New research finds that dolphins form social bonds over a decade and cooperate among groups to help each other find mates and fight rivals – a behavior that has not previously been confirmed among animals.
“These dolphins have stable, long-term alliances, and they have alliances between groups. Alliances are alliances, really.” Dr. Richard Connor, a behavioral ecologist at the University of Massachusetts Dartmouth and one of the paper’s lead authors. “But before our study, cooperative alliances between groups were thought to be unique to humans.”
The the findings, published Monday in the Proceedings of the National Academy of Sciences, appears to support the “social brain” hypothesis: that mammalian brains evolved to be larger in size relative to animals that track their social interactions and networks. Humans and dolphins are two animals with the largest brains in relation to body size. “It’s not a coincidence,” Connor said.
Connor’s team of researchers collected data between 2001 and 2006 by conducting extensive boat surveys in Shark Bay, Western Australia. The researchers tracked the dolphins by watching and listening to them, using unique identifying whistles to tell them apart.
Note 202 Indo-Pacific bottlenose dolphins (Tursiops aduncus), including during the peak mating season between September and November.
Back in the lab, they bored into data that focused on 121 adult male dolphins to observe patterns in their social networks. And over the next decade, they continued to analyze animal alliances.
The social structures of dolphins are flexible and complex. Researchers have found alliances between two or three male dolphins – like best friends. The groups then expanded to 14 members. Together, they helped each other find females to herd and mate with, and also helped steal females from other dolphins as well as defend against any attempts to “steal” from competitors.
“What happens as a male, you might be in a trio, grazing a female. And if someone comes to take that female, then the other males on your team and your second-rate alliance come in and help you,” he said. Dr. Stephanie King, Professor of Animal Behavior at the University of Bristol and one of the study’s authors. “These guys have a very clear idea of who’s on their team.”
These teams can last for decades and form when dolphins are still young, King said, although they don’t tend to reap the fruits of parenthood until their mid-teens. “It’s an important investment that starts when they are very young — and these relationships can last their entire lives.”
Sometimes, especially when groups of dolphins feel there is a danger to themselves, two second-tier alliances will band together to form a larger team. As a result, of the dolphins observed by scientists, each male was directly related to between 22 and 50 other dolphins.
The researchers’ observations show that in these groups, the tighter the gang – and the stronger the bonds between the dolphins – the more successful they are at attracting females.
King said it is their cooperative relationships, not alliance size, that give males greater reproductive success.
He said it is already widely known that dolphins are very social and cooperative, as well as being remarkably good at adapting and teaching behavior specific to their environment. Stephanie Finn Watsonformer director of translational medicine and research at the National Marine Mammal Foundation in San Diego, California, who was not involved in the study.
“The possibility that other cetaceans will develop similar alliances cannot be ruled out,” said Finn Watson. “These complex behaviors are likely limited to large-brained mammals.”
According to the researchers behind the paper, this is the only non-human example of these types of multi-level strategic alliances that has been observed. These findings also highlight the cognitive demands these animals face, Connor said, suggesting that dolphins’ large brains help them track different relationships.
“I would say dolphins and humans converged in the evolution of alliances between groups – an incredibly complex social system,” Connor said. “It’s amazing because we’re so different from dolphins.”
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