This species' systematics and genetics are extremely confusing.
Literally dozens of subspecies have been described at one time or another, and some 15-20 are currently considered valid depending on which author reviews them.
This is the South East Europe subspecies of the Yellow Wagtail and is named Black-headed Wagtail (Motacilla flava feldegg) for its distinguished black cap in males.
Females have a dark grey head and very washed-out dirty yellowish below and a white throat (2nd photo).
The Motacilla flava flava of western Europe has a blue-grey head with a white supercilium (line above each eye).
The British subspecies, Montacilla flava flavissima has a yellow head (the male) with a brighter yellow supercilium.

1st photo: A male Black-headed Wagtail
2nd photo: A female Black-headed Wagtail

Raysut Wast Disposal Site, Dhofar Region, Oman, 5 February 2017