At 5 weeks old, however, distances between SG were longer than those between FS (independent exact permutation tests: N = 60 pairwise comparisons, P = 0.007; Fig. 2a, b). This indicates that SG calls were as similar as FS calls at 1 week old, but less similar than FS calls at 5 weeks old. All these results remained significant after Bonferroni correction (P < 0.017).