March 28, 2008

Geese Flying in V

Stupid Question ™
June 6, 2002
By John Ruch
© 2002

Q: Why do geese fly in a V formation? How do they decide who’s the leader?
—Duane Ott

A: Nobody knows, though science’s armchair speculations on the subject are often presented as fact.

Almost all large migratory birds—geese, cranes, swans, pelicans—fly in some sort of V formation. Double and multiple Vs are known, as are U formations and diagonal lines. The “leader” appears to be a matter of position only; the birds regularly switch positions in the formation throughout their flight.

The V can be ragged and is sometimes discarded. Cranes are known to move into tighter groups when they hit “thermals”—updrafts of air they can glide on without flapping.

The most popular theory was put forth in a 1970 article in the journal “Science” and has been lazily quoted as absolute fact ever since. It says that upward airflow from the birds’ beating wingtips (a known aerodynamic effect) gives extra lift to their neighbors’ wings in the V formation, thus reducing the amount of work they all need to do. Math wankery has “estimated” energy savings of 20 percent and a 70 percent increase in flying range.

First of the theory’s many problems is that it would actually work best if the birds flew wingtip-to-wingtip in a straight line, which they never do. The standard excuse is that the birds on the ends of the line would get half the benefit, and that the V at least gives everybody some help. But it’s a fact that birds always change position in formation anyway, so being on the end for a while couldn’t hurt.

It’s also been noted that the truly sweet spot would be within the angle of the V, where birds could enjoy their neighbors’ updrafts without contributing their own. But birds never do this. The authors could only presume some sort of avian police that keep the birds in line, which frankly seems silly.

The study also reported that single birds flying in apparent solo migration actually fly 24 percent faster than birds in the V. They rationalized the birds were stragglers hurrying to catch up—but how could they, if the V has a significantly greater efficiency and range?

Similarly, Canada geese often have “scout” birds out front, apparently looking for danger and/or landing spots. What about their efficiency?
As for the lead bird, some say it gets no advantage and has to drop back when it’s tired. Others say it benefits from its neighbors like everybody else.

A simpler theory says that like bike racers, the birds in front produce a slipstream effect, reducing air resistance for those behind them and lessening their work.

But another theory says the birds in front create air turbulence, not a slipstream, and that the V formation keeps everybody out of it.

Konrad Lorenz, a famed expert on goose behavior, dismissed aerodynamics and said it’s really all about visibility. He noted that geese also stay slightly to each other’s side when walking, swimming and taking flight, all presumably to maintain a clear view ahead. He said it’s particularly noticeable when they’re swimming across a large body of water.

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