Hickory Holes

I noticed a fairy fresh hole in the trunk of our neighbor’s hickory tree the other day.

It’s a big one, but it’s so high up that I can’t imagine anything other than squirrels or a bird living in a tree that high above the ground.

And I’m concerned about the health of the tree. There’s a similar but smaller hole a few feet lower. Is the whole trunk hollow inside? I’m anxious to see if the tree leafs out fully this year.