyone (apparently, the small brown night-lamp sleeps the longest - the bat, breathing out as much as 19 hours a day).

Most surprisingly, Gravett and Munger found that their elephants did not sleep at all a few nights a month. Why?

Scientists worked in the Botswana Chobe National Park, 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 for lions. In the same way, they could escape from poachers or aggressively behaving under the influence of male hormones . One way or another, the elephants, apparently, did not get enough sleep after that - at least they did not sleep longer.

“A surprisingly short period of sleep in wild elephants is the same“ elephant in the room ”that cannot be overlooked for several theories of the functioning of sleep,” says Niels Rattenborg of the Ornithology Institute named after Max Planck. Some scientists believe that the dream came about as a result of evolution asmethod of reloading the brain , and preparing it for the day of training. Others think that sleep provides an opportunity to cleanse toxins accumulated per day. Some argue that sleep allows animals to consolidate memories created during wakefulness.

But if any of these ideas is true, how do elephants cope with such a short duration of sleep? “The hypotheses about restoring the body are starting to fall away,” says Manger. “You cannot call them generalized and applicable to the sleep of all mammals.” The idea of ​​memory consolidation works especially poorly: this should happen during the REM sleep phase, and Manger’s elephants experienced this phase only once every 3-4 days. How do they remember anything at all, not to mention maintaining their apocryphal long-lasting memories?

It is possible that elephants in a special way adapted to do without sleep. Suzana Herculano-Houzel from the University. Vanderbilt wonders if this adaptation is related to their large size. “They have to eat 17-18 hours a day, and it seems to me that they could only survive if they could learn how to sleep a little,” she says. - We know that you can’t do without sleep, but we don’t know what its duration in different animals depends on. One of the difficulties is getting good sleep data from different animals, and the elephant, as an obvious extreme case, is a very important case study. ”

Manger agrees that we can understand the nature and evolution of sleep well if we study completely different species 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 got enough sleep at night for a very long time,” he says.