Snooze news: Wild elephants may sleep less than any other mammal

Turns out, an elephant not only never forgets, but also almost never sleeps!

A new study according to the Witwatersrand University has found that African elephants in the wild average just two hours of sleep a night and regularly go nearly two days without sleep.

Lead author Paul Manger and colleagues monitored two free-roaming African elephant matriarchs in Chobe National Park, Botswana, for 35 days. The researchers outfitted the elephants with an actiwatch implanted in the trunk to track sleep accurately and a collar with a gyroscope to track sleeping position.

The researchers found that the elephants slept an average of two hours a day, which is the shortest known sleep time of any land mammal. On several days during the study period, the elephants went without sleep for up to 46 hours and travelled long distances of around 30 kilometres during these periods, possibly due to disturbances such as lions or poachers.

In addition, they slept lying down only every few nights. This could limit their potential for daily REM (rapid eye movement) sleep, raising questions about when elephants experience this sleep state. While only two elephants were tracked, this research provides new insights into the sleep behaviour of the species in the wild.

"Studies of sleep in captive elephants have shown that they sleep for four to six hours per day; however, the current study shows that in their natural habitat, wild, free-ranging elephants sleep only for two hours per day, the least amount of sleep of any mammal studied to date, but this appears to be related to their large body size," said Manger.

He added, "It appears that elephants only go into REM, or dreaming, sleep every three to four days, which makes elephant sleep unique."

The research appears in Journal PLOS ONE.