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.

Past studies have indicated that Pacific rats Rattus exulans are significant predators of the chicks of surface-breeding seabirds, namely gadfly petrels Pterodroma spp., on Henderson Island, central South Pacific. Further fieldwork in 2003 confirmed the heavy predation of chicks of Murphy's petrel P. ultima by rats. By extension, heavy predation is also likely each year on the endangered Henderson petrel P. atrata, for which Henderson Island is the only confirmed breeding site. To assess how important petrels are in the overall diet of rats, we conducted stable isotope analyses of rats from the shore, where petrels are most concentrated, and from about 1 km inland, where fewer nest. The carbon isotope results suggested that inland rats obtain about 30% of their food from marine sources, while the figure for shore rats was about 40%. We consider factors that may have acted to inflate these proportions. If, as suggested by these results, petrels are not the predominant component of the rats' diet, then rat populations and hence rat predation on petrels may not diminish even if petrel populations decrease further. In the light of probable low annual breeding success, we drew on vital rate information for the cahow P. cahow to model changes in the Henderson petrel population, and found a negative growth rate (λ = 0.9918) under present conditions. Growth rate became positive if annual adult survival rose above 0.95 or breeding success above 0.25, the latter unlikely while rats remain on Henderson. We conclude that the Henderson petrel population will probably continue to decline in the absence of conservation intervention.

Residues of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] averaging 6.44 parts per million in eggs and chicks of the carnivorous Bermuda petrel indicate widespread contamination of an oceanic food chain that is remote from applications of DDT. Reproduction by the petrel has declined during the last 10 years at the annual rate of 3.25 percent; if the decline continues, reproduction will fail completely by 1978. Concentrations of residues are similar to those in certain terrestrial carnivorous birds whose productivity is also declining. Various considerations implicate contamination by insecticides as a probable major cause of the decline.

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