A recent study published in research journal PLUS ONE has found that sleep in wild animals is likely not related to sunrise and sunset, and that other environmental factors are more crucial to the timing of sleep.
According to University of the Witwatersrand (Wits) Anatomical Sciences Professor Paul Manger this is the first study to indicate this.

Research conducted by nongovernmental organisation Elephants without Borders together with the Chobe National Park, in Botswana; Wits; and the University of California, in Los Angeles, used data loggers similar to wireless-enabled data tracking device ‘fitbit’ to study the sleeping patterns of wild animals, mainly focussing on elephants.

Two matriarch elephants had data loggers implanted in their trunks and – by installing a global positioning system collar with a gyroscope around their necks – the team could find out where and when the elephants were lying down to sleep. 

“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,” he noted.

The team also found that the wild elephants could sleep while standing up or lying down. Lying down to sleep only happened every three or four days and for about an hour, and they were only able to go into rapid eye movement (REM), or dreaming, sleep, while lying down.

“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,” said Manger.

Research also found that the two female elephants, when disturbed by predators, poachers, or a bull elephant, could go without sleep for up to 48 hours, and following the start of the disturbance would walk up to 30 km from where the disturbance occurred.

This put a great deal of distance between the elephant herd and any source of danger, at the expense of a loss of a night’s sleep.

Manger noted that understanding how different animals sleep is important for two reasons.

“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 way, helps us to understand how humans sleep, why we do, and how we might get a better night’s sleep,” he said.