Dolphins “Name” Themselves with Signature Whistles
Some bottlenose dolphin (Tursiops truncatus) whistles appear to convey the caller’s individual “name” information, which other dolphins can recognize even when the caller’s voice features are electronically removed, researchers report.
As infants, bottlenose dolphins develop their own signature whistles to use throughout their lifetimes. Group members repeat these whistles back during vocal interactions, and researchers have hypothesized that the whistles form a system similar to that of human names. Vincent Janik and colleagues studied a group of bottlenose dolphins in Sarasota Bay, FL, 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 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, 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.
