Contribution to the study of the diet of four owl species (Aves, Strigiformes) from mainland and island areas of Greece

The diets of the Barn Owl (Tyto alba), Little Owl (Athene noctua), Long-eared Owl (Asio otus) and Eagle Owl (Bubo bubo) were studied through analysis of pellets collected at 13 different continental areas and islands of Greece. The most important prey of the Barn Owl was mammals (mainly Microtus, Mus, Apodemus, Rattus and Crocidura), although birds and amphibians were of some importance on Antikythera island and Potidea (Central Macedonia), respectively. Average prey biomass ranged from 12.5 g to 42.8 g. The median prey biomass differed significantly between areas (p<0.001). The diet of the Little Owl was more diverse, consisting mainly of mammals (mostly Microtus, Mus, Apodemus, Micromys and Crocidura) in the Evros and Axios Deltas, mainly of insects (mostly Orthoptera and Coleoptera) in the Kitros Lagoon, Psara and Tilos islands, while birds and reptiles were common supplementary prey. Average prey biomass ranged from 0.7 g to 11.9 g. The median prey biomass differed significantly between the areas studied (p<0.001). The diet of the Long-eared Owl in both Nestos Delta and Porto Lagos consisted mainly of mammals (mostly Microtus, Mus and Apodemus), with some reptiles in the former area and birds in the latter. Average prey biomass was 18.5 g and 19.5 g respectively. The median prey biomass did not differ significantly between the two areas. The diet of the Eagle Owl in the Amvrakikos wetland consisted mostly of birds (62 \% by biomass) and mammals (36 \%, mainly Rattus norvegicus). Insects were the most important prey by numbers - 47 \% (1 \% by biomass). The prey diversity of the Eagle Owl was the highest while that of the Barn Owl was the lowest. Prey use by owls tended to clump by geographic area. We conclude that the owl species studied make use of prey according to the local availability and in accordance to the hunting abilities of each species.