1. Nestling ejection by host

The co-evolution between the little bronze-cuckoo Chalcites minutillus and their hosts, large-billed gerygone Gerygone magnirostris and mangrove gerygone G.evigaster.

Since parasitism by the common cuckoo Cuculus canorus reduce the breeding success of its hosts, many hosts have evolved anti-parasite behaviour such as parasitized egg rejection, and these behaviour promote parasites to evolve counter-adaptations such as laying mimetic eggs. It is a good example of a co-evolutionary arms race. However, the hosts of common cuckoo have never evolved anti-parasite behavior against cuckoo nestling even though it is not similar to own young and so huge. This paradox “the lack of nestling rejection in hosts of cuckoo” has been a long-standing question in evolution. However, the discoveries of alien nestling recognition and ejection of two Gerygone spp.(fig. 1), which are hosts of bronze-cuckoos (Sato et al. 2010 Biology Letters) provides an opportunity to begin disentangling the cognitive mechanisms involved in such anti-parasitism strategies. The little bronze-cuckoo Chalcites minutillus is common in mangroves and rainforests of tropical Australia and Southeast Asia, and specializes in parasitizing warblers of the genus Gerygone. The study was conducted in mangroves in Darwin, Northern Territory, Australia, where I focused on the main Australian host species, the large-billed Gerygone Gerygone magnirostris. The appearance of cuckoo eggs is very different from those of their hosts (figure 2). In the contrast the cuckoo chicks have blackish-colored skin and white down on the dorsal surface. It is closely resemble to the nestlings of its hosts (figure 2).

Our group reports this previously unknown behavior in the host species of little bronze-cuckoo. Using video cameras, I successfully recorded the moment when host birds ejected live cuckoo chicks from their nests.