The photographs of the wagtail at the Torness Power Station, Lothian, show a bird that has every bit the appeal of a classic Grey-headed Wagtail, a 'thunbergi'. Of course, the identification of flava wagtails to the subspecific or 'form' level can be quite a minefield, and it is not surprising that this individual has not been universally accepted as straightforward. Indeed, birds showing head patterns similar to this could easily invoke any of the following identification suggestions: thunbergi, plexa, macronyx, cinereocapilla, pygmaea and possibly flava x feldegg. Yikes!
Thankfully, knowing where the photo was taken helps a lot: pygmaea is a resident in Egypt; macronyx is from Southeast Asia and plexa is currently considered to be best 'lumped' as 'eastern' thunbergi (Pipits and Wagtails of Europe, Asia and North America, Alstrom and Mild). I don't even want to think about the nightmare of hybrids between forms!
|Grey-headed Wagtail: Torness, Lothian. (Photo: Peter M Macdonald)||Grey-headed Wagtail: Torness, Lothian. (Photo: Peter M Macdonald)|
The partially white throat of this individual might suggest cinereocapilla - Ashy-headed Wagtail. However, the white only extends only about halfway down the throat, the lower central half being yellow (particularly obvious in the head-on shot), which is typical of thunbergi. The whole throat region is clean-cut white on cinereocapilla, sharply demarcated from the yellow of the upper breast. That's the straightforward diagnostic difference between the two.
The half white throat is interesting but not extensive enough to consider other forms and this suggests a 1st-summer bird according to the literature. Can the primaries be used for ageing? Well you can not really tell here (are they worn and brownish?), and there is no useful moult contrast in the greater coverts (I watched a 1st-summer male flavissima with an easy-to-age mix of greater coverts at Flamborough Head in early May). This individual lacks the classic dark spotty 'necklace' of many thunbergi, but this is probably because it is a 1st-summer bird.
The head pattern doesn't really make me think of Ashy-headed. Why? Well, it is probably a gut thing here. I suppose the impression of thunbergi is of almost having a wheatear-like black mask, through the lores and ear coverts merging, but also contrasting, with gorgeous dark bluey-grey velvet crown. Whereas on Ashy-headed Wagtail the whole head looks blue-grey (greyer and less bluey?) with the black more restricted to loral region.
|Ashy-headed Wagtail: Corsica, April 2002. (Photo: Richard Patient)||Ashy-headed Wagtail: Corsica, April 2002. (Photo: Richard Patient)|
So, it appears to be to be normal, probably 1st-summer, Grey-headed Wagtail. I only hope it didn't call like a Citrine Wagtail...because then we'd have to reconsider macronyx and a potential first for Britain!