Follow the leader

Shawn and I were driving one day (probably looking for gas!) when we noticed the birds flying in the infamous V formation, indicating that fall is coming. It was a perfect V, not one bird out of formation. That got us wondering. What made the birds decide on a V and not a Z or an X? And who decides which bird gets to be the leader, or do they take turns? How do they know who goes in which place in the V? Another day in the Pyfrom family......