Creature Feature: Rescuing the Island Fox is a Complicated Long-Term Project
The foxes of the Channel Islands were recently rescued from the brink of extinction. Now keeping this species from disappearing is a matter of captive breeding and reintroducing foxes, keeping golden eagles away, restoring abused ecosystems, combating canine distemper, providing medical care, curbing wildlife feeding, reducing vehicle-animal collisions, trapping and radio-collaring, survivor monitoring, prey sampling, ……. and so on.
No one knows for sure how the Island Fox (Urocyon littoralis) ended up on the Channel Islands, five of which -- San Miguel, Santa Rosa, Santa Cruz, Anacapa, and Santa Barbara -- are now part of Channel Island National Park. Did the pioneering foxes that arrived on those distant shores more than 4,000 years ago float in on storm debris? Did Paleoindians transport them there?
This relative of the gray fox is quite small. A fully grown adult weighs no more than four to six pounds -- about the size of a small housecat -- and it’s unlikely to be more than 30 inches long, tail and all. Still, this little fox is the largest of the Channel Islands’ endemic land mammals.
The Island Fox is multi-hued (see accompanying photo). Its head is gray, its sides are a ruddy red color, it’s got white fur on its belly, throat and the lower part of its face, and the top side of its tail has a black stripe on it. It’s hard to mistake this animal for something else.
Over time, a distinct subspecies developed on six of the Channel Islands. (Two of the eight islands have no foxes.) Each subspecies has unique physical and genetic characteristics, such as body weight and number of tail vertebrae. Each is named according to its island of origin.
A slow motion catastrophe that began over 60 years ago nearly wiped out the island fox population on San Miguel, Santa Rosa, and Santa Cruz. The problem on these three northern islands was eagles, or to put a finer point on it, too many of the wrong kind of eagles.
For thousands of years, foxes thrived on the islands in the presence of bald eagles. The two species do not directly compete for the same food and pretty much leave each other alone. The foxes, which are omnivorous, subsist primarily on mice, lizards, crabs, birds, eggs, insects, berries, and cactus fruit. Bald eagles, which are true carnivores, mostly eat fish, sea birds, and carrion.
The fact that bald eagles are fiercely territorial makes their presence very beneficial to island foxes. That’s because bald eagles drive away golden eagles, which are profligate killers of island foxes. Unfortunately, the bald eagles of the Channel Islands were in terrible trouble by the early 1940s due to the relentless accumulation of DDT in the aquatic food chain. As top predators and consumers of fish and sea birds, and thus prime targets for biological amplification of DDT, they got way too much of this nasty chlorinated hydrocarbon in their systems, produced eggshells that were way too thin, and were soon unable to reproduce at all. The last bald eagle chick of that era was fledged in 1949, and soon there were no more resident bald eagles in the Channel Islands.
With bald eagles no longer patrolling the skies, golden eagles began moving in during the 1960s and were nesting on the islands by the 1990s. (Fish and sea birds aren’t important elements of the golden eagle diet, so this terrestrial feeder escaped the DDT disaster that befell the bald eagles.) In the 1990s when golden eagles could no longer prey on feral piglets (the pigs having been exterminated in many locales by the NPS), they began preying more heavily on foxes. Losses quickly exceeded replenishment and the fox population of the northern islands went into profound decline. By the early 2000s, only a small fraction of the original population remained and the future looked very grim for the harried survivors.
In 1999, at the same time golden eagles were making deep inroads in the fox population of the northern islands, canine distemper presumably introduced by pet dogs swept through the Catalina Island subspecies (Urocyon littoralis catalinae) far to the south and reduced the population by more than 90 percent (to around 100 individuals). An emergency vaccination program stopped the epidemic, a captive breeding and restocking program replaced some of the critical losses, and by early 2006 the Catalina Island population had rebounded to about 400. This is still far below the 1,300 or so level of ten years ago.
The Catalina Island subspecies remains a federally listed endangered species, as are the subspecies on San Miguel, Santa Rosa, and Santa Cruz Islands.
On the three northern islands with foxes, eagle predation was so bad that only direct human intervention could save the foxes from extinction. Having the right kind of eagles is, of course, basic to any recovery. In recent years, wildlife biologists relocated more than 40 golden eagles to the mainland from the northern islands and released nearly 50 young bald eagles. The strategy is working.
Three years ago this month, jubilation attended confirmation of the first successful bald eagle chick hatching on the islands in more than half a century. Now that the golden eagles are gone and it’s likely that resident bald eagles will be keeping them away, the future of the foxes on San Miguel, Santa Rosa, and Santa Cruz Islands no longer looks so bleak
Because DDT contamination remains serious at Catalina Island (due to decades-ago illegal dumping), it won’t be possible to have a truly self-sustaining bald eagle population there for a very long time. Meanwhile, biologists are using egg-pulling and artificial incubation to help insure that a resident bald eagle population will be on hand to discourage potential golden eagle invaders.
The island fox population remains distressingly small, so additional human assistance will be needed to make this wildlife drama play out the way we want it to. Reintroducing island foxes to areas where fox niche-spaces remain unfilled and helping individuals survive life-threatening injuries and diseases are two very effective ways to speed up the rate of recovery.
The NPS has been engaged in the captive breeding and restocking of island foxes for a number of years now, and with generally good results. On Santa Catalina, the combined efforts of the NPS, the Catalina Island Conservancy and the Institute for Wildlife Studies have done wonders for that subspecies. In the northern islands, the NPS is working with the Friends of the Island Fox organization and the Institute for Wildlife Studies to help restore fox numbers there.
To see an interesting video showing captive-bred island foxes being released into the wild on San Miguel Island in 2006, visit this site.
One of the more interesting aspects of the island fox recovery program is the operation of medical clinics – dubbed “foxpitals” – on each of the islands with endangered foxes. Most injuries occur during the winter/spring mating season when foxes become unusually aggressive . Lots of other mishaps cause tears, abscesses, bruises, and other problems. Foxes sometimes get scorched in wildfires, hooked by lost fishing lures, hit by cars on Santa Catalina, infected with parasites (such as ringworm), or injured in various and sundry other ways.
Most animals that are treated can be released back into the wild, usually in a matter of a few days or weeks. Recently, some foxes have been found to be suffering from a usually fatal form of ear cancer. Whether a cure for this potentially serious problem can be worked out awaits the results of ongoing research. There’s always something!
Postscript: Predation by foxes damn near exterminated the critically endangered loggerhead shrike (Lanius ludovicianus) on Navy-controlled San Clemente Island in the southern part of the archipelago. Fortunately, a fox control program employing nonlethal methods including live trapping (to keep foxes away during the shrike breeding season), electric fencing, and other tactics halted the shrike’s plunge toward ecological oblivion. The Navy no longer bothers to control foxes on San Clemente Island.