DECLINE OF AN ISLAND FOX SUBSPECIES TO NEAR EXTINCTION

Abstract

We documented a catastrophic decline in the island fox (Urocyon littoralis littoralis) population on San Miguel Island from 1994 to 1999, and used radiotelemetry to investigate mor- tality causes in the latter part of the decline. Annual population monitoring via capture-mark- recapture techniques revealed that densities of adult foxes declined up to 100% on 3 trapping grids monitored during the study period. The estimated population size on San Miguel declined from 450 adults in 1994 to less than 20 in 1999. Apparent survival of all age classes declined over the study. A radiotelemetry-based survival study conducted in 1998 and 1999 revealed high winter mortality, most likely due to golden eagle (Aquila chrysaetos) predation. Necropsy of 7 carcasses during the study period confirmed raptor predation for 5 carcasses. Three carcasses were infested with a pathogenic parasite, Angiocaulus gubernaculatus, not found in island fox populations on San Nicolas, San Clemente, Santa Catalina, Santa Cruz, or Santa Rosa Islands, and 2 carcasses had Uncinaria stenocephala and colonic granulomas from Spirocerca infection. Because pup production was low and reproductive effort limited in young females, the island fox population on San Miguel is unlikely to recover without significant intervention. In 1999, 14 island foxes were brought into captivity, and only 1 was known to exist in the wild on San Miguel Island.