Birds flying at dusk - crows and swifts

On the evening of 4 May I saw a lot of birds flying around. They seemed to be mainly crows with a few kites as well. They were flying for about 15 minutes before they decided onto the roof of a neighbouring building. They stayed there for a few minutes before flying off, presumably to their roosts. It was 6.05pm when they left. This is in Kuala Lumpur, Malaysia.

Then 40 minutes later I heard a lot of swifts flying around, both in front and at the back of my condo. They make quite a lot of  noise when flying. It was impossible to get a clear photo of the swifts with my camera as they fly so fast, but this video is better.

It was surprising seeing these 2 sets of birds on one evening. I wonder if it was due to an abundance of insects that evening.