Integrated Taxonomic Information System (ITIS): Pernis steerei (TSN 824110)itis.gov. Viitattu 10.11.201. (englanniksi)
iucnredlist.org
BirdLife: Pernis steereiIUCN Red List of Threatened Species. Version 3.1. 2013. International Union for Conservation of Nature, IUCN, Iucnredlist.org. (englanniksi)