With only 11 grams of EEG on the sloths' heads, the researchers came to terms with the natural sleeping behavior. Picture: Bryson Voirin
Reading aloud In their natural habitat, sloths sleep about 6 hours less each day than their captive counterparts. Overall, the animals sleep with only 9.6 hours per day, researchers found around Niels Rattenborg from the Max Plank Institute in Starnberg out. For their investigations in the tropical rain forest, the scientists used a newly developed portable device for measuring brain activity, which they attached to the head of the sloths. Animal sleep studies have so far only been conducted on captive animals. Only under laboratory conditions were the technically relatively complex investigations possible in which the brain waves of the animals were measured by electroencephalography (EEG). With a newly developed miniature EEG recorder, the team around Rattenborg was now for the first time able to investigate the sleep of three-finger sloths in their natural environment. For this they caught the animals, fastened the EEG device on the head of the sloths and then released them again. The small device weighs only 11 grams with batteries and therefore hardly affects the animals according to Rattenborg.

The recorded data surprised the researchers: previous studies in the laboratory had shown that the animals sleep just under 16 hours a day, but according to new records, sloths in their natural habitat spend only about 9.6 hours a day asleep. According to Rottenburg, it can not be ruled out that the different age of the examined animals in captivity and in the wild had an influence on the deviating sleeping behavior. But he suspects that the different circumstances of life are decisive: "Sloths in the wild must look for their own food and be alert to enemies. Therefore, they may only sleep as much as necessary. Maybe they sleep deeper than animals in captivity, "he explains to wissenschaft.de.

Experiments on animals in captivity could lead to wrong conclusions, says Rattenborg. For the past 40 years, researchers have been trying to figure out why some species get along with less sleep than others. In this way, one wanted to get to the function of sleep on the track. "It has now been shown that the sleep behavior of captive animals can be very different from their natural habitat, " explains Rattenborg. "In nature, animals may take a minimum amount of sleep. If we continue to explore the natural differences in the sleep behavior of different species of animals and someday explain them, we may also understand the reason why humans sleep. "He suspects that the results of his team will encourage other researchers using this technique as well To investigate the wild. He himself wants to continue the experiments with the portable EEG in future on ostriches.

Niels Rattenborg (Max Planck Institute, Starnberg) et al .: Biology Letters, DOI: 10.1098 / rsbl.2008.0203 ddp / science.de? Michael Böddeker advertisement

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