Flocks of Birds

I have always wondered why small birds sometimes fly in flocks. Are they talking to each other, communicating their direction of flight, or have they practiced so many times that they just know? The rippling black sea of fluttering wings has often delighted and dazzled me. Seeing a swooping flock never fails to make my heart race with excitement, and makes me wish that I was part of the flock, darting here and there above the fields and trees, and in complete unison through the cool air, the wind sailing through my feathers. 


There is some interesting information found in these two links:


http://answers.google.com/answers/threadview/id/595648.html
http://www.ehow.com/about_6389011_do-fly-together-large-groups_.html


But when it is all said and done, they admit that the real reason birds flock is still a mystery!