Urine tests show wild chimps regularly ingest alcohol from fermented fruit
Feb 26th 2026
A new Biology Letters study led by UC Berkeley graduate student Aleksey Maro and advisor Robert Dudley found metabolic byproducts of ethanol in most urine samples from wild chimpanzees in Uganda, showing these apes consume fermented fruit at levels comparable to light human drinking.
- Researchers analyzed 20 urine samples from 19 chimpanzees at Ngogo, Kibale National Park, Uganda, and published the results in Biology Letters.
- Seventeen of 20 samples were positive for ethyl glucuronide on strips sensitive to 300 ng/ml, and 10 of 11 samples tested with a 500 ng/ml cutoff were positive.
- The detected levels are comparable to light human drinking of one to two standard drinks within the prior 24 hours.
- Earlier fruit analyses estimated chimpanzees ingest about 14 grams of ethanol per day while eating roughly 4.5 kilograms of fruit, supporting dietary exposure to ethanol.
- Both male and female chimpanzees tested positive, while negative results were disproportionately from females in estrus and juveniles.
- The findings bolster the drunken monkey hypothesis but do not prove chimps selectively seek higher alcohol fruits, so behavior and physiological effects need more study.
- Researchers say commercial urine test strips make field surveys possible for other frugivores and could reveal widespread alcohol consumption in wild animals.