Vocalizations of juvenile cowbirds (Molothrus ater ater) evoke copulatory responses from females.

The functional attributes of the vocalizations produced by young male cowbirds during their first fall and winter, termed "vocal precursors," were tested by playing the sounds back to female cowbirds. Five classes of vocalizations were tested: subsong, plastic, formatted, and stereotyped song, and songs of nonconspecifics. Females responded selectively to the four classes of cowbird vocalizations. Stereotyped songs evoked the most responding but the key eliciting element was the inclusion of note clusters, which first occurred in plastic song. The data suggest that juvenile cowbirds possess vocalizations capable of evoking biologically relevant responses from companions early in development.