Population Explosion?

Does any one know the collective noun for  pigeons? I mean ,'flock' seems somewhat inadequate for a number such as this. I counted these in the photograph on the PC, calculating approximately 253, but at the time there were still others in the air or a little out of shot. 

That's a lot of pigeons for a small urban square and, judging by their behaviour, there will probably be even more after a few weeks...