Supporting Information

Appendix S1. References of molecular phylogenetic studies used to identify the sister pairs in our data set. Loadings of PCA results. Results of model fitting. Appendix S2. GenBank accession numbers. Appendix S3. Elevational differentiation (meters) and Euclidean distances of morphometrics and song measurements (PCs). Fig. S1. Phylogeny of the sister species pairs included in our data set. Color range indicates the degree of elevational differentiation in the left phylogeny and the amount of overlap in the right phylogeny.Fig. S2. Example of measurements taken from song spectrograms.Fig. S3. Example of morphological measurements taken from museum specimens.