Mechanics and Evolution of Tonal Sounds Produced by Feathers

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Birds are widely appreciated as being highly vocal, and for decades researchers have explored the mechanics and physiology of birds' vocal apparatus, the syrinx. However, birds also produce a wide variety of non-vocal communication sounds. Examples include the 'winnowing' sound snipe make with their tail-feathers, or the 'whistling' sounds ducks and doves make with their wings during flight. This research project will examine the physical mechanics of how some feathers flutter to produce loud tonal sounds during flight, and how and why sounds produced by feathers has repeatedly resulted in the evolution of non-vocal acoustic communication in birds.Three complementary approaches will be used. First, natural history collections (museum skins and sound recordings) of over 20 families of birds that produce these sounds will be surveyed to establish the feather morphologies and diversity of these sounds. Second, wind tunnel tests will be conducted on isolated feathers to test the biomechanics of how feathers flutter to produce sound. Third, field experiments will be conducted on a range of hummingbird species as a benchmark for the laboratory experiments, to explore the relationship between behavioral displays and sounds that are produced, and to examine the evolution of these signals.This research will uncover the physical mechanisms responsible for causing feathers to produce tonal sounds, and how a diversity of sounds can be produced with feathers of varying size and shape. These sounds are often produced during elaborate courtship displays, and understanding the mechanics of how feathers produce tonal sounds will provide insights into the evolution of signals. More broadly, this research will foster scientific development abroad through collaborations with scientists in Latin America. The results of this research will be disseminated through peer-reviewed scientific publications and to a broader public audience, such as through educational modules for middle school science students. Ultimately, this research may have technological applications, such as new types of sound production devices.