ON THE RELATIONS BETWEEN THE YELLOWHAMMER (EMBERIZA CITRINELLA) AND THE PINE BUNTING (EMBERIZA LEUCOCEPHALOS) IN FORESTED STEPPE TRANSURALIA

摘要

We studied the phenotypic composition of populations and the variability of the song in two Bunting species in three localities at the western border of the sympatry zone: in the south of the Tyumen region and in the centre and south of the Kurgan Region. Over the last several decades, the zone of contact of the studied species has expanded significantly. The Pine Bunting started breeding regularly in the area in the end of the 20th century and at present it is considered as a common species comparable in abundance to the Yellowhammer. The share of phenotypic hybrids varies from 25% to 50% reaching its maximum at the boundary of the Pine Bunting nesting range. East of this boundary the hybridization level is reduced, this being seen in a sharp decrease in the share of "leucocephala hybrids". An aalysis of the phenotypic variability of the hybrids shows that they may be divided into two groups similar in coloration to the parent species. The study results let us presume that the hybridization is limited and hybrids return mostly to backcrossing with the parent species. This presumption also finds its support in an analysis of song structure: there the Yellowhammer and the Pine Bunting have songs of different, easily distinguishable dialects.