Some can be seen covered with those cement board so that the entrance hole will be so small until it is very difficult to find and enter the BHs.
You know why most people opt for a very small entrance holes?
Most common excuse will be because my Sifu says that a big hole will make your BH too bright.
Some will come out with this reasoning that if you open the hole too big there will be too much air blown into the BH.
Some will also give excuses that the larger the entrance hole the more prone it will be to those owls.
I don't actually accept any of those excuses.
My main concept is how to bring in as many swiftlet into my BH especially a new one.
Too small will make them find it difficult to enter.
Too big will not be an easy to control both the light and the air coming in during windy season.
My choice will always be 3 feet wide by 4 feet high.
The 4 feet high will help to allow those birds to fly in direct from a steep angle when they return home.
The 3 feet width will allow me to install adequate number of tweeters on the two frames of my entrance hole.
In Lenggong BH case, during my report writing I wrote to the owner that the first thing that I wish to do with the BH was to open the main entrance hole.
"So what will happen to those bright light Harry?" he asked.
My answer to him is simple. Just block those light from entering your nesting rooms using partitions.
You know that they harm the nesting room so you need to think very deep on how to reduce those light.
If you can handle this important part in reducing those bright light, you have no problem to have those larger sized entrance holes.
Have a look at the Lenggong main entrance hole: