Foxes come in a variety of colors and patterns, even within the red fox species. This variabity is known as color morphs or phases. There are three main morphs of red foxes: red, cross, and silver/black. The specific genetics and prevalence of each morph differs between geographic regions and populations.
Red
The red morph is the most common and classic red fox phenotype. Their fur is reddish-orange on the back, sides, legs, head, and tail. The undersides are generally lighter, ranging from creamy white to light orange. Red foxes have white underparts and a white-tipped tail. Their ears often have black backs and edges. The face typically sports bold white and black markings.
Red is the “default” morph, as it is the most genetically dominant. Thus, most red fox populations worldwide are comprised predominantly of the red type. It likely arose first evolutionarily. In areas where only the red morph occurs, the only coat color variation comes from seasonal changes as the fox molts. For example, the fur of red foxes tends to be more grayish in winter.
Cross Fox
Cross foxes exhibit a dark cross-shaped marking across their shoulder area. The cross spans the length of the body horizontally and extends down the sides vertically.
This morph remains primarily red-orange on the head, legs, underparts, and tail. But the fur on the back and sides will be much darker, even blackish in some individuals. The cross stands out vividly against this dark background. There is rufousing along the cross, lightening it to a brown or red-grey. The shoulders are the darkest area.
Cross foxes occur alongside red foxes, but at a lower frequency. The cross pattern is controlled by a simple recessive gene. So a fox must inherit two copies of the allele to exhibit the trait. When a cross fox breeds with a red fox, their offspring will be red unless the red fox also carries a hidden “cross” allele.
Silver Fox
The silver fox represents another color phase that arises from a single genetic mutation. Silver foxes have black fur covering their backs, flanks, legs, and head. But their undersides, neck area, and tail tip remain creamy white to light reddish.
Thus silver foxes have a bicolor pattern with a stark delineation between the black upperparts and lighter undersides. The face retains characteristic white and black markings akin to other color morphs. The black fur may have a sprinkling of white hairs mixed in, giving it a silvery cast.
Silver foxes are sometimes called black foxes. But true black foxes have entirely black coats, lacking the contrasting lighter fur. Silvers simply have extensive dark pigmentation concentrated on the back and sides.
Distribution of Color Morphs
The geographic distribution and relative frequency of these three red fox morphs is quite variable. Some key patterns:
- In North America, red is overwhelmingly dominant. Cross foxes occur but are uncommon. True silver foxes are very rare outside of captive bred populations.
- In Europe and Western Russia, reds dominate but cross foxes can be locally common. Silvers occur at low frequencies.
- Scandinavia and Canada’s boreal forests have the highest densities of cross foxes, up to 20-30% of some populations.
- Silver foxes become increasingly common moving east in Russia. In far eastern Siberia, silver may even exceed red foxes in number.
- Introduced Australian foxes are almost exclusively red morphs, with cross and silver absent.
Causes of Morph Distribution
What factors underlie the geographical patterns in red fox coloration? Key determinants include:
- Genetic founder effects – The limited gene pool introduced when foxes colonized new regions.
- Climate – Colder climates seem to favor cross and silver foxes.
- Camouflage advantage – Background matching helps foxes hunt prey and evade predators.
- Random genetic drift – Small populations may lose color variants by chance over generations.
For example, during the last Ice Age, foxes likely spread across the Bering Land Bridge from Siberia to colonize North America. If these founding foxes happened to be predominantly red morphs, this would explain the continued rarity of cross and silver foxes in the New World.
In contrast, Scandinavia and northwestern Russia have ideal habitat conditions for cross and silver foxes. The snowy winters combined with darker forests and rocky terrain provide excellent background matching for these darker morphs. Natural selection has increased their frequencies there over time.
Other Red Fox Morphs
Beyond the three main morphs, other rare color variants of red foxes exist. These include:
- Platinum: Very pale, almost white fur across most of the body due to an extreme expression of the silver gene.
- Amber: A lighter, washed-out reddish coat.
- Pearl: Multi-colored foxes with fur mixing white, brown, and black.
- Badger: A melanistic subtype of the cross fox with more extensive black banding.
These unusual morphs sporadically arise from complex interactions between multiple genes. They illustrate the creative possibilities of red fox genetics and biology!
Conclusion
Red foxes demonstrate impressive diversity in fur coloration and patterning. The three most common morphs—red, cross, and silver—reflect different mutations in the fox genome. Their distribution across regions arises from founder events, natural selection for crypsis, and genetic drift over time. Rarer morphs also enrich the red fox family. Understanding color morph genetics provides insight into the history and adaptive evolution of vulpes vulpes.
