Humans have taken a major step forward in unlocking the mysteries of dolphin-speak and found their communication is more complicated than originally thought.
A researcher who spent three years listening to bottlenose dolphins living off the coast of Byron Bay has found certain whistles are linked to specific behavior.
Doctoral candidate Liz Hawkins from Southern Cross University's Whale Research Center in Lismore, New South Wales, listened in to more than 50 different pods of dolphins.
Using the starting and final frequency of the sound and its duration, she distinguished 186 distinct whistle types among the 1,650 recorded, of which 20 were common to more than one pod.
Hawkins also grouped the whistles into five classes based on tone and found they were related to certain behavior.
While socializing, dolphins made almost exclusively flat-toned or rising-toned whistles.
Traveling pods made mostly "sine" whistles, which rise and fall in bell curves, which Hawkins suggested could be advertising their pod to other pods.
"They could be talking to another pod and saying 'We are over here ... do you want to join?'," she said yesterday.
Resting was associated with "concave" whistles, sounds that went down in pitch and back up again, while downward-toned whistles were not found to be associated with any particular behavior.
One particular whistle was associated with feeding.
"They could be advertising they have found food, they could be advertising to other animals there is food there, or it could be referred to a particular type of feeding or a particular type of food," Hawkins suggested.
Hawkins noticed dolphins riding the bow wave her boat created had often made a particular sound, while in early research she found a group of dolphins living off Queensland's Moreton Island emitted a particular whistle when alone.
"That whistle could mean: 'I'm here, where is everyone?'," she said in New Scientist magazine.
Hawkins said the sounds were not evidence of a language but showed the dolphins were communicating "context-specific information."
"A specialist in linguistics would not call this a language," she said. "They are wild animals, and generally wild animals only make sounds or transmit information that is essential to their survival. It suggests their communication is a lot more complex than what was generally thought."
Hawkins said she hoped to take the project underwater to observe dolphin behavior and match the whistles to actions.
"There is only so much information you can get from looking at the surface activity," she said. "You really need to get under the water and to somehow eavesdrop and look what's going on with their lives under there."