Male dolphins have incredibly complex friendship groups

Dolphins have captured our imaginations for decades thanks to their acrobatics, cheerful and charismatic faces and intelligence. Researchers are now gaining even more knowledge in their complex social networks.

A document published yesterday in Proceedings of the National Academy of Sciences (PNAS) claims that male puffins form the largest known multilevel alliance network outside of humans. Humans form alliances for a variety of strategic reasons (economic, social, political, etc.), and dolphins appear to form similar complex strategic relationships among themselves. The international team of scientists says these cooperative relationships between groups increase men’s access to a contested resource: female mates.

Researchers from the University of Bristol, the University of Zurich and the University of Massachusetts looked at data on association and copulation (or short-term mating relationships) to model the structure of unions among 121 adult male Indo-Pacific killer whales in Shark Bay. The bay is a UNESCO World Heritage Site in the Gascoigne region of Western Australia and has a number of “outstanding natural features, including one of the largest and most diverse seagrass beds in the world,” according to UNESCO.

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The team found that male dolphins in the bay form first-order alliances of two to three males to jointly pursue these short-term mating relationships with individual females. Second-order unions of four to 14 unrelated males compete with other groups for access to female dolphins. Third-order alliances arise between cooperating second-order alliances.

By the late 1980s, the team had already discovered that adult male dolphins swim around in pairs and trios, cooperating to “herd” single females ready to conceive. They were the first to witness two pods cooperating to attack another group of dolphins, showing that just like humans, dolphins have cliques within larger alliances.

“Cooperation between allies is widespread in human societies and is one of the hallmarks of our success,” said co-author Stephanie King, associate professor of biological sciences at the University of Bristol, in a press release. “Our capacity to build strategic cooperative relationships at multiple social levels, such as trade or military alliances both nationally and internationally, was once thought to be unique to our species. We not only showed that male puffins form the largest known multilevel alliance network outside of humans, but also that cooperative relationships between groups, rather than simply alliance size, allow males to spend more time with females, thus increasing their reproductive success.

A study published in 2021 showed that male dolphins responded strongly to all allies who had consistently helped them in the past, even if they were not currently close friends. Furthermore, they did not react strongly to men who had not consistently helped in the past, even if they were currently friends. This indicates that these dolphins form social concepts of “team membership,” organizing allies according to a shared history of cooperation.

[Related: Five animals that can sense things you can’t.]

Intergroup cooperation in humans is thought to be unique and dependent on the evolution of pair bonds and male parental care. These are the other two characteristics that distinguish humans from our common ancestor with chimpanzees. “Our results show that intergroup alliances can arise without these features, from a social and mating system that is more similar to the chimpanzee,” said co-author Richard Connor, a professor emeritus at the University of Massachusetts who is now affiliated with the International University of Florida.

This research builds on exactly 40 years of studying Shark Bay dolphins and the 30th anniversary of the publication of the team’s discovery of two levels of male union formation.

“It is rare that a non-primate study is conducted by an anthropology department,” Michael Kreutzen, study author and head of the Institute of Anthropology at the University of Zurich, said in the release. “But our study shows that important insights into the evolution of features previously thought to be uniquely human can be gained by studying other highly social, large-brained taxa.”

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