Filling in the gaps: Acoustic gradation increases in the vocal ontogeny of chimpanzees ( <i>Pan troglodytes</i> )

Human vocal ontogeny is considered to be a process whereby large repertoire of discrete sounds seemingly emerges from smaller number acoustically graded vocalizations. While adult chimpanzee behavior highly graded, its developmental trajectory poorly understood. In the present study, we therefore examined size and structure at different stages ontogeny. Audio recordings were collected on infant (N = 13) juvenile semi-wild chimpanzees Chimfunshi Wildlife Orphanage, Zambia, using focal ad libitum sampling. All observed call types measured. These predominantly grunts, whimpers, laughs, screams, hoos, barks squeaks. A range spectral temporal acoustic parameters extracted, fuzzy c-means clustering was used quantify repertoire. The repertoires both best described with same clusters. However, compared infants, clusters less distinct one another could extracted only when low level overlap between permitted. Moreover, significantly higher for juveniles. Overall, this pattern shows greater in vocalizations suggesting trend toward increased gradation This may imply contrast humans, become increasingly proficient signals effectively rather than developing larger more