Human language is like magic, letting us easily discuss complex, even abstract ideas just by stringing words together. We owe much of this to syntax, a breakthrough that enables more elaborate messages based on how we arrange words and phrases.
Lots of animals communicate vocally, combining otherwise meaningless sounds to make useful words. But then assembling those parts of speech like linguistic LEGOs has always been considered a uniquely human ability — until now.
And how do we know we're not alone? A little bird told us.
That bird is the Japanese great tit (Parus minor), a small East Asian songbird related to North America's chickadees. In a new study led by Toshitaka N. Suzuki, a biologist at Japan's Graduate University for Advanced Studies, scientists reveal this species has rules for compositional syntax, the first such evidence in any animal but us.
"This study demonstrates that syntax is not unique to human language, but also evolved independently in birds," says co-author David Wheatcroft, postdoctoral researcher at Uppsala University, in a statement about the study.
Language has two levels of syntactic structure, the study's authors note: phonology, which makes meaningful terms out of nonsense noises, and compositional syntax, which combines terms to create more meaning. Many birds and mammals can do the former, even mixing sounds to add meaning similar to how we use prefixes and suffixes. The Campbell's monkey, for example, can modify alarm calls by adding "-oo," increasing the generality of the call. But since "-oo" is never used alone, scientists consider it a suffix, and thus closer to phonology than compositional syntax.
P. minor uses a compound phrase that seems to mean something like 'Watch out! Come here.' (Photo: scientre/Flickr)
With the Japanese great tit, however, the researchers found something eerily human. Not only do they use complex calls as "words" to convey different concepts, but they also chain those words together to form compound dispatches. And the order of words even seems to influence the overall meaning.
Bird is the word
Birds in this family, Paridae, make intricate "chicka" or "chick-a-dee" calls (for which chickadees are named). These include different note types (A, B, C and D) that birds use for various purposes like reporting food, mobbing predators or social cohesion. Past research has shown these notes have unique functions: Carolina chickadees, for example, use more D notes when discovering food or mobbing a predator, the researchers write, "and D-rich calls serve to attract flock members to the callers."
In the new study, the researchers found that P. minor combines calls to a degree never seen in other birds. It often uses an "ABC" call — three notes that tell friends and family to scan for danger — followed by D — which, as with chickadees, beckons fellow birds. When the ABC-D call was made, the birds responded with both behaviors: First they scanned for predators, then they flew toward the speaker.
Here's a recording of the ABC and D calls, followed by the ABC-D combo:
(Audio: Toshitaka Suzuki)
Yet they barely responded when the call was played in reverse, D-ABC, suggesting ABC-D is more of a compound message than just two distinct phrases strung together. (In English, this might be akin to how the compound words "songbird" and "birdsong" have different — albeit related — meanings.) And given the high stakes, syntax rules could be a lifesaver for these tiny birds, since it doesn't do much good to check for danger after you've obeyed a preceding invitation.
Here's a comparison of the normal ABC-D call and the reversed D-ABC:
(Audio: Toshitaka Suzuki)
When used on its own, the ABC call essentially means "watch out!", the researchers write, and is produced when a hawk or other predator is nearby. Since D calls mean "come here," it seems like an odd request: "Watch out! Come here."
But the Japanese great tit apparently hears a unified message greater than the individual parts of the ABC-D call — especially given its apparent confusion at the sound of D-ABC. And according to the study's authors, that may be because ABC-D is a compound word, invented by birds to serve a precise purpose.
These illustrations show how P. minor reacted to various combinations of calls. (Image: Toshitaka Suzuki)
"Tits frequently combine these two calls into ABC-D calls when, for instance, the birds encounter predators and join forces to deter them," explains a press release about the research. "When hearing a recording of these calls played in the natural order of ABC-D, the birds are alarmed and flock together."
In other words, this bird can make words from other words. It's not a very complex example, but it's still a major discovery. Our ability to coin, combine and repurpose words lets us use a finite vocabulary to discuss virtually infinite topics, and although birds may not be in our league, this indicates they at least share the basic skill.
"The results lead to a better understanding of the underlying factors in the evolution of syntax. Because the tits combine different calls, they are able to create new meaning with their limited vocabulary," says co-author Michael Griesser, an anthropologist at the University of Zurich. "That allows them to trigger different behavioral reactions and coordinate complex social interactions."
Now that we're aware of this, the authors say they hope it will spur us to find syntax in other birds, and maybe other animals. "We hope people start looking for it," Wheatcroft tells Rachel Feltman of the Washington Post, "and find it everywhere."
But this revelation is also pretty newsworthy for humans — and not just because we need an ego check now and then. As Wheatcroft explains, studying syntax in songbirds could offer hints about our own early experiments with grammar.
"Understanding why syntax has evolved in tits," he says in a statement, "can give insights into its evolution in humans."