The island fox (Urocyon littoralis)
The island fox (Urocyon littoralis) is a small fox species that is endemic to six of the eight Channel Islands of California. There are six subspecies, each unique to the island it lives on, reflecting its evolutionary history. They are generally docile, show little fear of humans, and are easily tamed. Island foxes played an important role in the spiritual lives of native Channel Islanders. They have been likely semi-domesticated as pets, used as pelts, or for other functions, like pest control.
Taxonomy and evolution
The island fox shares the genus Urocyon with the mainland gray fox (Urocyon cinereoargenteus), the species from which it is descended. Its small size is a result of insular dwarfism, a form of allopatric speciation. Because the island fox is geographically isolated, it has not acquired immunity to parasites and diseases brought in from the mainland and is especially vulnerable to those that the domestic dog (Canis familiaris) may carry. In addition, predation by the golden eagle (Aquila chrysaetos) and human activities devastated fox numbers on several of the Channel Islands in the 1990s. Four island fox subspecies were federally protected as an endangered species in 2004, and efforts to rebuild fox populations and restore the ecosystems of the Channel Islands are being undertaken. Radio collars are being attached to foxes in an effort to track and locate the young foxes. To date these efforts have been largely successful.
There are six subspecies of the island fox, each of which is native to a specific Channel Island, and which evolved there independently of the others. The subspecies are:
- Urocyon littoralis littoralis (the nominate subspecies) of San Miguel Island;
- Urocyon littoralis dickeyi of San Nicolas Island;
- Urocyon littoralis catalinae of Santa Catalina Island;
- Urocyon littoralis clementae of San Clemente Island;
- Urocyon littoralis santacruzae of Santa Cruz Island;
- Urocyon littoralis santarosae of Santa Rosa Island.
Foxes from each island are capable of interbreeding, but have genetic and phenotypic distinctions that make them unique; for example, each subspecies has differing numbers of tail vertebrae. The fox did not persist on Anacapa Island because it has no reliable source of fresh water; Santa Barbara Island is too small to support the food needs of a viable fox population.
The small size of the island fox is an adaptation to the limited resources available in the island environment, or island dwarfism. The foxes are believed to have "rafted" to the northern islands between 10,400 and 16,000 years ago. Initially, fox populations were located on the three northern islands, which were likely easier to access during the last ice age — when lowered sea levels united four of the northernmost islands into a single mega-island (Santa Rosae) and the distance between the islands and the mainland was reduced — it is likely that Native Americans brought the foxes to the southern islands of the archipelago, perhaps as pets, or hunting dogs.
Origin and distribution
The scientific name Littoralis translates from Latin as "situated or growing on or near the seashore", or as an island-dwelling creature. Urocyon littoralis is the closest relative of the mainland species of grey fox (Urocyon cineroargenteus).
The distribution of the island fox is restricted to the six larger Channel Islands, 19-60 miles off the coast of southern California, USA. They include the islands of Santa Catalina, San Clemente, San Nicolas, San Miguel, Santa Cruz and Santa Rosa.
Urocyon littoralis is the smallest known species of fox in the United States. Until recently, the island fox was considered a subspecies of the grey fox. It is small and has a shorter tail, with two fewer vertebrae than the continental grey fox. Descended from the continental grey fox, Urocyon littoralis evolved into a single species over 10,000 years, retaining the characteristics of its ancestor, but in the process of evolution, its size has decreased and is now only two-thirds that of its ancestor.
The full species Urocyon littoralis comprises six distinct subspecies, one on each of the six islands it inhabits. The foxes on each of the islands are still capable of interbreeding, but there are a number of physical and genetic differences that are sufficient for their subspecies to be recognised as independent.
For example, the average number of caudal vertebrae differs considerably from island to island. All subspecies are named after the island they inhabit:
- Urocyon littoralis littoralis, the San Miguel Island fox;
- Urocyon littoralis santarosae, the Santa Rosa Island fox;
- Urocyon littoralis santacruzae, the Santa Cruz Island fox;
- Urocyon littoralis dickeyi, the fox of San Nicolas Island;
- Urocyon littoralis catalinae, the fox of Santa Catalina Island;
- Urocyon littoralis clementae, San Clemente Island fox.
Appearance
The coat of Urocyon littoralis is greyish white with black hair tips and cinnamon undercoat on the dorsal side, and pale white and rusty brown on the ventral surface. The chin, lips, nose and areas around the eyes are black, while the sides of the cheeks are grey. The ears, neck and sides of the limbs are brown.
The tail has a fine contrasting black stripe on the dorsal side with a stiff mane of hair. The underside of the tail is rust coloured.
The coat colour probably differs between foxes on different islands, although it is extremely variable between individuals, ranging from a completely greyish colour to brown or red.
Urocyon littoralis moult once a year, between August and November.
Young foxes have paler but thicker fur on the back than adults and their ears are also darker in colour.
Males have an average body length with tail of 716 mm (625 to 716 mm); females are 689 mm (590 to 787), of which the tail is between 11 and 29 cm. The weight of the animals ranges from 1.3 to 2.8 kg, with males being slightly heavier.
Life history
Urocyon littoralis, like their continental ancestors, are excellent tree climbers.
In captivity, foxes may initially show aggression towards humans, but soon become domesticated. Captive foxes are intelligent, friendly, playful and curious.
Urocyon littoralis can live for four to six years, but some can live up to 15 years.
The islands on which Urocyon littoralis live have a climate characterised by hot, dry summers and cool, wet winters. Although fox density is variable and determined by habitat, there is no ideal reference habitat for foxes. When fox populations were abundant, foxes could be found and observed in almost all habitats on the island, except those that were extremely poor due to human disturbance. Foxes inhabited foothill valleys and fields, coastal scrub, dunes, thorn scrub islands, coastal oak and pine forests, and salt marshes.
One of the main enemies of Urocyon littoralis is the golden eagle. Golden eagles have not always lived on the islands, but were attracted there by the feral pig population around 1995, when the eagles became extinct there. The disappearance of the eagle provided favourable conditions for the settlement of the northern islands by smaller golden eagles. The golden eagle began to successfully hunt the Urocyon littoralis, and over the next seven years, the Urocyon littoralis was driven to the brink of complete extinction. Surveys have shown that by the year 2000, the fox population on the three northern islands had indeed been reduced by 95%.
Nutrition
Urocyon littoralis hunt mainly at night, but are also active during the day. Their diet depends largely on where they live and is determined by the time of year. Their diet consists mainly of fruits and berries of all kinds (including bearberry, salicaria, quinoa, prickly pear and others). Of course, this predator is not lacking in animal protein; it feeds on small mammals, birds, reptiles, land snails, eggs and all kinds of insects, as well as edible remains of human waste.
Social behaviour and reproduction
Urocyon littoralis, upon reaching sexual maturity, create a pair that persists through the breeding and rearing of young. During the rest of the year, Urocyon littoralis live a solitary nocturnal and sometimes diurnal lifestyle until the next breeding season. Male and female pairs usually occupy adjacent territories up to 0.5-1 square miles apart, although their individual patches may overlap to varying degrees with each other and with those of neighbouring pairs. Urocyon littoralis live at higher densities than the grey fox, at around one square mile per fox. The territory boundaries of males change more frequently than those of females, and the plot of a mating female during the breeding season joins a common family plot with the male and is jointly protected.
Communication between foxes is by sight, sound and smell. Throughout the night, it is not uncommon to hear foxes barking, echoing each other. Vocal communication in the form of barks and growls, with muzzle expressions and body postures, helps to identify dominant or subordinate individuals. For example, submission may be expressed in the encounter by lowering the head, flattening the ears, whining, licking the partner and lack of direct eye contact (eye-to-eye gaze). Their acute sense of smell plays an important role in marking territories with urine and droppings, which are found at borders and along the foxes' main flight paths.
The rutting and mating seasons are from January to April and depend on latitude. They make their dens in holes in the ground, hollow tree trunks, piles of stones, bushes, caves and other artificial structures. Although they do not usually build their own shelters, if they do not have a suitable den, they will dig one of their own in the form of a small hole in the ground.
Pregnancy lasts between 51 and 63 days. The pups are born in a well-protected burrow carefully lined with dried plant debris. As in other canine species, males play an important role in feeding, protection and training. The average litter size is 4 fox cubs, but ranges from 1 to 10.
Newborn cubs are blind and helpless at birth and weigh approximately 100 grams. They are fed milk by their mother for the first 7-9 weeks, although they emerge from the den and begin to empty the food brought to them by their parents after one month of age.
Young foxes, after emerging from the den and becoming independent, usually remain close to their den on their parents' property for a while longer. They reach adult size by the end of the year, but usually leave their parents by the end of September. Cubs reach sexual maturity at 10 months of age and females give birth at one year of age.
Threats to their existence
Three main factors threaten Urocyon littoralis: habitat destruction, competition with feral cats for food and the threat of diseases imported from the mainland. For example, the fox population on the island of San Miguel has declined catastrophically in the last 5 years: whereas in 1994 the fox population was estimated at 450 animals, in 1998 it was only 40.
Little is known about the foxes on Santa Rosa Island. The fox population on Santa Cruz Island is around 100-133 animals. The main cause of mortality is golden eagles. On Santa Catalina Island, most of the foxes died in 1999 from rabies introduced with dogs.
Subsequent vaccination of the foxes has led to a partial recovery of the local fox population, which is now fairly abundant. The fox population in San Clemente is high, while that in San Nicolás fluctuates constantly. This has contributed to the fact that the island grey fox is now fully protected on all six islands.
Due to their isolated existence, Urocyon littoralis have no natural immunity to pathogens and diseases brought from the mainland and are particularly susceptible to those carried by local dogs. Significant numbers of foxes also die under car wheels on the islands of Santa Catalina, San Clemente and San Nicolas.
The total population of Urocyon littoralis declined from 6,000 individuals in 1994 to less than 1,500 in 2002. On the northern islands, where the decline is mainly due to hyper-predation by golden eagles, foxes are more abundant in more enclosed and protected habitats from above, such as thorny shrub thickets, sweet dill (Foeniculum vulgare) plantations and other woody and shrubby plant communities.
