The long-eared owl (Asio otus L. 1758) is a medium-sized owl from the family of typical owls (Strigidae). With time it has adjusted to life in the immediate vicinity of man and is becoming a more numerous species in the urban areas. In the IUCN Red List of Threatened Species the long-eared owl is classified as Least Concern (LC). It has the same status on the Red List of Plants and Animals of the Republic of Croatia and is protected by the Nature Protection Act. The aim of this thesis is to study the feeding habits of the long-eared owl population in the rural areas of Strošinci, Drenovaci and Bošnjaci along with the city of Županja during the winter of 2014/2015, and determine the width of the ecological niche of the overwintering long-eared owls in the studied areas. A correlation between the availability of prey and the floods of 2014 is also analysed. In the time period from October 2014 through February 2015 the sum of 1073 pellets was collected on all 4 locations. The dry method of cleaning was used to clean the pellets. The prey remains were identified under the magnifying glass with the help of determination keys, and as a result 2476 kinds of pray were identified. In those pellets the remains of 13 species of small mammals and the remains of birds of class Aves sp. were found. From the determined types of small mammals, most of them belonged to the family Muridae and Cricetidae among which the most dominant species was common vole (Microtus arvalis) with 80.60%. The average number of prey per pellet was 2.36. The long-eared owls in Županja caught the largest number of different types of prey (11) in January 2015, and the smallest number (2) belongs to the Bošnjaci owls during October 2014. The ecological niche of long-eared owls, according to Levin's Measure of Niche Breadth, has the widest breadth in Strošinci (5.92) and the narrowest in Bošnjaci (2.35). The largest percentage of overlapping width of the ecological niche is with those owls wintering in Bošnjaci and Županja, and the smallest between those that spent the winter in Strošinci and Županja. There were no statistically significant differences in the composition of prey of overwintering long-eared owls in studied areas with respect to the flooding of the habitat during the summer and fall of 2014.Number of page: 67Number of figures: 22Number of tables: 12Number of reference: 81Original in: CroatianKey words: Long-eared owl, Asio otus, winter feeding, pellets, small mammals, Županja, CroatiaDate of the thesis defence:Reviewers:Enrih Merdić, PhD, associate professorMirta Sudarić Bogojević, PhD, assistant professorAlma Mikuška, PhD, assistant professorThesis deposited