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.
Island Foxes are restricted to the six largest of the eight California Channel Islands located off the coast of southern California, USA. The view that foxes reached the northern Channel Islands by waif dispersal, followed by Native American assisted dispersal to the southern Channel Islands (Collins 1982, 1991a,b, 1993; Wayne et al. 1991; Goldstein et al. 1999), was challenged by Rick et al. (2009), who dated fossil fox bones. The oldest bone was dated at approximately 6,400 cal yr BP, several thousand years after humans colonized the islands. Thus, it is now unclear whether foxes reached the northern islands naturally or were introduced by humans.
Six distinct subspecies are recognized, one on each of the islands where they occur:
San Miguel Island Fox (Urocyon littoralis littoralis (Baird, 1858)), San Miguel Island,
Santa Rosa Island Fox (U. l. santarosae Grinnell & Linsdale, 1930), Santa Rosa Island,
Santa Cruz Island Fox (U. l. santacruzae Merriam, 1903), Santa Cruz Island,
Santa Catalina Island Fox (U. l. catalinae Merriam, 1903), Santa Caralina Island,
San Nicolas Island Fox (U. l. dickeyi Grinnell & Linsdale, 1930), San Nicolas Island, and
San Clemente Island Fox (U. l. clementae Merriam, 1903), San Clemente Island.
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
The Island Fox is considered to be a habitat generalist because it has been found using virtually all habitat types occurring on the Channel Islands (Coonan et al. 2010a, USFWS 2012). Use of diverse habitats likely is a function of ecological plasticity, limited predation and competition pressures, and characteristic high fox densities. Habitats used include beaches, sand dunes, bluffs, grasslands, sage scrub, cactus scrub, chaparral, oak woodlands, riparian woodlands, pine forests, marshes, and developed areas (e.g., towns, campgrounds). However, preferential use of some habitats has been detected. Island Foxes may prefer stabilized sand dunes (Sanchez and Hudgens 2012, Gregory et al. 2012, Garcelon and Hudgens 2012) and areas with higher topographic and vegetation structure diversity (USFWS 2012) such as shrublands and woodlands (Laughrin 1977, Crooks and Van Vuren 1996, Roemer 1999, Drake 2013). Conversely, some habitats appear to be used less, particularly types with low vegetation structure such as grasslands (Roemer 1999, Roemer and Wayne 2003).
Home range use by Island Foxes is influenced by various factors including topographic features, available habitat types, habitat-specific resource abundance, fox density, sex, and age (USFWS 2012). Mean home range sizes of 0.16-3.39 kmÂ² have been reported (Coonan et al. 2010a, Sanchez 2012, Drake 2013) Size generally is inversely related to fox density (Sanchez 2012) and is slightly larger for males. Also, foxes using grasslands tend to have larger home ranges than foxes using denser, more structurally diverse habitats. Den sites are variable and can occur in rocks, brush, log piles, earthen burrows, and man-made structures (Laughrin 1977, Moore and Collins 1995). Island Foxes exhibit both nocturnal and diurnal activity, and also are skilled climbers thereby allowing them to access resources in trees and large shrubs (Coonan et al. 2010a).Island Foxes are foraging generalists and consume a wide variety of items including rodents, birds, lizards, insects, snails, carrion, and fruits (Moore and Collins 1995, Cypher et al. 2011). Use of items varies by habitat-specific and island-specific availability, and also varies by seasonal availability (e.g., fruits, some insects, marine mammal carrion). Preferred items appear to include deer mice (Peromyscus maniculatus), lizards, beetles, Jerusalem crickets (Stenopalmatus spp.), earwigs (Forficula auricularia), and fruits of toyon (Heteromeles arbutifolia), manzanita (Arctostaphylos spp.), and prickly pear cactus (Opuntia spp.) (Cypher et al. 2011). Deer mice may be a particularly important food for parents to feed to growing pups due to ease of transport and high protein content (Laughrin 1977, Garcelon et al. 1999).
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
The Red List Status for the Island Fox is currently assessed as Near Threatened (it almost qualifies as threatened under criteria B1a and C2a. The species meets none of the criteria for the threatened categories (Critically Endangered, Endangered or Vulnerable). In regard to criterion A, population reduction, the species has not experienced a population reduction in the past 10 years or three generations. Four subspecies experienced declines in the 1990s, but have since increased significantly, to near pre-decline numbers. Criterion B concerns geographic range. The total range for the species is about 9,000 kmÂ², and the number of locations (considering past and future potential threats) is <10 (the species occurs on six islands) which would place the species in the Vulnerable category, but only if there was a continuing decline or extreme fluctuation in occurrence, occupancy, locations, or population size. Criterion C considers small population size. The number of mature individuals is approximately 4,000, whih would place the species in the Vulnerable category, but only if there was also a continuing decline and the number of mature individuals was <1,000 in each subpopulation, or if the population fluctuated extremely . Island Foxes do not meet criterion D, very small or restricted population size, because the number of mature individuals is >1,000 and number of locations is >5. Finally, Island Foxes do not meet the criteria for E, quantitative analysis. Recent estimates indicate that the probability of extinction in the next 50 years is <5% for each of the four Island Fox subspecies listed as endangered under the US Endangered Species Act (T. Coonan, National Park Service, C. Boser, The Nature Conservancy and J. King, Santa Catalina Island Conservancy, unpubl. data).
Although the species meets none of the criteria for the threatened categories, it is assessed as Near Threatened because of inherently small population sizes (none of the six subspecies exists at adult population levels considerably higher than 1,000 individuals), potential threats from disease and/or predation, and the continuing need for intensive management actions such as population size and survival rate monitoring, disease and Golden Eagle surveillance, and annual vaccination against rabies and canine distemper virus. If considered alone, some of the subspecies would likely meet criteria for a threatened category, due primarily to inherently small population sizes. However, previous Red List assessments have been conducted at the species level for Island Foxes. Because recent threats to subspecies have been mitigated, it is not necessary to consider Red List status for individual subspecies at this time.
According to IUCN Red List Guidelines (IUCN Standards and Petitions Subcommitee 2013), a species may be moved from a category of higher threat to one of lower threat if none of the criteria of the higher threat category has been met for five years or more. Therefore, to be moved to the Near Threatened category in 2013, Island Foxes must not have met criteria from any higher threat category (Critically Endangered, Endangered or Vulnerable) criteria in 2008 or later. The following demonstrates, category by category, that Island Foxes did not meet any of the threatened category criteria in 2008.
A. Population reduction:
As of 2008, had Island Foxes undergone a population decline over either 10 years or three generations (whichever is longer)? A recent life table matrix model (B. Hudgens, Institute for Wildlife Studies, unpubl. data) indicates Island Fox generation time is about four years. Therefore, from 1996-2008, was there a 90%, 70% or 50% decline in the overall number of island foxes? By 2008 the number of island foxes was approximately 2,500 adults, but the population in 1996 is unknown. In that time period, 1996-2008, four Island Fox subspecies had reached the nadir of their declines (in 1999-2000) and recovery was well under way on all islands, so much so that captive breeding had ceased on all islands by 2008. Thus, it is unlikely that there was a 50% or greater decline between 1996 and 2008, a period spanning three generations of Island Foxes.
B. Geographic range:
The range of Island Foxes comprises about 9,000 kmÂ², which meets the Vulnerable category if two of the following are met: the number of locations is less than 10, a continuing population decline, or extreme fluctuations. Although Island Foxes occur in <10 locations (six islands), there was no continuing decline in 2008, nor were there extreme fluctuations. Therefore, Island Foxes do not meet the geographic range criteria for any of the threatened categories.
C. Small population size and decline:
The number of mature Island Foxes was about 2,500 in 2008. That would place the species in the Endangered category, but only if there was a continuing decline, or a decline combined with either a) a low mature population size in each subpopulation, b) a high proportion of individuals occurring in just one subpopulation or c) or extreme fluctuations. Because there was no continuing decline in 2008, Island Foxes do not meet the small population size and decline criteria for any of the threatened categories.
D. Very small or restricted population:
The number of mature individuals in 2008 was 2,500, which is above the 1,000 required for a Vulnerable rating. Additionally, they did NOT have an area of occupancy of <20 kmÂ² or number of locations <6. Therefore, Island Foxes do not meet the very small or restricted population criteria for any of the threatened categories.
E. Quantitative Analysis:
There is no analysis that concludes that in 2008 the probability of extinction for Island Foxes was 50% in 10 years (Critically Endangered), 20% in 20 years (Endangered) of 10% in 100 years (Vulnerable). Thus, Island Foxes do not meet the quantitative analysis criteria for any of the threatened categories
- 2004Critically Endangered
- 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.
Fox populations on both San Miguel and Santa Cruz Islands declined by > 90% between 1995 and 2000. Similar declines also occurred on Santa Rosa and Santa Catalina Islands (Roemer 1999; Timm et al. 2000; Roemer et al. 2001a, 2002; Coonan 2003). By 2000, Island Fox populations on San Miguel and Santa Rosa islands had declined to only 15 individuals, all of which were brought into captivity (Coonan 2002, 2003; Coonan et al. 2010a). The Santa Cruz population dropped from an estimated 1,300 foxes in 1993 to as low as 50 foxes in 2001, including 10 pairs brought into captivity in 2002 (Roemer 1999, Roemer et al. 2001, Coonan et al. 2010a). Captive populations were maintained on the islands from which they were originally captured. Beginning in 2003, captive-bred foxes from each of the three northern islands (San Miguel, Santa Cruz and Santa Rosa) were released back into the wild. By 2008, all captive animals were released and populations were growing exponentially on all three islands. By 2011, wild fox populations had increased to an estimated 580 foxes with 400 adults on San Miguel Island, 450 foxes with 280 adults on Santa Rosa Island, and 1,200 foxes with 880 adults on Santa Cruz Island (Coonan 2012).
On Santa Catalina, Island Foxes were nearly completely eliminated on the eastern portion of the island by a canine distemper outbreak that swept through the population in 1999 (Timm et al. 2000), with only about 110 adult foxes remaining on the island in 2000. Translocations from the western portion of the island, beginning in 2003, have resulted in a steadily growing population, estimated at approximately 1,500 foxes in 2011. About 80% of the fox population now lives on the islandâs east end.
The San Clemente population has steadily increased from approximately 250 adults in 2001-2002 (Wolstenholme et al. 2003 ) to approximately 700 adults in 2011 (Gregory et al. 2012), with a total population (including young of the year) estimated around 1,100 (Garcia and Associates 2011). A small area of stabilized sand dunes on the north end of the island support the highest recorded density of foxes with density estimates ranging from 14->40 foxes/kmÂ² (Gregory et al. 2012, Sanchez and Hudgens 2011). Outside of the dunes, fox densities ranged from 2.5-7.8 adults/kmÂ² with densities generally highest in the north and lowest in the south (Gregory et al. 2012).
In contrast to the other populations, the San Nicolas Island Fox population has remained relatively stable over the past 10 years, though there is anecdotal and genetic evidence of a severe population decline to an effective population size of less than 10 breeding individuals in the 1970s (Laughrin 1980, Aguilar et al. 2004). Since 2000, estimated population size has fluctuated from 500-700 adults and 600-800 total, including young of the year (Garcelon and Hudgens 2012). The highest densities of animals occur in the stabilized dunes and coastal sage scrub on the western end of the island, where adult fox densities of over 25 foxes/kmÂ² have been recorded. Fox densities are much lower in the grasslands and barren cliffs in the south and east of the island, where recorded densities are only 1.9 foxes/kmÂ² (Garcelon 2010 ).
All current estimates of density and population size in island foxes have been derived from trapping data using modifications of a capture-recapture approach (Roemer et al. 1994). Density estimates prior to 2005 were generally calculated by dividing estimated population size within a trapping grid by the effective trapping area including a buffer determined by the mean-maximum distance moved (MMDM) by captured individuals. More recent density estimates were generally estimated from spatially-explicit mark-recapture analyses (Efford et al. 2004). Island-wide estimates were extrapolated either by simply multiplying the average densities of trapped areas by the total island area, or by multiplying densities of trapped areas within different habitat types by the area of each habitat on the island.
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).
Island Foxes have naturally low population levels (less than 1,500 on the larger islands and less than 500 on San Miguel) (Coonan et al. 2010a). Furthermore, they have extremely low levels of genetic variability (Gilbert et al. 1990, Wayne et al. 1991, Goldstein et al. 1999, Aguilar et al. 2004), and thus reduced ability to adapt to future environmental change. The possible introduction of new diseases from the mainland remains a threat to populations on all islands. Thus, these foxes will always be a âconservation reliantâ species, requiring careful monitoring and rapid management interventions to survive (Scott et al. 2010).
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).
In 2004, four of the six Island Fox subspecies were federally listed as endangered by the U.S. Fish and Wildlife Service (USFWS) under the federal Endangered Species Act (USFWS 2004). The northern Island Fox subspecies (San Miguel, Santa Rosa and Santa Cruz) were listed due to population declines caused by Golden Eagle predation, and Santa Catalina Island Foxes were listed because of a population decline likely due to canine distemper virus. The San Nicolas and San Clemente subspecies were not listed as endangered by USFWS, because USFWS had been petitioned only to list the three northern subspecies and the one on Santa Catalina Island (USFWS 2004). All six subspecies had been previously listed as threatened by the state of California (California Department of Fish and Game 1987).
Need for recovery actions
Northern Channel Islands
Dramatic fox population declines on San Miguel, Santa Rosa and Santa Cruz Islands were detected during the 1990s. The Island Fox population on San Miguel declined from an estimated 450 adults in 1994 to 15 in 1999 (Coonan et al. 2005). The Santa Cruz population declined from as many as 2,000 adults in 1994 to 50â60 in 2000 (Coonan et al. 2010a). Foxes on Santa Rosa may have numbered more than 1,500 in 1994 (Roemer et al. 1994) but declined to 15 animals by 2000 (Coonan and Rutz 2002). Prior to implementation of Island Fox recovery efforts, Roemer (1999) estimated time to extinction at five years for Island Foxes on San Miguel and 12 years for Island Foxes on Santa Cruz.Evidence from radio-telemetry studies showed that predation by Golden Eagles was the primary mortality factor for Island Foxes on the northern Channel Islands, and caused the massive decline of the three northern subspecies from 1994 to 2000 (Roemer et al. 2001). Golden eagle predation was identified as the cause of death for 19 of 21 radio-collared Island Foxes on Santa Cruz Island from 1993 to 1995 (Roemer et al. 2001). On San Miguel Island in 1998â1999, four of eight radio-collared Island Foxes were killed by Golden Eagles in a 4-month period (Coonan et al. 2005). Until the 1990s, Golden Eagles, which prey mainly on small mammals, had never bred on the Channel Islands, and their recent colonization of the islands was due to a prey base, feral pigs (Sus scrofa) and mule deer (Odocoileus hemionus), that was not present prehistorically (Latta et al. 2005; Collins and Latta 2006). The absence of Bald Eagles (Haliaeetus leucocephalus), which bred historically on the islands and prey mainly on fish and seabirds and whose presence may have kept Golden Eagles away, may also have allowed Golden Eagle colonization of the islands (Roemer et al. 2001). Island Foxes evolved in the absence of significant diurnal aerial predators such as Golden Eagles, and therefore may have been more vulnerable to predation than other small carnivores. Moreover, on much of the northern Channel Islands, historic sheep grazing changed the predominant vegetation from shrub to non-native grasslands, which offer much less cover from aerial predators.
Santa Catalina Island
At the same time that the National Park Service (NPS) was dealing with the issue of eagle predation and very low fox populations, The Santa Catalina Conservancy and its contractor, Institute for Wildlife Studies, were addressing a massive population decline of Island Foxes in 1999-2000, apparently caused by canine distemper virus (CDV). Foxes had declined on the eastern portion of the island, but not on the western portion, which was separated from the western portion by a narrow isthmus. The presence of CDV antibodies in Island Fox blood samples, observation of disoriented foxes, and the presence of CDV in a fox carcass led to the conclusion that the rapid decline (within one year) had been most likely caused by an outbreak of CDV. Later analysis indicated that the CDV was most like the strain present in raccoons, suggesting that the source of the diseases was not the unvaccinated dog and cat population on the island, but perhaps a stowaway raccoon (Coonan et al. 2010a).
The U.S. Fish and Wildlife Service issued a draft recovery plan for the four listed subspecies in 2012 (USFWS 2012). The plan presented recovery criteria that were based on population risk and on threats. To meet population risk-based criteria, fox populations must demonstrate demographic characteristics consistent with long-term viability, as measured by a population recovery tool that estimates extinction risk using adult mortality and population size estimates (Bakker and Doak 2009). To meet threat-based recovery criteria, land managers must develop monitoring programs and plans for mitigating the two primary threats to Island Foxes, disease and predation. The planâs recovery actions included removing the threats of predation and disease, managing captive island fox populations for recovery, and establishing island fox monitoring strategies. In reality most of those recovery actions had been completed by the land management agencies prior to release of the recovery plan.
Development of recovery actions
The major recovery actions for Island Foxes were those recommended by an ad hoc group of scientists first convened in 1999 by the NPS to recommend emergency actions that would prevent the extinction of Island Foxes (Coonan et al. 2010a). From 1999â2012, the NPS annually convened a group of experts to help evaluate the status of Island Foxes on Park lands, and to make findings regarding appropriate recovery actions. The Island Fox Conservation Working Group comprised a loose affiliation of public agency representatives, landowners, conservancies, zoological institutions, non-profits, and academics concerned about conservation efforts for the Island Fox. The working group served as a forum for information exchange and evaluation of recovery efforts, dividing into subject matter groups to tackle most issues. In most years the subgroups were concerned with captive breeding, wild fox populations, fox health (veterinary) issues, and education. The group annually reported the status of Island Foxes on all islands, listed findings in regard to threats to the species, and recommended appropriate mitigation actions. From 2004-2006 USFWS used the Island Fox Conservation Working Group to develop its draft Island Fox recovery plan.
In 2003, the Park completed a recovery strategy for Island Foxes on the northern Channel Islands (Coonan 2003). The recovery strategy focused on the major recovery actions of Golden Eagle translocation, Island Fox captive breeding and reintroduction, and disease mitigation via vaccination, as well as the larger, ecosystem-level actions of non-native ungulate removal and reintroduction of Bald Eagles. On Santa Catalina Island, the CDV-caused population decline was addressed by the Santa Catalina Island Conservancy and the Institute for Wildlife Studies. At the Conservancyâs request, IWS developed recovery actions, which included development of a vaccine against CDV, development of a captive breeding program, and translocation of foxes from the still populous western portion to the sparsely populated eastern portion of the island (Coonan et al. 2010a).
Implementation of recovery actions
Since 1999, recovery actions have been implemented, and most of them completed, on the northern Channel Islands and on Santa Catalina Island, and conservation measures have been implemented on the two other islands with foxes (San Nicolas and San Clemente). These actions included captive breeding and reintroduction of Island Foxes; capture and translocation to the mainland of Golden Eagles; development of a vaccination program for wild Island Foxes; development of epidemic response plans; removal of non-native ungulates from the northern Channels Islands; reintroduction of Bald Eagles; and development and implementation of Island Fox monitoring programs.
Development of captive breeding programs occurred simultaneously on the northern Channel Islands (for San Miguel, Santa Rosa and Santa Cruz Island Foxes) and on Santa Catalina Island (Coonan et al. 2010a). Upon receiving recommendations from the Island Fox Conservation Working Group, the Park began taking emergency recovery actions in 1999, focusing on two measures, the removal of the existing Golden Eagles on the islands, and captive breeding of the critically low Island Fox populations.
Because Island Foxes had not been bred in captivity before, the Park worked with local zoo staff, the Association of Zoos and Aquariums and other national experts to establish animal husbandry methods, including facility design and construction, diet, genetic management, pairing and breeding and release techniques (Coonan et al. 2010a, 2010b). Captive breeding was begun in situ on each island, because each subspecies was managed individually, and mainland facilities would have exposed captive foxes to a suite of pathogens unknown on the islands. Captive breeding began on San Miguel in 1999 and on Santa Rosa in 2000, when the remaining 15 foxes on each island were brought into captivity, respectively. In 2001 the IFCWG recommended beginning captive breeding on Santa Cruz, to avoid starting captive breeding with the kind of perilously low numbers that the programs on San Miguel and Santa Rosa began with. Accordingly, 20 foxes were brought into captivity on Santa Cruz in 2002. On Santa Catalina Island, IWS built pens and brought 12 pairs of foxes from the populated west end into captivity in 2001.
Despite the low number of founders, Island Fox captive populations grew quickly, and reached captive facility capacity, and the level at which releases could begin, in 2001 on Santa Catalina, 2003 on Santa Rosa and Santa Cruz, and 2004 on San Miguel. Island Fox captive breeding encountered challenges such as low reproductive success later in the program, evidence of stress in captive foxes, male aggression, female abandonment of pups, and an outbreak of mastitis in the Santa Rosa and San Miguel facilities. Video monitoring of captive foxes allowed identification of factors that led to successful reproduction and rearing (Calkins et al. 2013). Releases ceased in 2004 on Santa Catalina, and 2007-2008 on the northern Channel Islands. On the northern islands, reproductive success in the wild had begun to outpace that in captivity, and so all foxes were released by 2008. There are now no Island Foxes in captivity. Over the captive breeding period, 254 foxes were released to the wild on the northern islands and 57 on Santa Catalina, where reintroduction was augmented by translocation of juvenile foxes from the populous West end to the East end.
Reintroduction was very successful, due to generally high survival and high reproductive success of released foxes (Coonan and Schwemm 2009). Wild populations grew rapidly on San Miguel, Santa Cruz and Santa Catalina, though on Santa Rosa fox survival, and thus population growth, was retarded by Golden Eagle predation (Coonan et al. 2010a). Annual rate of increase (lambda) for recovering fox populations ranged from 1.3-1.9, and by 2011-2012, the adult populations on San Miguel, Santa Rosa and Santa Cruz were estimated at 400, 500, and >900 individuals, respectively, and there were >1500 total foxes on Santa Catalina (Coonan 2012). Foxes had reached pre-decline levels on San Miguel and Santa Cruz, 12 years after declines brought them perilously close to extinction.
Development of Vaccines
Staff from IWS worked with the Smithsonian National Zoological Park on the use of a vaccine against CDV for Island Foxes. The Canary pox virus recombinant CDV vaccine was tested in a small sample of Island Foxes and proved safe and effective, with vaccinated foxes seroconverting and exhibiting positive antibody titers. The vaccine was thereafter administered to all captive foxes on all islands and later to a portion of the wild populations, upon the advice of the Island Fox health group (Coonan et al. 2010a, Coonan 2012). Although the effectiveness of the vaccine has not been tested in a challenge study, evaluation indicates vaccination does produce antibody response consistent with protection, though annual booster is required to maintain adequate antibodies (Coonan et al. 2012). Vaccination of Island Foxes against CDV will continue indefinitely.
Because there is a naturally-occurring morbillivirus in Island Fox populations that likely confers some immunity against CDV (Clifford et al. 2006), not all wild foxes are vaccinated, to allow circulation of the morbillivirus. On most islands, foxes are vaccinated using a âvaccinated coreâ strategy, in which 80-100 foxes are vaccinated in one or two geographic core areas. This allows the natural morbillivirus to circulate among foxes on the rest of the island; protects foxes in areas that may be access points for CDV (such as near harbors) and theoretically protects a core group of individuals that could be used to start a captive breeding program, should CDV decimate the remainder of the population. On Santa Catalina, however, foxes are vaccinated in an island-wide strategy, because of the large number of landing sites on that island.
Wild Island Fox populations are also currently vaccinated against rabies, because a rabies epidemic among foxes could not be adequately mitigated, once detected. Unlike canine distemper virus, there is no naturally-occurring rabies among island foxes, so the vaccinated core strategy is not implemented; all trapped foxes are vaccinated against rabies (Coonan 2012).
Golden Eagle Removal
The Park established a cooperative agreement with the Santa Cruz Predatory Bird Research Group (SCPBRG) in 1999 for the purpose of relocating Golden Eagles from the northern Channel Islands. Personnel from the SCPBRG began eagle surveys and removal on Santa Cruz Island, the island with the most recent sightings, in late summer 1999. Golden Eagles were discovered breeding on both Santa Cruz and Santa Rosa Islands. By the end of 2006, 44 Golden Eagles had been removed, mostly from Santa Cruz Island, the majority by bownet trapping. Captured birds were released in north-eastern California, and satellite telemetry on the first released birds indicated that none attempted to return to the islands (Latta et al. 2005). Island Fox survival increased as the number of eagles on the island declined (Coonan et al. 2010a).
Genetic analysis of blood samples from captured eagles suggested that initial colonization of the islands by Golden Eagles had been rapid, perhaps the result of one colonization event by a family group (Sonsthagen et al. 2012). Rapid growth of the island eagle population ensued, to the point where carrying capacity was reached and young eagles began dispersing from the island population to the mainland. This implies that preventing future recolonization of the islands by dispersing mainland eagles will be crucial to Island Fox persistence. Actions that will prevent colonization include rigorous monitoring for evidence of predation and eagle presence, removal of non-native eagle prey, and re-establishement of a robust breeding population of territorial Bald Eagles.
Larger ecosystem recovery actions
The team of experts first convened by NPS in 1999 concluded that mitigating Golden Eagle predation on Island Foxes required not only the immediate, emergency recovery actions of eagle relocation and Island Fox captive breeding, but also larger, ecosystem-level actions that would tip the balance away from continued Golden Eagle use of the islands and toward conditions that would allow foxes to persist. Accordingly, the team called for both removal of feral pigs from Santa Cruz Island, since the non-native pigs facilitated the âhyperpredationâ visited upon foxes (Roemer et al. 2001), and the reintroduction of Bald Eagles to the northern Channel Islands, positing that the presence of breeding Bald Eagles would discourage nesting by Golden Eagles (Coonan and Rutz 2001). With the later discovery of deer bones in Golden Eagle nests on Santa Rosa Island (Latta et al. 2005; Collins and Latta 2006), the need to remove that prey source became apparent (Coonan and Dennis 2007), and the USFWS Island Fox recovery plan called for the removal of non-native ungulates from that island (USFWS 2012).
Reintroduction of Bald Eagles
The restoration of Bald Eagles to the northern Channel Islands, funded by the Montrose Settlements Restoration Program, comprised annual releases of young eagles from 2002-2006. Breeding by released Bald Eagles began in 2006, and as of 2012 there were >40 bald eagles on the northern Channel Islands, with breeding occurring on Anacapa, Santa Cruz and Santa Rosa islands (Sharpe 2012).
Removal of non-native ungulates
Prior to the discovery that feral pigs supported Golden Eagles on Santa Cruz Island and so facilitated predation on Island Foxes, the NPS had sought to remove feral pigs from that island because of the impacts to natural and cultural resources from pig rooting and foraging (NPS 1985). Accordingly, in 2005-2006 the NPS and The Nature Conservancy, co-owners of Santa Cruz Island, cooperated to remove feral pigs (>4,000 total) from Santa Cruz Island, thereby eliminating that non-native prey source for Golden Eagles (Morrison et al. 2007, Coonan et al. 2010a).
Non-native ungulates had existed on Santa Rosa Island since the early 20th century, when they were bought to the island for hunting purposes. Their phased removal was scheduled as part of a court settlement among the NPS, USFWS, the former island owners, and environmental groups to address ungulate impacts to water quality and endangered plant species (Coonan et al. 2010a). By the end of 2012, all elk had been removed from the island, and only a handful of deer remained (T. Coonan, NPS, unpubl. data).
Thorough Island Fox monitoring programs have been implemented on all six islands. For the four islands with listed subspecies, monitoring programs were established to track effectiveness of recovery actions and to chart the recovery of populations. These initial monitoring efforts have evolved into longer-term programs designed to track Island Fox population size, survival, mortality sources, and exposure to disease.
Because reintroduction and/or translocation occurred on all four of islands with listed subspecies, released foxes were radio-collared to monitor their survival and identify mortality sources. As of 2013, a sample of radio-collared foxes was maintained on all six islands to detect mortality causes such as disease. Annual survival of Island Foxes has been tracked for listed subspecies, and shows increased survival over time, with recovered populations exhibiting annual survival of 80-90% (Coonan et al. 2010a).
On the four islands with listed subspecies, a portion of the 50 or so radio-collared foxes are disease sentinels. These are young, unvaccinated foxes whose mortality may detect emerging diseases as well as the presence of diseases against which a portion of each Island Fox population is vaccinated (rabies and CDV).
For naturally small populations such as those of the Island Fox, population size is important to track, both to chart recovery of populations and to assess demographic viability. Prior to the declines of the 1990s, the NPS tracked population trends of Island Foxes on San Miguel, as part of its longterm ecological monitoring program. Population size of the four endangered subspecies has been monitored since reintroductions or translocations began, and population trends on San Clemente are also monitored. Guidance for population monitoring of all fox populations was developed through the efforts of the Island Fox working group (Rubin et al. 2007), who recommended using spatially explicit capture recapture (SECR) methods on multiple small (2 x 6 trap) grids. Density and population estimates from annual trapping have been used to document recovery of listed Island Fox populations (Coonan et al. 2010a).
Results from population and mortality monitoring have been incorporated into a ârecovery toolâ for land managers to use to assess recovery status of listed fox subspecies. Recent demographic modelling incorporated life-history characteristics of the well-studied Island Fox with environmental drivers and uncertainty to develop extinction probabilities for combinations of population size and annual mortality (Bakker et al. 2009, Bakker and Doak 2009). The demographic traits that best predicted extinction risk were adult population size and adult annual mortality rate, assessed jointly (Bakker and Doak 2009). Subspecies-specific graphs were developed that plotted risk isoclines across range of three-year average adult population sizes and mortality rates. Three-year averages of both adult population size and adult mortality have become the basis for assessing demographic recovery criteria for the Island Fox. Island managers and the Island Fox working group identified a predicted risk of quasi-extinction (decrease to a population size of <30) of less than five percent over 50 years as the population condition consistent with recovery. To account for uncertainty, the joint 80 percent confidence intervals for both population size and mortality must lie within the 5 percent extinction risk isoclines. Island Fox subspecies must meet this standard for five consecutive years before they may be considered for de-listing. This standard has now been adopted by the USFWS in the draft recovery plan for the Island Fox (USFWS 2012) as the demographic recovery criterion. As of 2012, use of the recovery tool indicated that San Miguel, Santa Cruz and Santa Catalina Island Foxes were close to demonstrating biological recovery, and Santa Rosa Island Foxes were several years from doing so (Coonan 2012).
Island Foxes from all islands are periodically surveyed for evidence of disease exposure, as result of recommendations from the Island Fox working group regarding vaccination and serological testing. The Fox Health group recommended that blood samples from Island Fox populations be collected annually, and that such samples tested at least once every five years for evidence of exposure to CDV, canine parvovirus (CPV), canine adenovirus (CAV) and Toxoplasma. Island Fox populations had been tested previously for disease (Garcelon et al. 1992, Roemer et al. 2001, Clifford et al. 2006), and recent serological testing (Coonan 2012) confirmed earlier conclusions that each Island Fox subspecies has had a unique history of pathogen exposure, and vulnerability to various canid diseases is not equivalent among subspecies.
Threat mitigation plans
The USFWSâ draft Island Fox recovery plan requires threat mitigation plans to be developed by each land management agency before Island Fox subspecies can be delisted. Such plans must demonstrate the agencyâs capability and willingness to detect and mitigate threats posed by the two most onerous mortality factors, predation and disease. An epidemic response plan has been developed for San Clemente Island Foxes (Hudgens et al. 2011) and plans are currently being developed for island foxes on the northern Channel Islands and Santa Catalina Island (B. Hudgens, IWS, unpubl. data). The plans detail appropriate pathogen monitoring and disease-specific mitigation actions, incorporating the specific operational capabilities of the respective agencies.
Gaps in knowledge
In some areas of San Nicolas Island, foxes have remained at a stable population density greater than 25 foxes/km2; however, this very high density is unusual in carnivore populations. Additional research on habitat use, diet and small-scale resource use, abundance, and fecundity are needed to explore density dependence and estimate carrying capacity on other Channel Islands. Research exploring the ecological drivers of the foxâs home range size, which varies significantly between studies, could have applications for disease transmission rates and inter-species competition, and ultimately inform us on density dependence by habitat type.
Many of the islands contain meso-predator species that likely compete with the Island Fox. San Clemente, Santa Catalina and until recently, San Nicolas contained non-native feral cats. The removal of feral cats from San Nicolas Island in 2011 presents a unique opportunity to document the effects of competitor removal from an isolated and well-documented system. Santa Rosa and Santa Cruz Island contain the only native meso-carnivore, the Island Spotted Skunk (Spilogale gracilis amphiala), which likely competes with the Island Fox (Crooks and Van Vuren 1995, Roemer et al. 2002). Foxes are competitively dominant to skunks (Roemer et al. 2002), and the latter increased on both islands when foxes declined. Skunks have apparently declined on Santa Cruz Island during the recent recovery of foxes, and have not declined on Santa Rosa, where the recovering fox population is perhaps one-half of its pre-decline number (Coonan and Guglielmino 2012). Further refinement knowledge is required about the relationship between these two meso-predators.
Apart from the threat of non-native predators, the greatest threat on these conservation islands is the possibility of a mainland disease introduction. A number of recent studies have addressed the threat of disease, including previous pathogen exposure (Clifford et al. 2006), pathogen transmission (Sanchez 2012), and Canine distemper virus titer persistence. However, additional research and management may be needed to prevent outbreaks, as new transmittable diseases arrive on the California coast.
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 Park 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).