Palla's Leaf Warbler 
(Chích hông vàng, Phylloscopus proregulus)

Pallas's leaf warbler (Phylloscopus proregulus) or Pallas's warbler, is a bird that breeds in mountain forests from southern Siberia east to northern Mongolia and northeast China.

The bird is strongly migratory, wintering mainly in south China and adjacent areas of southeast Asia; recently increasing numbers have been found in Europe in autumn.

Leaf warblers were formerly included in the Old World warbler family but are now considered to belong to the family Phylloscopidae, introduced in 2006.
The name Phylloscopus combines the Ancient Greek phullon meaning "leaf" and skopos meaning "seeker" (from skopeo, "to watch").
The specific proregulus is from Greek pro, "close to", and the name regulus, referring to the similar-looking goldcrest, Regulus regulus.