Cuckoo adaptations: trickery and tuning

Abstract

I suggest that the cuckoo's parasitic adaptations are of two kinds: ‘trickery’, which is how adult cuckoos and cuckoo eggs and chicks evade host defences, and involves adaptations that have co-evolved with host counter-adaptations, and ‘tuning’, which is how, once accepted, cuckoo egg and chick development are then attuned to host incubation and provisioning strategies, and which might not always provoke co-evolution. Cuckoo trickery involves adaptations to counter successive lines of host defence and includes: tricks for gaining access to host nests, egg trickery and chick trickery. In some cases, particular stages of host defences, and hence their corresponding cuckoo tricks, are absent. I discuss three hypotheses for this curious mixture of exquisite adaptation and apparent lack of adaptation: different defences best for different hosts, strategy blocking and time for evolution of defence portfolios. Cuckoo tuning includes adaptations involving: host choice and monitoring of host nests, efficient incubation of the cuckoo egg, efficient provisioning and protection of the cuckoo chick, and adaptations to avoid misimprinting on the wrong species. The twin hurdles of effective trickery in the face of evolving host defences and difficulties of tuning into another species' life history may together explain why obligate brood parasitism is relatively rare.