Recordings Reveal Regional Differences in Common Yellowthroat Songs

(June 6, 2014, The Auk: Ornithological Advances)—A new study on birdsongs demonstrates how public audio archives may become treasure chests of scientific discovery. Bird watchers and ornithologists have gone to great efforts to record birdsongs in the wild and donate them to repositories. Taking advantage of this resource, Rachel Bolus examined 127 of these recordings to identify differences in Common Yellowthroat songs across the U.S. Her bioacoustics analyses reveal that the song of this ubiquitous warbler shows distinctive and predictable variations across geographic regions and among genetically recognized subspecies. “This research highlights the potential for new discoveries using publicly available databases,” said Mark Hauber, the Editor-in-Chief of The Auk: Ornithological Advances. Bolus, who did the research as part of her doctoral studies at the University of Massachusetts, Amherst, wanted to find out how genetic differentiation and selection have affected the Common Yellowthroat’s song. She hypothesized that in this ubiquitous warbler, which displays differences in both physical appearance and migratory behavior across its three genetically distinct lineages, such differences would be paralleled by distinctive variation in songs. To test this, Bolus compared recordings of Common Yellowthroat songs in the collections of the Cornell Lab of Ornithology’s Macaulay Library of Natural Sounds, The Ohio State University’s Borror Laboratory of Bioacoustics, and xeno-canto.org. She grouped the recordings into three geographic regions based on recently identified genetically distinct populations of the species: eastern, western, and southwestern taxa.

Bolus listened to the recordings and broke each song into parts: phrases, notes, and internote durations (periods of silence), and also measured each song’s frequency and bandwidth. In her comparison of vocalizations from eastern and western populations, Bolus found that the two most consistent differences were in bandwidth and internote duration. The western birds’ songs had greater bandwidth, meaning that the birds sang notes both higher and lower within a song. The western birds also paused longer between notes, giving their songs greater internote durations. And the western birds added more elements—including upsweeps and downsweeps in pitch—per note than did eastern birds.

In her examination of birdsongs in the southwestern group, Bolus found that even though the birds in the southwestern region are more genetically similar to the birds in the eastern region, the southwestern birds sang more like the nearby western birds. Bolus suggests that the southwestern and western populations’ more geographically similar environment is an important influence on the qualities of southwestern songs.

Looking at possible physical explanations for differences in birdsong, Bolus discovered that individuals in populations of Common Yellowthroats with longer bills sang lower notes. And even though lower sounds have the potential to carry farther in dense habitat, she found no difference in how the birds sang across different habitats. In addition, migrant birds sing songs that are more similar than do the sedentary birds who stick to the same area year-round.Bolus also noted in her study that regional songs persist for a long time, and that changes in songs are probably greater among populations rather than within them. For example, she found at least two songs in recordings from the 2000s that existed in the same counties in the 1950s and 1960s.

Across geographic regions, though, songs of the Common Yellowthroat show divergence, which could eventually contribute to the rise of new species. If the birds in different regions sing different songs, “it would make it harder to find each other or interbreed with another group over time, because they’d be less likely to recognize each other,” Bolus said.Geographic variation in songs of the Common Yellowthroat is an open access article that can be viewed at http://aoucospubs.org/doi/full/10.1642/AUK-12-187.1.

Contact: Rachel Bolus, rachel.t.bolus@gmail.com

About the Journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology. The journal has been the official publication of the American Ornithologists’ Union (www.aou.org) since 1884. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years, and currently holds the top impact factor among ornithological journals.

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