The White-browed Shortwing (Brachypteryx montana) has been considered to be a single species distributed from the central Himalayas to the southeast Chinese mainland and the island of Taiwan, the Philippines and Indonesia. The mainland and Taiwan Island populations have recently been studied by an international team of researchers from Sweden, China, the UK and the USA. They analysed DNA, plumages, structure, songs and geographical distributions, and concluded that the continental and Taiwanese populations are actually three rather than one species.
These three species differ in all analysed aspects. In particular, in the two mainland species males are blue-grey in colour, whereas in the Taiwanese Island species males are brown like females of all three species. In one of the two continental species, immature males resemble adult males, whereas in the other one immature males are similar to females.
The songs are markedly different, especially between the mainland species. The two continental species were also found to breed in the same area in central China, where only one of them was previously known to occur.
The genetic analyses indicate that the three species have evolved separately for 4.1–5.8 million years. The same analyses revealed that the Javan population is more distantly related, and accordingly should be treated as a fourth species. Future studies are required on the remaining Philippine and Indonesian populations. Perhaps there are even more species involved.
This study, which concludes that the White-browed Shortwing is at least four different species, supports the view that although birds are better known than any other group of organisms, the number of bird species is underestimated.
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Per Alström et al. Taxonomy of the White-browed Shortwing (Brachypteryx montana) complex on mainland Asia and Taiwan: an integrative approach supports recognition of three instead of one species, Avian Research (2018). DOI: 10.1186/s40657-018-0125-6