Island Fox
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| Urocyon littoralis (Baird, 1857) |
The Island Fox (Urocyon littoralis) is a small fox that is native to six of the eight Channel Islands of California. It is the smallest fox species in the United States. There are six subspecies of the fox, each unique to the island it inhabits, 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.
The Island Fox shares the Urocyon genus with the mainland Gray Fox, the fox from which it is descended. Its small size is a result of island dwarfing, a kind of allopatric speciation. Because Island Foxes are geographically isolated they have no immunity to parasites and diseases brought in from the mainland and are especially vulnerable to those domestic dogs may carry. In addition, Golden Eagle predation 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.
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[edit] Taxonomy and evolution
The Island Fox shares the Urocyon genus with the mainland Gray Fox (Urocyon cinereoargenteus), the fox from which it is descended. Its small size is a result of island dwarfing, a kind of allopatric speciation (that is, speciation brought about by geographic isolation — in this case from larger relatives on the mainland), combined with natural selection for smaller size because of the limited resources of the islands.
There are six subspecies of Island Fox, each of which is native to a specific Channel Island, and which evolved there independently of the others. The subspecies are
- Urocyon littoralis littoralis 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.
Foxes from each island are capable of interbreeding, but have genetic and phenotypic distinctions that make them unique; for example, the subspecies have differing numbers of tail vertebrae.
The small size of the Island Fox is an adaptation to the limited resources available in the island environment. The foxes are believed to have "rafted" to the northern islands between 10,400 and 16,000 years ago.[2] 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.[3]
Based on the limited fossil record and genetic distance from their Gray Fox ancestors, the northern Island Foxes are probably the older subspecies, while the San Clemente Island Foxes have been only resident on their island for about 3,400–4,300 years, and the San Nicolas Island Foxes established themselves as an independent group about 2,200 years ago. The Santa Catalina Island Foxes are potentially the most recently evolved subspecies, having been on their island for about 800–3,800 years.[2][4] The foxes 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 foxes.
[edit] Physical description
The Island Fox is much smaller than the gray fox, roughly the size of a house cat, and is the second smallest of all foxes after the Fennec. 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. Island foxes weigh between 1.3 and 2.8 kg (2.8–6.2 lb.). The male is always larger than the female.[5] The largest of the subspecies occurs on Santa Catalina Island and the smallest on Santa Cruz Island.[5]
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.[5] 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.
[edit] Reproduction
Island Foxes typically form monogamous breeding pairs and are frequently seen together beginning in January and through the breeding season, from late February to early March. The gestation period is 33–50 days. The Island Fox gives birth in a den, a typical litter having one to five kits, with an average of two or three. Kits 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.[5]
[edit] Ecology and behavior
Their preferred habitat is complex layer vegetation with a high density of woody, perennially fruiting shrubs. The foxes live in all of the island biomes including temperate forest, temperate grassland and chaparral, with no island supporting more than 1,000 foxes. Island Foxes eat fruits, insects, birds, eggs, crabs, lizards, and small mammals, including the deer mouse. The foxes tend to move around by themselves, rather than in packs. They are generally nocturnal, albeit with peaks of activity at dawn and dusk. Activity also fluctuates with the season; they are more active during the day in summer than they are in winter.[5]
Island Foxes are not intimidated by humans, as they have historically been at the top of the island food chain and had no natural predators. They are quite easy to tame and are generally docile.[5] Island foxes communicate with each other using auditory, olfactory and visual signals. A dominant fox uses vocalizations, staring, and ear flattening to cause another fox to submit. They mark territory with urine and feces.
[edit] Conservation status
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.[6][7] Golden Eagle predation, discovered when foxes were radio-collared and monitored, proved to be the cause of the high mortality rates.[8]
Golden Eagle predation is the primary cause of Island Fox mortality. Golden Eagles were uncommon visitors to the Channel Islands before the 1990s, and the first Golden Eagle nest was recorded on Santa Cruz Island in 1999.[9] Biologists propose that the eagle may have been attracted to the islands by the expanding populations of feral livestock (such as pigs), as well as the decimation of the local Bald Eagle population due to DDT exposure in the 1950s—the Bald Eagles would have deterred the Golden Eagles from settling on the islands while they themselves subsisted on fish.[8] [10] Feral pigs on Santa Cruz Island and introduced deer and elk on Santa Rosa Island have likely provided alternative prey for Golden Eagles that has allowed the latter to colonize the islands and wreak havoc on the unwary island fox. [11]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, island foxes 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 3 subspecies of the island fox from extinction.[12]
Introduced diseases or parasites can devastate Island Fox populations. Because Island Foxes are isolated they have no immunity to parasites and diseases brought in from the mainland and are especially vulnerable to those domestic dogs may carry. A canine distemper outbreak in 1998 killed approximately 90% of Santa Catalina Island's fox population.[9] (It is difficult to vaccinate against or treat foxes for parasites and disease in the wild.)
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 severely endangered Loggerhead Shrikes in residence on San Clemente Island. The Island Fox population on San Clemente Island 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.[13] With the gradual recovery of the shrike population on San Clemente Island, the Navy no longer controls the foxes.[14] Automobile fatalities have also been high on San Clemente, San Nicolas, and Santa Catalina Islands.
[edit] Federal protection
In March of 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.[15] The IUCN still lists them as "lower risk."
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.[7] 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.[16]
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 eagles 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.[17]
Because the Channel Islands are almost entirely owned and controlled by either the Catalina Island Conservancy or the federal government, the fox has a chance to receive the protection it needs, including constant supervision by interested officials without the ongoing threat of human encroachment on its habitat.
[edit] See also
[edit] References
- ^ Roemer et al (2004). Urocyon littoralis. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes justification for why this species is critically endangered
- ^ a b Wayne, R.K. et al. 1991. A morphological and genetic-study of the Island fox, Urocyon littoralis. Evolution, 45:1849-1868
- ^ Collins, P.W. 1991. Interaction between Island Foxes (Urocyon littoralis) and Indians on islands off the coast of southern California. I Morphologic and archaeological evidence of human assisted dispersal. Journal of Ethnobiology, 11:51-82
- ^ Gilbert, D.A. et al. 1991. Genetic fingerprinting reflects population differentiation in the California Channel Island fox. Nature 344:764-767
- ^ a b c d e f Moore, C.M. and Collins, P.W. 1995. Urocyon littoralis. Mammalian Species 489:1-7
- ^ Roemer, G.W.. et al. 1994.Roemer, G.W., D.K. Garcelon, T.J. Coonan, & C. Schwemm. 1994. The use of capture-recapture methods for estimating, monitoring, and conserving island fox populations. Pages 387-400 in W.L. Halvorsen and G.J. Maender, eds. The Fourth California Islands Symposium: update on the status of resources. Santa Barbara Museum of Natural History, Santa Barbara, California.
- ^ a b Coonan, T.J. et al. 2004. Island fox recovery program 2003 Annual Report. National Park Service, Channel Islands National Park
- ^ a b Roemer, G. W., C. J. Donlan & F. Courchamp. 2002. Golden eagles, feral pigs and insular carnivores: How exotic species turn native predators into prey. Proceedings of the National Academy of Sciences, USA 99: 791-796.
- ^ a b Channel Islands National Park's Island Fox Home Page
- ^ Roemer, G.W. et al. 2001. Feral pigs facilitate hyperpredation by golden eagles and indirectly cause the decline of the island fox. Animal Conservation 4:307-318
- ^ Collins, P. W., and B. C. Latta. 2006. Nesting Season Diet of Golden Eagles on Santa Cruz and Santa Rosa Islands, Santa Barbara County, California. Santa Barbara Museum of Natural History Technical Reports - No. 3.
- ^ Courchamp, F., R. Woodroffe & G. Roemer. 2003. Removing protected populations to save endangered species. Science 302:1532.
- ^ United Sates Navy. 2000. San Clemente Island Range Complex Environmental Impact Study, San Clemente Loggerhead numbers on the increase
- ^ Kelly Brock, San Clemente Loggerhead Shrike Co-ordinator, personal communication.
- ^ U.S. Environmental Protection Agency. 2004. Endangered and Threatened Wildlife and Plants; Proposed Designation of Critical Habitat for the San Miguel Island Fox, Santa Rosa Island Fox, Santa Cruz Island Fox, and Santa Catalina Island Fox
- ^ Kohlmann, S. G. et al. 2003. Island fox recovery efforts on Santa Catalina Island, California, October 2001–October 2002, Annual Report. Ecological Restoration Department, Santa Catalina Island Conservancy, Avalon, California.
- ^ Catalina Island Conservancy. Catalina Island Fox
