Researchers at the University of California, Berkeley have found ethanol in the nectar of most plant species examined, meaning pollinators like bees and hummingbirds consume alcohol daily. An Anna's hummingbird drinks an amount equivalent to one human alcoholic beverage per day, yet shows no intoxication. The findings, published March 25 in Royal Society Open Science, suggest evolutionary tolerance to low-level ethanol.
Biologists at UC Berkeley conducted the first large survey of alcohol in floral nectar, detecting ethanol in samples from 26 of 29 plant species. Levels were mostly trace amounts from yeast fermentation, with one sample reaching 0.056% ethanol by weight, or about 1/10 proof. Hummingbirds and bees ingest this as they feed, with nectar providing their main energy source. An Anna's hummingbird, common along the Pacific coast, consumes roughly 0.2 grams of ethanol per kilogram of body weight daily—comparable to a human having one standard drink—yet metabolizes it without inebriation signs. Experiments showed these birds avoid sugar water above 1% alcohol, visiting feeders half as often at 2% concentrations. Feathers of Anna's hummingbirds contain ethyl glucuronide, a mammal-like ethanol byproduct. Aleksey Maro, a doctoral student involved, noted, 'Hummingbirds are like little furnaces. They burn through everything really quick.' Professor Robert Dudley added, 'They're burning it so fast, I'm guessing that they probably aren't suffering inebriating effects. But it may also have other consequences for their behavior.' The team estimated similar intake for sunbirds in South Africa and compared it to species like honeybees (0.05 g/kg/day) and tree shrews (1.4 g/kg/day). This work, part of a National Science Foundation project, highlights potential physiological adaptations to dietary ethanol across animals.
