Global study of bird song frequency

A study of the songs of most of the world’s passerine birds reveals that the frequency with which birds sing is highly dependent on body size, but sexual choice also has an impact . The new study from Max Planck Institute of Ornithological researchers and colleagues suggests that habitat features do not affect song frequency, thus rejecting long-term theory.

Many animals use acoustic signals to communicate. These signals have been developed to increase the efficiency of transmission and reception of the sounds, as this helps to find a companion or avoid predation. One of the basic characteristics of acoustic signals is the frequency of the sound. In wooded habitats, acoustic signals are exacerbated as a result of sound absorption and dispersal from foliage, which is particularly difficult for high-frequency sounds. Thus, theory from the 1970s predicts that animals living in densely vegetated habitats emit lower noises compared to those living in open areas. .

A team of researchers led by Bart Kempenaers from the Max Planck Institute of Ornithology in Seewiesen and Tomáš Albrecht from Charles University in Praha and the Czech Academy of Sciences analyzed the difference in song frequency of more than 5.000 species of passerine birds, including 85% of all passerines and half of all bird taxis. PhD student Peter Mikula collected song recordings exclusively from xeno-canto, a citizen science source of bird words, and from the Macaulay Library in the Cornell Ornithology Lab.

Relationship between song frequency and body size.

Contrary to theory, the study reveals that the peak frequency of a passerine song is not dependent on habitat type. If anything, the data shows that species living in densely vegetated habitats sing at lower frequencies, contrary to expectations. As would be expected from basic physical principles, the researchers found a strong relationship between song frequency and body size and the influence of shared ancestry. “Both limit the range of sound frequencies that an animal can produce,” says first author Peter Mikula. Heavier species sing at lower frequencies simply because of the larger vocal structures of the vocal apparatus.

The study also reveals that genres in which males outnumber females perform songs with lower frequencies than expected from their size. “This supports the notion that signal competition for companion access affects the frequency of acoustic signals,” says Bart Kempenaers. The frequency of a song can be an indicator of a person’s size and therefore of his or her leadership or fighting abilities. Thus, song frequency may affect reproductive success through competition with other males or even because it affects male attractiveness to females.

“Our results suggest that the global variation in passerine song frequency is driven mainly by natural and sexual selection causing evolutionary shifts in body size rather than by habitat-related selection. on sound propagation “, summarizes Tomáš Albrecht.

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Original publication

Peter Mikula, Mihai Valcu, Henrik Brumm, Martin Bulla, Wolfgang Forstmeier, Tereza Petrusková, Bart Kempenaers & Tomáš Albrecht

A global study of song frequency in passerines does not support the notion of phonetic change but suggests a place for sexual selection.

Ecology Letters

12 December 2020