Evidence for red fox (Vulpes vulpes) exploitation of anthropogenic food sources along an urbanization gradient using stable isotope analysis

As urban areas expand, wildlife show adaptations to urban ecosystems. We tested two hypotheses for urban populations of red fox (Vulpes vulpes (Linnaeus, 1758)) in urban areas: the population pressure hypothesis, which posits that urban foxes make do with suboptimal habitat, and the urban island hypothesis, which presumes that urban areas provide high-quality habitat. We investigated habitat quality by investigating anthropogenic food in fox diets across a rural–urban gradient in Lancaster, Pennsylvania (USA). We used stable carbon isotopes because human food can have a distinct stable carbon isotope signature. We collected fox hair and stomach samples from 21 locations and extracted land use and land cover characteristics within a 100 ha buffer area. We found that higher δ13C values in fox hair were positively correlated with impervious surface cover and developed open spaces, key metrics of urbanization, and negatively associated with agricultural land cover, an indicator of rural habitats. Overall, fox hair δ13C was less related to urbanization and more related to the availability of developed open spaces that provide habitat with vegetation cover and access to nearby food sources. Our results suggest that urban habitats are high quality and support the growing literature revealing that certain species may thrive in urban areas.