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The world of animal flight is a fascinating one—join us for a fun SciShow compilation all about birds, bats, and some species you might not expect!

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[Rose] When we wanna get from point A to point B as fast as possible, we take to the air.

But humans are newbies in the world of flight. While we've had commercial flights for over a century, other animals have been flying for a millennia.

And for good reason. From an evolutionary perspective, flight is awesome. Animals do things a little different from us, though.

So today, we're going to look at the bizarre world of of animal flight, from birds, to bats to... spiders? And snails? Oh come on!

Now you're really making stuff up. Flying snails? Alright.

I'll wait for it. Let's kick things off with the undisputed champions of the air: birds. These living dinosaurs constantly dazzle us with their aerial acrobatics.

So naturally, we've looked to them for tips and tricks. For instance, fighter pilots often fly in a V shape, an idea we humans totally stole from migrating birds. But not all birds fly in Vs, no matter how far they're flying.

Why not? Here's Hank to explain. 

(Hank) Think of a flock of birds you probably think of a classic V-shape with a leader with sets of trailing birds on either side.  But not all flocks fly this way.  Starlings, for example, travel in large, three-dimensional clusters that seem to move like a wave.

So, why do some species fly in Vs, and others in clumps?  Well, it turns out it has a lot to do with the individual birds themselves.
Some, like geese heading south for the winter, are making long treks.  The V formation helps them stay in visual contact with each other, avoid collisions, and conserve energy.  It's the structure of their wings that lets them take advantage of the V.  

As the wing flaps, each wing tip creates a vortex that spirals up from the bottom of the wing and over the top.  This vortex trails off behind each bird as it moves forward and is encountered by the next one in the line.

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The trailing bird positions itself to catch just the upwash of that vortex, or the upward force, and that requires being behind and just to the side of the leading bird.  Lots of birds behind and to the side of one another creates that V shape.

Studies have estimated that birds flying in this way can save around 15% of their energy.  So, why don't all birds fly this way?  We talked to Professor Eric Green from the Univeristy of Montana Bird Ecology Lab, and he explained that this has to do with the size of the bird.

You may have noticed that birds that fly in a V, like geese, pelicans, swans, and ibises, are typically larger creatures with a long wingspan.  These species move their wings only a few degrees up and down with each flap.  This motion creates vortices that lie pretty neatly behind the bird.  

Small birds, on the other hand, tend to flap their wings all the way up and down.  The vortices created by these motions are all over the place, not consistent enough for their flockmates to actually use.  And the small birds that do flap their wings like larger ones just don't generate a big enough vortex because of their size.

For small birds, flying in groups sometimes uses even more energy, not less, but these species have another need that's even more important: protection.  In 1971, evolutionary biologist William David Hamilton proposed a theory called "the selfish herd".

It suggests that  the risk to an individual is reduced if that animal places another animal between itself and a possible predator.  Repeat this across enough individuals and you end up with a herd, or in this case, a flock.  

Other theories offer similar explanations, but whether you're talking about schools of fish or swarms of insects, it's clear that this is a pretty common survival strategy.  So the next time you see a group of birds flying by, you'll know it might be to save energy, or it could just be to stay alive.

[end video]

[Rose]  I just had a weird thought.  Can you imagine if we flew planes in flocks?

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That would be a logistical nightmare. No wonder we don't mimic everything birds do. And actually, now that I think about it, there are other aspects of bird flight we don't usually copy, like their flat tails. Our planes have vertical ones.

Is that because we're better at flying than birds? Stefan, what do you think?

[Stefan] I don't know if you noticed, but nature is kind of awesome.  That's why so much of our technology is inspired by it. For adhesives modeled after insects to early plane wings based on birds.

But just because we try to mimic nature doesn't mean we can do it perfectly. And birds and airplanes are pretty good examples of our limits.

Take the vertical tales on most airplanes: we use them to keep our giant metal contraptions in the air and going the right way, but birds get by fine without them. That's because they're just way better at flying than we are, and for the most part we can't keep up.

The parts of an airplane all work together to keep in the sky and  facing the right direction. But thanks to all kinds of invisible air currents, that isn't as simple as it looks from your window seat. The vertical tail's main job is to stabilize something called "yaw." 

Yaw measures how much the plane is pointed to the left or right of the wind, specifically the relative wind, which is created by the plane zooming through the atmosphere at hundreds of kilometers an hour.

Yaw can change in lots of situations, like during turns or in unsteady air. And, when it does, it occasionally leads to a condition called "sideslip." This is where the plane has yawed but it hasn't completed changed its direction. Instead, it's still mostly moving in the direction it was, only at a funny angle. Kind of like a sports car drifting around a turn.

Normally, this just leads to a little inefficiency. But if it's not corrected, sideslips can get our of hand. If the plane yaws too much, it starts to affect how the air flows over the wings. And if too much air flow parallel to the wings instead of perpendicular, the plane can lose lift... which is kind of important for keeping it in the sky. 

That's where the vertical tail comes in. See, as the plane starts to sideslip, the side the tail will start to face into the relative wind and become more perpendicular to it. And as the wind pushes on the tail surface, it creates a force that ultimately nudges the whole plane back to face its original direction.

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