I've never seen a rook in the garden before but a few days ago this one appeared. It's never come back since then. What I did learn is that rook's have a crop under the beak where they store food to take back to the nest. You can see the bulge in one of the shots.
Thank you for the splendid Mike. I must admit the bit of trivia about the Rooks crop had passed me by until now and was brilliantly illustrated by your photos.