Data from: Why does noise reduce response to alarm calls? Experimental assessment of masking, distraction and greater vigilance in wild birds

1. Environmental noise from anthropogenic and other sources affects many aspects of animal ecology and behaviour, including acoustic communication. Acoustic masking is often assumed in field studies to be the cause of compromised communication in noise, but other mechanisms could have similar effects. 2. We tested experimentally how background noise disrupted the response to conspecific alarm calls in wild superb fairy-wrens, Malurus cyaneus, assessing the effects of acoustic masking, distraction and changes in vigilance. We first examined the birds’ response to alarm-call playbacks accompanied by different amplitudes of background noise that overlapped the calls in acoustic frequency. We then scored and videoed their response to alarm calls in two types of background noise, that did or did not overlap call frequency, but were broadcast at a constant amplitude. 3. Birds were less likely to flee to alarm calls in higher amplitudes of overlapping noise, demonstrating that noise itself compromised communication independently of environmental correlates. Background noise affected the response only if it overlapped in frequency with the alarm calls, implying that the effect was not due to distraction. Further, birds were equally vigilant during background noise of overlapping or non-overlapping frequency, indicating that the lack of response to alarm calls in overlapping noise was not due to enhanced vigilance and awareness that there was no predator. 4. We conclude that alarm-call reception was compromised by masking, a mechanism that is often assumed but rarely tested in an ecological context. Masking compromised reception of high-frequency ‘aerial’ alarm calls and so could reduce survival in background noise of similar frequency. While anthropogenic noise, which is often of lower frequency, is unlikely to affect communication with these calls, it could affect reception of acoustic cues of danger, or other conspecific or heterospecific alarm calls.

1. 人为及其他来源产生的环境噪声会影响动物生态学与行为学的诸多方面，其中包括声学通讯（acoustic communication）。野外研究中通常默认声学掩蔽（acoustic masking）是噪声环境下动物通讯受损的原因，但其他机制也可能产生类似效应。
2. 本研究通过实验探究了背景噪声如何干扰野生华丽细尾鹩莺（Malurus cyaneus）对同类报警鸣唱的响应，并评估了声学掩蔽、注意力分散以及警觉性变化所产生的效应。研究首先测试了在声学频率上与报警鸣唱重叠的不同振幅背景噪声伴随下，鸟类对报警鸣唱回放的响应；随后在两类背景噪声（分别与鸣唱频率重叠或不重叠，但播放振幅保持恒定）环境中，对鸟类的报警响应进行评分并录制视频。
3. 在振幅更高的重叠噪声环境中，鸟类更不易对报警鸣唱做出逃逸响应，这表明噪声本身可独立于环境关联因素损害通讯行为。仅当背景噪声与报警鸣唱在频率上重叠时，才会对鸟类的响应产生影响，这暗示该效应并非由注意力分散所致。进一步而言，在频率重叠与非重叠的背景噪声环境中，鸟类的警觉性水平并无差异，这表明重叠噪声环境下鸟类对报警鸣唱缺乏响应，并非源于警觉性提升以及误以为不存在捕食者。
4. 本研究得出结论：报警鸣唱的感知接收因掩蔽作用而受损，这一机制虽常被学界默认，但在生态学研究场景中鲜有实证验证。掩蔽作用会损害高频“空中捕食者”报警鸣唱的感知接收，因此在频率相似的背景噪声环境中可能降低个体存活率。尽管人为源噪声通常频率较低，不太会影响这类鸣唱的通讯，但它可能干扰危险声学信号或其他同类、异种报警鸣唱的感知接收。