Japanese great tits use syntax to communicate – just like humans

Japanese great tits have been found to communicate using syntax, combining calls using specific rules in order to convey important messages about food and danger. Scientist say the discovery shows syntax is not unique to humans, so could potentially shed light on how our own language evolved.

Combining words to generate meaning using rules allows humans to communicate complex messages. The rules that govern this ability – known as compositional syntax – had previously only ever been seen in human language. As a result, it had long been assumed this was a uniquely human trait.

However, an international team of researchers has now shown this is not the case. Publishing a study in the journal Nature Communications, the team looked at Japanese great tits, recording the 10 different "note types" in their vocal range. These are identified by letters – A, B, C and D, for example.

The birds use these vocalisation either on their own or in combinations. Specifically, they are known to use ABC to warn off predators, and D to say "come here". In the study, the team played recordings of different combinations of the note types to see if the birds could extract meanings from them.

They found the birds derived a compound meaning from an ABC-D call, approaching the object while scanning for danger. They were just as likely to show this approach and scan behaviour as the birds that listened to the ABC combination or the D note type when played on their own. When they played a D-ABC call, the birds did not respond, suggesting the information conveyed through the notes is governed by a note-ordering rule.

Study co-author David Wheatcroft, from Uppsala University in Sweden, said: "This study 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."

Researchers believe the finding suggests syntax could be an adaptation to social and behavioural complexity within communication systems. They wrote: "We provide the first experimental evidence for compositional syntax in a non-human vocal system... Signal combinations can increase the number of meanings that individuals can convey from a limited number of vocal elements and provide the basis for the generation of novel signals. Uncovering the cognitive mechanisms and socio-ecological functions of syntactic communication in animal models may provide insights into the evolution of structural complexity of human language."