Surveys conducted for foxes on San Nicolas Island have indicated substantial population fluctuations between the 1970s and the 1980s. Trap success during a survey in 1971 was 72%, and was only 4-5% during surveys in 1974 and 1977. By the 1980s, the population had apparently recovered and during survey efforts in 1998 capture success was 41%.
The U.S. Navy has funded IWS to monitor island foxes on San Nicolas Island annually since 2000. The Institute began the fox-monitoring program by establishing three capture-recapture trapping grids to examine the demography of the subspecies and to monitor changes in population parameters. Estimates of fox density on two of the grids are the highest ever recorded for a fox capture-recapture grid on any of the California Channel Islands (up to 27 foxes/km2). Island-wide population size was estimated at approximately 500 adults and, based on the three grids, appears to be stable. However, recent declines on other islands and past fluctuations on San Nicolas Island have raised the level of concern for this subspecies.
In 2006 we began a project to examine age-specific mortality rates for foxes residing on San Nicolas Island. This project, funded by the Department of Defense Legacy Program, involved developing an automated telemetry monitoring system that used receiving stations set up around the island to detect when collared foxes died. During the study foxes were equipped with telemetry collars that would emit a unique coded signal when it did not move within a designated period of
Over the past ten years, analysis of blood samples from adult foxes has indicated the presence of antibodies to canine adenovirus, canine distemper and canine parvovirus. To help prevent a catastrophic outbreak of canine distemper or rabies virus, IWS has incorporated a vaccination program into our trapping efforts in an effort to reduce the impact of such a disease outbreak. This effort, in combination with the Navy’s restrictions on domestic pets on the island, improves the protection of the fox population and decreases the chance that these diseases will cause the demise of foxes on the island.