Fig. 6
From: Vocal tract anatomy of king penguins: morphological traits of two-voiced sound production
Body posture of vocalizing king penguin and spectrogram and power spectrum of a male call. a: Adult king penguin in the typical calling position emitting a call. b: Spectrogram (FFT length 1024, 98.43% overlap, Blackman window) of an adult male king penguin call. Below the oscillogram of the call. c: Amplitude spectrum of the call section marked with a dotted rectangle in b (duration: 0.1 s). b and c: F0 = Fundamental frequency (first harmonic), 2F0 = Second harmonic. The pink and the red arrows indicate the two voices for F0 and 2F0, respectively