For more information about the IUCN Red List of Threatened Species, please visit the IUCN Red List website.
The API outputs the same data which is from the IUCN Red List website.
IUCN 2018. IUCN Red List of Threatened Species. Version 2018-1 <www.iucnredlist.org>
If you encounter any problems using the API, or would like to provide feedback of any kind, please contact the Red List team.