Pollinators Consume Alcohol Daily from Fermented Flower Nectar
Scientists at the University of California, Berkeley have discovered that bees and hummingbirds regularly consume small amounts of alcohol while feeding on flower nectar. This surprising finding reveals a previously overlooked aspect of pollinator biology and raises questions about how these animals have adapted to chronic alcohol exposure.
In the first comprehensive survey of its kind, researchers tested nectar from 29 different plant species and found ethanol, a type of alcohol, in samples from 26 of them. The ethanol forms when yeast organisms ferment the sugars naturally present in nectar. While most samples contained only trace amounts, one reached 0.056% ethanol by weight, equivalent to about one-tenth proof.
These concentrations may seem insignificant, but nectar serves as the primary energy source for many pollinators. Hummingbirds consume between 50% and 150% of their body weight in nectar daily. Using this data, researchers calculated that an Anna's hummingbird, a species common along the Pacific coast, consumes approximately 0.2 grams of ethanol per kilogram of body weight each day. This intake is comparable to a human drinking one alcoholic beverage daily.
The research team, led by doctoral student Aleksey Maro and postdoctoral fellow Ammon Corl, along with Professor Robert Dudley, used an enzymatic assay to measure ethanol levels accurately. They then estimated daily alcohol consumption for several nectar-feeding species, including two hummingbird species and three African sunbird species. The values ranged from 0.19 to 0.27 grams per kilogram per day. For comparison, the European honeybee consumed only 0.05 grams per kilogram daily, while the pen-tailed tree shrew, which feeds on fermented palm nectar, consumed 1.4 grams per kilogram daily.
Despite this regular alcohol intake, pollinators do not appear intoxicated. Experiments showed that Anna's hummingbirds willingly consume sugar water containing up to 1% alcohol but reduce their visits by half when concentrations reach 2%. The researchers suggest that hummingbirds regulate their intake, perhaps because higher concentrations rarely occur in natural nectar.
Previous studies revealed that hummingbird feathers contain ethyl glucuronide, a metabolic byproduct of ethanol processing. This compound indicates that birds break down alcohol similarly to mammals, suggesting evolutionary adaptations to dietary ethanol.
The effects of this chronic alcohol exposure remain unclear. Because hummingbirds have extremely fast metabolisms, they likely burn through ethanol quickly, preventing accumulation in their bloodstream. However, ethanol might influence behavior in subtle ways, similar to how nectar compounds like caffeine and nicotine affect pollinators.
This research forms part of a larger five-year project examining how hummingbirds and sunbirds adapt to various environmental challenges, including high altitudes, sugar-rich diets, and fermented nectar. The findings suggest that many animals may have developed specialized physiological pathways for processing dietary ethanol, challenging assumptions based solely on human alcohol metabolism. Understanding these adaptations could reveal important insights into how different species cope with ubiquitous environmental compounds.