Vocal trickery allows specialist screaming cowbird juveniles to escape host discrimination after leaving the nest

LAMA, F.; URSINO, C.A.; REBOREDA, J. C.; DE MÁRSICO, M.C.

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY

SPRINGER

Lugar: Berlin; Año: 2022 vol. 76

0340-5443

Agonistic interactions between obligate avian brood parasites and their hosts can lead to the coevolution at any stage of the nesting cycle, yet adaptations and counter-adaptations at the fledgling stage are poorly known. Young of the host-specialist screaming cowbird (Molothrus rufoaxillaris) closely resemble those of its greyish baywing (Agelaioides badius) host in appearance and begging calls. This overall similarity has shown to be adaptive to escape host discrimination after leaving the nest, but the role of acoustic signals in host deception remained unclear. We examined whether baywing parents are able to distinguish between begging calls of mimetic and non-mimetic fledglings and whether screaming cowbirds can trick host parents by vocally resembling host young. We conducted a field playback experiment using fledgling calls of screaming cowbird (mimetic), shiny cowbird (M. bonariensis; non-mimetic) and baywing (conspecific control) in the absence of any visual stimuli. Baywings were significantly less responsive to non-mimetic shiny cowbird calls than to the other call types and more responsive to screaming cowbird calls than to conspecific calls. The results support the idea that baywings cue in on species-specific acoustic signals for fledgling recognition and that vocal similarity to host young in screaming cowbirds plays a role in host deception. The observed host preference for screaming cowbird over conspecific calls further suggests that vocal mimicry in brood parasites could be reinforced by the expression of acoustic features that either act as a supernormal stimulus or exploit host?s pre-existing sensory biases.