I think this is a taivana Yellow Wagtail and not Citrine Wagtail. It is unusual in showing a pale centre to the visible ear-covert, but the greenish mantle and crown, including forecrown (grey in Citrine), very dark loral stripe and area around eye (paler in Citrine) and yellow on underparts extending to the undertail coverts (white in Citrine) are typical of summer taivana.
dave diskin