Red Fox - Behaviour - Reproduction and Development

Reproduction and Development

Red foxes reproduce once a year in spring. Two months prior to oestrus (typically December), the reproductive organs of vixens change shape and size. By the time they enter their oestrus period, their uterine horns double in size, and their ovaries grow 1.5-2 times larger. Sperm formation in males begins in August–September, with the testicles attaining their greatest weight in December–February. The vixen's oestrus period lasts 3 weeks, during which the dog-foxes mate with the vixens for several days, often in burrows. Copulation is accompanied by a copulatory tie which may last for more than an hour. The copulatory tie occurs when the bulbus glandis at the base of the male fox's penis enlarges. The gestation period lasts 49–58 days. Though foxes are largely monogamous, DNA evidence from one population indicated large levels of polygyny, incest and mixed paternity litters. Subordinate vixens may become pregnant, but usually fail to whelp, or have their kits killed postpartum by either the dominant female or other subordinates.

The average litter size consists of four to six kits, though litters of up to 13 kits have occurred. Large litters are typical in areas where fox mortality is high. Kits are born blind, deaf and toothless, with dark brown fluffy fur. At birth, they weigh 56–110 g and measure 14.5 cm in body length and 7.5 cm in tail length. At birth, they are short-legged, large-headed and have broad chests. Mothers remain with the kits for 2–3 weeks, as they are unable to thermoregulate. During this period, the fathers or barren vixens feed the mothers. Vixens are very protective of their kits, and have been known to even fight off terriers in their defence. If the mother dies before the kits are independent, the father takes over as their provider. The kit's eyes open after 13–15 days, during which time their ear canals open and their upper teeth erupt, with the lower teeth emerging 3–4 days later. Their eyes are initially blue, but change to amber at 4–5 weeks. Coat colour begins to change at 3 weeks of age, when the black eye streak appears. By one month, red and white patches are apparent on their faces. During this time, their ears erect and their muzzles elongate. Kits begin to leave their dens and experiment with solid food brought by their parents at the age of 3–4 weeks. The lactation period lasts 6–7 weeks. Their woolly coats begin to be coated by shiny guard hairs after 8 weeks. By the age of 3–4 months, the kits are long-legged, narrow-chested and sinewy. They reach adult proportions at the age of 6–7 months. Some vixens may reach sexual maturity at the age of 9–10 months, thus bearing their first litters at one year of age. In captivity, their longevity can be as long as 14 years, though in the wild they typically do not survive past 1.5 years of age.