A Japanese bird species combine their calls using specific rules to communicate important compound messages, a new study has found, suggesting that syntax is not unique to humans as previously thought.
Human communication is powered by rules for combining words to generate novel meanings. Such syntactical rules have long been assumed to be unique humans.
However, a new study by an international team of researchers demonstrates that syntax is not unique to humans. Instead, syntax may be a general adaptation to social and behavioural complexity in communication systems.
Researchers from The Graduate University for Advanced Studies in Japan, Uppsala University in Sweden and University of Zurich demonstrated that the Japanese great tit, known for its diverse vocal repertoire, have evolved syntax.
This small bird species experiences a number of threats, and in response to predators, they give a variety of different calls. These calls can be used either alone or in combination with other calls, researchers said.
Using playback experiments, they demonstrated that one call signifies "scan for danger" for example when encountering a perched predator, whereas another call signifies "come here," for example when discovering a new food source, or to recruit the partner to their nest box.
Tits often combine these two calls such as when approaching and deterring predators.
When these two calls are played together in the naturally occurring order, then birds both approach and scan for danger. However, when the call ordering is artificially reversed, birds do not respond, researchers 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," said David Wheatcroft from Uppsala University.
Japanese great tits use different calls to coordinate a variety of social interactions, each of which requires specific behavioural responses, researchers said.
Syntax provides rules for combining the elements from a small vocabulary to generate novel meanings that can be readily recognised. These rules may be an adaptation to social and behavioural complexity in communication systems, such as in human language.
The findings were published in the journal Nature Communications.
