Catastrophic decrease in an isolated population of kit foxes

Captures of San Joaquin kit foxes (Vulpers macrotis mutica) during annual l ivetrapping sessions at the California Army National Guard Training Site, C amp Roberts, decreased from 103 to 20 individuals from 1988 to 1991. This d ecrease continued through 1997 when only three kit foxes were captured. Sim ilar trends in relative abundance were evident in scent-station visitations and spotlighting observations. An outbreak of rabies virus may have contri buted to this catastrophic decrease in abundance because two foxes were fou nd dead due to rabies in 1990. Striped skunks (Mephilus mephitus) are the p rimary vectors of rabies virus in this region and a rabid skunk was trapped at Camp Roberts during 1989. Captures of foxes were positively correlated with captures of skunks and negatively correlated with proportions of rabie s-positive skunks submitted for testing to the San Luis Obispo Co. Public H ealth Department during the previous 2 years. Interference competition by c oyotes (Canis latrans) also may have contributed to this catastrophic decre ase because relative abundances of foxes and coyotes were negatively correl ated from 1988 to 1997, and coyotes were responsible for 59% of fox deaths during a 4-year telemetry study (1988 to 1991). The negative effects of inb reeding and interference competition by coyotes may hamper the recovery of this relatively-isolated population of foxes or eventually lead to its exti nction if recruitment continues to be poor.