Not only do dolphins have wingmen, but they form the largest complex social networks of any non-human animal, according to a new study published Monday in the Proceedings of the National Academy of Sciences.
Researchers have been studying the relationships between Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Western Australia’s Shark Bay since the early 1980s. In the new paper, they looked at the social networks of 121 of these adult male dolphins between 2001 and 2006, relying on the animals’ unique whistles to distinguish them from one another. The researchers found that each male had a direct link to 22 other males on average and was at least indirectly connected to all 120 of the others, writes Science’s Virginia Morell.
Previous studies had shown that male bottlenose dolphins use social connections to increase the likelihood of finding a mate, per Science. But the new paper provides a more complete picture of how the marine mammals use these networks.
“These males have a very, very clear idea of who is in their team,” Stephanie King, a co-author of the study and behavioral biologist at the University of Bristol in England, tells the Guardian’s Sofia Quaglia.
The male dolphins work in groups to find partners to herd and mate with, and they also collaborate to defend against others looking to take the females, writes the Guardian.
Here's how they do it: Each male dolphin belongs to a small group of “close friends,” perhaps two to three animals total. They look for mates together, and when they need backup, a second group of allies joins in, which brings the social circle to as many as 14 males. Sometimes, two groups of these second-order alliances may unite against a common threat—expanding a single dolphin’s alliance network to something between 22 and 50 others, per the Guardian. And these relationships can last for decades.
Richard Wrangham, a Harvard University primatologist who did not contribute to the research, likens the role of a dolphin in such a three-tiered network to being a member of “a platoon, a company and a regiment,” per Science.
The stronger the bonds between the dolphins, the more success they had in mating, writes the Guardian. More than the sheer number of connections, the strength of a dolphin’s network led to its breeding success, King says in a press release.
While other non-human animals cooperate, none of them form “multilevel alliances to accomplish goals,” Athena Aktipis, a cooperation theorist at Arizona State University who was not involved with the paper, tells Science. “It’s interesting and cool that the dolphins do.”
The research seems to support an idea called the “social brain” hypothesis—that some mammals evolved larger brains for navigating social networks, per the Guardian. Bottlenose dolphins are “a dramatic demonstration of the positive correlation between brain size and social complexity,” Wrangham tells Science.
“It’s not a coincidence” that humans and dolphins are the animals with the largest brains compared to the size of their bodies, Richard Connor, the paper’s first author and a behavioral ecologist with Florida International University, tells the Guardian.
While both humans and dolphins have extensive social networks, they seem to have evolved in different ways, according to Science. Researchers think that humans have intergroup cooperation because of our long-term partnerships in which males help raise offspring. In this way, each partner’s relatives expand the pair's social circle by taking an interest in raising their children. But dolphin males don’t help raise young, which shows that their social structure evolved for another reason, per Science.
“I would say that dolphins and humans have converged in the evolution of between-group alliances,” Connor tells the Guardian.
Mauricio Cantor, a behavioral ecologist at Oregon State University who did not contribute to the paper, tells Science that this new research “helps bridge the immense, perceived gap between humans and other animals.”