Interspecific sociality shapes whistle repertoire diversity and plasticity in sympatric dolphins

Animal communication is shaped by the need to share information. While intraspecies communication has been widely studied, interspecies communication remains poorly understood. Among social mammals, dolphins use complex, structured vocal signals that are both vertically and horizontally transmitted. They also form single-species groups (SSGs) and mixed-species groups (MSGs), offering an opportunity to explore acoustic repertoire across social contexts. We investigated whistle diversity in Guiana (Sotalia guianensis) and bottlenose (Tursiops truncatus) dolphins using unsupervised (PCA, ARTwarp) and supervised (Random Forest) machine learning. We compared sympatric SSGs and MSGs in Costa Rica with allopatric SSGs in Panama and Brazil. MSGs exhibited greater whistle diversity than SSGs, and their whistles were more acoustically similar than expected from random combinations of allopatric repertoires. Random Forest models trained on single-species data performed poorly when classifying MSG whistles, suggesting a reduction in species-specific acoustic identity. Because MSGs involve stable, cooperative associations, they may act as socially and acoustically integrated communities where selective pressure favors vocal convergence via social learning or signal matching. These findingsshow that dolphin vocal production is socially plastic and that prolonged interspecific sociality can drive convergence in learned signals—supporting vocal convergence in cetaceans and following patterns observed in birds and primates.