Data from: Crying wolf to a predator: deceptive vocal mimicry by a bird protecting young

Animals often mimic dangerous or toxic species to deter predators; however, mimicry of such species may not always be possible and mimicry of benign species seems unlikely to confer anti-predator benefits. We reveal a system in which a bird mimics the alarm calls of harmless species to fool a predator 40 times its size and protect its offspring against attack. Our experiments revealed that brown thornbills (Acanthiza pusilla) mimic a chorus of other species' aerial alarm calls, a cue of an Accipiter hawk in flight, when predators attack their nest. The absence of any flying predators in this context implies that these alarms convey deceptive information about the type of danger present. Experiments on the primary nest predators of thornbills, pied currawongs (Strepera graculina), revealed that the predators treat these alarms as if they themselves are threatened by flying hawks, either by scanning the sky for danger or fleeing, confirming a deceptive function. In turn, these distractions delay attack and provide thornbill nestlings with an opportunity to escape. This sophisticated defence strategy exploits the complex web of interactions among multiple species across several trophic levels, and in particular exploits a predator's ability to eavesdrop on and respond appropriately to heterospecific alarm calls. Our findings demonstrate that prey can fool predators by deceptively mimicking alarm calls of harmless species, suggesting that defensive mimicry could be more widespread because of indirect effects on predators within a web of eavesdropping.

动物通常会通过拟态危险或有毒物种来威慑捕食者；然而，拟态此类物种并非总能实现，而拟态无害物种似乎也难以获得反捕食收益。本研究揭示了一套独特的拟态系统：一种鸟类通过模仿无害物种的警戒叫声，欺骗体型达其40倍的捕食者，以此保护后代免遭袭击。我们的实验发现，当捕食者袭击巢穴时，褐刺嘴莺（Acanthiza pusilla）会模仿多种物种的空中警戒叫声——这是鹰属（Accipiter）猛禽飞行时的警戒信号。此场景下并无飞行捕食者出现，这表明这些警戒叫声传递了关于当前危险类型的虚假信息。针对褐刺嘴莺的主要巢捕食者斑噪钟鹊（Strepera graculina）开展的实验显示，该捕食者会将这些叫声视作自身正遭受飞行猛禽威胁的信号，或是抬头扫视天空搜寻危险，或是逃离现场，这证实了此类叫声的欺骗功能。这类干扰会推迟袭击行为，为褐刺嘴莺的雏鸟争取到逃生机会。这套精妙的防御策略利用了跨多个营养级的多物种间复杂互动网络，尤其利用了捕食者能够窃听异种警戒叫声并做出恰当反应的特性。我们的研究结果证实，猎物可通过模仿无害物种的警戒叫声来欺骗捕食者，这表明由于窃听网络中对捕食者产生的间接效应，防御性拟态的分布范围可能比此前认知的更为广泛。