Why do birds fly in formation?

Geese flying in a V formation

Migratory birds have many flight formations, called echelons. Each have their own set of advantages. The most common of these is the  V  shaped formation,  which can be called a Skein. Anyone who sees a flight of migrating geese will see its distinct shape.

This flight pattern provides the birds with two main advantages. The most obvious being that since each bird is slightly behind the next, all of the birds can see the lead bird, and the bird immediately in front and to the side, allowing them to coordinate their flight paths and not crash into each other or get lost. This is the primary reason that fighter jets also fly in formation. The only real difference being that they also do this to increase their fields of view and defensive ability.

Military aircraft flying in a V-formation

The second advantage, which is not as easy to see, is that this flight formation can increase the flight efficiency of the birds, allowing them to expend less energy in order to fly. This is essential for migrating birds that must travel long distances without landing, any conservation of energy is essential.  the conservation of energy occurs because instead of flying on the same relative plane, each bird is at a slightly lower altitude than the other. this difference allows the birds to take “advantage of the upwash vortex fields created by the wings of the birds in front”(1). This results in a reduction of air resistance, reducing some of the drag that the birds would otherwise have to overcome. So every bird that is behind another feels a reduction in drag, but what about the bird in front? extended studies on migrating birds have shown that when the lead bird tires, it falls to the end of one of the V’s arms, and one of the nearest two birds take its place. This rotation allows the flock to fly for much longer than would otherwise be possible.

A C-17 Globemaster III from the 14th Airlift Squadron, flies off after releasing flares. The smoke swirls are caused by wing vortices at the plane's wingtips. (http://en.wikipedia.org/wiki/File:C17-Vortex.JPG)

Amazingly, a group of researchers at Stanford have devised a flight pattern for airliners that borrows from this same energy saving mechanism to increase fuel efficiency. The proposed arrangement is to have three airplanes, spaced about 4 miles behind each other, and would have an increase of fuel efficiency of about 12 percent.

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2 Comments

Lorena Barba posted on October 9, 2012 at 7:42 pm

One has to be careful with the explanations of this behavior and its mechanics. It is somewhat misleading to say, as the article in “Everyday Mysteries” does that:
“Each bird flies slightly above the bird in front of him, resulting in a reduction of wind resistance.”

This makes it sound like there was some magic reduction in “air resistance”, which is not entirely correct.

What happens is that the birds in the back fly in the upwash of the birds in the front, therefore getting some free lift. This means they need to generate less total lift with their wings, which IN TURN means that there will be a savings in INDUCED drag.
http://en.wikipedia.org/wiki/Induced_drag

lneves posted on October 10, 2012 at 3:16 pm

I thought that I explained the mechanics of the upwash in the third paragraph;

” This difference allows the birds to take ‘advantage of the upwash vortex fields created by the wings of the birds in front’ (1). This results in a reduction of air resistance, reducing some of the drag that the birds would otherwise have to overcome.”
Does this not explain the process? I don’t go into detail on the reduction of induced drag specifically, but I do explain that it is not “magical”.