Why do birds fly in V-formation ?

Scientists know the answer.

Each bird takes a special position relative to the tip of the wing of the bird in front, and this facilitates their flight. The wings of a bird flying in front of the key create edge eddies similar to the wings of an airplane. These streams stretch along the whole flock: the air falls and then rises, and the following birds in a key try to fly so as to hit the rising air, while avoiding falling - for this, each bird flies at an angle of 45 degrees to its predecessor and tries to match it pace with a flap of wings.