Drunk Birds? How Ethanol From Fermented Fruit Affects Wildlife

The relaxed feeling you get after a cold beer or a glass of wine is down to the ethanol content of the beverage. This is a naturally occurring substance produced by the fermentation of sugars. For example, the fermentation of sugars in grape juice produces wine, but other fruits can ferment as well. If an animal comes along and eats the fermented fruit, they can get inebriated, and many of them do! Scientists can now use a technique called mass spectrometry to test for the presence of ethanol metabolism in the feathers and livers of birds. The results are very revealing.

Animals and Ethanol

In any ecosystem where you find fruit or nectar, you are going to find ethanol. So, fruit- and nectar-eating animals (frugivores and nectarivores) likely consume it on a regular basis. These animals have genes that break down ethanol. Several animals, including primates and birds, have been seen consuming fermented fruit. If they consume too much, these animals have been observed wandering around in an inebriated state.

There are pros and cons associated with the consumption of ethanol for animals. It is a source of calories, and the distinctive smell can guide animals to food sources. Some scientists have even speculated that the endorphins and dopamine triggered by ethanol consumption make animals feel relaxed and help with their sociability. However, getting inebriated is a dangerous situation for animals. While they are in this ‘relaxed’ state, animals are less likely to sense a predator approaching. Birds are more likely to crash into things. There is even evidence that ethanol consumption changes the singing behavior of zebra finches, affecting the acoustic features and consistency of their song.

Measuring Ethanol Consumption

Measuring the natural rates of ethanol consumption in animals is challenging, so scientists have instead measured ethanol metabolites. These are the chemicals that the body produces when it breaks down ethanol. One study has measured dietary ethanol exposure by testing the feathers and livers of birds (including hummingbirds) for the ethanol metabolite called ethyl glucuronide (EtG). It found that birds that fed on nectar had EtG in their feathers and sometimes in their livers. However, birds that were granivores (seed eaters), omnivores, invertivores (invertebrate eaters), and vertivores (vertebrate eaters) also had EtG in their bodies. It is possible that some birds obtained ethanol indirectly by eating prey that had consumed ethanol.

Importantly, this study demonstrates that birds are exposed to dietary ethanol and that this exposure varies both within and between species. It provides a baseline so that future research can explore the physiological and behavioral risks associated with different levels of ethanol consumption and examine how birds’ bodies have evolved to allow them to break down ethanol.

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