After habitat loss and degradation, the leading threats to biodiversity are over-exploitation and invasive alien species. For birds, newly synthesised data using the standard classification schemes for utilisation and threat types for the IUCN Red List allow novel analyses on the importance of these threats and permit the calculation of Red List Indices (RLIs) to show trends in the status of birds driven by these factors. At least 45.7% of extant bird species (4,561 species) are used by humans, principally for pets (37.0%) and for hunting for food (14.2%), but other uses include sport hunting, ornamentation and traditional medicine. Much of this use drives trade at an international scale, involving at least 3,337 species (33.9%, substantially higher than previous estimates), mostly for the pet trade. RLIs show that although successful control and management of use and trade have led to some species improving in status, this has been outweighed by the number of species deteriorating in status owing to unsustainable exploitation. Overall, the RLI showing trends in extinction risk driven by issues related to use shows a negative slope: human use of birds is currently unsustainable. Similarly, and of relevance to the Convention on the International Trade in Endangered Species (CITES), the RLI for internationally traded bird species showing trends in extinction risk driven by issues related to international trade is also declining: international trade remains a threat to the world's birds. Invasive species impact at least one third of the world's threatened bird species (398 species, 32.6%), with mammals being the most important (impacting 81.1%), particularly through predation by carnivores and rodents. The RLI illustrating impacts of invasive species shows that they are driving a deterioration in the status of the world's birds. RLIs for the impacts of use and invasive species will be important indicators to help track progress towards the target of significantly reducing biodiversity loss by 2010.
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