The Diversity of Small Mammals along a Large River Valley Revealed from Pellets of Tawny Owl Strix aluco

SIMPLE SUMMARY: The Vistula River in Central Europe is widely recognized for its high nature value and attracts attention of numerous researchers as an example of a dynamic river flowing in an extensively managed floodplain. In this study of diversity of small mammals along the Vistula valley, we analyzed the diet of tawny owl Strix aluco, a common predator considered an efficient collector of rodents and shrews. Altogether 19 species, including 12 rodents, 5 soricomorphs (shrews and relatives), 1 carnivore, and 1 bat species were recorded. High species richness of small mammals can be attributed to a mosaic of agricultural land and the remnants of riparian forest and meadows in the Vistula floodplain. Out of the four most numerous species, two (bank vole Clethrionomys glareolus and yellow-necked mouse Apodemus flavicollis) are typical forest inhabitants, and two (striped field mouse A. agrarius and common vole Microtus arvalis) are associated with urban and agricultural land. This study of small mammals indicates the important role of natural large river valleys in the maintenance of local biodiversity. ABSTRACT: The Vistula River is one of the largest European semi-natural rivers of high ecological value that functions as an ecological corridor. To assess the structure of small mammal communities along the Vistula River, an analysis of the diet of an opportunistic predator, the tawny owl Strix aluco, was used. A total of 6355 individuals of 19 species were found, including 5 soricomorph species, 12 rodents, 1 carnivore, and 1 bat species. Tawny owls most frequently caught Apodemus agrarius, Clethrionomys glareolus, Apodemus flavicollis, and Microtus arvalis. Rodents dominated small mammal communities (90%), followed by soricomorphs (8%), and the share of Chiroptera was significant (2%). Using Ward’s method in cluster analysis, three clusters of sites with similar mammal communities were identified. The cluster that included 17 study sites with the dominance of agriculture habitats was inhabited by diverse mammal communities with a high number of species. In the cluster composed of three suburban forest sites, mammal communities had the lowest diversity, although the high species richness and the highest shares of the forest species (A. flavicollis, C. glareolus, and Nyctalus noctula). Mammal communities in the cluster were composed of three urban sites were dominated by A. agrarius and M. arvalis. The study indicates the high species richness of small mammals in floodplains of the Vistula River and the adjacent areas in central Poland. The floodplain offers suitable habitats for species associated with forests, water bodies, agricultural land, and developed areas. The data collected confirms earlier model predictions about the presence of well-connected local populations of forest mammals along the Vistula River.