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July 01, 2015

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Bird said to re-arrange sounds to create meaning—like people

July 1, 2015
Courtesy of the University of Exeter
and World Science staff

A bird known as the chestnut-crowned bab­bler can re­ar­range mean­ing­less sounds to cre­ate mean­ing­ful sig­nals—pre­viously thought to be a un­iquely hu­man skill, re­search­ers say.

“This is the first time that the ca­pa­city to gen­er­ate new mean­ing from re­ar­rang­ing mean­ing­less el­e­ments has been shown to ex­ist out­side of hu­mans,” said Si­mon Townsend of the Uni­vers­ity of Zu­rich in Switz­er­land, co-au­thor of a re­port on the find­ings. Al­though the bab­bler’s meth­od is very sim­ple, he added, “it might help us un­der­stand how the abil­ity to gen­er­ate new mean­ing in­i­tially evolved in hu­mans.”

Chestnut-crowned bab­bler (© Chris Tza­ros)


A highly so­cial bird from the Aus­tral­ian Out­back, the bab­bler may opt to re­ar­range ex­isting sounds be­cause it’s “quicker than evolv­ing a new sound al­to­geth­er,” said An­dy Rus­sell of the Uni­vers­ity of Ex­e­ter, an­oth­er co-au­thor.

Pre­vi­ous stud­ies show birds can string “d­if­fer­ent sounds to­geth­er as part of a com­plex song,” but usu­ally “these songs gen­er­ally lack a spe­cif­ic mean­ing,” said lead au­thor Sab­rina En­ges­ser from the Uni­vers­ity of Zu­rich in Switz­er­land. Fur­ther­more, “chang­ing the ar­range­ment of sounds with­in a song does not seem to al­ter its over­all mes­sage.”

The bab­bler, by con­trast, does­n’t sing. “In­stead, its ex­ten­sive vo­cal rep­er­toire is char­ac­ter­ized by dis­crete calls made up of smaller acous­tic­ally dis­tinct in­di­vid­ual sounds,” En­ges­ser said.

The re­search­ers no­ticed the bab­blers re­used two sounds, which the in­ves­ti­ga­tors des­ig­nat­ed as “A” and “B,” in dif­fer­ent ar­range­ments when tak­ing spe­cif­ic ac­tions. When fly­ing, they pro­duced a flight call “AB”, but when feed­ing their ba­bies they emit­ted what are known as prompt calls with the struc­ture “BAB.”

When the re­search­ers played the sounds back, they said, the birds showed they could tell them apart. The birds looked at the nests when they heard a feed­ing prompt call and looked out for in­com­ing birds when they heard a flight call. This al­so worked when the re­search­ers simply switched parts of the two calls in record­ings—show­ing, they ar­gued, that the two calls in­deed came from re­ar­rangements of the same sounds.

The au­thors say that in the chestnut-crowned bab­bler, the first sound el­e­ment “B” is what seems to dif­fer­entiate the mean­ing be­tween flight and prompt vo­cal­iz­a­tions, akin to cat and at in Eng­lish, where the c rep­re­sents the mean­ing-dif­fer­entiating el­e­ment, or pho­neme.

The findings are published in the research journal PLoS Biology.


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A bird known as the chestnut-crowned babbler can rearrange meaningless sounds to create meaningful signals—previously thought to be a uniquely human skill, researchers say. “This is the first time that the capacity to generate new meaning from rearranging meaningless elements has been shown to exist outside of humans,” said Simon Townsend of the University of Zurich in Switzerland, co-author of a report on the findings. Although the babbler’s method is very simple, he added, “it might help us understand how the ability to generate new meaning initially evolved in humans.” A highly social bird from the Australian Outback, the babbler may opt to rearrange existing sounds because it’s “quicker than evolving a new sound altogether,” said Andy Russell of the University of Exeter, another co-author. Previous studies show birds can string “different sounds together as part of a complex song,” but usually “these songs generally lack a specific meaning,” said lead author Sabrina Engesser from the University of Zurich in Switzerland. Furthermore, “changing the arrangement of sounds within a song does not seem to alter its overall message.” The babbler, by contrast, doesn’t sing. “Instead, its extensive vocal repertoire is characterized by discrete calls made up of smaller acoustically distinct individual sounds,” Engesser said. The researchers noticed the babblers reused two sounds, which the investigators designated as “A” and “B,” in different arrangements when taking specific actions. When flying, they produced a flight call “AB”, but when feeding their babies they emitted what are known as prompt calls with the structure “BAB.” When the researchers played the sounds back, they said, the birds showed they could tell them apart 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 also worked when the researchers simply switched parts of the two calls in recordings—showing, they argued, that the two calls indeed came from rearrangements of the same sounds. The authors say that in the chestnut-crowned babbler, the first sound element “B” is what seems to differentiate the meaning between flight and prompt vocalizations, akin to cat and at in English, where the c represents the meaning-differentiating element, or phoneme.