Many years ago, I was in a hide. I say many years ago it was more than that - it was at the tail end of the 80's so I am able to state, without exaggeration, that it was a couple of decades ago I was in a hide. I was in this hide (which I think was at Cley) and I was with Mark. Remember him dear reader? He said he had seen a lesser Kestrel, but hadn't. Anyway, we were sitting in said hide and a wagtail was near the hide to the right, and it looked kinda pale. In our youthful enthusiasm we thought that it could be a White Wagtail and we voiced this.
But then, from out of the darkness, a bearded birder leaned over to us, his face wizened by the salt spray of a thousand a sea watches. His right eye bulged out slightly more than his left from years of peering through german optics at distant gannets. He spoke - "You're a braver man than me to call that a White". That's what he said. "Really?" we said. "Yes" said the bearded birder bloke. He then kindly explained a little of the difference between alba and motacilla, and we dutifully scribbled in our notebook (remember them?) 'Juvenile Pied. 1".
I went to a local park yesterday, and there were loads of Pied Wagtails. Cracking little birds they are - all going mental in a big field. There were many differing shades of mantle and chest amongst them, but finer plumage details were not visible to call them anything other than Pied (you're a braver man than me - it haunts me still). But now, it seems that techniques in wagtail identification have come a long way. Indeed, there have been local reports of White Wagtails being identified when flying over.
Braver than me...
A Pied Wagtail doing Jacobs Ladder