Bioacoustics, Genetics, and Morphological Variability of Some Subspecies of the Bluethroat (Cyanecula svecica, Muscicapidae, Aves) in the Central Part of Its Distribution Range

The bluethroat (Cyanecula svecica) is a polytypic species with a trans-Palaearctic distribution and complex subspecies differentiation. The bioacoustics, genetics, and morphological variability were studied in the central part of the breeding range of this species. Most attention was paid to the polymorphic subspecies C. s. volgae. Across the whole range of this subspecies, white-star, red-star, and intermediate morphotypes occur together. Our study indicated an insignificant level of volgae divergence compared to three adjacent subspecies (C. s. cyanecula, C. s. svecica, and C. s. pallidogularis) for all of the characters examined. Differences in the song of C. s. volgae were found only when comparing it to cyanecula, but not to C. s. pallidogularis. The morphological characters of volgae overlap widely with all of the subspecies studied. According to the genetic markers (cyt b and ND2 mtDNA), no differences of C. s. volgae from C. s. svecica and C. s. pallidogularis were revealed. Thus, the main specificity of C. s. volgae is its pronounced color polymorphism. As we found no significant differences to exist between the red-star and white-star morphotypes within the polymorphic C. s. volgae population, neither in the song nor in the body size, nor in the genetic characteristics, C. s. volgae can be considered as an independent subspecies. We suggest the origin of volgae as a result of historical transformations of habitats by human activities, which might have led to the emergence of a secondary contact zone and hybridization of the western European white-star form C. s. cyanecula and the northern red-star form C. s. svecica.