Wagtail

Wagtail

Egg, Collection Museum Wiesbaden, Germany

The genus Motacilla was introduced by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae.[1] The type species is the white wagtail.[2] Motacilla is the Latin name for the pied wagtail; although actually a diminutive of motare, "to move about", from medieval times it led to the misunderstanding of cilla as "tail".[3]

At first glance, the wagtails appear to be divided into a yellow-bellied group and a white-bellied one, or one where the upper head is black and another where it is usually grey, but may be olive, yellow, or other colours. However, these are not evolutionary lineages; change of belly colour and increase of melanin have occurred independently several times in the wagtails, and the colour patterns which actually indicate relationships are more subtle.

mtDNA cytochrome b and NADH dehydrogenase subunit 2 sequence data (Voelker, 2002) is of limited use: the suspicion that there is a superspecies of probably 3 white-bellied, black-throated wagtails is confirmed. Also, there is another superspecies in sub-Saharan Africa, three white-throated species with a black breast-band. The remaining five species are highly variable morphologically and their relationships with each other and with the two clades have not yet been satisfactorily explained.

The origin of the genus appears to be in the general area of Eastern Siberia/Mongolia. Wagtails spread rapidly across Eurasia and dispersed to Africa in the Zanclean (Early Pliocene)[4] where the sub-Saharan lineage was later isolated. The African pied wagtail (and possibly the Mekong wagtail) diverged prior to the massive radiation of the white-bellied black-throated and most yellow-bellied forms, all of which took place during the late Piacenzian (early Late Pliocene), c. 3 mya.

Three species are poly- or paraphyletic in the present taxonomical arrangement and either subspecies need to be reassigned and/or species split up. The blue-headed wagtail (AKA yellow wagtail and many other names), especially, has always been a taxonomical nightmare with over a dozen currently accepted subspecies and many more invalid ones. The two remaining "monochrome" species, Mekong and African pied wagtail may be closely related, or a most striking example of convergent evolution.

Prehistoric wagtails known from fossils are Motacilla humata and Motacilla major.

Wagtails are slender, often colourful, ground-feeding insectivores of open country in the Old World. Species of wagtail breed in Africa, Europe and Asia, some of which are fully or partially migratory. Two species also breed in Alaska, and wintering birds may reach Australia.

They are ground nesters, laying up to six speckled eggs at a time. Among their most conspicuous behaviours is a near constant tail wagging, a trait that has given the birds their common name. In spite of the ubiquity of the behaviour and observations of it, the reasons for it are poorly understood. It has been suggested that it may flush up prey, or that it may signal submissiveness to other wagtails. Recent studies have suggested instead that it is a signal of vigilance[5] that may aid to deter potential predators.[6]

The genus contains 13 species.[7]

Image	Scientific name	Common Name	Distribution
	Motacilla flava	Western yellow wagtail	temperate Europe and Asia.
	Motacilla tschutschensis	Eastern yellow wagtail	North America in Alaska, Asia and Australia.
	Motacilla citreola	Citrine wagtail	South Asia
	Motacilla capensis	Cape wagtail	southern Africa from Uganda, the eastern DRCongo and Kenya, through Zambia and Angola to southern Africa, south to the Western Cape and the Cape of Good Hope.
	Motacilla flaviventris	Madagascan wagtail	Madagascar.
	Motacilla cinerea	Grey wagtail	western Europe including the British Isles, Scandinavia and Mediterranean region.
	Motacilla clara	Mountain wagtail	Guinea to Ethiopia south to South Africa.
	Motacilla alba - polyphyletic or paraphyletic	White wagtail	mountains of Morocco and western Alaska.
	Motacilla aguimp	African pied wagtail	sub-Saharan Africa from the Eastern Cape north to extreme southern Egypt and from Guinea to western Eritrea and Somalia.
	Motacilla samveasnae	Mekong wagtail	Cambodia and Laos, and is a non-breeding visitor to Thailand and Vietnam
	Motacilla grandis	Japanese wagtail	Japan and Korea.
	Motacilla maderaspatensis	White-browed wagtail	India
	Motacilla bocagii	São Tomé shorttail	São Tomé

• Voelker, Gary (2002): Systematics and historical biogeography of wagtails: Dispersal versus vicariance revisited. Condor 104(4): 725–739. [English with Spanish abstract] DOI: 10.1650/0010-5422(2002)104[0725:SAHBOW]2.0.CO;2 HTML abstract

Media related to Motacilla at Wikimedia Commons

• Chisholm, Hugh, ed. (1911). "Wagtail" . Encyclopædia Britannica (11th ed.). Cambridge University Press.
• Wagtail videos on the Internet Bird Collection