White‐crowned sparrow males show immediate flexibility in song amplitude but not in song minimum frequency in response to changes in noise levels in the field

• Published in: Ecology and evolution Vol. 7; no. 13; pp. 4991 - 5001
• Main Authors: Derryberry, Elizabeth P., Gentry, Katherine, Derryberry, Graham E., Phillips, Jennifer N., Danner, Raymond M., Danner, Julie E., Luther, David A.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.07.2017; John Wiley and Sons Inc
• Subjects: Acoustic noise; Amplitudes; anthropogenic noise; Background noise; behavioral plasticity; Biological evolution; birdsong; cultural evolution; Flexibility; Hypotheses; Males; Masking; Noise; Noise levels; Observational studies; Ontogeny; Original Research; Real time; Signal processing; Song; soundscape; Studies; Time; Urban areas; behavioral plasticity; anthropogenic noise; birdsong; cultural evolution; soundscape
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3037

The soundscape acts as a selective agent on organisms that use acoustic signals to communicate. A number of studies document variation in structure, amplitude, or timing of signal production in correspondence with environmental noise levels thus supporting the hypothesis that organisms are changing their signaling behaviors to avoid masking. The time scale at which organisms respond is of particular interest. Signal structure may evolve across generations through processes such as cultural or genetic transmission. Individuals may also change their behavior during development (ontogenetic change) or in real time (i.e., immediate flexibility). These are not mutually exclusive mechanisms, and all must be investigated to understand how organisms respond to selection pressures from the soundscape. Previous work on white‐crowned sparrows (Zonotrichia leucophrys) found that males holding territories in louder areas tend to sing higher frequency songs and that both noise levels and song frequency have increased over time (30 years) in urban areas. These previous findings suggest that songs are changing across generations; however, it is not known if this species also exhibits immediate flexibility. Here, we conducted an exploratory, observational study to ask whether males change the minimum frequency of their song in response to immediate changes in noise levels. We also ask whether males sing louder, as increased minimum frequency may be physiologically linked to producing sound at higher amplitudes, in response to immediate changes in environmental noise. We found that territorial males adjust song amplitude but not minimum frequency in response to changes in environmental noise levels. Our results suggest that males do not show immediate flexibility in song minimum frequency, although experimental manipulations are needed to test this hypothesis further. Our work highlights the need to investigate multiple mechanisms of adaptive response to soundscapes. The soundscape acts as a selective agent on organisms that use acoustic signals to communicate. Individuals may be able to change their behavior in real time (i.e., immediate flexibility) to avoid masking. We found that territorial white‐crowned sparrow males adjust song amplitude but not minimum frequency in response to changes in ambient noise levels. Our results suggest that behavioral flexibility in song minimum frequency is not contributing to soundscape‐based patterns in song variation in this species.