This indicator shows trends in the status of all birds worldwide driven only by the negative impacts of invasive alien species or the positive impacts of their control. It is based on BirdLife International’s assessments of extinction risk for all birds for the IUCN Red List, specifically the number of species in each Red List category of extinction risk, and the number moving categories between assessments owing to genuine improvement or deterioration in status driven by impacts of invasive alien species or their control. All other changes are excluded, whether from improved knowledge, or genuine impacts of other threats or their control. Trends for mammals and amphibians will be added when the index is updated in 2017.