African elephants in the wild sleep an average of two hours a day and regularly go nearly two days without sleep. This is according to a study published March 1, 2017 in the open-access journal PLOS ONE by Paul Manger from University of the Witwatersrand, South Africa, and colleagues.
African elephants are the largest land animal, and evidence suggests that larger mammals tend to sleep less. However, many studies on elephant sleep have been done in a captive setting or were unable to accurately distinguish rest from sleep.
To study in more detail how elephants sleep in the wild, Manger and colleagues monitored two free-roaming African elephant matriarchs in Chobe National Park, Botswana, for 35 days. The researchers outfitted the elephants with an actiwatch (a version of the consumer fitness and wellness tracker Fitbit) implanted in the trunk to track sleep accurately. “We reasoned that measuring 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,” says Manger. The team also installed a GPS collar with a gyroscope around their necks to determine where and when the elephants were lying down to sleep.
The main finding of the study was that the two matriarch elephants slept only two hours per day on average, and this sleep occurred mostly in the early hours of the morning, well before dawn. “The data also indicates that environmental conditions (temperature and humidity, but not sunlight) are related to when the elephants fell asleep and when they woke up (which happens well before dawn),” says Manger. “This finding is the first that indicates that sleep in wild animals is likely not to be related to sunrise and sunset, but that other environmental factors are more crucial to the timing of sleep.”
On several days during the study period, the elephants went without sleep for up to 46 hours and traveled long distances of around 30 km during these periods, possibly due to disturbances such as lions or poachers. In addition, they slept lying down only every few nights. This could limit their potential for daily REM (rapid eye movement) sleep, raising questions about when elephants experience this sleep state. “REM sleep (or dreaming) is thought to be important for consolidating memories, but our findings are not consistent with this hypothesis of the function of REM sleep, as the elephant has well-documented long-term memories, but does not need REM sleep every day to form these memories,” says Manger.
While only two elephants were tracked, this research provides new insights into the sleep behavior of the species in the wild. “Studies of sleep in captive elephants have shown that they sleep for four to six hours per day; however, the current study shows that in their natural habitat, wild, free-ranging elephants sleep only for two hours per day, the least amount of sleep of any mammal studied to date, but this appears to be related to their large body size,” says Manger. “In addition, it appears that elephants only go into REM, or dreaming, sleep every three to four days, which makes elephant sleep unique.”
Image courtesy Paul Manger