Low reproductive success or the Carrion Crow Corvus corone corone - Hooded Crow Corvus c. cornix hybrids.

Saino N.

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The reproductive success of pairs of different assortments was studied in an area of intergradation between Carrion Crow and Hooded Crow in north-Westem Italy during spring 1989. No significant variation in the mean size of the clutches laid by female carrion crows, hooded crows and hybrids was observed although hybrid females tended to lay fewer eggs. Female phenotype significantly influenced the number of chicks fledged; the nests of hybrid females produced on average significantIy less chicks than nests of the parental females. No significant variation in the mean number of chicks fledged was observed among nests of Carrion Crow, Hooded Crow and hybrid males. Evidences of assortative mating were observed; parental phenotipe tended to mate with individuals of their phenotype and avoided inter-phenotype mating. The results suggest that the 'dynamic equilibrium mode!' could partIy explain the phenomena in the hybrid zone studied. However, some aspects of the dynarnic of the Carrion/Hooded crow hybrid zone need to be examined more cIosely . A comparative analysis of the reproductive biology of sympatric and a1lopatric populations of the Carrion Crow and of the Hooded Crow and the analysis of other aspects of Crows biology in the hybrid zones are a1so needed