
Photo: Tisha Mukherjee · CC BY-SA 4.0 (May be cropped or resized)
Horornis fortipes
Range
Himalayas, South China and Southeast Asia
The brown-flanked bush warbler, also called the brownish-flanked bush warbler, is a bush warbler of the family Cettiidae, found in the Himalayas, South China and Southeast Asia (Wikipedia, general species account).
That short account is the only source read for the Bhutan guide. It does not name Bhutan specifically, and gives no plumage, size, habitat, diet or breeding information, so none is stated.