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Background The White-browed Shortwing (Brachypteryx montana) is widespread from the central Himalayas to the southeast Chinese mainland and the island of Taiwan, the Philippines and Indonesia. Multiple subspecies are recognised, and several of these have recently been suggested to be treated as separate species based on differences in morphology and songs. Methods We here analyse plumage, morphometrics, songs, two mitochondrial and two nuclear markers, and geographical distributions of the two mainland Asian taxa B. m. cruralis and B. m. sinensis and the Taiwanese B. m. goodfellowi. Results We conclude that these differ congruently in morphology, songs and DNA. Male B. m. goodfellowi is the most divergent in plumage (sexually monomorphic, unlike the two others; male similar to female), and B. m. cruralis and B. m. sinensis differ in male plumage maturation. The song of B. m. cruralis is strongly divergent from the others, whereas the songs of B. m. sinensis and B. m. goodfellowi are more similar to each other. Brachypteryx m. sinensis and B. m. goodfellowi are sisters, with an estimated divergence time 4.1 million years ago (mya; 95% highest posterior distribution [HPD] 2.8–5.5 mya), and B. m. cruralis separated from these two 5.8 mya (95% HPD 4.1–7.5 mya). We also report notable range extensions of B. m. sinensis as well as sympatry between this taxon and B. m. cruralis in Sichuan Province, China. Brachypteryx m. montana from Java is found to be more closely related to Lesser Shortwing (B. leucophris) and Rusty-bellied Shortwing (B. hyperythra) than to the mainland Asian and Taiwanese taxa. Conclusion Our data support a recent proposal to treat the three mainland Asian and Taiwanese taxa as three species, separate from B. montana sensu stricto: B. cruralis (central Himalayas to south central China and south Vietnam), B. sinensis (north central to southeastern part of mainland China) and B. goodfellowi (Taiwan Island).

Molecular phylogenetic approaches have greatly improved our knowledge of the pattern and process of biological diversification across the globe; however, many regions remain poorly documented, even for well-studied vertebrate taxa. The Philippine archipelago, one of the least-studied ‘biodiversity hotspots’, is an ideal natural laboratory for investigating the factors driving diversification in an insular and geologically dynamic setting. We investigated the history and geography of diversification of the Philippine populations of a widespread montane bird, the White-browed Shortwing (Brachypteryx montana). Leveraging dense archipelago-wide sampling, we generated a multi-locus genetic dataset (one nuclear and two mtDNA markers), which we analyzed using phylogenetic, population genetic, and coalescent-based methods. Our results demonstrate that Philippine shortwings (1) likely colonized the Philippines from the Sunda Shelf to Mindanao in the late Miocene or Pliocene, (2) diversified across inter-island barriers into three divergent lineages during the Pliocene and early Pleistocene, (3) have not diversified within the largest island, Luzon, contrary to patterns observed in other montane taxa, and (4) colonized Palawan from the oceanic Philippines rather than from Borneo, challenging the assumption of Palawan functioning exclusively as a biogeographic extension of the Sunda Shelf. Additionally, our finding that divergent (c. 4.0 mya) lineages are coexisting in secondary sympatry on Mindanao without apparent gene flow suggests that the speciation process is likely complete for these shortwing lineages. Overall, these investigations provide insight into how topography and island boundaries influence diversification within remote oceanic archipelagos and echo the results of many other studies in demonstrating that taxonomic diversity continues to be underestimated in the Philippines.