Syntax has long been a pillar of human language, but new research appearing in the latest issue of the journal Nature Communications suggests that the ability to combine different words and phrases to generate novel meanings may not be an ability uniquely possessed by humans.

In the study, an international team of researchers demonstrated that Japanese great tits follow a specific set of rules to combine their calls and communicate complex messages. The findings indicate that syntax itself may be a general adaptation to behavior or social complexity in a communications systems, the authors explained in a paper published Tuesday.

While previous research has shown that non-human primates and birds can develop the ability to combine meaningless vocalizations, the evolution of syntax, the ability to combine various words to form compound phrases or sentence was believed to have been unique to human language. But the new study suggests that the Japanese great tit has, in fact, developed syntax of its own.

As co-author David Wheatcroft, a postdoctoral researcher at the Uppsala University Department of Ecology and Genetics , explained in a statement, the research “demonstrates that syntax is not unique to human language, but also evolved independently in birds. Understanding why syntax has evolved in tits can give insights into its evolution in humans.”

Correct order essential for calls to prompt desired reaction

The Japanese great tit, a small bird species that faces numerous threats, responds to the presence of predators using a vast array of different calls, Wheatcroft and his colleagues said. Each of the calls can be used on its own, or in combination with other calls, and playback experiments show that the combinations of these calls each take on their own, distinct meaning.

For instance, they demonstrated that ABC calls warned other great tits to “scan for danger” when encountering a perched predator, while D calls instructed the birds to “come here,” which can be used when the bird discovered a new source of food or for other purposes. When combined as an ABC-D call, they are used when approaching or deterring potential predators.

However, the researchers found that they only worked when the calls were in the correct order – artificially reversing the call (D-ABC) prompted no response from the birds. Wheatcroft and his colleagues believe that the great tits use different call combinations to coordinate various social activities, and take advantage of syntax to trigger specific behavioral responses from other great tits.

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Image credit: Toshitaka Suzuki et al.

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