A Pitt-Johnstown professor found syntax in the warbling duets of wild parrots

(Press-News.org) With a few minutes of searching, anyone can find videos online of chatty birds: macaws talk to their keepers, cockatoos sing to the camera, corvids mimic the jarring sounds of construction sites.  

Research has shown that some birds can understand and use words in context — so, when Polly speaks up from inside her cage, she may really want a cracker — but scientists know far less about how birds use their vocal abilities in the wild. Christine Dahlin, professor of biology at the University of Pittsburgh at Johnstown, is working to change that. 

“Ultimately I really want to understand how these birds are communicating in the wild,” she said. “I want to know what they are saying, and how they are saying it.”

In one of the first steps to figuring this out, Dahlin and colleagues combined fieldwork, manual sorting and machine learning to begin to decode the warble duets of mated Yellow-naped Amazon parrots, a critically endangered species with a habitat that stretches from southern Mexico to southern Costa Rica. The researchers found these duets have language-like properties, including syntax, collocates and an impressive lexicon.   

The work was published in the Journal of Avian Biology. 

Contact Professor Christine Dahlin at cdahlin@pitt.edu


Why warble?
Dahlin previously studied a less complex type of duet, a “standard duet” made up of far fewer notes, and found it had syntax and other rules. It was unclear whether warble duets, which draw from a much larger repertoire of notes, had similar rules.

“One hypothesis is that maybe warble duets have different notes simply to show their prowess,” Dahlin said. Yellow-naped parrots use these more complex vocalizations when they are fighting for territory. “So maybe the point is just to have a lot of variety — or maybe it’s something else entirely.” 

Some research suggests songbirds will match or not match another bird’s notes during a counter-duet to either escalate or de-escalate a situation. Dahlin was curious about the possibility, but soon realized she couldn’t study the warble duet matching patterns until she knew how many call types the birds were actually using. 

“That started this whole process.” 


In the field
Dahlin and field assistants made several trips to Costa Rica over three years to gather the data they needed. “We’d sit with an old-school video camera and directional microphone and wait for the birds to arrive at their territories,” Dahlin said of sitting in cattle pastures and observing large trees where the birds bred.

“The warble duets would get really fast and really loud when there was a territory dispute,” Dahlin said. “They just sounded very irate and like they were getting in each other’s faces. You could tell the context was changing.” The few physical altercations Dahlin caught in the wild were all preceded by warble duets.

It was, she said, studying animal behavior in its purest form. “Just recording the animals and then seeing what kind of behaviors they have.”

It took more than 10 years for Dahlin and undergraduate students to parse such a massive amount of data, especially with other projects to pursue. Ultimately, they found that of the hundreds of duets recorded, about 50 were warble duets from 13 pairs of parrots. Altogether, the warble duets contained more than 450 calls.


Flexible complexity
Standard duets consist of four call types. In the warbling duets, researchers identified 36 types of calls. 

“There are actually more than 36,” Dahlin said. “Some were rare, some only appeared once, so we didn’t even put them into a category.” 

The researchers needed a way to identify syntactic rules structuring this new, larger set of calls.  Owen Small (UPJ ’19) brought an idea to the team. He’d been using a program called Voyant Tools in a humanities class that he suggested might be useful. “We have this program we’re using to analyze literature,” he said. “Do you think we could use it for the birds?”

They gave it a try. “Voyant was able to run the same analysis as if it were a body of writing,” Dahlin said. “And the results show the parallels between these complex signals the birds are giving and our own language.”

Significantly, Dahlin said, they found what are known in human language as collocates, words that are often paired together — for example, “eat” and “food” or “grass” and “green.” 

The group uncovered more than 20 syntactic rules that the duets followed. Even so, there was very little repetition within a duet, which lasted for 5-10 seconds. “This shows that the parrots are being very precise,” Dahlin said. “They are not simply throwing random notes around.” 

This flexibility bound by rules indicates birds of a pair are taking part in an elaborate calculus.  

“They’re making multiple decisions,” Dahlin said. “Are they going to duet at all? If so, what kind? And what notes are they giving? All of this is happening very rapidly, and they have to do it in coordination with their partner.”

Next, Dahlin plans to return to the disregarded data, of both the warble and standard duets, to learn more about counter-duetting between pairs of Yellow-naped parrots. She also studies the birds’ dialects and other kinds of vocalizations and has plenty of questions about those aspects of their communication. Luckily, she said, “I’ve got years of sound recordings to dive into.”
 

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