WARSAW — Hummingbird feeders, which people use to attract the beautiful creatures to their homes and gardens, are typically filled with some variety of sugar water. Though this is an easy and accessible way to feed the bird, it is also a breeding ground for fermentation. In many cases, these feeders end up being full of alcohol.
This isn’t something that avian enthusiasts should worry about, however, as this fermentation process also takes place in nectar-rich flowers. The fact of the matter is, most hummingbirds are consuming large amounts of alcohol in their diets every single day.
So why aren’t our small avian friends keeling over while they fly? A recent study examines their diets, and explains exactly why hummingbirds are able to metabolize such high levels of alcohol.
Alcohol as a regular part of diets
Many factors influence animals to pick the diets that they do. Some fruits and nectars attract animals with their high sugar contents. And due to the presence of yeast, carbohydrates in fruit and nectar are prone to natural fermentation.
Until very recently, the concentration of ethanol in the nectar of flowers visited by birds was completely unknown. But that changed with the publication of a new study conducted by a team of biologists from the University of California, Berkeley.
The preliminary study, led by Robert Dudley of the Smithsonian Tropical Research Institute in Panama, studied the alcohol consumption of hummingbirds. Though the study was conducted under controlled laboratory conditions, Dudley argues that “the link with naturally occurring flowers is apparent… This shows that it is not only mammals and fructivores that consume alcohol as a regular part of their diet.”
Alcohol in the natural world
Ethanol is a naturally occurring substance, and is consumed by several different species, which can even be to their benefit. For example, exposure to gaseous ethanol was actually found to increase the longevity and fertility of fruit flies. Some species, such as the Malayan rat, enjoy especially high concentrations of the intoxicating substance. The rat feeds on palm trees, where the concentration of ethanol can be as high as almost 4%.
Though the benefits of alcohol are unknown to many animals, some have been shown to have a preference. In one study, when black-handed clinging monkeys (an endangered small primate inhabiting Central and South America) were given a choice between a sugar solution without ethanol and a solution with different concentrations of ethanol, they chose the solution with the highest concentration.
And, as we already know, ethanol plays an important role in the everyday life of hummingbirds.
“Every day, hummingbirds eat an amount of nectar equivalent to 80% of their total body mass,” says Robert Dudley, “the vast majority of this is water, and the rest largely consists of sugar”. However, he also admits that “even if the concentration of alcohol is very low, such high levels of consumption mean that there is a significant volume of ethanol being consumed… thanks to our bird feeders, we are not only breeding hummingbirds, but giving them a place at the bar”.
Drinking without getting drunk
In order to put this to the test, experts captured three adult male hummingbirds living in the wild, and provided them with solutions containing different contents of ethanol. The study found that hummingbirds can distinguish between different concentrations of ethanol, and that they prefer alcohol-free solutions and those with 1 to 2 percent ethanol.
“They feel no adverse effects. They do not get drunk.”
Hummingbirds appear to be only moderate drinkers — when the sugar water contained 2% alcohol, they drank only half of what they normally drink. Ethanol at a concentration of 1% poses no threat to hummingbirds and is likely to occur naturally, providing minimal energy benefits.
“They consume the same total amount of ethanol, but reduce the volume of the 2% solution consumed,” Dudley notes, calling the phenomenon “really interesting”.
But hummingbirds’ daily consumption of ethanol does not affect the unique perception or motor skills of small birds. In fact, even in spite of their alcohol consumption, hummingbirds can see colors in a much more sophisticated way than humans do.
“They metabolize alcohol very quickly,” says Dudley, adding that “this is similar to their consumption of sugars”. He continues to say that “they feel no adverse effects. They do not get drunk.”
Understanding human attraction to alcohol
However, even Dudley admits that additional research is needed in order to fully understand the birds’ behavior. For researchers, many questions remain, including whether alcohol content motivates hummingbirds to visit some flowers over others, or if it has any other impacts on their behavior. We also do not know exactly how much alcohol hummingbirds consume in their everyday search for food. Is alcohol attracting them to sources of food, or does it scare them away?
Since alcohol is a natural product of nearby sweet fruits, and of nectar found in plans, is ethanol an unavoidable component of the diet of hummingbirds and many other animals? This is not yet entirely understood. Further research on nectar and populations of feeding microbes may provide insight into additional nectar characteristics that may influence hummingbird preferences, such as pH, sugar concentration, and ethanol concentration exceeding 2%.
According to experts, studying the effects of ethanol on the lives of animals may also help to understand the human attraction to alcohol in the future.
