Utilisation of Anthropogenic Food by Red Foxes (<scp><i>Vulpes vulpes</i></scp>) 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 (<i>Vulpes vulpes</i>) 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 (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of whiskers collected from 93 foxes from across Britain to determine: (1) if stable isotope analysis (SIA) distinguished a difference in δ¹³C and δ¹⁵N 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 δ¹³C and lower δ¹⁵N, 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 δ¹³C. (4) No differences in δ¹³C and δ¹⁵N between subadults and adults were observed. (5) Season did not have a significant influence on δ¹³C and δ¹⁵N, despite winter demonstrating the highest δ¹³C and lowest δ¹⁵N 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.