Abstract The obligate brood parasitic common cuckoo ( Cuculus canorus ) is best known for its two-note “cu-coo” call, which is uttered repeatedly by adult males during the breeding season. This call advertises the male’s claim for his territory. A rare, aberrant version (“cu-kee”) was discovered in a population of cuckoos in central Hungary. In a playback experiment, we simulated conspecific territorial intrusions using either aberrant call sequences or normal calls (as control). Cuckoos responded to both calls similarly by approaching the speaker, flying around it several times, and perching on nearby trees. To identify the role of each note of these cuckoo calls, we also played sequences of the first (“cu”) or second (“coo” or “kee”) notes of the calls. Territorial males responded to first notes at similarly high frequencies as to each of the full calls, whereas responses toward either second note type were nearly absent. Thus, the first notes of both typical and aberrant cuckoo calls contain sufficient information to recognize conspecific males and the novel calls did not reduce the efficiency of male-male communication in cuckoos because the aberration occurred in the less functional second note. Significance statement Birds use songs and calls to communicate with each other, including advertising their territories to keep competitors away. However, when the acoustic signal is atypical and distorted, the receiver individual may not process it correctly. Common cuckoos recognize a territorial intruder by their well-known “cu-coo” calls. We studied a rare, aberrant version of the common cuckoo call (“cu-kee”), which differed from the normal call in the second note of the two-partite call. However, cuckoos responded similarly to both of the normal and aberrant calls in a playback experiment. When the first or second parts of the different calls were played separately, only the first part of the cuckoo calls was effective in eliciting territorial defence. Consequently, the aberrant second note did not reduce cuckoos’ communication efficiency.

中文翻译：

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与普通杜鹃 (Cuculus canorus) 异常叫声的有效同种交流

摘要 专性繁殖寄生杜鹃 (Cuculus canorus) 以其两音“cu-coo”的叫声而闻名，在繁殖季节，成年雄性会反复发出这种叫声。这个电话宣传了雄性对其领土的要求。在匈牙利中部的杜鹃种群中发现了一种罕见的异常版本（“cu-kee”）。在回放实验中，我们使用异常呼叫序列或正常呼叫（作为控制）模拟了特定的领土入侵。布谷鸟通过接近扬声器，在它周围飞来飞去几次，并栖息在附近的树上，对这两个呼叫做出了类似的回应。为了确定这些布谷鸟叫声的每个音符的作用，我们还演奏了叫声的第一个（“cu”）或第二个（“coo”或“kee”）音符的序列。领地男性对第一个音符的响应频率与每个完整的调用频率相似，而对第二个音符类型的响应几乎不存在。因此，典型的和异常的杜鹃叫声的第一个音符都包含足够的信息来识别同种雄性，而新的叫声并没有降低杜鹃雄性与雄性交流的效率，因为异常发生在功能较弱的第二个音符中。重要性声明鸟类使用歌曲和电话来相互交流，包括宣传他们的领地以让竞争对手远离。然而，当声学信号不典型且失真时，接收者个人可能无法正确处理它。普通杜鹃通过它们众所周知的“cu-coo”叫声来识别领土入侵者。我们研究了一个罕见的，普通布谷鸟叫声（“cu-kee”）的异常版本，与两方叫声的第二个音符中的正常叫声不同。然而，在回放实验中，布谷鸟对正常和异常呼叫的反应相似。当不同叫声的第一部分和第二部分分开播放时，只有布谷鸟叫声的第一部分才能有效地引发领土防御。因此，异常的第二个音符并没有降低杜鹃的交流效率。