|
Island Fox > Natural History > Conservation > Studies > Recent Events > Captive Releases > Ear Tumor Study > Survival Monitoring |
|
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%.
In the summer of 2000, the Institute began a fox-monitoring program on San Nicolas Island by establishing three capture-recapture trapping grids to evaluate the current demography of the subspecies and to monitor changes in population parameters. We are currently in our 5th year of trapping the three grids. Island wide population size is estimated at approximately 500 adults based on 2003 trapping results. 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). Further, populations on the three grids appear 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. Because the San Nicolas Island population appears to be comparatively free of various microscopic and macroscopic parasites prior exposure to pathogens may be limited. The lack of genetic variation and immunological experience could make this subspecies particularly susceptible to the introduction of a novel pathogen. Indeed, in 2001, 80% of the foxes tested were positive for canine distemper virus (CDV) antibodies. Care should be taken to avoid the introduction of lethal canine diseases by prohibiting domestic dogs on the island and by eradicating feral cats. |
