Male lyrebirds create a complex acoustic illusion of a mobbing flock during courtship and copulation.

Darwin argued that females' "taste for the beautiful" drives the evolution of male extravagance, but sexual selection theory also predicts that extravagant ornaments can arise from sexual conflict and deception. The sensory trap hypothesis posits that elaborate sexual signals can evolve via antagonistic coevolution whereby one sex uses deceptive mimicry to manipulate the opposite sex into mating. Here, the success of deceptive mimicry depends on whether it matches the receiver's percept of the model, and so has little in common with concepts of aesthetic judgement and 'beauty.' We report that during their song and dance displays, male superb lyrebirds (Menura novaehollandiae) create an elaborate acoustic illusion of a mixed-species mobbing flock. Acoustic analysis showed that males mimicked the mobbing alarm calls of multiple species calling together, enhancing the illusion by also vocally imitating the wingbeats of small birds. A playback experiment confirmed that this illusion was sufficient to fool avian receivers. Furthermore, males produced this mimicry only (1) when females attempted to exit male display arenas, and (2) during the lyrebirds' unusually long copulation, suggesting that the mimicry aims to prevent females from prematurely terminating these crucial sexual interactions. Such deceptive behavior by males should select for perceptual acuity in females, prompting an inter-sexual co-evolutionary arms race between male mimetic accuracy and discrimination by females. In this way the elaboration of the complex avian vocalizations we call 'song' could be driven by sexual conflict, rather than a female's preference for male extravagance.