Our aim was to determine dynamics in a population of tawny owls Strix aluco over 15-year period, in relation to year-to-year variation in environmental conditions. The research was carried out in a habitat mosaic of fields and forest in central Poland, over the 2004–2018 period. Numbers of pairs (territories) were established by the standard playback survey technique supplemented by searches for nest sites. The selected environmental factors studied in parallel were the acorn production, density changes in field and forest rodents, meteorological conditions in winter and density of martens (Martes spp.). At the start of the study period 20 nest boxes designed for tawny owls were placed out in the study area. This number was enlarged by additional 27 nest boxes placed in 2012. The number of owls in the area remained stable – in the range of 26–29 pairs, despite changes in nesting sites availability. However, moderate influence of rodent density and winter conditions on population abundance was detected. Also, peak in the rodent population coincided with greater clutch size and numbers of young owls reared. Densities of martens remained relatively stable throughout the study period, and there were no reported cases of these carnivores killing tawny owls, despite the former taking shelter in the owl-boxes.