Bottlenose dolphins have distinct “names” that they use to identify individuals in their social group, according to a study by scientists who followed groups of the animals off the east coast of Scotland.
The names are composed of whistles, which are signature high-pitched sounds each dolphin creates as they grow. They use the whistles throughout their lives to broadcast their locations to other dolphins at sea.
Many animals, including birds and primates, are capable of copying sounds and can learn to produce complex displays that tell others how fit they are, mainly for mating purposes. However, not many species can learn to associate specific sounds with particular individuals or objects.
“If we look at complex ability in communication in human language, one of the key features that is important to us is that we can copy sounds, we can invent new sounds,” said Vincent Janik, a biologist at St Andrews University who led the research.
“We can then use those sounds and attach some kind of meaning to them, and use them to refer to objects and to refer to external things in the world,” Janik said.
Dolphins make a lot of vocalizations to communicate with each other, including echolocation clicks, whistles to attract other animals to food locations and other noises to indicate how aggressive or friendly they feel.
The signature whistles are most often used by dolphins when they are traveling in groups and want to let their companions know where they are.
“Other contexts are particularly when groups meet at sea, they exchange information about who is present before the groups join, almost like a greeting,” Janik said. “You also often find them between mums and calves if they get separated.”
His team wanted to know how far dolphins were using these skills to identify each other and themselves. They watched a population of between 150 and 180 dolphins, following groups of between two and 20 dolphins at once, initially identifying and recording signature whistles and then playing these whistles back to the entire group.
To remove any potential familiarity dolphins might have had with particular voices, the sounds the researchers played back were computerized reconstruction of the original whistles.
“The way you see who is responding is to listen for the signature whistle to see if the animal produces its own whistle back to you when you play its whistle,” Janik said.
The results, published in the Proceedings of the National Academy of Sciences, showed that dolphins responded to their own signature whistle whenever they heard them by whistling their “name” back, but would ignore the whistles of others.