By Dr. Becker
In captivity, elephants may sleep for four to six hours daily, but it shouldn’t be assumed that the same would hold true in the wild. In fact, researchers from the University of the Witwatersrand in South Africa decided to study wild African elephants, living in Chobe National Park in Botswana, to find out if their sleeping habits varied from elephants in captivity.
After all, elephants in captivity have food and water provided, and no risk from predators, which suggests their sleeping patterns would be different from elephants in the wild.
Further, studies that have been done on free-roaming elephants in the wild were observational, in some cases with the elephants not being observed at night or mixing up sleep with resting. “[N]o unbiased, or remote monitoring, measure of rest/sleep in the wild free-roaming African elephant is currently available,” the researchers noted — until now. It turns out their assumption was correct, with their revealing study finding that elephants may sleep the shortest of amount of time of any mammal.
Elephants May Sleep Just 2 Hours a Day — or Less
The researchers monitored two African elephants for 35 days, using small activity monitors implanted in their trunks (in a reportedly nonharmful way) along with satellite-tracking collars with gyroscopes to detect their location and sleep position.1 It turns out that the activity of an elephant’s trunk is a useful gauge by which to determine if it’s asleep or awake, and the researchers considered an elephant to be sleeping if her trunk was inactive for a period of five minutes or more. The researchers explained:2
“Isolated bouts of [five] minutes of trunk inactivity may or may not be accompanied by the full physiological manifestations of sleep, but given the near impossibility of recording even the minimum polysomnographic parameters required to accurately determine physiological sleep in the elephant (in either the captive or wild setting), we feel that this proxy measurement provides an accurate estimate of the maximum amount of sleep of the elephant.”
The monitoring revealed that the elephants had an average daily sleep time of just two hours, mostly between 2 a.m. and 6 a.m., displaying the “shortest daily sleep time of any mammal recorded to date.” They slept both standing up and lying down, with the latter occurring only every third or fourth day.
It’s presumed that rapid eye movement (REM) sleep only occurs when the elephants are in the recumbent position (although this isn’t definitively known), so the researchers suggested the animals may have a limited ability to enter REM sleep on a daily basis. This is ironic, since REM sleep is when memory consolidation occurs, yet elephants are known to have good memories. “This finding contradicts one central hypothesis of REM sleep function,” study author Paul Manger, Ph.D., said in a news release.3
Another possibility is that elephants may exhibit REM sleep similar to birds (which have short sleep episodes composed of 90 percent slow wave sleep and 10 percent REM sleep) or horses, which have very brief episodes of REM sleep (16 to 23 seconds in length) while standing. “In this possible scenario, REM sleep could occur on an almost daily basis in the elephants while in standing sleep (except for those days with no sleep at all),” the researchers said.4
Elephants Can Go for 46 Hours Straight With No Sleep
Also remarkable, the researchers observed five occasions when the elephants went without sleep for up to 46 hours straight, traveling about 30 kilometers (18.6 miles) over a period of 10 hours during that time, possibly due to the risk of poaching or predation. “They exhibited no form of sleep rebound following a night without sleep,” the researchers noted, also adding that the amount of activity the elephants received did not affect the amount of sleep they got on any given night.
It appears the animals need a startlingly little amount of sleep, and spent only 17 percent of their time lying down. The most they slept during any day monitored was five hours.
It was also revealed that environmental conditions, such as ambient air temperature and relative humidity, predicted when the elephants went to sleep and woke up, and the elephants chose a new spot to sleep in each day. Although the research only involved two elephants, the researchers feel confident it is representative of the broader population, adding:5
“The current observations provide a far richer story of elephant sleep in their natural environment than would have been suspected from studies in zoo or circus animals and underscores the need to study sleep more broadly in the natural habitat in addition to controlled settings.”
How Long Do Other Animals Sleep?
Elephants may be the shortest sleepers recorded to date, but they’re not alone in this trait. Domestic horses, for instance, sleep just under three hours per day, compared to the domestic pony, which sleeps just over three hours. For comparison, other large-bodied mammals sleep decidedly longer, including the gray whale (nine hours) and the giraffe (4.6 hours, in captivity). That being said, it’s likely that wild giraffes sleep less than their captive counterparts, as is the case with elephants.
On the other end of the spectrum are sloths, which sleep for 15 to 20 hours a day, as does your average house cat (16 to 18 hours daily, on average). While it may seem remarkable that elephants (and many other animals) can sleep while standing, certain birds even take naps while they’re flying, using what’s known as unihemispheric sleep. Bottlenose dolphins also effectively shut down their brains in order to sleep with one side of their cranium and continue their inborn survival skill of surfacing to breathe when necessary.
Interestingly, while captive elephants have different sleep schedules than wild elephants, so too do wild elephants depending on their environment. Human activities cause African elephants to become nocturnal, particularly when they live near villages and farmland, possibly because it helps them avoid threats.6