The purpose of planting these trees around Bhs is to attract insects (wasps), when there are insects there will be Swiftlets.
The flowers are pollinated by very small wasps that crawl through the opening in search of a suitable place to lay eggs. Without this pollinator service fig trees could not reproduce by seed. In turn, the flowers provide a safe haven and nourishment for the next generation of wasps. This accounts for the frequent presence of wasp larvae in the fruit, and has led to a co evolutionary relationship.
But remember no matter how many figs trees you plant around your Bh’s compound if your Bh is poorly built then it is of no use.
Swiftlets may come to have free breakfast and lunch every day and after that they will fly back to their Bhs that has good Micro & design. So your effort of planting of the Figs trees is to serve others Bhs birds population.
This is due to its ability to produce large amount nectar which attracts lots of insects.It can be found everywhere. In fact I can find them just a few steps outside my house. It can be easily grown. It has plenty of dry seeds. If you don’t want to plant it from the seed you could pluck the small young trees around the roots of the big trees
Dry Lamtoro Seeds. You can plant it yourself.
Another one is the coconut tree. During the flower time it attracts lots of small beetles and black ants which is the favorite food of swiftlets. There are many types , plant those that doesn't grow tall. It is not advisable to have taller tress surrounding bhs.
The flowers of the coconut tree, Insect Love them. That is why places like Sabak Bernam, Bagan Datok,etc have huge population of Swiftlet because both have plenty of coconut plantations.