Essentially, foxes are small and medium-sized mammal (particularly rodents and lagomorphs) specialists; that is, they evolved to feed primarily on mice, rats, voles, rabbits, etc. This does not, however, mean that foxes only eat rodents and rabbits – nothing could be further from the truth. Indeed, the problem when it comes to describing what’s on the menu is that the Red fox, as a species, has an almost unimaginably catholic diet.
As a general rule of thumb, foxes are local opportunists – in other words, they take whatever prey is abundant (locally and seasonally) at the time. One study of foxes in Missouri, for example, recorded 34 different mammal species, 14 species of bird, 15 families of insects and 21 species of plants in the diet. Indeed, Mark Cardwine, in his 2007 Guinness Book of Animal Records, considered that, by a small margin (the Grey wolf, Canis lupus, being a very close second) the Red fox had the greatest dietary breadth of any member of the dog family.
A consequence of this unspecialised selection is that foxes can live almost anywhere and eat almost anything, switching prey as necessary. The presence of humans also has a significant impact in the composition of the diet and not just in terms of food put out by householders. A recent review of fox diet across Europe found both latitude and humans have an impact on fox diet. In a paper to Mammal Review in 2017, a team of ecologists at the University of Tartu in Estonia, led by Egle Soe, report the results of their literature review of 66 studies on fox diet from 17 European countries. The researchers found that, overall, the primary food categories in the diet of European foxes are rodents, lagomorphs and ungulate (mainly deer) carrion. When geography was taken into account, however, there was a tendency for more rodents and fewer birds to be included in the diet as latitude increases. Moreover, foxes ate more rabbits in areas with a higher human footprint. Soe and his colleague suggest that as climate change progresses, the diet of the Red fox will broaden to include a greater diversity of species.
With the foregoing in mind, we can see that the diet varies with habitat, season, and individual preference, which makes it extraordinarily difficult to generalise. As such, the dietary information provided on this site is not intended as a complete list of prey species, or a comprehensive review of the literature (many have written theses on that subject). Rather, it is a summary of the diet and feeding behaviour of the Red fox.
Meat and more
Foxes, along with all dogs, are classified within the taxonomic order Carnivora, from the Latin meaning ‘to devour flesh’. This taxonomy is slightly misleading because there are meat eaters that aren’t included in it, while some animals are included that eat very little meat (only about one-third of the Carnivora have a diet consisting of at least 60% meat). Consequently, animals that actively include meat in their diet (as opposed to those that may take meat very occasionally or incidentally while feeding on other things) are called carnivorans.
Carnivorans can be broadly split into two groups: those that depend on meat for their survival (the obligate carnivorans) and those that eat meat when available but also eat (and can survive on) other food sources (the facultative carnivorans). We won’t concern ourselves with it here, but some biologists go further, dividing carnivorans into hypercarnivores (diet with 70% or more meat), mesocarnivores (50-70%) and hypocarnivores (30% or less). Foxes fall into the facultative carnivoran group – taking animal prey as the opportunity arises, but also eating other foods, including plants, fruits, fungi and garbage. That said, Red foxes are carnivorous first and foremost and a study by Carolyn Jaslow at the University of Chicago in 1987 found that foxes were more efficient at digesting mice than they were fruit (89% vs. 51% efficient), suggesting an adaptation to a more carnivorous diet than an omnivorous one.
It sounds like a rather obvious statement, but food is a critically important resource for a fox – it’s worth fighting over, even with a golden eagle as 2016's Winterwatch showed; it plays a role in determining how big a territory is and thus how many foxes can live in an area; and it influences when a fox breeds. Indeed, in a study on the timing of Red fox reproduction, published in 1995, biologists at the University of Siena in Italy found a general trend for foxes living at higher latitudes to ovulate later than more southerly animals (see: Breeding Biology). This, the biologists suggest, reflects the reduced food availability in the north during winter.
Given how important food is as a resource, it is not surprising that much research has gone into establishing what foxes eat, with many hundreds of studies having been published worldwide. I will provide some examples of diets from selected areas in order to give an idea of the variability, but it is worth remembering that there are some inherent biases in the analysis of fox (indeed any animal) diet.
Studying the diet
Firstly, we have the issue that foxes scavenge, which means that simply finding remains of a certain species doesn’t necessarily imply predation. Finding cat or sheep remains in fox scat, for example, doesn’t necessarily mean that the fox killed the animal. Secondly, some components are more resistant to digestion than others and some may be unrecognisable or barely detectable by the time they leave the body in scat (fat and muscle tissue stripped from a carcass, for example). Consequently, it is not unusual for different dietary studies to yield different results, especially when using different sources (stomach contents, intestine contents, or scat contents).
A 1995 study by Paolo Cavallini and Teresa Volpi, for example, found that studies based on stomach contents recorded twice as many bird remains as those based on scat analyses, while an earlier study calculated that only just under half of small rodent teeth made it into the scat. Thirdly, is the format in which the results are presented. Frequently the data will be graphically displayed as a pie chart showing the percentage of the diet each animal or group constitutes. These data are typically collected from scat and/or stomach analysis and may show, for example, that 70% of the scats or stomachs contained rabbit remains. This tells us that most of the foxes in the study area were feeding on rabbits, but it doesn’t tell us how important rabbits are to the fox.
So, although most foxes had rabbit remains in their stomachs/scats, each could have had the remains of only a single rabbit – at the same time, 50% may have had 10-or-more voles in their stomach. Our pie chart would show rabbits as a bigger dietary component—and imply they were a more significant prey item—simply because more scats/stomachs contained them, even though voles are (when you correct for weight) a more important prey item. The point is that a degree of caution should be used when interpreting any dietary studies; they may not tell the whole story.
For those interested in the more physiological side of feeding, in a 1980 paper to Biogeographica, Darrell Sequeira summarised the studies of gut residence times in foxes. It seems that about 90% of a fox’s meal passes out within 48 hours (most within just over a day) and a fox defecates, on average, about five times per day. One study, published during 1955, gave some more detailed residence times: eight hours for mice; six hours for ‘other meat foods’; four hours for insects; and two hours for plant material. In his 1980 book The Red Fox, Huw Lloyd noted that food starts passing from the stomach—which can hold up to about a kilogram (2 lb. 3 oz.) of food and distend to around 900 mL (about 1.5 pints)—into the large intestine after about two hours; this is apparently a gradual process and it may be several hours before the stomach is empty.
According to Lloyd, food remains start appearing in the faeces five-to-ten hours after being eaten, but remnants may still be found in the intestines up to 24 hours after the meal. Being a carnivore, the Red fox has a short gut, with a small intestine of about 110 cm (3 ft 7 in.) long and a large intestine about 50 cm (20 in.) long; the caecum (the first part of the large intestine attaching to the appendix and involved in the digestion of plant material) is essentially vestigial.
Jan Englund’s data on captive silver foxes suggest the second meal of the day passes more slowly than the first. Fox faeces (above) are usually about two centimetres (three-quarters of an inch) thick and three-to-nine centimetres (1 – 3.5 in.) long; they’re expelled covered in a film of mucous, which probably helps protect the delicate tissues of the lower gut from sharp bones, teeth and claws in the prey remains. At the other end of the animal, the typical fox dental formula is 3/3 (incisors): 1/1 (canines): 4/4 (premolars): 2/3 (molars). The formula presents the number of teeth in the top and bottom (as top/bottom) of one side of the jaws – Red foxes have 42 teeth.
If food is such an important resource, how much time do foxes spend looking for it and what do they look for? The average adult fox requires between 350g and 550g (12 – 19 oz.) of food per day and the amount of time and effort devoted to sourcing food varies terrifically, both individually and according to season. During the cub-rearing season (late spring and early summer) the adults will spend most of their time searching for food for their rapidly growing offspring. At other times of the year, it seems that foxes spend about one-third of their waking time looking for food. Indeed, the foxes studied by J David Henry in the boreal forests of northern Canada spent some 35% of their day (about 5 hours) searching for food.