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Birds grow bigger beaks to attract potential mates: Study

Eric Pfeiffer
The Sideshow

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The Smithsonian compared bill size among sparrows to see how it affected mating habits. (Ray Danner)

If you’re a single bird comparing potential mates, size matters. At least, that’s what the results from a recent study suggest.

According to the study, certain species of birds even experience beak growth during mating season.

Conducted by researchers from the Smithsonian Conservation Biology Institute and published in the latest issue of Ecology and Evolution, the study compared beak size and growth by examining X-rays from thousands of horny bills (no pun intended) belonging to a species of tidal marsh sparrows.

“Traditionally, we’ve viewed bill size in terms of how it helps birds eat,” Russell Greenberg, head of SCBI’s Migratory Bird Center and paper co-author, said in a release from the Smithsonian. “By looking at the infrastructure of bird bills using X-rays, we discovered that male bill sizes change seasonally, suggesting that bills play a role in mating and fighting as well."

The beaks are able to experience growth during mating season because they are made of keratin, not bone, said the study, making them similar to fingernails on people. Interestingly, both the male and female bills grow during mating season, though the male bills tend to be larger and experience more substantial growth. The male bills studied were largest during the late spring and smallest during the winter months.

According to the Smithsonian, the study results match a similar study conducted by Washington’s National Zoo last summer, which looked at bill sizes of two subspecies of song sparrows.

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