| Summary: | Through the analysis of data from the Tengmalm's Owl population that inhabits the forest of the Alt Pirineu Natural Park, its diet is studied through the skulls of its prey. The main objective is to expand the scarce information on the biology of this species, resident in the area. The data set is collected from 2016 to 2021. Using the pellet samples available, it is investigated how the abundance of main prey affects the reproductive success and feeding ecology of the species. According to the optimal diet model, under conditions of prey abundance the species in question will select the most profitable items. Thus, the diet composition of the boreal owl will depend on the availability of its main prey items. The abundance of micromammals in the study area is then studied using data from the micromammal monitoring campaign in Catalonia (SEMICE). The main prey of the Tengmalm's Owl in the Alt Pirineu Natural Park are individuals of the family Muridae (Apodemus sylvaticus), individuals of the subfamily Arvicolinae (Microtus agresits, Microtus arvalis, Myodes glareolus and Arvicola sapidus) and individuals of the family Soricidae (Sorex araneus, Sorex coronatus and Crocidura russula). Through the analysis of the diet samples, it was found that the most abundant predatory species was wood mouse, followed by field vole and bank vole. The year with the highest abundance of small mammals was 2016 and the year with the lowest abundance was 2017. Data from the small mammal monitoring campaign (Semice) in the area are also analyzed to try to see if the proportions of small mammals in the field match the proportions in the diet samples. However, only the abundances from two different years coincide, so the results are not conclusive.
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