Wagtails are a group of passerine birds that form the genus Motacilla in the family Motacillidae. The common name and genus name are derived from their characteristic tail pumping behaviour. Together with the pipits and longclaws they form the family Motacillidae.
The forest wagtail belongs to the monotypic genus Dendronanthus which is closely related to Motacilla and sometimes included therein. The willie wagtail (Rhipidura leucophrys) of Australia is not a true wagtail; it is named as such for its similarity to the Japanese wagtail and belongs to the genus of birds known as fantails.
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.
mtDNAcytochrome b and NADH dehydrogenasesubunit 2 sequence data (Voelker, 2002) is of limited use: the suspicion that there is a superspecies of probably three 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.[citation needed]
Prehistoric wagtails known from fossils are Motacilla humata and Motacilla major.
Characteristics
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.[citation needed] 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]
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.
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.[8]
^
The date of 4.5 mya in Voelker (2002) is dubious as it does not rely upon hard data but is merely an estimate based on average values now known to be often wrong.
^Randler, C (2006). "Is tail wagging in white wagtails, Motacilla alba, an honest signal of vigilance?" Animal Behaviour71 (5): 1089-1093
^Hasson, O. (1991). "Pursuit-deterrent signals: communication between prey and predator". Trends in Ecology & Evolution, 6:325-329.
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