Acoustic features of birdsong extracted using Sound Analysis Pro 2011.

FM is defined as angle in direction derivatives. AM is measured across all frequencies. Wiener entropy is a unit-less value. Pitch goodness units can be converted to dB after baseline subtraction and transformed to a log scale. Definitions of song features are further summarized in http://soundanalysispro.com/manual-1 and in ‘Song recording and analysis’ section of methods [55].