The life of a red fox begins with the courtship of its parents, in December of the year before its birth. At this time, most foxes will travel in pairs or threes. Mating takes place soon thereafter, most commonly between mid-December and mid-February, although it can be as late as March or even early April. About two thirds of matings take place in January, though that figure can be different in different areas. Cubs are born 52-53 days after mating, so the majority of foxes bear their cubs in March. The peak birth period can be earlier in warmer areas, or later in colder areas.
In Minneapolis, in fact, I saw a fox cub about six weeks old in the first week of August, indicating that she was born in early June and conceived in mid to late April. It is possible that the year-round food supply and abundance of shelter in urban areas can extend the breeding season, so that cubs born earlier or later than the peak birth time survive in cities, whereas they might not survive in rural areas.
Space is an important resource for foxes. Each family needs several safe den sites in which to raise their cubs in addition to safe resting sites outside of the den. Den space seems to be readily available for urban and rural foxes alike. Foxes maintain territories, and it is common for them to have several different dens within their territory. Prior to parturition, the mated pair selects a den, called the natal den, in which to bear the cubs. This den is usually larger than other available dens, and has several exits. The other dens can be as simple as a single entrance leading to a hole where the foxes can take shelter. In urban areas, a great variety of den sites is available to foxes, but places to rest during the day are scarcer.
The natal den must be safe, because the fox family is most vulnerable to predators during the first two weeks after the birth of the cubs, which are blind and helpless for about ten days after birth. The vixen stays with them constantly for up to two weeks (longer in colder climates than in warmer climates), during which time she is dependent on the dog fox and any "helpers" for food. After this time, she may leave to hunt for herself, but will return regularly to nurse the cubs.
The parents may first move the cubs to an alternate den when they are about two weeks old. The cubs usually are moved at least once, and may be moved several times during their first summer. For example, all the dens I located were abandoned in late spring. In two of the rural dens, human disturbance might have led to the abandonment, but humans frequented the immediate areas of the urban dens at least every other day, so it is unlikely that human disturbance was the only cause of abandonment of the urban dens. This suggests that urban foxes, like rural foxes, move frequently between dens. Movement may help protect the vulnerable fox cubs from humans and other predators.
When the cubs are about five weeks old, they begin to venture outside the den. Weaning takes place at this time, so the parents bring back prey for the cubs to eat. Later in the summer the cubs learn to hunt for themselves, and their parents will provide less food and spend less time at the den. The cubs range farther from the den as they grow older, hunting for themselves but remaining in the territory of their parents.
October is the month during which dispersal of foxes is most likely to begin. Not all cubs disperse, and not all of those that disperse leave in their first year. More male cubs disperse than female cubs, and more cubs in rural areas disperse than cubs in urban areas (38% vs. 58% for females, and 75% vs. 96% for males, according to one set of studies). This may again be due to the steady supply of food in urban areas.
If the cubs do not disperse, they will remain on their parents' territory, but only the females (according to all the studies I could find) will actually remain in the family group. These "helper" foxes will remain through the next year, and possibly longer, but the name "helper" my be a misnomer. Although it was thought at first that they helped feed and raise their younger siblings, more recent studies showed that at least in some areas, survival of fox cubs was independent of the number of "helpers," indicating that if they do help raise the cubs, their help makes little or no difference. Where they do make a difference is in the event that the mother of the cubs is killed or ill. In this case, a "helper" may take over the role of mother to the cubs.
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Foxes are omnivorous, feeding on fruit, birds, small mammals, insects, and other invertebrates, especially earthworms. In rural areas, they may feed primarily on one species, but in urban areas, feeding studies have shown that the most common food for foxes is scavenged items. This category of food includes edible and inedible refuse discarded by humans, as well as food set out for foxes by humans. Table 3. Edible scavenged items found in the stomachs of 571 London foxes. From Harris (1981).
| Food type | Number of occurrences | % occurrence | % of diet |
|---|---|---|---|
| Meat and bones from poultry carcasses and meat joints | 278 | 48.7 | 18.4 |
| Bread | 61 | 10.7 | 3.1 |
| Dried fruit | 58 | 10.2 | 2.4 |
| Potato peelings | 48 | 8.4 | 1.6 |
| Bird seed | 11 | 1.9 | 0.4 |
| Bacon rind | 10 | 1.8 | 0.4 |
| Orange peel | 10 | 1.8 | 0.3 |
| Fish bones | 8 | 1.4 | 0.4 |
| Carrot peel | 6 | 1.1 | 0.2 |
| Cooked peas | 6 | 1.1 | 0.2 |
| Eggshell | 5 | 0.9 | 0.1 |
| Nuts | 5 | 0.9 | 0.2 |
| Apple peel | 3 | 0.5 | 0.1 |
| Tomatoes | 3 | 0.5 | 0.1 |
| Bananas | 2 | 0.4 | 0.1 |
| Runner beans | 2 | 0.4 | 0.1 |
| Cloves | 1 | 0.2 | < 0.1 |
| Chinese dinner | 1 | 0.2 | 0.1 |
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Although built primarily to provide shelter for humans, cities also provide an abundance of shelter for non-human animals. Foxes can take advantage of many of these, occasionally even setting up dens in occupied houses.
The most important factor affecting foxes in human areas seems to be human disturbance. It should be no surprise that fox densities are higher in quiet, owner-occupied housing areas or in isolated places like railway embankments than in busier urban areas. Foxes also avoid feral dogs, probably because dogs prey on cubs as coyotes do in the wild.
Given that fox densities are higher in urban areas than in rural areas, it is not surprising that the territories foxes keep are smaller. What is surprising is that these ranges are fluid, and shift from month to month, or even week to week. Food availability is generally higher in urban areas than in rural areas, but that availability may fluctuate greatly among specific sections of the city. A fox that constantly explored new areas and re-explored old ones would tend to be more successful than a fox that kept a stable territory.
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Most studies on fox mortality are inconclusive. They tend to rely on specimens recovered and returned to the investigator, and it is very unusual for a fox that died of natural causes to be recovered in this way. When foxes are sick or old and feel they're about to die, they don't wander up to some researcher and die in his front yard; they find an old den or a secluded hole in the woods, and lie down there.
That said, it is known that foxes in the wild rarely live longer than five years. Foxes that were recovered for study had most frequently died from human action. In areas where foxes were controlled, that control was the most common cause of death. In areas where they were not, specimens recovered for research had most often been killed on the nearby roads. Similar mortality rates are seen in rural populations from human action, most commonly trapping or hunting.
The other trend common across all fox populations was that foxes suffer the highest mortality rate in their first year. Of the 5-6 cubs born to an average fox litter, an average of 2-3 survive. This juvenile mortality is higher still in areas where foxes are controlled, resulting in a population weighted heavily in favor of younger foxes (because fewer survive to be old, the surviving foxes breed at an earlier age than they might in a more stable population). Interestingly, this is the only noticeable effect that fox control has on a fox population; it has been shown that numbers of foxes are not affected by the level of control.
One last item worth noting is that urban foxes, because of their higher densities, are more susceptible to epizootics of diseases such as rabies or sarcoptic mange. In fact, in the course of my study, I encountered many foxes with severe cases of mange, and was told that there had recently been a severe outbreak that had reduced the urban population somewhat. Rabies was not a problem in the Minneapolis-St. Paul area at the time of this writing.
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