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The stories of the world's best animal architects. There are house-proud bower birds who only find a mate if they decorate their homes perfectly, hornets who build electric ...
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AnimalsTranscript
00:00.
00:13Animals build homes out of sight, safe and warm.
00:19Some are skilled craftsmen with an eye for interior decoration.
00:25Others are squatters or burglars.
00:30There are extraordinary constructions keeping out the wilder wildlife.
00:36Look into an animal's home and reveal the very heart of their lives.
00:48Most of us are indoor creatures.
00:52Houses have ended our wild days.
00:57Yet we forget that animals build many more houses than we do.
01:03And they've been doing it for much longer.
01:07We think we alone invented building materials.
01:12But animals have done so as well.
01:17Scaled up to our size, termite mounds would be over a kilometer high.
01:25Animals have an eye for beauty.
01:28And so do we.
01:32Our homes reveal a lot about us.
01:36But this is the animal's story.
01:41In North America lives probably the most ambitious animal builder in the world.
01:53A kilometer or so of river is taken over by a single family of beavers.
02:00Dams flood the landscape creating ponds and canals that can cover several hectares.
02:08At the center is their lodge.
02:11A defensive moat surrounds a sturdy castle made of serious building materials.
02:24A beaver can gnaw through a tree in an hour or two.
02:29He often stops halfway and lets the wind do the rest.
02:34His teeth are reinforced with iron, which turns them orange.
02:44The teeth wear down a millimeter a day, but grow ten times faster than our fingernails.
02:53Even meter lengths are too heavy to drag over land,
02:56but by flooding the area the beavers can easily move the logs.
03:02Each dam needs about 50 tons and can be hundreds of meters long.
03:08Mud is used to seal any leaks.
03:12Everything has to be ready for winter.
03:28Of the beaver's rural community, most have left or are hidden housebound at this time of the year.
03:37The only sign is a ripple of heat from a chimney identifying the beaver's lodge.
03:46Inside, special cameras reveal new young, born early thanks to the protection of meter thick walls sealed with mud and
03:55straw.
03:56It's been minus 20 outside and still didn't freeze in here.
04:02The chimney is open as now it gets too hot.
04:09The only way in and out is to swim underwater.
04:13But that doesn't discourage a muskrat.
04:19Voles, mice and insects also find refuge here.
04:25The lodge has lodges.
04:30We never saw the landlords object to the muskrat,
04:33which is more than can be said for the cameras, which they soon censored.
04:47Outside, the itinerant and the homeless must wish they were somewhere safe and warm.
04:53F
04:54S
05:14Solid walls and underwater doors are not the only ways to try and keep the outside out.
05:24Prairie dogs live in an underground colony called a dog town, which can stretch over
05:32the horizon.
05:36The town is divided into coteries, extended families living behind a volcano-shaped front
05:42door with a quarter of a hectare of manicured lawn to provide food.
05:56Prairie dogs themselves may seem like fat vegetarian meerkats, but they're actually squirrels
06:04that bark and they don't like visitors.
06:12There's a father in charge, several wives, and different generations of youngsters.
06:20Each family rarely goes beyond their garden boundaries, and they all work together on
06:25their house.
06:26Time is spent on home improvements and household chores.
06:35The raised entrances are watchtowers, but are also chimneys and draw air through the burrows.
06:43The lower level holes are fresh air intakes.
06:49Inside each family home may be 30 metres of tunnelling with many different rooms.
06:57There are sleeping chambers where they spend most of the winter.
07:01Some even have an adjacent lavatory room.
07:04There are storage rooms, anti-flooding features, and escape hatches.
07:09It's warm in winter and cool in summer.
07:13It's an estate agent's dream.
07:21The pups, at a few days old, are tiny, bald, and blind.
07:26Their mother will stay with them in a special nursery, feeding them and sorting out bedding.
07:33Even at birth, prairie dogs are clearly builders with shovel-shaped heads, cylindrical bodies,
07:39and digger's claws.
07:47With so many corridors, it's possible that one might lead by mistake into a neighbour's house.
07:53And the neighbours could be burrowing owls.
07:58In the dark, the startled owls give a good impersonation of a rattlesnake.
08:21The owls have young, too, hatched in an abandoned part of the prairie dog burrow.
08:28They are, in effect, harmless squatters.
08:34The dog town is full of freeloaders.
08:39Hares and snakes find homes in this mixed neighbourhood.
08:44Dangerous characters like black-footed ferrets and swift foxes live in old burrows.
08:52Overall, wildlife increases wherever animals build homes, whether the builders like it or
08:58not.
09:07Maybe, as a response, prairie dogs have a community police service.
09:13Family members take turns watching out for predators.
09:25A prairie dog calls eagle.
09:30Families for up to a kilometre run for cover.
09:33The whole neighbourhood benefits.
09:41The prairie dogs even have different calls for different predators.
09:46Coyote sends them down their burrows.
09:49But calling badger needs a different response, as badgers can dig.
09:54So the dogs watch them nervously from the surface.
10:00Their calls may include information on size, direction and speed, even colour.
10:05It's one of the most sophisticated animal languages ever studied.
10:09And has arisen in response to the predators that are drawn to animal houses.
10:17Living close to your neighbour can provide some protection.
10:21But the problem is, it can also attract more predators.
10:31Southern carmine bee-eaters catch the eye of a hungry fish eagle.
10:48Predators have a major influence on how houses are built.
10:53Here, along the Luangua River in Africa, sandy cliffs are one of the few places
10:58out of reach of eagles, lizards and monkeys.
11:05A bee-eater pair takes turns digging the burrow with their beaks and feet.
11:20The centre of the colony is safer from predators than the edge.
11:24So the birds nest closely together in the middle.
11:28The result is evenly spaced lines of townhouses.
11:33But the denser the colony, the more attention it gets.
11:41The bee-eaters unite, screaming at the intruder.
11:48Noisy neighbours are a lifesaver.
12:00On every continent, animals converge to build homes together.
12:08A quarter of a million Socotra cormorants arrive on desert islands off Arabia
12:14to build simple mounds in the sand away from predators.
12:18Some debris is favoured for the nest, other bits rejected.
12:26The bird next door tries to steal from the collection.
12:44The chicks, when they hatch, must be protected from the neighbour's lethal beaks.
12:51So nests are built just out of pecking range.
12:59They end up building near-perfect geometric plots in their thousands.
13:18But the greatest animal houses in the world are caves.
13:29The day shift is returning.
13:33Cave swiftlets navigate into dark caverns by echolocation,
13:37like a bat, almost the only birds to do so.
13:41They make powerful clicks and listen to the sound bouncing off the walls.
13:59Male swiftlets choose tiny high-rise ledges, maybe a hundred metres above the cavern floor.
14:06They share the space with specialist spiders and unique cave centipedes.
14:13The best ledges have to be fought for,
14:16and a male battles over real estate in the pitch blackness.
14:23Swallows and martins normally use mud, but the swiftlets make their own walls.
14:29It's a sort of gluey saliva which they attach to the rock and build up layer by layer,
14:34making a tiny egg cup.
14:36It can be weeks of painstaking work.
14:51The saliva hardens into surely one of the most extraordinary animal houses in the world,
14:56a crystal chalice.
15:08The nests become as crowded as closely packed apartments.
15:13Woven in feathers darken the nests,
15:16but single white eggs glow in the lights.
15:25For generations, this cave has been one of the safest homes.
15:30That is, until a new predator found it.
15:39Men are here to collect a culinary delicacy for the famous bird's nest soup.
15:49The saliva is full of proteins and minerals,
15:52but apparently the nests don't taste of anything.
15:58The little homes are worth thousands of dollars a kilo.
16:02The legal trade alone in bird's nest soup is worth about half a billion dollars.
16:10Inevitably, wild cave swiftlets are in decline.
16:21Saliva is an extraordinary building material,
16:24but perhaps the most remarkable of all is silk.
16:37The coiled threads of protein are famously strong and light,
16:43which is why other animals steal them.
16:49A bronzy hermit hummingbird in Central America collects cobwebs.
16:58With the silk threads, she weaves a pocket anchored under a leaf.
17:03The leaf keeps out the rein and prying eyes.
17:07Camouflage is all the defense she needs.
17:20A lethal trap has become a different sort of home.
17:24A cradle.
17:27Baby hummingbirds grow up suspended in silk and fed on nectar.
17:42The second-hand web can carry the young and the parent birds,
17:47though it was originally made only to catch a fly.
17:55Even ordinary building materials can be transformed by the skill of the builder.
18:02A female red-rumped cacique in South America ties palm-leaf strands into loops and knots.
18:23The mother fassiks choose the nest site, build and bicker over space.
18:34The architectural blueprint is instinctive,
18:37but she adapts and refines the basic plan and her skill improves with practice.
18:44The foundations are made first, then a loop, the entrance to the nest.
18:51The door is extended into a tube, like a sock about 40 cm long.
18:58After up to three weeks' work, a nest is finished at the bottom.
19:05You can't leave your handiwork for long,
19:08or your older and cannier neighbours try and pull it apart and steal your building material.
19:26The final nest is this shape because there are egg thieves.
19:34This is a toko toucan.
19:36The nest tube must be long enough so that predators can't see the chicks or reach the bottom.
19:42Over the generations, caciques have extended their nests to keep the young safe.
19:53The toucan is trying an attack through the side of the nest.
20:00They have an unlikely ally.
20:04Caciques often nest near bees and wasps.
20:16The chicks are safe, though the nest seems to have acquired a new window.
20:24It looks like the parent may have to get materials for repair work.
20:34Building supplies are so important to some animals that in places the materials themselves have taken on a particular significance.
20:45Flightless cormorants build their nests from seaweed.
20:48On the shores of the Galapagos Islands, there isn't much else.
21:01It seems this is as much about their relationship as building the nest.
21:07They're like newlyweds, cooing over paint swatches.
21:16Colour is important and texture, and the females seem to weigh up each gift.
21:24Occasional exotic offerings a living sea urchin or a new shade of seaweed are brought to the nest and sometimes
21:33rejected.
21:34A gift that walks away is of no use.
21:41And size certainly doesn't impress her.
21:50The drying seaweed means more to the cormorants than mere construction materials.
21:58A nest becomes a special place.
22:01To be defended from curious visitors.
22:07And a perfect home for the eggs.
22:11We don't know exactly what they think or feel, but some scientists believe the effort seems to draw them closer
22:18together.
22:32The chick benefits from the parents' commitment to making the perfect home.
22:41The ultimate example of an animal that builds a palace to win round a mate can be found in the
22:47forests of New Guinea.
23:01This metre-wide woven wigwam is a seduction pad and is all about show.
23:10Carefully arranged flowers and fruits are placed in piles on manicured moss.
23:16Smaller treasures are towards the back to make the bower seem bigger.
23:20A trick human interior designers also use.
23:32Yet the male Vogelkopf bowerbird himself is modest, even drab.
23:41It may take many years to become a proficient enough house builder to reach this stage.
23:48If he sees a twig out of place, he'll push it in or remove it.
24:00His architectural eye is unique.
24:03His rival neighbours each have different colour schemes or floor designs or decorations.
24:09This particular male is going through a red phase.
24:22The flowers are changed regularly and the berries must be perfectly arranged, even the right way up.
24:31The floor is a challenge. Roots grow through the moss and have to be tackled.
24:37What he can't remove, he sweeps under the carpet.
24:59A rival male is singing.
25:04He must respond.
25:07We see perhaps now why the bower is the shape it is.
25:11It's a concert platform and the arch may help project his voice.
25:21He ends with a little dance.
25:25The audience has arrived.
25:28She seems interested, but he has disappeared.
25:32It's crucial in bowerbird courtship that he remains hidden.
25:37His house has to coax her in.
25:49Only when she's brought to a state of ecstasy over his decor does he dash out and try to mate.
26:01It's not entirely successful.
26:04Maybe she wasn't ready for his appearance.
26:07Or maybe his flowers or his floor weren't up to scratch.
26:12It's most frustrating.
26:24Perhaps he will tempt her back and maybe next time the bower will be looking at its best.
26:35Home decoration can occasionally be about more than impressing the perfect partner.
26:44The burrowing owls in Prairie Dog Town have a strange take on suitable suburban decor.
26:52Their landlords, the Prairie Dogs, would not approve of this innovation.
26:57What burrowing owls like is what the buffalo leave behind.
27:04They collect dung.
27:10The owl places the dung carefully around his front door.
27:17The burrowing owl chicks don't seem impressed by the collection of poop on the stoop.
27:25This is not how most wise animals treat their own doorsteps.
27:43In fact, this extraordinary bit of decoration is a trap for beetles, particularly dung beetles.
27:52The beetles find dung by smell.
27:56It is, to them, building material and food rolled into one.
28:06Tons of dung are trundled away.
28:10The dung ball, with an egg inside, is buried.
28:14A warm and delicious home, at least for a dung beetle larva.
28:21Birds and mammals almost never turn their homes into traps, as spiders do.
28:26Human beings and burrowing owls are said to be the only examples.
28:34A chick takes some dung down the burrow.
28:41Maybe it's learning the connection with food.
28:44It's a step in the right direction.
28:48The owl mother doesn't agree and turns it into a lesson on housework.
29:05Home's a hard work, and there's a lot for young animals to learn.
29:10Homemaking requires a sense of place, as well as working out how to get along in a community.
29:18The trap seems to have worked.
29:38Food is always critical, so many animal builders put a larder at the heart of their homes.
29:47The beaver's system of canals and ponds is a massive coal store.
29:57Beavers eat bark and leaves, and stocking the larder is a job that takes months.
30:05The beavers wedge the branches down in the mud.
30:12Even stored underwater, a potential burglar spots the stockpile.
30:24But the moose is soon told that this store is private property.
30:33A few tail slaps, and the intruder gets the message.
30:49A house is of little use if there's no food.
30:54Winter in outer Mongolia would be hard for a hamster without a well-stocked storeroom.
31:04Down the burrow, there are several rooms.
31:08In the bedroom, the young are kept warm in straw and fed by their mother.
31:19Next door is the larder.
31:22All autumn, they gathered seeds in their cheek pouches and brought them down here.
31:28Thanks to the seeds staying safe and dry, the hamsters can start a family while it's still barren outside.
31:37Our own earliest buildings may have been grain stores.
31:41Protecting food for winter enables house builders to move into colder areas where the homeless could never survive.
31:54Some homes go a stage further.
31:57They have a living larder.
32:05A mole's network of dark passages can be extended at up to two metres an hour and provide the mole's
32:13food.
32:21Earthworms burrow through the walls by accident, and the star-nosed mole has special worm-detecting feelers on its nose.
32:33This housebound animal has a curious reputation as the fastest eater on record.
32:39An earthworm can disappear in a quarter of a second.
32:46Not everyone can build a house where your food literally drops in for dinner, and not everyone likes earthworms.
32:57In China, bamboo is one of the fastest-growing plants.
33:02But I have heard of it occasionally growing back into the ground.
33:23Under the bamboo is half a kilometer of tunneling.
33:30Built over several years by bamboo rats.
33:46The tunnels follow the roots, which run along the ceiling like service pipes.
33:52She checks the bamboo by smell.
33:55If the roots put out a new shoot, she can sense the fresh growth, and when it's the right length,
34:01she harvests it.
34:04The house has become a farm.
34:15She has the same iron-coated teeth as the beavers.
34:20Both are rodents, which are the vast majority of mammal house builders.
34:27Her young have never been out.
34:29She's blocked the exits.
34:32The outside world might as well not exist.
34:41The little ones seem determined to explore, but may get lost in the network of tunnels.
34:46So she literally drags them around the labyrinth of her underground bamboo farm.
35:03American beavers build canals to carry trees, and Chinese bamboo rats harvest bamboo underground.
35:11But in South America, another animal takes the idea of a home farm a stage further.
35:20The entire state of the building has been discovered.
35:24The bloody hills meet more than a city who is a father.
35:27The mountainous fish are beautiful.
35:31The southern square is a buraya.
35:32The island is a永遠 to the hemisphere.
35:32From the winter of the river it's a river.
35:32It's a two-day.
35:39The river in the water, and is a river.
35:40The river is a river.
35:42The river in the north of the river.
35:46Leaf and grass-cutter ants take about 10% of the forest's growth underground
35:52to fungus farms.
35:56The white fungus grows on the chopped up leaves
35:59and is pretty much all that the ants eat.
36:03The fungus farm generates heat and carbon dioxide.
36:07Pipes lead to a large mound above the ground.
36:11The chimneys are like the raised prairie dog burrows,
36:14drawing the air through the nest.
36:18Nobody knew how big grass-cutter ant cities were,
36:23so scientists poured a liquid cement into an old nest.
36:30Once the concrete was set,
36:32they dug away the earth to reveal an extraordinary secret city.
36:43These are subterranean highways connecting the main chambers
36:47with side roads to fungus farms, huge rubbish pits, and temperature-controlled nurseries.
37:01This is one house for 12 million inhabitants.
37:06That's more than London or New York.
37:11On our scale, it's over a kilometer deep and eight kilometers across.
37:24The social insects are nature's finest architects.
37:33These three-meter-high termite bounds all point north to south.
37:43In the morning and evening, they face the sun and are warmed.
37:47But at noon, they're sideways on and so don't overheat.
37:53Our large buildings could follow this simple trick.
37:58However, this is not the whole story.
38:02Half the year, this is a swamp,
38:04and the sail-like shape and larger surface areas
38:07are perfect for keeping the colony dry as well as warm.
38:17Most termites avoid overheating
38:20by descending into lower levels during the hotter part of the day.
38:24But these termites have found an architectural solution to the problem.
38:38Finding an egg a thousand times your size in your house
38:42must be puzzling, terrifying when it starts to hatch.
38:51The gigantic aliens are lace-monitor lizards.
38:59Their exit is closed.
39:01The termites repaired the hole in the wall
39:04the monitor mother made to lay her eggs.
39:07They're trapped.
39:08They're trapped.
39:30It seems almost incredible that their mother would return to release them.
39:40These lizards could not have chosen a better nursery,
39:43protected from predators and incubated at the perfect temperature.
39:56The termites must repair the mound.
39:59They use mud and mortar out of their back end.
40:06The walls are essential to stay within half a degree centigrade of 30,
40:11whatever the weather outside.
40:16Far from the tropics, insects have resorted to central heating.
40:21In a hollow tree, a Japanese giant hornet starts to build a city
40:26with cavity walls and electric radiators.
40:31The queen first makes a few compartments.
40:35An egg in each hatches into a lava.
40:38It spins a silk cocoon for itself that has extraordinary properties.
40:43The silk is like a thermostatic electric blanket.
40:47It stores heat as electrical charge,
40:51which automatically turns back into heat if the nest cools.
40:58Her daughters pupate and emerge.
41:01They are the first battalion of builders.
41:04They add additional floors suspended in the middle.
41:09Supporting columns are moulded.
41:12They build with chewed-up wood pulp,
41:15the same material as paper.
41:21As more of the queen's larvae hatch,
41:24they start demanding food,
41:26banging and scraping their heads on the walls.
41:34The workers collect insects
41:36and mash them into a paste for the larvae.
41:46The outside walls are extended downwards with up to eight layers of cavity insulation
41:52and built-in flues and ducts.
41:54Like the termites, a few simple instructions may come together
41:58to build a surprisingly complex design.
42:02Scientists call this an emergent property.
42:06And what emerges after four months is a hornet's nest almost a metre tall.
42:22If it's cold, the nest is heated by the larvae and their silk blankets.
42:28But on hot days, cooling air is fanned in.
42:33This nest is held within two degrees of thirty.
42:37The colony behaves as much like a warm-blooded animal as a house.
42:47Towards autumn, the queen turns to producing new queens for next year.
42:54She and all her workers will soon die here, exhausted and now expendable.
43:00The city will crumble too and can never be reused.
43:05In the final days of her life, the queen ensured that a few larvae were fed
43:10and fresh queen hornets emerge.
43:15Each faces a winter of hibernation
43:18and in spring starts building a brand new edifice forty thousand times her size.
43:26For every home, there's a time to move on.
43:44There is one animal in the rainforests that builds the most extraordinary city of all.
43:52Army ants kill almost everything they can and carry it all back to their home.
43:59Their house is a living building entirely made of ants called a bivouac.
44:07The legs carry the weight of the whole nest.
44:19Big cities have big problems.
44:22The ants generate so much waste that they need a rubbish tip.
44:27The carcasses of dead insects and old cocoons are taken out of the city to the dump.
44:34Soon the colony sits in a sea of municipal waste and all the surrounding food has gone.
44:43So they unhook themselves at night and set off.
44:49Pupi and larvae are carried and the queen is protected behind a cavalcade of soldiers.
45:05A new site is chosen and living ropes become columns.
45:10They seem to build around a frame, but since every site is different,
45:14the design is never identical.
45:20The frame is filled in with walls to create corridors and rooms all made of ants.
45:27Their new neighborhood will be stripped of prey in a few days.
45:33If the ants couldn't move their city, they'd quickly eat themselves into extinction.
45:43All houses face the same dilemma.
45:47The beavers have felled hundreds of tons of wood.
45:51After four or five years, there's nothing left but bushes.
45:55The ponds have silted up and without logs for repair, things start to fall apart.
46:10The beavers make do for a while on shrubs like willow herbs,
46:14but even these they eat faster than can grow back.
46:21As their lake shrinks, they will abandon their home.
46:28Almost all homes become unsustainable eventually.
46:34The rivers are littered with empty lodges and broken dams.
46:41Every construction is an attempt to tame nature,
46:45and nature will always win in the end.
46:50Things are even tougher for prairie dogs.
46:54In summer, the land dries.
46:57The cattle and buffalo can move, but the dog towns can't,
47:01and the families have nowhere else to go.
47:06The owl family can all fly now.
47:09They can come and go.
47:12The prairie dogs eat the remaining grass until their neighborhood becomes a dust bowl.
47:23They face starvation.
47:29The young are a few months old, and now the colony turns against them.
47:34Neighbors start to hunt down cubs.
47:37Even cousins and aunts turn nasty.
47:41In a dry year, up to half of the young are killed.
47:58Stuck underground, out of sight, their home becomes a prison.
48:03A tomb.
48:10You can't rely on one place for long.
48:14The restless and the hungry follow the seasons in great migrations.
48:34The world is constantly changing,
48:39and even the wisest animals struggle to keep up.
48:56These are the homeless of the Earth.
49:00And until recently, we were among them.
49:07So how did we become the greatest homemaker of all?
49:13Our closest animal relatives are still homeless,
49:17unable even to keep out of the rain.
49:21Apes and monkeys don't make shelters,
49:24though a gorilla's hands and brain are easily up to the job.
49:30The priority for these mountain gorillas is to find fresh food,
49:35so they keep moving.
49:37A house would only tie them down.
49:43The signs of a nobility, however, are here.
49:47An improvised roof is better than none while it lasts.
49:56Our ape cousins build beds or even platforms woven from branches,
50:00but they never sit under them like a roof.
50:04Our ancient ancestors were not homemakers.
50:07We may have little instinct for how to avoid the problems that houses bring.
50:16Salvation does come in the end for the few remaining hostages inside their houses.
50:33In autumn, the rains replenish the land,
50:37and in spring, the grass grows back.
50:48The prairie dogs have done no permanent damage.
50:52They help the grassland over the years by mowing and fertilizing their gardens.
51:01The neighborhood returns to normal.
51:14The beavers have started a new life several kilometers downstream.
51:20They've found ponds built generations ago, overgrown and abandoned.
51:26The trees here have regenerated.
51:31The beavers have repaired the dams and reopened the canals.
51:37Animals like beavers and prairie dogs and army ants
51:41have learned hard lessons about how to build a home life that will last,
51:45that is sustainable.
51:48It's a lesson for us, of course, too, from animal homemakers.
52:26meaning and plenty of colors isGood to use
52:30so that it is easy to compare with an ancient site and the
52:30lights on the edge.
52:31The were mainly sunny days before the Ice C하게
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