Last updated: May 21, 2021
The island fox only lives on six of the eight Channel Islands off the coast of southern California--they are found nowhere else on Earth. Each island population is recognized as a separate endemic or unique subspecies.
The island fox, a descendant of the mainland gray fox, is the largest of the Channel Islands' native mammals, but one of the smallest canid species in the world.
Although foxes have always existed at low population sizes, four island fox subspecies underwent catastrophic declines in the 1990s. On San Miguel, Santa Rosa and Santa Cruz Islands at Channel Islands National Park, the decline was attributed to predation by golden eagles. The presence of non-native ungulates as a food source in addition to the DDT-caused decline of bald eagles, a natural competitor, facilitated the establishment of golden eagles as resident breeders on the islands. By 2000, predation on island foxes resulted in population declines to 15 individuals on San Miguel and Santa Rosa Islands, and less than 80 on Santa Cruz Island. In 2004, each of the park's island fox subspecies were federally listed as endangered.
In 1999, Channel Islands National Park began an island fox recovery program that included captive breeding and reintroduction of foxes, removal of resident golden eagles, re-establishment of bald eagles, and removal of non-native ungulates. This coordinated, organized and highly focused strategy was able to reverse the certain extinction of an endangered population. Today, the population has recovered within the park. Population trend and annual survival are currently monitored to ensure that recovery continues and future threats to the park's island fox subspecies are identified.
Quick and Cool Facts
- It is the only carnivore unique to California.
- Although the island fox is one of the smallest canids in the world, it is the largest native terrestrial mammal on the Channel Islands.
- The island fox is one-third smaller than its mainland ancestor, the gray fox. At 12 to 13 inches in height and 4 to 5 pounds, the island fox is about the size of a housecat.
- Some individuals have been known to live up to 15 years.
- Unlike nocturnal gray foxes, which hunt exclusively at night to avoid predators, island foxes have no natural predators, allowing them to be active duringdaylight hours with peaks in activity occurring at dusk and dawn.
- Visually, island foxes show signs of dominance or submission through facial expressions and body posture.
- They communicate by barking and sometimes growling.
- Their keen sense of smell plays an important role in the marking of territories. Island foxes are known to scent-mark their territories with a few drops of urine and tend to concentrate scats in particular areas, often conspicuously positioned on well-traveled paths.
The island fox is one third smaller than its mainland ancestor the gray fox. Environmental and ecological factors such as overcrowding, reduction in predators, food limitations, and genetic variations could have contributed to the natural selection for a smaller size.
The island fox has similar markings to the gray fox. They have gray coloring on the back, rust coloring on the sides,and white underneath. The face has a distinctive black, white, and rufous-colored patterns.
On each of the six islands, a different subspecies occurs, distinguished by both genetic and physical differences. For example, San Miguel Island foxes have shorter tails, due to one less tail vertebra, and longer noses than the other island foxes.
The island fox is found on six of the islands in the Southern California bight, including the three largest islands in the Channel Islands National Park (Santa Cruz, Santa Rosa and San Miguel islands). The other three islands which island foxes inhabit San Nicolas and San Clemente, owned by the US Navy, and popular Santa Catalina Island, which in large part is managed by the Catalina Island Conservancy.
Older research on the island fox dated them back on the northern Channel Islands to 10,400 to 16,000 years ago. Yet, geologists believe the northern Channel Islands were never connected to the mainland. The most plausible and accepted theory for foxes crossing the water barrier of the Santa Barbara Channel is one of "rafting." During the last ice age, 10-20,000 years ago, ocean levels were up to 400 feet lower than today's. The channel between the islands and mainland narrowed, perhaps to just four to five miles across. The northern islands became one large island we call Santarosae. The gray fox could have rafted on debris propelled by storms and/or currents. As the climate warmed and the ocean levels began to rise, Santarosae became the islands of Anacapa, Santa Cruz, Santa Rosa, and San Miguel. Due to the lack of a fresh water source, the foxes did not persist on Anacapa, but the other three islands had suitable habitat for foxes.
Recent archeological work, however, only dates the oldest island fox fossil at about 6,000 years before present, which is several thousand years after native people populated the island. This raises the possibility that gray foxes were brought to the islands by humans, and rapidly evolved into a smaller, separate species after that.
Island foxes brought to the southern Channel Islands of Santa Catalina, San Nicolas, and San Clemente by the Chumash native people who traded with the Gabrielino people of the southern islands. The Chumash considered the fox to be a sacred animal--a pet of the sun, and possibly a dream helper. The island Chumash performed a fox dance and probably used the pelts of foxes to make articles like arrow quivers, capes, and headdresses.
The climate of the California Channel Islands is semi-arid, and though rainfall amounts differ among islands the average rainfall across all islands is less than six inches per year. The native island vegetation is mostly coastal scrub, but these habitats have been heavily modified by the effects of introduced grazing animals and other human impacts. The northern islands (San Miguel, Santa Rosa and Santa Cruz) have significant areas dominated by non-native plant species, such as annual grasses and iceplant, whereas the southern islands (Santa Catalina, San Clemente and San Nicolas) have greater development impacts such as the naval bases and the town of Avalon. The larger islands (Santa Cruz, Santa Catalina, and San Clemente) also have perennial streams that support riparian vegetation and tree species. Foxes are found in most of these habitats on these islands, but they prefer shrubby or wooded areas such as chaparral, coastal scrub and oak woodlands.
Island foxes give birth to their young in simple dens, which are usually not excavated by the foxes themselves. By two months of age, young spend most of the day outside the den and will remain with their parents throughout the summer. Some pups disperse away from their natal territories by winter, although others may stay on their natal territories into their second year.
Island fox diets vary based upon food item diversity of the individual islands. On San Rosa Island, where food item diversity is high, deer mice, Jerusalem crickets, beetles, and earwigs are the preferred food. On other Channel Islands, diets include plant items such as fruits from cactus, manzanita, saltbushes and seafigs, as well as insects and deer mice when they are present. Occasionally, foxes forage along the shoreline for crabs and other marine invertebrates.
Island foxes are generally monogamous (mate for life), and breed only once a year. Pairs are seen together frequently beginning in January, and mating takes place in late February to early March. The gestation period is thought to be similar to the gray fox, which is around 52 days, and pups are born from late April through early May. Litter size ranges from one to as many as five pups, but two or three is considered average. Born in the protection of a den, pups are blind and helpless with short dark brown hair at birth. They emerge from the den at about one month of age, much furrier but still considerably darker than adults. They begin to resemble their parents by late summer.
It is believed that island fox pups undergo a period of extended parental care. In a recent study of island foxes, scientists found adults and pups in the same trap on 22 occasions. In 24 traps containing only pups, they found killed mice and other prey items outside the traps, apparently left by the parents for their young. As with most wild canids, males play an important role in the rearing of young.
The island fox, which only a short time ago was on the brink of extinction, provides an instructive example of how a coordinated, organized and highly focused strategy was able to reverse the certain extinction of an endangered population. Additional information about the strategies developed and implemented to reverse this situation may be found at Island Fox Conservation.
Due to these successful efforts, the IUCN Red List of Endangered Species now lists the island fox as near threatened.
The Decline of the Island Fox
The Warning Provided by Monitoring
From 1993 to 1999 the National Park Service monitored the population of island foxes on San Miguel Island. Each summer, foxes were trapped and tagged. When each fox was first captured, it was implanted with a device about the size of a grain of rice called a passive integrated transponder tag, or "PIT" tag. The tag gives each fox a permanent, unique number that can be read with a special scanner and allows scientists to monitor individual foxes over the years.
Park biologists estimated there to be over 400 foxes on San Miguel in 1994, but by 1995, an alarming decline had begun. With each passing year, fewer foxes were trapped in the monitoring grids. At the same time, rangers and visitors reported seeing fewer live foxes and more fox skeletons and carcasses. By 1998, the San Miguel population was down to a few dozen. Island fox populations on all three islands were naturally small and had historically fluctuated, but as far as was known had never been as low as they were during this period and had never come close to extinction.
In fall 1998, National Park Service biologists initiated a radio telemetry study of island foxes on San Miguel Island to determine causes of mortality. Of 15 radio collared foxes tracked from 1998 to 1999, 5 were believed to be killed by golden eagles and 2 died of other causes. This confirmed the results of an earlier study on Santa Cruz Island where golden eagle predation was identified as the cause of death for 21 of 29 fox carcasses. Golden eagle predation was unprecedented, and was considered unnatural because golden eagles had not previously bred on the islands and were, until this time, rarely observed.
Similar declines occurred simultaneously in the island fox populations on neighboring Santa Rosa and Santa Cruz Islands Fox mortality rates due to predation were so high that by 1999 the San Miguel and Santa Rosa fox subspecies were nearing extinction; on each of those islands total abundance had declined from approximately 450 and 1,500, respectively, to 15.
Eliminating the Major Cause for Decline
While the threat of critically low island fox population size could conceivably be improved through captive breeding and reintroduction, such efforts would be futile unless the threat from golden eagles was eliminated. Historically, the native bald eagle most likely deterred golden eagles from exploiting the Channel Islands as a food source. Golden eagle did not colonize the islands until their larger fish-eating relatives were wiped out by DDT, hunting, and egg collection. With the golden eagle's sharp talons, swiftness of flight, and 4 times the body mass of a fox, they easily preyed upon the vulnerable fox.
Interestingly, the first documented decline on San Miguel in 1995 coincided with the first golden eagle sightings on the island. Golden eagles had been live-captured and relocated from some areas in western North America to reduce depredation on livestock and it was surmised that similar translocation methods could be used to golden eagles from the Channel Islands. In late 1999 the National Park began working with its partners to relocate golden eagles to the mainland. Golden eagles nested on both Santa Cruz and Santa Rosa Islands from the mid-1990s to as recently as 2006.
In order to mitigate golden eagle predation on island foxes, The Santa Cruz Predatory Bird Research Group, with the support of the Park Service and The Nature Conservancy, trapped and relocated a total of 44 golden eagles, including 10 eaglets born on the islands to distant sites in northeastern California. Monitoring indicated that , none returned to the islands.5 Today the occasional golden eagle visits the islands, but the level of predation on island foxes is negligible; all three island fox subspecies in the park are recovering rapidly.
Predation by golden eagles was the primary mortality factor for foxes on the northern Channel Islands, but there were other threats as well. Introduced diseases or parasites could conceivably devastate island fox populations. In 1999-2000, on privately-owned Santa Catalina Island, about 90% of the fox population was recently lost due to canine distemper virus.
Due to their insular existence, island foxes have no built up immunity to parasites and diseases brought in from the mainland and are especially vulnerable to those a domestic dog might be carrying. In addition, it is extremely difficult to vaccinate against or treat foxes for these parasites and diseases in the wild. For this reason, pets are not permitted in Channel Islands National Park.
Eliminating Other Factors Contributing to the Decline
Domestic pigs had been brought to Santa Cruz Island in the mid-1800s as a food source, and subsequently became feral. By the mid-1990s the thousands of feral pigs on the island became a factor in the decline of island foxes. Golden eagles were able to successfully colonize the island, and begin breeding, because of the availability of piglets.
Simply relocating the existing golden eagles would not assure island fox recovery. With the substantial prey base provided by island pigs, dispersing golden eagles would continue to breed on the island. It would therefore be necessary to implement longer-term actions that would prevent sustained use of the islands by golden eagles. This resulted in a strategy that would require the removal of the feral pigs on Santa Cruz Island beginning in 2004, in a project implemented by the NPS and The Nature Conservancy, its partner in management of Santa Cruz Island. By 2006, no pigs remained on Santa Cruz Island.
In a similar manner, introduced mule deer supported golden eagle breeding on neighboring Santa Rosa Island. Deer and elk on that island were to be phased out as part of an agreement between NPS and the former owners of the island, and by 2012 non-native ungulates had been all but eliminated on Santa Rosa Island.
The Restoration of the Island Fox
The Captive Breeding Program
Captive breeding was a necessary - and ultimately successful - recovery action for island foxes, and it also provided an opportunity to study island fox reproductive biology, which was previously unknown. When foxes were first brought into captivity on San Miguel Island just before the 2000 breeding season, mated pairs were established by placing together males and females that appeared likely to have been paired in the wild, based on information available at capture. Because there were more females than males, some females were housed together.
In subsequent years as pups were born and reached maturity, they were assigned mates based on a computer program designed to prevent inbreeding in small populations, such as the fox, and maximize genetic heterozygosity (lack of similarity).
The success of the island fox breeding program is evident in data given in the 2011 Island Fox Meeting Report. Considering the northern Channel Islands exclusively, numbers that include pups are as follows: Santa Cruz, 1302; San Miguel, 516; Santa Rosa, 292.
As a result of research conducted during the captive breeding period, we now know that island foxes have induced estrus and ovulation, which is unique among canids and may be related to other distinctive features of their mating system. Island foxes differ substantially from wolves, the species perhaps best known for its complex social system, strong pair bonds, and solicitous parental care. All the canid species appear to be socially monogamous, but from there they diverge in terms of group size, degree of sociality, and age of dispersal of young. For example, male aggression toward females - something that appeared rather common even in the reproductively successful island foxes - is virtually unknown for other canid species, in which males tend to be very solicitous to females, especially during estrus and pregnancy. However, it is unclear whether this behavior is characteristic of free-ranging island foxes or merely an artifact of captive conditions. In another contrast with other canids, the reproductive rate was lower for captive-born island foxes, the opposite of what is usually observed in other canid species. This suggests that something, such as social experience during the juvenile period, might have been missing in the captive environment, something that apparently is less important to other canid species.
Reintroduction of the Bald Eagle
The process of bringing back the bald eagle to the northern Channel Islands led authorities to believe that they might prove to be a natural deterrent to the colonization of the golden eagle. In 2006 a bald eagle was observed escorting a golden eagle out of its territory on Santa Rosa Island. Newly released bald eagles were also seen chasing golden eagles off of a carcass provided for them. Historical evidence and studies have shown that the natural bald eagle food sources are marine fishes, seabirds and pinniped carcasses, suggesting that bald eagles pose little threat to the island fox.
From 2002-2006, the Institute for Wildlife Studies (IWS) released 61 bald eagles on Santa Cruz Island. In 2006, the first known nesting attempts occurred in the northern Channel Islands. Two pairs of eagles successfully fledged one chick each from nest at Pelican Harbor and Malva Real on Santa Cruz Island. Since 2006, there have been successful hatchings and Santa Cruz and Santa Rosa Islands. As of 2012 there are over 50 bald eagles on the California Channel Islands and over 30 known eagles on the northern Channel Islands.
Encouraging Native Plants
Island foxes evolved in an environment thick with native shrubs that later dwindled after the introduction of livestock grazing. Without shrubs for hiding cover, the foxes were especially easy for the golden eagles to catch. Today, the removal of nonnative grazers is showing astonishing results. Lush shrubs and wildflowers are coming back. Restoring the island's vegetation benefits the foxes and all native wildlife.
An Ecosystem Solution
Without the ecosystem-level changes of pig removal and bald eagle restoration, fox recovery was not assured. That those two ecosystem level actions were implemented in conjunction with island fox recovery actions was fortuitous. The two actions had been planned and funded separately from island fox recovery, but the value of those planned actions to island fox conservation was recognized when the complicated relationship among foxes, pigs, and eagles became apparent. The success of those ecosystem-level actions was facilitated by the islands' isolation and their limited, more defined ecosystems: once pigs were removed from the islands, there was little chance of them returning. The success of these ecosystem-level actions for island fox conservation underscores the importance of considering ecosystem-wide conditions in endangered species management.
The Current Status of the Island Fox
An affiliated group of management agencies, landowners, academics, and non-profits concerned with the conservation of the island fox has convened since 1999 to exchange information regarding the status and trend of the six island fox subspecies, and to work cooperatively on island fox conservations issues in such areas as captive breeding, wild population management, veterinary issues, and educational/outreach. In the most recent 2011 meeting of this group, the Island Fox Working Group, data was presented that indicated that 4 of the 6 island fox (Urocyon littoralis) subspecies were stable or increasing, with high survival, though island foxes still face potential threats from pathogens and predation.
Current Status on Santa Cruz Island
Recovered. Captive breeding ended in 2008 for the Santa Cruz Island Fox (Urocyon littoralis santacruzae) and all foxes were returned to the wild. Survival remains very high, and the populaiotn has increased steadily. Some areas now show less increase (fewer pups) as the population nears historic density.
Current Status on Santa Rosa Island
Recovered. Captive breeding continued for the Santa Rosa Island fox (Urocyon littoralis santarosae) until 2008 when all foxes were returned to the wild.The annual survival rate climbed to 90% in 2007-2009, but the incidental arrival of three juvenile golden eagles in spring 2010 caused survival to dip in that year. Since then survival has climbed above 90% and the fox population continues to increase.
Current Status on San Miguel Island
Recovered. Captive breeding continued for the San Miguel Island fox (Urocyon littoralis littoralis) until 2007 and all foxes were returned to the wild. The population continues to increase by about 25% per year with a high annual fox survival rate, 90%. As of 2011 the population had reach pre-decline levels (close to 400 adults) and can be considered biologically recovered. As the population has reached known historical levels, biologists are watching to see how the population stabilizes. Monitoring foxes via radio telemetry collars has also provided early identification of predation or disease threats. Annual vaccination of 60 - 100 individual foxes is protecting a larger potential survivor group in the event of introduced rabies or distemper virus.
Future Prospects of Threats to Species
The IUCN Red List of Endangered Species still lists the Island Fox as critically endangered as of a 2008 assessment. The US Fish and Wildlife Service will likely release a draft island fox recovery plan in 2012. Monitoring and mitigation of known threats (eagle predation and canine disease) will be a prominent recovery action in the plan. Island foxes may be vulnerable to impacts of future global climate change. Such impact could be direct, such as changes in acceptable temperature ranges, or indirect, such as impacts on floral or faunal food sources for the fox. Alternatively, global climate change may affect the distribution or virulence of pathogens, such as bacteria or parasites.
- 19 minutes, 32 seconds
Close to the mainland yet worlds apart, Santa Cruz Island is home to plants and animals that are found nowhere else on Earth. The introduction of of non-native, exotic plants and animals have caused the loss of some of these rare species and pushed many others, including the island fox, to the brink of extinction. In order to save these island species, as well as protect sacred Chumash Native American cultural sites, the National Park Service and The Nature Conservancy embarked upon a multi-year program to help restore balance to Santa Cruz Island’s naturally functioning ecosystems. This high-definition video documents the various aspects of this complex restoration program, including the removal of golden eagles, reintroduction of bald eagles, captive breeding island foxes, removal of sheep, and eradication of pigs. The Santa Cruz Island restoration program is part of the National Park Service mission, as mandated by Congress, to preserve unimpaired the natural and cultural resources and values of the national park system for the enjoyment, education, and inspiration of this and future generations.