A new study from the University of California, Berkeley has unveiled the intriguing relationship between hummingbirds and their inadvertent consumption of alcohol. A natural fermentation process in the nectar that hummingbirds consume raises the alcohol content in their diet.
Professor Robert Dudley was captivated by the thought of how hummingbirds might interact with alcohol that is present in the nectar from flowers or sugar water in feeders. Yeast and bacteria, which are often found in sugar-rich environments like flowers and feeders, engage in a fermentation process that produces ethanol from sugars.
“Hummingbirds are eating 80% of their body mass a day in nectar,” noted Professor Dudley. This means that even a small concentration of alcohol in the nectar could amount to a substantial intake in relation to their body mass. “Maybe, with feeders, we’re not only farming hummingbirds, we’re providing a seat at the bar every time they come in,” said Dudley.
To investigate, the researchers conducted experiments during the height of the COVID-19 pandemic, focusing on the hummingbirds visiting a feeder outside Professor Dudley’s office window.
The test subjects were three male Anna’s hummingbirds, native to the Bay Area. The team set out to observe how these hummingbirds responded to sugar water containing different concentrations of alcohol.
The findings of the research, published in the journal Royal Society Open Science, reveal that the hummingbirds were not deterred by sugar water containing up to one percent alcohol. Interestingly though, they halved their intake when the alcohol content was raised to two percent.
“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. That was 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%,” explained Professor Dudley.
It was also found that sugar water left in a feeder for two weeks had an alcohol content of about 0.05%.
“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,” said Professor Dudley. “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.
This research is part of a broader initiative by Dudley and his UC Berkeley colleagues, Jim McGuire and Rauri Bowie. The team aims to understand the role of alcohol in animal diets, especially in tropical regions where fermentation is common due to the abundance of fruits and sugary nectar. The project, funded by the National Science Foundation, will explore alcohol content in fruits in Africa and nectar in flowers at the UC Botanical Garden.
There have been isolated studies indicating that other animals might also be consuming alcohol through their diet. For example, a study in 2008 found that the nectar in palm flowers consumed by pen-tailed tree shrews in West Malaysia contained alcohol levels as high as 3.8%. Another study in 2015 discovered that slow lorises, a type of primate, preferred nectar with a higher alcohol content.
The latest study is a pioneering effort in linking birds to the consumption of ethanol through their diet. “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 explained. “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.”
Building on these findings, the next phase of research will involve quantifying the natural levels of ethanol present in flowers, and ascertaining the frequency with which birds consume it. In addition to hummingbirds, Professor Dudley plans to expand his research to other nectar-sipping birds. He has his sights set on Old World sunbirds and honey eaters in Australia, which, like hummingbirds in America, subsist mainly on nectar.
Professor Dudley has had a long-standing interest in alcohol consumption and its impact, an interest that extends beyond the animal kingdom to humans as well. His 2014 book, “The Drunken Monkey, Why we drink and abuse alcohol,” argues that humans’ attraction to alcohol may be an evolutionary adaptation that initially improved survival among primates. This interest, however, has transformed into a potential issue with the advent of industrial alcohol production, leading in some cases to excessive consumption and alcohol abuse.
“Why do humans drink alcohol at all, as opposed to vinegar or any of the other 10 million organic compounds out there? And why do most humans actually metabolize it, burn it, and use it pretty effectively, often in conjunction with food, but then some humans also consume to excess?” Dudley asked.
“I think, to get a better understanding of human attraction to alcohol, we really have to have better animal model systems, but also a realization that the natural availability of ethanol is actually substantial, not just for primates that are feeding on fruit and nectar, but also for a whole bunch of other birds and mammals and insects that are also feeding on flowers and fruits. The comparative biology of ethanol consumption may yield insight into modern day patterns of consumption and abuse by humans.”