Hawk mimicry and the evolution of polymorphic cuckoos

Abstract

The resemblance of some parasitic cuckoos to Accipiter hawks has been known since an- cient times. Recent experiments show that the hawk-like features of Common Cuckoos (Cuculus canorus) facilitate access to Reed Warbler (Acrocephalus scirpaceus) host nests. However, social infor- mation alerts hosts to see through the cuckoo's mimetic disguise. In turn, this has promoted the evo- lution of a cuckoo polymorphism to thwart host recognition. Here we show by comparative analyses that parasitic cuckoos with hawk-like features (yellow eyes, barred underparts, yellow legs) are more likely to be polymorphic (29% of species) than those without (8% of species). Phylogenetic analyses confirm correlated evolution of hawk-like features and cuckoo polymorphism. We suggest that mim- icry dynamics are particularly likely to promote the evolution of various guises in parasitic cuckoos to beat host defences.