So I fought my very first Hagraven in Skyrim today, and I've begun wondering if they're somehow related to the Harpies from Daggerfall (maybe they're one and the same, and "Hagraven" is just the Nordic word for "Harpy", like how "Skeever" seems to mean "Giant Rat"). Both are half human and half bird (although the Hagravens are more human than bird), and it seems the Hagravens live in the Reach, near the border of High Rock.

Another thing to note is how the Forsworn (who are Daedra worshippers) camps they live near are full of deer skulls. Could it be that they're a creation of Hircine?

And on a completely different topic...

Skeevers are distinct from rats; they're just rat-like. Look at the tails.

Hagravens might be construed as harpies though. They are a bit more human than daggerfall's harpies, but harpies are basically just bird-women, no?

Apparently Hagravens are also witches of Glenmoril.

Bethesda ran out of creature models.

I seem to recall reading somewhere that Hagravens are what Skyrim's witches aspire to become, suggesting that they used to be human (also note that the game's Glenmoril Coven seems to consist entirely of Hagravens). I don't know if Daggerfall's Harpies came from humans or are a separate race altogether.

EDIT: Ninja'd

I know I'm a little late to this discussion, but I just wanted to confirm that, yes, human witches can become Hagravens. There's a sidequest which involves the PC helping someone to stop this process.

Yeah, I remember hearing something like that.

Makes sense, don't some of the witches in Daggerfal morph from a beautiful girl into an old crone?

I can confirm this. The name of the book has slipped my mind, but there is a book in Dragonsreach which tells the story of Hagravens.

I don't remember the exact title but it's "______ Bestiary: Hagravens"