Are dolphins modulating whistles in interspecific group contexts?

Cetaceans depend highly on acoustic signals, such as whistles, for social communication. Mixed-species associations (MSAs), temporary or long-term encounters between different species, may play an important role on the acoustic dynamics of the species involved. Because of whistles’ communication function, we used these sounds to investigate the acoustic relationships of Tursiops truncatus when involved in different group contexts: in MSAs with two other delphinid species and in single species group. Acoustic recordings of T. truncatus single species groups and in associations with Globicephala melas and Grampus griseus were collected in the Western South Atlantic Ocean through a towed array of hydrophones. A total of 1267 whistles were analysed and acoustical parameters were extracted. To verify the differences among whistles produced in such contexts a support vector machine and random forest analysis were implemented. Both analyses revealed a clear separation of whistles from the single species versus the MSA as well as between both MSAs. The results indicate that interspecific associations may influence the whistle structure and suggests that T. truncatus whistles can be modified during interspecific interactions. These findings are useful to elucidate the possible factors underlying behavioural plasticity and interspecific associations and to understand dolphins’ acoustic communication.