The white wagtail (Motacilla alba) is a small passerine bird in the family Motacillidae, which also includes pipits and longclaws. The species breeds in much of Europe and the Asian Palearctic and parts of North Africa. It has a toehold in Alaska as a scarce breeder. It is resident in the mildest parts of its range, but otherwise migrates to Africa. In Ireland and Great Britain, the darker subspecies, the pied wagtail or water wagtail (M. a. yarrellii) predominates. In total, there are between 9 and 11 subspecies.
The white wagtail is an insectivorous bird of open country, often near habitation and water. It prefers bare areas for feeding, where it can see and pursue its prey. In urban areas it has adapted to foraging on paved areas such as car parks. It nests in crevices in stone walls and similar natural and man-made structures.
It is the national bird of Latvia and has featured on the stamps of several countries. Though it is 'of least concern', there are several threats against it, like being kept as pets and being used as food.
Description & appearanceThe white wagtail is a slender bird, 16.5 to 19 cm (6.5 to 7.5 in) in length (East Asian subspecies are longer, measuring up to 21 cm (8.3 in)), with the characteristic long, constantly wagging tail of its genus. Its average weight is 25 g (0.88 oz) and the maximum lifespan in the wild is about 12 years.
There are a number of other subspecies, some of which may have arisen because of partial geographical isolation, such as the resident British and Irish 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. Phylogenetic studies using mtDNA suggest that some morphological features have evolved more than once, including the back and chin colour. Breeding M. a. yarrellii look much like the nominate race except for the black back, and M. a. alboides of the Himalayas differs from the Central Asian M. a. personata only by its black back. M. a. personata has been recorded breeding in the Siddar Valley of Kashmir of the Western Himalayas. It has also been noted that both back and chin change colour during the pre-basic moult; all black-throated subspecies develop white chins and throats in winter and some black-backed birds are grey-backed in winter.
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 study in 2004 has suggested instead that it is a signal of vigilance to potential predators.
Voice, singing & callThe call of the white wagtail is a sharp chisick, slightly softer than the version given by the pied wagtail. The song is more regular in white than pied, but with little territorial significance, since the male uses a series of contact calls to attract the female.
Distribution & habitatThis 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 wagtails are residents 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.
Hunting & foodThe exact composition of the diet of white wagtails varies by location, but terrestrial and aquatic insects and other small invertebrates form the major part of the diet. These range from beetles, dragonflies, small snails, spiders, worms, crustaceans, to maggots found in carcasses and, most importantly, flies. Small fish fry have also been recorded in the diet. The white wagtail is somewhat unusual in the parts of its range where it is non-migratory as it is an insectivorous bird that continues to feed on insects during the winter (most other insectivorous birds in temperate climates migrate or switch to more vegetable matter).
Breeding, mating, chicks, juveniles & raiseWhite wagtails are monogamous and defend breeding territories. The breeding season for most is from April to August, with the season starting later further north. Both sexes are responsible for building the nest, with the male responsible for initiating the nest building and the female for finishing the process. For second broods in the subspecies personata the female alone builds the nest, which is a rough cup assembled from twigs, grass, leaves and other plant matter, as the male is still provisioning the young. It is lined with soft materials, including animal hair. The nest is set into a crevice or hole—traditionally in a bank next to a river or ditch—but the species has also adapted to nesting in walls, bridges and buildings. One nest was found in the skull of a walrus.
White wagtails will nest in association with other animals: particularly, where available, the dams of beavers and also inside the nests of golden eagles. Around three to eight eggs are laid, with the usual number being four to six. The eggs are cream-coloured, often with a faint bluish-green or turquoise tint, and heavily spotted with reddish brown; they measure, on average, 21 mm × 15 mm (0.83 in × 0.59 in). Both parents incubate the eggs, although the female generally does so for longer and incubates at night. The eggs begin to hatch after 12 days (sometimes as late as 16 days). Both parents feed the chicks until they fledge after between 12 and 15 days, and the chicks are fed for another week after fledging.
Though it is known to be a host species for the common cuckoo, the white wagtail typically deserts its nest if it has been parasitised. Moksnes et al. theorised that this occurs because the wagtail is too small to push the intruding egg out of the nest, and too short-billed to destroy the egg by puncturing it.