Ask A Scientist

Why do birds fly in a "V" shape when they migrate?

Asked by: Colleen Denmon
School: Jennie F. Snapp Middle School
Grade: 7
Teacher: Kimberly Coury
Hobbies/Interests: Dance
Career Interest: Fashion designer

 

Answer from Thomas Giardina

PhD Candidate in Biological Sciences

Research area: Evolutionary genetics
Interests/hobbies: Reading, playing games and spending time with family  

Because a flying "G" looks weird!

But seriously, you’ve probably seen Canada geese flying overhead in the last month or so, honking their brains out as they cruise down south for the winter. And you’re right; they do fly in a distinctive "V" formation. But why do migrating birds fly that way? 

The simple answer is: flying is hard. It takes a lot of effort to keep a bird in the air, and flying a long distance can be particularly tiring. Canada geese, for example, can migrate from Northern Canada to the Southern US — a  distance of up to 3,000 miles.  orget about pushing myself through the air; I wouldn’t want to make that trip in a car! How do geese do it?

Part of the answer is that "V." Like water, cutting through air leaves eddies and currents in your wake. As a lead goose flaps his wings, he sends vortexes of air spinning off behind him. If you’ve ever paddled a canoe, you might have noticed little whirlpools forming at the edge of the paddle as you stroke. A similar phenomenon occurs as a goose flies; you just can’t see it as easily. 

As the bird flaps, air moves downward.  But as that air spins out away from the goose, it moves back upward again. As a result, the bird is trailing two "whirlpools" of air, one behind each wingtip and rotating in opposite directions. 

Okay, so air moves as a bird flies. Who cares? Well, imagine that you’re goose #2, cruising along behind the lead goose. If you’re flying directly behind him, the vortexes from both his wings are pushing air directly downward, which is not good. After all, if you’re doing all this work fighting gravity, you don’t want to exacerbate the problem with a downward breeze. 

Now imagine that you’re behind goose #1, but off to one side. Suddenly that vortex of air is going to be moving upward — and now you’re in business! The vortex coming off goose #1 is actually helping keep you in the air, which means that flying becomes a great deal easier. As a result, the most optimal system is a lead bird, with two birds behind and slightly to the side, followed by two more birds behind and to the side, and so on, and so on, until — as if by magic — a flying "V"! 

But what about that goose in the lead? He has no upwash to coast on. Is he doomed to do more work than all the other geese behind him? Well, yes. But only for a time. Geese actually take turns with that lead position, so that no member of the flock is worn out by too much time in the front.

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Last Updated: 9/25/14