Grey Wagtail Bird is an elegant and attractive bird, with a very long white-edged tail which is pumped continuously, rocking the whole rear of the bird. In all plumages it shows a bright yellow vent and brownish-pink legs. The head and mantle are pure grey, the wings blackish with white edges to the long tertial feathers. In summer the male has a rich yellow on the breast, and a bright white supercilium and submoustachial stripe and a black throat. The Grey Wagtail Bird (female) typically has a white or dingy greyish throat, a buff supercilium and paler yellow underparts. In winter both sexes show a white throat, and the underparts are pale whitish-yellow.
Grey Wagtail Bird is more closely tied to water than its relatives, it breeds along fast-flowing streams and rivers, canals, lakesides and some larger slower rivers, which can provide perches on rocks, shingle, weirs and locks, plus cavities for nests in walls, roofs, rocks and culverts, with trees and bushes alongside. Commonly found on upland and mountain streams, and outside the breeding season it ranges more widely into lowland areas, also occurring on estuaries, coasts and sewage farms. It also appears in towns and cities, often using the flat roofs of tall buildings where rainwater collects.
The vocalizations of Grey Wagtail Bird are high pitched, as is typical for birds living around rivers, which produce a lot of low-frequency noise. The typical call is a disyllabic "dji'dih" or "chiddih", also uttered singly as "djitd" and often heard in flight. The anxiety call when near the nest is a rising "sweee" or "chwea". There is also a three- or four-syllable penetrating high-pitched call, "tsi'tsi'tsi'tsi". The song is a bright, high-pitched tinkling series of varying phrases of notes, not unlike a shorter, more rapid version of the Tree Pipit song, such as "di di ti'ti'ti chichichi chew trrrrrrr pink pink pink see-chew". Another phrase, sometimes introduced or sung singly, is a simple "si'si'si see-chew".