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.