Yellow Wagtail (Motacilla flava) - HBW 9, p. 781

Taxonomy: Motacilla flava Linnaeus, 1758, southern Sweden.
Relationships uncertain. Has been thought to form a superspecies variously with M. citreola, or with M. capensis, or with those two together with M. flaviventris, but recent molecular-genetic studies indicate that none of these arrangements is tenable. Taxonomy complex, and much further research needed. Recent studies, using mitochondrial DNA, suggest that races may represent three separate species, one in NE (based on tschutschensis), another in extreme SE (based on taivana and macronyx), and a third in W & C (based on nominate race); moreover, they also indicated that the NE group was closest to E nominate form of M. citreola and the SE group closest to W race (werae) of latter; other researchers, however, consider those two races of M. citreola to be inseparable in terms of morphology. In addition, several races (especially lutea, feldegg and taivana) have often been treated as separate species by various authors. Taxonomy is further complicated by the fact that some races are known to hybridize on fairly regular basis, thus confusing the picture with regard to distributional limits. Race plexa is perhaps indistinguishable from thunbergi; simillima possibly better included in tschutschensis, and angarensis in latter or in macronyx; and melanogrisea possibly inseparable from feldegg. Race alakulensis (from SE Kazakhstan) synonymized with thunbergi, alascensis (W Alaska) with tschutschensis, and aralensis (Aral Sea) and raddei (Transcaspia) with feldegg; proposed race zaissanensis (L Zaisan, in E Kazakhstan) is apparently an intergrade or hybrid form, and other suggested races superciliaris, dombrowskii and perconfusus similarly represent inter-racial hybrids. Pending further research, and bearing in mind above-mentioned details, all forms traditionally considered to belong in present species are treated as such and listed below. Seventeen subspecies currently recognized.