|Gray Fox range|
The gray fox (Urocyon cinereoargenteus) is a mammal of the order Carnivora ranging throughout most of the southern half of North America from southern Canada to the northern part of South America (Venezuela and Colombia). This species and the closely related Channel Island fox (Urocyon littoralis) are the only living members of the genus Urocyon, which is considered to be among the most primitive of the living canids. Though it was once the most common fox in the east, and still is found there, human advancement allowed the red fox to become more dominant. The Pacific States still have the gray fox as a dominant. Its specific epithet cinereoargenteus means 'ashen silver'.
The gray fox appeared during the mid Pliocene epoch ago (AEO) with the first fossil evidence found at the lower 111 Ranch site, Graham County, Arizona with contemporary mammals giant sloth, the elephant-like Cuvieronius, Large-headed llama, and the early small horses of Nannippus and Equus. Genetic analyses of the fox-like canids confirmed that the gray fox is a distinct genus from the red foxes (Vulpes ssp.). Genetically, the gray fox often clusters with two other ancient lineages, the east Asian Raccoon dog (Nyctereutes procyonoides) and the African Bat-eared fox (Otocyon megalotis). Chromosome number is 2n=66. Recent genetic analysis has shown that the gray fox migrated into the northeastern United States post-Pleistocene in association with the Medieval Climate Anomaly warming trend. The Channel Island fox is likely descended from mainland gray foxes.
Description and behavior 
The gray fox is mainly distinguished from most other canids by its grizzled upper parts, strong neck and black-tipped tail, while the skull can be easily distinguished from all other North American canids by its widely separated temporal ridges that form a U-shape. There is little sexual dimorphism, save for the females being slightly smaller than males. The gray fox ranges from 76 to 112.5 cm (30 to 44.3 in) in total length. The tail measures 27.5 to 44.3 cm (10.8 to 17.4 in) of that length and its hind feet measure 100 to 150 mm (3.9 to 5.9 in). The gray fox typically weighs 3.6 to 7 kg (7.9 to 15 lb), though exceptionally can weigh as much as 9 kg (20 lb). It is readily differentiated from the red fox by the lack of "black stockings" that stand out on the latter. In contrast to all Vulpes and related (Arctic and fennec) foxes, the gray fox has oval (instead of slit-like) pupils.
The gray fox's ability to climb trees is shared only with the Asian raccoon dog among canids. Its strong, hooked claws allow it to scramble up trees to escape many predators such as the domestic dog or the coyote, or to reach tree-bound or arboreal food sources. It descends primarily by jumping from branch to branch, or by descending slowly backwards as a domestic cat would do. The gray fox is nocturnal or crepuscular and dens in hollow trees, stumps or appropriated burrows during the day. Such gray fox tree dens may be located 30ft above the ground. Prior to European colonization of North America, the red fox was found primarily in boreal forest and the gray fox in deciduous forest, but now the red fox is dominant in most of the eastern United States since they are the more adaptable species to development and urbanization. In areas where both red and gray foxes exist, the gray fox is dominant.
The gray fox is monogamous. The breeding season of the gray fox varies geographically; in Michigan, the gray fox mates[how?] in early March, in Alabama, breeding peaks occur in February. The gestation period lasts approximately 53 days. Litter size ranges from 1 to 7. Kits begin to hunt with their parents at the age of 3 months. By the time they are 4 months old, the kits will have developed their permanent dentition and can now easily forage on their own. The family group still remains together until autumn when the young reach sexual maturity. Then, they disperse.
The gray fox is an omnivorous, solitary hunter. It frequently preys upon the eastern cottontail (Sylvilagus floridanus) in the eastern U.S., though it will readily catch voles, shrews, and birds. In California, the gray fox primarily eats rodents, followed by lagomorphs, e.g. jackrabbit, brush rabbit, etc. In some parts of the Western United States (such as in the Zion National Park in Utah), the gray fox is primarily insectivorous and herbivorous.  Fruit is an important component of the diet of the gray fox and they seek whatever fruits are readily available, generally eating more vegetable matter than does the red fox (Vulpes vulpes).
There are 16 subspecies recognized for the gray fox.
- Urocyon cinereoargenteus borealis (New England)
- Urocyon cinereoargenteus californicus (southern California)
- Urocyon cinereoargenteus cinereoargenteus (eastern United States)
- Urocyon cinereoargenteus costaricensis (Costa Rica)
- Urocyon cinereoargenteus floridanus (Gulf states)
- Urocyon cinereoargenteus fraterculus (Yucatán)
- Urocyon cinereoargenteus furvus (Panama)
- Urocyon cinereoargenteus guatemalae (southernmost Mexico south to Nicaragua)
- Urocyon cinereoargenteus madrensis (southern Sonora, south-west Chihuahua, and north-west Durango)
- Urocyon cinereoargenteus nigrirostris (south-west Mexico)
- Urocyon cinereoargenteus ocythous (Central Plains states)
- Urocyon cinereoargenteus orinomus (southern Mexico, Isthmus of Tehuantepec)
- Urocyon cinereoargenteus peninsularis (Baja California)
- Urocyon cinereoargenteus scottii (south-western United States and northern Mexico)
- Urocyon cinereoargenteus townsendi (northern California and Oregon)
- Urocyon cinereoargenteus venezuelae (Colombia and Venezuela)
See also 
- Urocyon progressus, also known as the progressive gray fox.
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- Cypher et al. (2008). Urocyon cinereoargenteus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 06 May 2008. Database entry includes justification for why this species is of least concern
- Maine Trappers Association fur auctions. Mta.homestead.com (2005-12-17). Retrieved on 2011-09-15.
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- "Sometimes confused with the red fox because of cinnamon-red fur on its sides, the gray fox is increasingly common in rich hardwood forests of the northeast.". Hikenewengland.com. Retrieved on 2011-09-15.
- "Gray fox are widespread in Connecticut.". Wildlifeofct.com. Retrieved on 2011-09-15.
- Paleobiology database, Collection 19656, Graham County, Arizona. Authority by the Dr. John Alroy, February 18, 1993.
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- Erik K. Fritzell, Kurt J. Haroldson (1982). "Urocyon cinereoargenteus". Mammalian Species. Retrieved 2011-11-27.
- Christine A. Bozarth, Stacey L. Lance, David J. Civitello, Julie L. Glenn, and Jesus E. Maldonado (2011-04). "Phylogeography of the gray fox (Urocyon cinereoargenteus) in the eastern United States". Journal of Mammalogy: 283–294. Retrieved 2011-11-27.
- T.K. Fuller, B. L. Cypher (2004). In C. Sillero-Zubiri, M. Hoffman, and D. W. Macdonald. Gray fox Urocyon cinereoargenteus. pp. 92–97 in Canids: foxes, wolves, jackals, and dogs. Status survey and conservation action plan. Cambridge, United Kingdom: IUCN Publications. Retrieved 2011-11-27.
- "Urocyon cinereoargenteus". Animal Diversity Web. Retrieved 2007-08-19.
- Boitani, Luigi (1984) Simon & Schuster's Guide to Mammals. Simon & Schuster/Touchstone Books, ISBN 978-0-671-42805-1
- Common Gray Fox (Urocyon cinereoargenteus). Nsrl.ttu.edu. Retrieved on 2013-01-26.
- Alderton, p. 122.
- Fedriani, J. M.; Fuller, T. K.; Sauvajot, R. M. and York, E. C. (2000). "Competition and intraguild predation among three sympatric carnivores". Oecologia 125 (2): 258–270. doi:10.1007/s004420000448.
- Goddard-Taylor, Gayle (Winter 2005–2006). "The Silver Ghost: The life and times of the gray fox". Sanctuary: the Journal of the Massachusetts Audubon Society (Massachusetts Audubon Society) 45 (2): 13–15.
- Alderton, p. 124.
- Alderton, David (1998) Foxes, Wolves, and Wild Dogs of the World. London: Blandford ISBN 081605715X
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