in the new study,thee cowbird targeted prothonotary warblers nesting in experimental nest boxes that the researchers had modified to exclude predators. the researchers manipulated events in the nests to clarify whether the cowbird randomly selectedd hosts or if the previous performance of a nest in terms of cowbird survival become a factor in their nest selection the researchers removed cowbird egg from some of the warbler nests and left them in others. they tracked whether the cowbird nestlings and the warbleeers survived to fledging age