The flutelike song of the hermit thrush (Catharus guttatus), a common North American bird renowned for its musicality, shares several characteristics with human music. The study, published in Proceedings of the National Academy of Sciences this week, is the first evidence of a bird song that makes use of the same mathematical principles underlying Western and many non-Western musical scales -- demonstrating the surprising convergence between human and animal song cultures.
There’s a long-running debate about the extent to which the structure of human musical scales derives from biological aspects (such as our auditory perception and vocal production) or as the product of historical, cultural accidents. In other words, is the origin of human music more biological or more cultural? For added perspective, researchers have turned increasingly to birds and whales.
If human music is culturally bound or dependent on specific characteristics of our voice and hearing system, then these traits should be absent from animal vocalizations. “If an aspect of music is found not only in humans, but also in a variety of non-human species, this would suggest that there may be something in our shared biology that predisposes us to find that aspect interesting, or attractive, or easy to sing,” says study coauthor Emily Doolittle of the Cornish College of the Arts.
So, Doolittle and a team led by W. Tecumseh Fitch from the University of Vienna studied song recordings of 14 male hermit thrushes sampled throughout the U.S. They analyzed the pitches and frequency of sounds in 71 song types that contain 10 or more notes. “The idea that hermit thrushes sing scales -- particularly pentatonic [five-note] scales -- seems to have captured the human imagination and has been repeated so often that many people assume it is true,” Doolittle tells Smithsonian. The team initially set out to refute these claims... they were surprised.
According to their statistical models, most of the hermit thrushes’ songs contain musical scales that are mathematically similar to the harmonic series commonly used in our musical scales. A harmonic series, Smithsonian explains, includes a fundamental base note followed by notes that continue to increase in audio frequency based on multiples of that note. This mathematical distribution is known as integer multiples.
Furthermore, the selection of this frequency doesn’t come from biological constraints of the hermit thrush’s vocal tract. Rather, the males simply seem to prefer singing in harmonic series. Maybe these notes are easier for the males to remember, Science explains, or perhaps they provide a ready yardstick for female hermit thrushes to measure them with. Either way, scale determination, it would seem, isn’t unique to humans and may be both culturally and biologically determined.