Guest post by Susan Milius
Songs of hermit thrushes offer a tantalizing suggestion that some of the conventions of human music might have an underlying biological basis.
In its somewhat melancholy songs, North America’s Catharus guttatus thrushes mix in strings of short, non-wavering tones. In 54 out of 71 thrush songs, two statistical methods showed those tones related to each other much as notes in human musical scales do, researchers report November 3 in the Proceedings of the National Academy of Sciences. The hermit thrushes “have a strong preference for the same simple ratios [such as 3:2] that humans seem to like,” says paper coauthor Tecumseh Fitch of the University of Vienna.
Such similarities fuel speculations that musical principles reflect something innate in how brains perceive or remember sounds.
First a thrush sings notes in their natural order. Then the recording rearranges the same natural notes from lowest pitch to highest as if the bird were singing them as part of a musical scale. A string of pure tones then presents a close, musiclike version.
A hermit thrush song with a note string judged to be harmonic (approximating simple ratio relationships like those in human musical scales) played at natural speed.
A hermit thrush song judged to be nonharmonic played at natural speed.
Credit: E.L. Doolittle et al/PNAS 2014