That's mobbing; they attack predators to drive them away. I used to see buzzards being harried all over the place whebn I lived in Cornwall. I once saw what I assumed to be a buzzard come over the spoil tip at the top of the hill, being chased by two ravens. After a bit, it had obviously had enough, and without so much as flicking a wingtip, it doubled round, quadrupled its speed, and sent them squawking halfway across the sky. So I got the binoculars on it, and of course it was a peregrine, which just casually went on its way in peace.
That's a Short-Eared Owl. They used to breed on the moors round where I lived.
