Urban lifestyle supports larger red foxes in Australia : an investigation into the morphology of an invasive predator

Adult body size, mass and condition predict reproductive success and survival, and hence fitness, in mammals and many other animals. Here, we assessed morphological variation and body condition in populations of the red fox (Vulpes vulpes) along an urban to natural land use gradient in the Sydney region, Australia. The red fox was introduced into Australia in the mid‐19th century and is a recent but successful urban adapter as well as a highly effective predator of naïve native species. As the red fox has successfully invaded urban environments in many parts of the world where it readily exploits anthropogenic sources of food, we hypothesized that individuals should be larger and in better condition in urban than in natural habitats. We found that individuals (N = 135) of both sexes had larger body mass and skeletal measurements in urban than in more natural habitats; body condition, by contrast, showed no consistent variation. Thus, the urban environment of Sydney provides conditions that favour an increase in size in red foxes so that individuals are now larger than, but in similar body condition as, their non‐urban counterparts. Increased body size and mass may enable red foxes to hunt a broader array of prey species, and as such would be of added concern for the management of native wildlife in Australia's urban environments, a possibility that warrants further investigation.