Have you ever wonder or see with your own eyes how your swiftlet fly out of a door with a grilled blocking it.
Why visiting a BH in Tumpat I took some time to capture the clip and see for yourself how these beautiful creature flew out of the BH through a grill door.
The gap between those bars were about 10 inches.
The owner wanted to prevent owls from entering but the owl were seen to still enter the BH.
There were some owl shit inside the BH.
Those birds seems to be very careful to fly out via the top part of the grill.
The one that entered seems to be a bit lower.
What ever you can observe from this flying out and in might give you some ideas what happened when you install a grilled door.
Enjoy the clip.