Small mammals in the diet of the tawny owl Strix aluco in selected sites of the Biebrza Basin and Knyszyn Forest in north-eastern Poland

The analysis of pellets of the tawny owl Strix aluco collected in the years 2009–2023 in 22 sites (ten in the Biebrza Basin and twelve in Knyszyn Forest) allowed for finding four species of Soricomorpha, nine species of Chiroptera and fifteen species of Rodentia (4, 5 and 12 in the Biebrza Basin and 4, 7 and 13 in Knyszyn Forest, respectively). Most common and most frequently caught by owls were: the bank vole Clethrionomys glareolus, the yellow-necked mouse Apodemus flavicollis and the common shrew Sorex araneus. Valuable species of bats included the pond bat Myotis dasycneme and the western barbastelle Barbastella barbastellus noted in Knyszyn Forest. Rare rodents found in both study areas were: the northern birch mouse Sicista betulina and the common dormouse Muscardinus avellanarius while the forest dormouse Dryomys nitedula was noted only in Knyszyn Forest. The European water vole Arvicola amphibius commonly noted in the Biebrza Basin was not found in Knyszyn Forest. On the contrary, the common pine vole Microtus subterraneus was reecorded only in Knyszyn Forest.