Researchers from The University of Western Australia have discovered male bottlenose dolphins can retain individual vocal labels, or “names”, to help recognise friends and rivals in their social network, much like humans.
The discovery paints a picture of the social intelligence of dolphins whereby no other non-human animals have been found to retain an individual “name” when they form long-term cooperative partnerships with one another.
Scientists from The University of Western Australia, University of Zurich and the University of Massachusetts, studied 17 well-known adult male dolphins in Shark Bay, Western Australia, where males are known for their formation of alliances. These bonds are as strong as those between mothers and calves and the friendships can last entire lifetimes.
Researchers collected recordings of the dolphins’ vocalisations using underwater microphones and determined the individual vocal label of each male. They then measured the similarity of these identity signals within and between other alliances to see whether males that had stronger social relationships had unique vocal labels or not.
Dr Stephanie King, from UWA Centre for Evolutionary Biology, said they discovered male dolphins retain individual vocal labels that allow them to track their cooperative partners, their competitors and help form fascinating multi-level alliances.
“This is an unusual finding as it is very common for pairs or groups of animals to make their calls more similar when they share strong social bonds. This can be seen in some parrots, bats, elephants and primates, and represents a means of advertising the strength of their relationships and their group membership” Dr King said.
“However with male bottlenose dolphins, it’s the opposite – each male retains a unique call, even though they develop incredibly strong bonds with one another.”
Previous research has shown vocal labels are similar to human names where dolphins use them to introduce themselves or even copy others as a means of addressing specific individuals.
Dr King said these “names” help males keep track of their many different relationships; who their friends are, who are their friends’ friends, and who are their competitors.
“Retaining individual names is more important than sharing calls as it allows dolphins to negotiate a complex social network of cooperative relationships. This formation of alliances within alliances is very unique and it’s the only example we have in the animal kingdom outside of humans. ”
Researchers also observed how male dolphins used physical contact to strengthen their relationships with one another.
“This included petting, stroking and performing synchronous behaviours as an alternative means of advertising their strong social bonds,” Dr King said.
“The next step will be to study the males’ relationships with one another more closely. It will be interesting to reveal whether all cooperative relationships within alliances are equal or not. This will further our understanding of the political landscape of dolphin alliances in Shark Bay.”
The study is published in Current Biology and supported by grants from the National Geographic Society, the Swiss National Science Foundation and The Branco Weiss Fellowship.