Do human impacts explain the number of birds threatened species on islands?

Marine islands are often referred to as nature's laboratories due to their singular geography and rich biodiversity. However, their unique distribution and isolation also make island fauna highly susceptible to recent human impacts. While conservation efforts are necessary, there is little research to explain why some islands host more threatened species than others. Locating regions with high numbers of threatened species is crucial to plan conservation actions that will provide the most benefit to biodiversity. The richness of threatened species may result from the interaction of environmental factors that promote species diversity, the occurrence of extinction-prone species, and human threats. While we have a good understanding of the processes that promote species diversity on islands, few studies have assessed the impact of human activities on island biotas. We analysed bird data on 1254 islands and found that the number of threatened species on islands can be mostly explained by the total species richness and spatial factors (i.e., area, isolation, and climate). The human appropriation of primary production (HANNP) and the proportion of land impacted by urbanization are the human impacts that most influence the threatened species richness on islands. Our results suggest that the expansion of urban areas and agriculture, especially on oceanic islands, must be carefully observed to prevent the imminent extinction of the endangered species in these ecosystems.