The red fox, like most other foxes is an opportunistic omnivore[1]. This means they are not picky eaters and will generally eat whatever they can scavenge[1]. Its diet mainly consists of fruits, berries, grasses, small rodents and birds[1]. Although a small portion of its daily diet is made up of invertebrates such as insects and crayfish[1]. Its diet will typically consist of 95% meats, and 5%[1]. In urban settings, red foxes are likely to rummage through trash as an easy method of obtaining foods[2]. They will eat just about anything they can find[2]. The red fox will continue to hunt and scavenge even when it is full[1]. They store excess food under leaves, snow or dirt for the wintertime[1]. If there is a litter of pups needing to be fed, alternatively, the mother will scavenge and feed them first before storing any excess food away[3]. In the winter seasons, food can become scarce and fighting over what remains buried under the snow with competitors can be a dangerous task[1]. Red foxes will generally use up their food storage and minimize hunting in winter to conserve energy[1]. Its main diet in winter will consist of small hibernating rodents and wild berries[1].
When looking at the nutritional value of foods, we consider the average daily requirement a mature red fox has to intake to meet dietary demands[4]. Based on the figures in The Nutritional Requirements of Domestic Animals, 1982 revised edition; daily Metabolizable energy is around 470 Kcal[4]. The ever scavenging fox requires a specific balance in ratio of their daily intake to keep up with its own fast paced lifestyle[1]. From the figures drawn out of the above mentioned book, ideal estimates of the proximate analysis groups are as described[4]. Majority of the diet should consist of proteins (20-30%) and carbohydrates (25-60%), this is what will keep the animal energized and healthy[4]. A decent portion of fat (15-30%) is also required in the diet, more leaning to the higher numbers when they need to plump up for winter[4]. Therefore, even though foxes are considered omnivores, 95% of their diet still consists of animal protein[1].
References:
1. Lanszki, J., heltai, M., 2002. Feeding habits of golden jackal and red fox in South-western Hungary During winter and spring. Mamm. Biol. 67, 129-136.
2. Plumer, L., Davison, J., saarma, U., 2014. Rapid Urbanization of Red Foxes in Estonia: Distribution, Behaviour, Attacks on Domestic Animals, and Health-Risks Related to Zoonotic Diseases. Plos. One. 9, 1-15.
3. Lindstrom, Erik., 1988. Reproductivee ffort in the red fox, Vulpesv ulpes, and future supply of a fluctuating prey. Oikos. 52, 115-119.
4. " TABLES ." Nutrient Requirements of Mink and Foxes, Second Revised Edition, 1982 . Washington, DC: The National Academies Press, 1982 .