Host provisioning behavior favors mimetic begging calls in a brood-parasitic cowbird

The vocalizations of some young brood-parasitic birds closely resemble those of their host’s young. Such similarities might arise because hosts bestow the greatest parental care in response to their own species’ call type. We used a playback experiment to assess the effectiveness of the nestling call structures of two brood parasites, the specialist screaming cowbird (Molothrus rufoaxillaris) and the generalist shiny cowbird (M. bonariensis), in stimulating parental provisioning in a shared host, the baywing (Agelaioides badius). Screaming cowbird begging calls closely resemble those of baywing young and thus should best exploit any bias for species-specific cues. Shiny cowbird calls, in contrast, are unlike baywings but can instead exploit non-specific sensory biases for long call duration and syllable repetition. We found playback of screaming cowbird’s mimetic calls elicited increases in feeding rates equivalent to those of playback of the host’s own young, while shiny cowbird calls ...