An Investigation of How Vehicular Noise Mitigation Affects Acoustic Communication in Avifauna




Gentry, Katherine E

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Noise disturbance from vehicular traffic affects the acoustic communicative behaviors of many terrestrial species and has become an increasingly widespread problem as urbanization and traffic densities continue to rise. This study investigates if noise mitigation (road closures) reduces the effect of vehicular noise on the acoustic communication of animals. Vocalizations of the Eastern wood-pewee (Contopus virens), a suboscine passerine, and the Northern cardinal (Cardinalis cardinalis), an oscine passerine, were studied in the greater Washington DC region. Song characteristics, including peak frequency, bandwidth, minimum frequency, and duration, examined the effect of noise on each species’ vocalizations. The songs were investigated in two noise conditions: areas exposed to a 36-hour weekly road closure and areas with a non-regulated change in traffic flow. Mixed-effect general linear statistical models were used to understand how noise condition, measures of background noise amplitude, and environmental variables, including vegetation, temperature and humidity, affect song characteristics. The statistical models incorporated two measures of the background noise when a bird song was detected-- flat-weighted equivalent continuous sound pressure level noise measurements (Leq) of low-frequency traffic noise and high-frequency noise, usually from other animals. Analysis of acoustic recordings indicated that routine, temporary relief from traffic noise affected the song characteristics exhibited by both species. The minimum frequency of Northern cardinal songs was predicted by high-frequency noise and weather conditions in addition to low-frequency noise and its interaction effect with noise condition. Northern cardinal bandwidth and duration measurements were predicted by the noise condition, but not by low-frequency traffic noise alone. Northern cardinal song bandwidth was also predicted by the interaction of noise condition with low-frequency traffic noise. In other words, only the Northern cardinals exposed to the 36-hour weekly road closure adjusted their song bandwidth. Furthermore, the bandwidth adjustments contrasted with the fluctuation in low-frequency background noise and optimized song propagation. Similarly, noise condition and its interaction with low-frequency traffic noise predicted the duration of Eastern wood-pewee songs; though, low-frequency traffic noise, and not noise condition, predicted the minimum frequency of their songs. In addition to traffic noise and noise condition, environmental variables and high-frequency background noise also predicted the song characteristics of the Eastern wood-pewee. The results suggest that the motivation for song adjustment in northern cardinals is highly attributable to their acoustic environment, while more factors than just background noise influence song adjustments by eastern wood-pewee. This study provides a greater understanding of how different bird species adjust their song in response to anthropogenic noise and the local environment and the potential mitigating impact of noise reduction for acoustic communication among terrestrial vertebrates in protected areas.



Urban ecology, Bird song, Conservation, Behavior