Science Puzzle
Why Do Geese Fly in a V?
Geese, swans, cranes and ibises often fly long distances in a V shape, with one bird at the point and the rest strung out behind in two lines. Each bird sits slightly behind and to one side of the bird in front, never directly behind it.
Why do big birds fly in a V?
The Answer
To save energy. A flying bird leaves rising air just beyond each wingtip, and a bird positioned there gets a free lift. In a V, nearly every bird is in that spot behind the one ahead.
A wing stays up by pushing air downwards. Behind the bird, the air in its wake sinks; but at each wingtip, air spills round from underneath and swirls upwards just outside the tip. A bird flying directly behind would be in the sinking air and have to work harder. A bird a little to the side, with its wing in the rising air, gets help for nothing.
In 2014 scientists fitted data loggers to a flock of northern bald ibises being led on their migration by a microlight. The birds in the V didn't just hold their places; they timed their wingbeats so that their wingtips followed the same path through the air as the wingtips of the bird ahead, staying in the rising air all the way. When a bird ended up directly behind another, it flapped out of step, which reduces the effect of the sinking air.
The leader gets no help, so the birds take turns at the front. Engineers have tested the same trick with aircraft flying in formation to save fuel.
The principle: Riding the upwash. Air swirls upwards just beyond a flying bird's wingtips, so a bird flying slightly behind and to one side gets free lift, and a V puts most of the flock in that position.