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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.

Between 1892 and 1930, 58 percent (30 taxa) of Hawaiian endemic forest birds either were greatly reduced or became extinct. The order in which the islands experienced major declines ofseveral forest birds is Oahu (ca. 1873-1887), Hawaii (1892-1900), Mo10kai (1893-1907), Maui (18941901), Kauai (after 1900), and Lanai (1926-1932). Loss of habitat, reduced food supply, introduced avian diseases, as well as predation by man, feral cats, mongooses, and Norway rats (Rattus norvegicus) all appear to have reduced some species ofbirds, but none ofthese factors adequately explains the accelerated rates ofdecline offorest birds that occurred after 1892. Although it has been assumed that roofrats (Rattus rattus) reached Hawaii with the first European ships at the end of the 18th century, there is circumstantial evidence, independent of the bird decline data, that indicates that this rat did not arrive until after 1840, probably between 1870 and 1880. The hypothesis is advanced that after its establishment on Oahu in the 1870s, R. rattus spread to the remaining large islands in the group, resulting in a stepwise accelerated decline offorest birds on each island in turn. Hawaii thus parallels some other Pacific islands where major reductions of birds have followed the establishment of R. rattus. The need for precautions to prevent rats from reaching rat-free islands in the Hawaiian group is emphasized.