Figure 3
Spectrogram (a) and waveforms (b) of a Chagos song recorded on the eastern side of the Chagos Archipelago (DGS) in August 2017. Detailed waveforms show the signal structure of the units within the song. Spectrogram parameters: Hamming window, 1024-point FFT length, 90% overlap. Note that the axes differ among plots. (c) Measurements (mean ± standard error (s.e.)) of the acoustic features. N is the number of measurements, \(u_{i}su_{j}\) stands for \(unit_{i} subunit_{j}\) where i and j are the unit and subunit numbers, \(\Delta f\) designates the frequency difference between the sidebands, f and d are the frequency and duration of the feature indicated in subscript, and when present, the number in brackets refers to the point measured as indicated on the spectrogram. \(F_{x}\) or \(G_{x}\) designate the xth harmonic of a sound, and Cf designates the carrier frequency of a sound.
