Elephants sleep an average of two hours a day — the shortest-known sleep time of any mammal on land, a new study has found.
They also regularly go almost two days without shuteye, a research team from the University of the Witwatersrand in South Africa discovered.
African elephants are the largest terrestrial animal, and evidence suggests that larger mammals are likely to sleep less. Many other studies, however, only probed their sleep in captive environments and also mistook mere rest for sleep.
Demystifying Elephant Sleep
Lead researcher and professor Paul Manger and his colleagues tracked two free-roaming African elephant matriarchs living in Botswana’s Chobe National Park for 35 days. They outfitted the subjects with an actiwatch — much like the fitness and health tracker Fitbit — to monitor sleep accurately and a GPS collar with a gyroscope to track and monitor position.
“[M]easuring the activity of the trunk, the most mobile and active appendage of the elephant, would be crucial, making the reasonable assumption that if the trunk is still for five minutes or more, the elephant is likely to be asleep,” said Manger in a statement.
The two elephants turned out to sleep two hours a day on average, with the sleep occurring mostly at pre-dawn. They went without sleep for up to 46 hours, traveling long distances of about 30 kilometers during those times, likely because of threats such as poaching or predation.
According to data, sleep in these wild creatures appear to be unrelated to sunrise or sunset, but rather are tied to environmental factors such as temperature and humidity.
They could also sleep while either standing up or lying down, which happened only every three or four days and for around an hour. It was in lying down that the elephants could reach rapid eye movement (REM) or dream sleep, which is believed to be vital for memory consolidation.
“The elephant has well-documented long-term memories,” explained Manger, “but does not need REM sleep every day to form these memories.”
The findings were discussed in the journal PLOS ONE.
Benefits Of Animal Sleep Research
Probing sleep in animals proves critical not only for stumbling upon new information for better wildlife conservation and management practices.
In an important nature reserve in Central Africa, researchers recently found that around 25,000 or 81 percent of the forest elephant population had been wiped out by poaching.
The remote, 2,900-square-mile Minkébé in Gabon, supposedly the frontliner in the battle against poaching that buoys the ivory demand in Asia, saw its elephant population disappearing fast from 2004 to 2014. It is threatened not just by Gabonese poachers, but by hunters from neighboring nations such as Cameroon.
These animal sleep studies also offer a better understanding of our own sleep as humans.
While it remains a mystery why we sleep, new research considers sleep a way to forget certain things learned throughout the day in order to grow neural connections that will store new memories.
A four-year experiment detected the shrinking of synapses or neural connections in mice while they slept, therefore positioning sleep as a way for the brain to keep learning new things and forming new memories.