New study deciphers bird sounds and reveals language precursors in babbler birds
Researchers from the Universities of Exeter and Zurich have uncovered evidence that chestnut-crowned babblers—highly social birds native to Australia’s arid Outback—use rearranged, meaningless sound elements to create distinct, meaningful calls. This finding suggests a simple form of phonemic structuring in a nonhuman vocal system and offers insight into possible early steps in the evolution of human language.
Until now, the ability to combine meaningless elements into meaningful signals was widely regarded as a defining feature of human language. While many animals, especially songbirds, sequence sounds in complex ways, those sequences have often appeared to lack the kind of element-level meaning observed in human phonemes. The new study demonstrates that chestnut-crowned babblers can generate different functional meanings by rearranging two acoustically distinct sound elements.
Sabrina Engesser, lead author from the University of Zurich, explains that unlike most songbirds, chestnut-crowned babblers do not produce long songs. Instead, their vocal repertoire consists of discrete calls assembled from smaller, acoustically distinct units. The team discovered two recurring acoustic elements, labeled A and B, that the birds use in different orders to signal different contexts—providing experimental evidence that reorderings of meaningless sounds can generate distinct meanings in a wild, nonhuman species.
Field observations and controlled playback experiments revealed that when the birds fly they typically emit an AB flight call, whereas when adults feed chicks in the nest they produce a BAB feeding-prompt call. Playback tests showed that listening birds responded appropriately to each call: they watched the nest in response to feeding-prompt calls and looked to the horizon for incoming birds in response to flight calls. Crucially, when the researchers recombined the acoustic elements—constructing flight-like calls from prompt elements and prompt-like calls from flight elements—listeners still responded according to the sequence, demonstrating that the meaning depended on the arrangement of the same components rather than on wholly different sounds.
Co-author Andy Russell of the University of Exeter, who has studied chestnut-crowned babblers since 2004, suggests a possible evolutionary explanation: recombining existing sounds to produce new meanings can be faster and more flexible than waiting for entirely new vocal elements to evolve. This combinatorial strategy could have adaptive advantages in complex social systems where rapid communication about changing contexts matters.
Simon Townsend, co-author from the University of Zurich, emphasizes the significance of the result: although the AB and BAB calls are structurally similar, they occur in distinct behavioral contexts and are reliably distinguished by receivers. The addition or omission of a single element at a specific position creates a contrast that functions much like a phoneme-driven difference in meaning. In simple terms, the presence of the first element “B” in one position appears to be the key that differentiates the calls’ meanings—analogous to how swapping a consonant can distinguish words in human languages.
The research team frames this arrangement as a rudimentary phoneme-like contrast. It is not equivalent to the complex, generative phonemic systems of human languages, but it represents a plausible early form of phoneme structuring. Such simple contrasts could have provided a foundation on which more elaborate combinatorial systems emerged in our hominid ancestors.
Source: Jo Bowler – University of Exeter
Image Credit: Jodie Crane
Original Research: The study, titled “Experimental Evidence for Phonemic Contrasts in a Nonhuman Vocal System,” was authored by Sabrina Engesser, Jodie M. S. Crane, James L. Savage, Andrew F. Russell, and Simon W. Townsend and published in PLOS Biology (online June 29, 2015). The paper reports acoustic analyses, natural observations, and controlled playback experiments that together demonstrate how the chestnut-crowned babbler uses the same acoustic elements in different orders to produce functionally distinct vocalizations.
Abstract
Experimental Evidence for Phonemic Contrasts in a Nonhuman Vocal System
The capacity to create new meanings by rearranging combinations of meaningless sounds is a cornerstone of human language. While many animals produce vocal sequences composed of acoustic elements that lack independent meaning, evidence that recombining such elements generates distinct, functionally meaningful signals has been limited. This study documents that chestnut-crowned babblers (Pomatostomus ruficeps), cooperative birds of Australia’s arid zone, employ the same acoustic elements (A and B) in different orders (AB or BAB) to form two distinct vocalizations associated with flight and feeding prompts. Through acoustic analysis, field observation, and playback experiments, the researchers found that the presence, absence, or position of a single element produces a phoneme-like contrast sufficient to alter the behavioral response of receivers. These results demonstrate that the ability to rearrange meaningless elements to create meaningful signals exists outside humans and suggest that simple phonemic contrasts may represent an early evolutionary step toward more complex generative phonemic systems.