Dolphins form social bonds for decades, cooperating among and between cliques to help one another find mates and fend off competitors, new research has found — behavior previously unconfirmed in animals.
“These dolphins have long-term stable alliances and they have alliances between groups. Alliances of alliances of alliances, really,” he said dr Richard Connor, behavioral ecologist at the University of Massachusetts Dartmouth and one of the lead authors of the publication. “But prior to our study, cooperative alliances between groups were thought to be unique to humans.”
That Results, published Monday in the journal Proceedings of the National Academy of Sciences, appear to support the “social brain” hypothesis: that mammalian brains have evolved to a larger scale for animals tracking their social interactions and networks . Humans and dolphins are the two animals with the largest brains in relation to body size. “That’s no coincidence,” said Connor.
Connor’s research team collected data between 2001 and 2006 by conducting intensive boat surveys in Shark Bay, Western Australia. The researchers tracked the dolphins by watching and listening to them and used their unique identification whistles to tell them apart.
They watched 202 Bottlenose dolphins in the Indo-Pacific (Tursiops aduncus), also during the main mating season between September and November.
Back in the lab, they pored over data focused on 121 of these adult male dolphins to observe patterns in their social networks. And for the next decade they continued to analyze animal alliances.
Dolphin social structures are fluid and complex. The researchers found alliances between two or three male dolphins – like best friends. Then the groups expanded to up to 14 members. Together, they helped each other find females for herding and mating, and they helped steal females from other dolphins and defend against “stealing” attempts by rivals.
“What happens as a male may be a trio herding a female. And if someone comes to take that woman, the other men on your team and your second-order alliance will come and help you,” he said dr Stephanie King, Professor of Animal Behavior at Bristol University and one of the authors of the study. “These men have a very, very clear idea of who is on their team.”
These teams can last for decades and are formed when the dolphins are young, though they typically don’t reap the rewards of fatherhood until their mid-teens, King said. “It’s a significant investment that starts at a young age — and those relationships can last a lifetime.”
Sometimes, especially when groups of dolphins feel threatened, two second-order alliances join together to form a larger team. As a result, among the dolphins observed by the scientists, each male was directly linked to 22 to 50 other dolphins.
The researchers’ observations show that in these groups, the more successful it is at attracting females, the closer the clique – and the stronger the bonds between the dolphins.
It’s their cooperative relationships, rather than the size of the alliances, that make males more successful at breeding, King said.
It’s already well known that dolphins are very social and cooperative, and are remarkably good at adapting to their environment and teaching their behavior, she said Stephanie Venn Watsonformer Director of Translational Medicine and Research at the National Marine Mammal Foundation in San Diego, California, who was not involved with the study.
“One wouldn’t rule out the possibility that other whales might develop similar alliances,” Venn-Watson said. “These complex behaviors will likely be limited to large-brained mammals.”
According to the researchers behind the paper, this is the only non-human example of this type of multi-level strategic alliance that has been observed. But these results also underscore the cognitive demands these animals face, suggesting that dolphins’ large brains help them keep track of the various relationships, Connor said.
“I would say that dolphins and humans have converged in the evolution of intergroup alliances – an incredibly complex social system,” said Connor. “And it’s amazing because we’re so different from dolphins.”