Decoding birdsong
MATING BIRDS’ SONG IS A LEARNT BEHAVIOUR AND IT GETS SWEETER OVER TIME
On a dewy summer morning, Karla Rivera-caceres, an ornithology researcher at the University of Miami, crouched in her usual workspace — the tall grasses of Costa Rica’s woodland — and heard something unusual.
Rivera-caceres studies bird song, and that day she was listening to the canebrake wren, a brown bird whose bland appearance belies an unusual and extremely complex call.
Canebrake wrens are songbirds, the subset of species whose calls develop beyond the standard tweet or chirp into full-ledged ballads — and within that group they are part of a somewhat exclusive club: duetting birds.
When two of these wrens communicate, they weave their songs into an elaborate, Sonny and Cherstyle duet. They warble back and forth, literally inishing each other’s phrases, with such high coordination that, to an outsider, they sound like a single voice.
But as Rivera-caceres sat listening that morning in 2011, she noticed something odd about this pair’s effort: Their duet was really bad.
The birds were sloppy. They chirped over each other. They sang the wrong responses and screwed up the timing. They were young, still inexperienced at singing, and it showed. As birdsong goes, their act was like a 5-year-old
belting opera. In the world of bird science, her observation proved huge.
Namely: it demonstrated that birdsong works even more like language than we think — that in order to achieve their Pavarotti-esque exchanges, wrens need to learn a speciic set of social rules
which are similar to what humans might call manners.
Rivera-caceres’ discovery launched her on a years-long research project at the University of Miami. Her indings
are already altering the way scientists conceive of birdsong.
“People think humans are so unique,” Rivera-caceres said, “But these birds are talking to each other, developing intimate codes. We’re not the only ones who communicate or hold complex thoughts.”
Humans have been fascinated by the music of birds for centuries. Expert bird watchers learn to identify species they might not even be able to see simply from their distinctive calls.
For scientists, calls and songs can tell different stories. Researchers are increasingly inding that
some birds are forced to alter songs to adapt to the surrounding din of humanity.
Comparisons between birdsong and human language date back to Darwin, Rivera-caceres said and scientists have long studied how baby birds learn the tunes of their songs — just like infants learns new words.
But Rivera-caceres’ focus was more like an avian Emily Post — she was interested in how those birds learned to use those songs and how their interactions relected a set of shared social guidelines, much like the subtle norms that govern human conversation with friends, family, and romantic partners.
If you aren’t a bird expert, the wrens’ song (loud, high-pitched and alternating between notes sort of like a see-saw) might sound like something off the Rainforest setting of a white noise machine. But to the trained ear, their calls are highly speciic and follow a strict set of rules.
“The rules are called ‘duet codes,’” said Rivera-caceres. “Every time a male sings one song type, the female will answer with a certain other song type.” People do this too, Rivera-caceres said: when someone asks about weather, they expect an on-topic answer, not a monologue on television or cooking.
The wrens’ tunes are also carefully timed to avoid pauses or interruption. “If they overlap, the birds stop singing,” said Rivera-caceres. Aversion to pauses and interruptions is also a convention of human conversation. That’s why, for example, people prefer not to speak over each other, or why delays between TV hosts and their correspondents can seem so awkward.
Human manners, as anyone with children will know, are learned with practice — often after many reminders not to interrupt. But when Rivera-caceres irst proposed her project, most researchers believed wrens were born with instinctive codes and rhythms, the way a chimp automatically knows how to grasp or grunt.
Few had challenged this theory, in part because duetting wrens are so dificult to study, with their young hard to ind in the wild. Even Rivera-caceres’ adviser, professor William Searcy at the University of Miami, doubted she could break new ground.
“He said it would be very dificult. It’s hard to study a system that few-to-no people have studied.” Rivera-caceres said. “But when I showed him these duets where the juveniles would do a terrible job at duetting with adults, he was excited.”
“I was excited because nobody had demonstrated that juveniles were worse at duetting than adults,” Searcy said.
Rivera-caceres’ discovery demonstrated that wren-world-etiquette was more like our own: that it was learned by trial-and-error.