Elephants Never Forget, and Barely Sleep Either

Elephant asleep
A baby elephant sleeps as a mahout feeds its mother before leaving for the jungle at Chitwan National Park in Chitwan, south of Kathmandu, Nepal, December 30, 2014. Wild African elephants sleep for as little as two hours a night, according to a study. Navesh Chitrakar/Reuters

Elephants are famous for their remarkable memories.

But scientists have recently discovered another odd feature about elephants: They sleep for the shortest time of any mammal.

Researchers fitted two wild African elephants in Chobe National Park in Botswana with the scientific equivalent of a fitness tracker in their trunks and a GPS collar to monitor when they went to sleep, and for how long. The study followed the elephants for 35 days.

The study, published in the journal PLOS One, found that the two matriarch elephants slept for an average of two hours per day, and sometimes stayed awake for up to 48 hours without sleep if threatened by predators or poachers. The animals can sleep standing up or lying down, and generally slept in the early hours of the morning.

Elephants in captivity sleep for around four to six hours a day. Larger-bodied mammals generally sleep for less time than smaller ones. Lack of sleep, even over a short period, can lead to brain damage in mammals.

The study also found that elephants only dream—by entering a deep kind of sleep known as Rapid Eye Movement (REM) sleep —every three to four days. REM sleep is thought to be part of the process of memory consolidation, but the researchers said the study's results cast doubt on this link.

"Given the well-known memory of the elephant this calls into question theories associating REM sleep with memory consolidation," Professor Paul Manger of the University of Witwatersrand in South Africa, who was involved in the study, told the BBC.

The study was carried out by researchers from the University of Witwatersrand, the University of California, Los Angeles, and Botswana-based NGO Elephants Without Borders.