Is it beneficial to be a city dweller? Impacts of urban conditions on red fox reproduction

Abstract

Various species inhabit cities around the world, and numerous changes in their biology can be observed. Among them, changes in the time of reproduction or productivity are often recorded in urban populations. Firstly, we compared selected reproductive features (i.e., litter size and time of breeding) of two red fox (Vulpes vulpes) populations, one living in the city of Warsaw and the other inhabiting a forest-field mosaic in Central Poland. Secondly, we investigated fox reproductive and social behaviour in an extensive camera trap study in Warsaw (2018–2021). By means of generalized linear mixed effects models, we identified which factors (fox social group size, share of natural food, and level of urbanization, created by using principal components analysis for habitat and landscape variables) affected the reproduction and/or social group size of urban foxes. We found that urban foxes started breeding about 2 weeks earlier than their rural counterparts and produced bigger litters (3.98 vs. 3.48 cubs). Opposite to rural foxes where only pairs of adult foxes were reported, in the urban population, social groups were observed with a mean number of 2.37 individuals. Interestingly, none of the studied factors affected group size or litter size in urban foxes, while breeding time was influenced by the level of urbanization and share of natural food. Earlier reproduction in urban areas is fairly frequently observed and may be attributed to altered environmental conditions in urban habitats, while higher productivity is probably a consequence of higher food availability.