Lost calls vary with individual identity but not dominance rank in male white-faced capuchins (Cebus imitator)

Long-distance vocalizations are crucial for facilitating group coordination and maintaining social relationships in many primates by allowing individuals to exchange information when visual contact is limited. These signals may convey information about both individual identity and social status. We investigated whether lost calls, the primary long-distance contact call of white-faced capuchins ( Cebus imitator ), vary according to caller identity and male dominance rank (alpha vs. subordinate). We quantified multiple acoustic features from 749 lost calls recorded from 24 males and analyzed acoustic variation using permutation-based classification, Random Forest models, and linear mixed-effects analyses. Lost calls showed strong evidence of individual distinctiveness, with classification accuracy significantly above chance and several acoustic features exhibiting greater between-individual than within-individual variation. In contrast, we found little evidence of dominance-related acoustic variation. Multivariate classification of rank did not significantly exceed chance expectations, and univariate analyses revealed no significant differences in fundamental frequency or call duration, with only a modest difference in formant dispersion. These findings indicate that lost calls primarily reflect individual differences rather than dominance-related variation and suggest that receivers infer socially relevant information through individual recognition and prior social knowledge rather than direct acoustic cues to dominance rank. Our results support the importance of vocal individuality in facilitating long-distance communication in socially complex primates.