What are they doing extremely complex mockery songs have in common with Tuvan throat singing, Beethoven’s Fifth Symphony, song “Show yourself“from Frozen 2and Kendrick Lamar “Duckworth“? According to recent article published in a journal Limits in psychology, the mockingbird follows similar musical rules as those used in human music when composing her songs.
“When you listen to a mockingbird for a while, you can hear the bird not randomly lowering the tunes it mimics,” said co-author Tina Roeske, a neuroscientist at the Max Planck Institute for Empirical Aesthetics. “We seem to follow similar clips of the melody according to consistent rules. However, to scientifically examine this conjecture, we had to use quantitative analyzes to check if the data actually supported our hypotheses.”
Mockingbirds are known for their ability to imitate other birds and certain sounds from their environment, provided that these sounds fall within the acoustic range of the mockingbird. For example, birds can mimic blue jays, but not ravens, frogs, but not bull frogs. Over half of the songs are mockery of mimicry, and the species boasts an impressive repertoire consisting of hundreds of types of phrases.
Over the decades, there have been numerous tests of mockery songs, and this is how scientists know that mockery usually repeats each syllable three to five times, separated by tiny breaths, before moving on to something new. (A “syllable” can be a single note or a set of notes.) One 1987 study classified thousands of phrases for a song of only four birds, concluding that although there are hundreds of types of syllables, most are not produced often; 25 percent appeared only once in the sample data.
What is less understood is how mockingbirds choose which syllables to sing – that is, how they move into composing their complex songs. This is not random sampling. This new study is the first attempt to qualify or quantify the specific compositional strategies that the mockingbird uses when composing its musical stylings: so-called “morphing modes,” akin to variations on a theme. To do this, the team reviewed the songs of five different mockingbirds; three were recorded in the field in mid-spring, and the other two are from a publicly available bird database (Xeno-canto).
All three authors provided a unique perspective on the study, Roeske’s specialty is statistical analysis of animal signals. David Rothernberg is a music philosopher at the New Jersey Institute of Technology who studies the connections between music and nature. And Dave Gammon is a field biologist from Elon University in North Carolina, who has studied mockery songs (and one bird in particular) for many years.
“When confronted with a complex mockery song, the musician will hear one thing, the ornithologist another, and the signal analyst something else,” the authors wrote of the rationale for this interdisciplinary approach. “The most complete human knowledge of any natural phenomenon comes from combining different human forms of knowledge – neither perspective denies the other. They are strongest when applied together.”
The team created spectrograms of mockery songs to visualize the syllables of the components. They listened to the recordings and made their own qualitative assessments of how the “ways of morphing” birds work (transitions between phrases). In the end, they reduced it all to the four basic compositional strategies used by the mockers as they moved from one sound to another: changing the tone, changing the pitch, stretching the transition, and squeezing the transition. They quantified the frequency of the four modes based on song samples from three of the five birds used in the study and found that approximately half of all morphings were timbre-based.
Admittedly, this is a simplification and “almost every transition involves a mixture of more than one of these ways,” the authors acknowledged. The four ways are not a strict classification system, but are more of a heuristic tool. “We use this as a basis from which verifiable hypotheses can be derived,” they wrote, comparing four ways with the minimal pairs commonly used in phonology (e.g., “house / mouse,” “drag / join,” and other word pairs that differ by one phoneme).