Ouch...just reading this thread! Just one of the reasons I'll never have a big bird. I'm too chicken...pun intended. Gussie is quite nippy...she IS a conure...but has, to date, never broken my skin. I believe she could, if she wanted to. Buddy, my recently departed lovie, rarely broke skin. She had various degrees of pressure when biting, starting with a warning nip & gradually escalating, as necessary, depending on how stubborn--or inattentive--I was being. She occasionally did go for blood...deliberately. The bite that annoyed me the most was the welt she would raise on the skin just below my collar bone. Never broke the skin there, just raised a welt. She knew just where to bite, depending on where she was at the time I annoyed her. Her favorites were just below my eye brow, my nostril, the upper part of my ear, my lip, the skin just below my collar bone, and, my least fave, the smallest but most prominant part of my chest...she knew where it was & went for it, even when it was covered with several layers of cloth! Fortunately she reserved that one for extreme irritation. And, fortunately, she was too small to perform an actual amputaion. I hope your big birds don't ever learn that trick!
My little bite pictures aren't even enough to post pictures of compared to those. 
