Dolphins ‘talk’ to each other, using the same process to make their high-pitched sounds as humans, according to a new analysis of results from a 1970s experiment.

The findings mean dolphins don’t actually whistle as has been long thought, but instead rely on vibrations of tissues in their nasal cavities that are analogous to our vocal cords.

Scientists are only now figuring this out, ‘because it certainly sounds like a whistle,’ said study researcher Peter Madsen of the Institute of Bioscience at Aarhus University in Denmark, adding that the term was coined in a paper published in 1949 in the journal Science. ‘And it has stuck since.’

The finding clears up a question that has long puzzled scientists: How can dolphins make their signature identifying whistles at the water’s surface and during deep dives where compression causes sound waves to travel faster and would thus change the frequency of those calls. [Deep Divers: A Gallery of Daring Dolphins]

To answer that question, Madsen and his colleagues analyzed recently digitized recordings of a 12-year-old male bottlenose dolphin (Tursiops truncatus) from 1977. At the time, the researchers had the dolphin breathe a mixture of helium and oxygen called heliox. (Used by humans, heliox makes one sound […]