The grey wagtail (Motacilla cinerea) is a member of the wagtail family, Motacillidae, measuring around 18–19 cm overall length. The species looks somewhat similar to the yellow wagtail but has the yellow on its underside restricted to the throat and vent. Breeding males have a black throat. The species is widely distributed, with several populations breeding in Eurosiberia and migrating to tropical regions in Asia and Africa. The species is always associated with running water when breeding, although they may use man-made structures near streams for the nest. Outside the breeding season, they may also be seen around lakes, coasts and other watery habitats. Like other wagtails, they frequently wag their tail and fly low with undulations and they have a sharp call that is often given in flight.
This slim wagtail has a narrow white supercilium and a broken eye ring. The upperparts are grey and the yellow vent contrasting with whitish underparts makes it distinctive. The breeding male has a black throat that is edged by whitish moustachial stripes. They forage singly or in pairs on meadows or on shallow water marshes. They also use rocks in water and will often perch on trees. They have a clear sharp call note and the song consists of trills.
The breeding season is April to July and the nest is placed near fast running streams or rivers on an embankment between stones and roots. The male in display, makes short flights up into the air and descends slowly with fluttering flight accompanied by a rapid series of chipping high notes. In Europe the nests are often made in holes in manmade structures. The clutch consists of 3–6 speckled eggs and multiple broods may be raised with declining numbers in the clutch in subsequent broods. The usual clutch size is five in Ireland and the breeding success is about 80% with predation of eggs or chicks being the main cause of breeding failure. The Canary Islands population typically have smaller clutches and the breeding season is not as short and well marked as in populations at higher latitudes. The incubation period is about two weeks with chicks fledging within a fortnight. They live for a maximum of 8 years in the wild.
In some parts of its range the white-throated dipper nests in the same habitats as the grey wagtail and there are some records of interspecific feeding of dipper chicks by adult wagtails.
These birds feed on a variety of aquatic invertebrates including adult flies, mayflies, beetles, crustacea and molluscs. They often forage along roadsides in winter, flushing with a sharp chi-cheep call and flying up further along the road but after some distance turning back to return to the original location.
In winter, they roost in small groups. Wintering birds have been known to return to the same sites, sometimes a small urban garden, each year.
Adults often have parasitic ticks, Ixodes ricinus, which can harbour Borrelia and thus can potentially disperse Lyme disease over a wide region. Coccidia such as Isospora sp. are known in this species. The common cuckoo is sometimes a brood parasite of this species, and kestrels may sometimes prey on them.
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