The Amazon rainforest is a deafeningly noisy place, a constant cacophony of jungle animals trying to make themselves heard. Amid the din, the male white bellbird has evolved a winning strategy—he may be the loudest bird on Earth.
“They just seem alien,” says Jeff Podos, a biologist at the University of Massachusetts at Amherst and co-author of a paper released today in the journal Current Biology. According to the study, the bird’s call is twice as loud as its cousin, the screaming piha, another Amazon native.
The bellbird’s call is at least nine decibels (dB) louder than that of the piha, reaching volumes of 125 dB—that’s similar to what you’d hear standing next to speakers at a rock concert. By comparison, a normal human voice is about 60 dB.
What really surprised scientists is the males will blast their notes directly into a curious female’s face, says Russ Charif, senior bioacoustician at the Cornell Lab of Ornithology, who wasn’t involved in the study.
Charif believes that the males may have evolved this trait to impress females, as the louder birds are presumably more fit. It’s likely “females use the loudness to assess the males, presumably preferring louder males,” he says by email. (Read why birds matter, and are worth protecting.)
“This is a cool study, appears to have been carefully done, and the results seem solid,” Charif adds, noting how tricky it is to record animals’ sounds in the wild. The research also offers more insight into the study of sexual selection, and how animals will go to incredible lengths to secure a mate.
Turning up the volume
Podos and colleagues didn’t set out to find the world’s loudest bird. Co-author Mario Cohn-Haft, curator of birds at the Instituto Nacional de Pesquisas da Amazônia in Manaus, Brazil, brought a specimen of a male white bellbird back for the museum after a research trip.
Back in his office, Cohn-Haft examined the animal and found its ribs were embedded in thick, well-defined abdominal muscle—prompting him to hypothesize the unusual structure had something to do with their high-volume calls.
Discovering that no one had published a study about bellbirds or their singing, the team set out into the rainforest to record the male bird’s sounds. (Females, which sport greenish yellow plumage, don’t vocalize at all.)
The team tracked and recorded wild pihas and bellbirds and classified their calls into three types. Those are the male pihas' call, the male bellbirds' Type 1 song—which is quieter and longer—and the male bellbirds' Type 2 song, which is louder and shorter. (Read about some of the world’s loudest animals.)
The authors then calculated the calls to see how loud each would be one meter away from the bird.
The pihas calls proved to be the softest, and the Type 2 bellbird calls the loudest. But the researchers weren’t able to say whether the distinct musculature is part of the bellbird’s singing talent.
There's a reason the Type 2 song is so simple and short—reaching such a high decibel requires some effort.
“If you asked a trumpeter to make the loudest sound they could,” Podos says, it would “make a sound like the bellbird—one pure crystal note.”
Bellbirds have a very precise courtship ritual, which always ends with the male pivoting on the branch and blaring one last note at the female. The sound is likely loud enough to damage the female’s hearing, but the scientists found no evidence of such an impact.
"She’s played this game before, so she knows what’s coming,” Podos says. For instance, when he puffs up in preparation to make that big call at her, the female often "flies off to a more reasonable distance." (Read about “moonwalking” birds and other avian courtship rituals.)
However, the team didn’t witness any successful copulations among the observed birds.
Bob Mulvihill, an ornithologist at the National Aviary in Pittsburgh, says that male birds generally will tone down courtship displays if the female seems fearful. For this reason he suspects the male bellbirds’ high-call volume teeters at the extreme edge of successful sexually selected traits.
Adds Mulvihill, it’s hard not to giggle at the idea of male wanting to woo a female so badly he blasts her right off the perch.
That is, Podos says, "adorably dorky."