Scientists from The University of Western Australia, University of Zurich and the University of MA, studied 17 well-known adult male dolphins in Shark Bay, Western Australia, where males are known for their formation of alliances. These alliances come in the forms of duos and trios and will sometimes feature larger alliances with other groups of dolphins. Analysis determined that males in an alliance kept their distinct vocal labels, which suggests that these calls may serve a objective similar to an individual name.
It has been widely known since the 1960s that both male and female bottlenose dolphins have their signature whistles, but King discovered the calls were tailored to individual dolphins when she started playing the whistles back to the animals themselves.
While parrots, bats, elephants and primates are also known to make vocal calls, they are very similar to one another.
"With male bottlenose dolphins, it's the opposite-each male retains a unique call, even though they develop incredibly strong bonds with one another", King says.
Dolphins may be more akin to humans than believed, said a study released on Friday, confirming that the marine mammals use individual "names" to identify friends and rivals among social networks.
"Retaining individual names is more important than sharing calls as it allows dolphins to negotiate a complex social network of cooperative relationships", lead scientist Stephanie King said. In other words, dolphins that were related didn't necessarily have similar names. It's not clear if this behavior is restricted only to bottlenose dolphins.
After collecting the recordings, the team were able to determine the "names" or individual vocal label of each male.
Signature whistles of two different male dolphins from Shark Bay, Western Australia.
She also learned that the dolphins can mimic each other's whistles, seemingly to address or call out to one another. They then determined the individual vocal label used by individual males, and measured the similarity of those identity signals within and between alliances in order to determine whether males with stronger social relationships used vocal labels that were more alike.
So how do these males keep track of all these different relationships, and how do they maintain such strong social bonds?
For decades it was thought that male dolphins would converge onto a shared signature whistle when they formed alliances with one another. "The bottlenose dolphin is, so far, the best studied small dolphin species, but evidence suggests that other species, such as spotted dolphins and common dolphins, also have signature whistles".
Because there can be up to 14 males in these second-level alliances, King says the dolphins must constantly keep track of various relationships.
"This included petting, stroking and performing synchronous behaviours as an alternative means of advertising their strong social bonds", Dr King said.