When you weigh more than 10,????? ???000 pounds, you need a lot of food just to survive. All those hours spent searching for grasses, roots and fruits means there's little time left over for sleep.

How little? Try two hours a day for African elephants in the wild, a new study found. If confirmed, that would be the shortest-known sleep time of any land mammal.

These herbivores can also regularly go nearly two days without sleeping at all, according to the paper published Wednesday in the journal PLOS ONE.

Researchers followed two free-roaming female elephants inside Botswana's Chobe National Park. They outfitted each matriarch with an "actiwatch" -- like a Fitbit for elephant trunks -- and a collar with a gyroscope to monitor the elephants' sleep times and sleeping positions.

Their study -- tiny as it is -- is one of the few to look at elephants in their natural habitats. Previous research has mainly involved elephants in captivity, and earlier observational data doesn't always distinguish between resting times and actual sleep.

A better understanding of how elephants behave in the wild can help inform and improve wildlife conservation efforts, said Paul Manger, lead author of the new study and a neuroscience professor at the University of the Witwatersrand in South Africa.

"As we build up more information, the ideas for conservation will become stronger and guided by real data -- and not just people's gut feelings," he said by phone from Johannesburg.

For the study, Manger and his colleagues tracked the two matriarchs over 35 days.

With the "Fibits," the researchers could measure how frequently the elephants moved their trunks throughout the day -- moments they called "acceleration events."

If the trunk didn't move at all for three minutes or longer, it suggested the animal was asleep. An African elephant's trunk can weigh between 270 to 290 pounds, so the appendage is unlikely to twitch or flop around as the pachyderm catches some z's.

The gyroscope-equipped collar told researchers if the pachyderms were standing and moving around, or lying down on their side, their preferred sleeping position.

The study suggests that African elephants in the wild sleep fewer hours than their peers in captivity. Earlier studies found that captive elephants can sleep between 3 to 7 hours, although some of that might include quick naps or moments of rest. Other small studies on elephants in their natural habitats estimated elephants spent 0.67 to 2 hours a day sleeping on their sides.

The difference in sleep times between elephants in captivity and in the wild likely has to do with food, Manger said.

African elephants can eat on the order of 700 to 900 pounds of food a day. If you're in a zoo, that grass is delivered daily by the bale. If you're in the wilds of Botswana, it might mean walking around 20 miles a day in a quest for calories.

"The larger the body size, the more food they need to literally shove into their mouths each day to keep themselves going," the professor said.

The team next hopes to study male African elephants in the wild. Unlike females, which tend to roam in a more confined space, male elephants can traverse across country lines, making it more complicated to gather data.

The team also plans to study multiple females in the same group, to see if they take turns sleeping in a kind of "cooperative vigilance," Manger said.

Throughout Africa, elephants are in danger due to hunting and human population growth. Populations of all elephants have plummeted from about 1.3 million in the 1970s to less than 500,000 today.

A tiny study on elephant sleeping habits won't change this dark reality. But every bit of more accurate data can help improve efforts to protect endangered wildlife.