Interspecific coexistence in corvids in an alpine valley of northwestern Italy

Abstract

A study on interspecific coexistence in corvids (Corvus corone comix, Corvus corone corone, Corvus frugilegus, Corvus monedula, Pica pica, Carrulus glandarius) has been carried out in the valley of Susa (northwestern Italy). Both ecological (niche and habitat choice) and behavioural (intra‐ and interspecific aggression) factors were considered. Niche analysis took into account the distribution of species on ground (foraging activity), as well as on trees (resting activity). Habitat use was described referring to types of field under cultivation associated with tree formations. Niche and habitat matrices were subjected to Cluster Analysis and Principal Components Analysis. As for intra‐ and interspecific aggressions, a few indices taking into account the number of aggressions together with the number of observations, the time of observation and the number of individuals, were used. Both niche and habitat analyses showed a clear ecological similarity between carrion and hooded crow. The rook resulted in ecological choices rather close to the crows whereas the magpie and, above all, the jay, showed different ecological requirements. Interspecific aggression indices suggested that the rook and the jackdaw were the most interactive species. Data on interspecific interactions confirmed that the crow is dominant over all other species with the carrion crow prevailing over the hooded crow. It is suggested that niche and habitat choices reflect major morphological differences among species and that interspecific interactions might enhance ecological segregation.

Key words:

• Birds
• Niche and habitat analyses
• Intra‐ and interspecific aggressions
• Mixed flocks