\Wag"tail`\, n. (Zo["o]l.)
Any one of many species of Old World singing birds belonging
to {Motacilla} and several allied genera of the family
{Motacillid[ae]}. 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 colors. 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}.
(a) Any one of several species of wagtails of the restricted
    genus {Motacilla}. They live chiefly on the shores of
    ponds and streams.
(b) The American water thrush. See {Water thrush}.
{Wood wagtail}, an Asiatic wagtail; ({Calobates sulphurea})
   having a slender bill and short legs.