Data from: Host provisioning behavior favors mimetic begging calls in a brood-parasitic cowbird

The vocalizations of some young brood-parasitic birds closely resemble those of their host’s young. Such similarities might arise because hosts bestow the greatest parental care in response to their own species’ call type. We used a playback experiment to assess the effectiveness of the nestling call structures of two brood parasites, the specialist screaming cowbird (Molothrus rufoaxillaris) and the generalist shiny cowbird (M. bonariensis), in stimulating parental provisioning in a shared host, the baywing (Agelaioides badius). Screaming cowbird begging calls closely resemble those of baywing young and thus should best exploit any bias for species-specific cues. Shiny cowbird calls, in contrast, are unlike baywings but can instead exploit non-specific sensory biases for long call duration and syllable repetition. We found playback of screaming cowbird’s mimetic calls elicited increases in feeding rates equivalent to those of playback of the host’s own young, while shiny cowbird calls failed to increase provisioning rates above those of no-broadcast control sessions. These results indicate that baywings discriminate between nestling call structures in favour of their own species calls when adjusting parental investment, and support the view that selection for optimal host provisioning can favour vocal mimicry by parasitic offspring.部分幼龄巢寄生鸟类（brood-parasitic birds）的鸣叫声与其宿主（host）幼鸟的鸣叫声高度相似。这类相似性的产生可能源于：宿主会针对自身物种的鸣叫声类型提供最多的亲代抚育。我们通过回放实验（playback experiment），评估了两种巢寄生鸟类的雏鸟鸣唱结构在刺激其共同宿主——栗翅牛鹂（Agelaioides badius）亲代育雏投喂行为方面的有效性：分别为专性寄生的啸声牛鹂（Molothrus rufoaxillaris），以及兼性寄生的辉牛鹂（M. bonariensis）。啸声牛鹂的乞食鸣唱（begging calls）与栗翅牛鹂幼鸟的鸣唱极为相似，因此能够最大化利用宿主对物种特异性鸣唱信号的感知偏好。与之相反，辉牛鹂的鸣唱与栗翅牛鹂的鸣唱差异显著，但其可通过长时长音节重复的非特异性感官偏好发挥作用。实验结果显示：播放啸声牛鹂的拟态鸣唱（mimetic calls）所引发的亲代投喂频率提升幅度，与播放宿主自身幼鸟鸣唱时的效果相当；而辉牛鹂的鸣唱则无法使育雏投喂率高于无播放对照组（no-broadcast control sessions）。上述结果表明，栗翅牛鹂亲鸟在调整亲代投入时，会依据雏鸟鸣唱结构区分鸣唱信号，优先识别自身物种的鸣唱；该结果支持了“自然选择对最优宿主育雏行为的塑造，可促进寄生后代演化出鸣唱拟态”这一学术观点。