West African Chimps Regularly Drink Alcoholic Palm Sap

Observations over 17 years show this isn’t just an experiment for the apes

Frank Sommariva/imageBROKER/Corbis

Humans aren’t the only animals that like to regularly imbibe. Fruit and other sugary wild foods can naturally ferment enough to bring a buzz. There’s plenty of anecdotes and small studies about animals that drink, but until now researchers have had very little evidence of non-humans actively seeking alcohol. Now, after watching one group of chimpanzees in south-eastern Guinea for 17 years, scientists have found a group of regular, habitual drinkers.

Human communities in the area harvest a sugary sap from raffia palms and ferment it into an alcoholic drink. For The Guardian, Ian Sample reports:

To extract the sweet, white sap, tappers cut a wedge in the tree and suspend a container beneath. They leave it there to fill and lay leaves over the top to keep the bugs out. In a few weeks, a single tree can yield 50 liters of sap. 

The researchers noticed that the chimpanzees were using folded, chewed leaves as a kind of sponge to soak up the fermented sap and drink it. They reported in Royal Society Open Science that the chimps would dip about nine times per minute and were able to soak up at least 10 milliliters per dip. Depending on how long the sap had been fermenting, the chimps were downing a drink with an average of 3.1 percent alcohol — that of a low-alcohol beer. Not all of troop members did this — only 13 of the 26 chimps the researchers observed would drink the palm sap. Also, while habitual it wasn’t exactly frequent. Over 17 years, the researchers recorded 20 drinking sessions, where more than one individual partook, and 51 drinking events, which they defined as an individual drinking and includes those that took place during a session.

Previously, a different research team watched treeshrews that scamper about the Malaysian rainforest sipping fermented nectar from another type of palm tree. But they weren’t sure if the little mammals were actually getting a buzz. These chimps just might be. Sample reports:

Kimberley Hockings, an author of the study at Oxford Brookes University, said they could not be sure if the chimps got drunk, but said the amounts they consumed were enough to “elicit behavioral changes in humans.” On one occasion, an adult male seemed restless after a session and while his companions made for their nests, spent the next hour swinging from tree to tree “in an agitated manner.”

Here’s one adult male, named Foaf, enjoying his fermented palm sap: