I noticed something unusual during my inspection of a few BHs in Sungai Patani, Segantang Garam, Kampung Bujang and Bumbung Lima Butterworth.
This weird behaviour happened during the first week of August 2014.
It seems that they seems to gather in large numbers when the Pukau external sound is played.
I am not sure what is causing this rare over crowding but you can easily say that they are obsessed with the sound.
This have something to do with their breeding cycle.
I have this gut feel that they will shortly start their breeding cycle.
They will fly all over the BH and many will try to find any hole to enter.
At Segantang Garam the nearby residential house experience swiftlet entering the main hall.
The owner said that they seems to fly all over the place and entered his house regularly.
He confirmed that during later part of the evening the number will be three to four times bigger.
At Kepala Batas closed to Bumbong Lima bridge the same thing was observed on a number of BH with their external sound in full blast.
I happened to be visiting a BH and the moment I changed the external sound to Pukau they came in big numbers.
Have a look at these video clips and look positively: