Ducks serve mussels to gulls, say scientists

A new discovery in ornithology shows that gulls, often perceived as opportunistic scavengers, can be impressively fast learners.

Courtesy of M. Kowalewski
The Common Pochard is one of three diving duck species involved in a food interaction between gulls and diving ducks on Szczecin Lagoon.

Gulls, it turns out, are smarter than we thought.

A team of ornithologists in Poland observing Herring gulls and Mew gulls wintering on the Szczecin Lagoon, on the German-Polish border, have spotted the birds following ducks, who inadvertently act as waiters for the gulls by retrieving mussels from the seafloor for them.

Ducks dive to the bottom to fetch mussels for themselves, while the gulls take the leftovers, and sometimes steal a snack straight from ducks’ mouths, according to an article published Wednesday in the bird science journal, The Auk. 

Often found stalking fishing trawlers and circling over landfills, gulls, a suborder that comprises dozens of species, are commonly perceived as opportunistic scavengers. But their behavior can appear quite deliberate and cunning, and it demonstrates an impressive level of adaptability as the birds keep managing to find new ways to eat.

This relationship between gulls and ducks seemed impossible to miss, but very little had been written about it, ornithologist Dominik Marchowski of Szczecin University said in a news release.

"The marginal study became major,” Mr. Marchowski said, “and we developed behavioral studies of birds and an analysis of pellets to confirm the scale of the phenomenon. In our opinion, these studies show that it's worth watching the seemingly obvious behavior of birds more closely, because they can hide interesting interactions."

Marchowski elaborated in an email to The Christian Science Monitor, saying his team's discovery “shows that before our own eyes, the dynamic processes of the creation of new ecological niches is happening, which in the long term can lead to coevolutionary episodes and greater specialization, and can have implications for the evolution of biological diversity.”

Gulls, says Marchowski, are fast learners. “If one intelligent gull discovers a new, easy way of gaining food, others can take advantage of this and if the method is effective, soon most individuals of the population start using it.” This is what likely happened among the gulls of Szczecin Lagoon, Marchowski says, and was probably due to “the closure of a big refuse dump,” which would have “resulted in a significant reduction of food stocks, forcing the gulls to seek other sources of food.”

Gulls also adapt to new conditions very quickly, and their behavior can indicate important issues, such as changes in an ecosystem, like the spread of invasive species – which Marchowski says is one of the most important environmental issues of the world today, right alongside climate change.

“The bird’s food, the Zebra Mussel,” Marchowski says, “is the background of our story.”

“This mussel is an invasive species in Poland, and massively present in the Szczecin Lagoon – as it also is in America, on the Great Lakes. The example of our story shows that not only ducks are involved in the interactions with this mussel; new trophic relationships are spontaneously arising.”

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