Friday, March 12, 2021

The Island Fox's Origin - The Gray Fox

Gray fox (left) with two island foxes at CALM Zoo, Bakersfield CA

In previous posts we've introduced the red fox, the most widely distributed land carnivore on the planet, kit and swift foxes (the Gemini foxes), who inhabit the arid regions of North America, and the arctic fox, a true species of the north. In this installment of Foxes of North America, we conclude with the progenitor to the island fox: the gray fox.

island fox

As we've previously discussed on the Friends of the Island Fox website, the island fox descended from the gray fox (the island fox's "progenitor" or ancestor) between 7,000–9,000 years ago. In evolutionary time, that's relatively recent. When you examine the canid family tree, you'll find that the gray fox and its predecessors have been continuously inhabiting southern North America and Central America since the middle Miocene (10 million years ago). The genus Urocyon is the most primitive living canine lineage, closest to the origin of all canid species.



gray fox, Southern CA

Gray Fox: The Fox of the Forest

Gray foxes are commonly associated with deciduous or mixed coniferous forests. In contrast to the red fox, which prefers forest openings–meadows and farmlands–the gray fox prefers the cover of woodlands. Forested habitats allow this inconspicuous fox to elude predators in a most unusual way for a canid: it climbs trees! 

One set of traits retained from the gray fox's early divergence from other carnivores, (and one that other canids have lost) are its highly re-curved, semi-retractable claws and rotating forearms. These feline-like qualities allow a gray fox to hug trees much the same way a cat does. The gray fox's relatively short leg to body ratio lowers its center of gravity, aiding in balance and making it easier to use trees as a means of escape and to forage for bird eggs and fruits. (Island foxes have inherited this climbing ability.)

Found from southern Canada to northern Columbia and Venezuela, the gray fox is the only fox species to range across both North and South America. Gray foxes are absent from the northern plains and Rockies, as their short legs make it difficult to navigate areas with deep snow. In Southern Canada, gray foxes live in coniferous forests, where dense foliage may help mitigate the effects of heavy snowfall.

gray fox, photo courtesy of Jim Carretta

The scientific name for gray foxes, Urocyon cinereoargentus, breaks down as follows: Urocyon is Greek for "tailed dog" and cinereoargentus translates to "silvery gray," which accurately describes this handsomely dappled fox. (Island fox's scientific name.) Its underside is a cinnamon-rufous color and there is white fur on the face, throat, belly and hind legs. The tail has a black tip, which helps distinguish it from the red fox, whose tail is white tipped. There are distinct black spots on either side of the muzzle. The long bushy tail makes the gray fox appear larger than it really is. In general, they stand about 14 inches at the shoulder; weigh from 7–13 pounds and are 31–44 inches long from head to tail. (Compare to the island fox)

The gray fox is the most omnivorous of the wild canids. Just like the island fox, their varied diet consists of small mammals, birds, fruits, nuts and invertebrates such as Jerusalem crickets and grasshoppers. Their diet varies throughout the year based on prey availability, which allows them to adapt to changing environments.

island fox family allogrooming

While mostly solitary, gray foxes do spend time in pairs or in small family groups through out the year. More than any other fox species, gray foxes can be seen allogrooming, which is when individuals socially groom each other and their pups to remove ticks and pests. If you visit a Channel Island, you can see that this trait has been carried over to island foxes, as they are often observed grooming each other.

The gray fox's tendency to prefer areas with thick tree coverage makes this elusive species the least studied of the North American foxes. Overall, the gray fox population is healthy, and habitat loss doesn't appear to be impacting the species for now. Farmers who raise poultry feel that gray foxes are pests, but biologists claim this threat is overstated. On the contrary, gray foxes provide a benefit to humans by keeping rodent populations in check.

Indigenous peoples realized the value of their neighbor the gray fox and thus began a relationship that would lead to the evolution of the island fox.

Previous installments:

How is the Island Fox Unique?

Red Fox: Life on the Edge

Gemini Foxes: Kit Fox and Swift Fox

Arctic Fox: Fox of the Tundra


Cyper, B.L. 2003. "Foxes (Vulpes species, Urocyon species and Alopex lagopus)." In Wild Mammals of North America: Biology, Management, and Conservation, 2nd edition by G. Feldhamer, B. Thompson, and J. Chapman (eds), pg 511–546. Baltimore: Johns Hopkins University Press.

Elbroch, M. and K. Rinehart. 2001. Behavior of North American Mammals. pg 105–111. Peterson Reference Guides.

Henry, J. D. 1996. Living on the Edge, Foxes. Minocqua, WI: Northword Press.