Disturbing!
Very disturbing. You are right, giant birds would be scary. If I were faced with one, I think I might just sit down and let it happen. Too scary.
I think that, if you wanted to add to this, you could change the puke a bit. I think the mama bird chews the stuff up before feeding it, right? Maybe not... But if so, you could make some nasty mashed up peoples, still showing some signs of humanity (faces, maybe some arms, organs, etc), but the rest of it being unidentifiable, mashed up flesh. Then, maybe you could add some people still alive somehow trying to get the hell out of there, but they can't because they're either glued to the mass of flesh and mama bird saliva or they've already fallen into the baby bird jaws.
Just something to think about. Awesome work!!!