Human languages are comprised of meaningful words, which themselves are built from different combinations of meaningless sounds, or building blocks. A new study shows that a pair of functionally distinct vocalizations (calls) of the chestnut-crowned babbler (Pomatostomus ruficeps), a highly cooperative bird of the Australian arid zone, is composed of distinct building blocks that are shared across the different calls.
“To our knowledge, this is the first time that the meaning-generating building blocks of a non-human communication system have been experimentally identified,” said Professor Simon Townsend, a researcher at the University of Warwick and the University of Zurich.
In 2015, Professor Townsend and colleagues demonstrated that the calls of the chestnut-crowned babbler seemed to be composed of two different sounds ‘A’ and ‘B’ in different arrangements when performing specific behaviors.
When flying, the birds produced a flight call ‘AB,’ but when feeding chicks in the nest they emitted ‘BAB’ provisioning calls.
In the new study, Professor Townsend and co-authors from Australia, Switzerland and the United Kingdom used playback experiments, previously used to test speech-sound discrimination in human infants, to probe the perception of the sound elements in babblers.
“Although the building blocks in the babbler system may be of a very simple kind, it might still help us understand how combinatoriality initially evolved in humans,” Professor Townsend said.
“Through systematic comparisons we tested which of the elements babblers perceived as equivalent or different sounds,” said Dr. Sabrina Engesser, from the University of Zurich.
“In doing so, we were able to confirm that the calls could be broken up into two perceptually distinct sounds that are shared across the calls in different arrangements.”
“Furthermore, none of comprising elements carried the meaning of the calls confirming the elements are meaningless.”
“This system is reminiscent of the way humans use sounds to form meaningful words,” said Professor Andy Russell, from the University of Exeter.
“These findings raise the exciting possibility that the capacity to generate meaning from meaningless building blocks is widespread in animals, but there are still considerable differences between such systems and word generation in language,” the scientists said.
“A focus on the acoustic distinctiveness of sounds in meaningful animal vocalizations offers a promising approach to investigate the building blocks of non-human animal communication systems.”
The findings were published online this week in the Proceedings of the National Academy of Sciences.
Sabrina Engesser et al. Chestnut-crowned babbler calls are composed of meaningless shared building blocks. PNAS, published online September 9, 2019; doi: 10.1073/pnas.1819513116