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May 08, 2006

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Dolphins may “name” themselves, study finds

May 8, 2006
Special to World Science

Some dolphin whistles appear to convey the caller’s individual “name” information, researchers report in a new study. The scientists found that these whistles are recognizable to other dolphins even when the caller’s voice features are electronically removed.

Bottlenose dolphins (Courtesy U.S. Marine Mammal Commission)

As infants, biologists believe, bottlenose dolphins develop individual “signature whistles” used throughout their lifetimes. Group members often repeat these whistles as they communicate. 

Researchers have hypothesized that the whistles form a system similar to that of human naming. 

Vincent Janik of the University of St. Andrews in Fife, U.K. and colleagues studied bottlenose dolphins in Sarasota Bay, Fla. They investigated whether individuals can discriminate among signature whistles independently of voice features, as is the case in human naming.

The researchers “computerized” the signature whistles so that their basic pitch contours remained the same, but other distinctive voice features were removed. The researchers then played these altered whistles to dolphins through an underwater speaker. 

In 9 out of 14 trials, the dolphin would turn more often toward the speaker if it heard a whistle resembling that of a close relative, they reported. 

This suggests dolphins can “use these whistles as referential signals, either addressing individuals or referring to them, similar to the use of names in humans,” Janik and colleagues wrote in a paper to appear in this week’s online early edition of the research journal Proceedings of the National Academy of Sciences. 

Researchers in the past, they wrote, have hypothesized that “signature whistles” serve as names “because captive bottlenose dolphins can be trained to use novel, learned signals to label objects.”

But “experimental proof for this hypothesis has been lacking,” they added. With this study, they argued, dolphins become “the only animals other than humans that have been shown to transmit identity information independent of the caller’s voice or location.”

Signature whistles may give dolphins an evolutionary advantage by helping individuals recognize each other and groups to maintain cohesion, they added.

Dolphins seem to develop signature whistles for themselves as infants, Janik and colleagues noted. “In signature whistle development, an infant appears to copy a whistle that it only heard rarely and then uses a slightly modified version as its own signature whistle. This process leads to individually distinctive signature whistles.” It also leads to wider variation in the whistles over larger geographic distances, they added.

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