Numbers of island foxes declined at alarming rates since 1994, with four of the six subspecies declining by as much as 95 percent. The primary threats causing these devastating declines were predation by golden eagles (Aquila chrysaetos) on the northern Channel Islands, canine distemper virus (CDV) on Santa Catalina Island, and collision with vehicles on San Clemente and San Nicolas Islands (2) (8).
Golden eagles had not always lived on the Channel Islands, but were attracted there by the introduction of wild pigs (Sus scrofa) (9). These impressive birds of prey colonized the northern Channel Islands in 1994 and began to prey heavily on foxes, quickly bringing the island fox to the brink of extinction (10). By 1999, only 14 individuals of the San Miguel subspecies remained (11).
On Santa Catalina Island, the introduction of CDV, (believed to be brought to the island by a domestic dog), caused the deaths of about 90 percent of the fox population in just one year, (1999 to 2000) (12). The introduction and spread of CDV, and other canine diseases, remains a potential threat to all the island fox subspecies (8).
In 1999, 32 foxes on San Clemente Island were either culled or permanently removed from the island to zoological institutions, as part of a programme to protect the endangered bird, the loggerhead shrike (Lanius ludovicianus). Another 49 were temporarily held in small pens while the shrikes were nesting, and in 2000, a further 71 foxes were held again. This practice has since been stopped, but the disruption this caused to reproduction and social systems is believed to have significantly affected the San Clemente Island fox population and contributed to its current Critically Endangered status (13).
Like any small, isolated island populations, the island fox remains extremely vulnerable to any catastrophic mortality source, be it predation, canine disease, or environmental extremes (1).