Why birds fly in a V formation

Why do many birds fly in a V formation? The wonderful video curators at The Kid Should See This came across this excellent 2014 clip above from the science journal Nature explaining research into the aerodynamic advantages of the formation. From Nature:

...UK's Royal Veterinary College put data loggers on ibises to record their position, speed and wing flaps when they migrated. The ibises position themselves within the V so that they benefit from the flow of air created by the bird in front. They carefully time their wing flaps with their flock mates', to get an extra lift when flying high.

More at Nature: "Precision formation flight astounds scientists"