Following urban predators – long-term snow-tracking data reveal changes in their abundance and habitat use

Urban habitats differ from natural environments, however some predatory species have become established in cities across the globe. The aim of our study was to compare the occurrence of the red fox and the stone marten in Warsaw during three time periods (1976–1978, 2005–2008, 2015–2021) and in different habitats. Generalized linear models were used to show factors affecting the density indices of these two species (i.e., frequency of occurrence of tracks of each species recorded during snow tracking on linear transects). The frequency of occurrence of tracks of these two species on transects increased over time and was explained by habitat type and distance from the city centre. The frequency of fox tracks was higher in more-natural habitats located far from the city centre. In the first period (1976–1978), this species was recorded only in forests and riparian areas. In the last period (2015–2021), its tracks were recorded frequently in built-up areas and cemeteries. From the beginning of the first period, the stone marten was recorded in a wider range of habitats than the fox and it colonized all habitat types in the subsequent periods, but a statistically significant increase was observed only for cemeteries. The frequency of occurrence of stone marten tracks was lower than that of red fox tracks in most natural and seminatural habitats (forests, parks, riparian areas). No relationship between the occurrence of the red fox and the stone marten was found. We speculate that the growth of the urban red fox numbers was driven by an increase in the national population as a result of anti-rabies vaccinations. In turn, the stone marten, being a synanthropic species, was present in the city centre from the beginning of the study, but it now occurs in a wider range of habitats.