Assessing carnivore diet by faecal samples and stomach contents: a case study with Alpine red foxes

Research on the feeding habits of mammalian carnivores relies mainly on the analysis of stomach contents and faecal samples, but the outcomes of these two methods have only been compared in a few studies, with contrasting conclusions. In an Alpine area of NW Italy, we analysed both fox faeces collected along standardised transects, and the stomach contents of road-killed individuals. Faecal analysis involved the identification of macroscopic fragments, the identification of earthworm chaetae, and the assessment of relative volumes using Kruuk and Parish's technique. Use of both methods indicated that the diet of the red fox included mainly fruit and mammals, but quantitative differences emerged. Garbage, birds, and cultivated fruit were over-represented in the stomach contents, while earthworms, mammals, and wild fruit prevailed in the faecal samples. Logistic Regression Analysis suggested that the method of analysis was the main factor in determining the occurrence of food items in fox diet. Nonetheless, evidence suggests that road-killed foxes may include a disproportionately high percentage of synanthropic individuals and therefore be biased towards anthropogenic food. Results suggest that by using Kruuk and Parish's technique, the main limitation of faecal analysis, i.e. the inaccurate estimation of the relative volume of each food item, can be overcome.