Gray fox

The gray fox (Urocyon cinereoargenteus) is a canid omnivore found across North and Central America. Along with its smaller relative, the island fox of California’s Channel Islands, it is one of only two living species in the genus *Urocyon*, a lineage that genetic studies place as the sister group to all other living canids. Its scientific name means “ashen silver,” a reference to the color of its tail.

This fox was once the most common fox in the eastern United States. Though still present there, deforestation and human expansion after European colonization allowed the red fox to become the dominant fox-like canid in that region. Despite this competition, the gray fox has adapted well to urban and suburban areas—southern Florida is a notable example—and it remains the prevalent fox in the Pacific states and the Great Lakes region.

The gray fox is distinguished from most other canids by its grizzled upper body, a black stripe running down the middle of its tail, and a strong neck ending in a black-tipped tail. Its skull is unique among North American canids, with widely separated temporal ridges forming a U-shape. Like other canids, it has angular, pointed ears and muzzle. Its claws are longer and more curved than those of many relatives. Females are slightly smaller than males, but otherwise there is little sexual dimorphism. Total length ranges from 76 to 112.5 cm, with the tail making up 27.5 to 44.3 cm of that. Hind feet measure 100 to 150 mm, and weight typically falls between 3.6 and 7 kg, though exceptionally large individuals can reach 9 kg. Unlike the red fox, the gray fox lacks black “stockings” on its legs. Its guard hairs are banded with white, gray, and black. White appears on the ears, throat, chest, belly, and hind legs, while black surrounds the eyes, lips, and nose. The gray fox has oval pupils, not slit-like ones like red foxes. It also has reddish coloration on the legs, sides, feet, chest, and the back and sides of the head and neck. Though it can weigh as much as a red fox, it appears smaller due to shorter fur and limbs. Its dental formula is 3.1.4.2 / 3.1.4.3 = 42.

The gray fox first appeared in North America during the mid-Pliocene, about 3.6 million years ago, with the earliest fossil found at the 111 Ranch site in Graham County, Arizona, alongside giant sloths, the elephant-like *Cuvieronius*, the large-headed llama, and early small horses (*Nannippus* and *Equus*). Late Pleistocene remains have been found in two northern California caves. Genetic analysis shows that after the Pleistocene, the gray fox moved into the northeastern United States during the Medieval Climate Anomaly warming period. Genetic studies confirm that the gray fox is a distinct genus from red foxes (*Vulpes* spp.), and *Urocyon* is sister to all other living canids. It often clusters genetically with two other ancient lineages: the Asian raccoon dog and the African bat-eared fox. Its diploid chromosome number is 66, with a fundamental number of 70; the autosomes include 31 pairs of sub-graded subacrocentrics and one pair of metacentrics. Recent mitochondrial DNA research suggests that eastern and western gray foxes in North America diverged into separate sister taxa during the Irvingtonian mid-Pleistocene. The island fox, a dwarf relative, likely descends from semi-domesticated mainland gray foxes that humans transported to the Channel Islands and between islands, originating from at least three or four matrilineal founders.

The gray fox lives in rocky, wooded, and brushy regions across the southern half of North America, from southern Canada (Manitoba through southeastern Quebec) down to northern South America (Venezuela and Colombia), though it is absent from the mountains of the northwestern United States. It prefers a mix of wooded and agricultural land in the Midwest, juniper forests and ponderosa pine in the West, and deciduous forests in the East. It is the only canid whose natural range spans both North and South America. In some areas, high populations occur near brush-covered bluffs. Toward the southern part of its range, such as Belize, it favors a mix of forest and farmland. In southeastern Mexico, it is often found near roads and human activity.

The gray fox is specially adapted for climbing trees. Its strong, hooked claws let it scramble up trunks to escape predators like domestic dogs and coyotes, or to reach arboreal food sources. It can climb branchless, vertical trunks up to 18 meters high and jump from branch to branch. It descends mainly by jumping or by backing down slowly like a domestic cat. It is primarily nocturnal or crepuscular.