A comparative study of the variability of owl diets in three localities of central Italy

Abstract

Trophic niches of three coexisting owl species (Asio otus, Strix aluco and Tyto alba) in three localities of central Italy were investigated by using the pellet analysis method. Furthermore, data on small mammal assemblage composition in two different environmental types (i.e. woodland and grassland) were drawn from previous studies performed in the study areas. The three owls preyed chiefly upon small mammals, while birds were occasionally eaten. The trophic niches of A. otus in the three study areas were significantly narrower than that of T alba and S. aluco. These latter species varied the size of their prey between the three localities, while A. otus preyed upon similarly sized prey in the three study areas. By using data on small mammal occurrence we tried to estimate the environmental type where the owls conducted their predatory activity : principal component analysis revealed that A. otus was linked to the cultivated fields as foraging habitat, while S. aluco and T alba were less selective in the choice of hunting habitat. Furthermore, discriminant analysis indicated that species dietary habits maintained their distinguishing features also in distant localities. However, it appeared that owls did not use foraging resource with an exclusive strategy : evidences from this study are consistent with the hypothesis of a selective use of the trophic resource by A. otus, while diets of T. alba and S. aluco showed differences between the three localities.