Dr. Donald Croll, University of California Santa Cruz
Abstract: Islands comprise only 5.3% of Earth’s land area yet maintain 19% of bird species, 17% of rodents, and 17% of flowering plants. Species diversity is disproportionately threatened on islands in relation to the islands’ proportion of both global land area and species, with 61% of all recorded extinctions in the past 500 years and 37% of all critically endangered species confined to islands. Birds on islands are particularly threatened, accounting for 95% of documented avian extinctions in the past 500 years, and 59% of birds currently listed as critically endangered. Because most seabirds breed on islands where there are exposed to land-based threats along with sea-based threats, they are the most threatened group of marine animals with 29% of species at some risk of extinction. To guide island-based seabird conservation actions, we identified all islands with extant or extirpated populations of the 98 globally threatened seabird species, as recognized on the International Union for Conservation of Nature Red List, and quantified the presence of threatening invasive species, protected areas, and human populations. We matched these results with island attributes to highlight feasible island conservation opportunities. We identified 1,362 threatened breeding seabird populations on 968 islands. On 803 (83%) of these islands, we identified threatening invasive species (20%), incomplete protected area coverage (23%), or both (40%). Most islands with threatened seabirds are amenable to island-wide conservation action because they are small (57% were <1km2), uninhabited (74%), and occur in high or middle-income countries (96%). Collectively these attributes make islands with threatened seabirds a rare opportunity for effective conservation at scale.