Allied male dolphins use vocal exchanges to “bond at a distance”

• Published in: Current biology 2022-04, Vol.32 (7), p.1657-1663.e4
• Main Authors: Chereskin, Emma, Connor, Richard C., Friedman, Whitney R., Jensen, Frants H., Allen, Simon J., Sørensen, Pernille M., Krützen, Michael, King, Stephanie L.
• Format: Article
• Language: English
• Subjects: alliances; Animals; Bottle-Nosed Dolphin; bottlenose dolphins; cooperation; Female; Grooming; Interpersonal Relations; Male; signature whistles; Social Behavior; social bonding hypothesis; vocal exchanges; Vocalization, Animal
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2022.02.019

Vocal interactions are intrinsic features of social groups and can play a pivotal role in social bonding.1,2 Dunbar’s social bonding hypothesis posits that vocal exchanges evolved to “groom at a distance” when social groups became too large or complex for individuals to devote time to physical bonding activities.1,3 Tests of this hypothesis in non-human primates, however, suggest that vocal exchanges occur between more strongly bonded individuals that engage in higher grooming rates4–7 and thus do not provide evidence for replacement of physical bonding. Here, we combine data on social bond strength, whistle exchange frequency, and affiliative contact behavior rates to test this hypothesis in wild male Indo-Pacific bottlenose dolphins, who form multi-level alliances that cooperate over access to females.8–10 We show that, although whistle exchanges are more likely to occur within the core alliance, they occur more frequently between those males that share weaker social bonds, i.e., between core allies that spend less time together, while the opposite occurs for affiliative physical contact behavior. This suggests that vocal exchanges function as a low-cost mechanism for male dolphins that spend less time in close proximity and engage in fewer affiliative contact behaviors to reinforce and maintain their valuable alliance relationships. Our findings provide new evidence outside of the primate lineage that vocal exchanges serve a bonding function and reveal that, as the social bonding hypothesis originally suggested, vocal exchanges can function as a replacement of physical bonding activities for individuals to maintain their important social relationships. •Allied males with weaker social bonds display higher whistle exchange rates•Allied males with stronger bonds display higher rates of affiliative contact•Whistle exchanges allow allies to maintain weaker yet vital social relationships•Multiple mechanisms are needed to service bonds in complex animal societies Vocal exchanges are posited to function as a replacement for physical bonding. Chereskin et al. show that, within dolphin alliances, strongly bonded allies engage in more affiliative contact behavior, while weakly bonded allies engage in more whistle exchanges. This illustrates that vocal exchanges can be used to maintain key social relationships.