Birdsong can be the perfect wake-up call for mellow mornings, with soft chirps and gentle warbles that ease you out of a deep slumber. But if your alarm clock was the male White Bellbird’s mating call, it would be more like waking up to the blaring of a fire alarm. Although it’s only about the size of a pigeon, this South American bird has a call louder than the howl of a howler monkey, and comparable to the hammering of a pile driver.
In fact, the White Bellbird has the loudest bird call ever documented, according to a paper published today in the journal Current Biology. Its short, booming, two-part call is three times the sound pressure level—a measure of sound intensity—of the Screaming Piha’s call, the previous record-holder.
“We could hear them all over the place, they’re kind of the soundtrack of these forests,” says Mario Cohn-Haft, one of the study’s authors and an ornithologist at Brazil’s Instituto Nacional de Pesquisas da Amazônia. “They give out these loud ringing sounds that sound like someone banging on metal, like a blacksmith.”
Cohn-Haft became familiar with the sound through his expeditions in the mountains of the Brazilian Amazon. Curious to find out how loud the bird actually is, he contacted Jeff Podos, a bioacoustician at University of Massachusetts Amherst. The two trekked into the mountains last December and again this February with calibrated sound level meters to record the amplitude of White Bellbird and Screaming Piha calls, which they adjusted for noise and distance to allow for comparison.
Richard Prum, an ornithologist at Yale University who was not involved in the study, says it’s impressive that the researchers were actually able to measure the bellbird's decibel level. “Volume is one of the hardest things to actually measure empirically in the wild because there are so many other elements that can interfere with accurate measurements,” Prum says. “They did an extremely good job of controlling for those elements.”
Part of the cotinga family, which includes umbrellabirds, pihas, and cocks-of-the-rock, White Bellbirds typically live in the high mountains of northern Brazil and southern Venezuela. The males are bright white with a striking black bill that has a wattle dangling from its top. Females, on the other hand, have green plumage accented with streaks of brown.
Since loud sounds are usually associated with long-distance communication, the researchers were surprised to observe that the males save their loudest calls for when a female is close by. They were also fascinated by how females, and the vocalist himself, can endure the calls without hearing damage. “She is effectively sticking her head in a speaker at a rock concert,” Cohn-Haft says.
On several occasions, the researchers observed females joining the males on their display perches. In these interactions, the suitor would turn his back to the female, then dramatically swivel around to face her as he bellowed the song’s second note. The female would always retreat as or just before the song began, but would remain in close range.
Loudness is definitely not a survival tactic—it increases the male’s risk of being detected by predators—so the researchers came to the conclusion that it must be a product of female choice. In other words, females actually prefer and encourage louder males.
“All the different species have gone into different aesthetic directions, just like genres of art,” says Prum, a cotinga expert. “Extreme volume can become aesthetically elaborate. There are lots of arts, whether it’s symphony or rock and roll, where volume is impressive—it’s just another brilliant color.”
Intense female selection is a theme among most birds of the cotinga family, leading to bizarre attributes like extravagant courting behaviors and superbly bright plumage. Within the family, the Screaming Piha has also evolved a loud call. “This convergent evolution tells us that volume is something that is salient,” Prum says.
The question remains, however, why bellbirds evolved to be loud as opposed to performing elaborate dances or donning bright plumage, which seem to be less risky tactics and less damaging to their hearing. Podos thinks it's related to how their beaks have developed. Since White Bellbirds almost exclusively feed on fruits, some the size of golf balls, they evolved a beak that can open very widely. This, in turn, provides them the perfect structure to produce their aggressively loud mating calls.
“The flaring out at the end gives them a big advantage,” Podos says. “They basically have the same anatomy as a bell or the end of a trombone.” The bird’s extraordinary syrinx and unusually thick and developed abdominal muscles are also thought to assist them in belting out their loud calls.
Inhabitants of the 3,000-feet high Amazonian cloud forests, White Bellbirds are part of an ecosystem filled with fascinating birds and species that have yet to be discovered. But these montane ecosystems are endangered by climate change, says Cohn-Haft. As warming occurs, the bird’s habitat zone will move uphill. “The White Bellbird is not considered endangered at the moment, but it will have nowhere to go if the climate continues to warm,” he says.
Cohn-Haft and Podos hope to return to the region early next year to try to satisfy their remaining curiosities about the loudest known creature of the bird world, such as the presence of any adaptations that help prevent hearing damage. They also hope to observe a successful courtship so that they can finally understand what makes these obnoxiously loud males attractive.