Fig. 1
From: Multiple song features are related to paternal effort in common nightingales
Example songs of nightingale song categories. The acoustic patterns that constitute categories are underlined in grey. (a): whistle song, characterized by a homotype series of repeated elements with a narrow frequency band and little or no frequency modulation. (b): trill song, characterized by a rapid broad-band trill consisting of repeated elements with little frequency modulation but covering a large frequency range. (c): buzz song, characterized by a long, non-repeated buzz element produced by a very fast repetition of sound units in a narrow and rather low frequency range