Fig. 1.

Oscillograms (top) and spectrographic illustrations (bottom) of skylark song. a Spontaneous song: singing spontaneously with no other conspecific around. b Reactive song: song in response to a territorial playback by the same bird as shown in a. Syllables of the same type are labeled with the same number, syllables found only in either spontaneous or reactive song (unshared syllables) are labeled with italic numbers, and syllables found in both contexts are labeled with bold numbers (note that some of those shared syllables are not displayed in both excerpts). Syllable duration is indicated above the oscillograms