Humans differ strikingly from other primates in the capacity for vocal learning. How and why such vocal flexibility evolved remains puzzling. Evidence of geographic variation in the pant-hoot calls of chimpanzees (Pan troglodytes) suggests that chimpanzees have some capacity for vocal learning, which is intriguing given the close phylogenetic relationship between humans and chimpanzees. Many questions remain, however, about the various factors that might contribute to variation in acoustic structure of pant-hoot calls, including body size, health, genetic relatedness, and within-individual variation. We are currently examining these factors in a study of longitudinal recordings from individuals in two neighboring chimpanzee communities in Gombe National Park, Tanzania. As in studies of sound change in human social groups, we need to understand the articulatory mechanisms that produce the vocalizations, to interpret acoustic variation against the backdrop of factors including body size, sex, and age. The same considerations in studies aimed at understanding the ontogeny of human vocalizations have prompted the development of age-specific articulatory synthesis models. We are adapting such models to design analysis-by-synthesis methods for our cross-population longitudinal study, and have organized this session to explore analogous methods for studying other vocalization types in chimpanzees and other non-human primate species.