Catalina's Foxes are Back!

A radiocollared Catalina Island Fox
(Urocyon littoralis catalinae)

The first year I lived on Catalina, I rarely saw a Catalina Island Fox -- we felt very lucky when we came across one. But all that has changed. These days we see foxes regularly, even on short trips around the Isthmus. These sightings are exciting – after all, just seven years ago this species was listed as endangered by the US Federal Government.

Anecdotes like ours, in and of themselves, are not convincing evidence that fox populations have recovered on Catalina Island. But our impression that foxes are more abundant is borne out by population estimates made by the Catalina Island Conservancy.  According to a January 19, 2012 LA Times story, there are now 1542 foxes on the island. The Catalina Island fox is back!

What happened to the Catalina Island Fox?
In 1998, the population of foxes on Catalina was about 1300.  Then foxes started dying.  In a matter of months, from late 1998 through 1999, the population plummeted to only about 100 animals, more than 80% of which lived on the West End of the island.

Researchers knew that foxes were dying, but they didn't know why. Residents saw dead and dying foxes, but researchers were able to recover only one carcass for necropsy. This isn't surprising, really -- Island foxes are only about half the size of an typical house cat and the island is large (45,000 acres) and rugged. On top of that, Northern ravens are efficient scavengers, quickly homing in on dead animals.

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The culprit turned out to be canine distemper virus (CDV).  Canine distemper virus (CDV) is carried by a number of mammals, including dogs, raccoons, and cats. Two lines of evidence in particular support this conclusion. Researchers found CDV (in addition to toxoplasmosis, a parasite), in the necropsied fox and they found antibodies to CDV in blood samples from surviving foxes.

Immunological analysis of blood from surviving foxes suggest that the disease started in Avalon and spread from there. Rumors as to the source of the disease were rampant, but wildlife biologists assumed that the disease was passed from a dog to the foxes. Then, surprisingly, genetic analysis of the virus indicated that the strain of CDV infecting the foxes was most similar to raccoon CDV.

Raccoons do not naturally live on Catalina, but it is possible for one to have infected an Island fox. Animals have been sighted on the island over the past several years, arriving as stowaways on visitors' boats or released by guests with a misguided notion of doing a good deed. Because raccoons represent a serious threat to native wildlife on the island, the Conservancy makes a concerted effort to remove them. There are tales, however, of a rogue raccoon still at large on the West End of the island.

Or maybe raccoons are not the bad guys here. Viruses can jump from one species to another -- think of bird and swine flu viruses -- so a dog that was infected with the raccoon-strain of CDV might still be at the root of the epidemic.

Apparently, foxes on the island had not been exposed to a virulent strain of CDV before the disease broke out. Researchers evaluated this by looking for antibodies to CDV in foxes' blood. When an animal comes in contact with a disease-causing organism, like a virus, their immune system forms antibodies to battle the infection. If the animal survives the initial exposure, it gains life-long immunity to the disease because some antibodies continue to circulate after the infection is vanquished. Blood samples taken before 1999 show that only about 20% of foxes carried antibodies to the disease, whereas samples taken during and after the epidemic show that nearly all surviving foxes had been exposed to CDV.

A Conservation Success Story
As the fox population took a nose-dive, the Catalina Island Conservancy sprang into action. Working with the Institute for Wildlife Studies, they started a vaccination program, trapping foxes and inoculating them against common diseases. To increase population size quickly, they began a captive breeding program and moved foxes from the West End of Catalina, where populations were still robust, to the East End of the island. They saw quick results: by 2004 the population had tripled to 300 animals and by 2010 it numbered over a thousand.

The outlook for Catalina Island foxes is good, but conservation concerns linger.  Foxes are struck by cars, killed by pets, and are susceptible to diseases other than CDV.  Vehicular traffic is a particular concern; of sixteen radiocollared foxes that died in 2009, eleven of them, mostly young males, were hit by cars.

Another concern are ear tumors in the foxes. Usually fatal, tumors are linked to the presence of ear mites. Mites pass between foxes and have been found at cat feeding stations, where foxes also feed. Treating animals for ear mites during the annual trapping effort has been effective in reducing mite prevalence and biologists with the Conservancy are hopeful that this will help reduce ear tumors.

The persistence of the Catalina Island fox is a credit to the Catalina Island Conservancy. By acting quickly (and having a little bit of luck), they have brought an iconic Catalina species back from the edge of extinction.

References:
My notes from the Catalina Island Conservancy Symposia -- 2010, 2011

Clifford, D. L. et al. 2007. Using pregnancy rates and perinatal mortality to evaluate the success of recovery strategies for endangered island foxes. Animal Conservation 10: 442-451.

Kohlmann, S. G., G. A. Schmidt, D. K. Garcelon. 2005. A population viability analysis for the Island fox on Santa Catalina Island, California. Ecological Modelling 183: 77-94.

Timm, Steven F., et al. 2009. A suspected canine distemper epidemic as the cause of a catastrophic decline in Santa Catalina Island foxes (Urocyon littoralis catalinae). Journal of Wildlife Diseases 45(2): 333-343.