Department of Natural Science, Malone University, Canton, Ohio, United States of America.
PLoS One. 2020 Oct 29;15(10):e0241035. doi: 10.1371/journal.pone.0241035. eCollection 2020.
Anthropogenic noise is an often-overlooked byproduct of urbanization and affects the soundscape in which birds communicate. Previous studies assessing the impact of traffic noise have focused on bird song, with many studies demonstrating the ability of birds to raise song frequency in the presence of low-frequency traffic noise to avoid masking. Less is known about the impact of traffic noise on avian alarm calls, which is surprising given the degree to which predator information within alarm calls may impact fitness. The objective of this study was to assess the impacts of traffic noise on the Black-capped Chickadees (Poecile atricapillus), a small non-migratory songbird with a well-studied and information-rich alarm call. We studied birds at eight locations in Stark County, Ohio, from 15 January to 7 March 2016, and used a taxidermic mount of an Eastern Screech-Owl to elicit alarm calls. In half of the trials, a pre-recorded traffic noise track was also broadcasted at 50 decibels. In noise trials, chickadee calls contained more introductory notes (P < 0.001), more total notes (P < 0.001), were of longer duration (P < 0.001), and had lower introductory and D-note peak frequencies (P = 0.032 and P = 0.041, respectively). No differences were noted in the number of D-notes per call between noise and control trials. Modifying alarm call duration and frequency, without changing the number of D-notes, may be a strategy that chickadees use to convey predator information and to coordinate a threat-appropriate mobbing response when it is not possible to change call type. Our results add to the small, but growing, literature documenting the effects of anthropogenic noise on avian alarm calls, demonstrate the flexibility and complexity of chickadee calls given in response to predators, and may partially explain why chickadees adapt well to urban areas.
人为噪声是城市化的一个经常被忽视的副产品，它会影响鸟类交流的声音环境。以前评估交通噪声影响的研究集中在鸟类的歌声上，许多研究表明，鸟类在低频交通噪声存在的情况下能够提高歌声频率，以避免被掩蔽。然而，人们对交通噪声对鸟类警报声的影响知之甚少，这令人惊讶，因为警报声中的捕食者信息在多大程度上可能影响适应性。本研究的目的是评估交通噪声对黑头山雀（Poecile atricapillus）的影响，黑头山雀是一种小型非迁徙鸣禽，其警报声具有丰富的研究信息。我们在 2016 年 1 月 15 日至 3 月 7 日期间在俄亥俄州斯塔克县的八个地点研究了鸟类，并使用了一只东部鸣角鸮的标本来引出警报声。在一半的试验中，还以 50 分贝的音量播放预先录制的交通噪声。在噪声试验中，山雀的叫声包含了更多的引言音符（P < 0.001）、更多的总音符（P < 0.001）、持续时间更长（P < 0.001），且引言音符和 D 音符的峰值频率更低（P = 0.032 和 P = 0.041，分别）。在噪声和对照试验中，每个叫声中的 D 音符数量没有差异。改变警报声的持续时间和频率，而不改变 D 音符的数量，可能是山雀在无法改变叫声类型的情况下传达捕食者信息并协调适当的警戒反应的一种策略。我们的结果增加了关于人为噪声对鸟类警报声影响的小而不断增长的文献，证明了山雀在面对捕食者时的叫声的灵活性和复杂性，并可能部分解释了为什么山雀能很好地适应城市地区。
