SELECTIVE AGGRESSIVENESS AND DOMINANCE AMONG CARRION CROWS, HOODED CROWS AND HYBRIDS

The frequencies of intra and inter-phenotype aggressions and dominance hierarchy were studied in mixed flocks of carrion crows (Corvus corone corone), hooded crows (Corvus corone cornix) and hybrids under field conditions. The study, carried out during winter in an area of Piedmont (NW Italy) where carrion crows and hooded crows live in sympatry and hybridize, showed that: 1) carrion crows were more aggressive and attacked hooded crows and hybrids more frequently than expected under the hypothesis of random encounters between phenotypes; 2) hybrids and hooded crows attacked carrion crows less frequently than expected; 3) carrion crows were much more likely to win inter-phenotype interactions than hybrids and hooded crows; 4) when attacked by a hooded crow a carrion crow was more likely to win the encounter than vice versa. It is suggested that carrion crows, being dominant over the other phenotypes, have easier access to food sources during periods of shortage, and that the selective aggressiveness of carrion crows against the other phenotypes is probably one of the mechanisms that promote the assortative mating previously observed in the same area.