Relative Pitch and the Song of Black-Capped Chickadees Chickadees, like people, have a strong sense of relative pitch. These birds use skillful, precise pitch changes to advertise their quality and attract mates Ronald Weisman and Laurene Ratcliffe ore than 2,000 years ago, the acer- descriptions of birdsongs. Donald Bor- Music and Relative Pitch Mbic philosopher Marcus Tullius ror, a master bioacoustician and field Relative pitch is the ability to produce Cicero observed that Roman songbirds biologist, found many of the song de- or recognize a note based on a refer- compose more excellent melodies than scriptions inadequate by modern stan- ence note. The ability to hum a simple any musician. He certainly doesn’t dards, as he wrote in his foreword to tune when given a set note with which stand alone in history on that count; it the 1967 reprinting of Mathews’s book. to start, as most people can, shows is a nearly universal human experience Borror acknowledged that Mathews relative pitch in action. A sense of to find joy and wonder in birdsong— lacked modern electronic equipment relative pitch is common among non- and to compare the songs to human and that his primary interest was in musicians even if they never use the music. People have been transcribing the musical content of birdsongs. To- term, but musical training develops melodies of birds into the notation of day, however, Mathews’s approach this knack. Trained singers have an ad- music since at least the 18th century; seems dated and quaint. Musical no- vanced appreciation of pitch change: Vivaldi’s Goldfinch concerto and Han- tation is simply unable to provide the They can produce precise relative fre- del’s Cuckoo and the Nightingale organ detailed, accurate and reproducible quency changes from one note to the concerto include musical notation for descriptions required in modern bio- next in a melody. birdsongs. In the early 1900s, the New acoustical analyses of vocal commu- To compare the appreciation for England naturalist and composer F. nication among songbirds. Mathews’s relative pitch among humans and Schuyler Mathews presented the songs approach helps musically trained peo- songbirds, it is necessary to under- of many North American birds in mu- ple recognize birdsongs, but it fails stand how musicians and bioacousti- sical notation in his Field Book of Wild to objectively describe birdsongs and cians measure pitch change. Musicians Birds and Their Music in order to help calls. For bioacousticians, accurate ob- describe the change between any two readers identify species common in the servations are a crucial first step in notes on the musical scale as an in- eastern United States. analyzing the role of songs in the life terval. The interval between any two Later biologists did not share of a species. adjacent notes is defined as a semi- Mathews’s enthusiasm for musical Modern ornithologists believe that tone. The ratio between the frequen- songbirds first appeared some 40 mil- cies (measured in cycles per second, lion to 50 million years before human or hertz [Hz]) of the higher and lower Ronald Weisman is a professor emeritus of psy- chology and biology at Queen’s University in beings. That people derive pleasure of two notes separated by a semitone Kingston, Ontario, where he was on the faculty for from birdsongs and recognize their is always 1.059, regardless of where 36 years. He received his Ph.D. with a concentra- musical features suggests that despite the two notes are located on the scale. tion in comparative psychology from Michigan the vast evolutionary gulf between Musicians speak of semitones and in- State University in 1964. He is the author of 90 birds and mammals, songbirds and tervals; bioacousticians use the terms articles and book chapters about animal cognition humans share some common auditory frequencies and frequency ratios. and evolution and continues to conduct research perceptual abilities. In this article, we Pianos and keyboards easily illustrate on songbird communication and the evolution focus on relative pitch, the ability to rec- the discrete intervals between notes. For of pitch perception. Laurene Ratcliffe is a profes- ognize relationships between acoustic example, hitting the E note in the fourth sor of biology, psychology and women’s studies frequencies. We review studies sug- octave (E4, 330 Hz), then counting at Queen’s University. She received her Ph.D. in biology, for research in animal behavior, from gesting that humans and songbirds down four keys (where both black and McGill University in Montréal in 1981. Address share the ability to perceive relative white keys are counted) and hitting the for Weisman: Department of Psychology, Queen’s pitch changes and exploring the evolu- C note in the same octave (C4, 262 Hz) University, Kingston, ON, K7K 3N6, Canada. tionary functions of birds’ perception produces a relative pitch change of four Internet: [email protected] and use of relative pitch. semitones, as measured by musicians, © 2004 Sigma Xi, The Scientific Research Society. Reproduction 532 American Scientist, Volume 92 with permission only. Contact [email protected]. Figure 1. Black-capped chickadees are noisy and highly social birds with two common vocalizations—their universal “chick-a-dee” call and the sweetly whistled “fee-bee” song. Males, like the one shown singing here from a post in his territory, sing the fee-bee song, primarily during the breeding season, when they use it to protect territory and to attract females. In this article, the authors show that the seemingly simple fee-bee song holds precise pitch cues that signal a male’s quality. (Photograph courtesy of Dan Mennill.) and a frequency ratio of 1.26, as mea- voice can vary in pitch continuously ent renditions of the same melody. In sured by bioacousticians. One can easily from one frequency to another, that is comparing relative pitch perceptions transpose a four-semitone pitch change not the way humans use their voices across species, we use low variabil- on a piano. For example, moving up or their musical instruments. People ity about mean frequency ratios in the the keyboard and hitting the E note in produce pitch changes with low vari- same song across singers to provide the fifth octave (E5, 659 Hz) and the C ability about their frequency ratios. evidence that songbirds, like people, note in the same octave (C5, 523 Hz) Humans recognize pitch changes have a strong sense of relative pitch. produces the same relative pitch change in discrete intervals and are good at as in the fourth octave: four semitones identifying notes relative to an exter- Black-Capped Chickadees or a frequency ratio of 1.26. Although nal reference pitch—in other words, Songbirds belong to the class Aves, they use different notations, musicians relative pitch. Most people easily rec- which includes all birds, the order and bioacousticians agree on the con- ognize a melody transposed to a differ- Passeriformes, consisting of perching stancy of pitch change across the keys. If ent key, or starting frequency, because birds, and the suborder Oscines, the one measured the frequencies produced the song maintains the same intervals, true songbirds. The true songbirds are by hitting E4 and then C4 on each of or frequency ratios, among the notes. distinguished from other perching birds 20 pianos, the average ratio should be Trained musicians, of course, are better by the anatomy of their vocal organ, the 1.26 with a very small standard devia- than others at identifying intervals and syrinx, and by the fact that they need tion among the pianos. The small stan- transposed melodies, but practically to learn their songs while juveniles dard deviation helps illustrate that pitch everyone has some sense of relative from adult members of the same spe- changes in music are discrete. pitch in simple melodies. For example, cies. Oscines are an evolutionary suc- Keyed instruments, such as pianos, people instantly recognize the song cess, comprising about half of the more are constrained to produce discrete “Happy Birthday” regardless of the than 9,000 species of birds and filling pitches, whereas keyless instruments, key in which it’s sung. niches in almost every environment on such as violins and human voices, can Human musicians have not artifi- the planet. Because songbirds are so produce pitches that vary continuous- cially adopted common scales to co- diverse in appearance and behavior, no ly. In practice, however, trained violin- ordinate their musical performances; single species can represent the whole ists and singers produce discrete pitch people, whether musicians or not, group. Our studies ask not whether all changes analogous to a piano’s keys. produce and perceive discrete, con- species of songbirds use relative pitch Put another way, although the human stant frequency ratios across differ- to produce and perceive songs but © 2004 Sigma Xi, The Scientific Research Society. Reproduction www.americanscientist.org with permission only. Contact [email protected]. 2004 November–December 533 semitonessemitones intervals andintervals their frequency and their frequencyratios across ratios an acrossoctave an octave semitones interval name semitones interval name ratio ratio 0 1.000 0 unison unison 1.000 1 1.059 1 minor secondminor second 1.059 2 1.122 2 major secondmajor second 1.122 4 1.260 4 major thirdmajor third 1.260 C C2 8 1.498 C C2 8 fifth fifth 1.498 12 2.000 12 octave octave 2.000 2 2 1 2 2 2 2 2 1 2 2 1 2 1 Figure 2. Piano keyboard illustrates the concept of a semitone—the musical interval between any two adjacent notes. When a black piano key lies between two white keys, those white keys are separated by two semitone intervals.