Original subtitles

Narrator: Humans were not the first

to build houses and high rises,

or live in cities and towns.

The animal world is full of these dwellings,

some elaborate, some simple,

but all built without blueprints.

Whether the products of instinct or intellect,

these structures are practical

and protect their owners from enemies and the elements.

Some homes are decorated for mates to move in;

others defended to push freeloaders out.

These are some of nature's finest architects,

engineers, and home builders.

Welcome to "the animal house."

Jackson Hole, Wyoming, home to one of

the most ambitious animal builders in the world.

Up to a mile or so of river is taken over by

a single family of beavers.

Dams flood the landscape, creating ponds and canals

that cover many acres.

At the center is their lodge.

A defensive moat surrounds a sturdy castle,

made of serious building materials.

A beaver can gnaw through a tree in an hour or two.

He often stops half way and lets the wind do the rest.

His teeth are reinforced with iron,

which turns them orange.

The teeth wear down an inch a month,

but grow ten times faster than our fingernails.

Even three-foot lengths are too heavy to drag over land,

but by flooding the area,

the beavers can easily move the logs.

Each dam needs about 50 tons,

and can be hundreds of yards long.

Mud is used to seal any leaks.

Everything has to be ready for winter.

Of the beaver's rural community, most have left or are hidden,

housebound at this time of year.

The only sign is a ripple of heat from a chimney,

identifying the beaver's lodge.

Inside, special cameras

reveal new young, born early thanks to the protection of

three foot thick walls, sealed with mud and straw.

It's been 40° below outside and still didn't freeze in here.

The chimney is open, as now it gets too hot.

[Beaver kits mewling]

The only way in and out

is to swim underwater.

But that doesn't discourage a muskrat.

Voles, mice and insects also find refuge here.

The lodge has lodgers.

We never saw the landlords object to the muskrat,

which is more than can be said for the cameras,

which they soon censored.

Outside, the itinerant and the homeless

must wish they were somewhere safe

and warm.

[Howling]

[Wind howling]

[Bison snorts ]

solid walls and underwater doors are not the only ways

to try and keep the outside out.

Prairie dogs live in an underground colony

called a "dog town,"

which can stretch over the horizon.

The town is divided into coteries,

extended families,

living behind a volcano shaped front door,

and with an acre or so of manicured lawn to provide food.

Prairie dogs themselves may seem like

fat vegetarian meerkats,

but they are actually squirrels that bark.

And they don't like visitors.

[ Barking ] there's a father in charge,

several wives

and different generations of youngsters.

Each family rarely goes beyond their garden boundaries,

and they all work together on their house.

Time is spent on home improvements

and household chores.

[Prairie dogs bark and chirp]

The raised entrances are watchtowers,

but are also chimneys,

and draw air through the burrows.

The lower-level holes are fresh air intakes.

Inside each family home there may be a hundred feet of tunnels

with many different rooms.

There are sleeping chambers,

where they spend most of the winter.

Some even have an adjacent lavatory.

There are storage rooms, anti-flooding features,

and escape hatches.

It's warm in winter and cool in summer.

It's a real estate agent's dream.

The pups, at a few days old, are tiny, bald and blind.

Their mother will stay with them in a special nursery,

feeding them and arranging the bedding.

Even at birth, prairie dogs are clearly builders,

with shovel shaped heads,

cylindrical bodies, and digger's claws.

With so many corridors,

it's possible that one might lead by mistake

into a neighbor's house,

and the neighbors could be burrowing owls.

[Owl shrieks]

In the dark, the startled owls

give a good impersonation of a rattlesnake.

[Owl hissing]

[ Owl imitates rattle ]

The owls have young, too,

hatched in an abandoned part of the prairie dog burrow.

They are, in effect, harmless squatters.

The dog town is full of freeloaders.

Hares and snakes find homes

in this mixed neighborhood.

Dangerous characters like black-footed ferrets

and swift foxes live in old burrows.

Overall, wildlife increases

wherever animals build homes...

Whether the builders like it or not.

Maybe as a response,

prairie dogs have a community police force.

Family members takes turns watching out for predators.

[ Barking ] A prairie dog calls "eagle!"

Families for up to half a mile around

run for cover.

The whole neighborhood benefits.

The prairie dogs even have different calls

for different predators.

"Coyote" sends them down their burrows...

But calling "badger“ needs a different response,

as badgers can dig.

So the dogs watch them nervously

from the surface.

Their calls may include information on size, direction,

and speed... even color.

It is one of the most sophisticated animal languages

ever studied, and has arisen

in response to the predators that are drawn to

animal houses.

Living close to your neighbor can provide some protection,

but the problem is, it can also attract more predators.

Southern carmin e bee-eaters

catch the eye of a hungry fish eagle.

Predators have a major influence on how houses are built.

Here along the Luangwa River in Africa,

sandy cliffs are one of the few places out of reach

of eagles, lizards and monkeys.

A bee-eater pair takes turns digging the burrow

with their beaks and feet.

Burrows may be up to six feet long,

simple tubes for two to five eggs.

The center of the colony is safer from predators

than the edge, so the birds nest closely together

in the middle.

The result is

evenly spaced lines of townhouses.

But the denser the colony, the more attention it gets.

[Birds squawking] Noisy neighbors

are life-savers.

On every continent,

animals converge to build homes together.

A quarter of a million socotra cormorants

arrive on desert islands off Arabia

to build simple mounds in the sand, away from predators.

Some debris is favored for the nest, other bits rejected.

The bird next door tries to steal from the collection.

The chicks, when they hatch,

must be protected from the neighbors' lethal beaks,

so nests are built just out of pecking range.

By treading the fine line between neighbors and predators,

they end up building near inch-perfect

geometric plots in their thousands.

But the greatest animal houses in the world

are caves.

Three and a half million bats live in this cave in Borneo.

[Bats screeching]

Each evening they leave the safety of their home

to feed on insects in the surrounding forest.

They gather outside the city gate

in a defensive whirlwind.

The swirling commuters are running a gauntlet

of bat hawks and peregrine falcons.

As the night shift leaves home,

the day shift is returning.

Cave swiftlets navigate into dark caverns

by echolocation... Like a bat...

Almost the only birds to do so.

They make powerful clicks,

and listen to the sound bouncing off the walls.

[Birds clicking]

Male swiftlets choose tiny high-rise ledges,

up to 300 feet above the cavern floor.

They share the space with specialist spiders

and unique cave centipedes.

The best ledges have to be fought for,

and males battle over real-estate

in the pitch blackness.

Swallows and Martins normally use mud,

but the swiftlets make their own building material.

It's a sort of gluey saliva, which they attach to the rock,

and build up, layer by layer, making a tiny egg-cup.

It can be weeks of painstaking work.

The saliva hardens into surely one of the most extraordinary

animal houses in the world,

a crystal chalice.

The nests become as crowded as closely packed apartments.

Woven-in feathers darken the nests,

but single white eggs glow in the lights.

For generations,

this cave has been one of the safest homes.

That is, until a new predator found it.

Men are here to collect a culinary delicacy,

for the famous birds' nest soup.

The saliva is full of proteins and minerals,

but apparently the nests don't taste of anything.

Yet, the little homes are worth

thousands of dollars a basketful.

The legal trade alone in birds' nest soup

is worth about half a billion dollars.

Inevitably,

wild cave swiftlets are in decline.

Saliva is an extraordinary building material,

but perhaps the most remarkable of all

is silk.

The coiled threads of protein are famously strong and light,

which is why other animals steal them.

A bronzy hermit hummingbird in Central America

collects cobwebs.

With the silk threads she weaves a pocket,

anchored under a leaf.

The leaf keeps out the rain

and prying eyes.

Camouflage is all the defense she needs.

A lethal trap has become a different sort of home...

A cradle.

Baby hummers grow up suspended in silk

and fed on nectar.

The second-hand web can carry the young and the parent birds,

though it was originally made only to catch a fly.

Even ordinary building materials

can be transformed by the skill of the builder.

A female red-rumped cacique in south America

ties palm leaf strands into loops and knots.

The mother caciques choose the nest site,

build, and bicker over space.

The architectural blueprint is instinctive,

but she adapts and refines the basic plan,

and her skill improves with practice.

The foundations are made first,

then a loop... The entrance to the nest.

The door is extended into a tube,

like a sock about 18 inches long.

After up to three weeks' work,

a nest is finished at the bottom.

You can't leave your handiwork for long,

or your older and cannier neighbors try and pull it apart,

and steal your building material.

The final nest is this shape because there are egg thieves.

This is a toco toucan.

The nest tube must be long enough so that predators

can't see the chicks or reach the bottom.

Over the generations,

caciques have extended their nests to keep the young safe.

The toucan is trying an attack through the side of a nest.

But caciques have unlikely allies.

They often nest near bees or wasps.

The chicks are safe,

though the nest seems to have acquired a new window.

It looks like the parent

may have to get materials for repair work.

Building supplies are so important to some animals

that in places the materials themselves have taken on

a particular significance.

Flightless cormorants build their nests from seaweed.

On the shores of the galapagos islands,

there isn't much else.

The males gather building material underwater.

It seems this is

as much about their relationship as building the nest.

They are like newlyweds cooing over paint swatches.

Color is important, and texture,

and the females seem to evaluate

each gift.

Occasional exotic offerings...

A living sea urchin or a new shade of seaweed...

Are brought to the nest,

and sometimes rejected.

A gift that walks away is of no use.

Size certainly doesn't impress her.

The drying seaweed

means more to the cormorants

than mere construction materials.

A nest becomes a special place,

to be defended from curious visitors...

And a perfect home for the eggs.

We don't really know what they think or feel,

but some scientists believe

housekeeping seems to draw them closer together.

The chick benefits from the parents' commitment

to making the perfect home.

The ultimate example of

an animal that builds a palace to win a mate

can be found in the forests of new Guinea.

This three-foot-wide woven wigwam is a seduction pad,

and is all about show.

Carefully arranged flowers and fruits

are placed in piles on manicured moss.

Smaller treasures are towards the back,

to make the bower seem bigger...

A trick human interior designers also use.

Yet the male vogelkop bowerbird himself is modest,

even drab.

It may take many years to become

a proficient enough house builder to reach this stage.

If he sees a twig out of place,

he'll push it in or remove it.

He has a vision of his ideal construction.

His architectural eye is unique.

His rival neighbors each have different color schemes,

or floor designs, or decorations.

This particular male

is going through a red phase.

The flowers are changed regularly,

and the berries must be perfectly arranged,

each turned just the right way.

The floor is a challenge...

Roots grow through the moss and have to be tackled.

What he can't remove, he sweeps under the carpet.

A rival male is singing.

He must respond.

Now we see why the bower is the shape that it is.

It's a concert stage, and the arch may help

project his voice.

[Singing]

He ends with a little dance.

The audience has arrived.

She seems interested, but he has disappeared.

It's crucial in bowerbird courtship

that he remains hidden.

His house has to coax her in.

Only when she is brought to

a state of ecstasy over his decor

does he dash out and try to mate.

It's not entirely successful.

Maybe she wasn't ready for his appearance.

Or maybe his flowers or his floor weren't up to scratch.

It's most frustrating.

Perhaps he will tempt her back, and maybe next time,

the bower will be looking at its best.

Home design can, occasionally,

be about more than impressing the perfect partner.

The burrowing owls in prairie dog town

have a strange take on suitable suburban decor.

Their landlords, the prairie dogs,

would not approve of this innovation.

What burrowing owls like

is what the buffalo leave behind...

Dung.

The owl places the dung carefully around

his front door.

The burrowing owl chicks don't seem impressed by

the collection of poop on the stoop.

This is not how most wise animals

treat their own doorsteps.

[Chick squawks, insects buzz]

In fact, this extraordinary bit of decoration

is a trap for beetles... Dung beetles.

The beetles find dung by smell.

It is, to them, building material and food

rolled into one.

Tons of dung is trundled away.

The dung ball, with an egg inside, is buried,

a warm and delicious home...

At least, for a dung beetle larva.

But the remarkable little owls have second guessed them.

They collect dung to collect beetles.

A chick takes some dung down the burrow.

Maybe it's learning the connection with food.

It's a step in the right direction.

The owl mother doesn't agree,

and turns it into a lesson on housework.

Homes are hard work,

and there's a lot for young animals to learn.

Homemaking requires a sense of place,

as well as working out how to get along in a community.

The trap seems to have worked.

Food is always critical,

and so, many animal builders put a larder

at the heart of their homes.

The beavers' system of canals and ponds

is a massive cold store.

Beavers eat bark and leaves,

and stocking the pantry is a job that takes months.

The beavers wedge the branches down in the mud.

Even though it's stored underwater,

a potential burglar spots the stockpile.

But the moose is soon told this store is private property.

A few tail-slaps,

and the intruder gets the message.

A house is of little use

if there is no food.

Winter in outer Mongolia would be hard for a hamster,

without a well-stocked storeroom.

Down the burrow are several rooms.

In the bedroom, the young are kept warm

and fed by their mother.

Next door is the larder.

All Autumn they gathered seeds in their cheek pouches

and brought them down here.

Thanks to the seeds staying safe and dry,

the hamsters can start a family

while it is still barren outside.

Our own earliest buildings may have been grain stores.

Protecting food for winter enables house builders

to move into colder areas

where the homeless could never survive.

Some homes go a step further...

They have a living larder.

[Sniffing]

A mole's network of dark passages

can be extended at seven feet an hour,

and provides the mole's food.

Earthworms burrow through the walls by accident,

and the star-nosed mole

has special worm-detecting feelers on its nose.

This housebound animal has a curious reputation

as the fastest eater on record.

An earthworm can disappear in a quarter of a second.

Not everyone can build a house

where your food literally drops in for dinner.

Bamboo is one of the world's fastest growing plants.

In China, it occasionally appears to be growing

right back into the ground.

Under the bamboo

is a quarter of a mile of tunnels...

Built over several years by bamboo rats.

The tunnels follow the roots,

which run along the ceiling like service pipes.

She checks the bamboo by smell.

If the roots put out a new shoot,

she can sense the fresh growth,

and, when it is the right length,

she harvests it.

The house has become a farm.

She has the same iron-coated teeth as the beavers.

Both are rodents,

which are the vast majority of mammal house builders.

Her young have never been out.

She's blocked the exits.

The outside world might as well not exist.

The little ones seem determined to explore,

but may get lost in the network of tunnels.

So she literally drags them around the labyrinth

of her underground bamboo farm.

American beavers

build canals to carry trees,

and Chinese bamboo rats harvest bamboo underground,

but in South America,

another animal takes the idea of a home-farm

to a whole new level.

Leaf and grass cutter ants

take about 10% of the forest's growth

underground to fungus farms.

The white fungus

grows on the chopped-up leaves,

and is pretty much all that the ants eat.

The fungus farm generates heat and carbon dioxide.

Pipes lead to a large mound above the ground.

The chimneys are like the raised prairie dog burrows,

drawing the air through the nest.

Nobody knew how big grass cutter ant cities were,

so scientists poured a liquid cement

into an old nest.

Once the concrete was set,

they dug away the earth to reveal

an extraordinary secret city.

The ants shifted

40 tons of soil, billions of loads.

There are subterranean highways connecting the main chambers,

with side roads to fungus farms,

huge trash pits, and temperature controlled nurseries.

This is one house

for 12 million inhabitants...

A city larger than London or New York.

On our scale it would be

a mile deep and five miles across.

It must be one of the greatest engineering achievements

in the animal world.

These 10-foot-high termite mounds

all point north to south.

Their flat sides face east and west,

warming in the morning and afternoon sun.

But during the heat of midday,

the sun hits only the thin blade edge at the top of the mound.

Our large buildings

could follow this simple trick.

However, that's not the whole story.

Half the year this is a swamp,

and the sail-like shape

and large surface areas are perfect for

keeping the colony dry and comfortable.

Most termites avoid overheating by descending into lower levels

during the hotter part of the day,

but as the land here floods during rainy season,

these termites climb up into their skyscraper

to escape the problem.

Finding an egg 1,000 times your size

in your house must be puzzling...

Terrifying when it starts to hatch.

The gigantic aliens

are lace monitor lizards.

Their exit is closed.

The termites repaired

the hole in the wall the monitor mother made to lay her eggs.

They are trapped.

Incredible though it seems,

their mother has returned to release them.

These lizards could not have chosen a better nursery,

protected from predators,

and incubated at the perfect temperature.

Now the termites must repair the mound again.

They use mud, and mortar out of their back end.

The walls keep the mound within a degree of 86° fahrenheit,

whatever the weather outside.

Far from the tropics, other insects have resorted to

central heating.

In a hollow tree, a Japanese giant hornet

starts to build a city with cavity walls

and electric radiators.

The queen first makes a few compartments.

An egg in each hatches into a larva.

It spins a silk cocoon for itself

that has extraordinary properties.

The silk is like a thermostatic electric blanket.

It stores heat as an electrical charge,

which automatically turns back into heat if the nest cools.

Her daughters pupate and emerge.

They are the first battalion of builders.

They add additional floors, suspended in the middle.

Supporting columns are molded.

They build with chewed-up wood pulp,

the same material as paper.

As more of the queen's larvae hatch,

they start demanding food,

banging and scraping their heads on the walls.

The workers collect insects

and mash them into a paste for the larvae.

The outside walls are extended downwards,

with up to eight layers of cavity insulation,

and built-in flues and ducts.

Like the termites, a few simple instructions

may come together to build a surprisingly complex design.

Scientists call this an "emergent property."

And what emerges, after four months,

is a hornet's nest several feet tall.

If it's cold, the nest is heated by the larvae

and their silk blankets, but on hot days,

cooling air is fanned in.

Like the termite mound,

the nest is kept close to 86° fahrenheit.

The hive behaves as much like

a warm-blooded animal as a house.

Towards Autumn, the queen turns to producing new queens

for next year.

She and all her workers will soon die here,

exhausted and now expendable.

The city will crumble, too,

and can never be reused.

In the final days of her life, the queen ensures that

a few larvae are fed, and fresh queen hornets emerge.

Each faces a winter of hibernation,

and in spring starts building a brand new edifice,

40,000 times her size.

There is one animal in the rainforest

that builds the most extraordinary city of all.

Army ants kill

almost every living thing they can,

and carry it all back to their home.

Their house is a living building entirely made of ants,

called a bivouac.

The legs carry the weight of the whole nest.

Big cities have big problems.

The ants generate so much waste

that they need an off-site landfill.

The carcasses of dead insects and old cocoons

are taken out of the city to the dump.

Soon the colony sits in a sea of municipal waste,

and all the surrounding food has gone.

So, they unhook themselves

at night and set off.

Pupae and larvae are carried,

and the queen is protected behind a cavalcade of soldiers.

A new site is chosen,

and living ropes become columns.

They seem to build around a frame,

but since every site is different,

the design is never identical.

The frame is filled in

with walls to create corridors and rooms,

all made of ants.

Their new neighborhood will be stripped of prey in a few days.

If the ants couldn't move their city,

they'd quickly eat themselves into extinction.

All houses face the same dilemma.

The beavers have felled hundreds of tons of wood.

After four or five years

there is nothing left but bushes.

The ponds have silted up, and without logs for repair,

things start to fall apart.

The beavers make do for a while on shrubs like Willow herbs,

but even these they eat faster than they can grow back.

As their lake shrinks, they will abandon their home.

Almost all homes become unsustainable, eventually.

The rivers are littered with empty lodges

and broken dams.

Every construction

is an attempt to tame nature,

and nature will always win in the end.

Things are even tougher for prairie dogs.

In summer, the land dries.

The cattle and buffalo can move, but the dog towns can't,

and the families have nowhere else to go.

The owl family can all fly now.

They can come and go.

The prairie dogs eat the remaining grass,

until their neighborhood becomes a dust bowl.

They face starvation.

The young are a few months old

and now the colony turns against them.

Neighbors start to hunt down cubs.

Even cousins and aunts turn nasty.

In a dry year,

up to half of the young are killed.

Stuck underground, out of sight,

their home becomes a prison, a tomb.

The prairie dogs are facing a problem

most animals face all the time.

You can't rely on one place for long.

For many, the risks are too great.

The restless and the hungry

follow the seasons in great migrations.

The world is constantly changing,

and even the wisest animals struggle to keep up.

[Elephants trumpeting]

These are the homeless of the earth,

and until recently, we were among them.

So how did we become the greatest homemaker of all?

Our closest animal relatives are still homeless,

unable even to keep out of the rain.

Apes and monkeys don't make shelters,

though a gorilla's hands and brain

are easily up to the job.

The priority for these mountain gorillas is to find fresh food,

so they keep moving.

A house would only tie them down.

The signs of an ability, however, are here.

An improvised roof is better than none...

While it lasts.

Our ape cousins build beds or even platforms

woven from branches.

But they never sit under them.

Our ancient ancestors were not homemakers.

We may have little instinct for how to avoid

the problems that houses bring.

[Thunder rolling]

Salvation does come in the end

for the few surviving holdouts inside their houses.

In Autumn, the rains replenish the land,

and in Spring, the grass grows back.

The prairie dogs have done no permanent damage.

They help the grassland over the years,

by mowing and fertilizing their gardens.

The neighborhood returns to normal.

[ Barking ]

the beavers, too, have started over,

rebuilding in ponds abandoned years ago

that now foster another generation of trees.

We may be new to building,

but beavers have known for a long time

that all houses are hard to sustain,

and each one is only a temporary victory over nature.

Yet still we build.

For whether we're ants or bowerbirds,

prairie dogs or people,

it's good to have a place to call home.