Utilisation of Anthropogenic Food by Red Foxes () in Britain as Determined by Stable Isotope Analysis.

Dietary analyses utilising visual methods to identify stomach and faecal contents have shown that urban red foxes () in Britain consume human-derived (anthropogenic) food to varying degrees. Anthropogenic foods have been implicated in poor health outcomes for synanthropic species that consume them; therefore, it is important to examine the degree of such foods in the British fox diet. We analysed the carbon (δC) and nitrogen (δN) stable isotope ratios of whiskers collected from 93 foxes from across Britain to determine: (1) if stable isotope analysis (SIA) distinguished a difference in δC and δN between rural and urban foxes, and whether any difference was suggestive of anthropogenic food use; (2) the proportion of anthropogenic food consumption in urban foxes compared to rural foxes using a Bayesian mixing model; (3) whether sex, age or season of collection influenced fox diet as assessed by SIA, in relation to anthropogenic food use. We found the following: (1) urban fox diet was significantly different to rural foxes; urban foxes demonstrated significantly higher δC and lower δN, a pattern consistent with anthropogenic food consumption. (2) Food provided either directly or indirectly by humans contributed an estimated 34.6% of urban fox diet compared to approximately 6% of rural fox diet. (3) Across rural and urban foxes combined, there were significant isotopic differences between males and females, with females demonstrating higher δC. (4) No differences in δC and δN between subadults and adults were observed. (5) Season did not have a significant influence on δC and δN, despite winter demonstrating the highest δC and lowest δN seasonal means. Potential negative outcomes of anthropogenic food consumption are likely to disproportionately impact females more than males and urban-dwelling foxes more than rural foxes.