Acoustic Changes in Marmoset Monkey Parental Contact Calls

Abstract

The importance of contingent vocal feedback in vocal development has been demonstrated in humans, zebra finches, and marmoset monkeys. However, the precise role of parental vocal feedback in marmoset monkey vocal development remains unknown. Previous studies examined only the acoustic changes in infant vocalizations over development, ignoring potential acoustic changes in parental vocalizations. In this study, we tracked the vocalizations of infant marmoset monkeys (Callithrix jacchus, n = 10) from the first postnatal day (P1) until they produced mature, adult-like calls two months later (P60). We also tracked the vocalizations of the mother and father marmosets (females: n = 3; males: n = 3) throughout the infants’ vocal development. Both the infant and parent marmoset vocalizations changed throughout development. A linear mixed effects regression analysis revealed that the infants’ and fathers’ acoustic parameters were positively correlated, indicating that the fathers’ vocalizations acoustically changed as infant vocalizations developed into more mature “phee” calls. Interestingly, the infant and parent calls did not converge throughout development, but the infant calls did increase in similarity to the initial parent acoustics. These results suggest that marmoset monkey parents, particularly fathers, employ a form of “parentese,” acoustically exaggerating their vocal feedback to drive infant vocal development. This study provides evolutionary insights into the acoustic changes that parental vocalizations undergo when parents interact with developing infants.