Experimentally broadcast ocean surf and river noise alters birdsong structure

Anthropogenic noise and its effects on acoustic communication have received considerable attention in recent decades. Yet, the natural acoustic environment’s influence on communication and its role in shaping acoustic signals remains unclear. Using landscape-level playbacks of ocean surf and river noise in coastal and riparian habitat, respectively, we investigated how water-generated noise influences spectral and temporal song characteristics in six songbird species. We recorded individuals defending territories across 37 sites, with each site representing one of four acoustic environments: naturally quiet ‘controls’, naturally noisy ‘positive controls’ adjacent to the ocean or a whitewater river, ‘phantom’ playback sites with continuous broadcast of low-frequency water noise, and ‘shifted’ playback sites with continuous broadcast of high-frequency water noise. We predicted that song structure would generally correlate with background sound amplitude and that signal features would differ across site types based on the spectral profile of the acoustic environment. No two species altered songs in precisely the same way. However, song structure of all six species varied with amplitude and/or frequency of background noise, providing strong evidence that natural soundscapes influence vocal behavior.

Methods
Data were collected and processed as described in the methods of "Experimentally Broadcast Ocean Surf and River Noise Alters Birdsong Structure."