Development of vocal production in bearded capuchin monkeys: is there space for vocal learning?

Abstract

Abstract In contrast to language acquisition by humans, in non-human primates vocal production seems independent of learning, with subtle modification related to body growth. Recently, studies showed that changes in the acoustic parameters of some primates calls are influenced by calls of conspecifics. This can be considered a simple form of vocal production learning. In this paper, we investigated the vocal development of bearded capuchin monkeys to understand whether the calls changes along the development and if these modifications are influenced by experience or by body growth alone. Immatures between 1–36 months old were followed and the calls emitted by them were recorded. We analyzed acoustically six vocalizations (CN, chihui, hip, trill, squeal, WS). The six vocalizations did not become more stereotyped over the course of development, but CN, chihui, trill, squeal, and WS had acoustic changes throughout the development. CN and chihui, two low frequency gradual calls, developed faster. The development of chihui was not explained by the body growth and it is possible it develops from CN, another gradual call. CN, trill, squeal and WS had acoustic changes related to body growth. Hip was the only vocalization not explained by the development. This vocalization is emitted in several stressful situations and the acoustic changes could be influenced by internal state of the caller. We conclude vocalizations of bearded capuchin monkeys change with body growth but the acoustic structure and function of the call affect the course of vocal development.