Shiny Cowbird (Molothrus bonariensis) Science Article 9
Host selection by brood parasitic Shiny Cowbirds (Molothrus bonariensis) was studied at two sites in Buenos Aires Province, Argentina. The eggs of the parasite are either spotted or immaculate, so host selection was studied with respect to egg type as well as to site. Immaculate eggs were rare at both sites. Cowbirds in this region prefer to parasitizenests of birds larger than themselves. This preference contrasts with that of almost all other brood parasites, and even that of Shiny Cowbirds in other parts of the species’ range. One large species, the Chalk-browed Mockingbird (Mimus saturninus) was used frequently and consistently at both sites.
PAUL MASON, The Auk 103: 61-69