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 diff...