Dolphins Name Themselves with Signature Whistles
FIFE, Scotland, May 9, 2006 (ENS) - Some bottlenose dolphin whistles appear to communicate the caller's individual "name" information, which other dolphins can recognize even when the caller's voice features are electronically removed, Scottish and U.S. researchers report.
As infants, bottlenose dolphins develop their own signature whistles to use throughout their lifetimes. Signature whistles are individually distinctive signals given by the dolphins.
Members of dolphin groups repeat these whistles back during vocal interactions, and researchers have found that the whistles form a system similar to that of human naming.
The study's lead author Dr. Vincent Janik from the University of St. Andrews and his colleagues studied a group of bottlenose dolphins in Sarasota Bay, Florida, to investigate whether individual discrimination through signature whistles is independent of voice features, as it is in human naming.
The researchers synthesized signature whistles so that the caller's individual voice features were removed but the frequency-modulation shape remained the same.
The researchers played these altered whistles to dolphins through an underwater speaker.
In nine out of 14 cases, the dolphin would turn more often toward the speaker if it heard a whistle resembling that of a close relative, demonstrating that the signature whistle frequency modulation shape contains information that is used by the listeners.
Since voice features are affected by changing water pressure, voice-independent "names" might be a reliable way to convey identity, the researchers say.
This is done by using playback techniques in the wild and discrimination experiments with captive individuals, he says.
Working with the dolphins in Sarasota Bay, Dr. Janik and his two colleagues recorded the unique whistles dolphins use to distinguish one another, and they are exploring other functions of these sounds in the lives of the dolphins.
Dr. Laela Sayigh of the University of North Carolina's Center for Marine Science, a co-author of the study, says dolphins learn the individually distinctive signature whistles "which sets them apart from most other non-human mammals."
The third team member is Dr. Randall Wells, a conservation biologist with the Chicago Zoological Society, based at Mote Marine Laboratory, in Sarasota, Florida, where the dolphin signature whistle study was conducted.
Dr. Wells serves as director of Mote’s Center for Marine Mammal and Sea Turtle Research. He helped to initiate and now directs the 30 year long Sarasota Dolphin Research Program, the world's longest running dolphin program focusing on dolphins.
Dr. Wells says the program uses an collaborative approach in conducting studies of bottlenose dolphins within the unique long term "natural laboratory" of Sarasota Bay, which is the year 'round home of more than 140 identifiable resident dolphins.
Dr. Wells and his colleagues have documented the movements of more than 120 dolphins in a 40 square mile area of Sarasota Bay. They have discovered the social organization of dolphin groups based on sex, age, and reproductive condition and have been able to establish family trees through observations and blood analysis of these dolphins.
The study on dolphin use of signature whistles was presented in December at the 16th Biennial Conference on the Biology of Marine Mammals in San Diego.
It will be reported in an upcoming issue of Proceedings of the National Academy of Sciences, a U.S. publication.