Striped Field Mouse Invading Human-Modified Environments of Lithuania during Last Five Decades

The striped field mouse ( Apodemus agrarius ) is expanding in several European countries, but the details of this process are not always documented due to a lack of long-term studies. We conducted an analysis of changes in relative abundances and proportions of A. agrarius in small mammal communities in nine different habitat groups in Lithuania during 1975–2023. We found an increase in the abundance and proportion of A. agrarius , increasing synanthropization of the species, and tolerance to anthropogenization of habitats. Temporal variations in the relative abundance and proportion of species were observed, with lower values in February–July and higher values in September–January. The main finding is a remarkable increase in species presence in the country after the 1990s, with a peak observed in the 2010s–2020s, confirmed by eight local studies. During these decades, it was the third most abundant species, representing 19.8–20.0% of the individuals caught. It is also important to note that A. agrarius has recently been most abundant in commensal habitats (0.029 ± 0.006 individuals/trap day), with the highest species proportion in agricultural areas (24.8 ± 1.8%). There are many indications that the expansion of A. agrarius in Lithuania is becoming invasive.