entire flock of birds can make hairpin turns in an instant." - Peter Freiderici
Still, to date, no one really knows how the birds do what they do. However, with all our technological innovations, from high-speed photography to computer simulations there may soon come a time when we discover the secrets behind how thousands of birds can fly together in what looks like the most beautifully choreographed fashion of something that could only be achieved after hours and hours, week by week of practice.
Until then, I suggest you just take in this magnificent sight and thoroughly enjoy it. I assure you that you will long remember it, and if you ever doubted that there's magic in the world, you will likely come away an inspired believer.