African Elephants Sleep Just Two Hours Per Day, and Nobody Knows Why
That’s less than any other animal on record
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Elephants are pretty neat. They have incredible memories, they can problem-solve, and they do adorable things with their trunks. These feats of mental and physical exertion seem all the more impressive in light of new research indicating that elephants in the wild don’t get much downtime. As Ed Yong reports for The Atlantic, a recent study has found that African elephants sleep for just two hours a day on average—less than any other animal recorded thus far.
Most research into animals’ snooze patterns has focused on creatures in captivity. Studies have shown, for instance, that captive elephants sleep between three and seven hours each day. To find out how long elephants sleep in the wild, a team of researchers at South Africa’s University of the Witwatersrand, Johannesburg (also known as “Wits”) tranquilized two female elephants and fitted their trunks with "actiwatches"—basically scientific-grade Fitbits.
Measuring the movement of the elephants’ trunks, the team reasoned, would be the best way to tell whether or not the animals were sleeping. The trunk is “the most mobile and active appendage of the elephant,” Paul Manger, professor at Wits’ School of Anatomical Sciences, said in a press release. "[I]f the trunk is still for five minutes or more, the elephant is likely to be asleep.”
Data collected from the actiwatches indicated that the elephants slept for about two hours each day, mostly in the early morning. Sometimes, Helen Briggs reports for the BBC, the elephants stayed awake for days at a time as they traveled long distances, possibly to evade lions or poachers. But they never seemed to catch up on rest by sleeping longer, Yong writes in The Atlantic.
This insomnia wasn’t entirely surprising. Previous studies have indicated that large mammals tend to slumber less than smaller ones, possibly because they need to spend so much time eating, Sam Wong writes in The New Scientist. But even among large animals, elephants are comparatively light sleepers; giraffes, for example, sleep about five hours per day.
Speaking to Briggs at the BBC, Manger noted that scientists are “not really sure” why elephants spend most of their days awake, and that “[s]leep is one of those really unusual mysteries of biology.”
The elephants’ scanty shut-eye time has indeed raised a mess of thorny questions about the purpose of sleep as we know it. Various studies have theorized that sleep clears toxins out of the brain, and gives mammals a chance to reset their brains for a new day of learning and memory formation. But if this were true, how could elephants maintain their extraordinary memories? Elephants, as the saying goes, never forget. And as it turns out, they don’t sleep much either.