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.

Elizabeth P Derryberry,Julie E Danner,David A Luther,Raymond M Danner,Graham E Derryberry,Katherine Gentry,Jennifer N Phillips

doi:10.1002/ece3.3037

Elizabeth P Derryberry, Julie E Danner + Show 5 more

Open Access

https://doi.org/10.1002/ece3.3037

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Abstract

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.

Highlights

Selection acts on organisms to maximize the transfer of information from signaler to an intended receiver during communication (Endler, 1993; Morton, 1975)
We find that song amplitude, but not song minimum frequency, changes in predicted directions with changes in background noise levels over a timescale of seconds (Figure 3)
Most other species examined show immediate flexibility in song amplitude, but species vary in flexibility in song minimum frequency

Summary

| INTRODUCTION

Selection acts on organisms to maximize the transfer of information from signaler to an intended receiver during communication (Endler, 1993; Morton, 1975). Soundscapes can change within a generation, vary dramatically from day to day and even moment to moment (Pijanowski et al, 2011), and individuals better able to change their behavior in response are expected to have more successful communication (Patricelli & Blickley, 2006) This plastic response can occur during development (an ontogenetic response), for example, through selective attrition of masked signals or passive acquisition of signals that transmit well, or through short-term adjustments (immediate flexibility) (Patricelli & Blickley, 2006). All three mechanisms are probably at work in many species, and yet we do not know the extent to which current signal variation reflects changes in the vocal phenotype over generations through evolution or developmental modification or is primarily a real-time response to changes in noise levels (i.e., immediate flexibility). | 4993 frequency could allow for singing at a higher amplitude (Nemeth & Brumm, 2010)

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Findings

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| CONCLUSIONS