How many species of Brownish-flanked Bush Warbler are there?


Brownish-flanked Bush Warbler Horornis fortipes davidianus Henan Province, China. Photo: Shuaishuai Xu.

The Brownish-flanked Bush Warbler (Horornis fortipes) is a small, non-descript, mostly brownish bird that occurs in montane areas from northern Pakistan to east China and northern Vietnam and Laos. In contrast to its dull appearance, its song is remarkable: a drawn-out monotonous whistle that terminates with a flurry of two or three short whistles at alternating pitches.

A group of researchers from China and Uppsala University has analysed DNA, songs and appearances from throughout the range of this bird. They found that the Brownish-flanked Bush Warbler consists of at least three independently evolving groups, which diverged between one and two million years ago. Such long-separated populations may be more appropriately treated as different species. A fourth genetically distinct population was identified from the island of Taiwan. However, this population is much younger, and was estimated to have colonized Taiwan at the most 400 000 years ago.

The hypothesis that the Brownish-flanked Bush Warbler consists of three species instead of one is contradicted by the finding that the songs are very similar across the vast geographical distribution. As a general rule, closely related bird species have different songs. Moreover, also the appearances differ only subtly among the different populations. Based on these results, the authors concluded that the Brownish-flanked Bush Warbler consists of three populations that are at the early stages of the speciation process. If these populations persist and continue to diverge, with time, they will likely evolve into separate species.

Listen to the Brownish-flanked Bush Warbler.


Wei, C., Dong, L., Li, S.-H., Alström, P., Liu, Y., Xia, C., Yao, C.-T., Zhang, Y. 2019. From the Himalayas to a continental island: Integrative species delimitation in the Brownish-flanked Bush Warbler Horornis fortipes complex. Molecular Phylogenetics and Evolution (

Free access until 25 January 2018 at


Prof. Per Alström

Nyheter från institutionen för ekologi och genetik

Last modified: 2022-04-30