I saw all those tube openings and my first thought was Chipmunk condos.

I don't have NICE piles of cats like in the pictures, but I do have some small stacks of good mufflers, tail pipe and such that the chipmunks just love to store their nuts in and make nests in.

I just about stepped on a little chipmunk the other day as it was chasing it's mother around and they ran across my path. I stopped and stepped back, the mom turned and went back and waited on the side of the path where they had come from as it was a dead end on the other side where the little bewildered chipmunk was trying to figure out where it should go. I waited until it got back to it's mom then went about what I was doing..

I have to watch where I walk a bit as there are frogs, toads, friendly snakes and such around the yard.

hope you don't mind the hijack, but chipmunk condos might be of interest to some, then again maybe not.