Selection of foraging habitat and flocking by Crow Corvus corone phenotypes in a hybrid zone

Little is known about the ecological mechanisms that maintain the parapatric ranges and narrow areas of hybridization in the Carrion Crow Corvus c. corone and Hooded Crow Corvus corone cornix. The winter ecology of parental populations and of hybrids was studied in an area of intergradation in NW-Italy. Carrion Crows and Hooded Crows showed sharply different foraging habitat preferences. The former selected pastures and meadows whereas the latter selected maize stubbles. The habitat selected by the two morphs corresponded to those prevailing in the areas of allopatry adjacent to the hybrid zone. Hybrids were less selective than the parental populations. Each of the parental morphs showed a significant tendency to avoid heterotypic flocks. It is concluded that the adaptation to different foraging habitats probably contributes to the maintenance of parapatric distributions by the parental populations and that hybrids may be better adapted to live in the hybrid zone. The assortative composition of the flocks could indicate the existence of pre-mating isolating mechanisms between the crow morphs.