More than US$21 billion is spent annually on biodiversity conservation. Despite their importance for preventing or slowing extinctions and preserving biodiversity, conservation interventions are rarely assessed systematically for their global impact. Islands house a disproportionately higher amount of biodiversity compared with mainlands, much of which is highly threatened with extinction. Indeed, island species make up nearly two-thirds of recent extinctions. Islands therefore are critical targets of conservation. We used an extensive literature and database review paired with expert interviews to estimate the global benefits of an increasingly used conservation action to stem biodiversity loss: eradication of invasive mammals on islands. We found 236 native terrestrial insular faunal species (596 populations) that benefitted through positive demographic and/or distributional responses from 251 eradications of invasive mammals on 181 islands. Seven native species (eight populations) were negatively impacted by invasive mammal eradication. Four threatened species had their International Union for the Conservation of Nature (IUCN) Red List extinction-risk categories reduced as a direct result of invasive mammal eradication, and no species moved to a higher extinction-risk category. We predict that 107 highly threatened birds, mammals, and reptiles on the IUCN Red List-6% of all these highly threatened species-likely have benefitted from invasive mammal eradications on islands. Because monitoring of eradication outcomes is sporadic and limited, the impacts of global eradications are likely greater than we report here. Our results highlight the importance of invasive mammal eradication on islands for protecting the world's most imperiled fauna.conservation | restoration | invasive species | island | eradication T he rate of global species decline and extinction is rapid and likely to increase (1-4), although at least US$21.5 billion is spent annually worldwide on conservation of biodiversity (5). Improving conservation outcomes has focused largely on highlevel increases in efficiency, including the distribution of funding across countries (5), or on identifying the ecoregions, habitats, and species most in need (6). Although great strides have been made in promoting evidence-based conservation (7), systematic evaluations of the effectiveness of different actions taken to protect biodiversity at the global scale are rare, with the exception of protected areas (8).Islands occupy ∼5.5% of the terrestrial surface area but contain more than 15% of terrestrial species (9), 61% of all recently extinct species, and 37% of all critically endangered species on the International Union of the Conservation of Nature (IUCN) Red List (10). Invasive nonnative mammals (hereafter, "invasive mammals") are the main cause of animal extinctions on islands and are one of the most important threats to remaining insular biodiversity (10-12). Eradicating invasive mammals from islands is an increasingly common conservation tool and has been ...

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To eradicate invasive Norway rats, an aerial broadcast of the rodenticide Brodifacoum-25W Conservation was conducted on 2,777-ha Rat Island, within the Aleutian Islands Unit of Alaska Maritime National Wildlife Refuge, between 29 September and 5 October 2008. During subsequent visits to Rat Island (in spring and fall 2009) to check for evidence of remaining rats and to look for evidence of nontarget mortality, personnel found an unexpectedly high number of dead birds: more than 420 carcasses, mostly glaucous-winged gulls and bald eagles, but also included 24 other species. Some carcasses had tissue suitable for analysis and were collected. Seventy bird carcasses were necropsied and cause of death was determined for 50 birds; 45 died of brodifacoum toxicosis. Necropsy determined almost all gulls and eagles had extensive hemorrhaging, consistent with brodifacoum poisoning. All eagles and all but 1 gull tested positive for brodifacoum residues. Positive tests for brodifacoum also were recorded for single specimens of emperor goose, northern fulmar, pelagic cormorant, peregrine falcon, rock sandpiper, and gray-crowned rosy finch. Two Lapland longspurs tested positive for exposure to brodifacoum. Nontarget bird mortality from brodifacoum exposure at Rat Island was higher than predicted in the Environmental Assessment.

The intentional and unintentional movement of plants and animals by humans has transformed ecosystems and landscapes globally. Assessing when and how a species was introduced are central to managing these transformed landscapes, particularly in island environments. In the Gulf of Alaska, there is considerable interest in the history of mammal introductions and rehabilitating Gulf of Alaska island environments by