Vocally mediated coordination during a cooperative task in parrots

Studying vocal coordination in a cooperative setting provides insights into how animals process social information, coordinate their actions, and make decisions in complex social settings. It can also reveal how animals use vocal signals to navigate complex social interactions that might not be apparent in solitary or non-cooperative contexts. To our knowledge, experimental evidence for intentional vocal communication in controlled experiments has been demonstrated only in dolphins. Here, we investigate whether peach-fronted conures (Eupsittula aurea) can use vocal communication to coordinate behaviour in a cooperative task. We chose parrots due to their complex social systems, their vocal learning and mimicry skills, and their advanced cognitive abilities. We tested four individuals pairwise in all combinations in the loose string paradigm, which requires synchronization of the two individuals to retrieve a food reward by simultaneously pulling a string. To verify that the parrots used vocal communication to solve the task, we tested them first under three control conditions where visual information and simple behaviour sufficed to solve the tasks. We then compared their vocal behaviour in the control conditions with their vocal behaviour in a task without visual information. During performance of the latter task, the birds demonstrated significantly higher call rates and variability and specific associations between call types and trial outcome compared to the control conditions. After the performance of the task, the birds used vocal convergence more often after failed trials, potentially as a reconciliation mechanism. Our results indicate that peach-fronted conures can use vocalizations to coordinate the solving of a cooperative task, and that vocal convergence may serve as a bonding mechanism following unsuccessful cooperative efforts.