Today I watched for 10 minutes a flock of pigeons flying round the domes of a mosque across the road. There were other pigeons sat on one of the domes, and occasionally some of these would join the flock while some of the flyers would settle on the dome. There was no haste in the flying, so they couldn't have been chasing insects, no aggression, so there was no conflict between birds, so what were they doing?

I know swallows flock and fly around before 'going to bed' at night, but this was in the middle of the day and featured common pigeons.

Do all bird species do this 'orbiting' of landing spots and if so why?