Science1 publisher3 min readPublished
Broad beaks and big bodies predict which birds call loudest
Joao Menezes and Jeff Podos of UMass Amherst report in Evolution that body size and especially beak width track call volume across 123 bird species. Their tests of mating behaviour, habitat density and flight ability found no general reason why extreme loudness evolved.
The Scientist · Science desk
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What happened
- The survey grew out of a 2019 measurement by Podos and a colleague that put the white bellbird's call at 125 decibels, then the loudest bird call on record.
- Podos carried an industrial-grade sound meter and a laser rangefinder through woods, swamps and fields in western Massachusetts, recording whatever birds he found.
- Menezes extended the measurements across Brazil, from the Atlantic Forest near Sao Paulo to the mountains around Rio de Janeiro.
- Gabriel Mindlin, a University of Buenos Aires biophysicist not involved in the work, called the link between anatomy and loudness sensible and plausible.
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Why it matters
- constraint Because volume tracks size and beak width, a small, narrow-billed species has less physical room to get loud, and any behavioural explanation has to be tested against that baseline.
- capability With 123 species measured, loudness becomes a trait biologists can compare across birds, as they have long compared the timing and frequency of song.
- decision Researchers hunting for why extreme volume evolved have reason to test mating or habitat pressures within single lineages such as the bellbirds, since no bird-wide pattern appeared.
A Canada goose can honk at about 100 decibels, chainsaw volume, while a starling's chatter rarely rises above 70 [6]. Decibels are logarithmic, so that 30-point gap is roughly a thousandfold difference in sound intensity [14]. Ornithologists have had little explanation for it [6]. Decades of birdsong research went into cataloguing the timing and frequency of calls, and loudness was largely left alone [7].
Menezes and Podos now have an anatomical answer to part of the question. The heavier the bird, the louder its call tended to be, and the same held for broader beaks [13]. According to the Science News account, beak width was the stronger of the two [2]. Gabriel Mindlin, a University of Buenos Aires biophysicist who studies birdsong and was not involved, gave the physical case. "Larger birds have the potential to generate greater respiratory pressures and flows, while morphological features such as beak opening can affect how efficiently acoustic energy radiates," he said [12].
Mindlin's account gives the pattern a plausible physical basis, though the result is still a comparison across species. The report does not give effect sizes, how far body size and beak width overlap as predictors, or how the analysis handled relatedness between species. The thing this doesn't tell you is direction. A wide beak permits a loud call, but the comparison cannot say whether selection for volume widened beaks, or whether beaks widened for some other reason and volume followed.
The ecological half of the study came up empty. Mating behaviour, habitat density and flight ability were each tested, and none explained volume consistently across species [3]. "We weren't able to find an overarching pattern that applies to birds in general," Menezes said [4]. That wording leaves room for a pressure that works inside particular lineages.
The sample matters here. It was built from whatever birds Podos could find around western Massachusetts [8] and from Menezes's fieldwork across Brazil, which ran from the soft chirps of a hermit hummingbird to the yelps of a red-legged seriema [9]. The authors call the result the largest vocal-volume dataset to date, at 123 species [10]. In my view, a null result on a sample gathered this way counts against a single bird-wide driver of loudness more than it counts against any one pressure acting in some groups.
The bellbirds show both halves of the finding. The bare-throated bellbird, a stout, broad-billed species, can top 130 decibels, louder than a jackhammer [1]. That is five decibels above the 125 that made its Amazonian cousin, the white bellbird, the loudest bird call ever measured when Podos and a colleague reported it in 2019 [15][5]. Its anatomy fits the new result. Its call is a mating call [1], and mating behaviour was one of the pressures that failed to explain volume across the full set [3].
What to watch
- Whether the Evolution paper reports the beak-width effect separately from body size, with a correction for relatedness between species.
- Lineage-level tests of mating system or habitat within the bellbirds and their relatives, where a pressure absent from the bird-wide data could still appear.
- Volume data from birds outside the Americas, to test whether the size and beak pattern holds beyond Massachusetts and Brazil.