KEY POINTS:
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, NSW, has found certain whistles are linked to specific behaviour.
PhD candidate Liz Hawkins from Southern Cross University's Whale Research Centre in Lismore listened in on 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 1650 recorded, of which 20 were heard frequently and were common to more than one pod.
Ms Hawkins also grouped the whistles into five classes based on tone, and found they were related to certain behaviour.
While socialising, dolphins made almost exclusively flat-toned or rising-toned whistles. Travelling pods made mostly "sine" whistles, which rise and fall in bell curves, which Ms 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.
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 behaviour. 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," Ms Hawkins suggested.
She also noticed that dolphins riding the waves her boat created 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 definitely mean: 'I'm here, where is everyone?'," Ms Hawkins said.
She added 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.
"They are wild animals and generally wild animals only make sounds or transmit information that is essential to their survival.
"It basically suggests their communication is a lot more complex than what was generally thought."
Ms Hawkins said she hoped to take the project underwater to observe the dolphins' behaviour and try to match the whistles more closely 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."
- AAP
