Re: Ducks fly in a V pattern. Why is one side of the V longer ?

According to an article in The Birder's Handbook (p. 59) the most widely 
believed explanation for flying in a V formation has to do with reducing 
the effort needed to fly for the flock overall. It is believed that all of 
the trailing birds have to flap less to fly the same distance if they are 
in the wake of a leading bird. However, the separations necessary to take 
advantage of this effect are not usually seen when the flight patterns are 
explicitly analyzed. Another explanation that has been proposed is that the 
V formation allows for better visual contact among the birds, thereby 
reducing the effort needed to avoid each other in flight.

As to why one leg of the V might be longer than another I can only 
speculate, but my guess would be that symmetry of flight formation is not a 
priority among the birds and they just join up to whichever leg of the 
formation they happen to be approaching. If this leg has more individuals 
than the other it doesn't really matter to the bird as long as they are in 
the formation.