A new study explores how dolphins use their individual signature whistles (equivalent to their “names”) to stay in touch with each other. Not only do they call back and forth with each other’s “name”; but when one dolphin calls out the signature whistle of another, the other one will swim over to see what’s up – like two friends shouting out to each other in a crowd.
Background to this latest study: Last year, we noted that dolphins use signature whistles to introduce and identify themselves to each other. Sort of like saying, “Hello, I’m Dolly. Nice to meet you.” “You, too. I’m Phinn.”
So when, for example, pods of bottlenose dolphins meet in the ocean, they exchange whistles. It is, by any standard, a very complex and sophisticated communication system.
Next, earlier this year, the same team at St. Andrew’s University in Scotland demonstrated that when bottlenose dolphins in captivity get separated from each other, they call out to each other by name. A report in Wired explained how the team had analyzed recordings of dolphins who had been captured off the coast of Florida and held in separate nets for just a few hours.
During the captures, the dolphins can’t see each other, but can hear each other and continue to communicate. In their analysis, Stephanie King and Vincent Janik showed that some of the communications are copies of captured compatriots’ signature whistles — and, crucially, that the dolphins most likely to make these were mothers and calves or closely allied males.
They seemed to be using the whistles to keep in touch with the dolphins they knew best, just as two friends might if suddenly and unexpectedly separated while walking down a street. Moreover, copying wasn’t exact, but involved modulations at the beginning and end of each call, perhaps allowing dolphins to communicate additional information, such as the copier’s own identity.
That possibility hints at what linguists call referential communication with learned signals, or the use of learned rather than instinctively understood sounds to mentally represent other objects and individuals. As of now, only humans are known to do this naturally.
“We learn language and refer to objects. This has been shown with captive dolphins and captive gray parrots, but hasn’t been seen in the natural communication system of any species,” said King. “We’re not saying that this is what they’re doing, but we’re definitely suggesting that we should look into it.”
Now, in a third step, the same team has shown that when dolphins hear their own signature whistles, they call back.
“Every time a dolphin heard its signature whistle, it called back, sometimes multiple times.”In the new study, the team began by recording the signature whistles of 12 dolphins living off the east coast of Scotland. Then they modified the whistle sounds slightly to make them sound as if a second dolphin was making the first dolphin’s whistle sound. And then the researchers played back the modified whistles using underwater speakers.
According to King: “Every time a dolphin heard its signature whistle, it called back, sometimes multiple times.”
Better yet, not only did the dolphins call back, but they even swam toward the speakers that were playing the sound, as if they were friends trying to find each other in a crowd by calling out each other’s names.
Here’s an example of a signature whistle:
And the computer-modified whistle:
Now comes another key question: Are these whistles really the equivalent of names? According to Peter Tyack, another marine biologist at St. Andrews: “To get at the issue of naming, we have to go beyond the function of the communication to a more cognitive question.”
That takes us back to the intriguing question of whether dolphins use referential communication (where words or signals mentally represent other objects and individuals). For example, Tyack says, does hearing another dolphin’s whistle bring up in the dolphin’s mind an image of that particular animal?
It’s a more difficult question to explore, but doubtless one that the St. Andrews team is working on.
(The new study is published by the Proceedings of the National Academy of Sciences.)