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.
Vocal precursors to adult song, typically called subsong and plastic song, occur in many songbirds but have been studied thoroughly in few species. The most extensive studies have focused on the structural organization of the sound and the nature of the ontogenetic mechanisms underlying transitions in vocal maturation (Marler & Peters, 1982a,b). Functional properties of precursors have typically not been studied.
Experimental tests of the functional properties of the adult songs developed by acoustically naive songbirds, songs often resembling vocal precursors in their impoverished species-specific detail, have typically been found to be inferior to