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.

近几十年来，人为噪声及其对声学通讯的影响已受到广泛关注。然而，自然声学环境对通讯的影响及其在塑造声学信号中的作用仍未明确。本研究分别在海岸与河岸栖息地开展景观尺度的海浪与河流水声回放实验，探究水体产生的噪声如何影响6种鸣禽的鸣声频谱与时域特征。我们在37个样地中记录了保卫领地的鸣禽个体，每个样地对应以下4种声学环境之一：自然安静的‘对照样地’、紧邻海洋或急流河道的自然嘈杂‘阳性对照样地’、持续播放低频水体噪声的‘幻影’回放样地，以及持续播放高频水体噪声的‘移位’回放样地。我们预测，鸣声结构通常会与背景声振幅相关，且根据声学环境的频谱特征，不同样地类型的鸣声信号特征会存在差异。没有任何两个物种的鸣声改变模式完全一致，但6种鸣禽的鸣声结构均随背景噪声的振幅和/或频率发生变化，这为自然声景影响发声行为提供了强有力的证据。