Dolphins can whistle their names
2006-05-10 13:15
Washington - They might not yell out "Flipper!", but dolphins know each other by "name", according to a new study.
Bottlenose dolphins, which starred in the 1960s television series Flipper, are the only animals besides humans that use sounds conveying distinct personal identification to represent themselves and recognise members of their group, researchers said.
Scientists have speculated for years that bottle-nosed dolphins' whistling transmitted more identity information than the communications of other animals, which can often express species and group identity.
But in the study published on Monday in the Proceedings of the National Academy of Sciences, scientists said they determined that dolphins communicate in a more sophisticated way than other animals, expressing and understanding specific "names" more in the way humans do.
The scientists, led by Vincent Janik of the University of St Andrews in Scotland, wanted to test whether dolphin whistles contained an expression of identity that was separate from the dolphin's personal "voice".
Signature whistles
Working with a group of bottlenose dolphins in Sarasota, Florida, they synthesised the animals' signature whistles, stripping out any other intonation and sound that were features of the dolphin's voice while leaving the frequency modulation shape. The approach could be compared to isolating the pure syllables of a human's name from the accents and other voice characteristics which might identify the speaker.
To test whether the dolphins recognized "names" reproduced in this way, through an underwater speaker the scientists played back to individual dolphins the synthesized whistles of a close relative to see if they reacted. Usually the close relatives were mothers or independent offspring.
The researchers compared the reactions to responses to synthesised calls from unrelated dolphins.
In 9 out of 14 cases, the dolphins reacted to the "name" of the close relative, demonstrating that the personal sounds of a dolphin's voice are not essential for identification.
The scientists suggested that this higher ability of personal identification expression is necessary in the dolphins' environment, where water pressure changes could distort voice recognition.
"This finding does not mean that dolphins do not have individually specific voice features. However, sound production is greatly affected by changing water pressure, which would make voice recognition more difficult than in air," the study said.
"In such conditions, signature whistles can facilitate contact between individuals."
The scientists had no clear understanding of why five dolphins in their study did not react to the synthesised "names" broadcast through the speakers.
But they guessed that it involved "a motivational issue", such as the relationship between the animal being tested and the name being broadcast.