Introduction to Sonograms
I am starting a new series on auditory bird song identification using sonograms. This post will serve as an introduction on how to translate what you see on a sonogram to what you hear in a bird’s song. Before we learn about how to read a sonogram, we must first define what a sonogram is. A sonogram is a visual representation of a sound showing pitch on the y-axis and time on the x-axis.
Volume is shown by darkness on a sonogram. the darker a sound, the louder it is. For example, the song of the Northern Flicker starts off soft and then becomes louder.
Pitch is how high or low something sounds on a musical scale. Inflection is simply a change in pitch such as a rise or fall in pitch. Now lets look at various types of inflection and pitch.
The dawn song of this Carolina Chickadee contains notes that are monotone (mostly) – that is, they do not change in pitch.
One extra thing to notice about this song is a faint “replica” of each note located relatively one octave higher than the “parent note.” This is known as a harmonic and can be found in many bird songs and calls.
Upslur vs. Downslur
The song of this Northern cardinal contains notes (the first three) that rise in pitch (upslurred) and notes (the last six) that fall in pitch (downslurred).
Overslur vs. Underslur
Some birds give calls that first rise and then fall (overslur) or first fall and then rise (underslur). The call of this Eastern Wood-Peewee contains both – first two short overslurs (can be hard to hear) connected to an underslur followed by a pause and then an overslur (before the spike).
Sometimes the above terms can apply to a series of notes as well as the individual notes themselves. Take, for example, the song of this Prairie Warbler that is an upslurred series of notes (technically they are so close it is a trill).
Of course, a series of notes does not have to be upslurred or downslurred. For example, the above song of the Northern Cardinal is a monotone series of first upslurred and then downslurred notes.
Sharpness of Inflection
The sharpness of inflection is how “steep” a particular note appears. The more vertical a note looks, the less whistle-like a whistle will sound. Rather, an almost vertical whistled not will sound like a pop or click. This can be observed in the song of a Field Sparrow. The initial notes sound more like whistles than do the end notes.
Another great example is the Worm-eating Warbler that has a very mechanical, insect-like trill with notes that barely if at all resemble whistles.
Pitch and Tone Quality
Another thing that affects the tone quality of a whistle is the pitch. For example, the song of a Common Ground-Dove, which has a low pitch, sounds very different from the sibilant, high-pitched whistle of an alarm call of the American Robin.
Noise is essentially sounds containing so many different wavelengths that they are indistinguishable. This gives a rough quality to bird songs and calls and shows up as a vertical blur on a sonogram. Take, for instance, the call 0f the Red-tailed Hawk, which sounds rough because it has so much noise.
A trill is a repetition of an element at a fast rate. When I say element, I mean a specific sound. This sound can be a distinct, separate note or one long, wavy note. Trills can sound very different depending on pitch, sharpness of inflection and rate. The trill of a Swamp Sparrow is fairly loose and musical.
As notes start to be repeated even faster, the trill often takes on a burry quality like the “breep” call of this Great Crested Flycatcher.
When the rate of a trill gets even faster than that, a call or song often starts to sound buzzy like the “peent” call of the American Woodcock.
A bird can sometimes sound nasal if it produces multiple sounds at once, which our brains then process as a single sound. Each of these sounds is called a partial. For example, the Red-breasted Nuthatch has a call that sound nasal.
However, a bird’s call can have partials but not sound nasal. This can occur if the fundamental (lowest) partial is the loudest. Additionally, the call can sound piercing rather than nasal if the second from the bottom partial is the loudest like in the call of this Killdeer.
Some birds have voice breaks, in which the pitch rapidly changes mid-note. This is evident in the call of the Red-shouldered Hawk.
One final piece about reading sonograms. Some birds, especially finches, produce two sounds at the same time that conflict rather than producing partials like a nasal sound. This is known as polyphony and can be identified by rising and falling notes at the same time on a sonogram. A great example of this is the call of the Hermit Thrush.
Thanks to earbirding.com for the information.
Thanks to xeno-canto.org for sonograms and sounds.