Influence of Sound Reflections from Urban Structures on Synthesized Sounds Mimicking the Chipping Sparrow's (Spizella passerina) Trill Songs
Recently natural habitats have been rapidly transformed into urban environment characterized by anthropogenic structures and low-frequency background noise. While loud anthropogenic noise may be detrimental to acoustic signal transmission by masking the signal, sound reflection on urban structures may be beneficial for the animals by amplifying the original signal. To investigate how horizontal anthropogenic structures (e.g., parking lot and sidewalks) influence the amplitude and transmission of synthesized songs mimicking Chipping Sparrows' trill songs, we conducted playback experiments over grass and concrete ground types and recorded the songs at 3m, 12.5m, 25m and 50m from the speaker. We then compared energy contained within the song elements and gap between elements across different substrates. In this study, we tested the following hypotheses: (1) sound reflections generated by urban structure increase energy within trill songs, and (2) sound reflections generated by urban structure increase reverberation of trill songs. If the first hypothesis is supported, we predicted that the energies contained in the songs played over urban structures would be greater than songs played over grass for each recording distance. Additionally, we predicted that songs played over anthropogenic structures would retain more energy over distance. If the second hypothesis is supported, we predict that the amount of energy contained in the gap between elements would be greater when the songs are played over anthropogenic structures than when songs are played over grass. Interestingly, synthesized songs played over anthropogenic structures contained a significantly higher energy than songs played over grass at each distance from the speaker. Regardless of substrate types, songs decayed at similar rates over distance.
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