INTRODUCTION

The study of vocal development in nonhuman animals has focused primarily on vocal production. However, vocal development involves not only production, but development of appropriate usage and appropriate responses to the calls of others. The relative neglect of usage and responses has led to a distorted view of vocal development as emphasized by Seyfarth & Cheney (Chapter 13) for monkeys and West et al. (Chapter 4) for birds. The argument is often made that nonhuman mammals differ fundamentally in vocal development from both birds and human beings but, as we have argued previously (Snowdon & Elowson 1992) and Seyfarth & Cheney (Chapter 13) argue, primates are similar to humans and birds if all three components of vocal development – production, usage and response – are evaluated.

In this chapter we argue that when functionally similar vocalizations are chosen from species that have similar social organization, then similar developmental processes will be found regardless of the taxon studied. We examine the idea that nonhuman primate vocal structures are fixed and review evidence that vocal plasticity may be quite common. We then provide three examples of phenomena from our research with marmosets and tamarins that illustrate how plasticity in pygmy marmoset trill vocalizations can be influenced by changes in social companions, how infant babbling in pygmy marmosets is a social interaction, and how the structure and usage of food-associated calls is acquired by cotton-top tamarins, and how social environments can inhibit the expression of these calls.