Deep in the Serra do Mar mountains of Brazil, a curious call echoes from high in the jungle canopy. The sound is practically deafening, a loud metallic pang that cuts through the forest’s thick foliage.
The bare-throated bellbird, which produces such calls to attract female mates, is no larger than a dove. And yet his song is louder than a jackhammer or a chain saw. It’s louder than an elephant’s trumpet.
It is, according a new scientific study, one of the loudest birdsongs ever recorded.
“They can even exceed elephants and lions and wolves and bison,” said João Menezes, an evolutionary biologist and lead author of the study, recently published in the journal Evolution.
Joining the bellbird at the top of the volume charts, the researchers found, is another Brazilian species: the red-legged seriema.
The two birds now join a previously identified bellbird species as the loudest avians known to science.
The study also uncovered a few of the anatomical traits that allow these birds to belt such powerful songs, answering many of the questions underlying the mysteries of birdsong.
“This new study is by far the largest cross-species comparison of sound amplitude in birds,” said Gonçalo Cardoso, an ornithologist at the University of Porto who was not involved with the research. “This is just the tip of the iceberg.”
The new work focuses specifically on amplitude, a measure of the height of a sound wave, which helps determine how far a sound can travel. Amplitude is a major component of loudness and is crucial to our perception of sound.
“Until recently, it was very impractical to go out into the field and measure amplitude,” Dr. Menezes said.
To accurately measure amplitude, researchers have to be able to distinguish one bird from many and pinpoint its exact distance from where they are recording. Because of that difficulty, birdsong amplitudes have remained a black box for researchers. Even the Canada goose, one of the most well-known and easily identifiable bird species alive today, has not had its amplitude measured, according to Dr. Menezes. “It’s kind of stepping into a whole new world,” he said.
In the new work, Dr. Menezes and his colleagues used two tools to measure birdsong in the wild. One of them, a range finder, is the same laser device golfers use to measure the distance to holes on a course. The other instrument, a sound level meter, allows researchers to pinpoint whichever bird is making the call, isolating it from background noise and other birds.
The researchers began their work early in the Covid-19 pandemic, when lockdowns kept quiet streets in Amherst, Mass.
“It was just this wonderful time where you can walk outside unmolested, no trucks, no buses, and get beautiful, scintillatingly clear recordings,” said Jeff Podos, a behavioral ecologist and bird expert at the University of Amherst and a co-author of the study. The team then moved on to the Atlantic Forest, jungles and savannas of Brazil, where there is a much greater diversity of bird species.
In total, the researchers documented 123 birdsong amplitudes, creating a database they could plumb for insights about what enables the birds to sing such different songs.
They found that amplitude varied widely across species, with the softest songs coming from hummingbirds, whose tunes registered around 50 decibels — similar to the sound of moderate rainfall.
But the bare-throated bellbird and the red-legged seriema stood out from the crowd.
The bellbird lives in the Atlantic Forest of Brazil, while the seriema, which is about as tall as a crane, lives on the country’s savanna.
Bellbirds have a distinct metallic chirp, while seriemas sing elaborate, melancholic songs that have been the subject of poetry. Both birds produced tunes that registered between 121 and 122 decibels.
“The bellbirds are really super interesting,” Dr. Podos said, “because not only are they that loud, but they make those loud sounds with that small body size.”
Birds are capable of singing with such volume in part because they have a uniquely evolved organ called a syrinx, which takes air from the lungs and projects it through the long tube of the trachea.
“It’s like a tube which serves the same function that a tube on a musical instrument does, like a trombone or a trumpet,” Dr. Podos said. “It helps concentrate the energy into a narrow range of frequencies, so it’s easier to hit louder peaks.”
By comparing the birds’ anatomies with their calls, the researchers found two additional features that contribute to amplitude: beak width and overall bird size. Wide beaks act like the bells on the end of brass instruments, allowing the birds to project a broader sound. Bigger birds, Dr. Menezes said, are aided by hardier, stronger throats.
“Larger birds tend to have larger, bulkier muscles, which can create more internal air pressure,” he said. “And air pressure is exactly what generates loud sounds.”
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