Elephants in the wild sleep just two hours a day, according to new research published in the journal PLOS One — the least amount of sleep of any mammal ever recorded.
In April 2014, scientists at the University of Witwatersrand in South Africa tagged two female elephants in Chobe National Park in Botswana with GPS tracking collars and Actiwatches, a Fitbit-like device for wildlife. By tracking the elephants’ movements and vitals for 35 days, the researchers were able to record when the animals fell asleep, and for how long. On average, the females slept two hours a day, spread out in several bursts over the night, but could stay awake for up to 48 hours if being tracked by a predator or avoiding a bull elephant during mating season, for example.
In contrast, elephants in captivity sleep three to seven hours a day.
Scientists say the research casts doubt on several sleep-wellness theories. Longer, sleep, particularly deep Rapid Eye Movement (REM) sleep, is believed to help reset brains for a new day of learning, clear out toxins, and aid with the consolidation of memories. But while elephants are known to have strong, long-term memories, the two animals in the study only got REM sleep every three to four days. “The hypotheses about restorative functions start to go out the window,” lead author Paul Manger told The Atlantic. “You can’t say that these are general things that apply to sleep across all mammals.”