Males make these calls to get in touch with less close group members, as a substitute for physical contact.
Considered one of the most intelligent animals, dolphins maintain complex social networks, talk to each other and even call each other by their ‘name’. Bottlenose males use physical contact, such as gentle petting, to reinforce bonding with group members with whom they have strong ties. However, to address those less close they use whistles. The new findings, published in Current Biology, show how these calls, which require less time and effort, can be vital for bringing large groups together.
An international team of scientists used nine years of behavioral and acoustic data from a population of dolphins in Shark Bay, Western Australia, to assess how males reinforced and maintained their valuable alliances.
“Many animals, including humans, use tactile contact to strengthen and reaffirm important relationships. But as the number of close social relationships increases, so do the demands on the time and space available for relationship maintenance through physical contact,” explains Emma Chereskin, from the School of Biological Sciences. “Male bottlenose dolphins form multi-level strategic alliances, and we wanted to know how they maintain multi-alliance relationships in large groups,” she says.
By following pods of dolphins and documenting their physical and acoustic behavior, the research team was able to identify the different ways males bonded with one another.
“We found that within core dolphin alliances, strongly linked allies engaged in more affiliative contact behavior, such as petting and rubbing, while weakly linked allies engaged in more hissing exchanges. This illustrates that these weaker but still key social relationships can be maintained with vocal exchanges,” says Stephanie King, also from Bristol.
The social link
In the social bond hypothesis, British anthropologist and evolutionary biologist Robin Dunbar posited that vocalizations and language evolved as a form of ‘vocal grooming’ to replace physical grooming, as ever-larger groups placed impossible demands on the environment. time available for physical contact behaviors. However, tests of this hypothesis in nonhuman primates suggest that vocal exchanges occur between individuals with stronger bonds who engage in higher rates of grooming, and thus provide no evidence for physical bond replacement.
“Our findings provide new evidence that vocal exchanges may serve a bonding function, ” says Chereskin, “but more importantly, and in line with the social bonding hypothesis, that vocal exchanges may function as a replacement for physical bonding, allowing allied male dolphins to bond over a distance.” In his opinion, “this evidence in support of the hypothesis of social bonding outside the primate lineage raises new and exciting questions about the origins and evolution of language in all taxa.”
