There is evidence of changes in the vocal structure of song birds and monkey calls in response to modifications of the social group composition. Nevertheless, the rapidity and significance of such changes has been rarely investigated. In the present study, we investigated the vocal responses of captive bottlenose dolphins (Tursiops truncatus) to strong modifications of their environmental and social situation. We followed individuals (3 males and 2 females) originating from 2 different and distant groups before and after their grouping, as well as during capture. Clear differences occurred between the pre- and post-grouping contexts with changes in whistle repertoires as revealed by the emergence of new whistle types. Moreover, the capture appeared as a very particular situation. First, whistle types that were not found before and after capture appeared in that context. Second, even common whistle types that were produced in all contexts, showed changes in their acoustic structure at the time of capture (8 of 11 parameters measured). Vocal changes may therefore be reliable indications of stress. These results suggest new lines of research about the significance of vocal changes to evaluate animal states and social bonds’ creation.