Composition of Couples, Biotopic Preferences, and Relative Life Duration of Birds in a Hybrid Yellowhammer (Еmberiza citrinella) and Pine Bunting (E. leucocephalos) Population (Passeriformes, Emberizidae) in the Altai Mountains.

The relationships between the yellowhammer (Еmberiza citrinella) and the pine bunting (Еmberiza leucocephalos) represent quite a rare case of mass hybridization in a broad sympatry zone. The hybrid population was monitored from 2008 to 2019 in a model area in the Altai Mountains, Russia, with the purpose to identify the potential pre- and postcopulatory isolation mechanisms in these species. The area selected as the model one is the only place in the vast secondary contact zone of the two species distinguished by the maximum hybridization level and a high proportion of birds with phenotypes of both parental species in approximately equal proportions. During the observation period, the proportion of phenotypic hybrids increased from 32 to 58%. Nevertheless, the population retains some precopulatory isolation mechanisms that are manifested in the positive mating assortativity and partial biotopic segregation between the species. On par with individuals featuring parental phenotypes, hybrids participate in breeding and successfully bring out nestlings: the phenotypic composition of feeding birds does not differ from the phenotypic composition of the population as a whole. However, the life span of hybrids is shorter; this applies even to birds featuring parental species phenotypes with slightly expressed characters indicating their hybrid origin. [ABSTRACT FROM AUTHOR]