Once a Wren house...

Someone has been carving the entrance to the wren house and it is much larger. It still has sticks in it from last year when Mr Wren filled it. He usually starts at least three nests before settling down with his mate. Any likely nest his stuffs with sticks to keep others away.
But this carving is different. I wonder who it is with teeth to have done it. A squirrel? Any suggestions?
I don't think a bird will settle in it.