Vocal mimicry of host fledglings by a specialist brood parasite: a counter-defense against host discrimination?

DE MÁRSICO, MARÍA C.; LAMA, FLORENCIA; GANTCHOFF, MARIELA G. ; REBOREDA, JUAN C.

Pirenópolis

Congreso; XXIV International Bioacoustics Congress; 2013

International Bioacoustics Council

Vocal mimicry of host fledglings by a specialist brood parasite: a counter-defense against host discrimination?  María C. De Mársico1,2, Florencia Lama1, Mariela G. Gantchoff1, Juan C. Reboreda1 1Departamento de Ecología, Genética y Evolución & IEGEBA-CONICET. Ciudad Universitaria, Pabellón II, Piso 4 (C1428EHA), Buenos Aires, Argentina. 2Corresponding author: de_marsico@ege.fcen.uba.ar   Obligate avian brood parasites lay their eggs in nests of individuals of other species (hosts) which rear the parasitic offspring at the expense of their own reproductive success. In response to fitness losses, hosts may evolve defenses against parasitism which may, in turn, favour the evolution of counter-defenses in parasite populations. The screaming cowbird (Molothrus rufoaxillaris) is a South American specialist brood parasite that uses primarily a single host, the baywing (Agelaioides badius). Screaming cowbird fledglings are indistinguishable from baywings in plumage color, which has been suggested as a case of evolved mimicry in response to host discrimination against dissimilar young. We investigated whether host mimicry by screaming cowbirds extends to vocal cues. During the 2009-2010 breeding season we recorded the begging calls of 13 baywing, 13 screaming cowbird and 20 ?non-mimetic? shiny cowbird (M. bonariensis) fledglings and quantified the similarity among species in six call parameters (minimum and maximum frequency, bandwidth, peak frequency, number of syllables and call duration). A discriminant function analysis better distinguished between shiny cowbirds and the other two species than between baywings and screaming cowbirds. Call duration and number of syllables separated shiny cowbirds from the others, whereas peak frequency separated baywings from screaming cowbirds. In 2012 we conducted a field experiment in which we broadcast calls of baywing, screaming cowbird and shiny cowbird fledglings at 15 active baywing nests by the end of the nestling stage. Baywings responded more strongly to ?mimetic? than ?non-mimetic? calls, as expressed by significantly shorter response latencies, more time spent close to the speaker and more adults responding when broadcasting conspecific and screaming cowbird calls than shiny cowbird calls. Our results support the occurrence of vocal mimicry of baywing fledglings by screaming cowbirds and highlight its adaptive role in driving host attention towards parasitic young after leaving the nest.   Financial Support: ANPCyT, Universidad de Buenos Aires