Or does this represent an early stage in selection for traits that will make the separation stronger? Or is it the early stages of producing a third species through hybridization? Possibilities are multiple.Well I can't argue against any of these points! However, regarding human v bird perception of distinctiveness of traits, isn't that applicable to the entire discipline of taxonomy?! We judge differences in morphology, plumage and vocalisations through human eyes and ears.
I'm not sure how to interpret introgression from a species-level taxonomic perspective. Presumably it represents two distinct and previously disjunct species lineages that have expanded in range and are in the process of merging into a single species? If so, how does one treat the birds outside the contact zone? Is this comparable to Pine Bunting v Yellowhammer?
Niels