Buzzard (Buteo buteo)

Moore Reserve.
Not a brilliant shot. There was another buzzard on the frozen lake being harassed by a rook. He had a rabit and the rook kept creeping up and pulling his tail to distract him. He had long trousers and white at the nape of his neck and on his belly. I thought he might have been an eagle at first but he wasn't big enough. I'm sure I've seen a picture of one with trousers. Perhaps european.