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(A) Spectrogram and (B) power spectrum of the coo call used as a naturalistic harmonic sound in this study. The coo consists of the first harmonic or fundamental (h1) and five prominent harmonics with amplitudes above −50 dB (2nd to 6th harmonics, h2–h6; FFT size: 1024, Hann window). The interval between h1 and h2 is one octave and that between h2 and h3 is a perfect fifth.
