A scientific study revealed that two species of native Brazilian birds, the bare-throated araponga (Procnias nudicollis) and the seriema (Cariama cristata), rank among the animals with the highest calls ever recorded by science. The sounds emitted by both exceeded 120 decibels (dB) peak, a level comparable to or higher than that generated by extremely loud tools, such as jackhammers and chainsaws.
This discovery was made by researchers from the University of Massachusetts Amherst, in the United States, including the Brazilian João C.T. Menezes, during his postgraduate work. The findings were published in the scientific journal Evolution.
Research Objective
However, the scientists' purpose went beyond merely classifying noise. The investigation aimed to understand which physical attributes influence the intensity of the calls and to verify whether vocal volume is linked to the environment where the species live or their social structure.
To achieve this goal, the researchers measured the vocal amplitude of 123 types of birds in locations near Amherst, Massachusetts (USA), and in various regions of Brazil. Among the examined species, 113 had never had their call volume cataloged before.
Menezes clarifies that there is still little information available about bird vocal amplitude. The results suggest that certain Brazilian species are close to the maximum sound production limit observed in these animals. He told g1 that 'we can say with certainty that the Amazonian and Atlantic Forest arapongas and the seriema emit the loudest calls ever measured.'
Contextualizing Previous Records
The new discoveries also provide context to a previous record. In 2019, members of the same university identified the white araponga, found in the Amazon, as the bird with the loudest documented call, reaching peaks of up to 125.4 dB, a feat later recognized by the Guinness World Records.
Thus, the current research does not define a single absolute champion. Different species may occupy the top depending on the methodology used by researchers to calculate the volume. However, for the scientists, the main focus lies in understanding why some birds evolved to produce such powerful sounds.
Physical Characteristics Found
The researchers identified two physical characteristics that help explain the variations in volume: body size and beak opening width. Generally, larger birds tend to produce louder sounds, also possessing more developed muscles that facilitate greater air compression and, consequently, a more vigorous sound emission.
Additionally, birds with stronger vocals exhibit notably wide oral openings. The comparison made by the scientists relates to musical instruments; wider structures, such as the bells of wind instruments, can aid in sound amplification.
The seriema was pointed out as the largest species among those analyzed, while the arapongas demonstrate exceptionally wide beak openings relative to their body size.
Ecological and Evolutionary Hypotheses
Despite these advances, the researchers have not yet fully elucidated the reason why certain species produce such extreme sounds. Before the study, the scientists formulated several hypotheses about the possible ecological and evolutionary functions of these intense calls.
One theory was that noisier birds might have more limited flight capabilities, using sound as compensation for reduced mobility. Another possibility considered was that species living in dense forests needed louder calls to ensure communication when vision is ineffective.
The researchers also speculated that birds with louder calls might show a higher incidence of polygamy, since calls capable of covering long distances could aid in locating potential mates. However, the collected data did not widely confirm these assumptions.
Menezes emphasizes that 'among the ecological factors we studied, none clearly explained why some species evolved louder calls than others. This does not mean that habitat, flight capacity, or mating system are never important, but rather that they do not seem to be general rules for birds as a whole.'
For the scientists, although body size and beak opening help explain how certain birds generate such strong sounds, they do not yet fully clarify why this ability evolved. 'There must be something particularly efficient in the way they produce or radiate the sound that body size and beak width alone do not explain. Discovering this 'something extra' is precisely one of the questions arising from the study,' he adds.
Methodological Challenges in Sound Measurement
Determining the exact volume of a call in a natural environment is a complex process because the intensity of the sound depends directly on the distance between the bird and the measuring equipment. A call that sounds deafening up close may be poorly recorded hundreds of meters away. For this reason, an alternative would be to capture the animal and conduct experiments in a laboratory under controlled conditions.
However, this method proves impractical when the research covers numerous species and multiple global regions. To conduct field measurements, the scientists employed laser rangefinders, capable of measuring the distance to the bird, along with high-resolution portable sound meters. The combination of these instruments allowed them to correlate the recorded intensity with the animal's distance, thus obtaining comparable measurements between species.
With this methodology, the researchers managed to significantly increase the number of species for which reliable data on the amplitude of their calls exists.
The study partially answered the posed questions, leaving others pending. Scientists now know that larger birds with wider mouths tend to emit louder sounds. Nevertheless, these characteristics do not fully explain how some relatively small species achieve volumes comparable to those of much larger animals.
For Menezes, two points should guide future investigations: what is the mechanism that allows these birds to produce and radiate such powerful sounds, and what is the evolutionary advantage of this ability. 'Now we want to better understand what is special about these species that allows them to produce and radiate such intense sounds.'
There remains uncertainty about the costs associated with this behavior. An extremely loud call may favor communication or competition for mates, but it can also increase the bird's vulnerability to predators. 'What is interesting now is to directly test what advantages these extremely loud calls offer and what costs come with them. It is quite possible that different species reached extreme amplitudes through completely different evolutionary paths,' concludes the Brazilian researcher.
Therefore, for the researchers, discovering which birds are the loudest is only the starting point. The central question becomes understanding why evolution led distinct species to develop such an extreme vocal capacity.