Share 'Garden mystery'

Image a little dark but wondering what might have caused this flurry of digging activity, which I've never seen before in our garden. Whatever it is it's determined to get into the tree box from the bottom and in doing so has dug out a considerable amount of soil. Note soil mound next to wall, about a foot high. Because the entrance hole is only a few inches high it can't be a cat or fox and I've…