Question: Why do geese fly in a V?
Answer: There are advantages to flying a V. The first advantage is aerodynamic. As a single bird flaps, it disturbs the air by creating wingtip vortices. These vortices create a downwash that increases the drag on the wings, which is not desirable. However, as we all know for every action there is a reaction. So, the downwash created by the first bird creates an upwash for the second bird. The second bird flies behind and slightly above it. The second bird receives lift and a reduction of drag which means this bird does not have to flap as often or as hard as the first bird.
There is some advantage for the first bird. It saves energy by having the second bird dissipate the upwash. In a long V the birds that use the most energy are the first and the last birds in the V. That's why birds flying in formation will change positions often.
In one study, the researchers monitored the heartbeat of pelicans when flying. The heartbeat of pelicans flying by themselves was significantly higher than the heartbeat of pelicans flying in formation.
Another reason for flying in a V formation would be to maintain visual contact with other birds in the flock. Remaining in a flock offers protection for all the birds.