Hummingbirds Are Sipping Booze All Day

We humans think we're having all the fun ... who knew that hummingbirds and other nectar-drinking animals are flitting about tippling alcohol from dawn to dusk?

Of course, they're not sidling up to cafe tables for Aperol spritzes—rather, nectar-filled flowers and backyard feeders are providing alcohol to hummingbirds thanks to fermenting yeast, according to a new study from the University of California, Berkeley that shows hummingbirds are consuming alcohol produced by natural fermentation.

You may know about birds like cedar waxwings and robins getting loopy on fermented fruit. This is actually not fun. Life is hard for birds, and they need all their wits to avoid threats such as outdoor cats, cars, and window collisions.

Animals and alcohol are a topic ripe for research. Knowing this, and that feeders and flowers are natural places for yeast and the bacteria that metabolize sugar and produce ethanol, UC Berkeley biologist Robert Dudley set out to answer some questions.

How much alcohol do hummingbirds consume in their daily quest for sustenance? Are they attracted to alcohol or repelled by it? Since alcohol is a natural byproduct of the sugary fruit and floral nectar that plants produce, is ethanol an inevitable part of the diet of hummingbirds and many other animals?

"Hummingbirds are eating 80% of their body mass a day in nectar," explains Dudley in a press statement from Berkeley. "Most of it is water and the remainder sugar. But even if there are very low concentrations of ethanol, that volumetric consumption would yield a high dosage of ethanol, if it were out there. Maybe, with feeders, we're not only farming hummingbirds, we're providing a seat at the bar every time they come in."

With research to explore these questions taking place during the height of the pandemic—and field testing in the wilds of Central America and Africa prohibitive—the team set their sights on the male Anna's hummingbirds visiting the feeders outside of the scientists' Bay Area office.

The findings of the study reveal that hummingbirds happily sip from sugar water with up to 1% alcohol by volume, finding it just as attractive as plain sugar water. Interestingly, when the sugar water contains 2% alcohol, our moderate tipplers sipped only half as much.

"They're consuming the same total amount of ethanol, they're just reducing the volume of the ingested 2% solution. So that was really interesting," Dudley said. "That was a kind of a threshold effect and suggested to us that whatever's out there in the real world, it's probably not exceeding 1.5%."

When they tested the alcohol level in sugar water that had sat in the feeder for two weeks, they found a much lower concentration: about 0.05% by volume.

"Now, 0.05% just doesn't sound like much, and it's not. But again, if you're eating 80% of your body weight a day, at .05% of ethanol you're getting a substantial load of ethanol relative to your body mass," he said. "So it's all consistent with the idea that there's a natural, chronic exposure to physiologically significant levels of ethanol derived from this nutritional source."

"They burn the alcohol and metabolize it so quickly. Likewise with the sugars. So they're probably not seeing any real effect. They're not getting drunk," he added.

The study is part of a long-term project by Dudley and some of his UC Berkeley colleagues investigating the role that alcohol plays in animal diets, especially in the tropics, where many animals have no choice but to consume fermented fruits and sugary nectar.

Previous research has shown that the nectar in palm flowers eaten by pen-tailed tree shrews in West Malaysia had levels of alcohol as high as 3.8% by volume, about the same level as Beck's beer. Another study found a similar alcohol concentration in the nectar eaten by the slow loris—and that both slow lorises and aye-ayes preferred nectar with higher alcohol content.

"This is the first demonstration of ethanol consumption by birds, quote, in the wild. I'll use that phrase cautiously because it's a lab experiment and feeder measurement," Dudley said. "But the linkage with the natural flowers is obvious. This just demonstrates that nectar-feeding birds, not just nectar-feeding mammals, not just fruit-eating animals, are all potentially exposed to ethanol as a natural part of their diet."

The next step, he said, is to measure how much ethanol is naturally found in flowers and determine how frequently it's being consumed by birds. He plans to extend his study to include Old World sunbirds and honey eaters in Australia, both of which occupy the nectar-sipping niche that hummingbirds have in America.

The study was published in the journal Royal Society Open Science.