This is a "Bat Tube", a device that allows bats to leave a building but does not allow them to return. This tube is installed in my new house (The Grange House)which has a bat problem. You can see here a bat that had just come through, taking flight.
Here is another bat that is crawling through.
One more bat coming through. Unfortunately, there are still cracks that the bats are escaping through. These cracks still need to be filled before the bat tube can work; currently if they can't get back into the tube, they can just go to a crack.
You can see another bat taking flight here.