Hagravens are aggressive, bird like humanoids often found in Skyrim. Coming in contact with one can cause Brain Rot, a disease that reduces Magicka. Legend has it they were once Witches but gave up their humanity to become Hagravens (as shown in the quest Repentance). Revered by the Forsworn, they despise nature, and hunt down Spriggans to capture and sacrifice. In the book The Madmen of the Reach, it is noted that the Hagravens were in the Reach since "the beginning" and side with the Forsworn. They are often found with Witches or Forsworn, and are exclusively female. Hagravens have a distinct raspy breathing and heavy, wet sounding footsteps.
Some Hagravens are something called Forsworn Matriarchs. They are in command of a specific Forsworn redoubt. Named Matriarchs include Petra, Melka, and Drascua. Matriarchs are normally tended to by Forsworn, but there are several occasions where they are accompanied by witches and hags like other Hagravens.
In some rare cases, Hagravens may drop a Daedra Heart.