<P> Female silver foxes generally breed during their first autumn, but a number of factors that contribute to their breeding success . Age, food, population density, and mating system (polygyny or monogamy) all affect impregnation success rates and litter size . Higher population density leads to a higher incidence of failure in producing pups . Silver foxes have litters that typically range from 1 to 14 pups, with the average being 3 to 6 pups . Litter size generally increases with age and abundance of food . Scientists have observed an increase in reproductive success with age in silver fox morphs, which may be attributable to yearlings breeding an average of nine days after adults . Success in larger litters depends highly on the availability of extra-parental care via the assistance of unmated females . This is particularly notable in higher density populations, where some females fail to produce pups . </P> <P> Silver foxes engage in a system of biparental care, which is associated with their seasonal monogamous mating scheme . For a given litter, males contribute a large investment in the offspring by both feeding and protecting the den . While the pups are early in development, the male secures food for the nursing vixen . Whereas males are more vigilant in defending the den, females also defend their offspring aggressively . </P> <P> In captivity, differential reproductive success can be attributed to variation in the competition capacity among individual females . Competition capacity is defined as the ability of individuals to dominate resources such as food or nesting sites . The competition capacity of the mother directly influences the fitness of her offspring . In one experiment where vixens, whose competition capacities were categorized as high, medium, or low, were bred under standard farming conditions, competition capacity was positively associated with the number of healthy offspring raised to weaning . This study has led to the use of competition capacity as a more encompassing measure of reproductive fitness for the silver fox . Some vixens have also been noted to engage in infanticide . These vixens generated more weaned cubs during their next reproductive cycle than those who did not engage in infanticide . This may suggest the conservation of efforts or investment to increase future reproductive success . Infanticidal vixens infrequently adopt and help to raise the young of neighboring vixens after eating their own . </P> <P> While silver foxes are opportunistic feeders and will consume any food presented to them, they prefer a more carnivorous diet when meat is available . When meat is scarce, they rely more heavily on plant material . Like the red morph, the silver fox adapts different strategies when hunting different prey . When hunting smaller mammals, the foxes adapt a "mousing position" from which they can locate prey based on sound . Subsequently, the foxes launch themselves, pin prey to the ground using their forepaws, and kill it by biting . Quicker terrestrial prey requires more practiced behavior, often involving stalking and rapid pursuit . When prey escapes to hidden caches or burrows, foxes are known to occasionally nap beside the entrances and lie in wait for prey to reemerge . </P>

Where does the term silver fox come from