Nature (1982–…): Season 30, Episode 2 - The Animal House - full transcript
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.
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.