Regarding the entrance, I had to buy a smaller drill bit to get the right size entrance, as the entrance size largely determines what kind of birds will settle in the birdhouses. This type of bird prefers only small fans and eats on a very strict diet, lots of salad and pure protein in insects. This is why they want to keep the entrance small - to help them achieve their dream body.
Thanks for the comment :)
Hahaha. Interesting. It makes sense. Thanks for the feedback