ANCHORAGE (AP) -- In the misty morning light, a single goose suddenly rose from the pond in Chester Creek on the city's east side.
Within a wing beat, 20 other geese followed, honking lustily and pumping their wings.
Before the birds cleared the birches on the shore, they had begun to spread into two lines trailing the leader. Then, as the small flock circled just above treetops and wings creaked rhythmically, the birds drifted into their unmistakable V-shaped formation.
As yellow leaves litter the ground and the nights grow cold, many of the estimated 3,500 local Canada geese will take flight. Whether they are commuting to parkland for a late fall snack or launching the annual migration to Oregon, few sights speak more dramatically of pending winter than the V-like skein traversing the sky.
''There's something about that view. It's really cool,'' said biologist Karen Laing, with the U.S. Fish and Wildlife Service. ''It kind of brings us into that part of nature. ... It feels like the seasons are changing.''
But why do they do it?
Scientists have studied the question by photographing geese and other large migratory birds and then measuring the birds' relative positions while calculating wind resistance and air speed. They've settled on two main hypotheses, according to Laing.
By spreading out in a V, with each trailing bird slightly higher and farther behind than the one in front, the geese may be able to keep track of one another in flight.
The pilots of fighter jets often follow the same procedure.
''It's a good way to fly in a group,'' Laing said. ''You know where the other birds are and don't hit them.''
But the most intriguing explanation may be the most practical. The formation creates an aerodynamic shape that saves energy.
As each goose flies, some air is lost over each wing, creating a sort of slipstream of upwelling turbulence, according to an article in the Encyclopedia of North American Birds, published by the Audubon Society.
''In the 'V' formation of Canada geese, for example, each bird flies, not directly behind the other, but aside or above the bird in front,'' the article says. ''By so doing, each bird rests its inner wing tip in flight on the rising vortex of air from the bird's wing in front of it.''
As a result, geese in formation may be able to fly 71 percent farther than a lone goose making the same effort, according to an often cited study.
Actual geese in flight don't often stay in the optimal slot, so the energy savings might not be that dramatic, according to biologists.
Maybe the formation serves some kind of social function among young birds that remain with adults for up to a year while they memorize migratory routes and feeding grounds.
''I would suspect they kind of learn (the formation) from each other,'' Laing said.
''They do communicate with each other about when they're going to take off,'' she said. ''They have a little head flip when they're going to go. So they really have talked about it.''
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