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 — signature high-pitched sounds that are created by individual dolphins as they grow — which they then use throughout their lives to broadcast their locations to other dolphins they meet 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. But 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.”
Dolphins make a lot of vocalisations 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 travelling 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,” said Janik. “You also often find them between mums and calves if they get separated.”
His research team wanted to know how far dolphins were using these skills to identify each other and themselves. They watched a population of around 150-180 dolphins living off the east coast of Scotland, 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. In order to remove any potential familiarity dolphins might have had with particular voices, the sounds the researchers played back were computerised re-construction 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,” said Janik. The results, published in the Proceedings of the National Academy of Sciences, showed that dolphins responded to their own signature whistles whenever they heard them by whistling their own “name” back, but would ignore the whistles of others. Sometimes the dolphins would turn their attention to the researcher’s boat or even swim up to it when they heard their whistles.
“The interesting thing about these is that they are not voice recognition,” said Janik. “In humans you can have different people say the same word and I’d still be able to tell who’s speaking. What we also do is have names, so they are very different call types. The dolphins do the same thing, they’re developing a completely new call type, a melody or whistle, which is not dependent on their voice features.”
A spokesperson for the conservation charity Whale and Dolphin Conservation said that the research showed “once again just how intelligent some dolphins are. We already know that they, like us, are self-aware [they recognise themselves in the mirror] and use tools to hunt for food. This evidence of their communication skills just adds to the growing body of emerging scientific evidence that demonstrates the existence of cetacean culture and that cetaceans are well developed cognitively.” He added that it was “therefore important that we develop a more sophisticated approach to ensure that unique cetacean cultures are not lost and that the wider conservation implications of these unique cultures are taken into consideration in conservation management.” © Guardian News & Media 2013
