Fowl-mouthed study finds that diet shaped duck, goose beaks

Waterfowl beaks vary along a duck-to-goose gradient (left to right), primarily because of differences in diet. Credit: Aaron Olsen

From Charles Darwin’s famous finches to a new study that takes a rare look at a common order of birds—waterfowl—evolution has a tendency to reveals itself through bird beaks.

And this new study confirms through a rigorous analysis that the main evolutionary force driving the shape of duck, goose and other waterfowl beaks is their .

“This is the most comprehensive look to date at the relationship between diet and beak shape,” said Aaron Olsen, author of the study in Functional Ecology and a postdoctoral researcher in Brown University’s Department of Ecology and Evolutionary Biology.

“Waterfowl have really interesting beaks relative to other birds,” Olsen said. “They are very curvy with very diverse shapes.”

Working at the University of Chicago and the Field Museum of Natural History, Olsen sought to determine what accounts for that diversity.

He expected that diet might play a substantial role, but rather than just compare simple dietary categories with beak caliper measurements as many naturalists have, he engaged in a more detailed analysis. He carefully measured the 3-D form of the beaks of 136 specimens of waterfowl, covering 51 species and 46 genera, including two extinct species. One fossil, Presbyornis, dates back tens of millions of years. Then he paired those measurements with detailed data that he gathered from the research literature on the diet of each bird.

Regardless of his expectation, if diet and beak shape had little to do with each other, the math would have yielded low correlations.

“What this analysis asks is, ‘What are the patterns of correlation between these two datasets?’,” Olsen said. “What’s nice about that…

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