Mammal Species of the World
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- Original description: Baird, S.F., 1857 . Mammals. In Reports of explorations and surveys for a railroad route from the Mississippi River to the Pacific Ocean. Beverly Tucker, Printer, Washington, D.C., 8 (part1):143, 757 pp.
Urocyon littoralis, the island grey fox, can be found on the six largest Channel islands, about 30 to 98 kilometers off of the southern California coast in North America. These islands are Santa Catalina, San Clemente, San Nicholas, San Miguel, Santa Cruz, and Santa Rosa Islands.
(Claybourne & Collins 1995, Wayne et al. 1991, Chapman 1999, Schmeckpepper 1999)
Biogeographic Regions: nearctic (Native )
Other Geographic Terms: island endemic
endemic to a single state or province
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (250-1000 square km (about 100-400 square miles)) The range includes six islands off the southern California coast: Santa Catalina, Santa Cruz, Santa Rosa, San Miguel, San Nicolas, and San Clemente (Roemer et al. 2004); these are the six largest of the eight Channel Islands. Archeological and geological evidence suggests that foxes arrived on the three northern islands minimally 10,400-16,000 years ago and dispersed to the three southern islands 2200-4300 years ago (Wayne et al. 1991), or Native Americans may have translocated foxes from the northern islands to the southern islands (Moore and Collins 1995). Genetic data indicate that all island foxes are descended from one colonization event (see Moore and Collins 1995). Extent of occurrence is not more than several hundred square kilometers.
Island grey foxes resemble dwarf versions of the grey fox (Urocyon cinereoargenteus). This is the smallest fox species known from the United States. Adult males weigh 2.00 kilograms on average, while adult females weigh 1.88 kilograms. Body length, including head and tail, ranges from 59 to 79 centimeters. Tail length alone ranges from 11 to 29 centimeters. Height at the shoulder is from 12 to 15 centimeters.
Fur is greyish-white and black with cinnamon underfur on the dorsal side, and with pale white, yellow, and rusty-brown on the ventral surface. The chin, lips, nose, and areas around the eyes are lined in black while the sides of the rostrum are grey. The ears, neck, and sides of the limbs are cinnamon-colored. The tail has a contrasting thin black stripe on the dorsal side with a mane of stiff hairs. The underside of the tail is a rusty color. Fur color may differ among islands and be highly variable among individuals, ranging from overall greyish to honey brown and red. Island grey foxes molt once a year during the fall months from August to November. At that time, the fur coat fades in color and the fur tips curl at the ends.
Young foxes tend to have a paler but thicker dorsal fur coat compared to adults. In addition, the ears are darker in color compared to adult foxes.
(Claybourne & Collins 1995, Crooks 1994, Chapman 1999, Schmeckpepper 1999, Weston date unknown, Fritzell et al. 1999)
Range mass: 1 to 2 kg.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Size in North America
Average: 716 mm males; 689 mm females
Range: 625-716 mm males; 590-787 mm females
Average: 2 kg males; 1.9 kg females
Range: 1.6-2.5 kg males; 1.5-2.3 kg females
Differs from U. CINEREOARGENTEUS primarily in smaller size (e.g., tail length 110-290 mm vs. 275-445 mm; usually more than 300 mm in CINEREOARGENTEUS) and somwhat darker overall coloration (Moore and Collins 1995).
California Coastal Sage and Chaparral Habitat
This taxon is found in the California coastal sage and chaparral ecoregion, located along the southern coast of California and Pacific coast of Baja California, has extremely high levels of species diversity and endemism. The eight Channel Islands are also part of this ecoregion, as are Isla Guadalupe and Isla Cedros. The climate is Mediterranean, with cold wet winters and dry hot summers. Precipitation levels range between 150 to 500 millimeters per annum. Vegetation typically grows on soils made of volcanic rocks on the base of the San Pedro Martir Mountains and on soils of sedimentary origin closer to the coastal zone.
The California coastal sage and chaparral supports a diversity of habitats including montane conifer forests, Torrey pine woodland, cypress woodlands, southern walnut woodlands, oak woodlands, riparian woodlands, chamise chaparral, inland and coastal sage scrub, grasslands, vernal pools, and freshwater and salt marshes. Coastal sage scrub, chamise chaparral, and oak woodlands dominate much of the landscape. Coastal sage scrub is a diverse and globally rare habitat type occurring in coastal terraces and foothills at elevations below 1000 meters (m), interspersed with chamise chaparral, oak woodland, grasslands, and salt marsh. This habitat type is characterized by low, aromatic and drought-deciduous shrublands of Black Sage (Salvia mellifera), White Sage (Salvia apiana), Munz’s Sage (Salvia munzii), California Sage (Artemisia californica), California Buckwheat (Eriogonum fasciculatum), California Brittlebush (Encelia californica), Toyon (Heteromeles arbutifolia), Lemonade Berry (Rhus integrifolia), and a diverse assemblage of other shrubs, herbaceous plants, cacti and succulents. Opuntia, Yucca, and Dudleya are some of the most common succulent genera, with the latter represented by several species endemic to the ecoregion.
The Island Fox (Urocyon littoralis), and Santa Catalina Shrew (Sorex willetti) are endemic mammals found in the ecoregion. Some of the specialist mammalian species found in the California sage and chaparral are: San Diego Pocket Mouse (Chaetodipus fallax), Merriam's Kangaroo Rat (Dipodomys merriami), and Stephens's Kangaroo Rat (Dipodomys stephensi).
The Rosy Boa (Charina trivirgata), California Legless Lizard (Anniella pulchra), and several relict salamanders are examples of the unusual and distinctive herpetofauna. Some endemic reptile species found in the ecoregion are: San Clemente Night Lizard (Xantusia riversiana), found only on the Channel Islands; Red-diamond Rattlesnake (Crotalus ruber), San Diego Banded Gecko (Coleonyx variegatus abbotti), and Coast Horned Lizard (Phrynosoma blainvillii).
Nutall’s Woodpecker (Picoides nuttallii) is endemic to the California sage and chaparral ecoregion, as are several endemic subspecies, which occur in the Channel Islands. Virtually all of the ecoregion is included in the California Endemic Bird Area. The California Gnatcatcher (Polioptila californica) is a further relict species found in the ecoregion. The coastal populations of the Cactus Wren (Campylorhynchus brunneicapillus) are a notable occurrence of this bird, which is usually found in more arid regions.
- World Wildlife Fund & C. Michael Hogan. 2013."California coastal sage and chaparral". Encyclopedia of Earth, National Council for Science and the Environment, Washington DC ed.Mark McGinley.
- L. Arriaga et al., editors. La Reserva de la Biosfera "El Vizcaíno" en la Peninsula de Baja California. Centro de Investigaciones Biológicas de Baja California Sur, A.C. Baja California Sur, México.
Habitat and Ecology
Although fox density varies by habitat, there is no clear habitat-specific pattern. When fox populations were dense, foxes could be trapped or observed in almost any of the island habitats, except for those that were highly degraded owing to human disturbance or overgrazing by introduced herbivores. More recently, foxes have become scarce owing to precipitous population declines. On the northern Channel Islands where the declines are principally a consequence of hyperpredation by Golden Eagles (Aquila chrysaetos) (Roemer et al. 2001a, 2002), foxes are more numerous in habitats with dense cover, including chaparral and introduced stands of fennel (Foeniculum vulgare) (G. Roemer, pers. obs.).
Channel island foxes can be found in all types on habitats of the Channel islands. This includes valley and foothill grasslands, coastal sage/scrub, coastal bluff, sand dune areas, island chapparral, southern coastal oak woodland, island woodland, southern riparian woodland, pine forests, and coastal marshes.
(Claybourne & Collins 1995, Fritzell et al. 1999)
Terrestrial Biomes: savanna or grassland ; chaparral ; forest
Comments: This fox occurs in all habitat types on the islands, but it is most abundant in woodland and chaparral, especially where there is a middle shrub layer. It takes shelter in thick vegetation, holes in the ground, brush piles, rock piles, and hollow trees; does not excavate its own burrow (Biosystems Analysis 1989).
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Island grey foxes are omnivorous, with a diet consisting mostly of insects and fruits. Their diet depends on seasonal and regional abundance of food items. Fruits and berries include manzanita, toyon, saltbush, prickly pear cactus, ice plant, and the fruits of sea-figs. They also feed on deer mice and birds. Sometimes these foxes feed on reptiles such as lizards, amphibians, land snails, and human refuse, but not as frequently since these items are not as abundant on the islands. In addition, they are known to scavenge for food on beaches along the coastline.
(Claybourne & Collins 1995, Garcelon et al. 1999, Chapman 1999, Schmeckpepper 1999, Weston date unknown)
Animal Foods: birds; mammals; amphibians; reptiles; insects; mollusks
Plant Foods: fruit
Primary Diet: omnivore
Comments: Generally omnivorous. One study found scat to contain mammal remains 32% of the time, insect (beetles, grasshoppers, and Jerusalem crickets) 90% of the time, and plant material about 50% of the time. According to California Department of Fish and Game (1990), insects (particularly grasshoppers, crickets, and beetles) and fruits are the most important foods; also consumes birds and their eggs, mammals, and grasses.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 1 - 5
Comments: This species is represented by six island populations.
1000 - 2500 individuals
Comments: Population size was estimated to be approximately 1,660 in 2001 (T. Coonan, pers. comm., in USFWS 2001), 1,219-1,538 in 2002 (Roemer et al. 2004). Population estimates for each island as of 2002 are as follows: Santa Catalina: 224; Santa Cruz: 77-97; Santa Rosa (45); San Miguel: 28; San Nicolas: 435-734; San Clemente: 410 (Roemer et al. 2004).
On some islands, exists at higher densities than fox populations on the mainland; in the 1970s, estimated density in trapped habitats varied from 20.4 per square mile on Santa Cruz to 0.8 per square mile on Santa Catalina (Laughrin 1980). On Santa Cruz Island, mean home range size was about 24-35 ha (core area 4-7 ha), varying insignificantly with sex and season (Crooks and Van Vuren 1996).
Competition with feral cats or habitat degradation by introduced livestock may account for low density on some islands.
Life History and Behavior
Comments: Primarily nocturnal, though not infrequently observed during daylight hours.
Lifespan, longevity, and ageing
Since there is little sexual dimorphism and relatively equal sex ratios in population, it is suggested that this species forms monogamous bonds.
Mating System: monogamous
Mating season of island grey foxes occurs from January to April, depending on latitude.
After mating, female foxes give birth to a litter of kits in 50 to 63 days. Although average litter size is 2 to 3 kits, it can range from 1 to 5 kits.
These kits are born in dens. Dens include ground holes, hollow trees, rock piles, shrubs, caves, and man-made structures. These dens are usually found, not made by the fox. However, if the fox is unable to find an appropriate den, she will dig a hole in the ground. The den serves to protect the kits from harsh weather, predators, and other dangers.
Kits are born blind, weighing approximately 100 grams. They reach adult weight by their first winter. They depend on their mother for milk during the first 7 to 9 weeks. Around May to June, after being weaned, they emerge from their dens and forage for food with their parents. Both parents take care of the kits. An interesting observation is that when both parents and kits are caught in traps while foraging, the parents still care for the kits and provide food to them.
Fox kits remain with their parents during the summer but become independent by September. Young foxes usually stay around the den area while the parents disperse from it. They reach sexual maturity at about 10 months old. Island foxes are able to breed after one year of age.
(Claybourne & Collins 1995, Crooks 1994, Crooks & Van Vuren 1996, Garcelon et al. 1999, Nowak 1999, Chapman 1999, Schmeckpepper 1999, Weston date unknown, Fritzell et al. 1999)
Range number of offspring: 1 to 5.
Average number of offspring: 2.5.
Range gestation period: 50 to 63 days.
Average number of offspring: 2.6.
Average age at sexual or reproductive maturity (female)
Sex: female: 365 days.
Parental Investment: altricial ; extended period of juvenile learning
Breeds in February-early March. Young are born from late April through May after a 50-day gestation period. Adult females produce one litter of 1-5 (usually 2) young per year. Young remain with parents until August or September (Biosystems Analysis 1989). Spatial relationships among males and females suggest monogamy (Crooks and Van Vuren 1996).
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2004Critically Endangered
- 1996Lower Risk/conservation dependent
- 1994Rare(Groombridge 1994)
- 1990Rare(IUCN 1990)
Urocyon littoralis is classified as "rare/lower risk" by the IUCN and "threatened" by the State of California and is protected by the California state law. There are no more than 1,000 foxes on each island and as few as 40 foxes on the smaller islands. Since their genetic variation is low, they are susceptible to disease and the consequences of environmental changes caused by man.
In 1993, their population was monitored by park biologists on San Miguel Island. This research revealed that this population of island foxes dropped from 450 in 1994 to less than 40 today. Similar outcomes are shown on the other islands. Populations on some islands have dropped as much as 90% in the past four years. This has sparked the park biologists to start a conservation team consisting of island fox researchers, captive breeding experts, canid genetics, wildlife disease experts, veterinarians, other canid biologists, and golden eagle researchers.
Threats to the island fox include loss of habitat, habitat changes resulting from the introduction of new herbivores, competition with feral cats, diseases brought by domestic dogs, and car accidents.
Measures and programs taken into effect to protect the island fox include disease investigations, elimination of feral cats, and potential captive breeding programs. The U.S. Navy and U.S. Park Service occupy their islands in order to help protect them. This species is currently a candidate for the U.S. ESA to be classified as threatened or endangered. It is already considered endangered by the State of California. Enforcing such protection is difficult, however, because they live on small remote islands.
(Nowak 1999, Chapman 1999, Schmeckpepper 1999, Weston date unknown, Fritzell et al. 1999, IUCN 1999, Wilson and Reeder 1993, National Park Service 1999)
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: critically endangered
National NatureServe Conservation Status
Rounded National Status Rank: N1 - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G1 - Critically Imperiled
Reasons: Restricted to the California Channel Islands (six islands); population size is less than 1,500; recent declines have occurred on five of the six islands; predation and disease are primary threats.
All of the current estimates of density and population size in Island Foxes have been conducted using modifications of a capture-recapture approach (Roemer et al. 1994). In its simplest application, population size is determined by multiplying average density among sampling sites times island area. Population estimates could be improved by first determining habitat-specific estimates of density and multiplying these densities times the area covered by the specific habitat (Roemer et al. 1994), an approach amenable to analysis with geographical information systems. However, density estimates made from aggregating home ranges suggest that the use of capture-recapture data may also overestimate density. For example, fox density estimated at Fraser Point, Santa Cruz Island using the capture-recapture approach was 7.0 foxes/km² (Roemer et al. 1994). A simultaneous estimate of density based on the distribution of home ranges for 14 radio-collared foxes with overlapping home ranges was approximately 31% lower (4.8 foxes/km²) (Roemer 1999). Thus the size of island fox populations may be lower than current capture-recapture analyses suggest.
Global Short Term Trend: Decline of 50-70%
Comments: Since 1995, populations on Santa Cruz, Santa Rosa, San Miguel, and Santa Catalina islands have dramatically declined; the Santa Cruz island population decreased from 1,300 to fewer than 100 individuals (2002 Endangered Species Bulletin 27(3):29). A 40-60 percent decline in fox abundance on San Clemente Island occurred between the late 1980s and late 1990s (Roemer and Wayne 2003).
Four of the six island populations experienced precipitous declines in the late 1990s and early 2000s (Roemer et al. 2004).
Global Long Term Trend: Increase of 10-25% to decline of 30%
Comments: Trapping data for San Nicolas Island suggest a decline in the 1970s, during which time there was an increase in the feral cat population (Laughlin 1980). In the 1980s, population may have been stable on San Miguel, Santa Rosa, Santa Cruz, and San Nicolas islands; the population on Santa Catalina Island almost certainly declined, whereas status on San Clemente Island was unknown (California Department of Fish and Game 1990).
Degree of Threat: Very high - medium
Comments: Current primary threats incude predation by golden eagles on the northern Channel Islands and the possible introduction of canine diseases to all populations (Roemer et al. 2004). Canine distemper recently caused a large decline in the Santa Catalina population (Roemer et al. 2004). Recovery actions for the San Clemente loggerhead shrike, including a predator control program that involved euthanasia and confinement of foxes, likely contributed to the recent decline of foxes on San Clemente Island (Roemer and Wayne 2003). All populations are relatively small and vulnerable to demographic stochasticity and environmental extremes (Roemer et al. 2004).
Recently, there has also been a management conflict between island foxes and the San Clemente Island loggerhead shrike (Roemer and Wayne 2003). Island Foxes were euthanized on San Clemente Island in 1998 as part of a programme to protect nesting shrikes (Elliot and Popper 1999; Cooper et al. 2001). Although euthanasia of foxes has stopped, a number of foxes are now retained in captivity each year, during the nesting and fledging stage of the shrike, and subsequently released back into the environment. The impact to fox reproduction and the potential disruption of the social system are unknown, but may be significant. These actions may have contributed to a 60% decline in the fox population on San Clemente Island (Cooper et al. 2001; Schmidt et al. 2002; Roemer and Wayne 2003). Considering the precipitous declines in foxes on four of six islands and the continued decline in the San Clemente population, this current management practice needs further scrutiny.
The species was formerly a category II candidate for federal listing, but is not currently listed by the U.S. Fish and Wildlife Service (USFWS) as threatened or endangered under the Federal Endangered Species Act. The species is listed by the state of California as a threatened species (California Department of Fish and Game 1987). The current legal status has not been sufficient to prevent recent catastrophic population declines. In June 2000, the USFWS was petitioned to list the populations on the three northern Channel Islands and Santa Catalina Island as endangered (Suckling and Garcelon 2000). The USFWS recently proposed to list these four subspecies as endangered (USDI 2001).
The three subspecies on the northern Channel Islands occur within the Channel Islands National Park. Approximately two-thirds of Santa Cruz Island is owned by The Nature Conservancy (TNC), and managed as the Santa Cruz Island Preserve. The Preserve is within the boundaries of the Channel Islands National Park, and the TNC and NPS (National Parks Service), co-manage natural resources together under a cooperative agreement. Approximately 87% of Santa Catalina Island is owned by the Santa Catalina Island Conservancy, a non-profit conservation organization, and both San Clemente and San Nicolas Islands are owned and managed by the U.S. Navy.
Based upon recommendations from an ad hoc recovery team, the Island Fox Conservation Working Group, the National Park Service (NPS) began initiating emergency actions in 1999, with the objectives being to remove the primary mortality factor currently affecting Island Foxes (Golden Eagle predation), and to recover populations to viable levels via captive breeding. Between November 1999 and June 2002, 22 eagles were removed from Santa Cruz Island and relocated to north-eastern California. In 1999, the NPS established an Island Fox captive breeding facility on San Miguel Island, added a second facility on Santa Rosa in 2000 and a third on Santa Cruz Island in 2002 (Coonan 2002, 2003; Coonan and Rutz 2000, 2002). Fourteen foxes were originally brought into captivity on San Miguel; current captive population is now 28. There are currently 45 foxes in captivity on Santa Rosa, and 12 adult foxes in the Santa Cruz facility that produced a single litter of five pups (Coonan 2002, 2003).
The NPS has prepared an Island Fox recovery plan for the northern Channel Islands (Coonan 2001) and an island-wide restoration plan for Santa Cruz Island (USDI 2002). The measures taken thus far on the northern Channel Islands (golden eagle removal and captive breeding) will form the basis for long-term recovery for the subspecies on the northern Channel Islands. In addition, the reintroduction of Bald Eagles (Haliaeetus leucocephalus), the eradication of feral pigs, and the removal of exotic plants have been recommended and are being implemented (Roemer et al. 2001a; USDI 2002). Demographic modelling indicates that recovery to viable population levels could take up to a decade (Roemer et al. 2000).
On Santa Catalina Island, The Santa Catalina Island Conservancy has taken a series of measures to mitigate the effects of canine distemper virus on that subspecies. Close to 150 foxes from the west end have been field-vaccinated for CDV and both translocation and captive breeding programmes have been established to aid in recolonizing the eastern portion of the island (Timm et al. 2000, 2002).
Although the Island Fox Conservation Working Group recognized the need for a species-wide recovery plan, there is currently no formal vehicle to accomplish such a planning effort, because the species is not listed under the Federal Endangered Species Act. Nonetheless, the Working Group recognized that the following actions need to be implemented in order to insure recovery of island fox populations to viable levels (Coonan 2002, 2003):
Complete removal of Golden Eagles from northern Channel Islands.
? Implement monitoring/response program for future golden eagles.
? Remove feral pigs from Santa Cruz Island.
? Reintroduce bald eagles to the northern Channel Islands.
? Eliminate canine distemper as a mortality factor on Santa Catalina Island.
? Vaccinate wild foxes against canine distemper virus, as needed.
? Monitor populations for diseases causing morbidity and mortality through necropsy and faecal and blood testing.
? Enforce no-dog policy on islands, and vaccinate working dogs.
? Educate the public about potential disease transmission from domestic dogs.
? Establish and maintain captive breeding facilities on San Miguel, Santa Rosa, Santa Cruz and Santa Catalina Islands.
? Supplement wild populations with captive-reared foxes.
? Implement annual population monitoring of each subspecies/population.
? Halt management actions to protect the San Clemente loggerhead shrike that are adversely affecting the San Clemente island fox.
? Develop adaptive management programme.
Island Foxes currently are kept in captivity on four islands. The National Park Service's captive breeding programme maintains facilities on San Miguel, Santa Rosa and Santa Cruz Islands, in which there are currently 28, 45 and 17 island foxes, respectively. The Santa Catalina Island Conservancy and the Institute for Wildlife Studies have established a captive breeding facility on that island, and there are currently 12 adult pairs of foxes there (Timm et al. 2002). Small numbers (1?4) of San Clemente Island foxes are kept in a total of four zoos on the mainland with a variable number of foxes held in captivity each year on that island (Cooper et al. 2001).
Gaps in knowledge
It is known that wild Island Fox pairs are unrelated and that extra-pair copulations occur (Roemer et al. 2001b), but little is known about how foxes select mates and whether mate choice could play a role in improving the currently low reproduction characterizing captive foxes (Coonan and Rutz 2002). Controlled mate-choice experiments are needed.
It has been suggested that intense predation by Golden Eagles could have altered Island Fox activity patterns and selected for greater nocturnal activity in those foxes that have survived predation (Roemer et al. 2002). The survival of the remaining wild Island Foxes on Santa Cruz Island is being monitored, but there has been no attempt to document daily activity levels (Dennis et al. 2001). The pattern of daily activity of wild Santa Cruz Island Foxes needs to be assessed, and compared to the activity of captive and captive-reared foxes that are released into the wild. If captive-reared foxes are more active during diurnal and crepuscular periods than their wild counterparts, it is probable that captive-reared foxes reintroduced into the wild will suffer higher mortality owing to Golden Eagle predation.
There has been only a single study that has examined dispersal in Island Foxes (Roemer et al. 2001b) and the number of dispersal events recorded was small (n=8). Additional information on Island Fox dispersal patterns on different islands and during periods of high and low density are needed.
Biological Research Needs: See Roemer et al. (2004) for a review of recent and current research.
Global Protection: Few (1-3) occurrences appropriately protected and managed
Comments: San Miguel, Santa Rosa, and Santa Cruz islands are included in the Channel Islands National Park. About two-thirds of Santa Cruz Island is owned by The Nature Conservancy and co-managed with the National Park Service. Approximately 87% of Santa Catalina Island is owned by the Santa Catalina Conservancy (a nonprofit conservation organization). San Clemente and San Nicolas islands are owned and managed by the U.S. Navy. Take, sell, and possession are prohibited by California law.
Relevance to Humans and Ecosystems
Economic Importance for Humans: Positive
Native Americans used the Channel island fox for many purposes. Their fur was used for arrow-quivers, capes, blankets, and headdresses for ceremonial dances. Since they are docile in nature, they were also kept as pets. Native Americans used the island fox in their religious and ceremonial practices. They served as totems, dream-helpers, and legendary characters. Native Americans also had burials for these foxes, suggesting they were of religious importance.
Today, Urocyon littoralis are sometimes hunted.
(Collins 1991, Nowak 1999)
Stewardship Overview: See Roemer et al. (2004) for a list of recommended conservation measures, which include removal of golden eagles and reestablishment of bald eagles in the northern Channel Islands; removal of feral pigs from Santa Cruz Island; elimination of canine distemper as a mortality factor on Santa Catalina Island; public education; captive breeding and supplementation of wild populations with captive-reared foxes; population monitoring; and halt of management activities that are detrimental to island foxes (particularly those associated with San Clemente loggerhead shrike).
The island fox (Urocyon littoralis) is a small fox that is native to six of the eight Channel Islands of California. There are six subspecies of the fox, each unique to the island it lives on, reflecting its evolutionary history. 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.
Taxonomy and evolution
The island fox shares the Urocyon genus with the mainland gray fox, 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 no immunity to parasites and diseases brought in from the mainland and is especially vulnerable to those the domestic dog may carry. In addition, predation by the golden eagle 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.
- 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 and,
- Urocyon littoralis clementae of San Clemente Island.
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 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.
Based on the limited fossil record and genetic distance from its gray fox ancestors, the northern island fox subspecies are probably the older subspecies, while the San Clemente island fox has been only resident on its island for about 3,400–4,300 years, and the San Nicolas island fox established itself as an independent group about 2,200 years ago. The Santa Catalina island fox is potentially the most recently evolved subspecies, having been on its island for about 800–3,800 years. 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 demands of the fox.
The island fox is significantly smaller than the gray fox and perhaps the smallest fox in North America, averaging slightly smaller than the swift and kit foxes. Typically the head-and-body length is 48–50 cm (18–20 in.), shoulder height 12–15 cm (4–6 in.), and the tail is 11–29 cm (4–11 in.) long, which is notably shorter than the 27–44 cm (10–17 in.) tail of the gray fox. This is due to the fact that the island fox generally has two fewer tail vertebrae than the gray fox. The island fox weighs between 1 and 2.8 kg (2.2 and 6.2 lb). The male is always larger than the female. The largest of the subspecies occurs on Santa Catalina Island and the smallest on Santa Cruz Island.
The island fox has gray fur on its head, a ruddy red coloring on its sides, white fur on its belly, throat and the lower half of its face, and a black stripe on the dorsal surface of its tail. In general the coat is darker and duller hued than that of the gray fox. The island fox molts once a year between August and November. Before the first molt pups are woolly and have a generally darker coat than adult foxes.
The island fox typically forms monogamous breeding pairs which are frequently seen together beginning in January and through the breeding season, from late February to early March. The gestation period is 50–63 days. The female island fox gives birth in a den, a typical litter having one to five pups, with an average of two or three. Pups are born in the spring and emerge from the den in early summer; the mother lactates for 7–9 weeks. Sexual maturity is reached at 10 months, and the females usually breed within the first year. Island foxes live for 4–6 years in the wild and for up to 8 years in captivity.
Ecology and behavior
Its preferred habitat is complex layer vegetation with a high density of woody, perennially fruiting shrubs. The fox lives in all of the island biomes including temperate forest, temperate grassland and chaparral, with no island supporting more than 1,000 foxes. The island fox eats fruits, insects, birds, eggs, crabs, lizards, and small mammals, including deer mice. The fox tends to move around by itself, rather than in packs. It is generally nocturnal, albeit with peaks of activity at dawn and dusk. Activity also fluctuates with the season; it is more active during the day in summer than it is in winter.
The island fox is not intimidated by humans, although at first may show aggression. It is quite easy to tame and is generally docile. The island fox communicates using auditory, olfactory and visual signals. A dominant fox uses vocalizations, staring, and ear flattening to cause another fox to submit. Signs of dominance and submission are visual, such as facial expression and body posture. Its main vocalizations are barking and growling. The island fox marks territory with urine and feces.
A decline in island fox populations was identified in the 1990s. On San Miguel Island the decline began in 1994, the adult population falling from 450 to 15 in 1999. Similar population declines were discovered on Santa Cruz Island, where the population decreased from 2,000 adults in 1994 to less than 135 in 2000, and on Santa Rosa Island where foxes may have numbered more than 1,500 in 1994 but were reduced to 14 animals by 2000. Golden eagle predation, discovered when foxes were radio-collared and monitored, proved to be the cause of the high mortality rates.
Golden eagle predation is the primary cause of island fox mortality. The golden eagle was an uncommon visitor to the Channel Islands before the 1990s according to data gathered by Dr. Lyndal Laughrin of the University of California Santa Cruz Island Reserve, and the first golden eagle nest was recorded on Santa Cruz Island in 1999. Biologists propose that the eagle may have been attracted to the islands in the 1960s after the decline of the bald eagle. The golden eagle replaced the bald eagle and began to feed on feral pigs due to the decimation of the local bald eagle population due to DDT exposure in the 1950s—the bald eagle would have deterred the golden eagle from settling on the islands while it subsisted on fish.
The feral pigs on Santa Rosa were exterminated by the National Park Service in the early 1990s which removed one of the golden eagle's food sources. The golden eagle then began to prey on the island fox population. Feral pigs on Santa Cruz Island and introduced deer and elk on Santa Rosa Island were introduced almost seventy years prior to island fox decline, therefore, the golden eagle most likely did not seek these animals as alternative prey. This has occurred most likely as a result of a process known as 'apparent competition'. In this process, a predator, like the golden eagle, feeds on at least two prey, for example, the island fox and feral pigs. One prey item is adapted to high predation pressure and supports the predator population (i.e. pigs), whereas the other prey item (i.e. the island fox) is poorly adapted to predation and declines as a consequence of the predation pressure. It has also been proposed that complete removal of golden eagles may be the only action that could save three subspecies of the island fox from extinction. However, the pigs on Santa Cruz Island were killed by the Nature Conservancy under the idea that they brought the eagles to the foxes.
Introduced diseases or parasites can devastate island fox populations. Because the island fox is isolated, it has no immunity to parasites and diseases brought in from the mainland and are especially vulnerable to those the domestic dog may carry. A canine distemper outbreak in 1998 killed approximately 90% of Santa Catalina Island's fox population. After several years of carefully trapping the foxes and vaccinating them against distemper and rabies, their population has reached 1,542, surpassing the population of about 1,300 seen before the animals were ravaged by the disease that scientists believe was introduced by a pet dog or a raccoon from the mainland that hitched a ride on a boat or a barge.
Diminished food supply and general degradation of the habitat due to introduced mammal species, including feral cats, pigs, sheep, goats, and American bison, the latter having been introduced to Catalina Island in the 1920s by a Hollywood film crew shooting a Western, also has had a negative effect on fox populations.
The foxes threaten a population of the severely endangered Clemente Island loggerhead shrike in residence on San Clemente Island. The island fox population has been negatively affected by trapping and removal or euthanasia of foxes by the United States Navy. Since 2000, the Navy has employed different management strategies: trapping and holding foxes during the shrike breeding season, the installation of an electric fence system around shrike habitats, and the use of shock collar systems. With the gradual recovery of the shrike population on San Clemente Island, the Navy no longer controls the foxes.
The populations of Santa Cruz Island Foxes, San Miguel Island Foxes, and Santa Rosa Island Foxes have dramatically rebounded from 70 to 1,300 for the Santa Cruz foxes and from 15 to hundreds each of the other two.
In March 2004, four subspecies of the island fox were classified as a federally protected endangered species: the Santa Cruz island fox, Santa Rosa island fox, San Miguel island fox and the Santa Catalina island fox. As of 2013, the IUCN lists the entire species as near threatened, an improvement from its previous status of "critically endangered".
The National Parks Service has initiated captive fox breeding programs on San Miguel, Santa Rosa and Santa Cruz Islands, successfully increasing the numbers of resident foxes. In 2004, there were 38 San Miguel island foxes, all in captivity; 46 foxes in captivity on Santa Rosa Island and 7 in the wild (golden eagle predation prevented the release of captive foxes into the wild); Santa Cruz Island had 25 captive foxes and a stable wild population of around 100 foxes. The Catalina Island Conservancy also runs a captive breeding program on Catalina Island; in 2002, there were 17 foxes in captive breeding programs and at least 161 wild foxes. The Catalina Island Conservancy determined that there were 1,500 Santa Catalina Island foxes in 2012, and the population was stabilized.
A key to the recovery of the island fox is the removal of the golden eagle from the Channel Islands, ecosystem restoration and disease control. To ensure survival of the island fox, golden eagles are being moved from the northern islands to the mainland. Maintaining and increasing the bald eagle population on the islands would help to displace the golden eagle. However, the program is extremely resource-intensive and is at risk for cancellation. Removal of feral pigs from Catalina Island and Santa Cruz Island is underway, removing both the golden eagle's food and competition for the island fox. To eliminate the risk of disease, pets are not permitted in Channel Islands National Park. A vaccination program has been initiated to protect Catalina Island foxes from canine distemper.
Because the Channel Islands are almost entirely owned and controlled by either the Catalina Island Conservancy, The Nature 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.
According to the Nature Conservancy summer 2009 magazine, the Santa Cruz Island fox population has rebounded to a population of 700 from being fewer than 100.
While it has been assumed that the foxes existed on these islands long before native people settled on the islands, archaeologists are now challenging this theory. Rene Vellanoweth believes that the foxes were brought to the island with the indigenous people, and had not been there upon their arrival. Vellanoweth also believes that the foxes were moved from island to island with the people, which caused interbreeding amongst the species. He believes the key to restarting the fox population is to do what the indigenous people did: mix their species and move them from island to island, creating a higher genetic diversity and assisting them in recovery.
Recently, a document was released by the U.S. Fish and Wildlife Service as a draft recovery plan for the San Miguel Island fox, Santa Rosa Island fox, Santa Cruz Island fox, and the Santa Catalina Island fox. The plan was released on 14 September 2012, and is currently in the draft plan stage.
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Names and Taxonomy
Comments: Each of the islands has been regarded as having its own endemic subspecies. Genetic distances among the island populations, as estimated by morphometrics, allozyme electrophoresis, mtDNA restriction-site analysis, and analysis of hypervariable minisatellite DNA, are not well correlated; there are no distinct trends of genetic variability with founding time (Wayne et al. 1991). This species has been regarded as possibly conspecific with U. cinereoargenteus by some authors, but it was recognized as a separate species by Jones et al. (1992) and Wozencraft (in Wilson and Reeder 2005). It has been placed in the genus Canis or the genus Vulpes by some authors (as recently as the 1970s).