Do hummingbirds drink alcohol? More often than you think
Flowers, backyard feeders likely provide hummingbirds with alcohol,
thanks to fermenting yeast

Date:
June 22, 2023
Source:
University of California - Berkeley
Summary:
Animals that eat fruit or sip nectar often ingest alcohol because
naturally occurring yeasts turning sugar into ethanol. But how
do animals feel about that? A new study details an experiment to
determine whether hummingbirds are turned off by alcohol in sugar
water. At 1% by volume, no. At 2% by volume, they consume much
less. The implication is that hummingbirds have adjusted to small
amounts of alcohol likely present in flowers and backyard feeders.


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You may not realize it, but that backyard hummingbird feeder filled with
sugar water is a natural experiment in fermentation -- yeast settle in
and turn some of the sugar into alcohol.

The same is true of nectar-filled flowers, which are an ideal gathering
place for yeast -- a type of fungus -- and for bacteria that metabolize
sugar and produce ethanol.

To University of California, Berkeley biologist Robert Dudley, this
raises a host of questions. How much alcohol do hummingbirds consume
in their daily quest for sustenance? Are they attracted to alcohol or
repelled by it? Since alcohol is a natural byproduct of the sugary fruit
and floral nectar that plants produce, is ethanol an inevitable part
of the diet of hummingbirds and many other animals? "Hummingbirds are
eating 80% of their body mass a day in nectar," said Dudley, UC Berkeley professor of integrative biology. "Most of it is water and the remainder
sugar. But even if there are very low concentrations of ethanol, that volumetric consumption would yield a high dosage of ethanol, if it were
out there. Maybe, with feeders, we're not only farming hummingbirds,
we're providing a seat at the bar every time they come in." During the
worst of the COVID-19 pandemic, when it became difficult to test these questions in the wilds of Central America and Africa, where there are nectar-feeding sunbirds, he tasked several undergraduate students with experimenting on the hummers visiting the feeder outside his office
window to find out whether alcohol in sugar water was a turn-off or a
turn-on. All three of the test subjects were male Anna's hummingbirds
(Calypte anna), year-round residents of the Bay Area.

The results of that study, published this week in the journalRoyal Society
Open Science, demonstrate that hummingbirds happily sip from sugar water
with up to 1% alcohol by volume, finding it just as attractive as plain
sugar water.

They appear to be only moderate tipplers, however, because they sip only
half as much as normal when the sugar water contains 2% alcohol.

"They're consuming the same total amount of ethanol, they're just
reducing the volume of the ingested 2% solution. So that was really interesting," Dudley said. "That was a kind of a threshold effect
and suggested to us that whatever's out there in the real world, it's
probably not exceeding 1.5%." When he and his colleagues tested the
alcohol level in sugar water that had sat in the feeder for two weeks,
they found a much lower concentration: about 0.05% by volume.

"Now, 0.05% just doesn't sound like much, and it's not. But again, if
you're eating 80% of your body weight a day, at .05% of ethanol you're
getting a substantial load of ethanol relative to your body mass,"
he said. "So it's all consistent with the idea that there's a natural,
chronic exposure to physiologically significant levels of ethanol derived
from this nutritional source." "They burn the alcohol and metabolize
it so quickly. Likewise with the sugars.

So they're probably not seeing any real effect. They're not getting
drunk," he added.

The research is part of a long-term project by Dudley and his UC Berkeley colleagues -- herpetologist Jim McGuire and bird expert Rauri Bowie, both professors of integrative biology and curators at UC Berkeley's Museum
of Vertebrate Zoology. They seek to understand the role that alcohol
plays in animal diets, particularly in the tropics, where fruits and
sugary nectar easily ferment, and alcohol cannot help but be consumed
by fruit-eating or nectar-sipping animals.

"Does alcohol have any behavioral effect? Does it stimulate feeding at
low levels? Does it motivate more frequent attendance of a flower if
they get not just sugar, but also ethanol? I don't have the answers to
these questions. But that's experimentally tractable," he said.

Part of this project, funded by the National Science Foundation, involves testing the alcohol content of fruits in Africa and nectar in flowers in
the UC Botanical Garden. No systematic studies of the alcohol content of
fruits and nectars, or of alcohol consumption by nectar-sipping birds,
insects or mammals, or by fruit-eating animals -- including primates --
have been done.

But several isolated studies are suggestive. A 2008 study found that
the nectar in palm flowers consumed by pen-tailed tree shrews, which
are small, ratlike animals in West Malaysia, had levels of alcohol as
high as 3.8% by volume.

Another study, published in 2015, found a relatively high alcohol
concentration -- up to 3.8% -- in the nectar eaten by the slow loris,
a type of primate, and that both slow lorises and aye-ayes, another
primate, preferred nectar with higher alcohol content.

The new study shows that birds are also likely consuming alcohol produced
by natural fermentation.

"This is the first demonstration of ethanol consumption by birds, quote,
in the wild. I'll use that phrase cautiously because it's a lab experiment
and feeder measurement," Dudley said. "But the linkage with the natural
flowers is obvious. This just demonstrates that nectar-feeding birds,
not just nectar- feeding mammals, not just fruit-eating animals, are
all potentially exposed to ethanol as a natural part of their diet."
The next step, he said, is to measure how much ethanol is naturally
found in flowers and determine how frequently it's being consumed by
birds. He plans to extend his study to include Old World sunbirds and
honey eaters in Australia, both of which occupy the nectar-sipping niche
that hummingbirds have in America.

Dudley has been obsessed with alcohol use and misuse for years, and
in a 2014 book, The Drunken Monkey, Why we drink and abuse alcohol,
presented evidence that humans' attraction to alcohol is an evolutionary adaptation to improve survival among primates. Only with the coming of industrial alcohol production has our attraction turned, in many cases,
into alcohol abuse.

"Why do humans drink alcohol at all, as opposed to vinegar or any
of the other 10 million organic compounds out there? And why do most
humans actually metabolize it, burn it, and use it pretty effectively,
often in conjunction with food, but then some humans also consume to
excess?" he asked.

"I think, to get a better understanding of human attraction to alcohol,
we really have to have better animal model systems, but also a realization
that the natural availability of ethanol is actually substantial, not
just for primates that are feeding on fruit and nectar, but also for a
whole bunch of other birds and mammals and insects that are also feeding
on flowers and fruits," he said. "The comparative biology of ethanol consumption may yield insight into modern day patterns of consumption and
abuse by humans." In addition to McGuire and Bowie, other co-authors
of the paper are former undergraduates Julia Choi and Lilianne Lee,
graduate student Aleksey Maro and postdoctoral researcher Ammon Corl, all
of UC Berkeley. The work was supported by the National Science Foundation (DEB-1831833) and UC Berkeley's Undergraduate Research Apprentice Program.

* RELATED_TOPICS
o Plants_&_Animals
# Food_and_Agriculture # Beer_and_Wine # Food # Nature
o Earth_&_Climate
# Water # Environmental_Issues #
Energy_and_the_Environment # Rainforests
* RELATED_TERMS
o Common_ethanol_fuel_mixtures o Methanol o Hummingbird o
Alcohol_fuel o Honey o Alternative_fuel_vehicle o Carnivore
o Sponge

========================================================================== Story Source: Materials provided by
University_of_California_-_Berkeley. Original written by Robert
Sanders. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Julia Choi, Lilianne Lee, Aleksey Maro, Ammon Corl, Jimmy
A. McGuire,
Rauri C. K. Bowie, Robert Dudley. Hummingbird ingestion of low-
concentration ethanol within artificial nectar. Royal Society Open
Science, 2023; 10 (6) DOI: 10.1098/rsos.230306 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230622142345.htm

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