Birds may be drinking on the wing, but in moderation

(Press-News.org) A new paper published in Ecological and Evolutionary Physiology examines alcohol consumption in avian species. 

In “The proof is in the plumage: a method for detecting dietary ethanol exposure in birds by testing for ethyl glucuronide in feathers,” authors Cynthia Y. Wang-Claypool, Ammon Corl, Joseph Jones, Jimmy A. McGuire, Rauri C.K. Bowie and Robert Dudley investigated whether birds that eat sugar-rich foods—like fruit and nectar—might regularly consume alcohol produced by natural fermentation. Alcohol naturally results from fermentation of sugary foods like fruit and nectar. 

Avian inebriation may reduce survival and reproductive success, including, but not limited to, increased predation risk due to impaired flight performance as well as injury or death due to accidental collisions during flight.

The authors hypothesized that detection and levels of a byproduct of alcohol metabolism called ethyl glucuronide (EtG) would vary among species with different dietary specializations, specifically suggesting that nectarivores and frugivores would have higher levels of EtG than other dietary groups. “To date, occurrence of this molecule has not been studied in vertebrates other than humans and several other mammalian taxa,” they noted.

Ethyl glucuronide stays in the body after alcohol breaks down. Using chemical analysis, the authors tested feathers and liver samples from 17 bird species, largely determined by what samples they could obtain from salvage specimens donated to the Museum of Vertebrate Zoology in Berkeley, California. “The method that we used to test for EtG requires destructive sampling of feathers, and we necessarily used specimens that the museum already had in abundance,” they wrote.

As expected, hummingbirds (i.e., predominantly nectar feeders) often had EtG in their feathers, suggesting sugar-rich foods like nectar may ferment and produce ethanol. “Artificial nectar feeders (like those in people's yards) might be a source of ethanol if the sugar water ferments. This might explain high EtG levels in Anna’s Hummingbirds from urban areas," the authors note. However, EtG was also present in birds with other diets, like seeds, insects, and other animals.

The results suggest that avian exposure to ethanol is not restricted to species with diets specialized on sugary foods. Therefore, the authors conclude, “exposure of animals to ethanol could be much more widespread than has been previously recognized.” 

Ecological and Evolutionary Physiology primarily publishes original research examining fundamental questions about how the ecological environment and/or evolutionary history interact with physiological function, as well as the ways physiology may constrain behavior. For EEP, physiology denotes the study of function in the broadest sense, across levels of organization from molecules to morphology to organismal performance and on behavior and life history traits.

Contact: Mallory Gevaert / mgevaert@uchicago.edu

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