What Does the Fox Eat?
A few weekends ago (many weekends now, as I kept forgetting to finish writing this post), my younger sibling and I were pulling into my parent’s driveway when we noticed movement in the middle of the yard. Backing up slightly, our headlights illuminated a thrilling scene — a red fox in middle of a well-earned Friday night meal consisting of what appeared to be some kind of small mammal (my best guess was a squirrel). After watching with my own eyes for a while, I took out my phone and filmed the video posted below before my parents pulled in behind us and the fox ran off. I went over to inspect the area where he was eating, but didn’t find anything — unfortunate for my own curiosity, but good that we didn’t cause him to abandon his meal.
As is so often the case with these sorts of surprise interactions with wild animals, seeing this fox brought up what I thought was an interesting question — namely, what do urban and suburban foxes eat? Typically, when we think of urban wildlife, we think of opportunistic scavengers that feed mostly on the garbage cast aside by us humans, the main characters of the city ecosystem. There is certainly some truth to this picture of the urban food chain and, indeed, the concentrated abundance of edible material is a big part of the appeal of cities for many species that are tolerant enough of human activities to be able to take advantage of it. And yet, as this encounter made quite clear, there are also some city creatures who will seek out more “natural” food sources — including the meat of other animals — to supplement their usual diet of pop tarts, homegrown tomatoes, and bird seed. So, what is typical of foxes?
Luckily for us (I’m just going to assume that you are as interested in this question as I am), there is a surprisingly extensive scientific literature on what red foxes (Vulpes vulpes) eat when they find themselves living on human dominated landscapes, and a recent review paper by Castañeda et al. (2019) that helpfully aggregates much of it into one place. The paper, which compares the diets and home range sizes of red foxes and domestic cats, reported that across the studies they looked at, mammals were the most common food category consumed by red foxes, with a relative frequency of occurrence of 48%. In second place, was anthropogenic refuse (that’s science for garbage), with a relative frequency of occurrence of 19% percent. On the surface, these results would seem to suggest that foxes living near people have a higher preference for fresh meat that the stereotypes surrounding urban wildlife might suggest, but things become a bit more interesting when we dive deeper into the data.
As part of their review, Castañeda et al. divided the studies that they looked at up into two categories based on the habitats in which the studies were conducted — habitats with high anthropogenic pressure (dense settlements and villages) and habitats with medium anthropogenic pressure (croplands and rangelands). Of the studies that looked at diet, 77% percent were performed in areas with medium anthropogenic pressure and only 29% were conducted in areas with high anthropogenic pressure (note that these percentages also include studies that looked at just cats). This is interesting because, when they broke things down by habitat, the authors found that both cats and foxes fed significantly less on mammals and invertebrates in high anthropogenic pressure habitats compared to medium anthropogenic pressure habitats. This would suggest that the numbers cited above, which do not distinguish between habitat, may be biased slightly towards the dietary preferences of rural foxes — that is to say, wild mammals may make up a smaller percentage of the diet of city foxes compared to rural ones.
Of course, this is just one review, and without more studies of fox diet in high anthropogenic pressure habitats, it’s hard to be sure about how generalizable this distinction between higher and lower pressure habitats is. One study reviewed by Castañeda et al. analyzed the stomach contents of 212 red foxes collected in Zurich, Switzerland, and found that scavenged human food waste was by far the most common food category being consumed, with its frequency of occurrence increasing in animals living closer to the city center. The consumption of “natural” food items (including small mammals) also seems to decline closer to the city center, though it isn’t clear to me if the authors found this to be statistically significant. Another study looking at the contents of 1,939 fox scats found in Oxford, England also found that scavenged human food waste was the most important food item for foxes living in the city, though to a lesser degree and without any observed pattern with respect to human pressure (I don’t think they looked; Doncaster et al. 1990). On the other hand, a study comparing the stomach contents of foxes living in the densely populated South Bay Area of California to less densely populated Monterey County found that while rodents were more commonly consumed in Monterey County than South Bay, birds and rodents were much more commonly consumed that garbage in both areas (Meckstroth et al. 2007).
Overall, it would seem that urban foxes have a very diverse diet which can vary widely depending on what is available. In the Zurich study, for example, the authors found that the city’s foxes were feeding not only on small mammals (frequency of occurrence = 29.5%) and scavenged human food (over 60%), but also birds (23.6%), invertebrates (31.6%), domestic animals (10.4%), fruits and veggies (both cultivated [49.1%] and wild [22.6%]), pet food (6.1%), and bird seed (9.4%). Just about all the studies I looked at in detail included a similar diversity of food categories, though their frequencies of occurrence varied. A few also found some interesting seasonal differences in the consumption of different food categories, with foxes in Zurich feeding more on birds, invertebrates, and cultivated fruit and vegetables during the spring and summer than during the winter. Similarly, the Oxford study found seasonal variations in the consumption of small mammals, birds, fruit, and invertebrates that mostly corresponded with their availability on the landscape.
So, the answer the question “what does the (urban) fox eat?” is…pretty much anything that is edible, can fit in his mouths, and is available in the area at the time of year he's looking. This can include other wild animals like rodents and birds, scavenged human food waste, and all sorts of other things. Of course, just because foxes can eat certain things, doesn’t necessarily mean that you should make those things available if you can help it. While foxes aren’t really all that dangerous to humans and their pets compared to some other urban and suburban predators, they can still become habituated to anthropogenic food sources in ways that can lead to conflict. No matter what the more-than-human part of your neighborhood is like, it’s probably a good idea to make sure that your trash cans are secure and that you take any pet food (and pets!) inside at night. Doing this will make it easier to live peacefully with your animal neighbors so that you can enjoy cool encounters like this one in your own backyard!
Sources:
Castañeda, I., Bellard, C., Jarić, I., Pisanu, B., Chapuis, J. L., & Bonnaud, E. (2019). Trophic patterns and home‐range size of two generalist urban carnivores: a review. Journal of Zoology, 307(2), 79–92.
Contesse, P., Hegglin, D., Gloor, S. A. N. D. R. A., Bontadina, F., & Deplazes, P. (2004). The diet of urban foxes (Vulpes vulpes) and the availability of anthropogenic food in the city of Zurich, Switzerland. Mammalian biology, 69(2), 81–95.
Doncaster, C. P., Dickman, C. R., & Macdonald, D. W. (1990). Feeding ecology of red foxes (Vulpes vulpes) in the city of Oxford, England. Journal of Mammalogy, 71(2), 188–194.
Meckstroth, A. M., Miles, A. K., & Chandra, S. (2007). Diets of introduced predators using stable isotopes and stomach contents. The Journal of Wildlife Management, 71(7), 2387–2392.
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