(USAToday) - Forget the bananas. To a chimpanzee, the best treat might be a nice Riesling.

Scientists report that chimps in western Africa have taken to purloining drinks from vats of palm wine left unguarded by humans.

No crystal goblet needed: the animals fashion leaves into "sponges," sometimes taking advantage of the leaves humans place atop the wine containers to keep out debris. Never before have researchers documented repeated tippling by wild apes.

"There are reports from (locals) that chimps can consume an entire container in one sitting," says Kimberley Hockings of Britain's Oxford Brookes University, the head of a new study reporting the imbibing chimps. "They probably would drink more if they had easier access to it."

Hocking and her colleagues have yet to spot a definitively drunken chimp. But they have seen the animals collapse into sleep right after a drinking session.

On a separate occasion, when it was time for the group to rest, one particularly heavy tippler named Foaf "just couldn't settle. He was going around annoying all the other chimpanzees," Hockings says. She's not sure why, but she thinks it might have been the booze talking.

Green monkeys imported to the Caribbean are known to toss back tourists' cocktails, and Asian primates called slow lorises lick alcoholic nectar off a flower in their native forests. But until now no one had documented wild great apes with a drinking habit.

The chimps studied by Hockings and her colleagues live near the town of Bossou, Guinea, where palm wine is consumed at ceremonies and offered to guests. To make it, the local people tap raffia palms and position plastic containers high in the trees' crowns to catch the sap. But once a year or so on average, a group of chimps gets there first.

The scientists' tests of the wine showed it was roughly 3 percent alcohol, about the same as a weak lager, though some wine was nearly 7 percent alcohol. Between 1995 and 2012, half of the identified grown and immature chimps around Bossou were observed going on a bender, the researchers report in this week's Royal Society Open Science.

But the University of California, Berkeley's Katharine Milton thinks the alcohol was not the draw. Alcohol is "toxic," she notes, and ingesting large amounts of it would be a liability to an animal that makes its living climbing trees.

The chimps were probably not drawn by the alcohol itself, agrees Thibaud Gruber of Switzerland's University of Neuchatel. "Chimps love honey," he says. "It's more likely that the sugar is what they are interested in."