Birds are a lot smarter than most people typically give them credit for. Recent research suggests that some are as intelligent as apes. Crows can count, exhibit self-restraint, and hold grudges. Parrots use grinding tools (like a mortar and pestle). And according to research published in Nature Communications today, it seems that Japanese great tits use a complex syntax in their calls.

An international team of researchers headed by Toshitaka Suzuki of the Graduate University for Advanced Studies (SOKENDAI) discovered that the small birds combine distinct notes in their vocal repertoire in different ways to communicate meaning. Just like human syntax creates boundless different meanings out of a set number of words arranged in different ways, the songbirds communicate different meanings based on the order of the notes they sing.

The Japanese great tit (Parus minor) uses more than 10 different note types in its vocalizations (each labeled in this study by a letter). The researchers tested how wild birds responded to certain recorded bird calls with known meanings. For instance, one combination of notes, "ABC," is used when the birds are mobbing predators to drive them off. In response to that sound, birds begin to look around for predators. Another, "D," is used when a bird is alone in its nest and calling to its mate, and birds typically approach the source of that sound.

The researchers played these notes in different orders (listen above) to see how wild birds would react, finding that the order of the notes did matter. When they heard the combination of notes "ABC-D," they scanned the horizon for predators and came toward the speaker playing the notes, a combination of the normal reactions to each of the two calls. So the notes can be combined to create a sort of sentence, in essence. But when the syntax was reversed and the researchers played "D-ABC," the birds did not show these behaviors, suggesting that a different order of the same notes doesn’t have the same meaning.

In other words, the birds have specific syntactical rules that govern their communication. This is rare evidence of non-human vocal syntax, although finches have previously been shown to have some awareness of syntax as well.