Learned recognition of brood parasitic cuckoos in the superb fairy-wren Malurus cyaneus

Cuckoo hosts defend themselves against parasitism by means of mobbing, egg rejection, and chick rejection. However, each of these defenses is prone to costly recognition errors, and hosts are therefore more likely to deploy these defenses if they observe a cuckoo in the vicinity of their nest. The success of such response plasticity depends on accurate recognition of sympatric cuckoo species, but the mechanism by which hosts recognize cuckoos is largely unknown. Here, we use microgeographic variation in exposure to cuckoos in superb fairy-wren (Malurus cyaneus) hosts to test whether recognition of cuckoos is dependent on learning. We compare mobbing by superb fairy-wrens in response to freeze-dried specimens of a shining bronze-cuckoo (Chalcites lucidus) and a honeyeater control (Lichenostomus penicillatus) at 2 heavily parasitized sites and 2 rarely parasitized sites. Hosts at heavily parasitized sites mobbed the cuckoo intensively, including production of a distinctive whining call that appears to instigate group mobbing. By contrast, hosts at the rarely parasitized sites showed little reaction to the cuckoo, and their responses were similar to those given to the control. Furthermore, individuals with past experience of cuckoos mobbed the cuckoo specimen even when cuckoos were absent from the site, and did so significantly more than naive individuals. The extreme variation in response to cuckoos on such a small geographic scale and in relation to past exposure to cuckoos is consistent with learned recognition of cuckoos rather than local genetic adaptation.