Relations between the Yellowhammer (Emberiza citrinella) and the Pine Bunting (Emberiza leucocephalos) in the Forested Steppe of the Trans-Urals

We studied the phenotypic composition of the populations and variability of songs in two bunting species in three localities on the western border of the sympatry zone: in the southern part of Tyumen’ oblast and in the center and southern of Kurgan oblast. 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 at the end of the 20th century, and at present it is considered 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’s 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 analysis of the phenotypic variability of the hybrids shows that they can be divided into two groups similar in coloration to the parental species. The study results let us presume that the hybridization is limited and hybrids return mostly to backcrossing with the parental species. This presumption also finds support in an analysis of the song structure: the yellowhammer and the pine bunting have songs of different, easily distinguishable dialects.