被普通布谷鸟寄生的苇莺巢。那个较大的蛋是寄生蛋。

据6月5日的《科学》杂志报道说，当一只布谷鸟希望将它自己的一枚蛋偷偷地放入一个苇莺的巢中，这时苇莺会发动一场激烈的抵御行动，它们会成群地攻击这些寄生的鸟，同时发出很响且刺耳的叫声，并用它们的鸟喙发出噼啪之声。

新的研究显示，这些苇莺可通过观察它们的邻居而学习这种行为，但这种过程是受到生物学支配的 – 当研究人员用一种无害的假的鹦鹉来取代布谷鸟的话，则这些苇莺就不会学到这种技能。 某些鸟的群体发展出了针对诸如布谷鸟这类托卵寄生鸟的抵御行为，但这种行为不会快到成为遗传学变化的结果。 为了对替代性的解释进行调查，英国的Nicholas Davies 和Justin Welbergen设计了这样的实验：在这些实验中，他们让幼小且没有经验的苇莺观察它们的邻居的针对布谷鸟和假鹦鹉的行为。 这些天真的苇莺在观察了它们的邻居之后会采取群攻的行为来抵挡布谷鸟，但却不会抵挡鹦鹉，这表明，这些苇莺已经具有学习新的行为的基础，并只会对真正的威胁进行抵抗。 这种特质从长远看会对苇莺的群体有好处，因为像群攻这样的行为如果应用在错误的情况下则会产生反效果，例如，会吸引捕食者前来。

推荐原始出处：

Science 5 June 2009:DOI: 10.1126/science.1172227

Social Transmission of a Host Defense Against Cuckoo Parasitism

Nicholas B. Davies*, and Justin A. Welbergen

Coevolutionary arms races between brood parasites and hosts involve genetic adaptations and counter-adaptations. However, hosts sometimes acquire defenses too rapidly to reflect genetic change. Our field experiments show that observation of cuckoo (Cuculus canorus) mobbing by neighbors on adjacent territories induced reed warblers (Acrocephalus scirpaceus) to increase the mobbing of cuckoos but not of parrots (a harmless control) on their own territory. In contrast, observation of neighbors mobbing parrots had no effect on reed warblers’ responses to either cuckoos or parrots. These results indicate that social learning provides a mechanism by which hosts rapidly increase their nest defense against brood parasites. Such enemy-specific social transmission enables hosts to track fine-scale spatiotemporal variation in parasitism and may influence the coevolutionary trajectories and population dynamics of brood parasites and hosts.

Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.