Data from: Deception by flexible alarm mimicry in an African bird

Deception is common in nature, but victims of deception discriminate against and ultimately ignore deceptive signals when they are produced too frequently. Flexible variation of signals could allow evasion of such constraints. Fork-tailed drongos (Dicrurus adsimilis) use false alarm calls to scare other species away from food that they then steal. We show that drongos mimic the alarms of targeted species. Further, target species reduce their response to false alarm calls when they are repeated. However, the fear response is maintained when the call is varied. Drongos exploit this propensity by changing their alarm-call type when making repeated theft attempts on a particular species. Our results show that drongos can evade the frequency-dependent constraints that typically limit deception payoffs through flexible variation of their alarm calls.

欺骗在自然界中极为普遍，当欺骗信号过于频繁时，受欺骗的对象会对其产生辨别排斥反应，并最终完全忽略此类信号。信号的灵活变异可使欺骗者规避这类约束。叉尾卷尾（Fork-tailed Drongo，学名*Dicrurus adsimilis*）会通过发出虚假警报叫声吓跑其他物种，进而窃取它们的食物。本研究证实，卷尾会模仿目标物种的警报叫声。进一步而言，当虚假警报叫声重复出现时，目标物种对其反应会逐渐减弱；但倘若叫声发生变化，目标物种的恐惧反应则会持续存在。卷尾会利用这一特性：当针对某一物种反复实施食物窃取行为时，它们会切换警报叫声的类型。本研究结果表明，卷尾可通过灵活调整警报叫声的类型，规避通常会限制欺骗收益的频率依赖性约束。