The V formation possibly improves the efficiency of flying birds, particularly over long
migratory routes.
[1] All the birds except the first fly in the
upwash from one of the
wingtip vortices of the bird ahead. The upwash assists each bird in supporting its own weight in flight, in the same way a
glider can climb or maintain height indefinitely in rising air. According to a 1970 paper, in a V formation of 25 members, each bird can achieve a reduction of
induced drag and as a result increase their range by 71%.
[2] The birds flying at the tips and at the front are rotated in a timely cyclical fashion to spread flight
fatigue equally among the flock members.
Canada geese, ducks and swans commonly form a skein in V formation.
[3]