Monday, November 06, 2006

Honk time

I love these fall morning when just at sunrise Canada geese skim the treetops, tooting their horns as if to warn one and all to get out of the way, They are heading south, and apparently in one heck of a hurry. Their racket would have toppled the walls of Jericho.

Yesterday, a highflying vee went by that stretched halfway across the sky, hundreds of geese, with one black beak drilling the way for the others to follow. How, I wondered, does the cohort decide who gets to lead? And how does he (she?) know where to go?

And why the vee?

Scientists have tried to find the reason geese fly in vees, so far not successfully. There are two theories on the table - aerodynamic efficiency and ease of communication.

The aerodynamic analysis was first done by aerospace engineers Peter Lissaman and Carl Shollenberger in 1970. The advantage of formation flying derives from something called "wingtip vortex," they say. On the downstroke, air beneath a bird's wing is pushed downward. Beyond the wingtip, air moves upward to restore the displaced air. This updraft provides extra lift to the next bird in line.

Presumably, geese will adopt positions in flight that optimize their aerodynamic advantage. With ideal spacing, birds flying in a vee can gain a 70 percent range increase over a bird flying alone, according to the calculations of Lissaman and Shollenberger.

Observations of actual flights, however, show that geese are seldom in optimum position for maximizing lift. This has led other researchers to suggest that geese fly in vees to keep each other in view and optimize communication.

The important thing here is that both theories assume an advantage for the birds, to be explained, ideally, by some sort of analysis based on physical laws. It is a fundamental tenet of science that things don't happen by chance, or just to please the human watcher. We may find the vee formations beautiful, as the geese stream south in the golden light of a rising sun, but our aesthetic sense has zero value as an explanation.