Tho diet of Tawny Owl as a function of urbanization was studied in Central Poland in 1976-1984. The pellets were collected from 24 sites in habitats along an urbanization gradient ranging from the large, relatively undisturbed Kampinos Forest (1441 prey items), through small woodlots surrounding Warsaw (686) and into the city of Warsaw (2567). Diet varied due to urbanization: the proportions of mammals and amphibians were lowest in the city center (respectively 11.3% and 0%), but the proportion of birds, largely House Sparrow Passer domesticus increased from 2.9% in the forest to 88.7% in the city. Niche breadth and seasonal variation declined with urbanization. Relationships between diet composition and habitat structure of owl's hunting range in the city, as well as on the seasonal diet variation from owls hunting in forests, let to conclude that the owls were able to exploit locally abundant prey from a variety of habitats. Although the highest densities of Field Mouse Apodemus agrarius were noted in parks and cemeteries, our data suggest that Tawny Owls catch this species more effectively in small gardens and secondary growth areas. The predation on Field Mouse by a pair of owls breeding in an urban cemetery was low. Approximately 3.2% of the population were removed by the owl predation, considerably less than in a more rural population.
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