Hummingbirds are among the most fascinating and colorful birds in the world, with their dazzling plumage, acrobatic flight, and high metabolism.
They feed mainly on nectar from flowers and sugar water from feeders, which provide them with the energy they need to sustain their rapid wing beats and body heat.
However, nectar and sugar water are not just pure sources of sugar: they also contain small amounts of alcohol, produced by yeast and bacteria that ferment the sugars.
Do hummingbirds drink alcohol intentionally or accidentally? How does alcohol affect their behavior and health? A new study sheds some light on these questions.
How hummingbirds encounter alcohol
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Alcohol is a natural byproduct of the breakdown of sugars by yeast and bacteria, which are ubiquitous microorganisms that live in various environments, including flowers and feeders, as per Phys.org.
When hummingbirds visit flowers or feeders to sip nectar or sugar water, they inevitably ingest some alcohol along with the sugars.
The amount of alcohol varies depending on the type and freshness of the nectar or sugar water, as well as the temperature and humidity conditions that affect the rate of fermentation.
A team of researchers from the University of California, Berkeley, led by Prof. Dr. Robert Dudley, conducted an experiment to measure the alcohol content of sugar water in a hummingbird feeder over time.
They found that after two weeks, the sugar water had an alcohol concentration of about 0.05% by volume, which is equivalent to a very light beer.
However, this concentration may be higher or lower in different locations and seasons.
The researchers also conducted a survey of published studies on the chemical composition of floral nectar from various plant species that are visited by hummingbirds.
They found that most nectars had very low or undetectable levels of alcohol, ranging from 0% to 0.02% by volume, but some nectars had higher levels of alcohol, up to 0.6% by volume, which is comparable to a weak wine.
These nectars came from plants that have specialized structures or mechanisms that promote fermentation, such as thick corollas, closed petals, or extrafloral nectaries.
The researchers estimated that hummingbirds consume about 80% of their body mass in nectar or sugar water per day, which means that they may ingest up to 0.4 grams of alcohol per day.
This is equivalent to a human drinking about 10 cans of beer per day.
To test how hummingbirds react to alcohol in sugar water, the researchers conducted another experiment using three male Anna's hummingbirds (Calypte anna) that visited a feeder outside their office window, as per ScienceDaily.
They offered the hummingbirds sugar water with different concentrations of alcohol: 0%,1%, or 2% by volume.
They recorded the number and duration of visits to each feeder and calculated the amount of sugar water and alcohol consumed by each bird.
The results showed that hummingbirds did not avoid sugar water with alcohol: they visited the feeders with 1% alcohol as frequently and for as long as the feeders with 0% alcohol.
However, they visited the feeders with 2% alcohol less frequently and for shorter periods than the feeders with 0% or 1% alcohol.
This suggests that hummingbirds have a threshold for alcohol tolerance and preference, which may be around 1.5% by volume.
The researchers also observed the behavior of the hummingbirds after they drank from the feeders with alcohol.
They did not notice any obvious signs of intoxication or impairment, such as staggering, falling, or flying erratically. The hummingbirds continued to perform their normal activities, such as chasing rivals, courting females, and preening feathers.
The researchers concluded that hummingbirds are accustomed to ingesting small amounts of alcohol from natural sources, such as nectar and sugar water, and that they are not deterred by moderate concentrations of alcohol up to 1% by volume.
However, they may reduce their intake of sugar water with higher concentrations of alcohol above 1.5% by volume, possibly to avoid negative effects on their metabolism or behavior.
