Individuality in the vocalizations of adult and infant coppery titi monkeys (Plecturocebus cupreus

Abstract

Many primates use acoustic communication to maintain social relationships. Specifically, territorial, pair-bonding primates participate in coordinated vocal duets. Recognition of neighbors should be selected for, as identifying conspecifics may decrease the need for costly territorial behaviors. While similar species show vocal individuality, it is unknown if vocal individuality is innate or develops over time. To understand individuality across life stages, we analyzed 169 duet vocalizations from 30 adult titi monkeys (Plecturocebus cupreus) and 600 trills from 30 infants. We estimated 16 features of adult pulse-chirp vocalizations and 9 features of infant trills from spectrograms and used discriminant function analysis with leave-one-out cross-validation to classify individuals. We correctly classified adults with 83% accuracy and infants with 60% accuracy. We used a multi-variate variance components model to estimate how variance in features was partitioned within- and between-individuals. Between-individual variance was the greatest source of variance for all features for adults, and 4/5 features for infants. Despite little sex-specificity and high overlap between duetting adults, the pulse-chirp vocalization is individually distinct. Further, the trills of infants are individually distinct, though to a lesser degree than adults. This study provides evidence for vocal individuality at multiple life stages in a territorial primate.