Why do birds fly in a V formation?

As a bird flaps, air swirls off the tips of its wings, creating an area of rising air just behind and to the side. By flying in that sweet spot, the bird behind gets a small free lift and needs less effort to stay aloft. A 2001 study of great white pelicans found their heart rates were around 11 to 14 percent lower when flying in formation than when flying alone. In 2014, researchers tracking northern bald ibises with GPS loggers found the birds positioned themselves precisely and even timed their wingbeats to catch the upwash. Leaders tire fastest, so geese and other large birds take turns at the front, sharing the hardest job across the flock.