Some animals are known for being loud; for example, howler monkeys are said to be aptly named. When a number of them let loose their lungs in concert, the din can be heard up to three miles away. These New World monkeys—found in tropical Central and South America—often cry at dawn or dusk. Large throats and specialized, shell-like vocal chambers in the males help to turn up the volume on their distinctive calls. The sound sends a clear message to other monkeys: this territory is already occupied by a troop.
Likewise, American bison are noisy animals. Their bellows, used to announce the male’s presence and establish dominance within the herd, have been compared to the hammering of a pile driver or revving up a Chevy truck.
But these contenders for “loudest terrestrial animal on the planet” can now move over, because there’s a new, top talent in town. And it only weighs about half a pound.
A hearing conundrum
In a recent study published in the science journal Current Biology, biologists report that they have now recorded the loudest bird calls ever documented. Surprisingly, they’re made by dove-sized, male white bellbirds that live in the cloud forests of the northern Amazon. Not only are white bellbird squawks, made as part of their mating rituals, the loudest bird cries ever recorded, they outblast those of bison and howler monkeys, animals that are bigger and weigh far more than the birds.
White bellbirds are part of an ecosystem that is filled with fascinating birds and other animal and plant species that have yet to be discovered. Part of the Cotinga family, which includes cocks of the rock, pihas and umbrella birds, 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.
Now recognized as the loudest in the world, bellbirds’ short, booming, two-part calls have a sound pressure about three times that of screaming pihas, an Amazon species now demoted to the second loudest bird singer. Jeffrey Podos, coauthor of the study and a bioacoustician at University of Massachusetts Amherst, says the songs are so deafening that they reach decibel levels equal to the loudest human instruments.
In fact, the researchers were made to wonder how white bellbird females listen to the males at close range without damaging their hearing.
A preference for bluster
To conduct their study, researchers used high-quality sound recorders—plus special, sound-level meters and high-speed video to slow the action for later examination—and watched females join males on their display perches. In these types of interactions, the males sing their loudest songs. A male suitor turns his back to a female, then dramatically swivels around to face her as he bellows the song’s second note directly at her. The female always retreats as or just before the song begins but remains in close range.
Why a female willingly stays so close to a male as he sings so loudly—effectively, as if she’s sticking her head in a speaker at a rock concert—is still unknown. It may be that although they risk damaging their hearing systems, the females just want to assess the males up close.
Since loudness is definitely not a survival tactic—it increases the male’s risk of being detected by predators—the researchers conclude that it must be a product of female choice. In other words, females actually prefer and encourage louder males.
The scientists also attempted to identify adaptations—such as beak and head size; unusually thick, well-developed abdominal muscles and ribs; and the shape of the throat—to learn how these may influence the unusual aptitude the birds have for the deafening song transmissions.
One thing that does seem to be apparent is that there is a trade-off for this behavior: as white bellbird and screaming piha songs get louder, they get shorter. This may be because the birds’ respiratory systems have a finite ability to control airflow and generate sound.
A trombone-like instrument
The question remains, however, why white bellbirds evolved to be loud as opposed to donning bright plumage or performing elaborate dances as other birds do, which seem to be less risky tactics and less damaging to their hearing. Jeffrey Podos thinks it may be 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 wide and that flares out at the end. In fact, their beaks basically have the same anatomy as the bell at the end of a trombone. The birds’ extraordinary syrinxes and unusually thick and developed abdominal muscles are also thought to assist them in belting out their aggressively loud mating calls.
A diversity of birdsong
Just like genres of music, animal species have followed different paths into aesthetics. Whether it’s rock and roll or a classical symphony orchestra, there are some arts where volume is impressive—it’s just another brilliant color in the palette of biodiversity.
While we don’t know yet how such small birds managed to get so loud or what makes these noisy males so attractive to female white bellbirds, we do know that birdsong is the glue that holds bird societies together. And the volume of those tunes might just be a matter of personal taste.
Here’s to finding your true places and natural habitats,