We live fairly near the hybrid zone between the Hooded and Carrion crows in the West of Scotland. A hybrid lived for several years in the surrounding gardens and school playing field even though it never looked the healthiest of birds and had, what the vets would described as, an ‘unthrifty’ appearance. As well as hybrids, Hooded Crows are reported occasionally since the hybrid zone is narrow at this point and hoodies occur on the islands of Arran and Ailsa Craig where they are said to prefer the higher ground compared with the Carrion Crow.
Discussion has centred on whether the new findings offer support to the arguments in favour of considering the two forms as two species, or as subspecies of one species. Over the years they have flitted between being regarded as two species or one. Linnaeus originally described them as two species but throughout the later part of the 20th century, the one species view prevailed with the Hooded Crow listed as a subspecies, Corvus corone cornix, alongside the Carrion Crow, C. c. corone. Then, in 2002 the British Ornithologists’ Union recommended that the two forms should be recognised as separate species (Knox et al 2002). The reasons for this (non-random mating and reduced fitness of the hybrids) and how they fit the Evolutionary Species Concept are explained by Parkin et al (2003) and by Parkin (2003). Parkin (2003) concludes: