The researchers went out of their way to calculate the alcohol content of the drink, and came up with an average of 3.1 percent. That’s about a quarter of the strength of your typical Riesling. They also estimated how much the chimps were drinking — on average, about a quart (1 liter) per session for each adult chimp. During one of the drinking sessions, a chimp drank 3 liters of wine.

“Some of the chimpanzees at Bossou consumed significant quantities of ethanol and displayed behavioral signs of inebriation,” the researchers wrote. Although the scientists didn’t collect detailed data about the behavioral effects, they noted that some of the chimps rested right after a drinking bout.

Does all this mean that chimps are natural-born drinkers? Hockings acknowledged that Bossou’s chimps took advantage of an alcoholic drink that humans had collected, but she pointed out that “they learned and continue to ingest palm wine on their own accord.”