Female aquatic warblers (Acrocephalus paludicola) are attracted by playback of longer and more complicated songs

Male aquatic warblers are relatively unusual in producing three different song structures, A, B and C. The shorter A-B songs have been shown to function in male-male aggressive interactions, and it was speculated that the longer and more complex C songs might function in female attraction. The present playback experiments were carried out on hormone-implanted females in a large, experimental aviary. When playback was of a male singing C songs, females were attracted faster and for longer periods than when the same male produced A-B songs. Females gave relatively few sexual displays, but gave more in response to playback of C songs than to A-B songs. Aquatic warblers have an unusually promiscuous mating system with high rates of extra-pair fertilisation and multiple paternity within broods. Sexual selection through intense sperm competition may have accentuated the evolution of structurally distinct songs for female attraction and aggressive interactions between rival males.