Grey Wagtail 
(Chìa vôi núi, Motacilla cinerea)

The gray wagtail (Motacilla cinerea) is a member of the wagtail family, Motacillidae.
The bird has the yellow on its underside and vent.

Passeriformes, Passerina, passerina: Latin passerinus sparrow-like, (i.e. sparrow-sized) (passer sparrow).
Motacillidae, Motacilla: From Latin motacilla (“wagtail”), the word is a diminutive of motare, "to move about".
cinerea is Latin for "ash-grey" from cinis, "ashes".