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Traffic noise is becoming a more prominent fixture in urban environments as cities and highways expand to accommodate the growing human population. Birds, in particular, rely heavily on vocal communication and have recently been shown to change the structure of their signals in response to environmental noise. Our objective was to determine the impact of traffic noise on Red-winged Blackbird (Agelaius phoeniceus) song structure and song timing. We recorded bird songs using a directional microphone and installed permanent recording devices to monitor daily song patterns at both high traffic noise sites and low traffic noise sites throughout southern Ontario, Canada. Our results indicate that at sites with high traffic noise, Red-winged Blackbirds sing songs with fewer introductory syllables, which are an important component of individual recognition and repertoire formation. In addition, the typical diurnal singing pattern of birds associated with noisy urban sites is more homogeneous than that of birds associated with quiet rural marshes. In the early morning and evening, singing effort was higher at rural sites than at urban sites, while in the midday singing effort at urban sites was higher than at rural sites. Birds at our noisy urban sites appear to be avoiding acoustic masking by increasing song production during the quiet part of the day and decreasing song production during the noisy rush hour periods. Based on our results, urban noise is impacting communication structure and the daily pattern of song production in a marsh-nesting species. These results have important implications for avian conservation and land use planning for urban development.
