| Summary: | The diets of the breeding Tengmalm's Owl and Ural Owl were studied in Central Finland in 1976-84. Ural Owls used more voles than Tengmalm's Owls, 92 % and 74 %, respectively . The most important prey species of the Ural Owl was Arvicola terrestris and those of the Tengmalm's Owl were Clethrionomys voles and Microtus agreslis . The annual variation in food composition was larger in the Tengmalm's Owl than in the Ural Owl. Fluctuations in the numbers of breeding Ural Owls were, and the numbers of breeding Tengmalm's Owls were not correlated with the numbers of voles eaten. Breeding success, estimated by the number of fledglings, was dependent on the proportion of voles in the diet .
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