Wagtail, any bird of the Passerine genus Motacilla, with about thirty species, ranging over the greater part of Europe, Asia, and Africa, and to Alaska. Wagtails are active, graceful birds, generally found in open pastures, and by the banks of ponds and streams, feeding on insects and small molluscs. They are continually in motion, and derive their scientific and popular names from their habit of jerking the tail up and down. Five species are British. The Pied Wagtail (M. lugubris) is about 7 inches long, with black-and-white plumage. It is one of the best-known British birds, and no one who has ever seen it standing on a stone in a stream and flirting its tail can ever mistake it. Other British species are the Yellow Wagtail (M. rayi), the Blue-headed Wagtail (M flava), the White Wagtail (M. alba), and the Grey Wagtail (M. boarula). Some of these are formerly placed in different genera, principally on account of their coloration.