Natural World (1983) s31e06 Episode Script

1 I'm fascinated by the glimpses we sometimes get into an animal's hidden world.
Over the years, I've found different ways to peer inside.
They say, if you want to understand people, look in their houses.
I think the same may be true for wildlife.
I've never been invited in and, on occasions, I've not been entirely welcome.
I think that was pretty clear.
Oh, dear! Despite setbacks, I've seen skilled builders I've discovered squatters and burglars I've noticed interior decoration I've found storerooms and air conditioning and even en-suite bathrooms I've visited animal cities and huge communities.
Wild homemakers are special creatures, more like us, trying to keep out the wilder wildlife.
Peering into an animal's house can tell you so much about them.
It's a window into their private dramas and the intimate stories we rarely see.
Most of us are indoor creatures.
Houses have ended our wild days.
Yet, we forget that animals build many more houses than we do.
And they've been doing it for much longer.
We think we alone invented building materials, but animals have done so, as well.
Scaled up to our size, termite mounds would be almost a mile high.
Animals have an eye for beauty and so do we.
Our homes reveal a lot about us, but this is the animals' story.
In North America lives probably the most ambitious animal builder 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 centre 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 halfway and lets the wind do the rest.
but grow ten times faster than our fingernails.
Even metre 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 metres 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 beavers' lodge.
Inside, special cameras reveal new young, born early, thanks to the protection of metre-thick walls, sealed with mud and straw.
It's been minus 20 outside and still didn't freeze in here.
The chimney is open, as now it gets too hot.
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.
WOLF HOWLS 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're actually squirrels that bark.
And they don't like visitors.
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.
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 may be 30 metres of tunnelling with many different rooms.
There are sleeping chambers, where they spend most of the winter.
Some even have an adjacent lavatory room.
There are storage rooms, anti-flooding features, and escape hatches.
It's warm in winter and cool in summer.
It's an 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 sorting out 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 neighbour's house, and the neighbours could be burrowing owls.
In the dark, the startled owls give a good impersonation of a rattlesnake.
OWL HISSES MENACINGLY 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 neighbourhood.
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 service.
Family members takes turns watching out for predators.
A prairie dog calls "Eagle!".
Families for up to half a mile around run for cover.
The whole neighbourhood 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 colour.
It's 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 neighbour can provide some protection.
The problem is, it can also attract more predators.
Southern carmine 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.
The centre 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.
The bee-eaters unite, screaming at the intruder.
Noisy neighbours are a life-saver.
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 favoured 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 neighbours' lethal beaks, so nests are built just out of pecking range.
They end up building near inch-perfect geometric plots in their thousands.
But the greatest animal houses in the world are caves.
3.
5 million bats live in this cave in Borneo.
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.
The birds of prey grab anything that tries to go it alone.
As the nightshift leaves home, the dayshift 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.
Male swiftlets choose tiny high-rise ledges, maybe 100 metres above the cavern floor.
They share the space with specialist spiders, cave centipedes and bats.
The bats have left a stinking mountain of droppings over 30 metres high.
It's the biggest indoor lavatory in the world.
This is a cave with double the population of Manhattan and no plumbing.
And it's crawling with cockroaches.
The cockroaches feed on the droppings, and anything else that falls to the floor.
The best ledges have to be fought for, and a male battles over real estate in the pitch blackness.
Swallows and martins normally use mud, but the swiftlets make their own walls.
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 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 bird's nest soup.
The saliva is full of proteins and minerals, but apparently the nests don't taste of anything.
The little homes are worth thousands of dollars a basketful.
The legal trade alone in bird's 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 .
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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 defence she needs.
A lethal trap has become a different sort of home - a cradle.
Baby hummingbirds 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 40 centimetres 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 neighbours 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.
They have an unlikely ally.
Casiques often nest near bees and 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.
It seems this is as much about their relationship, as building the nest.
They're like newlyweds cooing over paint swatches.
Colour is important, and texture, and the females seem to weigh up 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.
And 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 .
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and a perfect home for the eggs.
We don't know exactly what they think or feel, but some scientists believe the effort 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 round a mate can be found in the forests of New Guinea.
This metre-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 interior designers 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.
His architectural eye is unique.
His rival neighbours each have different colour 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, even the right way up.
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.
We see perhaps now why the bower is the shape it is.
It's a concert platform and the arch may help project his voice.
He ends with a little dance.
The audience has arrived.
She seems interested, but he has disappeared.
It is 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 decoration 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.
They collect 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.
In fact, this extraordinary bit of decoration is a trap for beetles, particularly dung beetles.
The beetles find dung by smell.
It is, to them, building material and food, rolled into one.
Tons of dung are trundled away.
The dung ball, with an egg inside, is buried.
A warm and delicious home, at least for a dung beetle larva.
Birds and mammals almost never turn their homes into traps, as spiders do.
Human beings and burrowing owls are said to be the only examples.
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.
Home making 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, 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 larder is a job that takes months.
The beavers wedge the branches down in the mud.
Even stored underwater, a potential burglar spots the stockpile.
But the moose is soon told that this store is private property.
A few tail-slaps and the intruder gets the message.
A house is of little use if there's no food.
Winter in Outer Mongolia would be hard for a hamster, without a well-stocked store room.
Down the burrow, there are several rooms.
In the bedroom, the young are kept warm in straw 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's 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 stage further.
They have a living larder.
A mole's network of dark passages can be extended at up to two metres an hour and provide 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 - and not everyone likes earthworms.
In China, bamboo is one of the fastest growing plants, but I have heard of it occasionally growing back into the ground.
Under the bamboo is a quarter of a mile of tunnelling, 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's 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 a stage further.
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 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.
There are subterranean highways connecting the main chambers, with side roads to fungus farms, huge rubbish pits and temperature-controlled nurseries.
This is one house for 12 million inhabitants.
That's more than London or New York.
On our scale, it is a mile deep, and five miles across.
The social insects are nature's finest architects.
These three-metre-high termite mounds all point north to south.
In the morning and evening they face the sun and are warmed, but at noon, they are sideways on and so don't overheat.
Our large buildings could follow this simple trick.
However, this is not the whole story.
Half the year this is a swamp and the sail-like shape and larger surface areas are perfect for keeping the colony dry, as well as warm.
Most termites avoid overheating by descending into lower levels during the hotter part of the day.
But these termites have found an architectural solution to 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.
It seems almost incredible that their mother would return to release them.
These lizards could not have chosen a better nursery - protected from predators and incubated at the perfect temperature.
The termites must repair the mound.
They use mud and mortar out of their back end.
The walls are essential to stay within half a degree centigrade of 30, whatever the weather outside.
Far from the tropics, 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 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 moulded.
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 almost a metre 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.
This nest is held within two degrees of 30.
The colony 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 ensured that a few larvae were 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.
For every home, there comes a time to move on.
There is one animal in the rainforest that builds the most extraordinary city of all.
Army ants kill almost everything 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 a rubbish tip.
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 neighbourhood 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 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 neighbourhood becomes a dust bowl.
They face starvation.
The young are a few months old and now the colony turns against them.
Neighbours 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.
THUNDER RUMBLES Salvation does come in the end for the few survivors 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 fertilising their gardens.
The neighbourhood returns to normal.
The beavers have started a new life a couple of miles downstream.
They have found ponds built generations ago, overgrown and abandoned.
They have repaired the dams and re-opened the canals.
The trees here have regenerated, thanks to the fertile silt clogging the old ponds.
We can begin to see why not every animal makes a home.
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.
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, like a roof.
We may have started with twisting branches into shelters, but there is another way to get out of the rain.
In Kenya, on Mount Suswa, baboons use caves at night.
Caves like these contain the earliest evidence of human habitation.
The monkeys' fingers and sense of balance take them along ledges impossible for leopards and hyenas to follow.
Many of our phobias may have originated here, with bats and snakes, and strange, ghostly noises in the dark.
We probably became serious builders only a few hundred thousand years ago, at the most.
It is extraordinary what we have achieved.
We don't often realise how fragile all this is.
Our cities have all the problems of animal cities - burglars and squatters, and getting the food in and the rubbish out.
To feed the city, we eat up the wilderness.
We forget that we kick animals out of their homes to do so.
Maybe we can be reminded by the refugees, by an urban generation of peregrines and pigeons, gulls and bats and foxes.
Animals will share our world, if we let them.
We can make space and help with protection, food and warmth.
We are homemakers, we understand.
We can build a world, surely, where animals can have a home, too.
I'm coming home, I'm coming home Tell the world I'm coming home Let the rain wash away All the pain of yesterday I know my kingdom awaits And they've forgiven my mistakes I'm coming home, I'm coming home Tell the world I'm coming.