<b>Allied male dolphins use synchronous displays to strengthen social bonds in a cooperative context (Data, R Code and Supplementary Videos)</b>

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.从萤火虫、招潮蟹、无尾两栖类到类人猿，动物界诸多类群的雄性个体均会在交配场景中展现同步行为。此类行为大多服务于求偶竞争，但仅有极少数物种会以协作模式同步完成信号发出动作。例如人类的同步互动便属于协作性同步：人际间的同步行为能够提升亲密度、协作能力与群体凝聚力。有趣的是，西澳大利亚鲨鱼湾的雄性印太瓶鼻海豚（Indo-Pacific bottlenose dolphin）所组成的多层级联盟，同样存在协作性同步行为。成年雄性会结成成对或三人组的联盟，协同驱赶单只处于发情期的雌性，在此过程中它们会展现出复杂的同步展示行为。这类展示包括围绕雌性同步转向、跃出水面以及多次浮出水面的动作环节，但目前其具体功能尚无定论。本研究借助搭载于无人机的视频素材，结合40年的行为学观测数据，探究了哪些社会因素会影响雄性海豚的同步展示行为表现。研究结果显示：雄性海豚在完成亲和性接触行为后，会进行时长更长的同步展示；而社会联结较弱的雄性个体之间，同步行为的精准度更高。结合该种群近期关于发声同步的研究成果，本研究证实雄性海豚会通过同步行为来维持并强化自身的社会联结。本研究结果表明，在层级嵌套的复杂社会系统中，海豚与人类殊途同归，均通过同步展示行为来维系多重社会联结。