Babbler birds 'convey meaning'
Babbler birds do more than babble - they appear to communicate like humans, scientists have revealed.
The chestnut-crowned babbler, from Australia, re-arranges apparently random sounds to produce calls that convey meaning, researchers found.
Such an ability was previously thought to be a uniquely human skill.
Lead scientist Dr Sabrina Engesser, from the University of Zurich in Switzerland, said: "Although previous studies indicate that animals, particularly birds, are capable of stringing different sounds together as part of a complex song, these songs generally lack a specific meaning and changing the arrangement of sounds within a song does not seem to alter its overall message.
"In contrast to most songbirds, chestnut-crowned babblers do not sing. Instead its extensive vocal repertoire is characterised by discrete calls made up of smaller acoustically distinct individual sounds."
The findings, published in the online journal Public Library of Science Biology, are said to shed light on the early evolution of language.
Babblers were shown to combine two sounds - classified as A and B - to generate code-calls associated with specific behaviours.
In flight the birds produced an "AB" call, but when feeding chicks in the nest the sound they made was "BAB".
When the sounds were played back, listening birds seemed to understand what they meant. Birds looked at nests when they heard a feeding prompt call, and scanned the sky for incoming birds when they heard a flight call.
Even when the meaning was changed by editing the sounds, turning feeding calls into flight calls and vice-versa, the birds responded appropriately.
Co-author Professor Andy Russell, from the University of Exeter, said: "We think that babbler birds may choose to rearrange sounds to code new meaning because doing so through combining two existing sounds is quicker than evolving a new sound altogether."
Colleague Dr Simon Townsend, from the University of Zurich, added: "This is the first time that the capacity to generate new meaning from re-arranging meaningless elements has been shown to exist outside of humans.
"Although the two babbler bird calls are structurally very similar, they are produced in totally different behavioural contexts and listening birds are capable of picking up on this."
The first sound element "B" is the element that distinguishes the meaning of flight and feeding calls, known as a "phoneme", said the researchers.
In the same way the letter "c" is the phoneme that differentiates the meaning of the English words "cat" and "at".
"Although this so-called phoneme structuring is of a very simple kind, it might help us understand how the ability to generate new meaning initially evolved in humans" added Dr Townsend.
"It could be that when phoneme structuring first got off the ground in our hominid ancestors, this is the form it initially took."