Another reason why geese fly in "V" formation:

If you had a long flight South, would you want your only view to be the North end of the guy (goose) in front of you?

The military took a lesson from the "V" formation, it allows better visual communication between its members. In a straight line, all you could see is the goose (fighter, bomber, etc) in front of you, but in a "V" you see all the geese in front of you, as well as the ones in the other side of the V.

It has another use in the jet age. Flying in a V avoids the lead guy burning your fin off....

Ever check out the Thunderbirds from the 60's and 70's? See how the #4 guy in the diamond always had a black fin? Dat ain't paint! ! ! ! !

Good point. I've seen our Canada geese flying in W's and sort of W's as well. It's not like there needs to be only one lead. It's just that the stronger or best rested gets to the front to aid the rest in making the journey.

Also to add to an earlier post about why this is different from airliners avoiding each others wake. When it's done like this where the following goose is "in the zone" it's sort of like a kayaker that is surfing on a standing wave in a river. He's getting a free ride which is what the trailing geese are doing. But if the trailing line falls back a hair then much like the kayaker in the standing river wave that falls off the front or to one side the gain is gone and they are on their own. Which explains why the V's can be seen constantly forming together and breaking up.

So I understand this.

There are two things on an airplanes wing- there are wingtip vortices and there are downwash and upwashes. The Downwash and upwash creates an energized current of air which is helpful to the back geese. The wingtip vortices the geese avoid because they are in a V formation whith a large enough V for the vortices to not touch the back geese. BUT, should one geese fly right behind another- he will go in those vortices and there will be a negative effect on his flight efforts. Did I get that correct?

It's a feel thing. The geese fly where they do because it is less work for them when following. We can talk about it until the cows come home but won't ever feel it unless we are reincarnated as a goose. Because of this we have to trust and assume that they fly where they do because they can feel that the air in the wake of the front goose is making it easier for our trailing goose to fly the distance.

It really comes down to my standing river wave analogy. If the geese all synchronize their wing beats in the right phasing then they will experince some small energy transfer through the vortex from the goose in front. Because of the area the lagging geese are in the benifit to them will be a combination of the tip vortex and the wing downwash.

Also keep in mind that since geese are ornithopters (wing flappers) any tip vortices will hardly be steady. This would be why you see the geese in a V all beating their wings in time with each other but not necessarily in phase. The sligth phase shift in the flapping would be what the geese feel is required to best ride on the energy of the goose in front.

I think the V formation introduces 3rd harmonic which is in direct proportion to the mass