MOSAIC DISTRIBUTION AND BREEDING HABITATOF THE HOODED CROW Corvus corone cornix ANDTHE MAGPIE Pica pica IN PADANA PLAIN (NORTHERN ITALY)

Fasola M. & Brichetti P.



Abstract:

The density distribution and habitat use ofbreeding Crow and Magpie were studied over 12 900 km2 ofthe plain , by winter roadside counts and observations on the nest site s ofthe preceeding breeding season. The densities of the two spe cics varied widely (from zero to 3.2 breeding pairs/km2 in the Crow and from zero to 1.9 in the Magpie), despite the adaptability of the species and the uniformity of the habitat. The limits of the derisity z ones did n o t coincide with any evident environmental change. The Crow and Magpie replaced one another both in their geographical distribution and in the local n est placing. The terr itor ie s of the two species were statistically discriminated by habitat characteristics, of which the most important were the cxtcnsion of poplar plantations, fields, Acacia woods and buildings. The two species were more segregated in habitat use in the areas of overlap than in areas of segregation, because the Magpie shifted in the use of the same 4 important habitat characteristics where it coexisted with the Crow. We conclude that competitive exploitation of similar resources, behavioural interference and predation on nests determine in th e Crow and Magpie a mosaic distribution of contiguous terr itorie s in the areas of coexistcnce, the coexistence changing gradually in to segregation in other zones. The prevalence of each species in different zones is determined by minor environmental characteristics of the uniform plain, su eh as prevailing cultivation. lt is unclear how the sharp changes in density are determ ined in the apparently uniform plain and why both specie s are absent from a large zone.