
Photo: (c) Jagdish Singh Negi, some rights reserved (CC BY) · CC-BY (May be cropped or resized)
Cettia brunnifrons
Range
Northern Pakistan to central China
The grey-sided bush warbler is a bush warbler found from northern Pakistan to central China. It split from Cetti's warbler about five million years ago (Wikipedia, general species account).
That short account is the only source read for the Bhutan guide. It does not name Bhutan, and gives no plumage, size, habitat, diet or breeding information, so none is stated.