As each bird flaps it's wings, it creates an uplift for the bird immediately following. By flying in V formation, the whole flock has at least 71% greater flying range than if each bird flew on it's own.

When a goose flies out of formation, it suddenly feels that drag and resistance of trying to go it alone and quickly gets back into formation to take advantage of the lifting power of the bird in front.

When the lead goose gets tired, it rotates back into the formation, and another goose flies point at the head. The geese in formation honk from behind to encourage those up front to keep up their speed.

When a goose gets sick or wounded and falls out of formation, two other geese will fall out with that goose and follow it down to lend help and protection. They stay with the fallen goose until it is able to fly or it dies, and only then do they launch out on their own, or with another formation to catch up with their own flock