The cross fox is a color variant of the red fox, which has been the subject of much debate among biologists and taxonomists. While they share many physical and behavioral characteristics with the typical red fox, the cross fox displays distinct black and white markings on its fur coat that set it apart. Determining whether the cross fox is truly a distinct subspecies of the red fox or simply a color morph has implications for how it is classified and conserved. This article will examine the evidence on both sides of this debate and provide an overview of the key similarities and differences between the red fox and the cross fox.
Basic Description and Range of the Cross Fox
The cross fox (Vulpes vulpes crucigera) is named for the dark cross-shaped pattern on its back and shoulders, which contrasts sharply with its reddish-brown or yellowish-red fur. The rest of its fur is typically lighter than a typical red fox. The dark cross marking varies in shape and size between individual cross foxes. The tail is bushier than a typical red fox with a dark stripe along the top and white tip. Their legs and underside are black or very dark brown.
| Cross Fox | Red Fox |
|---|---|
| Black or very dark brown legs | Red or reddish legs |
| Dark cross pattern on back and shoulders | No distinct markings, solid red/orange coat |
| Dark stripe on bushy tail with white tip | White tip on tail but no stripe |
| Weighs 8-10 lbs | Weighs 8-15 lbs |
The cross fox inhabits the northern regions of North America, including Alaska, Canada, and the cooler parts of the continental United States. They are found in taiga and tundra habitats. Their range overlaps with that of the more common red fox across much of Canada and Alaska.
Origins and Genetics of the Cross Fox
The cross fox is not considered a separate species from the red fox. Rather, it is believed to be a color variant or phase of the red fox that arose due to genetic mutations influencing its fur coloration. The cross fox’s distinct black and white markings are linked to two recessive genes that affect melanin distribution and levels:
- The silver gene (S) reduces red and yellow pigments, causing the fur to become black and white.
- The melanistic mask gene (M) causes darker pigment in parts of the body, leading to the cross pattern.
For a red fox to display the coloration of a cross fox, it must inherit one copy of the silver gene and one copy of the melanistic mask gene from each parent. If the fox inherits two copies of either gene, it will be very dark (melanistic) or very pale (silver), not a cross fox.
The cross fox coloring follows basic Mendelian genetics – two recessive genes must be inherited to display that phenotype. About 1 in 4 red fox pups born in litters within the cross fox range display the distinctive cross pattern. The rest are typically normal red morphs. Some melanistic and silver foxes are also born occasionally.
The cross fox genes emerged as mutations long ago and have been maintained in modern red fox populations at low frequencies. The recessive nature of the genes means most individuals continue to be homozygous for the red coat. Continued interbreeding between red and cross foxes maintains the gene pool.
Comparison of Red Fox and Cross Fox Traits
As color phases of the same species, red foxes and cross foxes are very similar in their physical features, habits, habitat, diet and behavior:
| Trait | Red Fox | Cross Fox |
|---|---|---|
| Species | Vulpes vulpes | Vulpes vulpes |
| Weight Range | 8-15 lbs | 8-10 lbs |
| Body Length | 18-35 in | 18-35 in |
| Tail Length | 12-22 in | 12-22 in |
| Habitat | Forests, grasslands, tundra | Taiga, tundra |
| Diet | Omnivorous – small mammals, birds, eggs, plants, fruit | Omnivorous – small mammals, birds, eggs, plants, fruit |
| Behavior | Nocturnal, social, territorial | Nocturnal, social, territorial |
| Life Span | 2-5 years | 2-5 years |
The cross fox does tend to be slightly smaller than red foxes on average, with a maximum weight of about 10 lbs compared to 15 lbs for red foxes. Their fur density and thickness also tends to be a bit greater, which is beneficial for surviving cold northern winters. However, these are simply population tendencies, not fixed traits that differentiate the two color phases. There are no consistent physiological or behavioral differences between individual red and cross foxes where their ranges overlap.
Interbreeding and Hybridization
In areas where red foxes and cross foxes inhabit the same territory, interbreeding readily occurs. Cross foxes do not form separate social groups or exclude red foxes from their territories or reproduction.
Cross foxes can mate with both red foxes and other cross foxes. The offspring may display a range of fur colors depending on the genetics inherited from each parent. For example, a cross fox mating with a red fox could produce a litter of pups including both red and cross color morphs. The ability to interbreed and produce fertile offspring provides evidence that red foxes and cross foxes belong to the same species group.
The cross fox genes can also enter new red fox populations through interbreeding along the borders of their geographic ranges. Young male foxes, in particular, sometimes disperse over long distances which allows genetic exchange between distant populations. The cross fox pattern has appeared in red fox populations far outside the natural cross fox range in this manner.
Classification Confusion and Debate
The relationship between the red fox and cross fox has been controversial and clouded in taxonomic confusion for decades. At various points, the cross fox has been classified as:
- A distinct species, Vulpes crucigera
- A subspecies of the red fox, Vulpes vulpes crucigera
- A red fox color morph
Originally the cross fox was named as its own species, separate from V. vulpes, in the early 1800s. This was based only on its different fur coloration. However, as more observations accumulated on cross fox anatomy, behavior, reproduction, and habitat, it became clear they aligned closely with the common red fox.
By the 1900s, most experts recognized the cross fox as the same species as the red fox. However, some continued to label it a separate subspecies based on the distinct geographic range of the cross fox pattern. Over the last decades, the consensus has shifted decisively to considering the cross fox simply a color phase rather than a true subspecies. This reflects the overwhelming evidence of cross foxes and red foxes interbreeding freely where their ranges meet.
A minority of biologists still argue the cross fox merits subspecies status. However, most classification authorities including the Integrated Taxonomic Information System (ITIS) currently group the red fox and cross fox together as a single species (Vulpes vulpes) without distinct subspecies. Both color phases are capable of interbreeding and exchanging genetic material across their range.
Conservation Status
Neither the red fox nor cross fox is considered threatened or endangered currently. The global population of red foxes likely exceeds several million. They are widespread and abundant across most of the Northern Hemisphere.
However, some local populations are under pressure from habitat loss, overhunting, and competition from non-native red foxes introduced to Australia and other areas. But there are no major threats specific to cross foxes. Their population size and trends follow the status of the overall red fox population within their northern range.
Having the cross fox recognized as simply a color variant of the red fox, rather than a separate subspecies, also ensures they are not vulnerable to being wiped out. The genes can persist through interbreeding even if cross fox numbers decline in certain areas. Keeping the gene pool shared helps maintain genetic diversity within the species as a whole.
Conclusion
While visually striking due to its fur color pattern, extensive evidence confirms the cross fox is not a distinct species or subspecies from the common red fox. The two color morphs show no reproductive isolation or major physiological differences. Cross foxes arose from genetic mutations within ancient red fox populations which were then maintained at low frequencies through interbreeding. Continuing gene flow between red and cross fox populations keeps them genetically and behaviorally indistinguishable beyond coat color. Taxonomists no longer recognize separate subspecies designations for the different color phases. The cross fox remains an intriguing example of naturally evolved coat color variation within a widespread and highly adaptable canid species.
