does a sparrowhawk ground feed on worms?

We have an acre garden next to a field. A small bird of prey is currently everyday sitting on various trees branches, as well as posts, and is constantly going down onto the lawn or border edges. I can't believe we have that many mice or voles running round and after a few seconds returns to the tree and appears to have nothing in its beak. Its brown with a lighter breast and bright yellow legs. Do they also feed on worms? many thanks in anticipation