No frequency shift in the “D” notes of Carolina chickadee calls in response to traffic noise
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Loud, low-frequency traffic noise can mask songbird vocalizations, and populations of some urban songbird species have shifted the frequency of their vocalizations upward in response. However, the spectral structure of certain vocalization elements may make them resistant to masking, suggesting that species that use these notes could be more successful in areas with high levels of traffic noise. To test this idea, we recorded Carolina chickadees (Poecile carolinensis), whose calls feature “D” notes with an overtone spectral structure, along a traffic noise gradient in Durham and Orange Counties, North Carolina, USA. Frequency parameters of “D” notes did not change with noise level suggesting the possibility that these notes can be communicated effectively in noise, but further investigation is needed to test this hypothesis directly. In addition, we performed a playback experiment demonstrating how the use of spectrograms to measure note frequencies is unreliable, especially when recordings are made in noisy areas. We used an alternative method based on the predictable frequency structure of “D” notes. Our experiment is one of few that address the effects of urban noise on calls produced by both sexes as opposed to song produced only by males during the breeding season. Understanding how vocalizations with different spectral structures may be affected differentially by traffic noise will increase our ability to predict how the expansion of noisy areas may impact songbird community composition in the future.
KeywordsAnimal communication Calls Traffic noise Noise masking Carolina chickadee Poecile carolinensis
We thank Ed Ibarguen and the Washington Duke Inn and Golf Club for providing transportation between sites during data collection, and Sara Childs and the Office of the Duke Forest for permitting access to the Duke Forest for field recordings. We thank Susan Peters for the help in all aspects of the project, especially her help in synthesizing notes for playback and suggesting improvements to the manuscript. Thanks to Stephen Nowicki and his lab at Duke University for their encouragement and suggestions, the S.P.I.C.E. Lab at the University of Central Florida for editing a draft of the manuscript, and Mohamed Noor at Duke University for his prompt and thoughtful feedback on an early draft of the manuscript. Duke University provided logistical and financial support. The project was funded by a Duke University Undergraduate Research Support Grant to MKG.
The Duke University Institutional Animal Care and Use Committee approved the project under Protocol No. A237-11-09.
The experiments performed here comply with the current laws of the United States of America.
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