The Proof Is in the Plumage: A Method for Detecting Dietary Ethanol Exposure in Birds by Testing for Ethyl Glucuronide in Feathers

AbstractEthanol is a naturally occurring molecule produced via fermentation of sugar-rich foods by yeast. Ethanol catabolism is followed by production of secondary metabolites such as ethyl glucuronide (EtG), which can be measured to provide a retrospective view of dietary exposure. To date, occurrence of this molecule has not been studied in vertebrates other than humans and several other mammalian taxa. Here, we describe a method of testing for the presence of EtG in bird feathers and livers using mass spectrometry. Birds that regularly consume fruit and nectar may accordingly be ingesting ethanol on a chronic basis. We predicted that avian species with diets rich in fermentable sugars consume physiologically significant amounts of ethanol and therefore accumulate detectable levels of EtG. The suitability of EtG assays was tested across 17 avian species representing a diversity of diets. Assays of avian feathers yielded positive results for 10 of 17 avian species; EtG was also present at substantial levels in the livers of two of five study species. We found that EtG was present in nectarivorous hummingbirds but also in species in other trophic niches (three granivores, one omnivore, three invertivores, and one vertivore). Dietary exposure to ethanol may thus be much more widespread than has previously been recognized, and diverse features of avian nutritional ecology (e.g., secondary consumption via ingestion of prey items) may contribute to its accumulation in tissues.