Geese fly formation theory
If we consider only aerodynamic factors in the geese fly there are many ways that provide the same benefits to flying in group. They could go one after another, like cyclists in a race for example, getting the same aerodynamic effect.
But flying in this way reveals a big problem, and this is where we enter the social factors, and it’s when the need to defecate in flight comes. In other flight configurations they would shit on each other, and the last of the group would be totally covered in shit.
Solution to fly together and clean: fly in V.