Siberian Grey-headed Wagtail
Wagtail archive see here:
Siberian Grey-headed Wagtail Motacilla flava plexa
Charles Vaurie, 1959 (The Birds of the Palearctic Fauna, Whitherby,London) and others described the Siberian race of the Grey-headed WagtailM.f.thunbergi as duller and more greyish on the mantle and the colour of the crown grading into the colour of the mantle, less contrasting than in nominate thunbergi as shown in the pictures.
Ahlstrom & Mild, 2003, however (Pipits & Wagtails of Europe,Asia and North America, Helm,London) found a complete overlap with nominate thunbergi when comparing skins.