Reading Sonograms

Sonograms are to sound what a rainbow is to light. Raw sound and raw light are both complex compilations of many frequencies acting constructively and destructively. The mathematical algorithm used to process sounds acts in the same way a prism acts on light, spreading natural sounds into discrete frequencies and tracking their changes over time.

If someone were to insist on my describing the song of Townsend's Warbler, I would probably say, "tsee tsee tsee tsee ZEEE zurt zurt." Others familiar with this song might argue about the consonants, but the emphasis and the vowel sound tend to be remarkably consistant from listener to listener.

In the sonogram of Townsend's Warbler pictured above, "tsee", "ZEE" and "zurt" notes are easily distinguished. "Ee" sounds almost always refer to higher frequency sounds. The rough rule of thumb, from high to low, is ee(long), ay, e(short), a(short), oo, ur, o(long). This is, of course, very subjective and there are not nearly enough vowel sounds to really get the point across in a consistent manner. The top note on a piano (c'''') is at 4.186 kHz which tells us about where most of the frequencies in the Townsend's song are. We cannot expect every description using double e vowels sounds represent these frequencies. Sonograms clearly describe note relationships in a song or call much better.

In modern, gray-scale sonograms, darker means louder. This was not always the case and older, black and white sonograms (like those in the Golden Guide) contain a bit less information. Song variability within a population also limits the usefulness of any single sonogram (just as any single recording cannot completely describe a song.) Nothing can replace the brute force approach of just getting out in the field and listening and practicing.

Sonograms can look frustratingly similar as can be seen here in comparisons between Townsend's Warbler and Black-throated-gray Warbler. Note that Townsend's sings at consistantly higher frequencies, most of the notes at the beginning are more uniform and discrete. Black-throated-gray throws out lower, broader spectrum notes that sound burrier in general, but there are no drawn out buzzy notes. Play the Western Birds tape while you look at the sonograms. Practicing the relationship between taped sound and sonogram will help in learning how to visualize songs from their sonograms.

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