before it's in the papers"
August 03, 2010
TO THE WORLD SCIENCE HOME PAGE
Dolphins may “name” themselves, study finds
and World Science staff
Some dolphin whistles appear to convey the caller’s individual “name” information, researchers report in a new study.
The whistles of bottlenose dolphins seem to carry this information, which is recognizable to other dolphins even when the caller’s voice features are electronically removed, the scientists found.
As infants, biologists believe, bottlenose dolphins develop their own “signature whistles” to use throughout their lifetimes. Group members repeat these whistles as they communicate. Researchers have hypothesized that the whistles form a system similar to that of human names.
Vincent Janik of the University of St. Andrews in Fife, U.K. and colleagues studied bottlenose dolphins in Sarasota Bay, Fla., to investigate whether individuals can discriminate among signature whistles independently of voice features, as is the case in human naming.
The researchers reconstructed signature whistles so that the pattern of changing pitches over time remained the same, but other voice features that differ among individuals were removed. The researchers played these altered whistles to dolphins through an underwater speaker.
In 9 out of 14 cases, 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,” they wrote, in a paper published in this week’s online early edition of the research journal Proceedings of the National Academy of Sciences.
Researchers in the past, they added, 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. This study demonstrates that bottlenose dolphins extract identity information from signature whistles even after all voice features have been removed from the signal. Thus, dolphins are 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, the researchers wrote. “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.”
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