How can elephants see in the night

How do elephants sleep?

A huge body needs a lot of relaxation, one might think - but apparently the opposite is the case: The largest land animal on earth - the African elephant - is the record holder among the short sleepers among mammals: The pachyderms sleep on average only two hours a day and they often stay awake all the time, according to a study.

Why do we have to sleep at all? Amazingly, sleep is still a mystery. "While there are many hypotheses about how sleep works, its ultimate purpose has yet to be discovered," says Paul Manger of the University of Witwatersrand. One thing is clear: people have to get enough sleep, otherwise there is a risk of life-threatening damage or loss of performance. There are individual differences, but on average around seven hours are considered cheap. As far as the typical length of sleep is concerned, however, there is an enormous range in the animal kingdom.

Big ones have little need for sleep

Comparisons have already revealed a clear trend: larger animals usually need less sleep than small ones. But does this rule also apply to the record giant - the African elephant? To answer this question, Manger and his colleagues examined the natural sleep behavior of wild pachyderms.

They equipped two elephant cows from the Chobe National Park in Botswana with measuring collars that had a GPS transmitter for localization and an activity data logger. This device mainly recorded the movements of the trunk. If the elephant's tool stands still for a long time, it means that the pachyderms are sleeping, explain the biologists.

The evaluations showed: On average, the elephant women only slept two hours a day, mostly in the early hours of the morning. According to the researchers, this is the shortest known length of sleep in a mammal. The researchers also documented that the elephant ladies sometimes stayed awake for up to 46 hours. According to the observations, this was the case when predators, poachers or elephant bulls in heat were in their vicinity. Then the animals were evidently literally vigilant.

REM sleep while lying down

When they slept, the animals mostly stood. But they also lay down every three or four days and for about an hour. The researchers suspect that only then do the elephants enter what is known as REM sleep. This means that they may not dream every day like we do, but only every few days. “REM sleep (or dreaming) is important to us for consolidating memories. Obviously elephants can form memories even without REM sleep, because their good memory is literally proverbial, ”says Manger.

“Understanding how different animals sleep is important for two reasons, the scientist emphasizes:“ Firstly, it helps us to understand the animals themselves and to collect new information that can be used to develop better management and conservation strategies. And secondly, such studies provide information for sleep research: How different animals sleep and why they do it helps us to understand how and why people sleep and it may provide clues as to how we could get better sleep, ”says the scientist.

Original work by the researchers:

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January 13, 2019

© - Martin Vieweg