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Rodents remain one of the most widespread and damaging invasive alien species on islands globally. The current toolbox for insular rodent eradications is reliant on the application of sufficient anticoagulant toxicant into every potential rodent territory across an island. Despite significant advances in the use of these toxicants over recent decades, numerous situations remain where eradication is challenging or not yet feasible. These include islands with significant human populations, unreceptive stakeholder communities, co-occurrence of livestock and domestic animals, or vulnerability of native species. Developments in diverse branches of science, particularly the medical, pharmaceutical, invertebrate pest control, social science, technology and defense fields offer potential insights into the next generation of tools to eradicate rodents from islands. Horizon scanning is a structured process whereby current problems are assessed against potential future solutions. We undertook such an exercise to identify the most promising technologies, techniques and approaches that might be applied to rodent eradications from islands. We highlight a Rattus-specific toxicant, RNA interference as species-specific toxicants, rodenticide research, crab deterrent in baits, prophylactic treatment for protection of non-target species, transgenic rodents, virus vectored immunocontraception, drones, self-resetting traps and toxicant applicators, detection probability models and improved stakeholder community engagement methods. We present a brief description of each method, and discuss its application to rodent eradication on islands, knowledge gaps, challenges, whether it is incremental or transformative in nature and provide a potential timeline for availability. We outline how a combination of new tools may render previously intractable rodent eradication problems feasible.

Rodent eradications undertaken on tropical islands are more likely to fail than eradications undertaken at higher latitudes. We report on 12 independent rodent eradication projects undertaken on tropical islands that utilized the results of an in situ bait availability study prior to eradication to inform, a priori, the bait application rate selected for the eradication. These projects also monitored bait availability during the eradication. The results from our analysis verified the utility of bait availability studies to future rodent eradication campaigns and confirmed the influence of two environmental factors that can affect bait availability over time: precipitation prior to the study and the abundance of land crabs at the study site. Our findings should encourage eradication teams to conduct in-depth assessments of the targeted island prior to project implementation. However, we acknowledge the limitations of such studies (two of the projects we reviewed failed and one removed only one of two rodent species present) and provide guidance on how to interpret the results from a bait availability study in planning an eradication. Study design was inconsistent among the twelve cases we reviewed which limited our analysis. We recommend a more standardized approach for measuring bait availability prior to eradication to provide more robust predictions of the rate at which bait availability will decrease during the eradication and to facilitate future comparisons among projects and islands.

On the 21st of October, 1972, hurricane "Bebe" devas- tated a large part of Funafuti atoll, Ellice Islands. Among the most spectacular geomorphological alterations caused by the hurricane was a storm beach 19 km long, 4 m high and 37 m wide. The amount of coral debris washed up from the offshore coral reefs onto the reef flat was estimated at 2.8 x 10 tons of material (Baines, Beveridge and Maragos, 1974). The oceanside reef communities of the SE and E rim of the atoll had been totally destroyed, and those of the inner reefs of the lagoon side had been heavily damaged. Eight months after the storm a quantitative analysis of the resettlement and recruitment of coral species on 7 reef sections was carried out: the destruction of the biophysiographic zones could be described as increasing from the northern border and also to the W rim of the atoll. Near the centre at Fongafale the lagoon reef flat was covered by thick carpets of the brown alga Dictyota bartaysii, possibly brought about by eutrophication effects. The resettlement of the reef flat by corals began with the recolonization of branching corals as well as regeneration of the very few surviving massive corals: about 80% of the number of new colonies belong to Acropora (mainly A. humilis and A. hyaclnthus), and about 20% to Pocillopora eydouxi, Porltes lutea (?) and some Faviidae. The percentage of the area settled by the massive coral species is, however, greater than that settled by the branching species. Nevertheless, in the long-term, branching corals are expected to have a decisive influence on the future structural and biophysiographic zonation of the reef edge and reef flat, due to their more numerous young colonies, which are evenly scattered over the reef area, and due to their rapid growth rate. Consequently, an Acropora humilis - hyacinthus-community or an Acropora - Pocillopora eydouxi-assemblage can be predicted as the future biophysiographic zone.