Temporal Changes in Bank Vole Populations Indicate Species Decline

Because of their wide distribution, short life cycle, rapid reproduction, and sensitivity to the environment, rodents can indicate changes in habitat quality and climate variables. Long-term studies are needed to verify these changes and assumptions about their causes. We analyzed small mammal trapping data in Lithuania, covering the period 1975–2023, with 1821 trapping sites and 57,426 small mammal individuals, with a focus on the bank vole (Clethrionomys glareolus). The aim of this study was to assess temporal changes in the relative abundance and proportion of this species in small mammal communities in relation to their habitats. With 21,736 captured individuals, C. glareolus was a dominant species in the country; its proportion in general was 37.9%, with 60.0% in forests. Open habitats, meadows and agricultural land were characterized by the lowest species proportions. Our main findings were the confirmation of decreasing abundances and proportions of C. glareolus since the 1990s, the absence of cyclical fluctuations in the relative abundances of the species in general and in forest habitats, and the introduction of a south–north cline in species proportions. The status of this temperate and boreal forest species is subject to change, with implications for the diversity of the mid-latitude small mammal community.