Based on ML and BI phylogenetic trees of two thrush complexes, we found that different combinations of priors (evolutionary scenarios: population size and divergence time) yielded different results by Bayesian species definition on each node, but the results of the analysis using algorithms 0 and 1 were similar (Table 5). This result indicated a convergence of MCMC chains. Combined with the guidance tree (Fig. 3), the results showed that nodes 3 and 4 had high speciation probabilities =1.000 when using combinations of priors that represent different evolutionary scenarios. At the same time, these two nodes of the guide tree were supported by high posterior probabilities (PPs> 95%). For nodes 1 and 2, the choice of different evolutionary scenarios resulted in different speciation probabilities that were low in most cases. Therefore, the prior probability distribution had a greater influence on the speciation probabilities between Naumann’s thrush and the dusky thrush and between the red-throated thrush and the black-throated thrush.
We used five morphological features to further analyze the classification status of the species in the two thrush complexes. The PCA showed that the five quantifiable traits were difficult to distinguish between Naumann’s and the dusky thrush or the red-throated thrush and the black-throated thrush. These traits were not sufficient to constitute the boundary of the species (Fig. 4a and b). We classified the Naumann’s and dusky thrush complexes as one group and the red-throated and black-throated thrush complexes as another group and conducted PCA of both groups (Fig. 4c). Although there was a small amount of intersection between the two groups, there was separation between them. All the results from the above molecular and morphological analyses indicated that the two thrush complexes should be two independent species (Naumann’s thrush, T. naumanni , and the red-throated thrush, T. ruficollis ), while the dusky thrush (T. naumanni eunomus ) should be a northern subspecies of T. naumanni , and the black-throated thrush (T. ruficollis atrogularis ) should be a black-throated subspecies of T. ruficollis .