Preliminary evidence for signature and copied whistles among spinner dolphins in the Southwest Atlantic Ocean: Beacon purpose?

In order to evaluate strategies of cohesion in a fission-fusion society, the occurrence of signature and copied whistles were investigated in free-ranging spinner dolphins, Stenella longirostris. Through an one-element hydrophone array towed over the Brazilian continental shelf break, a group of approximate 400 dolphins were recorded at 96 kHz/24 bits while navigating. The preliminary results demonstrated 218 similar signals that fit into previous definitions of signature or copied whistles. These whistles were produced in bouts with an inter-whistle interval of 0.066—11.56 s (mean ± SD: 2.66 ± 2.72) that varied from 2 to 32 repetitions comprising six different contour shapes. Thus, these data support previous hypothesis that these signals are important units in the dolphin’s repertoire. It may also suggests a potential use on individual direction and localization, where repeated contours could be acting as a beacon to direct and locate the animals within the group. Additional research to ascertain the natural function of these vocalizations may clarify the basis for acoustic badges of membership and group organization of this cosmopolitan species.