Wagtails
There are three breeding species of wagtail in the UK, but we have included a couple of scarcer passage subspecies of two species, from continental Europe (White Wagtail and Blue-headed Wagtail), for comparison.
Tail length
In short, the Pied/White Wagtails have long tails; Yellow/Blue-headed Wagtails have relatively short tails; and Grey
Wagtail has a very long tail. Even birds in flight can be split into one of three with a working knowledge of tail length.
Colour
Pied/White Wagtails are essentially black, grey and white birds, lacking strong yellow tones ( juveniles have a yellowish buff hint in places). Yellow/Blue-headed Wagtails are largely grey and yellow (notably green-backed), with white in places. Grey Wagtails are grey backed but have brilliant lemon yellow on the undertail (and belly in breeding plumage).
Call
Learn wagtail calls and even fly-by birds can be identified, at least to the three species here (not necessarily to subspecies). Note that Yellow Wagtails are summer visitors, not appearing until April, and departing in the autumn.