Changes in the Carrion/Hooded Crow Hybrid Zone and the Possible Importance of Climate

During the last Ice Age the European Crow population was forced to retreat to ‘refugia’ in the Balkans and the Iberian Peninsula. These isolated groups developed striking plumage differences, the grey-andblack Hoodie in the east, and the all-black Carrion in the west. Voice and general behaviour changed but little, so that when the ice retreated and the separate groups expanded to meet in middle Europe, they were able to interbreed and produce fertile hybrids, but only over a narrow zone of overlap. Recent climatic changes have brought about a marked shift in the position of this zone in Scotland.