Chimpanzees in West Africa get inebriated during lengthy "drinking sessions" featuring the fermented sap of palm trees — normally used to make palm wine — according to a new study published Wednesday.

The report in the journal Royal Society Open Science focused on primates living in Guinea, which use palm fronds to soak up the fermented sap of raffia palms that can contain up to 6.9 percent alcohol — stronger than most beers.

"The habitual and voluntary consumption of ethanol has been documented until now, only in humans," apart from anecdotal observations in wild apes, said Kimberley Hockings of Oxford Brookes University, one of the report's co-authors.

While baboons in South Africa are known to steal fermenting grapes from vineyards and monkeys are known to sneak the odd cocktail from unsuspecting resort tourists, the chimpanzees in Boussou are unique because their alcohol consumption is not the result of any human interaction, the report said.

Some of the chimps "consumed significant quantities of ethanol and displayed behavioral signs of inebriation," the study found. While researchers note that no detailed behavioral data was collected — "some drinkers rested directly after imbibing fermented sap."

The behavior though is still quite rare, Hockings said, requiring researchers to combine their data from observations dating back to 1995. Researchers said they observed 51 "drinking events" by individual primates over that period of time.

"One adult male in particular accounted for 14 of 15 events," they said.

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