Why do geese fly in a V shape?

It takes lots of energy to fly, because they are constintly flapping their wings trying to create lift. An updraft around the birds wing tips is created with all the flapping they do. If the bird behind the first one can fly in a special spot behind and slightly above the first bird they can save their energy. Using less energy means flying longer distances for the geese. When the first bird gets tired it falls to the back and the next bird takes its place.