Figure 3. Beak morphology and representative song
spectrograms from eight species of Darwin's finches.
Interspecific variation is evident in both morphology
and song structure. Each of these songs includes trilled
segments, which we define as song segments composed
of two or more repeated acoustic units. Birds with larger,
more cumbersome beaks tend to produce trills with lower
rates of syllable repetition and with more narrow frequency
ranges.Modified from Podos (2001).