Nature (1982–…): Season 33, Episode 12 - Animal Homes: The Nest - full transcript

They're our
planet's first builders,

nature's architects
and engineers,

crafting homes of
spectacular design

in every corner of the globe.

Some are elegantly simple,

others, surprisingly complex.

So, it looks like a
teenager's bedroom,

from the outside,
but if you were

to cut this right down the
middle and look inside...

Whether they were
made by beaks or paws,

these homes have
a universal purpose:



to keep their owners safe
from a dangerous world

as they give birth

and raise a family.

It makes it a perfect bear home.

It's secure; it's dry.

Our story starts

with the most
prolific of builders.

A bird's nest is
no simple matter.

Each one must match its maker,

large or small,

whether from course red clay

or the finest silken threads.

This is where the homelife

of wildlife begins.



MORGAN: From nature's
most mundane materials,

birds weave wonders...

Delicate circles of
grass and twigs...

elaborately woven
baskets of vines,

imposing castles
of wood and mud.

These are works of art
so skillful, so beautiful,

it's hard to believe
they were fashioned

by beaks, instead of hands.

I'm Chris Morgan
and all around me

are examples of animal
art and architecture.

These bird nests are from Yale's

Peabody Museum
of Natural History.

It's a collection that
started over 100 years ago

and every one of these
fantastic creations tells a story.

Look at this.

This is the luxury
end of the market.

It looks like a big Russian hat.

This is built by North
America's largest duck species,

the eider duck, and
talk about resourceful:

the female sits there

and plucks down
from her own breast,

creating this big blanket.

And, sometimes, when
she leaves the nest,

she'll even pull this blanket

over the eggs, to
keep them warm.

Really important,

when you're from
a place like Alaska.

This is really the minimalist
approach to a nest.

Just a dip in the
ground, a small wall

to help prevent the
eggs from rolling out.

It's the nest of
the Arctic tern,

from the wild coast
of Nova Scotia.

These eggs have these
beautiful cryptic markings on them,

so they're really, really
difficult for predators to see.

I've never been this close
to one of these nests 'cause,

by the time you
usually get this close,

the adults are dive-bombing
you from the sky.

This one's my favorite.

Look at the size of that.

It's built by a
firewood-gatherer.

What a perfect name.

The entrance is
in the roof here.

There are spines all
over these branches.

It's the perfect
fortress, really.

And I love this
finishing touch here.

There's a snakeskin.

It's almost like "Look what
happened to the last guy."

From the most basic...

a classic bluebird nest.

To the fairytale.

Look at this. It's even
got a rain awning.

From elaborate construction...

It's made of 5,000
beakfuls of mud.

To extreme resourcefulness...

Here's a boot that
was found in 1899.

These nests

are just a small sample

of the work birds do every year.

Even the smallest of all
builds a beautiful home.

A female Anna's
hummingbird plays the roles

of surveyor,
architect, and builder.

She begins her nest
with a platform of soft,

fluffy fibers plucked
from nearby plants.

She's chosen a small tree branch

that offers a bit of scaffolding

to anchor her construction.

Working in a circle,

she uses her own small
frame to shape the cup.

Now, she needs a special
thread to tie it all together.

It's made by another
skillful architect

and, fortunately, she can
find it almost anywhere:

spider silk.

As the nest grows around her,

she works the inside
of the bowl with her feet,

compressing the resilient fibers

into a thick wool.

With her needlework
and footwork almost done,

she begins to shingle
the outside wall

with lichen, seeds,

and moss.

And, suddenly...

it's perfect,

a finished little home for the
tiny hummingbirds to come.

There are

some 10,000 bird
species in the world today

and each of their nests

is a custom-made cradle of life.

Millions of creatures
enter the world

from these remarkable structures

and the nest will remain
the center of gravity

for the rest of their lives.

All the colorful courting
and competition,

the dazzling
feats of navigation,

the marathon migrations,

they all come down to this:

a parent's obligation

to the next generation.

An osprey has just arrived home

for the nesting season,

to a secluded cove on
the Connecticut coast.

He's flown some 3,000 miles,
all the way from South America,

to reclaim a nest he
built here 4 years ago.

We can only imagine his surprise

to find it completely gone.

[Peeping]

Like many homes

along the shores
of the Northeast,

his nest fell victim to
an October superstorm.

But he's one tough bird,
determined to rebuild.

It's only March,
but time is ticking

and it will take him
at least 2 weeks

to build a nest that
will work this season.

The good news is there
are plenty of building supplies

strewn around on the beach...

Maybe even some
from his old nest.

Some mud and a little
seaweed provide a dab of mortar.

He could use some help.

He and his mate of several years

rendezvous here in the spring.

She should've arrived by
now, but she hasn't returned.

His efforts have
caught the attention

of a new female,
who's looking for a mate.

To impress her,

he turns his back in
a possessive stance,

crouching low and
flexing his wings.

Though younger,
she's slightly bigger,

as is usual with birds of prey.

Now that he's
gotten her attention,

he has to work around her.

This is probably her
first nesting season,

and she has no idea what to do.

She retreats, to
observe his progress

from a bird's-eye view.

Gradually,

the nest begins to take shape.

The young female is starting
to get the hang of things,

and brings in a
bit of nest lining.

[Splash]

One by one, trip by trip,

hundreds of sticks pile up.

It's an extraordinary effort.

He's a bird weighing
all of 3 or 4 pounds,

yet his nest will weigh
in at 400 or more.

And, when he takes a
break from the construction,

he courts his new mate

by bringing her a fresh fish.

It's not just a nest these
two osprey are building.

By working together
and sharing meals,

they are building a bond

that may last them for years.

Their nest is now
quite an achievement.

In fact, it's developed into
a property worth stealing.

[Foreboding music plays]

[Tweet]

A trespasser has
flown into their territory.

[Chirping]

This is something
our male cannot allow.

It's another male and, if
he can unseat our hero,

he can take his
nest and his female.

[Chirping]

[Flurry of chirping]

Our male takes to
the air in combat.

The female stands her ground.

She fends off a direct attack,

then regains the nest.

[Chirping]

The invader has been vanquished

and our male returns
home to a worthy reward.

Gently, he balances on
the female's back and,

folding his talons,
so as not to hurt her,

they mate.

Soon, the female will lay eggs

in the home they
have built and defended

and then, this nest

and all they've invested
in it will begin to pay off.

While ospreys are woodworkers,

red ovenbirds are sculptors

of mud and clay.

On a fencepost of a
sheep pasture in Uruguay

sits the ruins of
an old nest dome...

An ovenbird home
from generations ago,

now worn down

to just the barest foundation.

It's a secure perch

with a commanding
view of the open meadow.

[Chirping]

The female flutters
and calls in excitement

and her mate comes

to inspect the property.

They're eager to close on
the site and begin building here.

All they need
is a slight assist,

from the weather.

[Thunder rumbles]

Rain is essential for
builders who work with mud.

The wet red clay can now
be mixed with vegetation

and turned into
custom-blended adobe

they are skilled at shaping.

Facing more than a
month of construction,

the couple gets to work.

They keep a close watch on
how big the internal space must be.

It needs to accommodate
a clutch of 2 to 4 eggs

and an adult to incubate them.

As the home takes shape,

lots of other birds

begin showing an interest in it.

A saffron finch

and a kiskadee flycatcher

will mark the location.

One of them might
use the place next year,

when the ovenbirds
have moved on.

But it's the shiny cowbirds

that are getting too close.

The glossy black ones are males,

but it's the
dull-colored females

that seem most fascinated

with the structure.

The ovenbirds now spend

almost as much effort
defending the little house

as they do building it.

At last, the dome
is almost finished.

Only a large front
opening remains

when the ovenbirds
suddenly begin working

on an intriguing
internal structure.

Inside the simple dome,

the birds are crafting
a remarkable foyer...

A curved wall that will seal off

the main section
of the interior.

But they leave an opening
at the top of the wall

that gives them access to
the roomy inner chamber.

The home now has an
elaborate 2-part entrance...

A security measure that
makes it easy to defend.

It's a tight squeeze in and
out, even for the owners.

Both parents come and go.

For the next 2 weeks
or so, they will take turns

incubating the eggs,

shouldering the duties together,

just as they have

from the very moment
they began to build.

Building with adobe
is an age-old practice.

We humans have been
using it for some 10,000 years.

But imagine a much
older architecture,

structures older than dinosaurs.

On the floor of a dark
tropical forest in Australia,

there are modern creatures
that have revived the art

of these ancient nests.

This is an Australian
brush-turkey.

With his dramatic yellow
wattle and bright-red head,

he's a colorful character,
but, despite his looks,

he's not a close relative
of the turkey, at all.

He's from an entirely
different family...

The megapodes,

the original bigfoot.

He's using those big feet

to kick up leaf litter
into an enormous pile

that can reach 13 feet
across and 4 feet high.

This is one gigantic nest,

and it belongs to this
brush-turkey, alone.

As a territorial male,
he will build the mound

and tend it for the
entire nesting season.

A female,

with her more
demure yellow collar,

has been observing
on the sidelines

and now jumps in

to do a little
excavation of her own,

in anticipation of egg-laying.

Not all megapodes build mounds,

but the brush-turkey
specializes in it.

Sometime in the distant past,

they departed from
their ancestors' tradition

of sitting on eggs
to incubate them.

They turned to another
source of warmth.

As this giant pile of
sticks and leaves decays,

it heats up.

Brush-turkeys can
tell, to the very degree,

whether it's warm enough
to incubate their eggs

and she takes the
mound's temperature

with her sensitive beak.

It's a go.

This is what the male

has been waiting
and working for.

But he's so anxious and excited,

he can't leave
well enough alone.

She's in no hurry,

laying one large, white
egg with each visit.

She may contribute
several eggs to this nest

before moving on to another,

and the eggs may
not even be his.

As soon as she's up,

she tries to bury
the egg deeper,

but the male insists
on doing it himself.

Every egg is
carefully distributed.

The mound may contain
as many as 50 eggs,

that come from several females,

placed less than a foot apart

and arrayed in a circle
2 feet below the surface.

Now, the mound acts
like a giant compost heap,

generating so much heat
that the eggs incubate in place

without ever being
touched by a parent.

But the temperature
is all-important.

It must be kept precisely
between 91° and 95°

for the embryos to develop.

Outside, the male
monitors the mound,

constantly checking

its internal temperature,

adjusting the
decaying vegetation

to keep it just right.

Each egg must incubate
for about 50 days,

until, deep in the mound,

a brand-new
dinosaur-like foot appears.

Once out of the egg,

the chick must
struggle to the surface

all on his own.

There will be no
parents to greet him.

The incubating mound freed them

of all further parental duties.

One by one, the
little brush-turkeys

set out on their own,

foraging in the leaf
litter for insects to eat...

instinctively using the
footwork they will need

to build their own
mounds in the future.

Now, this mound may look
like it belongs to a brush-turkey,

but it's for a slightly
different construction project.

Okay.

Everything a nest-builder
could need, right here.

My production team has
gathered all sorts of materials...

Oh, this looks good.

And challenged
me to build a nest.

Yep. I've never actually done
this before, believe it or not.

[Chuckle]

Birds, of course,

have to do all the collecting

for themselves.

And, while I'm crashing
around in this brush,

they are very selective
about what they choose.

After all, they have to carry

every bit of material back
to the site themselves.

Let's see what we can do here.

How hard can this be?

A little foundational
framework of sticks.

Hmm. No, that's
not going to work.

I'm struggling to get
something going, here,

and I've got two hands
and opposable thumbs.

I can't believe they
do this with just a beak

and their feet.

They make this look so easy.

The truth is,

they, too, have to practice.

It can take a young bird
several seasons to get it right.

I'm understanding
that completely.

Third time's the charm?

Here we go,

some slightly smaller pieces.

Kind of interlace it as I go.

Not quite sure how to deal
with the floor of the nest.

That could be an option.

This is an afternoon's
work for me,

but birds can spend
weeks on a project like this.

Oh, ivy. Yes, ivy,
to bind it all together.

Let's do a weaver-bird number.

Oh, yeah. Oh, yeah.

Look at that.

Once the outer structure
is fairly complete,

birds shape and
weave a soft inner cup

to cradle the fragile eggs.

It's starting to look very cozy.

I'd make a hummingbird proud.

And, as some nests are part

of the courtship
ritual, there's often a bit

of decoration,
an original touch.

This will bring in the ladies.

All right.

I'm feeling pretty good
about my little nest.

I'd love to know what
a bird would make of it,

but the next-best thing may be

Professor Corey
O'Hern of Yale University.

He's a structural
engineer who's finding out

some surprising things
about how birds build.

- So, this one's
a modern artist.

I brought some
nests for Corey to put

through the lab's
nest-testing machine.

It's a crusher that
measures structural stress...

That's how much
force it takes to distort

and, ultimately,
destroy a structure.

The same principles apply
to bridges and skyscrapers.

Here's a traditional
robin's nest.

This particular nest
has a lot of weaving.

The small fibers

are taken around the
nest in a circular fashion

and they're going in
and out of the other fibers.

Even though each
fiber is very flimsy,

if you mat them together,
if you weave them together,

it can be very strong.

- And beneath the weaving

is an inner cup of
dried, packed mud

that gives the nest walls
a lot of additional strength.

How about this guy? Ha.

It's the not-very-imposing
nest of a catbird,

but it's got some surprises.

I mean, one thing that
strikes me about this

is just how feather
light that is, you know?

You can see, again,
the key feature is

that the fibers are interwoven,

so, one thing
that's important is

the numbers of
entanglements and crossings.

- Weaving is the secret
to a nest's success.

It's all the ways that
strands cross back and forth

and lock together
that give nests

such impressive
structural integrity,

from the giant sticks of ospreys

to the spider-silk
thimbles of hummingbirds.

One thing that I do is I
do computer modeling.

I can't create in
the computers, yet,

structures that rival
these, in terms of strength.

So, even though we call
them "bird brains," they have

some innate
knowledge of building

that we can't master.

- Yeah, it's really fascinating.

I'm dying to get them
under the machine,

to see how they compare.

Time to put a nest to the test.

Oh, it's going.

Wow.

And...

we squash it.

- Okay, so this nest can sustain

about 12 Newtons
before it breaks.

- That's about 2.7
pounds of force.

That's still fairly impressive.

Before it was put in...

- But the surprise is
that the whole structure,

dry and brittle as it is,

just seemed to bounce
right back into shape.

It was resilient.

- There's a lot
of spring to this.

Now,

the robin's nest.

Oh, wow!

- So, I think it's broken.

There was a peak stress
of around 40 Newtons.

- That's engineering-speak

for being nearly 3 times
as strong as the catbird nest.

But this one cracked completely.

You know, the mud casing broke.

Now, you see some of the
internal structure of the nest.

Here's the ball,
where the bird sits,

but, now, you can clearly
see the mud packing.

- Right, and that's where

that additional strength
over the other one is coming.

And, now, my masterpiece.

- Oh! It looks like
a Christmas wreath.

Okay, here we go.

It's lowering. It's
made contact.

We're at the previous levels.

We're at 25.
- Wow!

[Snap]
- Oh!

That didn't sound good.

But it seems to have withstood
quite a good deal of pressure.

What did it get up to on...?
- It was around 70.

Was it really?
- Yes.

Not bad.

That's about 15.7
pounds of force.

Well, what's your
assessment of my nest, then?

- Um, I think you
cheated, in several ways.

Let's analyze this nest.

So, first,

you're using very
long, almost branches.

The key issue is:

what can the robin,
what can the catbird use?

They can only
use a small fraction

of the weight of themselves,

and so they're using
fibers and twigs.

Another thing that I notice
is that you're using ivy

to wind, presumably,
with your fingers...

- Noone said I couldn't do that.

Around these large twigs,

whereas a bird,
all it has is its beak,

and so you should've
made this nest

with your mouth and no hands.

- To be fair. Okay.

That's the brilliant
thing about birds' nests:

the materials are
light and weak,

and yet, when crafted
by a well-practiced beak,

they hold up to all
manner of wind and rain,

sometimes for years.

It's late May

at the osprey cove on
the Connecticut coast.

For 8 long weeks, the
female has been confined

to the nest,

incubating this year's
clutch of two eggs.

She turns them,

while keeping her sharp
talons carefully away,

and settles back down.

Until...

a baby osprey emerges
from beneath her.

But it's not the first chick
in the nest this season.

House sparrows have moved in,

tucking their own nests

deep inside the
osprey's stack of sticks.

They can have

from two to four
clutches a year.

So, the once solitary
house high on the pilings

has become a lively

residential complex

with little sparrows
chirping constantly

and darting in and out.

Sometimes building a nest

is just the beginning

of a complicated life
with the neighbors.

The adobe dome of the ovenbirds

is being tested by the elements.

[Thunder rumbles]

You might imagine that
a mud home would melt

into quite a mess in
the frequent spring rains,

but, once dried in
its finished shape,

it's almost as hard as concrete.

As the weather clears,

the ovenbirds drop their guard,

and both come out to feast
on insects and invertebrates

that emerge after a downpour.

It's just the opportunity
a cowbird needs.

Cowbirds have been hanging
around the adobe homestead

like a dark cloud,

despite the ovenbirds'
efforts to shoo them away.

And, with both parents
out of the house,

a cowbird female darts in.

It's not what you think...
She's no predatory egg thief.

She doesn't want
to raid the nest.

She wants to add to it.

Cowbirds make no
nests of their own

and must use someone else's.

She's back out in a flash,

having just laid an egg next
to those of the ovenbirds'.

Her plan is to have the
diligent couple raise her chick,

incubating it in
their cozy home,

both working hard

to see it fledge.

It's a strategy that often
works for the cowbird.

But not always.

Once back in the nest,

the ovenbird senses
something's up.

She's detected the strange egg.

It's just a bit smaller
than the ones she laid.

She hesitates for a moment.

And then evicts it.

The home invasion

has backfired.

The ovenbirds' nest

is still secure.

The cowbirds must
turn elsewhere.

And, just across the
border in Argentina,

chalk-browed mockingbirds
are high on their list

of likely foster parents.

Their sturdy bowls
of tightly packed twigs

are tucked in all
through the thorny scrub

that dots the open grassland.

The female can lay up
to 4 lovely speckled eggs,

one per day.

She'll incubate
them for 2 weeks,

taking brief breaks

to find food.

The deeper the
nest is in the brush,

the harder it is for
predators to find,

but the cowbirds

have been keeping a close
eye on their comings and goings.

A mockingbird nest

would be the perfect
place to leave their eggs,

if they can just get past
the vigilant homeowners.

In the darkness
just before dawn,

the cowbirds make their move.

With infrared cameras,

we can see the
mockingbirds are already up,

agitated, ready to
fend off the assault.

As a mockingbird
chases one invader away,

another seizes the moment.

In seconds, the
cowbird slips in and out,

laying a small, round egg

right next to the
mockingbird's larger, oval one.

And, in nest after nest,

other cowbirds do the same.

A mockingbird returns

just seconds too late.

She hesitates for a moment,

then turns the egg,

as though it were her own.

But timing is everything.

If the cowbird is caught,

there's hell to pay.

The mockingbird is furious.

[Squawking]

Yet, intent on her purpose,

the cowbird still
manages to lay her egg.

[Suspenseful music plays]

But, having witnessed the crime,

the mockingbird
won't stand for it,

and she removes the
offending egg immediately.

And so it goes in
the thorn thickets

as dawn approaches,

the cowbirds
sneaking into nests...

the mockingbirds,

screaming their objections.

[Squawking]

Until one actually picks
up the invading egg-layer

and throws her out of the house.

Here's that again.

As day dawns,

the mockingbirds
settle in on their eggs,

turning them and
keeping them warm.

But, in nest after nest,

there are eggs that
are just a bit different.

In the daylight, we
see they're all speckled,

but some are a little smaller

and not quite the same color

and, ingeniously, these
are the eggs that hatch first.

From the smaller egg, a
little cowbird has emerged

to get a head start
over the other chicks.

It's utterly dependent on
its mockingbird parents.

And, as their other
eggs begin to hatch,

they set about
hunting for them all.

The gaping pink mouths
belong to the baby cowbirds.

The yellow mouths
are little mockingbirds.

It's an intense time.

In 13 to 14 days,

all the chicks will fledge.

Throughout the thorn brush,

mockingbird parents work hard

to fill the hungry mouths,

but that leaves many
chicks home alone,

waiting for the telltale
sound of a returning parent.

Their only defense is to lie low

and keep quiet,

but sometimes, nests meant
to provide safety and security

can just as easily
become a deathtrap.

[Flurry of chirping]

The liophis snake makes off
with the bigger mockingbird chick,

leaving only the
terrified young cowbird

for this mother to raise.

Even after the
chicks have fledged,

the mockingbirds provide for
them for another week or two.

Mockingbird parents

and their cowbird chicks
perch together in the brush,

neither noticing what an
odd little family they make.

Yet, the chicks will take up

the battle finesse
and furious combat

when it comes time
to lay eggs of their own.

The osprey nest

has produced two
healthy chicks this year

and, by the end of July,

they're as big as their parents.

But their bright-orange
eyes have yet to turn

the pale yellow of an adult's...

and their feathers are
still trimmed with white,

marking them as juveniles.

Though they've already been
taking short flights to the dock

and up to the branches
all around their cove,

learning how to master
their almost-6-foot wings

will take a lot of practice.

Not all their flights look
entirely on purpose...

and they're still
tied to the nest,

crying like babies for their
father to bring them fish.

As always,

he answers their calls.

It will be another month

before they can truly
fish for themselves,

and so the nest
remains the center

of the young ospreys'
security and support.

Their mother perches
nearby, watching over them.

But her long ordeal at the
nest is over until next year.

Now, the youngsters
must build the muscles

to power their mighty wings.

That will take a few
more weeks, yet.

But, then, they
will finally leave

the only home
they've ever known.

It's now the end of February
on the Connecticut coast.

In a week or two,
birds will start arriving

from wintering grounds far away.

Our osprey may
already be on the wing.

And this is where they'll
come back to, this very nest.

After all, they're coming home.

An osprey can live for 25 years,
so our male will come back here

and have many more families
over the summers to come.

And, three or four
years from now,

his chicks will come back

and try their hand
in the same territory,

so, in some ways,
they never leave home;

this becomes the family cove.

Home.

What powerful
feelings that evokes.

And a nest is a place
of such ancient origin,

such promise for the future.

It has a hold, even on us.

And it's no wonder.

Deep in our primate past,
we, too, once lived in trees.

Like so many birds,
we found food there.

Perhaps the figs were fruiting,

and we followed the
ripening feast from tree to tree

and it's here we began to build.

In the shelter of
the upper branches,

beyond the reach
of lions and leopards,

we made nests, our
first rustic homes.

They may have served
us for just a night,

a comfy hammock,

suspended in safety,
so we could sleep.

And, all these eons later,

there is still nothing
better, at the end of the day,

than jumping into
our very own beds

and feeling safe and secure

at home.

To learn more about what you've
seen on this "Nature" program,