Why do swans, geese, and ducks fly in V formation?
Because it makes their journey easier.
Everything that flies experiences air turbulence that slows it down (drag). Some of the turbulence is created by the act of flying. For instance while rising up (lift) cones of swirling air called vortices roll off the wingtips and induce drag. Here’s a dramatic photo of a wingtip vortex, enhanced by red smoke.
The right and left wing vortices swirl in opposite directions — the left spins clockwise, the right counter-clockwise — resulting in two trailing swirls behind the airplane or bird. Watch it happen in this video as the airplane passes through a cloud.
The induced drag is especially hard on large or heavy birds (swans and geese) and birds with small wings relative to their size (ducks) so these birds line up in Vs to reduce the turbulence.
Here’s how the line works.
In the photo below, four tundra swans are flying in the direction of the blue arrow. Behind the leader, the blue lines show that each following bird has its right wingtip in line with the left wingtip of the bird ahead of it.
Now I’ll draw the vortices and their spinning directions using blue for the left wing, red for the right wing. Blue/left spins clockwise. Red/right spins counter-clockwise.
When the blue vortex meets the red vortex at the wingtip, they cancel each other out. By lining up in this fashion, each bird has one wing that experiences less turbulence. That makes it easier to fly.
The lead bird is out there alone, though. He’s the only one who gets no assistance so he tires before the rest of the flock. The flock solves this by changing leaders when the first one needs to rest. The lead bird drops back into the V and another bird takes his place.
Long, long ago birds solved the problem of wingtip turbulence. When we invented airplanes we found out what it was all about.
(Credits: Tundra swans in blue sky by Chuck Tague. Line of swans by Marcy Cunkelman. Red vortex photo by NASA via Wikimedia Commons; click on the image to see the original. Video by whosyourcaddy on YouTube. Today’s Tenth Page is inspired by a diagram on page 123 of Ornithology by Frank B. Gill.)