Japanese great tits (Parus minor) are able to combine distinct elements of their vocalizations together and extract a compound meaning from them, finds a study in Nature Communications. This process, known as compositional syntax, had previously only been recorded in human language, and shows that animal communication may be more complex than previously thought.
Birds within the family Paridae produce structurally complex vocalizations (such as ‘chicka’ or ‘chick-a-dee’ calls) that are composed of different note types (such as A, B, C and D). Japanese great tits have more than ten note types in their vocal repertoire, which they use either on their own or in combination with one another. They are known to produce two distinct types of ‘chicka' call - 'ABC' in order to warn off predators, and 'D' in order to signal a mate to approach - but whether they can meaningfully combine these calls was previously unknown.
Toshitaka Suzuki and colleagues played recordings of different combinations of tits' vocal repertoire to birds of the same species in the wild in order to observe their responses. They find that the birds extract different meanings from ABC and D calls, and a compound meaning from ABC-D calls. In fact, birds that listened to the combined ABC-D call were just as likely to both scan the horizon for predators and approach the loudspeaker as other birds were to display either one of these two behaviours when listening to the ABC call or the D call alone, respectively. However, birds rarely scanned and approached when the note ordering was artificially reversed (‘D-ABC’). This indicates that the information conveyed by the notes is combined through a specific note-ordering rule.
These results present experimental evidence for compositional syntax in birds, which most likely evolved as a way of increasing the number of meanings that can be conveyed by a limited vocal repertoire.