BTB is a very new idea of how you can increase your BH tenants but using those birds.
The term BTB = Burung Tarik Burung (your birds lure other birds).
As we are well aware these swiftlet are born with the instinct to live in a colony.
They love to group together to have better success of survival.
If they see a large crowd of their own species they will join the fun.
How do you want to use this weakness which they have?
Well what you can try to explore is to have them to build a crowd at your BH LMB hole.
First you need to make sure that you have around 10-20 nests (minimum).
Without the number you might have a tough time to apply the idea.
If you owned a flock of them about 30-40 birds you can apply this simple technique.
So how do you create a situation where they will gather at a place and attract others to join them?
Well you might want to reduce the size of your lmb hole.
Reduce to a small hole so that when your tenants return home in the evening they need to slow down and ques up to enter the reduced in sized hole.
Another method is to play a sound that will make them to slow down and slowly enter the hole.
The external sound that can do this is named as NBU (no body but you).
You might want to combined the two things.
First reduce the size of the lmb to about 1.2 feet high by 1.5 feet long.
Second change your external sound to NBU.
Once these two things are carried out your tenants will slow down and they will take some time to enter the now reduced in sized hole and the action will pull other birds that pass your BH rooftop.
Try and monitor the result.
I am trying the technique on a few BHs that I have their keys with me but one close decipel claimed that within 2.5 months his tenants shot up from 30 to 300 birds.
Within 2.5 months the bird counts shot up 10 times.
Nothing to loose if you should try this BTB technique and if you observed any improvements plese share it with me at firstname.lastname@example.org
You might want to call me at +60177551318.