What might dolphins be saying with all those clicks and squeaks? Each other’s names, suggests a new study of the so-called signature whistles that dolphins use to identify themselves.

Whether the vocalizations should truly be considered names, and whether dolphins call to compatriots in a human-like manner, is contested among scientists, but the results reinforce the possibility. After all, to borrow the argot of animal behavior studies, people often greet friends by copying their individually distinctive vocal signatures.

“They use these when they want to reunite with a specific individual,” said biologist Stephanie King of Scotland’s University of St. Andrews. “It’s a friendly, affiliative sign.”

In their new study, published Feb. 19 in Proceedings of the Royal Society B, King and fellow St. Andrews biologist Vincent Janik investigate a phenomenon they first described in 2006: bottlenose dolphins recognizing the signature whistles of other dolphins they know.

Signature whistles are taught to dolphins by their mothers, and the results were soon popularized as evidence of dolphin names. Many questions remained, though, about the whistles’ function, and in particular about the tendency of dolphins to copy each others’ signatures.

Dolphin Talk: In the first audio clip below, a male dolphin makes his signature whistle. In the second clip, a second male copies that signature in a communication of his own.







Audio: Stephanie L. King

To investigate these possibilities, King and Janik’s team analyzed recordings made over several decades by the Sarasota Dolphin Research Program, a Florida-based monitoring project in which pairs of dolphins are captured and held in separate nets for a few hours as researchers photograph and study them.

During the captures, the dolphins can’t see each other, but can hear each other and continue to communicate. In their analysis, King and 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.”

Robert Barton, a cognitive scientist at England’s Durham University who has previously chafed at the notion that dolphin vocal signatures could be considered names, cautioned against reading too much into their communications. He noted that dolphins captured in the Sarasota project do copy each other’s signatures, but only infrequently.

King and Janik see this as supporting an identity-rich meaning for the copied whistles, which seem to be used specifically in communication with select individuals. From Barton’s perspective, other interpretations are equally possible, including a very limited importance for copying.

“Many things are possible,” said Barton of the proposition that dolphins communicate referentially, “but there is little evidence for it,” at least not from experiments that rigorously exclude alternative interpretations.

To biologist Shane Gero of Dalhousie University, who studies communication between sperm whales with seemingly name-like calls, debates over the nature of dolphin vocalizations reflect historical tensions in the study of animal behaviors.

A century ago, human-like traits were excessively attributed to animals. During the 20th century, the scientific pendulum swung back, to the point where animals were assumed unintelligent unless their abilities could be experimentally demonstrated in controlled settings.

For most animals, including dolphins, that’s logistically difficult, and animal intelligence may be deeply underappreciated as a consequence. Just because we don’t officially recognize complex thought in whales and dolphins doesn’t mean it’s not there; given their rich social lives and demonstrated cognitive capacities, names certainly aren’t implausible.

“It all comes back to how these calls are perceived,” Gero said. “It’s tough to get at meaning. Do dolphins doing the copying and dolphins being copied share a meaning?”

“We still need to show that experimentally,” King said, “but that’s why it’s quite exciting.”

Citation: “Vocal copying of individually distinctive signature whistles in bottlenose dolphins.” By Stephanie L. King, Laela S. Sayigh, Randall S. Wells, Wendi Fellner and Vincent M. Janik. Proceedings of the Royal Society B, 20 February 2013.