Summary

Based on examinations of museum specimens (n = 320) and field descriptions of birds in nature (n = 487), the variability between Kamchatka Motacilla (alba) lugens and Spectacled M. alba ocularis white wagtail plumages were examined. Their populations are phenotypically variable, but both forms diagnostically correspond to Maуr’s Rule by 75%. In Kamchatka, there is a large area of sympatry (700 km) in which both lugens and ocularis breed annually, and thus regularly hybridize. The southern boundary of this zone is on the border line connecting the villages of Esso and Ust-Kamchatsk. Specific external attributes of each form and their various combinations in single individuals as most likely evidence of hybridization revealed. The frequency of mixed pairs and hybrids on the Kamchatka Peninsula is relatively small, with an uneven level of hybridization in different areas. Isolating barriers that prevent hybridization are suspected. Hybrid population inhabiting the southern part of Kamchatka Peninsula are presently evolve independently toward introgressive hybridization.
The Kamchatka hybridization zone is not the only place where these forms interact. Individuals with hybrid phenotypes have been observed in the lower Amur and Shantar Islands, which also suggests these are areas of sympatry. It is likely that lugens is on its way to becoming a distinct species, but full reproductive isolation of this form has not yet extended to Kamchatka or other parts of the region. Therefore, the taxonomic status of Kamchatka wagtails cannot presently be ascertained for certain. Its nomenclature, as well as for other subspecies in similar situations, requires status different that what is currently accepted within the Code of Zoological Nomenclature, and reflects an intermediate stage between species and subspecies.
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Recomended citation

Lobkov E.G. Kamchatka wagtail Motacilla (alba) lugens (Gloger, 1829): variability, relationships with the Spectacled white wagtail Motacilla alba ocularis (Swinhoe, 1860), and the taxonomic status // Far East. J.Orn 2: 27-55 (2011) (In Russian)