Duetting is a coordinated form of acoustic communication with participants uttering calls or songs simultaneously and/or sequentially. Duetting is often observed in pair-bonded species, with mated females and males both contributing to the communal vocal output. We observed duetting between the sexes in the common cuckoo (Cuculus canorus), an obligate brood parasitic species without known pair formation. Specifically, female cuckoos use their sex-specific bubbling calls for duetting, while male cuckoos use a 3-note variant (“cu-cu-coo”) of their typical and well-known 2-note (“cu-coo”) territorial advertisement calls. The maximum frequency of the elements in the male’s 3-note variants was higher relative to the 2-note calls, while durations of both the elements and the inter-element intervals were shorter. The vast majority (95 %) of the 3-note calling was detected together with the bubbling call, implying an intersexual duetting function, with the female calls preceding these male calls in 67 % of cases. The two call types in duetting followed each other rapidly (mean response time of females was 1.30 ± 0.71 SD s, and 0.76 ± 0.53 SD s in males), and typically overlapped with each other (95 %). Frequently (90 %), the male call was repeated 2–3 times, whereas the female call was repeated less frequently (9%). Our results are consistent with a main function of duetting in intersexual communication and coordination between female and male cuckoos.

二重奏是一种协调形式的声音通信，参与者同时和/或顺序发出呼叫或歌曲。在配对物种中经常可以观察到二重奏，交配的雌性和雄性都有助于共同发出声音。我们在杜鹃（ Cuculus canorus ）中观察到雌雄之间的二重配对，杜鹃是一种专性巢寄生物种，没有已知的配对形成。具体来说，雌性杜鹃使用其性别特定的冒泡叫声进行二重唱，而雄性杜鹃则使用其典型且众所周知的二音（“cu-coo”）领地的三音变体（“cu-cu-coo”）广告电话。雄性 3 音符变体中元素的最大频率相对于 2 音符叫声更高，而元素的持续时间和元素间间隔都较短。绝大多数（95%）的三音符叫声与冒泡叫声一起被检测到，这意味着两性二重唱功能，在 67% 的情况下，女性叫声先于男性叫声。二重唱中的两种叫声类型快速地相互跟随（女性的平均响应时间为 1.30 ± 0.71 SD 秒，男性为 0.76 ± 0.53 SD 秒），并且通常相互重叠（95%）。男性叫声经常重复 2-3 次（90%），而女性叫声重复次数较少（9%）。我们的结果与雌性和雄性杜鹃之间的两性交流和协调中二重奏的主要功能一致。