Of all natural patterns, the one I think that moves me most, is the sight of a flock of wild geese.
A single goose passing high overhead carries with it a sense of freedom and adventure. “He is,” in the words of Hal Borland, “the yearning and the dream, the search and the wonder, the unfettered foot and the wind’s-will wing.”
But a complete formation of geese is, for me, the epitome of wanderlust. Each one leaves me, no matter what I happen to be doing, wondering how long it will take me to pack my bags. And it’s not just migratory restlessness, the knowledge that by dawn the flock will be in other climes. I don’t feel the same way about swallows. There’s something about the goose formation itself, that arrowhead symbol of limitless horizons, that hints at appropriate and meaningful adaptation. A sense not only of going somewhere, but of doing so together in the best possible way.
Observations of geese in passage, show that they invariably adopt a “vee” formation, flying on the same level, equally spaced out but not necessarily along arms of equal length. The important thing seems to be that the vee must have an apex – that the leading bird should always have others on either side.
It has been suggested that this characteristic formation is nothing more than a simple consequence of the fact that geese have immobile eyes on the sides of their head; and that, with the beak pointed forward, the best way to keep a neighbouring bird in full view is to take up a place just behind it, either to the left or right eye side. But direct measurement of flights of Canada geese shows that the angle between the arms of the vee formation varies even in a single species between 28 and 44 degrees, which doesn’t necessarily correspond with the fixed angle of clearest focus.
Another theory suggests that the vee formation allows one goose, presumably a stronger and more experienced bird, to lead the way, cleaving a path through the air for the others. But, once again, field studies show that the leadership changes constantly and that this position, far from being reserved for wise old ganders, is in fact shared out amongst the younger and weaker members of the flock.
The answer seems to be largely aerodynamic. A recent computer study shows that there is an upwash beyond and behind the tip of a moving wing that can be useful to other birds nearby. If the spacing between wings is optimal, this saving in energy can be considerable. For instance, a formation of twenty-five birds can, just by adopting the most favourable formation, increase their effective range by 71 per cent.
And this seems to be precisely what happens. Travelling geese usually fly in groups of around twenty individuals and invariably adopt a vee formation. If they flew in line abreast on a common front, the birds in the centre would enjoy twice as much uplift as the ones on the ends of the line. But as soon as the line is bent backwards, the ones at the rear begin to pick up additional upwash from all those in front, which effectively cancels out most of the disadvantage of their position. And as they travel, other small inequities which may exist are dealt with by regular and democratic changes of place.
– Lyall Watson, Beyond Supernature: A New Natural History of the Supernatural
Notes:
Live & Learn 