Brood Parasitism of the Shiny Cowbird, Molothrus bonariensis on Chestnut-Capped Blackbird Agelaius ruficapillus, in Eastern Buenos Aires Province

Abstract

Information about brood parasitism of the Shiny Cowbird on the Chestnut-Capped Blackbird in E Argentina is very scarce. Data of 29 active nests of this blackbird from 3 localities of E Buenos Aires province (Bernal, Hudson and General Lavalle), were studied. Ten of these nests were parasitized (34.5 %), suggesting a considerable incidence of parasitism. An adverse effect over the Chestnut-capped Blackbird brood was detected through a lower number of host eggs and chicks in parasitized nests. A revision of available data is presented and results are compared with those from other authors.