Is there a specific bird that a harpie had under her human part? So there is a mythical creature called a harpy, who was a half woman, half bird. Anything on what type of bird it was?

I'm not aware of any specific species being mentioned in the myths.

Traditional depictions generally seems to have considered the bird part to be some kind of bird of prey (given the size and the claws).

Further, given their nature as befouling creatures, I'd expect some kind of scavenger bird, like a vulture or buzzard.