Data from: Alarming features: birds use specific acoustic properties to identify heterospecific alarm calls

Vertebrates that eavesdrop on heterospecific alarm calls must distinguish alarms from sounds that can safely be ignored, but the mechanisms for identifying heterospecific alarm calls are poorly understood. While vertebrates learn to identify heterospecific alarms through experience, some can also respond to unfamiliar alarm calls that are acoustically similar to conspecific alarm calls. We used synthetic calls to test the role of specific acoustic properties in alarm call identification by superb fairy wrens, Malurus cyaneus. Individuals fled more often in response to synthetic calls with peak frequencies closer to that of conspecific calls, even if other acoustic features were dissimilar to that of fairy-wren calls. Further, they then spent more time in cover following calls that had both peak frequencies and frequency modulation rates closer to natural fairy-wren means. Thus, fairy wrens use similarity in specific acoustic properties to identify alarms and adjust a two-stage antipredator response. Our study reveals how birds respond to heterospecific alarm calls without experience, and together with previous work using playback of natural calls shows that both acoustic similarity and learning are important for interspecific eavesdropping. More generally, this work reconciles contrasting views on the importance of alarm signal structure and learning in recognition of heterospecific alarms.

窃听异种报警叫声（heterospecific alarm calls）的脊椎动物，需将报警声与可安全忽略的声音区分开来，但目前学界对识别异种报警叫声的机制仍知之甚少。尽管脊椎动物可通过经验学习识别异种报警声，但部分类群也能对与同种（conspecific）报警叫声声学特征相似的陌生报警声做出反应。本研究以华丽细尾鹩莺（Malurus cyaneus）为研究对象，利用合成叫声（synthetic calls）测试特定声学特性（acoustic properties）在其报警声识别中的作用。当合成叫声的峰值频率与同种报警声更接近时，即使其他声学特征与细尾鹩莺报警声存在差异，个体的逃逸频次也会更高。此外，当合成叫声的峰值频率与调频速率均更接近野生细尾鹩莺的平均水平时，个体在逃逸后会花费更多时间藏匿于遮蔽处。由此可见，细尾鹩莺通过特定声学特性的相似性来识别报警声，并以此调控两阶段反捕食响应（antipredator response）。本研究阐明了鸟类在无经验的情况下如何对异种报警声做出反应，结合此前利用自然叫声回放开展的相关研究可知，声学相似性与学习过程均在种间窃听（interspecific eavesdropping）行为中发挥关键作用。从更广泛的视角来看，本研究调和了学界关于报警信号结构与学习过程在异种报警声识别中的重要性的对立观点。