For something we spend roughly one third of our lives doing, there's still a whole lot we don't know about why and how we sleep. Just as some researchers are trying to unlock its secrets in humans, others are turning their attention to the animal world to move the science forward. Among those is a team at South Africa's Wits University, who has sought answers by using Fitbit-like activity trackers to gauge the sleep quality of wild elephants.
While we mostly take our shut-eye lying down over seven or eight hours, animals sleep in all kinds of weird and wonderful ways. Giraffes, for example, can survive on as little as five minutes of sleep a day, while the bottlenose dolphin avoids drowning while dozing by only shutting down half of its brain, using the other half to maintain a low level of alertness. And incredibly, a study last year found that seabirds actually squeeze in some shut-eye during flight.
But what about elephants? Behavioral studies carried out in zoos have suggested that elephants sleep for four to six hours a day, but what about those in the wild? Looking to get some insight into how these lumberers slumber, the scientists from Wits teamed up with researchers from the University of California and the NGO Elephants Without Borders to monitor their sleep, by borrowing some tech from the fitness tracker world.
The researchers used what they describe as a scientific equivalent of a Fitbit, implanting the small activity tracker into the trunks of two matriarch elephants. They also fitted them with GPS collars and gyroscopes to keep tabs on where and when they 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," says Paul Manger, from Wits' School of Anatomical Sciences.
The team monitored the two elephants for 35 days and found a few surprises. Most significant was the fact that the elephants slept for an average of only two hours a day and usually before the sun came up. After analyzing local temperature and humidity conditions as part of the study, the scientists say that environmental factors other than sunlight seem to play a role in determining sleep patterns.
"The data also indicates that environmental conditions 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."
Another interesting tidbit from the study was that the elephants slept both standing up and lying down, although lying down to sleep only occurred once every three or four days and only for about an hour at a time. The scientists say this is likely to be REM sleep, meaning that elephants don't dream on a daily basis, but only every few days instead.
"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.
The elephants also had a few sleepless nights. On five different occasions, the team found that the animals went up to 46 hours without sleeping and traveled around 30 km (18 mi) in 10 hours, something they believe may have been triggered by predators or poaching events. Interestingly, the animals showed no attempt to catch up on the missed sleep the following night.
"Understanding how different animals sleep is important for two reasons," says Manger. "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."
You can hear from Manger in the video below. The research was published in the journal PLOS One.
Source: Wits University
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