Humans are not the only animals to give each other names, suggests new research on dolphin communication.
Researchers have found that wild bottlenose dolphins call back to a recorded copy of their own signature whistle, in effect answering to their own names. This finding joins accumulating and compelling evidence that humans might not have a monopoly on learned vocal labeling, the ability to pair acoustic signals with specific objects.
“Our results present the first case of naming in mammals, providing a clear parallel between dolphin and human communication,” said Stephanie King, a marine biologist at University of St Andrews and co-author on the study, published in Proceedings of the National Academy of Sciences. “It’s now clear that signature whistles have meaning in that they are labels for particular individuals and can be used by animals to address a social companion.
Last year, King and colleagues at St Andrews had found that captive dolphins whistled to close relatives when separated. To signal to their friends, the dolphins copied their relatives’ signature whistles, much as human friends might call each other’s names from across a pool.
But researchers had been unsure if that language was unique to dolphins in captivity – did dolphins have names in the wild?
To find out, researchers first recorded the signatures whistles of pods of wild dolphins off the coast of Scotland, in St. Andrews Bay. The scientists then modified the “voice” of the whistles, to ensure that the dolphins would be reacting to the whistle itself, and not just employing voice recognition. Using underwater speakers, they then played the recordings to the dolphins – and waited, and listened.
When a dolphin heard its signature whistle, it called back and swam toward the speakers, as if responding to another dolphin’s call to come. But the dolphins did not respond to recordings of a whistle that was not their own – after all, that wasn’t their name.
“Our study shows that dolphins will only reply when they hear a copy of their whistle, sometimes multiple times, but will not reply in this way to other whistles,” said King. “Showing that dolphins can be addressed in this way was the missing link to demonstrate that signature whistles can function as names.”
Naming is highly unusual among animals – the authors believe that it may be the first instance of it in mammals. While other animals have been found to emit calls to other members of their social groups – radioing that a predator is near or that found has been found – those sounds are inherited, not learned, King said.
And that those signatures are learned is a critical distinction, one that parallels those sounds to human language. As in human language, the dolphin appears to have attached meaning to a roster of whistle sounds. Those sounds stand for and refer to something or someone – in this case, different dolphins.
Still, King cautioned again too strong a comparison to human language, noting that a dolphin’s signature whistle accounts for about half of all the whistles that a dolphin emits and that much is still unknown about that other half of dolphins sounds.
“Do dolphins have a language? We still don’t know that,” said King.
“Now we understand how dolphins use their individually distinctive signature whistles the next step is to look at the function of non-signature whistles to gain an even greater insight into their complex communication system,” she said.