Why Birds Fly in a 'V'.

October 23, 2001 12:11 PM

Why Birds Fly in a 'V'. And I thought it was because they liked the view.
posted by MeetMegan (29 comments total)

Kvist and his team in Lund studied the metabolic rate of small birds called Red Knots while they were flying in wind tunnels.

I'm just chuckling over the thought of confused birds trapped in a wind-tunnel, flapping like mad, and not going anywhere.
posted by ratbastard at 12:24 PM on October 23, 2001

Q: Why is one side of the V always longer than the other?

A: Because there's more birds on that side!
posted by jennyb at 12:28 PM on October 23, 2001

Sucks for the lead bird.
posted by goto11 at 12:44 PM on October 23, 2001

French scientists have exposed the long-held bird secret of why birds fly in a V formation.

not meaning to give the scientific community a hard time, but where's the mystery? i always thought it was pretty obvious why birds fly in this pattern. it's called drafting. here's a nice explanation, with cycling as an example. same holds for other racing. while we're at it, maybe the birds would be interested in these stickers.
posted by mich9139 at 12:45 PM on October 23, 2001

Sucks for the lead bird.

Nope, that bird also gets the benefit of drafting. Something to do with...uh...I bet mich9139's links will tell you.
posted by lbergstr at 12:48 PM on October 23, 2001

Actually, direct aerodynamic experiments haven't managed to show why the V formation works. Looking indirectly at the effort expended (assuming a correlation between pulse and effort) is a very elegant way to see that it does seem to have some effect.
posted by djfiander at 12:51 PM on October 23, 2001

Is this a purely behavioral phenomenon? In other words, would any ol' bird figure out that this pattern is more efficient over time? Or is there some survival advantage that has influenced the bird gene pool in favor of those birds who fly in a "V"?

Anyone know enough in this field to hazard a guess?
posted by marknau at 12:55 PM on October 23, 2001

Ok, here's what I love (emphasis mine):

"Our results provide empirical evidence that, compared with solo flight, formation flight confers a significant aerodynamic advantage which allows birds to reduce their energy expenditure while flying at a similar speed," Henri Weimerskirch, of the National Center for Scientific Research in Villiers en Bois, said.

He and his colleagues added that birds flying in formation can enjoy an aerodynamic advantage which allows them to reduce their energy expenditure while flying at a similar speed to the other birds.

I think some of those Reuters boneheads took that article about the temporary effects of smoking pot to heart.
posted by UrbanFigaro at 1:08 PM on October 23, 2001

I also read in USAir's in-flight crapazine that the geese honk at each other as a method of encouragement. Fo' real.
posted by theJaybird at 1:29 PM on October 23, 2001

I remember seeing a study once where they were trying to calculate the cost-benefits of flying airliners in formation. I think it only became beneficial on long-distance, international flights. They have a hard enough time keeping planes from bumping into each other on the ground, could you imagine flying 4 or more 747s in formation?
posted by fluxcreative at 1:35 PM on October 23, 2001

marknau, there's a bit of a survival advantage in being able to make it south for the winter (or back up north, for that matter) without collapsing from exhaustion. Naturally, those birds that don't figure out the benefits of drafting are going to be spending much more energy than their cohorts, they can't really afford to be wasting energy. Plus, if you're too pooped to pop, or you can't make it to the big spring orgy, your "can't figure out how to fly the smart way" genes aren't likely to get passed down to the next generation in any great numbers.

And the lead birds aren't stupid enough to stay the lead bird the whole time. Just like in group cycling, the lead will drop back for a while and let someone else take over. Everybody shares the load, and they all get there in better shape than if they'd done it alone.
posted by stefanie at 1:40 PM on October 23, 2001

Is this a purely behavioral phenomenon? In other words, would any ol' bird figure out that this pattern is more efficient over time? Or is there some survival advantage that has influenced the bird gene pool in favor of those birds who fly in a "V"?

I don't have a link for this, but the V pattern, and the patterns of flight birds assume when the V comes across obstacles and wind and other variables, are (according to some scientist somewhere, anyway) all predictable given a very simple set of rules for flying. (These rules specify, roughly, how far behind the bird in front of you to fly, on what side and how far to the side (depending on other birds in front of him, etc.), which direction to go around an obstacle in your path, etc.) So it's complex behavior in the mathematical sense, too -- i.e., once you know the solution, it's very simple....
posted by mattpfeff at 2:06 PM on October 23, 2001

Fluxcreative: That brings up the coolest mental picture.
posted by pheideaux at 3:09 PM on October 23, 2001

Hasn't anyone seen the Mighty Ducks? They fly in a V because the other team can't see who has the puck, then they score a goal.
posted by ktheory at 4:09 PM on October 23, 2001

This java simulation of flocking behavior made the rounds almost a year ago, perhaps what mattpfeff was thinking of. It is modellable.
posted by dhartung at 4:28 PM on October 23, 2001

I like V. Remember the part when the hot alien got naked, but then took off all her skin? It really freaked me out.
posted by hellinskira at 4:30 PM on October 23, 2001

I thought the link would explain why birds fly in a "V" formation. After reading it, they only seemed to have explained why birds fly together.

In other words, is there anything special about the "V" formation that makes it more aerodynamic than a straight line formation?
posted by Witold at 6:00 PM on October 23, 2001

And the lead birds aren't stupid enough to stay the lead bird the whole time. Just like in group cycling, the lead will drop back for a while and let someone else take over. Everybody shares the load, and they all get there in better shape than if they'd done it alone.

Actually, can you imagine the lead bird trying to retire to the back of the pack only to have all of the other birds follow him in tight-V-formation circles? hehe

Nope, that bird also gets the benefit of drafting. Something to do with...uh...I bet mich9139's links will tell you.

If my physics education hasn't failed me, I'm pretty sure that the lead bird would feel absolutely no effects (positive or negative) from the drafting flock.
posted by fooljay at 6:09 PM on October 23, 2001

mattpfeff, dhartung: See also Boids, the original simulation of flocking behavior. Buried among the many references on that page is a link to this applet, in which the original Boids algorithm is tweaked to reproduce the V formation.
posted by jjg at 6:40 PM on October 23, 2001

They're not flying in a "V". They're flying in the roman numeral "5"...and they're trying to tell us something.
posted by mikegre at 7:41 PM on October 23, 2001

If my physics education hasn't failed me, I'm pretty sure that the lead bird would feel absolutely no effects (positive or negative) from the drafting flock.

At sufficiently high speeds, the leading object in a pair will experience lower air resistance than if it were traveling at the same speed by itself. For example, racecars do benefit from having another racecar sitting on their tail at 200 mph. I think the effect is because of the drop in air pressure behind an object as it moves through the air, or because the air trailing an object becomes disturbed and choppy -- if the pair of objects is close enough together and traveling fast enough, they pass through the air more as if they are one object.

Sorry if that's vague, I don't think I ever studied the details....
posted by mattpfeff at 9:51 PM on October 23, 2001

Actually the drafting only works if the birds/cars/etc are not too close to the lead bird/car/etc. If they get to close they encounter "dirty air" which is turbulent and causes the followers to lose aerodynamic lifting force/downforce.
posted by riffola at 10:06 PM on October 23, 2001

I would guess that the bird doesn't actually have to figure anything out about this V formation, that it probably naturally evolves as the birds fly. After all, if all you're aware of is how hard you're working and if you suddenly drift into a nice, easier airstream, you're going to stay there. A few miles of mayhem and newbie birds will just fall into the easiest air. A few long distance commutes and it just looks right to be a bit back and a bit right of another bird. Voila! Fancy V formation.
posted by dness2 at 12:23 AM on October 24, 2001

> Actually the drafting only works if the birds/cars/etc are
> not too close to the lead bird/car/etc. If they get to close
> they encounter "dirty air"

I imagine they would.

Goose A to Goose B: "Jesus, Morty! Your ass smells awful."
Goose B to Goose A: "So bill me."
posted by pracowity at 12:35 AM on October 24, 2001

OK, I used to be an aerodynamicist. The reason birds fly in a V is not 'drafting' in the 2D, car- or bike-sense, and it's not quite the same effect.

Wings (bird and aircraft) work because air pressure is higher on the lower surface on the wing than the top one, right? Well, one side effect of this is that at the 'tip' of the wing the air from the bottom spills to the top surface (like water would spill down from a table-edge, only in reverse). If the bird was standing still, that would form a nice little whirlwind at the tip of the wing; but it doesn't. So the spillover actually creates a vortex, what aero engineers call a trailing vortex. That vortex trails the wing tip in 3D, and because of the bird's displacing air sideways as well (ok, I am simplifying a lot here), it trails off to form one-half of a V shape.

Thus, the trailing vortices actually transfer energy from one bird to the next.

Now, this last part is hazier in my memory, but I believe that since birds fly in sub-sonic speeds (don't laugh, it's important), the vortices can actually carry some energy backwards to the leading birds. I don't think it's even though, the trailing birds benefit more.

Hope that makes some sort of sense...
posted by costas at 3:19 AM on October 24, 2001

I read somewhere that dolphins swim in a formation which allows each of them to keep one eye on their fellow dolphins and the other eye on the ocean itself in search of prey and predators. Is it possible part of the bird's V formation is also for this reason? A V formation would allow all but the lead bird to keep one eye on their group and the other eye on the rest of the world.
posted by ZachsMind at 6:30 AM on October 24, 2001

At sufficiently high speeds, the leading object in a pair will experience lower air resistance than if it were traveling at the same speed by itself.

Exactly, but I don't know of any birds that fly fast enough to get this effect...

Now, this last part is hazier in my memory, but I believe that since birds fly in sub-sonic speeds (don't laugh, it's important), the vortices can actually carry some energy backwards to the leading birds. I don't think it's even though, the trailing birds benefit more

Wouldn't that be backwards? The faster the fly, the greater the lead effect?
posted by fooljay at 8:34 AM on October 24, 2001

"Wouldn't that be backwards? The faster the fly, the greater the lead effect?"

Yes, to a point: after a certain Mach fraction (0.9 or so) portions of the flow may become supersonic, at which point air pressure cannot be transmitted backwards and then the effect stops.

True, most birds will never go that fast (although I think that the Peregrine Falcon can get somewhat close in a dive) and no birds flying in formation will ever do. However, as a good aero guy I had to define the flight envelope. Yeah, I am an aero geek still :-)...
posted by costas at 9:12 AM on October 24, 2001

I remember some from physics but most of my aero (and hydro) comes from 27 years of sailing...
posted by fooljay at 6:59 PM on October 24, 2001