Shortest-Sleeping Mammal? African Elephants Sleep Only Two Hours Per Day

A new study published in the journal PLoS ONE has revealed that wild African elephants (Loxodonta africana) sleep an average of two hours a day and regularly go nearly two days without sleep.

African elephants. Image credit: Ro Dobby.

African elephants. Image credit: Ro Dobby.

African elephants are iconic mammals of the continent and the largest land animal; and evidence suggests that larger mammals tend to sleep less.

Behavioral studies of elephant sleep in zoos record that they sleep around four hours per day and can sleep standing up or lying down.

To study in more detail how elephants sleep in the wild, Dr. Paul Manger from the Witwatersrand in Johannesburg, South Africa, and co-authors monitored two free-roaming African elephant matriarchs in Chobe National Park, Botswana, for 35 days.

The researchers outfitted the elephants with an activity data logger implanted in the trunk to track sleep accurately, and a collar with a gyroscope to track sleeping position.

“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,” Dr. Manger explained.

The team found that the elephants slept an average of two hours a day, which is the shortest known sleep time of any land mammal.

“We found that these two elephants were polyphasic sleepers, had an average daily total sleep time of two hours, mostly between 02:00 and 06:00, and displayed the shortest daily sleep time of any mammal recorded to date,” the authors said.

“We observed on five occasions that the elephants went without sleep for up to 46 hours and traversed around 30 km in 10 hours, possibly due to disturbances such as potential predation or poaching events, or a bull elephant in musth.”

“They exhibited no form of sleep rebound following a night without sleep.”

This could limit their potential for daily REM (rapid eye movement) sleep, raising questions about when elephants experience this sleep state.

“REM sleep 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,” Dr. Manger said.

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,” Dr. Manger said.

“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.”

“In addition, it appears that elephants only go into REM, or dreaming, sleep every three to four days, which makes elephant sleep unique.”

“Understanding how different animals sleep is important for two reasons,” he added.

“First, it helps us to understand the animals themselves and discover new information that may aid the development of better management and conservation strategies, and, second, knowing how different animals sleep and why they do so in their own particular way, helps us to understand how humans sleep, why we do, and how we might get a better night’s sleep.”

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N. Gravett et al. 2017. Inactivity/sleep in two wild free-roaming African elephant matriarchs – Does large body size make elephants the shortest mammalian sleepers? PLoS ONE 12 (3): e0171903; doi: 10.1371/journal.pone.0171903

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