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A framework for birdsong mechanics
To be functional, the sound waves that comprise a bird's song must both carry useful information and survive traveling through the environment to another bird. The authors of the new study say scientists aren't sure how much of the global bird soundscape is a consequence of phylogenetics and how much has been shaped by the physics of species' habitats. Earlier studies have often reduced songs to basic measures, such as average pitch, neglecting the timing and frequency patterns that make songs information-rich.
The study authors write, "These approaches do not fully capture the rich informational content embedded in a song's intricate spectro-temporal architecture—the very patterns of frequency and amplitude modulations that carry its meaning. In this work, we explicitly treat birdsongs as vectors of information to map the global diversity of acoustic communication and uncover its environmental drivers."
Some prior work proposed that habitats shape animal calls because forests, humidity and background noise distort sound differently, while others linked birdsong to body size, beak shape, mating systems and cultural learning. This study ties all of these together through the songs of 3,160 passerine species collected through a citizen science project. The team says passerines are an ideal test case because they occupy nearly every land habitat, include more than 6,000 species and represent more than 60% of all birds.
The eight building blocks of birdsong
The researchers used automated sound analysis to sort recordings into eight recurring acoustic motifs. They characterized each song by its modulation power spectrum, a sound representation that maps energy across spectral and temporal modulation dimensions. They found that most songs combine between two and eight motifs, much like combining elements in a musical phrase.
The eight motifs included three types of trills at different speeds, three types of whistles with differing pitch modulation and two more complex structures that the researchers call atonal chaotic notes and harmonic stacks.
The study authors write, "Notably, most species (65.3%) display their dominant motif in more than 80% of their songs. In the other species (34.7%), the dominant motif is used to a lesser extent, which allows for greater song variability. Given that passerines share a keen ability to resolve complex spectrotemporal modulations, these eight motifs are certainly perceptually distinguishable by all passerine species."
Patterns of birdsong across the world
The team found several song patterns that reflect both a species' evolution and ecology, including those involving social behavior, body form and mating systems. For example, they found that species that use long-range communication produce a higher proportion of flat whistles and slow trills. Meanwhile, species signaling at close range were more likely to use faster and more complex motifs, like harmonic stacks and ultrafast trills.
Mating systems were also correlated with a smaller but consistent shift in motif composition, with more complex sounds, like fast-modulated whistles, occurring more often in polygynous species. However, the team says phylogeny accounted for the largest percentage of variation, at 82% of the explained variation in motifs.
When they mapped where motifs occur, compared them with bird traits and evolutionary relationships, and modeled how well sounds travel in forested and open habitats, they found that habitat and sound physics strongly shape the global map. This is largely due to the way sound travels in dense, humid environments, like tropical rainforests, versus more open and less humid environments.
A trade-off appears to exist between encoding more information and transmitting it over long distances. Birds in tropical rainforests tended to use simpler sounds, especially flat whistles and slow trills, which retain their identity over long distances in dense vegetation. On the other hand, birds in temperate regions more often favored fast, complex trills and whistles, even though they degrade more easily over longer distances.
The study authors write, "Although our results support the acoustic adaptation hypothesis in tropical rainforests, where species preferentially use song motifs resilient to signal degradation, they reveal a contrasting regime in temperate latitudes. In these regions, more complex and degradation-prone motifs are favored. We propose that this shift is driven by shorter interindividual communication distances and more intense sexual selection, which together outweigh the costs of propagation constraints."
This study highlights how animal communication is shaped not only by evolution and courtship but also by the physical world through which sound travels. There are some limitations, as not all species are covered in the study and the use of open-source collections for bird songs can result in inaccurate species identification. However, the team says its framework provides a robust foundation for scaling up evolutionary hypotheses on signal transmission that were previously formulated at local scales.
Written for you by our author Krystal Kasal, edited by Lisa Lock, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Quentin Bacquelé et al, The global biogeography of passerine songs, Science (2026). DOI: 10.1126/science.aee6239
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Citation: Why and how birdsong differs across the world—and the eight motifs that tie them together (2026, July 24) retrieved 24 July 2026 from https://phys.org/news/2026-07-birdsong-differs-world-motifs.html
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