Diet of Tawny Owl ( Strix aluco ) and Long-Eared Owl ( Asio otus ) in Lithuania as Found from Pellets

Abstract

Diet composition and food niches of two common and widespread in Lithuania owl species, Tawny Owl (Strix aluco) and Long-eared Owl (Asio otus), were analysed from irregularly collected pellets. S. aluco was characterised by a more diverse diet and a wider food niche: 14 small mammal (93.1% of the recovered items) and two amphibian (5.2%) species, a few passerine birds (1.1%) and representatives of three Coleoptera groups (0.6%) were recovered, whereas for A. otus – nine small mammal and two Carabidea species. By numbers, primary food resources of S. aluco were C. glareolus (31.4%), M. arvalis (27.9%) and A. flavicollis (14.3%), whereas of A. otus - M. arvalis (70.8%), all Microtus voles constituting 95.2%. Diet diversity of S. aluco was more than twofold higher (Shannon’s H = 2.62 vs. 1.16). According to biomass, main foods consumed by S. aluco were C. glareolus, M. arvalis and A. flavicollis (27.6, 25.0 and 22.4%, respectively). For A. otus, Microtus voles represented 95.8% of biomass consumed (M. arvalis – 64.3%). Levins’ measure of food niche breadth for S. aluco was B = 5.51 and for A. otus – B = 2.22. The average number of prey items per pellet was 2.84 ± 0.11 (max. 10) for S. aluco and 1.75 ± 0.03 (max. 7) for A. otus.