birds congregate together

and then at some point they lift off

and they start flying together in a flock.

You got all these birds,

that are just moving almost like they're a microorganism.

You've got like one individual bird

and it'll be leading the pack

and then when it turns the other ones turn.

It's just a fascinating thing, this flock behavior of birds.

Today, on Smarter Every Day I wanna talk about that.

It has to do with a mathematical algorithm

called Boids algorithm.

And I've got a computer scientist buddy named Ben Eater

who's gonna walk us through that

by showing us the map.

Oh my goodness!

(car engine running)

You can't see it on film yet 'cause of the pixel resolution

but there is a ton over there,

and they're all coming to meet right here.

(laughing)

Boom!

And we're off,

okay they're waiting about a mile down the road,

let's go look at 'em.

(car door opening)

We're gonna see if we can see 'em.

(car engine running)

There they are.

(car engine running)

Try to do this safely here.

(car engine running)

And we'll go to the service road just off of the interstate.

Oh, man!

(car engine running)

This is what I normally see every day.

(soft guitar music)

Let's just watch the birds.

When you're watching 'em,

think about it at the bird level,

like one individual bird,

and think about it from the perspective of the whole flock.

It's beautiful.

And you can see like, it's almost like fluid flowing.

When you can see like areas of high pressure

or high bird density, areas of low bird density.

It's beautiful, I'll quit talking now

let's just watch birds 'cause they're cool.

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Every single bird is making decisions

based on a very simple set of criteria.

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So I've watched the birds

in this specific location for years and I love it.

It's magical every time.

But I've recently learned

that this is an example of what's called emergent behavior.

The decisions of a single bird

when thrown in the mix

with the decisions of a myriad of other birds

creates this beautiful aerodynamic dance.

I didn't fully understand

how this works in flocking birds

until recently when I was at my friend

Ben Eater's place out in California.

Ben designs and builds his own computers

from the individual electronic components,

demonstrating how these simple components

are combined to make complex modern computers.

Ben Eater is an amazing programmer

with a YouTube channel you should definitely check out.

- And there is an algorithm

that simulates flocking behavior in birds.

- [Destin] Oh really?

- Which is called the Boids algorithm,

like bird, -oid object.

- [Destin] Okay.

- Or sounds like a New Yorker saying bird.

- [Destin] Okay.

- [Destin] So you're about to show---

- [Ben] I thought this.

- [Destin] What?

I didn't see this.

- [Ben] No, you don't see this before.

- [Destin] No.

- [Ben] So this is just an implementation

of the Boids algorithm.

- [Destin] Oh, okay, okay, so it's very difficult,

but like I'm tracking some of 'em,

and they are kinda gravitationally

pulled towards the other one.

Is that what I'm seeing?

- Yeah, so there's actually

three things going on here.

So let me show you what they are.

(keyboard typing)

- [Destin] Is this how actual birds work?

- Quite possibly.

- [Destin] Really?

- Yeah.

So they're doing a couple of things.

So one, let me, (keyboard typing)

- [Destin] Are you changing parameters on the fly?

- I'm gonna change the code

so that they don't do all the things that they're doing.

So we can just isolate each one.

- [Destin] Okay.

- So I can just show you what it's doing.

So the first thing that they do

is they just fly towards the center of mass.

- [Destin] Okay.

- So it's just a bunch of different things,

they all have a velocity

and it says every time period,

every tick, every frame, whatever.

- [Destin] But is drifting.

- And that's because they're not turning immediately.

And this is why I went with this algorithm,

there's a lot of different parameters you can tune.

- [Destin] Okay.

- So one parameter you can tune is like,

how quickly does it drift towards that center of mass?

- [Destin] Okay.

- And so what you'll see is

if we keep this running for a while,

that ball will just get more and more dense,

and they'll all just kinda collapse into one point.

- [Destin] Like a singularity.

It's like, okay, got it.

- They're just all attracted to each other.

But that will eventually collapse onto itself.

And so, the other, the second of the sort of three things

that you do in a Boids simulation like this,

is you tell the objects to avoid each other.

So instead of just coming in and eventually collapsing,

if they get too close to something they'll turn away from.

- [Destin] Because the birds would fall out of the sky.

- Yeah, 'cause birds don't hit each other.

- [Destin] Oh okay, so they're like,

they're attracted, but they're kind of like both electrons

and they repel just a little bit.

- Yeah, so we've got two rules right,

which is fly towards the center of the flock,

and then avoid other birds.

- [Destin] Okay.

- And that gives you this,

you get this sort of like jumbly clouds.

- [Destin] So that's only two rules.

- [Destin] Okay. - Yep, that's two rules

And you get that.

- [Devin] Okay.

- And then the third rule is

try to match your velocity with the other birds.

And velocity is speed and direction.

- [Devin] Okay.

- So this will start to get them

to align in the same direction.

So now they're gonna try to match vectors.

And now you sort of see - [Devin] Oh!

the flocking behavior.

- [Devin] That is so pleasant.

Dude!

- And that is essentially the Boids algorithm.

And then there's a few things you can do.

- [Devin] Wait, wait, so we're seeing three things in there.

- You're seeing three things going on.

- [Devin] So they're attracted to each other.

- Attracted to each other.

- [Devin] They're trying not to hit each other.

- Yep.

- [Devin] And they're trying to match vectors.

- Right.

- [Devin] Wow!

- And then you get this flocking behavior

that looks like birds,

it looks like fish, it looks like insects,

it's pretty cool.

- [Devin] Dude, it's really cool.

- And so you can do other things,

you can say instead of flying towards the center

of the, sort of the average position of all the birds

fly towards the ones that are within some radius of you,

which is actually a little bit more realistic

'cause birds don't know where all the other birds are,

they just know where the ones near them are.

- [Devin] Right.

(keyboard typing)

- And that makes it a lot more interesting

because now you get these little groups that break off.

- [Devin] Yeah, which I see that often in nature.

But that's a little more broken than I'm used to.

So what parameter are you changing there?

- So I have this visual range parameter

so we can crank it up a little bit.

(keyboard typing)

And they'll form tighter groups,

maybe that was a little too much (laughs).

They're just flying in one group.

(keyboard typing)

There you can see.

- [Destin] It's starting to feel more like

the assembly of a murmuration.

What's interesting is when they pass,

okay, yeah, there you go,

it took 'em a while,

but they all got together. - Yeah.

- [Destin] That feels normal.

- Yeah.

- [Destin] That feels more real.

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- I am in love with this.

It's just math.

That's all this is.

Each bird is making decisions based on math.

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Pick a bird and watch it

and watch the decisions it makes.

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As they present their bodies to you,

they get like really dark.

You see that pattern right there.

It's really dark.

But as they point towards you away from you

the aspect angle of their bodies is thinner

so they look transparent.

But then they'll flash in another direction

and they get solid looking again as a cloud.

There you go, see it?

Isn't that awesome?

Look at that.

Okay, the cool thing about living where I live is,

I'm up next to Wheeler National Wildlife Refuge.

And every year,

thousands of cranes come down here to winter.

Today, as I was driving by,

I noticed that there were thousands of 'em

and they're all flying in a flock.

But I noticed that the flock for these cranes

is very different than the small birds.

And I think it has to do with the fact that the shape of,

I'm sorry, they're flying overhead, and I get excited.

The reason the big birds point in one direction

and stay going in one direction

is because they're less maneuverable than the small birds.

And that's fascinating to me.

The overall shape of the flock

is a function of the maneuverability

of what would it be the largest bird in the flock?

The least maneuverable bird in the flock?

Maybe.

Okay, here's a walking trail.

I've done this since I was a little boy.

And it goes to a hidden observatory

so that we can see these birds that have migrated here.

(shushing)

Be very quiet.

I really like little bridges here.

(footsteps)