Whistle convergence among allied male bottlenose dolphins (Delphinidae, Tursiops sp.)

Dolphins are adept at learning new vocalizations (whistles) throughout life , an ability thus far demonstrated in few nonhuman mammals. In dolphins, th is ability is well documented in captivity but poorly studied in the wild, and little is known of its role in natural social behavior. This study docu ments the previously unknown phenomenon of whistle convergence among habitu ated free-living male bottlenose dolphins (Tursiops sp.). Over a 4 yr study period. three male subjects formed an alliance, spending most of their tim e together and cooperating to herd females. Within individuals, whistle rep ertoires were more variable than expected based on previous studies, mostly performed with captive dolphins, but became less so during the course of t he study. Among individuals, the distinctiveness of individual repertoires decreased such that the three males were virtually indistinguishable by the end of the study. Initially, some whistle types were shared. By the end of the study, the three males had formed a close alliance, and had all conver ged on one particular shared whistle form which they had rarely produced be fore forming the alliance. The results are discussed in terms of their impl ications for the prevailing 'signature whistle' hypothesis, as well as poss ible mechanisms and functional significance of whistle convergence among co operating males.