Allied male dolphins use synchronous displays to strengthen social bonds in a cooperative context.

From fireflies to fiddler crabs and anurans to apes, males from across the animal kingdom perform synchronous displays in the mating context. Most do so in competition for mates, but few species synchronise signal production cooperatively. For example, synchrony in humans is cooperative; where interpersonal synchrony increases affiliation, cooperative ability, and group cohesion. Interestingly, multi-level alliances of male Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia, also engage in cooperative synchrony. Adult males form pairs or trios to cooperatively herd single oestrus females, during which males perform elaborate synchronous displays. These displays comprise synchronous turns, leaps, and surfacing bouts around the female, but the function remains equivocal. Here, we used drone mounted video coupled with 40 years of behavioural data to investigate what social factors influence the performance of these synchronous displays by male dolphins. We found that males perform synchronous displays for longer after engaging in affiliative contact behaviour, and that those with weaker social bonds engaged in more precise synchrony with each other. Aligning with recent research on vocal synchrony in this population, we provide evidence that male dolphins use synchrony to both maintain and strengthen their social bonds. These findings suggest that dolphins have converged with humans on the use of synchronous displays to sustain multiple social bonds in nested, complex social systems.