(Science: ornithology) Any one of many species of old world singing birds belonging to Motacilla and several allied genera of the family Motacillidae. They have the habit of constantly jerking their long tails up and down, whence the name. Field wagtail, any one of several species of wagtails of the genus Budytes having the tail shorter, the legs longer, and the hind claw longer and straighter, than do the water wagtails. most of the species are yellow beneath. Called also yellow wagtail. Garden wagtail, the indian black-breasted wagtail (Nemoricola Indica). Pied wagtail, the common European water wagtail (Motacilla lugubris). It is variegated with black and white. The name is applied also to other allied species having similar colours. Called also pied dishwasher. Wagtail flycatcher, a true flycatcher (Sauloprocta motacilloides) common in southern australia, where it is very tame, and frequents stock yards and gardens and often builds its nest about houses; called also black fantail. Water wagtail. Any one of several species of wagtails of the restricted genus Motacilla. They live chiefly on the shores of ponds and streams. The American water thrush. See Water thrush. Wood wagtail, an Asiatic wagtail; (Calobates sulphurea) having a slender bill and short legs.