Foxes have been surveyed on Santa Catalina Island only intermittently over the past 30 years. The population size appeared to be low in the 1970s based on trap success rates, but had increased by the late 1980s. A study conducted by the Institute in 1989 and 1990 indicated densities of foxes were quite variable across the island. In 1998 a brief trapping effort showed continued high trapping success (26%) in areas with previous high densities.
During the summer of 1999, residents on the island reported finding dead foxes around the city of Avalon, and in some of the coves where camps are operated. By the early fall of 1999 few foxes were being observed on the island and a brief trapping effort resulted in no foxes being captured. In November 1999 the Santa Catalina Island Conservancy contracted with the Institute to investigate the potential cause of the decline. Blood samples obtained from trapped individuals, and an analysis of one of the fox carcasses indicated that canine distemper virus had infected the population. From trapping efforts, it appeared that the foxes located on the west end of the island (separated from the rest of the island by a narrow isthmus) had not been infected with the disease and were still present in good numbers. With the permission of the California Department of Fish and Game we began testing an experimental vaccine that could be used to protect the remaining foxes on the island. Foxes are so sensitive to canine distemper that administering the vaccine used on domestic dogs will cause the animals to develop the disease. A test facility was constructed and animals were given the experimental vaccine. All foxes survived, and those given the vaccine developed antibodies against canine distemper. The results of the survey in 2000 suggested that fox densities were extremely low on the 87% of the island east of the west end isthmus. Recovery efforts included the vaccination of the remaining animals on the island against canine distemper, maintenance of a captive breeding facility to promote the recovery of the population, and translocation of juvenile foxes from the west end of the island to the eastern portion of the island.
Translocation of Island Foxes
Because of the catastrophic decline of foxes on the eastern 80% of Santa Catalina Island due to the canine distemper virus, that portion of the island was augmented with foxes from the west end of the island where foxes were not exposed to the disease. The canine distemper virus generally moves quickly through a wild population and then, because there are too few uninfected individuals, burns out and is no longer a major threat to the remaining animals. Because we believed that the threat from canine distemper virus had diminished after the initial outbreak, an effort was undertaken to start restoring foxes on the eastern portion of the island. Juveniles were used in this translocation effort as they had not yet established a breeding territory and would normally be looking for a new area in which to establish themselves.
Beginning in January 2001, 10 juvenile foxes (5 males: 5 females) were trapped each year on the west end of the island and given a complete medical examination. All foxes were inoculated with the experimental canine distemper vaccine to provide them with protection if they were ever exposed to the virus. They were then equipped with radio-telemetry collars and released in an area on the eastern portion of the island that previously supported a high density of foxes.
In order to determine how translocated foxes would survive in comparison to foxes that were not moved, an additional 10 juvenile foxes were equipped with radio-telemetry collars and then released where they were captured on the west end. The status of all 20 of these animals was determined on a regular basis by relocation from the air and ground to evaluate movements and survival. In addition, pups produced by the mated foxes in the captive breeding facility were released on the eastern half of Catalina Island to support the recovery.
Canine Distemper Vaccination Program
Based on the success of tests conducted using the experimental canine distemper virus vaccine, the California Department of Fish and Game authorized the Institute to inoculate foxes on Santa Catalina Island with the new vaccine. By April 2001 there were 150 foxes included in the vaccine study. Institute biologists periodically recaptured these individuals and collected blood samples to determine the level of antibody protection afforded by the vaccine. At the same time they continued to monitor the radio-collared foxes on the island to develop estimates of productivity and survival. We worked closely with researchers at the National Zoo (Dr. Richard Montali) and the University of Wyoming (Dr. Elizabeth Williams) to determine the effectiveness of the experimental vaccine.
Captive Breeding Facility
In the fall of 2000, work began on an island fox captive breeding facility on Santa Catalina Island. The purpose of the facility was to produce foxes that could be released onto the eastern 80% of the island where the fox population was devastated by canine distemper virus. The facility, funded by the Santa Catalina Island Conservancy, was not only used to produce foxes for release, but also provided a "safety net" or "insurance" against another major decline of the remaining wild foxes on the island.
Each of the 12 breeding pens was 30 ft wide by 100 ft long, and contained a 10 x 30-ft covered area to provide protection from the elements. A 3 ft-wide ground skirt was buried along the side of the pens to prevent animals from digging in or out of the pens. Each pen contained rock piles, branches, and natural vegetation to provide the foxes with some of the elements found in their natural environment. Two den boxes were constructed under the covered portion of the pen. The plywood boxes contained a 6-inch-diameter PVC pipe that formed the entrance/exit, and the entire structure was covered with soil to simulate an underground den.
A video camera with infrared illuminators was placed into each den box to allow monitoring of pup rearing. Four additional cameras and infrared illuminators were placed outside the den boxes to observe fox behavior within the remainder of the pen. The signals from all 72 cameras terminated at a trailer set up at the facility to monitor fox activity. The trailer was equipped with video monitors, time-lapse recorders and video switching devices that provided an opportunity to view activities in all the pens during both day and night.
Starting in March 2001, pregnant foxes were captured and then released into a few of the pens. A number of females gave birth in the den boxes provided. After the pups emerged from the den boxes and were weaned by the female, food items (fruit, live prey, insects, etc.) were provided to help prepare the foxes for foraging on their own in the wild. When the young foxes reached adult weight in the fall of each year, they were equipped with radio-telemetry collars and released into the wild. From fall 2001 to fall 2004, a total of 79 juvenile and adult island foxes were released on eastern Catalina Island to augment the population.
Kolmann et al. (2003, 2005) developed a population model that addressed the viability of the fox population, and the best strategies to recover the species. They suggested that 150 individuals in each subpopulation would have a low probability of extinction by maintaining genetic diversity and resiliency to random influences. IWS proposed recovery activities that included: 1) annual mark-recapture trapping to detect demographic changes, 2) monitoring of released foxes to determine survival rates, and 3) continued inoculations of canine distemper vaccine.
Starting in 2006, the Santa Catalina Island Conservancy took over the role of monitoring the fox population. This included continued annual trapping of the fox population to determine trends, tracking radio-collared foxes to assess mortality rates, and continuing the vaccination of foxes to help prevent another catastrophic outbreak of canine distemper. As of early 2010, the Conservancy estimated that the fox population had grown to over 900 individuals; a truly remarkable population recovery over a very short period of time.