Reproductive trait variation shapes small mammal population dynamics and persistence under environmental change, so clearer characterization of its temporal, spatial, and habitat-related patterns in agroecosystems would improve assessment of population processes in human-modified landscapes. We analysed long-term reproductive data for the striped field mouse (Apodemus agrarius) from central and northern Europe, collected over multiple decades in Slovakia and Lithuania, to test the effects of temporal factors (year, month), spatial context (region), habitat type, and biological traits (female body size and body condition) on litter size and breeding seasonality. The impact of these factors on litter size was assessed utilizing Generalized Linear Models (GLMs), augmented by nonparametric tests. Mean litter size was slightly higher in Lithuania than in Slovakia (6.87 ± 0.14; median 7 vs. 6.33 ± 0.06; median 6). Northern populations exhibited greater temporal variability with longer and less synchronised breeding seasons. Litter size increased with female body size, but not body condition. The effects related to the habitat, including those among agroecosystems, were weak and inconsistent. Temporal factors accounted for most of the observed variation. Embryo resorption rates were similar between regions (~ 10–20%), indicating comparable levels of prenatal mortality. The absence of reduced litter size in agricultural or other anthropogenic habitats likely contributes to the species' persistence and ongoing range expansion. This highlights the importance of long-term datasets for evaluating population dynamics in the context of environmental change.