Race robustipes has been treated as a separate species (then often including H. acanthizoides as a race); song, although very similar to those of other races, on average reaches lower frequencies#R. Four subspecies recognized.
H. f. pallidus (W. E. Brooks, 1871) – NW Himalayas from N Pakistan (Swat, Hazara and Murree Hills) and Vale of Kashmir E to W Nepal; non-breeding at lower altitudes.
H. f. fortipes Hodgson, 1845 – Brownish-flanked Bush-warbler – E Nepal E to S China (SE Xizang), Bhutan, NE India and W & N Myanmar.
H. f. davidianus (J. P. Verreaux, 1871) – #RC, S & SE China S to N Laos and N Vietnam; non-breeding also at lower altitudes.
H. f. robustipes (Swinhoe, 1866) – Taiwan Bush-warbler – Taiwan.
davidianus is spreading north in China with first records for Liaoning, Hebei & Beijing all since 2012. Several of these have been singing, territorial birds, breeding suspected but still to be confirmed.
Clement, P. (2019). Brownish-flanked Bush-warbler (Horornis fortipes). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/58742 on 25 April 2019).