Birdsong across thousands of species is comprised of a combination of the same eight building-block sounds, according to a new study that offers fresh insights into one of nature’s most enduring mysteries.
Passerine birds typically sing to attract mates or ward off rivals and their songs can vary from single, repeated notes to complex melodies.
Songbirds are extremely diverse, making up almost 60 per cent of all birds. Known species of songbirds number over 6,500, all going back on the evolutionary timeline to an ancestor that lived over 50 million years ago.
But the diversity and sound architecture of birdsong is largely understudied, researchers from the Bioacoustics Research Lab in CRNL, France, say. It remains unclear, for example, how different song patterns emerge in bird species living in different environments.
The new study, which involved an analysis of around 116,000 songs from 3,160 species, revealed that the astonishing variety came from just eight basic acoustic motifs such as trills, whistles and harmonic notes.
The nature of each song is influenced by the local environment of the species, according to the study published in the journal Science.
Researchers said they used a new method to capture the full complexity of birdsong. Instead of just analysing simple sound features, like pitch or frequency, they examined the detailed patterns across time and frequency, allowing them to compare songs at an unprecedented scale.
They concluded that the eight basic acoustic motifs evolved early in the history of birdsong and were repeatedly adapted to local conditions.
Researchers also noted that each songbird species typically used only about five of the eight motifs in its repertoire.
Most species rely heavily on one dominant motif but some use a more balanced mix of motifs. Some environmental constraints appear to determine how birds combine the eight motifs, particularly the way sound travels in an area, as well as local pressures on the species to communicate clearly.
For instance, flat whistles are favoured in tropical rainforests where dense vegetation limits sound transmission. In comparison, ultrafast trills are common in temperate regions where close-range communication and intense seasonal mating favour more “information-rich songs”, scientists say.
The findings represent “one of the most comprehensive analyses of passerine song evolution to date”, animal behaviour expert Elodie Briefer, who was not involved in the study, said.
“In addition to advancing our understanding of avian communication, their approach could be used to study the evolution of complex acoustic systems across other biological groups.”
