Pete, I've asked the exact same question every time I see these crazy birds all take off together. I really don't know how they can flow so close together. The only thing I can think of is all that yelling they do all the time must be like honking the horn in your car in dense traffic. At least, that's how they do it in India!
I'm not very good with numbers but there must be more than 25 there - lol
How do they not bump into each other, and how can you fly in that turbulence.
Nice to see a flock and realise that not every thing is becoming extinct!