I used to go birdwatching on Goss Moor in Cornwall, and there was a ruined hut where a pair of them roosted regularly. One winter I was walking across there after we'd had several inches of snow overnight, and there was one of them out hunting. It was probably starving as they can't catch their prey when everything's covered in snow. It spotted me coming and flew off with its head turned round 180 degrees, so it was looking straight back over its back.