The Shiny Cowbird (Molothrus bonariensis) is a generalist brood parasite known to have parasitized more than 200 species, many of which are able to rear cowbird young. Here I provide new records of Shiny Cowbird parasitism on three globally threatened birds from the Pampas of South America: Black-and-white Monjita (Xolmis dominicanus; vulnerable), Pampas Meadowlark (Sturnella defilippii; vulnerable), and Yellow Cardinal (Gubernatrix cristata; endangered). Cowbirds parasitized 24 out of 32 monjita nests, four out of 17 cardinal nests and three out of 169 meadowlark nests. These are the largest nest samples reported for the monjita and for the meadowlark, documented detailed parasitism records were lacking until now. In the case of the cardinal, data reported here complement information recently obtained in northeastern Argentina. Although habitat loss and illegal trapping may represent more important threats than brood parasitism, more studies are needed in order to establish the impact of brood parasitism on the fragmented and declining populations of these threatened Pampas passerines.