Which Wagtail? Death Mystery.

I was delivering to a farm near Horeb this morning, well inland, when I saw a Wagtail in the yard that looked like a White Wagtail. The separation in colour between the head and the back was at least as distinct, if not more, than the bird in Jon's photo. Indeed, if I'd seen it at Llanrhystud I'd definitely have considered it to be a White Wagtail. But inland? Any thoughts? Later I saw another strange sight. A Chaffinch impaled through the chest on top of a hedge. It was one of those hedges that have been flailed to death, leaving countless vertical splinters. Was it an accident? A misjudgment by the bird? Or had it been caught, say by a Sparrowhawk, to be eaten later. Balanced out in the open on spindly twigs, it didn't look to me like the sort of spot that a hawk would wish to tear a finch apart, but I really don't know. Any ideas about that one?