There's an old saying that elephants never forget. You also can say they almost never sleep.
Scientists say a first-of-its-kind study tracking the sleep behaviour of wild elephants found the world's largest land mammal sleeps two hours per day on average, and some days not at all, and does so mostly standing up.
This represented the shortest-known sleep time of any mammal. Previous research showed captive elephants got four to six hours daily.
"Sleep needs to be studied in an animal's natural environment if we are truly to understand it," said Paul Manger, a research professor in the School of Anatomical Sciences at the University of the Witwatersrand in South Africa who led the study published in the journal PLOS ONE.
The researchers monitored two free-roaming female African elephants in Botswana's Chobe National Park for 35 days.