Charles Darwin was a busy man.
When he wasn’t advancing his
groundbreaking theory of evolution by natural selection, he could be found
carefully analyzing the contents of bird vomit and droppings. No, this wasn’t
an obscure hobby. He was getting his hands dirty to stack up more evidence to
support one of his many hypotheses.
He suspected that some birds had
an unusual way of transporting plants to new locations. “Freshwater fish, I
find, eat seeds of many land and water plants; fish are frequently devoured by
birds, and thus the seeds might be transported from place to place,” he wrote
in Origin of Species.
In the same passage, Darwin
described a set of experiments in which he stuffed seeds into the stomachs of
dead fish, and then fed those fish to birds. After several hours, the birds
would either excrete or regurgitate the seeds and “several of these seeds
retained the power of germination,” he wrote. But until now, those experiments
had not been shored up with research in the wild. Last month, a paper
published in Biology Letters finally validated Darwin’s
notion that fish-eating bird puke could help spread organisms like plants over
great distances.
Moonlight Regurgitation
After a long day of fishing,
cormorants gather together to roost under the moonlight and vomit up pale
brown, marble-sized pellets that look like mini, mucous-covered meatballs. If
you slice one open, you will find the hard-to-digest portion of the cormorant’s
recent feast. The pellets are mainly composed of bits of fish, but as Darwin
noted, they also sometimes contain the plant seeds and invertebrates that those
fish were chowing down on before they were taken prey.
A great cormorant will travel far
from its daytime fishing site to its nighttime roost—up to 30 miles on a
regular day, and even further during migration, says the study’s lead author
Casper van Leeuwen from the Netherlands Institute of Ecology. “That means the
plant seeds or aquatic invertebrates could be transported over quite some
distance inside of a bird that has indirectly ingested them.”
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