Parasitism of the black-crowned waxbill (Estrilda nonnula) by the pin-tailed whydah (Vidua macroura): Implications for host-specific adaptation by a generalist brood-parasite

In the African brood parasitic finches (Viduidae), complex nestling mouth markings have evolved to mimic those of their estrildid finch hosts, reducing the chances of detection or discrimination by host parents. Most Vidua species are highly host-specific whereas the Pin-tailed Whydah Vidua macroura is less so, potentially limiting its evolutionary potential for mimicry. Here we document parasitism of a novel host, the Black-crowned Waxbill (Estrilda nonnula), by the Pin-tailed Whydah. Of the 28 active Black-crowned Waxbill nests that we located in central Cameroon, six were parasitized by Pin-tailed Whydahs. Unlike the remarkable similarity of Pin-tailed Whydah nestling mouth markings to those of a previously described host in southern and central Africa, the Common Waxbill (Estrilda astrild), Pin-tailed Whydahs have mouth patterns that differ conspicuously from their Black-crowned Waxbill hosts in central Africa. Across its range, the Pin-tailed Whydah appears to be a generalist brood parasite of hosts in the genus Estrilda, but precise nestling mimicry is limited to particular species. The behavioral, ecological, and evolutionary mechanisms that allow different degrees of similarity to persist between Vidua and their hosts require further study.