Vocalization analyses
The PCA evidenced differences in vocalizations among subspecies. The first three PCs explained 65% of song variation. PC1 correlated with the fundamental frequency of the first and the last note, PC2 correlated with the mean duration of the first and intermediate notes and PC3 did not strongly correlate with any song variable (Table S4). Subspecies statistically differed in PC1 (F = 11.32, p ˂ 0.01) and PC2 (F = 18.43, p ˂ 0.01), whereas no significant differences were found for PC3 (F = 2.87, p = 0.09). In particular, pairwise comparisons showed thatT. r. jaczewskii significantly differed from T. r. ruficapillus and T. r. cochabambae in PC1 and from T. r. marcapatae in PC2 (Table S5). In turn, T. r. cochabambaediffered from all subspecies in PC2 (Table S5). These differences can be observed in the space delimited by the first two PCs (Figure 4). No differences were found in the rest of the pairwise comparisons between subspecies for PC1, PC2 or PC3 (Table S5).
The results of the individual song variables provided more detail about song variation and showed substantial differentiation among subspecies. In fact, the ANOVA indicated significant differences for most song variables (Tables S6 and S7). Moreover, the Bonferroni contrasts showed significant differences in at least one variable for almost all subspecific comparisons, with the only exceptions of T. r. subfasciatus vs. T. r. ruficapillus and T. r. subfasciatus vs. T. r. marcapatae (Table S8). Therefore, and consistently with the PCA result, both T. r. jaczewskii andT. r. cochabambae significantly differed in their songs from all other subspecies, being the subspecies with the most differentiated vocalizations. In addition. T. r. jaczewskii was the subspecies that differed in more song variables from the rest (and particularly so from T. r. cochabambae and T. r. ruficapillus ) (Table S8).