Island Fox Long-term Monitoring
Island foxes (Urocyon littoralis) are one of the smallest canid species in the world, and are the most geographically restricted, occurring only on the six largest of the eight Channel Islands. Weighing at most 4-5 pounds, island foxes are one-third smaller than their mainland relative, the gray fox, yet they are the largest native terrestrial predator on the islands. Island foxes rapidly evolved within the past 10-15,000 years, perhaps after 1-2 gray foxes rafted out to the islands during the late Pleistocene. At that time sea levels were lower and distance from the mainland to the island was smaller. Native Chumash are thought to have domesticated island foxes and transported them from the northern to the southern Channel Islands. Island foxes eat almost everything on the islands, including deer mice, birds, insects, and berries and fruits. Unlike mainland carnivores, island foxes are not strictly nocturnal; they can be observed foraging in the daytime as well. They live 8-10 years in the wild and generally mate for life, with females producing a litter of 1-5 pups in the spring.
The park’s long-term monitoring program detected a rapid decline of island foxes on San Miguel Island in the 1990s, in parallel with a decline on Santa Cruz Island. Radiotelemetry revealed the cause to be predation by golden eagles, which had colonized the islands in the 1990s due to an absence of bald eagles, and the presence of non-native ungulate prey (feral pigs and introduced mule deer). Island foxes declined as much as 95% on the northern islands; by 2000, only 15 remained on San Miguel and Santa Rosa, and 50-60 on Santa Cruz. Subsequently, those three island fox subspecies, along with the subspecies on Santa Catalina Island, were listed as endangered by the U.S. Fish and Wildlife Service. Acting with partners, the NPS began aggressive recovery actions in 1999 including trapping and relocation of golden eagles and captive breeding and reintroduction of island foxes. These were combined with other larger-scale ecosystem recovery actions like the reintroduction of bald eagles and removal of feral pigs from Santa Cruz Island. Island foxes now thrive again in the wild on park islands, and their recovery has been one of the most rapid of any endangered species. To track recovery and detect future threats to the species, Inventory & Monitoring Program biologists intensively monitor island fox survival and population trends on park islands.