A jackhammer reaches 130 decibels. So does the mating call of the bare-throated bellbird, an extreme acoustic output newly tied to heavier bodies and wider beaks by researchers reporting in the journal Evolution on September 29.
Mapping Avian Volume from Massachusetts to Brazil
Ornithologists have spent decades cataloging the timing and frequency of birdsong to understand communication. Yet the sheer volume of bird voices has gone largely unexplored.
To get a read on the racket, University of Massachusetts Amherst behavioral ecologist Jeff Podos utilized a high-grade industrial sound meter and a laser rangefinder in the fields, swamps and forests of western Massachusetts. After logging vocalizations across a few dozen species, Podos enlisted João Menezes to help turn the collection into a broader evolutionary analysis.
Menezes recorded avian calls across the Atlantic Forest near São Paulo, the mountains of Rio de Janeiro, and beyond. The researchers captured audio data ranging from the soft chirps of the dusky-throated hermit hummingbird to the piercing yelps of the red-legged seriema. Ultimately, the team compiled a dataset comprising 123 species.
How Anatomy Drives Acoustic Power
The resulting evolutionary analysis revealed a physical correlation: heavier birds and those with broader beaks tended to produce louder calls. The bare-throated bellbird (Procnias nudicollis), a stout South American forest dweller characterized by a broad bill and a blue-green throat patch, utilizes this anatomical framework to generate a metallic mating cry.
This relationship between anatomy and acoustic performance is supported by biophysicist Gabriel Mindlin of the University of Buenos Aires. Mindlin, who was not involved in the research, noted that larger birds possess the potential to generate greater respiratory pressures and flows. Furthermore, morphological traits such as beak opening can affect how efficiently acoustic energy radiates.
From the Amazonian White Bellbird to a Broader Trend
The investigation into avian noise extremes dates back to 2019, when Podos and a colleague identified the Amazonian white bellbird (Procnias albus), a cousin of the bare-throated bellbird, as a record-setting vocal powerhouse with calls reaching 125 decibels. The dataset published in Evolution demonstrates that the white bellbird’s performance is part of a broader trend linking body mass and bill width to acoustic output.
Unanswered Questions in Behavioral Ecology
While the anatomical mechanics are increasingly clear, the evolutionary pressure that drove certain species to evolve such volume remains a mystery. Menezes and Podos examined several potential ecological factors, including mating behavior, habitat density, and flight ability. None of these variables provided an explanation that consistently held across species.
For now, the question of why evolution cranked up the volume on these avian megaphones remains a puzzle.
