Fig. 1. Analysis of acoustic parameters of the pups’ calls. (A) Spectrogram and oscillogram of a pup’s call (window size 1024). A pup’s call is composed of a fundamental frequency and relative harmonics. From the oscillogram, we measure the total duration of the signal (d_tot, ms). Each colour represents an amplitude class of 3 dB. (B) Power spectrum [Hamming window with a frame length of 186 ms (4096 points) and a frequency grid resolution of 5.4 Hz]. The frequencies of the pup’s call and their relative amplitudes, such as the first frequency, termed the fundamental frequency (FundFreq), and the first three harmonics with peak amplitude (F_max1–3) can be measured from the power spectrum. (C) Fundamental frequency (calculated using the auto-correlation method). This process is used to follow the frequency modulation of an isolated harmonic. The different parameters, such as the duration of the ascending part (d_asc), the duration of the descending part (d_desc), the start frequency (F_start), the maximal frequency (F_max) and the end frequency (F_end), can be measured using this method. (D) Amplitude envelope (RMS calculation). The parameters measured were the loudest intensity (RMS_max), the average intensity (RMS_averT) and the duration between the beginning and the time at which the highest amplitude peak occurs (t_Amax).