Fig. 1

Variance – covariance principal component analyses of (a) contact calls and (b) alarm calls identified significant (both one-way PERMANOVA: P < 0.001) differences of call characteristics among local populations across the species’ entire distribution range (colours are as given in Table 3). Ovals in a) denote the three well defined contact call clusters (I to III). PCA1 in a) and b) was highly correlated with gap length (loading > 0.9). PCA2 in a) correlated with the difference in highest and lowest frequency (loading = 0.72), in b) with call length (loading = 0.89); PCA = here Principal Component Axis