Hummingbirds collect more than just sugar when they visit flowers. A new study from the University of California, Berkeley, shows that they also ingest measurable amounts of alcohol.
In the first large-scale survey of alcohol in floral nectar, biologists detected ethanol in samples from 26 of 29 plant species examined. This suggests that hummingbirds, bees, and other pollinators regularly consume small but consistent amounts of alcohol throughout the day as part of their daily foraging. The findings, published in Royal Society Open Science, raise new questions about the physiological and ecological effects of ethanol exposure in these species.
Nectar-Based Alcohol
Researchers used an enzymatic assay to measure ethanol in 147 nectar samples collected at a botanical garden. Ethanol was detected in 48% of these samples. Most concentrations were at trace levels, produced by yeast naturally fermenting sugars in the nectar, but one sample reached 0.056% ethanol by weight, roughly 0.1 proof; far less than a light beer.
While these concentrations appear low, their impact may be significant when considering the volume of nectar consumed by pollinators. Hummingbirds consume between 50% and 150% of their body weight in nectar each day. At the ethanol concentrations observed, an Anna’s hummingbird, commonly found along the Pacific coast, ingests about 0.2 grams of ethanol per kilogram of body weight daily. For comparison, this is equivalent to a 155-pound human consuming one standard alcoholic drink over the course of a day.
A Buzz They Never Feel
Even though the birds regularly take in alcohol, they do not show clear signs of being impaired by it. Earlier experiments at a feeder outside UC Berkeley professor Robert Dudley’s office showed that Anna’s hummingbirds do not mind alcohol levels below 1% in sugar water, but they visit feeders about half as often when the level reaches 2%.
“Somehow they are metering their intake, so maybe zero to 1% is a more likely concentration that they would find in the wild than anything higher,” Dudley said.
“Hummingbirds are like little furnaces,” added Maro. “They burn through everything really quick, so you don’t expect anything to accumulate in their bloodstream. But we don’t know what kind of signaling or appetitive properties the alcohol has. There are other things that the ethanol could be doing aside from creating a buzz, like with humans.”
The Building Evidence
This isn’t the first time the Berkeley team has looked into this question. In a related study, former graduate student Cynthia Wang-Claypool found traces of ethyl glucuronide, which is a byproduct of ethanol metabolism, in hummingbird feathers. This shows that the birds not only ingest alcohol but also process it in a way similar to mammals.
“The laboratory experiment was showing that yes, they will drink ethanol in their nectar, though they have some aversion to it if it gets too high,” said Corl. “The feathers are saying that, yes, they will metabolize it. And then this study is saying that ethanol is actually pretty widespread in the nectar they consume.”
The team estimated daily ethanol intake for several nectar-feeding species and compared these values with those of other animals, including the European honeybee, the pen-tailed tree shrew, fruit-eating chimpanzees, and humans consuming 1 standard drink per day. The pen-tailed tree shrew had the highest intake at 1.4 grams per kilogram per day, while the honeybee had the lowest at 0.05 grams. Nectar-feeding birds fell in the middle, with values between 0.19 and 0.27 grams per kilogram daily when feeding on native flowers.
An Evolutionary Relationship
This research is part of a five-year National Science Foundation project investigating how hummingbirds and sunbirds adapt to different environments, including high-altitude habitats, sugar-rich diets, and fermented nectar sources. Researchers also included sunbirds, which occupy a similar ecological niche in Africa as hummingbirds do in the Americas, in the ethanol dosage estimates.
Dudley suggested the implications may reach well beyond birds and bees.
“These studies suggest that there may be a broad range of physiological adaptations across the animal kingdom to the ubiquity of dietary ethanol,” he said, “and that the responses we see in humans may not be representative of all primates or of all animals generally. Maybe there are other physiological detoxification pathways or other kinds of nutritional effects of ethanol for animals that are consuming it every day of their lives.”
Hummingbirds and other nectar feeders have been regularly exposed to ethanol in their diets long before humans recognized or studied this phenomenon. The research suggests that animals across many species have also been exposed to fermented food sources, which may have contributed to the development of metabolic adaptations and tolerances that are only now beginning to be studied.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.