Birds are consuming alcohol more often than we realized

Researchers have found that some birds may ingest traces of ethanol through everyday foods. This behavior has fascinated ecologists who are keen to see if it affects flight or general health – especially when birds consume nectar, fruits, or even insects that have fed on fermenting plants.

The research was led by Dr. Robert Dudley and colleagues from the Museum of Vertebrate Zoology at the University of California, Berkeley.

The team studied the presence of ethyl glucuronide (EtG) in feathers to investigate which species might be getting a dose of ethanol from their usual meals.

Birds might be consuming alcohol

Many people assume that only fruit-eating animals face the risk of consuming fermented sugars. Yet the scientists discovered traces of EtG in the feathers of species with diets as varied as seeds, insects, and other animals.

The researchers focused on birds from different regions because diet and environment can influence the amount of alcohol in foods like fallen fruit or sugar water.

“Artificial nectar feeders might be a source of ethanol if the sugar water ferments,” noted Cynthia Wang-Claypool, the study’s lead author.

One surprising clue came from hummingbirds. They rely heavily on nectar, which can ferment in nature or in backyard feeders. 

Bird feathers reveal their alcohol exposure

EtG is a small molecule made when ethanol breaks down in the body. Tests on human hair link higher EtG levels to heavy alcohol consumption. This marker offers a long-term look at someone’s drinking habits.

In birds, feathers have a growth cycle that might capture EtG at certain stages. Once the feather stops growing, blood flow in the shaft fades.

Any EtG embedded during growth can remain, giving a partial snapshot of whether a bird encountered ethanol-rich items.

Bird diets and hidden sources

Birds categorized as nectarivores or frugivores might seem most likely to ingest alcohol. Some, however, tested negative for EtG in this study. That might mean the sugary food they ate did not ferment enough, or that their feathers had grown when they had no exposure to ethanol.

Meanwhile, certain seed and insect eaters showed the marker. One possibility is that prey items or seeds could ferment or contain ethanol-producing microbes.

Another hypothesis involves arthropods that feast on sweet fruit or nectar, indirectly passing along traces of alcohol to the birds that consume them.

Potential for unplanned drinks

Some hummingbird feeders have been known to form low levels of ethanol. People who leave sugar water out for too long might inadvertently offer these tiny flyers more than just a sugary treat.

The researchers found that Anna’s hummingbirds frequently tested positive for EtG, suggesting they might encounter small amounts of fermented sugar on a regular basis.

“Exposure of animals to ethanol could be much more widespread than has been previously recognized,” said Dudley. He noted that birds could be consuming more ethanol than we realize. 

Records of alcohol consumption

The team measured EtG in bird livers as well, though the short-term nature of organ tissue might explain why fewer samples tested positive.

Feathers, on the other hand, can retain markers over a longer interval. Still, differences in molt timing or feather wear could influence how much EtG gets stored or later eroded.

In humans, alcohol studies typically use hair or blood analysis. That method provides clues about a person’s intake over several weeks or months.

For birds, flight feathers might develop at specific times of year, which leads to gaps in our understanding of their exposure outside of molt season.

Studying how alcohol affects birds

The discovery of EtG in avian feathers will spark questions about how often birds face fermented foods in the wild.

More testing on their feeding choices might reveal whether certain species are partial to overripe fruit or sugar-based liquids that can ferment in warm weather.

Future projects may examine whether ethanol affects bird behavior, flight, and daily activities. If small-bodied birds process ethanol differently than larger species, a few sips could have effects that are not yet fully known.

Studies might also check how seasonal shifts or migration patterns influence exposure to fermenting nectar or fruits.

Implications for bird watchers

These findings might change how people maintain backyard feeders. Some might refresh the sugar water more often to reduce fermentation.

Others could keep an eye on local fruit crops that drop to the ground, especially in warmer months when yeasts flourish.

The biology behind alcohol metabolism is familiar in human medicine but less so in birds. The presence of EtG in feathers opens the door for more analyses of avian life, particularly in species that rely on sugar-laden meals.

The study is published in the journal Ecological and Evolutionary Physiology.

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