Our city foxes have advantages, which is why there are more around to spot

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Margery W. writes: This year, for the first time, foxes have been seen in my neighborhood in West Somerville! We are happy to have them. Here is a photograph, taken Nov. 10 in my backyard. Are foxes common here? Do they prey on rabbits? We love those bunnies, but they are overrunning our gardens and eating everything in sight.

Good questions, Margery. Red foxes (Vulpes vulpes), with reddish coats, black legs and white tail-tips, which distinguishes them from any other species of fox, have the largest natural distribution of any land carnivore. They live throughout Europe, Asia and North America. They live in mountains and deserts and forests and coastal regions. They are one of the most adaptable animals of any species. And, yes, they even live in dense human-dominated areas such as Cambridge, Somerville and Boston. In cities, red foxes take advantage of humanmade travel corridors such as train tracks and bike paths to travel between fragmented patches of habitat.

Urban areas can support a surprisingly large number of foxes. In rural areas, there might be only 0.2 foxes per square kilometer, but in cities you might find as many as 16 foxes per square kilometer (0.38 square miles)! This is largely due to the greater availability of food in cities and the lack of predators.

Despite their presence in urban areas, red foxes go mostly unnoticed. They develop different behaviors in urban areas than in rural areas. Urban foxes in the Northeast are largely nocturnal due to lack of forested areas in which they can hide during the day. They spend their days under porches, in abandoned buildings, under garden sheds or in vacant lots, cemeteries or golf courses. Not only do these locations hide them from people, but they provide protection from bad weather and predators. You are most likely to spot a red fox near dawn or dusk, when they are coming or going from their nocturnal rounds.

Urban red foxes eat more discarded food and compost than their rural counterparts. A recent study suggests that human-derived food accounts for about 35 percent of an urban fox’s diet compared with just 6 percent of a rural fox’s diet. In answer to Margery’s question: Yes, red foxes eat rabbits. They also eat other small mammals, such as squirrels and rodents. Because they are omnivores and scavengers, they eat birds, fallen fruit, insects, snails and dead animals. In urban areas they find and consume edible trash as well as dog food or bird food (although they are more likely to be interested in the critters that are attracted to bird feeders than the birdseed itself).

Researchers in Great Britain analyzed the whiskers of foxes in rural and urban areas. Since whiskers grow over weeks or months, the researchers were able to understand fox diets over longer periods than they if they had examined fox scat. (They examined the carbon and nitrogen isotopes within the whiskers to reach their conclusions.)

The researchers found that city fox diets were 22 percent birds, 19 percent pet food, 17 percent fruit, 16 percent human food, 16 percent mammals and 10 percent invertebrates such as worms, snails, crabs and clams. (Obviously foxes near coastlines ate more clams and crabs.) Rural fox diets were 32 percent birds, 32 percent mammals, 26 percent fruit, 4 percent invertebrates, 3.5 percent pet food and 2.5 percent human food. In other words, rural foxes ate very little human food waste or pet food. (Of course, this study was conducted across the pond, so our Northeastern foxes might eat differently, but it is likely that urban foxes eat more edible trash than rural foxes.) Despite the dietary shift of urban foxes, they are still good hunters and can help keep the rodent and rabbit populations under control.

Another observation from this study was that individual foxes are unique eaters. Rural and urban foxes tended to specialize in certain foods – once a fox got good at finding a certain food, it kept going after it, avoiding other meals that took more effort.

Foxes are extremely adaptable and change eating habits with the seasons. They might eat fallen fruit in late summer and fall and eggs during the spring. They might scavenge in the winter when food sources are limited and also in the summer when food waste from cookouts and potlucks is especially abundant. 

Studies have shown that red foxes cross streets most often after midnight when traffic is lowest. They also cross fewer streets than would be expected if their movements were random, suggesting that they intentionally avoid traffic when they can. Nonetheless, auto accidents are one of the biggest causes of red fox deaths. Another cause of death is rodenticide poisoning. (To protect foxes, hawks, owls and other wildlife, do not put out poison baits for rodents. Electronic zappers or snap traps are safer choices.)

City fox families are often larger than country fox families: Urban females tend to have larger litters (four or five kits) compared with rural females who produce three or four kits and get help caring for them, as young urban female foxes tend to stay with their parents to help raise younger siblings; in rural areas, the young females are more likely to find their own territory. Thus, in urban areas, foxes have become more social and tolerant around other foxes, especially closely related ones.

Red foxes have smaller ranges in urban areas than in rural areas because food is more abundant in cities. Young urban foxes have better survival rates, too, because food sources are more consistent and there are fewer predators.

Although they may look big, red foxes weigh only 7 to 15 pounds. Their bones are 30 percent less dense than the bones of pet dogs. My small pug-terrier mix weighs 20 pounds, more than the largest fox. 

They do not hibernate, so will be active all through the winter. If you have a fox den in your neighborhood, you do not have to worry – foxes are wary and avoid people. Do not feed them. Foxes that rely on themselves to find food remain wild and wary of people; if you feed them, they can become emboldened, which can lead to problems.

Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.

Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.

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