Comparison of the trophic niche of four sympatricowls (Asio otus, Athene noctua, Strix aluco and Tyto alba) in Mediterranean central Italy

Abstract

Diet composition and trophic niche overlaps between four sympatric Strigiformes (Athene noctua, Strix aluco, Asio otus, Tyto alba) are studied in an agro-forested area of Mediterranean central Italy (province of Rome). Athene noctua preyed mainly on insects and other invertebrates, while the remaining three species feed mainly upon rodents and shrews. Judged by overlap estimates, the diet composition of Athene noctua is very different from those of the other three owl species. Asio otus preyed almost exclusively on Microtus savii, a rodent species very abundant in open cultivated fields but completely lacking from bushy ecotones and forested areas. Tyto alba and Strix aluco fed frequently upon rodent species (Apodemus, Mus, Clethrionomys) quite abundant in bushy ecotones and forested areas, but also upon Microtus savii. The mean prey size was very similar in all but one owl species (Athene noctua), which ate significantly smaller organisms. The diet composition of the four sympatric owls was quite similar to that of four snakes of the same area (Vipera aspis, Elaphe longissima, Elaphe quatuorlineata, Coluber viridiflavus), but a more detailed analysis suggests some differences in the habitat used for predatory activity by these morphologically and phylogenetically diverging predators.