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.

The rugged islands where the original Robinson Crusoe was marooned in the south-east Pacific are remarkable for the number and variety of endemic plants, some of which are pollinated by a beautiful endemic hummingbird. They are also the main breeding station of a fur seal, which once numbered millions but was later thought to be extinct, and several widespread seabirds. So far the only losses appear to be the endemic sandalwoods and widespread elephant seal, but the other wildlife is now threatened by deforestation, erosion and competition or predation from introduced species. There is a need for more support for local conservation measures, since the islands may soon start to undergo rapid development.

During the austral summer of 1996/1997 we studied south polar skuas at Svarthamaren, Dronning Maud Land, Antarctica, where the world's largest known colony of Antarctic petrels is found. Our censuses suggested approximately 250 full-grown skuas and 140,000 breeding pairs of petrels were present. During their breeding season, skuas did not visit the open sea at least 200 km from the site; they relied entirely on prey caught and scavenged from the petrel colony. Because the site is so isolated, we asked whether the prey (petrels) had swamped the predators (skuas), or whether there was evidence that predator numbers were limited by the size of the prey population. Particularly at the end of the petrel incubation period, we found a close correspondence between the energy required by adult skuas and their chicks, ascertained from time budget studies, and the rate at which petrel eggs disappeared from the colony. This suggests that, in this closed system, the predator population was limited by the prey population, and that predator swamping was not an advantage that petrels gained by nesting in this remote location.

The cuckoo Cuculus canorus is divided into various gentes, each laying a distinctive egg and favouring a different species as host. It has long been assumed that the gentes remain distinct because female cuckoos lay the same egg‐type as their mother and prefer the same host, developing this preference by imprinting on their foster parents. We tested whether imprinting occurred by laboratory experiments with 7 cuckoos originating from reed warbler Acrocephalus scirpaceus nests. Two were transferred soon after hatching to robin Erithacus rubecula nests and were raised by robins, while the other five were raised by reed warblers. When about 12 d old, the nestling cuckoos and their foster parents were transferred from the wild to aviaries, where the fosterers continued to raise the cuckoos to independence. The fosterers were then released and the cuckoos retained and presented, at one and two years of age, with a behavioural choice between robins and reed warblers. None of the cuckoos (five females and two males) displayed a consistent preference for the host that reared them even, in the case of females, after oestradiol implantation. We discuss the inadequacies of our experiment and present data on cuckoo egg types to test whether natal philopatry might be sufficient to maintain the gentes. We suggest that mitochondrial DNA studies, now underway, will help to resolve the issue.

No abstract