african pied wag tail
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 gray, but may be olive, yellow, or other colors. However, these are not evolutionary lineages; change of belly color and increase of melanin have occurred independently several times in the wagtails, and the color patterns which actually indicate relationships are more subtle.
Wagtails are slender, often colourful, ground-feeding insectivores of open country in the Old World. They are ground nesters, laying up to six speckled eggs at a time.
The wagtails form the passerine bird genus Motacilla. They are small birds with long tails which they wag frequently. Motacilla, the root of the family and genus name, means moving tail. The Forest Wagtail belongs to the monotypic genus Dendronanthus which is closely related to Motacilla and sometimes included herein.
Prehistoric wagtails known from fossils are Motacilla humata and Motacilla major
Three species of wagtail 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.
The origin of wagtail 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)where the sub-Saharan lineage was later isolated. The African Pink 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), approximately around 3 mya.