Who or What Did This to My Grandma’s Tree?

I was doing winter preparation work at my grandma's house over the weekend when I noticed these holes in her tree. Who did it?!

Looking at these holes, I'm pretty impressed. Almost perfectly round and symmetrical. Even more impressive? The fact the holes are in the underside of the tree branch, I'm standing under the branch looking up taking these pictures.

Either way, my grandma wants me to get a chain saw and cut off that tree branch. I guess I know what I'll be doing next weekend.