Island Fox

The island fox (Urocyon littoralis) is a small fox that is native to six of the eight Channel Islands of California. It is the smallest fox species in the United States. Other names for the island fox include coast fox, short-tailed fox, island gray fox, Channel Islands fox, Channel Islands gray fox, California Channel Island fox and insular gray fox.

Physical Description

The island gray fox is about a foot high and weighs about three or four pounds. They have gray fur on their backs, a ruddy red coloring on their sides and white fur on their bellies.

Taxonomy and Evolution

The island fox shares the Urocyon genus with the mainland gray fox (Urocyon cinereoargenteus), the fox from which it is descended.

There are six subspecies of island fox, each of which is native to a specific Channel Island, and which evolved there independent of the others. The subspecies are Urocyon littoralis littoralis of San Miguel Island, Urocyon littoralis santarosae of Santa Rosa Island, Urocyon littoralis santacruzae of Santa Cruz Island, Urocyon littoralis dickeyi of San Nicolas Island, Urocyon littoralis catalinae of Santa Catalina Island and Urocyon littoralis clementae of San Clemente Island. Foxes from each island are capable of interbreeding, but have genetic and phenotypic distinctions that make them unique, for example, the subspecies have differing numbers of tail vertebrae.

The small size of the island fox is an adaptation to the limited resources available in the island environment. The foxes are believed to have "rafted" to the islands about 15,000 years ago. Initially located on the northern islands, which were probably easier to access during the last ice age--when lower sea levels united four of the northernmost islands into a single mega-island and the distance between the islands and the mainland was reduced--it is likely that humans brought the foxes to the southern islands of the archipelago, perhaps as pets or hunting dogs.

Based on genetic distance from their gray fox ancestors, the northern island foxes are probably the older subspecies, while the San Clemente Island foxes have been only resident on their island for about 3,400 years, and the San Nicolas Island foxes established themselves as an independent group about 2,200 years ago. The Santa Catalina Island foxes are the youngest subspecies, having been on their island for about 800 years.

The foxes did not persist on Anacapa Island because it has no reliable source of fresh water.

Behavior, Feeding and Habitat

Their preferred habitat is complex layer vegetation with a high density of woody, perennially fruiting shrubs. The foxes live in all of the island biomes include temperate forest and rainforest, temperate grassland and chaparral. They are not intimidated by humans, as they have historically been at the top of the island food chain and had no natural predators. No island supports more than 1,000 foxes. Island foxes eat fruits, insects, birds, eggs, crabs and small mammals, including the deer mouse. The foxes tend to move around by themselves, rather than in packs. They are generally diurnal, albeit with peaks of activity at dawn and dusk.

Island foxes mate for life and are monogamous. Breeding only once a year, a typical island fox litters has one to five kits, which are born in the spring and emerge from the den in early summer. Island fox kits initially have much darker fur than adult foxes. The expected life span of an island fox is about five years.

Endangerment and Recovery Efforts

The island fox is currently a candidate for classification as a federally protected endangered species.

The major threats to the foxes are golden eagle predation, canine distemper and parasites introduced by housecats. A captive fox breeding program is increasing numbers of resident foxes, and a vaccination program is protecting Catalina Island foxes from a strain of canine distemper which was probably introduced to the population by an infected dog visiting from the mainland. The golden eagles may have been attracted by the expanding populations of feral livestock (mmm, tasty piglets!) as well as the decimation of the local bald eagle population due to DDT exposure in the 1950s—the bald eagles would have deterred the golden eagles from settling on the islands while they themselves subsisted on fish.

The fox competes for food and habitat with introduced mammal species, included feral cats, pigs, sheep, goats and American bison, the last of which were introduced to Catalina Island in the 1920s by a film crew shooting a Western.

The foxes themselves threaten a population of severely endangered loggerhead shrikes in residence on San Clemente Island.

Because the Channel Islands are almost entirely owned and controlled by either the Catalina Island Conservancy or the federal government, the fox has a chance to receive the protection it needs, including constant supervision by interested officials without the ongoing threat of human encroachment on its habitat.

Sources

• Channel Islands National Park's Island Fox Home Page
• Institute for Wildlife Studies – Island Fox
• Island Gray Fox – World Conservation Union – Canid Specialist Group