Yellow-rumped flycatcher 
(Ficedula zanthopygia, Đớp ruồi vàng), also known as Korean flycatcher or tricolor flycatcher

The yellow-rumped flycatcher (Ficedula zanthopygia), also known as Korean flycatcher or tricolor flycatcher, is a species of flycatcher found in eastern Asia. 

The bird breeds in eastern Asia including parts of Mongolia, Transbaikal, southern China, Korea and western Japan; and winters in parts of the Malay Peninsula and South Asia.

The genus name Ficedula is from Latin and refers to a small fig-eating bird (ficus, "fig") supposed to change into the blackcap in winter.
xanthos,-E,-on, yellow of various shades, golden or pale yellow; also red-yellow, chestnut, auburn
-py·​ga. ˈpīgə variants or -pygia. ˈpijēə : creature having (such) a rump.