The genus Hieraaetus, sometimes known as hawk-eagles, denotes a group of smallish eagles usually placed in the Buteoninae or Aquilinae subfamilies of accipitrids.
They are medium-sized birds of prey inhabiting Europe, Asia, Africa, New Guinea and Australia.
Little eagle, Hieraaetus morphnoides ― Australia
Pygmy eagle, Hieraaetus weiskei ― New Guinea
Ayres's hawk-eagle, Hieraaetus ayresii ― Africa
Wahlberg's eagle Hieraaetus wahlbergi (formerly Aquila wahlbergi) ― Africa
Booted eagle Hieraaetus pennatus ― Eurasia and Africa
Bonelli's eagle (Aquila fasciata, formerly H. fasciatus)
African hawk-eagle (Aquila spilogaster, previously a subspecies H. f. spilogaster or A. f. spilogaster)
Rufous-bellied eagle (Lophotriorchis kienerii, formerly H. kienerii)
Some authorities retain Bonelli's eagle and the African hawk-eagle in Hieraaetus. Also, some retain Wahlberg's eagle in Aquila, whilst still recognizing Hieraaetus as a separate genus.
Molecular genetic research has found Hieraaetus to be polyphyletic with Aquila.
The British Ornithological Union moved Bonelli's and booted eagles to Aquila in 2005, but was silent on the position of the non-European Ayres', little, and pygmy eagles.
This could create a taxonomic problem: the booted eagle is the type species of Hieraaetus, moving it would make that name a junior synonym of Aquila. Consequently, should any other hawk-eagles be retained as a distinct group, they would need to get a different genus name.
Sometimes the entire genus is merged into Aquila. This was the approach taken with The Clements Checklist between 2001 and 2009: starting in the 2001 revisions to the 5th edition, and retained in the printed 6th edition of 2007.
Christidis and Boles (2008) used an alternative approach. Accepting that both Aquila and Hieraaetus are polyphyletic, they moved spilogaster and fasciatus with the Aquila genus and retained the other former Hieraaetus group along with morphnoides and Aquila wahlbergi within the new delimitation of Hieraaetus.
The Clements Checklist, in its 2009 revisions, followed the same approach as Christidis & Boles, moving Aquila wahlbergi into Hieraaetus; restoring the booted, little and Ayres' eagles back to Hieraaetus.
As of 2014, the BOU lists the booted eagle on their Category D and E lists as H. pennatus, not A. pennata.
The pygmy eagle, or New Guinea hawk-eagle, H. morphnoides weiskei was formerly considered a subspecies of the little eagle H. morphnoides; it has been recognized as a separate species by some authorities.
Whether the fossil "Hieraaetus" edwardsi (Middle -? Late Miocene of SW Europe) belongs to the hawk-eagles proper (if there is such a thing) or into Aquila has not been determined.
Hieraaetus kienerii was found to be distinct, and has been assigned to a separate genus, Lophotriorchis.
DNA sequences from remains of the extinct giant eagle Harpagornis moorei (Haast's eagle) were found to be similar to those of the little eagle, suggesting that Haast's eagle also belongs in Hieraeetus.