Many animals live in groups, characterised by frequent changes in size and composition due to fission and fusions of subgroups. Such fission-fusion dynamics are hypothesised to have important implications for the evolution of several aspects of social behaviour, including communication. This thesis investigated the interplay between flock social behaviour and vocal communication in two species of parrots, the orange-fronted (Eupsittula canicularis) and peach-fronted conure (Eupsittula aurea). More specifically, it investigated three aspects of the interplay between contact call matching by imitation and fission and fusion decisions. Firstly, it investigated how contact call matching by imitation affected the ability of individuals to be vocally recognisable, demonstrating reliable individual signatures in contact calls - a prerequisite for individual vocal recognition using contact calls. Secondly, it investigated the potential for unintended receivers to eavesdrop on contact call interactions, demonstrating the possible utilisation of social information about vocal matching behaviour (matching or being matched) in the flock fusion decisions of wild orange-fronted conure flocks. Finally, it investigated how wild orange-fronted conures mediated these flock decisions, demonstrating a potential communicative mechanism for facilitating fissions and fusions. Overall, this thesis provides new insight into the interplay between flock social behaviour and vocal communication in orange-fronted and peachfronted conures, emphasising the importance of contact call matching by imitation in their flock dynamics.