Stringing together meaningless sounds to create meaningful signals was previously thought to be the preserve of humans alone, but a new study published in the journalPLOS Biology reveals that Australian babbler birds are also able to communicate in this way.
Researchers at the Universities of Exeter and Zurich discovered that the chestnut-crowned babbler (pictured) – a highly social bird found in the Australian Outback – has the ability to convey new meaning by rearranging the sounds in its calls. Such relatively sophisticated communication reveals a potential early step in the emergence of the elaborate language systems humans use today.
“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,” said Sabrina Engesser, from the University of Zurich. “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.”
Study co-author Andy Russell from the University of Exeter believes 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.
The researchers noticed that chestnut-crowned babblers reused two sounds “A” and “B” in different arrangements when performing specific behaviours. When flying, the birds produced a flight call “AB”, but when feeding chicks in the nest they emitted “BAB” prompt calls.
When the researchers played the sounds back, the listening birds showed they were capable of discriminating between the different call types by looking at the nests when they heard a feeding prompt call and by looking out for incoming birds when they heard a flight call. This was also the case when the researchers switched elements between the two calls: making flight calls from prompt elements and prompt calls from flight elements, indicating that the two calls were indeed generated from rearrangements of the same sounds.
“This is the first time that the capacity to generate new meaning from rearranging meaningless elements has been shown to exist outside of humans,” observed co-researcher Simon Townsend, from the University of Zurich. “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 authors report that in the chestnut-crowned babbler, the first sound element “B” is what seems to differentiate the meaning between flight and prompt vocalisations, akin to “cat” and “at” in English, where the “c” represents the meaning differentiating element, or phoneme.
“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,” says Townsend. “It could be that when phoneme structuring first got off the ground in our hominid ancestors, this is the form it initially took”.
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