White Wagtail

Description:

The White Wagtail is a slender bird, 16.5–19 cm (6½–7½ in) in length (East Asian subspecies are longer, measuring up to 21 cm (8¼ in), with the characteristic long, constantly wagging tail of its genus. The nominate subspecies Motacilla alba alba is basically grey above and white below, with a white face, black cap and black throat. There are a number of other subspecies, some of which may have arisen because of partial geographical isolation, such as the resident British form, the Pied Wagtail M. a. yarrellii, which now also breeds in adjacent areas of the neighbouring European mainland. The Pied Wagtail, named for naturalist William Yarrell, exchanges the grey colour of the nominate form with black (or very dark grey in females), but is otherwise identical in its behaviour. Other subspecies, the validity of some of which is questionable, differ in the colour of the wings, back, and head, or other features. Some races show sexual dimorphism during the breeding season. As many as six subspecies may be present in the wintering ground in India or Southeast Asia and here they can be difficult to distinguish

Habitat:

This species breeds throughout Eurasia up to latitudes 75°N, only being absent in the Arctic from areas where the July isotherm is less than 4 °C. It also breeds in the mountains of Morocco and western Alaska. It occupies a wide range of habitats, but is absent from deserts. White Wagtail is resident in the milder parts of its range such as western Europe and the Mediterranean, but migratory in much of the rest of its range. Northern European breeders winter around the Mediterranean and in tropical and subtropical Africa and Asiatic birds move to the Middle East, India,and SouthEast Asia.Birds from the North American population also winter in tropical Asia

Notes:

The most conspicuous habit of this species is a near-constant tail wagging, a trait that has given the species, and indeed the genus, its common name. In spite of the ubiquity of this behaviour, the reasons for it are poorly understood. It has been suggested that it may flush prey, or signal submissiveness to other wagtails. A recent study has suggested instead that it is a signal of vigilance to potential predators