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There are 5 important questions to answer to decide if any proposed vertebrate eradication is feasible. Richard Griffiths discusses it here

Rat eradication is a highly effective tool for conserving biodiversity, but one that requires considerable planning eff ort, a high level of precision during implementation and carries no guarantee of success. Overall, rates of success are generally high but lower for tropical islands where most biodiversity is at risk. We completed a qualitative comparative review on four successful and four unsuccessful tropical rat eradication projects to better understand the factors influencing the success of tropical rat eradications and shed light on how the risk of future failures can be minimised. Observations of juvenile rats surviving more than four weeks after bait application on two islands validate the previously considered theoretical risk that unweaned rats can remain isolated from exposure to rodent bait for a period. Juvenile rats emerging after bait was no longer readily available may have been the cause of some or all the project failures. The elevated availability of natural resources (primarily fruiting or seeding plants) generated by rainfall prior to project implementation(documented for three of the unsuccessful projects) may also have contributed to project failure by reducing the likelihood that all rats would consume sufficient rodent bait or compounding other factors such as rodent breeding. Our analysis highlights that rat eradication can be achieved on tropical islands but suggests that events that cannot be predicted with certainty in some tropical regions can act individually or in concert to reduce the likelihood of project success. We recommend research to determine the relative importance of these factors in the fate of future tropical projects and suggest that existing practices be re-evaluated for tropical island rodent eradications.

The impacts of house mice (Mus musculus), one of four invasive rodent species in New Zealand, are only clearly revealed on islands and fenced sanctuaries without rats and other invasive predators which suppress mouse populations, influence their behaviour, and confound their impacts. When the sole invasive mammal on islands, mice can reach high densities and influence ecosystems in similar ways to rats. Eradicating mice from islands is not as difficult as previously thought, if best practice techniques developed and refined in New Zealand are applied in association with diligent planning and implementation. Adopting this best practice approach has resulted in successful eradication of mice from several islands in New Zealand and elsewhere including some of the largest ever targeted for mice; in multi-species eradications; and where mouse populations were still expanding after recent invasion. Prevention of mice reaching rodent-free islands remains an ongoing challenge as they are inveterate stowaways, potentially better swimmers than currently thought, and prolific breeders in predator-free habitat. However, emergent mouse populations can be detected with conventional surveillance tools and eradicated before becoming fully established if decisive action is taken early enough. The invasion and eventual eradication of mice on Maud Island provides a case study to illustrate New Zealand-based lessons around mouse biosecurity and eradication.

The introduction of invasive rats, goats, and rhesus macaques to Desecheo National Wildlife Refuge, Puerto Rico led to the extirpation of regionally signifi cant seabird colonies and negatively impacted plant and endemic reptile species. In 2012, following the successful removal of goats and macaques from Desecheo, an attempt to remove black rats using aerially broadcast rodenticide and bait stations was unsuccessful. A review of the operation suggested that the most likely contributors to the failure were: unusually high availability of alternative foods resulting from higher than average rainfall, and insufficient bait availability. In 2016, a second, successful attempt to remove rats was conducted that incorporated best practice guidelines developed during a workshop that focused on addressing the higher failure rate observed when removing rats from tropical islands. Project partners developed a decision-making process to assess the risks to success posed by environmental conditions and established go/no-go decision points leading up to implementation. Observed environmental conditions appeared suitable, and the operation was completed using aerial broadcast of bait in two applications with a target sowing rate of 34 kg/ha separated by 22 days. Application rates achieved on the ground were stratified such that anticipated high risk areas in the cliff s and valleys received additional bait. We consider the following to be key to the success of the second attempt: 1) monitoring environmental conditions prior to the operation, and proceeding only if conditions were conducive to success, 2) reinterpretation of bait availability data using the lower 99% confidence interval to inform application rates and ensure sufficient coverage across the entire island, 3) treating the two applications as independent, 4) increasing the interval between applications, 5) seeking regulatory approval to give the operational team sufficient flexibility to ensure a minimum application rate at every point on the island, and 6) being responsive to operational monitoring and making any necessary adjustments.

This plan sets out the operational detail, logistics and framework for a planned eradication of introduced Pacific rats from Late Island (1,731ha) in the Kingdom of Tonga. The method for the eradication is the delivery of grain-based bait containing the anticoagulant brodifacoum, into every potential rodent territory on the island. This will be done during the driest part of the year when rodents are potentially most vulnerable due to lower relative availability of natural food supplies. Because of the island’s size and complex topography, the bait will be applied aerially using a helicopter with an underslung bait spreading bucket. Aerial application has been successful in eradicating rodents from many islands around the world, and the logistics and methodology are based upon similar successful operations. Mitigation measures will be required for key non-target species, especially the Friendly-ground dove. Monitoring of rodents and native species before and after the operation will be required to assess the success and effect of the operation.

Invasive species pose an enormous threat in the Pacific: not only do they strongly affect biodiversity, but they also potentially affect the economic, social, and cultural wellbeing of Pacific peoples. Invasive species can potentially be managed and that their impacts can potentially be avoided, eliminated, or reduced. However, neither the costs nor the numerous benefits of management are well understood in the Pacific. Thus, the goals of this project were: A) to account for both the costs and benefits of managing invasive species; B) to prepare empirically grounded advocacy materials to help increase investment in the management of invasive species; C) to help governments prioritise investment in managing these species; and D) to build capability for undertaking economic assessments in the future. To accomplish these goals, we undertook cost-benefit analyses (CBAs) of managing five species that are well established on Viti Levu, Fiji: spathodea campanulata (African tulip tree), herpestus javanicus (small Asian mongoose), papuana uninodis (taro beetle), pycnonotus cafer (red-vented bulbul), and merremia peltata (merremia vine). Next, we conducted a comprehensive training programme on the CBA for invasive species management for professionals from the Pacific. Third, we collaborated with Pacific organisations to develop a uniform guide to conducting CBAs with numerous examples from the region. We also designed a flexible Microsoft Excel-based tool for conducting CBAs, enabling professionals who did not attend the training course to nevertheless undertake rigorous CBAs on invasive spsecies management. Finally, we developed advocacy material and publicised findings from this project to promote investment in invasive species management. This report details these activities in turn. It also includes numerous appendices that include the tools, guidance documents, and advocacy materials developed under this project.