Subject: V-formation flying
Date: Oct 31 09:52:29 1996
From: Dennis Paulson - dpaulson at mail.ups.edu


I was cleaning out my e-mail box and found this; it's long, but I thought
it might interest those of you who admire birds, as I do, in good part
because of their flight. The "prevailing wisdom" is that birds fly in
lines and vees to gain aerodynamic advantage (lift) from the air currents
generated by the birds in front of them. I have long questioned this, my
alternative being that the birds fly in formation so they don't run into
each other! Smaller, more agile birds, fly in clumps, but when you get up
to a certain size, lines and vees are the rule.

>Date: Tue, 8 Oct 1996 13:53:35 -0500
>Sender: The scientific discussion of Ornithology
> <ORNITH-L at UAFSYSB.UARK.EDU>
>From: Paul Hess <phess at salsgiver.com>
>Subject: V-formation flying
>To: Multiple recipients of list ORNITH-L <ORNITH-L at UAFSYSB.UARK.EDU>
>
>Dennis Paulson's hypothesis on the advantages of V- or staggered-formation
>flying is a fresh and welcome perspective on this old question. Here are a
>few thoughts in the spirit of his call for further discussion...
>
>My own contrarian -- and unconfirmed -- view agrees with his but goes a step
>further to suggest that birds find a V or staggered formation advantageous
>for the same two reasons warplane pilots do: 1. It most easily and
>efficiently maintains the closest safe distance apart by using a fixed,
>angular point of reference on the bird/plane ahead. 2. It enables birds to
>*avoid* rather than take advantage of the trailing vortices ahead, just as a
>fighter pilot would want to avoid the preceding plane's prop wash or jet
>exhaust -- while again maintaining the tightest possible formation.
>
>I hasten to admit that the aerodynamics of fixed-wing and flapping flight
>are extremely different, and that there are theoretical advantages of lift
>to be had under certain strictly limited conditions of flight speed,
>distance apart, angle, amount of overlap with the wing ahead, and mutual
>wing-beat timing and frequency. There's no reason why birds couldn't learn
>to combine all those conditions with precision, but in practice it just
>doesn't look as if they're being met. In fact it looks as if the wingtip
>vortices of the bird just ahead, plus the combined disordered turbulence all
>the preceding birds, would create a worse-than-useless situation for the
>birds toward a flock's rear. The complex trailing vortex patterns
>illustrated in Rayner 1988 and Vogel 1994 (cited below) show what I mean.
>
>The fascinating question Dennis raised is a real poser: Why do many species
>adopt the V at higher altitudes but fly directly behind each other when just
>above the sea surface? It has been suggested that at the surface they don't
>need the others' wings for lift because the wave-air interface provides it
>for them. This is logical, fits the facts, and certainly does not support
>the hypothesis suggested above. The low-level lift afforded by convection
>created by air-sea surface temperature gradients and air currents created
>mechanically by even slight sea-surface swell or chop is more powerful than
>we intuitively imagine -- as any albatross and shearwater can attest. Birds
>with relatively high wing loading like cormorants, swans, geese, ducks, and
>large shorebirds, as well as birds with relatively low wing loading like
>cranes, storks, pelicans, and big gulls all show this differential flight
>pattern. I can't reconcile it with my hypothesis, but it might have
>something to do with the point Dennis made that these straight-line flocks
>are typically flying just offshore at an angle to the direction of the waves.
>
>This whole intriguing issue is open to little more than speculation at the
>moment, which is all I'm doing. I hope the controversy appeals to enough
>ORNITH-L readers to continue the discussion for a while. Even after all
>these years the various hypotheses have never been tested adequately -- and
>to my knowledge these contrasting high- and low-level flock patterns have
>not been addressed at any length. But a few references to valiant efforts
>at analysis may be of interest (in chronological order):
>
>Lissaman, P.B.S., and C.A. Schollenberger. 1970. Formation flight of birds.
>Science 168:1003-1005.
>
>Gould, L.L., and F. Heppner. 1974. The vee formation of Canadian Geese. Auk
>91:494-506.
>
>May, R.M. 1979. Flight formations in geese and other birds. Nature 282:778-780.
>
>Badgerow, J.P., and F.R. Hainsworth. 1981. Energy savings through formation
>flight? A re-examination of the vee formation. J. Theor. Biol. 93:41-52.
>
>Hainsworth, F.R. 1989. Wing movements and positioning for aerodynamic
>benefit by Canada geese flying in formation. Can. J. Zool. 67:585-589.
>
>The subject is reviewed briefly in:
>
>Ehrlich, P.R., et al. 1988. The Birder's Handbook. Fireside (Simon &
>Schuster), New York (p 59).
>
>Vogel, S. 1994. Life in Moving Fluids. 2nd ed. Princeton Univ. Press,
>Princeton NJ (p 288).
>
>Vortex action in flapping flight is discussed well in:
>
>Rayner, J.M. 1988. Form and function in avian flight. Current Ornithology
>5:1-66.
>
>I would appreciate other recent references, as I haven't researched the
>subject in several years.
>
>Best regards,
>Paul Hess
>Natrona Heights PA
>phess at salsgiver.com

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416