Territorial song does not isolate Yellowhammers (Emberiza citrinella) from Pine Buntings (E. leucocephalos)

Western Palearctic Yellowhammer and eastern Palearctic Pine Bunting are considered a pair of young sister species. A huge area of sympatry is in western Siberia where they hybridize extensively despite striking plumage differences. The somehow dominant Yellowhammer pushes the hybrid zone further east. Territorial songs of the two taxa are almost indistinguishable. We tested 15 song types from both species from various localities inside and outside the hybrid zone in playback experiments on German Yellowhammer males. All songs elicited territorial behavior in almost every experiment. Reaction intensity de­ pended on one out of 25 investigated sonagraphic parameters and was the weaker the further away the recording site of the playback was from the experimental site regardless of the taxon. Songs from the hybrid zone elicited disproportionately strong response so that a reinforcement of reproductive isolation through song can be excluded. Song seems to be more conserved than morphological features and has thus prevented a complete genetic divergence in this pair of subspecies groups.