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Open Access Publications from the University of California

A Trap Monitoring System to Enhance Efficiency of Feral Cat Eradication and Minimize Adverse Effects on Non-Target Endemic Species on San Nicolas Island


Feral cats have significant negative impacts on island ecosystems and are a major threat to resident seabird populations. In an attempt to restore populations of Brandt’s Cormorants, western gulls, and other native species on San Nicolas Island, California, feral cats were targeted for eradication. In over 83 successful feral cat eradications from islands, removal by padded leg-hold traps was the most commonly used eradication technique. However, the size of San Nicolas, 5,896 ha (14,562 acres) and the presence of >600 diminutive (average 1.7 kg) endemic island fox presented challenges. A telemetry-based trap monitoring system was developed to remotely check trap status, decrease staff time spent checking traps, and decrease response time to captured animals to limit fox injuries and mortalities due to exposure. This system enabled a team of 6 staff to maintain daily checks of approximately 250 traps and have a response time to captures of <60 minutes during daylight hours. Field staff were trained to assess fox health in the field, and a mobile veterinary hospital was established on island to treat any injuries. The trap monitoring system was composed of transmitter units connected to traps, an island-wide repeater system, a GIS database with field PDA data collection, and a user interface hosted on a local internet network. When activated, each transmitter sent a trapspecific ID code every 4 hours, indicating it was operational. When sprung, a modified ID code was transmitted every 30 minutes until the trap transmitter was reset. Repeaters relayed trap status data, both to a dedicated PC where a set of scripts filtered the raw data to find capture events, and simultaneously to the internet. A web-based software user interface was designed to combine capture events with location information from a GIS database, allowing field staff to quickly identify which traps were sprung and plan the most effective route between all sprung traps. Ultimately, this system was a powerful adaptive management tool that increased staff efficiency and minimized effects on non-target species.

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