Why do elephants need so little sleep?
The pachyderms hardly need any sleep
African elephants sleep less than any other verified mammal. In a study in the wild in Botswana, two female elephants slept an average of only two hours a day.
(AP) · On several days, the two observed elephants did not sleep at all. They also only lay down to sleep about every third day, otherwise they rested standing, as researchers led by Paul Manger from the Witwatersrand University in Johannesburg report in the specialist magazine “Plos One”. Previous studies on the sleep of elephants have mainly been done with animals living in captivity.
Documenting the sleep behavior of the two 30-year-old female African elephants (Loxodonta africana) in the Chobe National Park for 35 days required some technology. The matriarchs of their respective flocks were first stunned from a helicopter. They were then given a collar with a GPS location transmitter and a 3-D sensor that could be used to document the animal's body position.
Sensor in the trunk
In addition, the three-ton pachyderms were implanted about one and a half meters above the tip of their trunk with the core of an “Actiwatch” bracelet in order to document their sleep rhythm.
Similar to studies with captive elephants, the researchers considered an elephant asleep if the animal did not move its trunk for more than five minutes. A measurement with sensors in the elephant's brain would be too costly and, according to the researchers, was rejected for ethical reasons. The researchers could not say whether the sleeping behavior of male elephants in the wild is congruent with that of the observed matriarchs.
According to the study, the observed elephants slept significantly less than captured animals. The animals living in the wild also lay down to sleep less often. When an elephant sleeps standing, its trunk rests on the ground and its eyes are closed.
Big mammals sleep little
With an average sleep duration of two hours, the female elephants sleep the shortest of all mammals observed in similar studies, as the researchers report. This is followed by a horse with about three hours. According to experts, large mammals generally sleep less than very small ones. A captive giraffe slept 4.6 hours in a study. However, gray whales appear to have a long sleep of at least nine hours.
"One of the unexpected results of this study was the observation that the elephants did not seem to have slept on four individual days during the study period," the researchers explained. One animal went as far as 46 hours without sleep. Such sleep deprivation is presumably due to the fact that the matriarchs wanted to bring their respective herds to safety from enemies, for example from a large pride of lions.
According to the study, elephants do not sleep in one piece. The two animals observed slept an average of four and five times a night, respectively. There was a main sleep time of about an hour, then several shorter periods of rest of 15 to 20 minutes. The elephants looked for a new place to sleep every night. The study in Chobe National Park took place in April and May 2016.
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