Black Vultures
A lot of people don't think of Vultures as birds of prey, and I think that because of Turkey Vultures which are pretty timid and stick to carrion. Black Vultures though? Nah. These things are aggressive and in some parts of the country are a real nuisance because they'll prey on small livestock like piglets, chickens, lamb and calves.
I got pretty close to these guys, but you wanna be really careful doing that. No quick movements, no loud noises. When frightened they empty the contents of their stomach. I've heard the smell is horrific.