You may not realize it, but that backyard hummingbird feeder filled with sugar water is a natural experiment in fermentation—yeast settle in and turn some of the sugar into alcohol.
You may not realize it, but that backyard hummingbird feeder filled with sugar water is a natural experiment in fermentation—yeast settle in and turn some of the sugar into alcohol.
The same is true of nectar-filled flowers, which are an ideal gathering place for yeast—a type of fungus—and for bacteria that metabolize sugar and produce ethanol.
To University of California, Berkeley biologist Robert Dudley, this raises a host of 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,” said Dudley, UC Berkeley professor of integrative biology. “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.”
During the worst of the COVID-19 pandemic, when it became difficult to test these questions in the wilds of Central America and Africa, where there are nectar-feeding sunbirds, he tasked several undergraduate students with experimenting on the hummers visiting the feeder outside his office window to find out whether alcohol in sugar water was a turn-off or a turn-on. All three of the test subjects were male Anna’s hummingbirds (Calypte anna), year-round residents of the Bay Area.
The results of that study, published this week in the journal Royal Society Open Science, demonstrate that hummingbirds happily sip from sugar water with up to 1% alcohol by volume, finding it just as attractive as plain sugar water.
They appear to be only moderate tipplers, however, because they sip only half as much as normal when the sugar water contains 2% alcohol.
“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.
