Flipper's Call Sign

By Kelli Whitlock Burton
ScienceNOW Daily News
8 May 2006

Like When dolphins talk to friends or family, they call each other by name, according to a new study. The mammals identify themselves with signature whistles developed early in life, but unlike other animals, dolphins don't rely on voice recognition to tell who's talking to whom. Each whistle contains specific frequency patterns unique to each animal, announcing a dolphin's identity to other animals that may be hundreds of yards away.

As young calves, bottlenose dolphins listen to the whistles of others and then create their own sound. In their dark underwater environment, dolphins use these whistles to locate other members of their group who may have fallen out of sight. Earlier studies had found that when dolphins hear a familiar signature whistle, they turn toward the sound. But while this suggested dolphins used the whistles to identify each other, it wasn't clear what role voice recognition played in the process.

For the new study, published online this week in Proceedings of the National Academy of Sciences, scientists synthesized signature dolphin whistles, retaining the message but masking the individual voice. They played two 30-second sound tracks over an underwater speaker for a group of 14 wild dolphins captured off the coast of Sarasota, Florida. One whistle simulated that of a family member and the other of an unknown animal. When scientists monitored the dolphins' responses, they found that nine of the 14 animals turned toward the speaker when they heard the simulated whistle of a family member. "This tells us that the frequency modulation carries the identity information," says Vincent Janik, a marine biologist at the University of St. Andrews in Fife, United Kingdom, and lead author of the study. "This has nothing to do with voice."

Studying this in wild animals instead of captive ones suggests that the behaviors are natural and not taught by humans, says Marc Lammers, a marine bioacoustician at the University of Hawaii. However, the lack of a controlled environment leaves some questions unanswered. For example, is it possible dolphins turned their heads because they heard an unfamiliar sound and not just because it was a whistle they recognized? And then there's the question of the head turning altogether. "They were looking at the head movements and what percentage of the time the animal moved its head more than 20 degrees," Lammers says. "Well, I would want to know, how much do they do that anyway?"