This is meant to be a brief, non-technical introduction to interpreting sonagrams. A sonogram (synonyms: sonagram or spectrogram) is a representation of a sound with frequency (pitch) on the y-axis vs. time on the x-axis. Sonograms provide images that can be intuitively interpreted and directly measured and compared qualitatively and quantitatively. Many types of bird vocalizations are readily recognizable on sonograms, and it is easy to distinguish the different main types of vocalizations, e.g. whistles, trills, nasal notes, harsh calls, chips, etc. Some sound types have harmonics, which are consecutive multiples of the fundamental (main) frequency. The fundamental frequency is typically the lowest band of a series of harmonics; if the sonogram is in color it will be in the brightest color, while in a grayscale sonogram it will be the darkest and widest harmonic.
Screeches or hisses are broadband, indistinct ‘smears’. The harsher or harder the note the more distinct the pattern. Rattles are quickly repeated, short hard screech-type notes.
Nasal sounds such as quacks or caws appear as series of several closely spaced harmonics of similar power, such that it is often difficult to determine which is the fundamental frequency. Metallic sounds can look similar but typically have more widely spaced harmonics and often harsh components.
Whistles are thin mostly horizontal notes, with or without harmonics. If harmonics are present, the sound is typically richer than if they are lacking. The less discrete or “fuzzier” looking the whistle, the buzzier it sounds.
Chirps and chips are very short nearly vertical broadband notes. Trills are quickly repeated series of chirps or chips.
Warbles are complex mixes of quickly modulated whistles and sometimes other notes.
Not all qualities of bird sounds are readily apparent in sonograms, for example it is difficult to distinguish a “hoot” or a “coo” from a whistle, except by their typically low pitch.