Why do birds fly in a V?

When in groups, birds often fly in a V formation. This formation is a likely that they are traveling a far distance. In order to reduce the amount of energy spent on their journey, birds fly in a V shape. In the V formation, each bird flies a little behind and above the bird in front of it. This way, each bird (except the front one) experiences less wind resistance and therefore doesn't have to exert as much effort flying. Each bird takes a turn leading the V formation to allow the others to rest. Another advantage of the V formation is that the birds in the back can keep an eye on the other birds to make sure no bird gets lost or falls behind.