Exploiting Nest Defense Behavior of Hosts: A Case Study of Successful Parasitism by a Common Cuckoo.

In this study, we document the case of a common cuckoo () successfully locating and parasitizing the nest of a gray bushchat () by exploiting the latter's nest defense behavior in Liuzhi, Guizhou, southwest China. We found that the common cuckoo could identify the secluded nest site by observing the host's defense behaviors (e.g., frequent lunging and emitting alarm calls), and successfully laid its egg in the nest despite aggressive host defense. This phenomenon provides strong support for the "host activity hypothesis." The nest defense behavior exhibited by the gray bushchat aimed at protecting its nest, inadvertently provided cues to the common cuckoo regarding its nest site. This finding reveals a complex coevolutionary relationship between parasitism and antiparasitism, highlighting the dual role of the host's nest defense behavior in both reducing brood parasitism and providing parasites with nest-site cues. Our findings offer a new perspective for further exploring the behavioral strategies of parasitic birds and the evolutionary dynamics of the host's nest defense behavior.