University of Utah biologist Franz Goller and colleagues investigated how cowbirds pull off this vocal trick and discovered the answer is surprisingly complex.

Birds produce sound using the syrinx, a vocal organ with two separate sound sources—one on the left and one on the right. To create the gurgling, bubbling quality in their songs, cowbirds rapidly switch between these two sides, according to new research led by Goller, a U professor emeritus of biology.

But the researchers discovered the watery effect is also associated with the way these birds control their breathing.

“What’s striking about the cowbird syrinx is that the left pair of vocal folds is much bigger than the right pair. One idea is that the high frequencies are made on the right side only. The portions of these introductory notes that have the watery timbre are alternations of left and right contributions,” said Goller, who has long studied birds’ vocalizations with funding from the National Institutes of Health and is now a professor emeritus at the U. “We were able to pinpoint the exact mechanism by which this sound coloration is generated.”

His findings were reported last month in the journal Current Biology.

Listen to the sounds brown-headed cowbirds make.

A biologist, a physicist and a psychologist walk into a lab…

Goller’s interdisciplinary research team, which included a physicist and psychologist, focused its study on brown-headed cowbirds, Molothrus ater, one of six species in its genus and the one common in Utah. They also studied starlings that they raised with cowbirds in an experiment to see how they imitate cowbird songs.

Cowbirds belong to the Icteridae family, whose other members, such as blackbirds, can also produce sounds with an unusual timbre—a musical term that refers to the character or feel of a note as opposed to its pitch.

“Typically, when we talk about timbre, we often think of the upper vocal track, so above the sound source. There are filter qualities that we use in speech all the time. That you recognize a voice of an individual is based exactly on these filter qualities,” Goller said. “But a lot of sound coloration features are also generated at the source, and we know very little about that. Here we managed to study in detail how this watery quality of cowbird song comes about through rather complex interactions between respiration and cowbirds’ two sound sources.”

Read the entire article by Brian Maffly in @ The U.