Table 1 Description of the acoustic parameters used in the analysis

Duration [ms]^*

Duration

Call duration measured within the adjusted start- and end thresholds

DFA2 mean [Hz]^*

Distribution of frequency amplitudes

Frequency at which the distribution of frequencies reaches the second quartile of the total distribution, mean values across time segments

DFB1ch mean [Hz]^*

Modulation of the first dominant frequency band

Mean deviation between 1st dominant frequency band and floating average curve

Range mean [Hz]^*

Frequency range

Mean difference between the highest and the lowest frequency

PFtr mean [Hz]^*

Trend of the peak frequency

Mean deviation between the peak frequency (PF) and the liner trend

Cs mean^*

Consistency of time segments

Mean correlation coefficient of all successive time segments of the call

F0 mean [Hz]⁺

Fundamental frequency

Mean fundamental frequency across all time segments in which a harmonic structure could be detected

Noise [%]⁺

Noisiness

Percentage of time segments in which no harmonic or disturbed structure could be detected

Hnr1 ⁺

Harmonic to noise ratio

Harmonic to noise ratio in the first third of the overall call frequency (1 = no noise)