Environmental factors shape animal signals by influencing how sound propagates through natural habitats. The acoustic adaptation hypothesis predicts that signal features promoting effective propagation should be favoured, yet the role of habitat-mediated propagation in shaping song-type prevalence remains unclear. In songbird populations with multiple song types, some are commonly shared while others are rare. We tested the hypothesis that common song types in a population of Bachman’s Sparrows possess acoustic features that enhance propagation relative to rare song types. We quantified the acoustic features of common and rare song types and conducted sound propagation experiments. Common song types had shorter inter-syllable gaps, higher peak frequency, broader frequency bandwidth, and higher maximum frequency than rare song types. Consistent with predictions, common song types propagated more effectively for two of five propagation metrics, exhibiting higher amplitude envelope correlation and lower tail-to-signal ratios. Tree density showed a non-significant trend in which common song types exhibited higher amplitude envelope correlation as tree density increased, whereas wind speed and signal height did not influence propagation. Together, these results provide partial support for the hypothesis that propagation efficiency contributes to song-type prevalence, yet social processes during song learning likely play an equal or greater role.
Songbird, song learning, song types, acoustic propagation, acoustic degradation