I have been working for some time to develop a standardized vocabulary for describing bird sounds. In 2007 I published an article in Birding magazine called “Describing Bird Sounds in Words,” which provides a good introduction to my system. My thinking about describing bird sounds continues to evolve, however, and some of the article does not reflect my current thinking, particularly in terms of nasality and polyphony. I welcome help in refining the terminology further.
Glossary
Note: this glossary is still under construction.
Accelerating: Describes a rhythm that increases in speed. example
Alternating variety: In this type of variety, a bird repeatedly sings one songtype, then a second, then the first one again, in an “ABABAB…” pattern.
Beats: Rapidly repeating rhythmic elements in a bird sound, giving the sound a burry, buzzy or trilled quality. Beats can be formed by frequency modulation (FM), amplitude modulation (AM), rapid repetition of elements, the superimposition of two different frequencies during polyphony, or any combination of these. See this page for examples.
Burry: Denotes a tone quality characterized by rapid beats (ca. 10 - 125 Hz), but more musical than a buzzy sound. Example. The term “burry” comes from the word “burr,” originally used to describe the trilled sound of the letter “r” in the Scottish dialect of English, and applied by analogy to certain bird sounds.
Buzzy: Denotes a tone quality characterized by rapid beats (ca. 20 - 250 Hz), but less musical than a burry sound. Example. Originally, an analogy to the sound made by a bee’s wings.
Clear: Describes a bird sound that has no texture; that is, one that contains neither beats nor noise.
Crescendo: An increase in volume.
Decelerating: Describes a rhythm that decreases in speed.
Decrescendo: A decrease in volume.
Downslurred: Falling in pitch. example
Duration: The length of a sound in time.
Eventual variety: In this type of variety, a bird with multiple songtypes sings one of them over and over before eventually switching to another.
Fundamental (frequency): The dominant (usually the lowest) frequency in a simple or harmonic sound. A whistle is a simple sound that consists only of a harmonic frequency, while other musical sounds (such as the sounds of most musical instruments) consist of a harmonic series, meaning that in addition to the fundamental the sound contains one or more higher frequencies which are integer multiples of the fundamental. Not every bird sound has a fundamental frequency. Noisy sounds, like the call of the Steller’s Jay, have little or no harmonic structure, and so a fundamental cannot be identified.
Harmonic series: A sound consisting of a fundamental frequency and one or more overtones (harmonics) at integer multiples of the fundamental.
Hertz (abbreviated Hz): The international unit of measurement of frequency. Sounds are produced by vibrating objects; the faster the frequency of the vibrations (that is, the more vibrations per second), the higher-pitched the sound. A sound with a frequency of 1 Hz contains one vibration (or “cycle”) per second. Human hearing is typically in the range of 20 to 20,000 Hz (that is, 0.2 to 20 kilohertz, kHz).
High-sibilant: Describes a whistled sound above about 6 kHz. These sounds are high-pitched enough that they do not sound musical; instead they sound like the sibilant sound of the letter “s.” However, they have no noise content. example
Immediate variety: In this type of variety, consecutive strophes are always different; thus the bird sings with a pattern like “ABCDE…”.
Indeterminate (pitch/intonation): Describes a sound whose pitch or intonation cannot readily be identified, particularly because of its short duration.
Inflection: The change in pitch within a single sound. Types of inflection include usplurs, downslurs, monotones, overslurs, and underslurs. examples
Kilohertz (abbreviated kHz): A unit of measurement of frequency equal to 1000 Hz, or 1000 cycles per second.
Monotone: Maintaining a constant pitch. example
Musicality: A measure of the extent to which pitch can be ascribed to a bird sound. In order for a bird sound to be musical, it must be relatively clear and pitched below about 7 kHz. See the discussion on this page.
Noise: In acoustical terms, noise is aperiodic sound. “White” noise contains roughly equal energies at all frequencies. Sounds that consist almost entirely of noise include the sounds of waterfalls and radio static. Many bird sounds contain a great deal of noise, such as the call of the Steller’s Jay. Examples
No variety: Bird songs are classified as having “no variety” if the bird sings with a single songtype, repeating it over and over without ever switching to another.
Overslurred: Rising and then falling in pitch. example
Pitch: To acousticians, pitch is the subjective impression of frequency. In laymen’s terms, pitch refers to how high or low a sound is on the musical scale. Because pitch is defined as subjective, it is not a quality that can be measured on a spectrogram; it exists only in your ear. (What can be measured on the spectrogram is called frequency.) Many (most?) bird sounds defy pitch classification by the human ear. See the discussions on the pitch and inflection and musicality pages.
Polyphony/polyphonic: The vocal organ of birds, called a syrinx, functions very differently from the human vocal organ, called a larynx. The syrinx is located farther down, where the trachea splits into two bronchi to travel to the lungs, and it has the ability to produce two separate sounds simultaneously, one from each lung. However, most birds rarely or never use this ability; instead they sing with only one of their two voices their entire life, or else they switch off, sometimes within single notes, as Northern Cardinals do. When a bird does use both sides of its syrinx simultaneously, it has the ability to create two harmonically unrelated sounds at once. This situation is called “polyphony,” and such sounds are termed “polyphonic.”
Repertoire: The total collection of all songtypes that an individual bird can sing.
Rhythm/Rhythmic pattern: Broadly speaking, the behavior of a sound in time: the pattern of when a bird is producing sound and when it is not. In acoustic terms, this is essentially the same as the “envelope” of the sound, or the graph of its amplitude over time. Rhythm is one of the four basic characteristics of sound that the human ear can perceive, the others being volume, tone quality, and pitch.
Sharpness (of inflection): A measure of how quickly a sound changes in pitch. The more rapidly it changes, the sharper the inflection. example
Songtype: A particular song that a bird “knows” how to sing. The collection of all songtypes that a particular individual can sing is known as its repertoire. In some species (e.g., White-crowned Sparrow, Indigo and Lazuli Buntings), males can only sing a single songtype, which means their repertoire size is 1 and they must sing by default with no variety. Other species may know more songtypes (e.g., Eastern Meadowlark, in which a single male may know up to 100 different songtypes). See strophe.
Strict (rhythm): A rhythm that does not change in speed, i.e., one that neither accelerates nor decelerates.
Strophe (rhymes with “trophy”): A single discrete instance of song from an individual bird. Consecutive strophes may be of the same songtype or different songtypes. For example, if an Eastern Wood-Pewee sings “pee-yoo-wee… pee-yerr… pee-yoo-wee… pee-yerr,” then it has sung four strophes, but only two songtypes (because the two songtypes were repeated once each).
Texture: In acoustical terms, the part of tone quality that deals with periodicity. In bird sounds, texture refers to beats and noise content. A bird sound can contain beats or noise both; or it can have neither, in which case we say it is a clear sound.
Timbre (rhymes with “amber”): A synonym of “tone quality.”
Tone quality: One of the four basic characteristics of sound that the human ear can perceive, the others being volume, rhythmic pattern, and pitch. Tone quality is what would allow you to tell a trumpet from a violin, for example, if each instrument were to play the same note. Synonymous with “timbre.”
Underslurred: Falling and then rising in pitch. example
Upslurred: Rising in pitch. example
Variety: A description of the way in which a songbird deploys its repertoire. See alternating variety, eventual variety, immediate variety, and no variety.
Volume: In acoustical terms, a measure of the amplitude of a sound; in laymen’s terms, its “loudness.” One of the four basic characteristics of sound that the human ear can perceive, the others being tone quality, rhythmic pattern, and pitch.