Elephants eat 300-400kg of food every single day. They are almost always looking for fruits, grasses, and other food items, which leaves them little time to sleep. According to a study published Wednesday in the journal PLOS One, the giant African elephants sleep just two hours daily on average. That’s the shortest known sleep time for any mammal.
Elephants sometimes stay awake for days
Researchers led by Prof Paul Manger of the University of the Witwatersrand in South Africa tracked two female giants in Botswana to understand their natural sleep patterns. Elephants held in captivity have been extensively studied over the last few decades. But Prof Paul Manger wanted to learn more about their sleep patterns in the wild.
Researchers implanted a fitness tracker-like device under the skin of the trunk. The device was not harmful to the animals in any way. It recorded the sleep based on the trunk staying still for five minutes or more. Scientists had also fitted a satellite-tracking collar with a gyroscope to track the animals’ location and sleeping position. Both the female animals were tracked for five weeks.
Manger and his colleagues found that the mammals would sleep only two hours, mainly between 2am and 6am. Sometimes they would stay awake for many days, traveling long distances to escape threats like human poachers and lions. Even when they do sleep, they do so mostly standing up. The elephants spent merely 17% of their sleep time lying down.
The animal’s REM patter contradicts the central REM hypothesis
Researchers found that the animals went into rapid eye movement (REM) every 3-4 days, when they slept lying down. REM is associated with body movements, loss of muscle tone, and dreaming. Also, scientists believe REM helps in the consolidation of memories. Since it is well known that elephants have good memories, and now we know that they go into REM once every 3-4 days, it calls into question the central hypothesis of REM sleep.
Prof Manger said the animal’s short sleep time is related to their body size. Smaller body mammals tend to sleep longer than larger mammals. For instance, the little brown bat sleeps 19 hours a day, the armadillo 17 hours, sloths 14 hours, and humans 8 hours. By comparison, the domestic horses are comfortable with only three hours of daily sleep.
Why do captive elephants sleep longer?
Previous studies have shown that captive elephants get 4-7 hours of daily sleep, which includes quick naps and moments of rest. That is much higher than 0.67 to 2 hours of sleep a day in the wild. Prof Manger said the difference is largely due to food. The animals in zoo get the food delivered to them by caretakers. But those in the wild have to sometimes walk around 20 miles a day in search of massive food they need to survive.
Scientists now plan to study male African elephants in larger numbers in the wild. Males tend to roam more widely, making it more difficult to gather data. They also plan to monitor multiple females in the same group to see whether the mammals take turns sleeping to maintain “cooperative vigilance.”