A Population Monitoring Framework for Five Subspecies of Island Fox (Urocyon littoralis)

Rubin, Ester; Bakker, Vickie; Efford, Murray; Cohen, Brian; Stallcup, Jerre; Spencer, Wayne; Morrison, Scott

Island foxes (Urocyon littoralis) inhabit the six largest Channel Islands off the coast of southern California, with a separate subspecies recognized on each island: San Miguel Island fox (U. l. littoralis), San Nicolas Island fox (U. l. dickeyi), San Clemente Island fox (U. l. clementae), Santa Catalina Island fox (U. l. catalinae), Santa Rosa Island fox (U. l. santarosae), and Santa Cruz Island fox (U. l. santacruzae). Due to their limited geographic distribution and small population sizes, foxes on all six islands have been listed as Threatened by the State of California, and all subspecies except those on San Nicolas and San Clemente have been listed as Endangered by the U.S. Fish and Wildlife Service (USFWS) due to recent precipitous population declines and high risk of extinction. Due to the persistent high risk of this island species, robust monitoring of fox populations and their threats is a key component of recovery and long-term management. This document presents a framework for population monitoring for five subspecies of island fox on San Miguel, San Nicolas, Santa Catalina, Santa Rosa, and Santa Cruz Islands. A monitoring framework previously developed for the U.S. Navy on San Clemente Island, in addition to years of monitoring and research on all six islands, provided the foundation for the current effort. This document thus represents the first comprehensive synthesis of monitoring data, objectives, and protocols across multiple Channel Islands with foxes. Sections 1-3 of this report describe the considerations and approaches used to identify specific monitoring objectives, determine parameters to address these objectives, and develop protocols to measure these parameters. Sections 4-8 present illustrative island-specific examples of monitoring scenarios designed to address current monitoring objectives, but with different levels of effort and precision. We provide at least two alternative trapping scenarios for each island, along with expected precision (e.g., for resulting population estimates), effort required, and estimated habitat representation. It is expected that island managers will tailor and adapt protocols for on-the-ground use, based on their resources and priorities, understanding that there is generally a trade-off between monitoring intensity and information value.