Behaviour 2019
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Immediate flexibility in a vocal mimic, the gray catbird (Dumetella carolinensis), varies with noise level
Shannon K Eppert1, Dana L Moseley1,2. 1James Madison University, Harrisonburg, VA, United States; 2Smithsonian Migratory Bird Center, Washington, DC, United States

Many birds sing higher minimum frequencies in urban areas, which avoids the masking effects of anthropogenic low-frequency noise, but the mechanism behind this difference is not well understood. Immediate flexibility is the ability to alter song in real-time in the presence of sudden noise, allowing for better signal transmission. We investigated if male catbirds alter their song in the presence of anthropogenic versus high-frequency noise playback compared to pre-playback. We tested 17 male gray catbirds (Dumetella carolinensis) along an urban gradient from VA to DC. Compared to pre-playback, catbirds sang significantly higher minimum frequencies during low-frequency noise playback, but with a small effect size of 55 Hz overall. This result begs the question of whether this shift is a byproduct of the Lombard effect and if it would enable masking avoidance. Habitat was a significant factor as catbirds on noisier, urban habitats both increased minimums more (141 Hz) and decreased maximum frequencies more (-90 Hz) than rural catbirds. Together these shifts may lead to greater energy concentrated in a narrower frequency bandwidth, thus enhancing signal transmission for urban birds.