Birdsong study explains why birdsong differs worldwide

A new study in Science offers a global explanation for why birdsong differs from place to place. Researchers analyzed more than 116,000 songs from 3,160 passerine species and found eight recurring sound motifs that appear across the group.

The work, by Quentin Bacquelé and colleagues, gives researchers a broad framework for comparing bird songs beyond simple measures such as average pitch. According to the study, birdsong must carry information while also remaining recognizable as it moves through forests, open areas and other habitats.

Why does birdsong differ around the world?

The study says global birdsong patterns reflect both ancestry and environment. Evolutionary history explained the largest share of variation in motif use, while habitat and the physics of sound transmission also helped shape which sounds species used.

Birdsong is used for communication across space, including attracting mates, holding territory and signaling to rivals, according to the researchers. A song that works well in dense, humid vegetation may be different from one that works over shorter distances or in more open habitats.

Eight motifs tied thousands of songs together

The researchers focused on passerines, a bird group they said is well suited to a global test because it spans nearly all land habitats, includes more than 6,000 species and accounts for more than 60% of bird species. The songs in the analysis came from a citizen science collection.

Using automated sound analysis, the team classified recordings by a method called modulation power spectrum, which measures how sound energy changes across frequency and time. The study found that most songs combine two to eight motifs, rather than relying on a single sound type.

The eight motifs included three trill types at different speeds, three whistle types with different pitch patterns, plus two more complex forms the authors described as atonal chaotic notes and harmonic stacks. The study reported that 65.3% of species used their dominant motif in more than 80% of their songs, while 34.7% used their main motif less often, allowing more variation.

Habitat and behavior shaped song choices

The researchers found that species using long-distance communication tended to produce more flat whistles and slow trills. Species communicating at closer range were more likely to use faster or more complex motifs, including harmonic stacks and ultrafast trills.

The study also linked mating systems to song structure. Polygynous species showed a smaller but consistent shift toward more complex sounds, including fast-modulated whistles, according to the researchers.

Phylogeny accounted for 82% of the explained variation in motifs, the study found. After mapping motif locations and comparing them with traits, evolutionary relationships and habitat models, the researchers reported that sound travel through different environments helped explain global patterns.

In tropical rainforests, birds tended to use simpler sounds such as flat whistles and slow trills, which the study says hold their identity better over distance in dense vegetation. In temperate regions, birds more often used faster, more complex trills and whistles, even though those sounds are more vulnerable to degradation over longer distances.

The researchers said the findings support acoustic adaptation in tropical rainforests and point to a different pattern at temperate latitudes, where shorter communication distances and stronger sexual selection may favor complex songs. The study noted limits, including incomplete species coverage and possible identification errors in open-source song collections, but said the framework can help test broader ideas about how animal signals evolve.

This story draws on original reporting from Phys.org.