Cuckoos versus hosts: Australian rules

Brood parasitism by cuckoos imposes high reproductive costs on hosts, selecting for the evolution of host defences. Cuckoos retaliate by evolving counter-adaptations to host defences, giving rise to a coevolutionary arms race between the two parties. In Europe, the arms race between cuckoos and their hosts centres on the egg stage of the breeding cycle and it has driven the evolution of cuckoo eggs that accurately mimic those of their hosts. In this talk, I present the results of field experiments on Australian cuckoos and their hosts. Here, cuckoos seem to have defeated host defences mounted at the egg stage and the arms race has moved on to the chick stage, with chick rejection by hosts leading to near perfect mimicry of host chicks by cuckoo nestlings. I consider the strategies used by generalist cuckoos, whose offspring must mimic diverse host young to survive to fledge, and I discuss why co-evolution has taken a different course in Australia versus Europe.

Rebecca Kilner
Department of Zoology
University of Cambridge
U.K.