New study reveals hummingbirds get drunk on alcohol-laced nectar

“Hummingbirds are eating 80% of their body mass a day in nectar,” said Dudley. “Most of it is water and the remainder sugar. Maybe, with feeders, we’re not only farming hummingbirds, we’re providing a seat at the bar every time they come in.”

Exploring the Alcohol Consumption of Hummingbirds.

Led by Dudley, the research team sought to determine the amount of alcohol hummingbirds consume daily and whether they are attracted to or repelled by it. The team conducted experiments using male Anna's hummingbirds (Calypte anna), a species that can be found in the Bay Area all year round.

The results revealed that hummingbirds are attracted to sugar water containing up to 1% alcohol by volume, finding it equally appealing as plain sugar water. What was more interesting, however, was that they reduced their intake by half when the alcohol content reached 2%.

"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 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%," Dudley explained.

Alcohol Consumption and Its Effects.

Contrary to what some might assume, hummingbirds do not become intoxicated from consuming alcohol-laced nectar.

The researchers discovered that hummingbirds quickly metabolize and burn off the alcohol and sugars, preventing any noticeable effects. "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," Dudley remarked.

The Significance of Alcohol in Animal Diets.

This research forms part of a broader project by Dudley and his colleagues at UC Berkeley investigating the role of alcohol in animal diets, especially in tropical areas where fruits and nectar ferment easily.

While no systematic studies have been conducted on alcohol consumption by fruit-eating or nectar-sipping animals, a few isolated studies provide suggestive evidence of palm flowers consumed by pen-tailed tree shrews in West Malaysia which were found to contain alcohol levels as high as 3.8% by volume.

“This is the first demonstration of ethanol consumption by birds, quote, in the wild,” Dudley added. “I’ll use that phrase cautiously because it’s a lab experiment and feeder measurement. 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.”

Dudley aims to measure ethanol content in flowers and determine how often birds consume it. He plans to expand the study to include Old World sunbirds and honeyeaters in Australia, two species that share the nectar-sipping niche with American hummingbirds.

Implications for Human Alcohol Consumption.

Dudley, the author of the 2014 book ‘The Drunken Monkey, Why we drink and abuse alcohol’, has presented evidence of humans’ attraction to alcohol being an adaptation to improve survival.

“I think, to get a better understanding of human attraction to alcohol, we really have to have better animal model system, 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,” Dudley reflected.

Dudley believes that studying the comparative biology of ethanol consumption in animals will provide insights into patterns of consumption and abuse and help us fully understand our relationship with alcohol.

Study Abstract

Both frugivores and nectarivores are potentially exposed to dietary ethanol produced by fermentative yeasts which metabolize sugars. Some nectarivorous mammals exhibit a preference for low-concentration ethanol solutions compared to controls of comparable caloric content, but behavioural responses to ethanol by nectar-feeding birds are unknown. We investigated dietary preference by Anna's Hummingbirds (Calypte anna) for ethanol-enhanced sucrose solutions. Via repeated binary-choice experiments, three adult male hummingbirds were exposed to sucrose solutions containing 0%, 1% or 2% ethanol; rates of volitional nectar consumption were measured over a 3 h interval. Hummingbirds did not discriminate between 0% and 1% ethanol solutions, but exhibited significantly reduced rates of consumption of a 2% ethanol solution. Opportunistic measurements of ethanol concentrations within hummingbird feeders registered values peaking at about 0.05%. Ethanol at low concentrations (i.e. up to 1%) is not aversive to Anna's Hummingbirds and may be characteristic of both natural and anthropogenic nectars upon which they feed. Given high daily amounts of nectar consumption by hummingbirds, chronic physiological exposure to ethanol can thus be substantial, although naturally occurring concentrations within floral nectar are unknown.