Answers (2)
i dont think anyone truly knows. they only have theorys on it. it is thought that as each bird flaps its wings, it creates uplift for the bird immediately following. By flying in a "V" formation, the whole flock adds at least 71% greater range than if each bird flew on its own.
There are so many reasons, aerodynamics is a lot like hydrodynamics so here's an experiement that can be done at home with water. Get a bowl of water and put an object that will float on it. Then without touching the object put a finger next to it in the water and move the finger away from it. The object will move the direction the finger is moving, same with air. I hope that was a good answer but there are so many reasons, I can think of more.