Invasive alien species are a major threat to native insular species. Eradicating invasive mammals from islands is a feasible and proven approach to prevent biodiversity loss. We developed a conceptual framework to identify globally important islands for invasive mammal eradications to prevent imminent extinctions of highly threatened species using biogeographic and technical factors, plus a novel approach to consider socio-political feasibility. We applied this framework using a comprehensive dataset describing the distribution of 1,184 highly threatened native vertebrate species (i.e. those listed as Critically Endangered or Endangered on the IUCN Red List) and 184 non-native mammals on 1,279 islands worldwide. Based on extinction risk, irreplaceability, severity of impact from invasive species, and technical feasibility of eradication, we identified and ranked 292 of the most important islands where eradicating invasive mammals would benefit highly threatened vertebrates. When socio-political feasibility was considered, we identified 169 of these islands where eradication planning or operation could be initiated by 2020 or 2030 and would improve the survival prospects of 9.4% of the Earth’s most highly threatened terrestrial insular vertebrates (111 of 1,184 species). Of these, 107 islands were in 34 countries and territories and could have eradication projects initiated by 2020. Concentrating efforts to eradicate invasive mammals on these 107 islands would benefit 151 populations of 80 highly threatened vertebrates and make a major contribution towards achieving global conservation targets adopted by the world’s nations.

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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.

Within Holmes et al. (2015) we investigated the cost of invasive vertebrate eradications on islands, by (1) describing five major cost centers to allocate costs and improve reporting, (2) providing examples of these allocations with a retrospective look at 42 projects plus four planned projects, and (3) discussing factors that will influence cost for eradication projects. Recently errors within this paper associated with island size and costs, plus insufficient detail on cost context, were brought to our attention and affect this second component of our paper. We provide corrected numbers here and footnotes on cost origin and context (Table 1). This revised sample set does not include the predator eradication on Baltra Island due to previously unknown errors, nor ungulate eradication projects on San Clemente, Pinta and Santa Catalina and predator eradication on Wake, because these eradication projects followed extended periods of control, confounding allocation to an eradication project alone. Our updated project list included 37 successfully completed projects and four planned projects. These updates do not impact the rationale for the major cost centers associated with invasive vertebrate eradication projects, nor the discussion of factors that will influence the cost of eradication projects.Native currencies were converted to USD using historical mean annual exchanges rates based on eradication end date, or year costs were reported, and then adjusted for inflation. We considered eradication end date to be the year that major eradication operations (and thus cost) ceased. This typically coincided with the end of confirmation of eradication for hunting/trapping for ungulates and predators or the end of toxicant application (or other methods) for rodent projects. For the purposes of our study, we used historical US inflation rates to standardize data into USD2013. We expect that different inflation rates from project costs incurred in non-US economies would also impact normalized 2013 project cost.We also updated subsequent analyses using those data (Table 2) and calculations in the discussion. Area continued to show a positive relationship with