0:00:14 > 0:00:17I'm fascinated by the glimpses we sometimes get
0:00:17 > 0:00:19into an animal's hidden world.
0:00:22 > 0:00:27Over the years, I've found different ways to peer inside.
0:00:49 > 0:00:54They say, if you want to understand people, look in their houses.
0:00:58 > 0:01:01I think the same may be true for wildlife.
0:01:05 > 0:01:07I've never been invited in
0:01:07 > 0:01:11and, on occasions, I've not been entirely welcome.
0:01:15 > 0:01:18I think that was pretty clear. Oh, dear!
0:01:22 > 0:01:26Despite setbacks, I've seen skilled builders...
0:01:28 > 0:01:30I've discovered squatters and burglars...
0:01:32 > 0:01:34I've noticed interior decoration...
0:01:35 > 0:01:39I've found storerooms and air conditioning
0:01:39 > 0:01:42and even en-suite bathrooms...
0:01:42 > 0:01:45I've visited animal cities
0:01:45 > 0:01:47and huge communities.
0:01:49 > 0:01:53Wild homemakers are special creatures,
0:01:53 > 0:01:58more like us, trying to keep out the wilder wildlife.
0:02:04 > 0:02:09Peering into an animal's house can tell you so much about them.
0:02:11 > 0:02:14It's a window into their private dramas
0:02:14 > 0:02:16and the intimate stories we rarely see.
0:02:27 > 0:02:32Most of us are indoor creatures.
0:02:32 > 0:02:34Houses have ended our wild days.
0:02:36 > 0:02:41Yet, we forget that animals build many more houses than we do.
0:02:42 > 0:02:46And they've been doing it for much longer.
0:02:46 > 0:02:52We think we alone invented building materials,
0:02:52 > 0:02:54but animals have done so, as well.
0:02:55 > 0:03:00Scaled up to our size, termite mounds would be almost a mile high.
0:03:04 > 0:03:06Animals have an eye for beauty
0:03:06 > 0:03:08and so do we.
0:03:11 > 0:03:15Our homes reveal a lot about us,
0:03:15 > 0:03:18but this is the animals' story.
0:03:20 > 0:03:24In North America lives probably the most ambitious
0:03:24 > 0:03:26animal builder in the world.
0:03:32 > 0:03:37Up to a mile or so of river is taken over by a single family of beavers.
0:03:37 > 0:03:42Dams flood the landscape, creating ponds
0:03:42 > 0:03:44and canals that cover many acres.
0:03:47 > 0:03:50At the centre is their lodge -
0:03:50 > 0:03:53a defensive moat surrounds a sturdy castle,
0:03:53 > 0:03:56made of serious building materials.
0:04:03 > 0:04:08A beaver can gnaw through a tree in an hour or two.
0:04:08 > 0:04:12He often stops halfway and lets the wind do the rest.
0:04:12 > 0:04:18His teeth are reinforced with iron, which turns them orange.
0:04:23 > 0:04:26The teeth wear down a millimetre a day,
0:04:26 > 0:04:30but grow ten times faster than our fingernails.
0:04:32 > 0:04:35Even metre lengths are too heavy to drag over land,
0:04:35 > 0:04:39but by flooding the area, the beavers can easily move the logs.
0:04:41 > 0:04:45Each dam needs about 50 tons and can be hundreds of metres long.
0:04:47 > 0:04:49Mud is used to seal any leaks.
0:04:51 > 0:04:54Everything has to be ready for winter.
0:05:08 > 0:05:12Of the beaver's rural community, most have left or are hidden,
0:05:12 > 0:05:15housebound, at this time of year.
0:05:16 > 0:05:19The only sign is a ripple of heat from a chimney,
0:05:19 > 0:05:21identifying the beavers' lodge.
0:05:25 > 0:05:28Inside, special cameras reveal new young,
0:05:28 > 0:05:33born early, thanks to the protection of metre-thick walls,
0:05:33 > 0:05:35sealed with mud and straw.
0:05:35 > 0:05:40It's been minus 20 outside and still didn't freeze in here.
0:05:40 > 0:05:45The chimney is open, as now it gets too hot.
0:05:48 > 0:05:50The only way in and out
0:05:50 > 0:05:55is to swim underwater, but that doesn't discourage a muskrat.
0:05:58 > 0:06:02Voles, mice and insects also find refuge here.
0:06:04 > 0:06:05The lodge has lodgers.
0:06:08 > 0:06:12We never saw the landlords object to the muskrat,
0:06:12 > 0:06:15which is more than can be said for the cameras,
0:06:15 > 0:06:17which they soon censored!
0:06:25 > 0:06:29Outside, the itinerant and the homeless
0:06:29 > 0:06:32must wish they were somewhere safe and warm.
0:06:32 > 0:06:37WOLF HOWLS
0:06:53 > 0:06:56Solid walls and underwater doors
0:06:56 > 0:07:00are not the only ways to try and keep the outside out.
0:07:04 > 0:07:09Prairie dogs live in an underground colony called a dog town,
0:07:09 > 0:07:13which can stretch over the horizon.
0:07:15 > 0:07:19The town is divided into coteries, extended families,
0:07:19 > 0:07:22living behind a volcano-shaped front door,
0:07:22 > 0:07:25and with an acre or so of manicured lawn to provide food.
0:07:35 > 0:07:40Prairie dogs themselves may seem like fat vegetarian meerkats,
0:07:40 > 0:07:43but they're actually squirrels...
0:07:43 > 0:07:46that bark.
0:07:46 > 0:07:48And they don't like visitors.
0:07:51 > 0:07:52There's a father in charge,
0:07:52 > 0:07:57several wives, and different generations of youngsters.
0:07:57 > 0:08:02Each family rarely goes beyond their garden boundaries,
0:08:02 > 0:08:06and they all work together on their house.
0:08:06 > 0:08:11Time is spent on home improvements and household chores.
0:08:14 > 0:08:17The raised entrances are watchtowers,
0:08:17 > 0:08:21but are also chimneys, and draw air through the burrows.
0:08:22 > 0:08:25The lower-level holes are fresh air intakes.
0:08:28 > 0:08:32Inside each family home may be 30 metres of tunnelling
0:08:32 > 0:08:34with many different rooms.
0:08:37 > 0:08:40There are sleeping chambers, where they spend most of the winter.
0:08:40 > 0:08:43Some even have an adjacent lavatory room.
0:08:43 > 0:08:46There are storage rooms, anti-flooding features,
0:08:46 > 0:08:48and escape hatches.
0:08:48 > 0:08:51It's warm in winter and cool in summer.
0:08:51 > 0:08:54It's an estate agent's dream.
0:08:59 > 0:09:05The pups, at a few days old, are tiny, bald and blind.
0:09:05 > 0:09:08Their mother will stay with them in a special nursery,
0:09:08 > 0:09:11feeding them and sorting out bedding.
0:09:11 > 0:09:15Even at birth, prairie dogs are clearly builders,
0:09:15 > 0:09:18with shovel-shaped heads, cylindrical bodies,
0:09:18 > 0:09:20and digger's claws.
0:09:25 > 0:09:27With so many corridors,
0:09:27 > 0:09:31it's possible that one might lead by mistake into a neighbour's house,
0:09:31 > 0:09:35and the neighbours could be burrowing owls.
0:09:36 > 0:09:38In the dark,
0:09:38 > 0:09:43the startled owls give a good impersonation of a rattlesnake.
0:09:44 > 0:09:48OWL HISSES MENACINGLY
0:10:00 > 0:10:02The owls have young, too,
0:10:02 > 0:10:06hatched in an abandoned part of the prairie dog burrow.
0:10:06 > 0:10:09They are, in effect, harmless squatters.
0:10:12 > 0:10:16The dog town is full of freeloaders.
0:10:16 > 0:10:21Hares and snakes find homes in this mixed neighbourhood.
0:10:23 > 0:10:26Dangerous characters, like black-footed ferrets
0:10:26 > 0:10:28and swift foxes, live in old burrows.
0:10:30 > 0:10:35Overall, wildlife increases wherever animals build homes,
0:10:35 > 0:10:38whether the builders like it or not.
0:10:46 > 0:10:48Maybe as a response,
0:10:48 > 0:10:52prairie dogs have a community police service.
0:10:52 > 0:10:56Family members takes turns watching out for predators.
0:11:04 > 0:11:07A prairie dog calls "Eagle!".
0:11:07 > 0:11:11Families for up to half a mile around run for cover.
0:11:11 > 0:11:14The whole neighbourhood benefits.
0:11:19 > 0:11:24The prairie dogs even have different calls for different predators.
0:11:24 > 0:11:28"Coyote" sends them down their burrows,
0:11:28 > 0:11:31but calling "Badger" needs a different response,
0:11:31 > 0:11:34as badgers can dig,
0:11:34 > 0:11:38so the dogs watch them nervously from the surface.
0:11:38 > 0:11:41Their calls may include information on size,
0:11:41 > 0:11:45direction and speed, even colour.
0:11:45 > 0:11:48It's one of the most sophisticated animal languages ever studied
0:11:48 > 0:11:51and has arisen in response to the predators
0:11:51 > 0:11:53that are drawn to animal houses.
0:11:57 > 0:12:01Living close to your neighbour can provide some protection.
0:12:01 > 0:12:05The problem is, it can also attract more predators.
0:12:10 > 0:12:15Southern carmine bee-eaters catch the eye of a hungry fish eagle.
0:12:27 > 0:12:32Predators have a major influence on how houses are built.
0:12:32 > 0:12:35Here, along the Luangwa River in Africa,
0:12:35 > 0:12:38sandy cliffs are one of the few places out of reach
0:12:38 > 0:12:40of eagles, lizards, and monkeys.
0:12:45 > 0:12:48A bee-eater pair takes turns digging the burrow
0:12:48 > 0:12:50with their beaks and feet.
0:12:58 > 0:13:03The centre of the colony is safer from predators than the edge,
0:13:03 > 0:13:07so the birds nest closely together in the middle.
0:13:07 > 0:13:10The result is evenly-spaced lines of townhouses.
0:13:13 > 0:13:15But, the denser the colony,
0:13:15 > 0:13:17the more attention it gets.
0:13:20 > 0:13:24The bee-eaters unite, screaming at the intruder.
0:13:28 > 0:13:30Noisy neighbours are a life-saver.
0:13:39 > 0:13:43On every continent, animals converge to build homes together.
0:13:48 > 0:13:50A quarter of a million Socotra cormorants
0:13:50 > 0:13:53arrive on desert islands off Arabia
0:13:53 > 0:13:58to build simple mounds in the sand away from predators.
0:13:58 > 0:14:01Some debris is favoured for the nest, other bits rejected.
0:14:05 > 0:14:08The bird next door tries to steal from the collection.
0:14:24 > 0:14:25The chicks, when they hatch,
0:14:25 > 0:14:29must be protected from the neighbours' lethal beaks,
0:14:29 > 0:14:33so nests are built just out of pecking range.
0:14:38 > 0:14:41They end up building near inch-perfect
0:14:41 > 0:14:44geometric plots in their thousands.
0:14:56 > 0:15:02But the greatest animal houses in the world are caves.
0:15:07 > 0:15:113.5 million bats live in this cave in Borneo.
0:15:16 > 0:15:19Each evening, they leave the safety of their home
0:15:19 > 0:15:22to feed on insects in the surrounding forest.
0:15:27 > 0:15:31They gather outside the city gate in a defensive whirlwind.
0:15:35 > 0:15:39The swirling commuters are running a gauntlet
0:15:39 > 0:15:42of bat hawks and peregrine falcons.
0:15:42 > 0:15:45The birds of prey grab anything that tries to go it alone.
0:15:55 > 0:15:58As the nightshift leaves home,
0:15:58 > 0:16:00the dayshift is returning.
0:16:02 > 0:16:06Cave swiftlets navigate into dark caverns by echolocation,
0:16:06 > 0:16:09like a bat, almost the only birds to do so.
0:16:11 > 0:16:13They make powerful clicks,
0:16:13 > 0:16:16and listen to the sound bouncing off the walls.
0:16:28 > 0:16:32Male swiftlets choose tiny high-rise ledges,
0:16:32 > 0:16:36maybe 100 metres above the cavern floor.
0:16:36 > 0:16:38They share the space
0:16:38 > 0:16:40with specialist spiders,
0:16:40 > 0:16:41cave centipedes
0:16:41 > 0:16:43and bats.
0:16:44 > 0:16:47The bats have left a stinking mountain of droppings
0:16:47 > 0:16:48over 30 metres high.
0:16:50 > 0:16:53It's the biggest indoor lavatory in the world.
0:16:55 > 0:16:59This is a cave with double the population of Manhattan
0:16:59 > 0:17:01and no plumbing.
0:17:03 > 0:17:05And it's crawling with cockroaches.
0:17:07 > 0:17:09The cockroaches feed on the droppings,
0:17:09 > 0:17:12and anything else that falls to the floor.
0:17:18 > 0:17:22The best ledges have to be fought for,
0:17:22 > 0:17:27and a male battles over real estate in the pitch blackness.
0:17:29 > 0:17:32Swallows and martins normally use mud,
0:17:32 > 0:17:35but the swiftlets make their own walls.
0:17:35 > 0:17:38It's a sort of gluey saliva, which they attach to the rock,
0:17:38 > 0:17:42and build up, layer by layer, making a tiny egg-cup.
0:17:42 > 0:17:45It can be weeks of painstaking work.
0:17:57 > 0:17:58The saliva hardens
0:17:58 > 0:18:03into one of the most extraordinary animal houses in the world,
0:18:03 > 0:18:05a crystal chalice.
0:18:15 > 0:18:19The nests become as crowded as closely-packed apartments.
0:18:19 > 0:18:22Woven-in feathers darken the nests,
0:18:22 > 0:18:25but single white eggs glow in the lights.
0:18:31 > 0:18:36For generations, this cave has been one of the safest homes.
0:18:37 > 0:18:40That is, until a new predator found it.
0:18:46 > 0:18:48Men are here
0:18:48 > 0:18:52to collect a culinary delicacy for the famous bird's nest soup.
0:18:55 > 0:18:58The saliva is full of proteins and minerals,
0:18:58 > 0:19:02but apparently the nests don't taste of anything.
0:19:04 > 0:19:08The little homes are worth thousands of dollars a basketful.
0:19:08 > 0:19:13The legal trade alone in bird's nest soup
0:19:13 > 0:19:15is worth about half a billion dollars.
0:19:16 > 0:19:20Inevitably, wild cave swiftlets are in decline.
0:19:27 > 0:19:30Saliva is an extraordinary building material,
0:19:30 > 0:19:34but perhaps the most remarkable of all is silk.
0:19:44 > 0:19:48The coiled threads of protein are famously strong and light...
0:19:50 > 0:19:53..which is why other animals steal them.
0:19:55 > 0:20:01A bronzy hermit hummingbird in Central America collects cobwebs.
0:20:05 > 0:20:10With the silk threads, she weaves a pocket, anchored under a leaf.
0:20:10 > 0:20:13The leaf keeps out the rain, and prying eyes.
0:20:13 > 0:20:16Camouflage is all the defence she needs.
0:20:27 > 0:20:30A lethal trap has become a different sort of home -
0:20:30 > 0:20:32a cradle.
0:20:33 > 0:20:37Baby hummingbirds grow up suspended in silk
0:20:37 > 0:20:39and fed on nectar.
0:20:49 > 0:20:53The second-hand web can carry the young and the parent birds,
0:20:53 > 0:20:56though it was originally made only to catch a fly.
0:21:01 > 0:21:05Even ordinary building materials can be transformed
0:21:05 > 0:21:07by the skill of the builder.
0:21:10 > 0:21:13A female red-rumped cacique in South America
0:21:13 > 0:21:16ties palm leaf strands into loops and knots.
0:21:29 > 0:21:33The mother caciques choose the nest site,
0:21:33 > 0:21:36build and bicker over space.
0:21:41 > 0:21:44The architectural blueprint is instinctive,
0:21:44 > 0:21:47but she adapts and refines the basic plan,
0:21:47 > 0:21:50and her skill improves with practice.
0:21:50 > 0:21:53The foundations are made first,
0:21:53 > 0:21:57then a loop, the entrance to the nest.
0:21:58 > 0:22:01The door is extended into a tube,
0:22:01 > 0:22:04like a sock about 40 centimetres long.
0:22:04 > 0:22:08After up to three weeks' work, a nest is finished at the bottom.
0:22:12 > 0:22:15You can't leave your handiwork for long,
0:22:15 > 0:22:18or your older and cannier neighbours try and pull it apart
0:22:18 > 0:22:21and steal your building material.
0:22:34 > 0:22:38The final nest is this shape because there are egg thieves.
0:22:40 > 0:22:43This is a Toco toucan.
0:22:43 > 0:22:46The nest tube must be long enough
0:22:46 > 0:22:49so that predators can't see the chicks or reach the bottom.
0:22:49 > 0:22:53Over the generations, caciques have extended their nests
0:22:53 > 0:22:55to keep the young safe.
0:23:00 > 0:23:03The toucan is trying an attack through the side of a nest.
0:23:08 > 0:23:10They have an unlikely ally.
0:23:10 > 0:23:14Casiques often nest near bees and wasps.
0:23:23 > 0:23:25The chicks are safe,
0:23:25 > 0:23:28though the nest seems to have acquired a new window.
0:23:31 > 0:23:35It looks like the parent may have to get materials for repair work.
0:23:40 > 0:23:43Building supplies are so important
0:23:43 > 0:23:46to some animals that, in places, the materials themselves
0:23:46 > 0:23:49have taken on a particular significance.
0:23:51 > 0:23:54Flightless cormorants build their nests from seaweed.
0:23:54 > 0:23:58On the shores of the Galapagos Islands, there isn't much else.
0:24:07 > 0:24:11It seems this is as much about their relationship,
0:24:11 > 0:24:13as building the nest.
0:24:13 > 0:24:18They're like newlyweds cooing over paint swatches.
0:24:23 > 0:24:25Colour is important, and texture,
0:24:25 > 0:24:28and the females seem to weigh up each gift.
0:24:31 > 0:24:35Occasional exotic offerings - a living sea urchin,
0:24:35 > 0:24:37or a new shade of seaweed -
0:24:37 > 0:24:41are brought to the nest, and sometimes rejected.
0:24:41 > 0:24:44A gift that walks away is of no use.
0:24:48 > 0:24:50And size certainly doesn't impress her.
0:24:57 > 0:25:00The drying seaweed means more to the cormorants
0:25:00 > 0:25:02than mere construction materials.
0:25:05 > 0:25:08A nest becomes a special place,
0:25:08 > 0:25:11to be defended from curious visitors...
0:25:14 > 0:25:17..and a perfect home for the eggs.
0:25:17 > 0:25:22We don't know exactly what they think or feel,
0:25:22 > 0:25:24but some scientists believe the effort
0:25:24 > 0:25:26seems to draw them closer together.
0:25:38 > 0:25:42The chick benefits from the parents' commitment
0:25:42 > 0:25:44to making the perfect home.
0:25:48 > 0:25:52The ultimate example of an animal that builds a palace
0:25:52 > 0:25:55to win round a mate can be found in the forests of New Guinea.
0:26:08 > 0:26:12This metre-wide woven wigwam is a seduction pad
0:26:12 > 0:26:14and is all about show.
0:26:17 > 0:26:19Carefully arranged flowers and fruits
0:26:19 > 0:26:22are placed in piles on manicured moss.
0:26:23 > 0:26:25Smaller treasures are towards the back,
0:26:25 > 0:26:30to make the bower seem bigger, a trick interior designers use.
0:26:40 > 0:26:45Yet the male Vogelkop bowerbird himself is modest, even drab.
0:26:45 > 0:26:50It may take many years to become a proficient enough
0:26:50 > 0:26:53house builder to reach this stage.
0:26:55 > 0:27:00If he sees a twig out of place, he'll push it in or remove it.
0:27:07 > 0:27:10His architectural eye is unique.
0:27:10 > 0:27:14His rival neighbours each have different colour schemes,
0:27:14 > 0:27:16or floor designs or decorations.
0:27:16 > 0:27:20This particular male is going through a red phase.
0:27:29 > 0:27:32The flowers are changed regularly
0:27:32 > 0:27:35and the berries must be perfectly arranged, even the right way up.
0:27:39 > 0:27:40The floor is a challenge.
0:27:40 > 0:27:44Roots grow through the moss and have to be tackled.
0:27:44 > 0:27:47What he can't remove, he sweeps under the carpet.
0:28:05 > 0:28:06A rival male is singing.
0:28:11 > 0:28:13He must respond.
0:28:13 > 0:28:17We see perhaps now why the bower is the shape it is.
0:28:17 > 0:28:23It's a concert platform and the arch may help project his voice.
0:28:28 > 0:28:31He ends with a little dance.
0:28:33 > 0:28:34The audience has arrived.
0:28:34 > 0:28:39She seems interested, but he has disappeared.
0:28:39 > 0:28:43It is crucial in bowerbird courtship that he remains hidden.
0:28:43 > 0:28:46His house has to coax her in.
0:28:56 > 0:28:59Only when she is brought to a state of ecstasy over his decor
0:28:59 > 0:29:03does he dash out and try to mate.
0:29:07 > 0:29:13It's not entirely successful. Maybe she wasn't ready for his appearance.
0:29:13 > 0:29:18Or maybe his flowers or his floor weren't up to scratch.
0:29:18 > 0:29:21It's most frustrating.
0:29:31 > 0:29:33Perhaps he will tempt her back and maybe next time,
0:29:33 > 0:29:37the bower will be looking at its best.
0:29:42 > 0:29:45Home decoration can, occasionally,
0:29:45 > 0:29:48be about more than impressing the perfect partner.
0:29:51 > 0:29:55The burrowing owls in prairie dog town have a strange take
0:29:55 > 0:29:58on suitable suburban decor.
0:29:58 > 0:30:01Their landlords, the prairie dogs,
0:30:01 > 0:30:04would not approve of this innovation.
0:30:04 > 0:30:09What burrowing owls like is what the buffalo leave behind.
0:30:11 > 0:30:13They collect dung.
0:30:18 > 0:30:22The owl places the dung carefully around his front door.
0:30:22 > 0:30:27The burrowing owl chicks don't seem impressed by the collection
0:30:27 > 0:30:29of poop on the stoop.
0:30:29 > 0:30:35This is not how most wise animals treat their own doorsteps.
0:30:49 > 0:30:53In fact, this extraordinary bit of decoration
0:30:53 > 0:30:58is a trap for beetles, particularly dung beetles.
0:30:58 > 0:31:02The beetles find dung by smell.
0:31:02 > 0:31:07It is, to them, building material and food, rolled into one.
0:31:13 > 0:31:15Tons of dung are trundled away.
0:31:17 > 0:31:20The dung ball, with an egg inside, is buried.
0:31:20 > 0:31:25A warm and delicious home, at least for a dung beetle larva.
0:31:28 > 0:31:31Birds and mammals almost never turn their homes into traps,
0:31:31 > 0:31:34as spiders do.
0:31:34 > 0:31:37Human beings and burrowing owls are said to be the only examples.
0:31:41 > 0:31:44A chick takes some dung down the burrow.
0:31:48 > 0:31:51Maybe it's learning the connection with food.
0:31:51 > 0:31:53It's a step in the right direction.
0:31:55 > 0:31:59The owl mother doesn't agree and turns it into a lesson on housework.
0:32:11 > 0:32:15Homes are hard work and there's a lot for young animals to learn.
0:32:17 > 0:32:19Home making requires a sense of place,
0:32:19 > 0:32:23as well as working out how to get along in a community.
0:32:25 > 0:32:27The trap seems to have worked.
0:32:44 > 0:32:46Food is always critical,
0:32:46 > 0:32:51so many animal builders put a larder at the heart of their homes.
0:32:55 > 0:32:59The beavers' system of canals and ponds is a massive cold store.
0:33:04 > 0:33:06Beavers eat bark and leaves
0:33:06 > 0:33:09and stocking the larder is a job that takes months.
0:33:11 > 0:33:15The beavers wedge the branches down in the mud.
0:33:19 > 0:33:23Even stored underwater, a potential burglar spots the stockpile.
0:33:31 > 0:33:35But the moose is soon told that this store is private property.
0:33:40 > 0:33:44A few tail-slaps and the intruder gets the message.
0:33:56 > 0:33:59A house is of little use if there's no food.
0:33:59 > 0:34:04Winter in Outer Mongolia would be hard for a hamster,
0:34:04 > 0:34:07without a well-stocked store room.
0:34:11 > 0:34:15Down the burrow, there are several rooms.
0:34:15 > 0:34:19In the bedroom, the young are kept warm in straw
0:34:19 > 0:34:20and fed by their mother.
0:34:25 > 0:34:29Next door is the larder.
0:34:29 > 0:34:32All autumn, they gathered seeds in their cheek pouches
0:34:32 > 0:34:33and brought them down here.
0:34:33 > 0:34:37Thanks to the seeds staying safe and dry,
0:34:37 > 0:34:41the hamsters can start a family while it's still barren outside.
0:34:44 > 0:34:48Our own earliest buildings may have been grain stores.
0:34:48 > 0:34:49Protecting food for winter
0:34:49 > 0:34:52enables house builders to move into colder areas
0:34:52 > 0:34:55where the homeless could never survive.
0:35:01 > 0:35:03Some homes go a stage further.
0:35:03 > 0:35:06They have a living larder.
0:35:12 > 0:35:15A mole's network of dark passages
0:35:15 > 0:35:18can be extended at up to two metres an hour
0:35:18 > 0:35:20and provide the mole's food.
0:35:28 > 0:35:31Earthworms burrow through the walls by accident
0:35:31 > 0:35:37and the star nosed mole has special worm-detecting feelers on its nose.
0:35:40 > 0:35:43This housebound animal has a curious reputation
0:35:43 > 0:35:46as the fastest eater on record.
0:35:46 > 0:35:51An earthworm can disappear in a quarter of a second.
0:35:53 > 0:35:56Not everyone can build a house where your food literally
0:35:56 > 0:36:01drops in for dinner - and not everyone likes earthworms.
0:36:04 > 0:36:09In China, bamboo is one of the fastest growing plants,
0:36:09 > 0:36:13but I have heard of it occasionally growing back into the ground.
0:36:30 > 0:36:35Under the bamboo is a quarter of a mile of tunnelling,
0:36:35 > 0:36:40built over several years by bamboo rats.
0:36:53 > 0:36:55The tunnels follow the roots
0:36:55 > 0:36:59which run along the ceiling, like service pipes.
0:36:59 > 0:37:02She checks the bamboo by smell.
0:37:02 > 0:37:06If the roots put out a new shoot, she can sense the fresh growth
0:37:06 > 0:37:09and when it's the right length, she harvests it.
0:37:11 > 0:37:13The house has become a farm.
0:37:22 > 0:37:26She has the same iron-coated teeth as the beavers.
0:37:26 > 0:37:31Both are rodents, which are the vast majority of mammal house builders.
0:37:33 > 0:37:36Her young have never been out.
0:37:36 > 0:37:38She's blocked the exits.
0:37:38 > 0:37:42The outside world might as well not exist.
0:37:47 > 0:37:50The little ones seem determined to explore,
0:37:50 > 0:37:53but may get lost in the network of tunnels.
0:37:53 > 0:37:56So, she literally drags them
0:37:56 > 0:37:59around the labyrinth of her underground bamboo farm.
0:38:10 > 0:38:14American beavers build canals to carry trees
0:38:14 > 0:38:18and Chinese bamboo rats harvest bamboo underground,
0:38:18 > 0:38:20but in South America,
0:38:20 > 0:38:23another animal takes the idea of a home farm a stage further.
0:38:52 > 0:38:55Leaf and grass-cutter ants
0:38:55 > 0:39:01take about 10% of the forest's growth underground, to fungus farms.
0:39:02 > 0:39:05The white fungus grows on the chopped-up leaves
0:39:05 > 0:39:09and is pretty much all the ants eat.
0:39:09 > 0:39:13The fungus farm generates heat and carbon dioxide.
0:39:13 > 0:39:17Pipes lead to a large mound above the ground.
0:39:17 > 0:39:21The chimneys are like the raised prairie dog burrows,
0:39:21 > 0:39:23drawing the air through the nest.
0:39:24 > 0:39:29Nobody knew how big grass-cutter ant cities were,
0:39:29 > 0:39:34so scientists poured a liquid cement into an old nest.
0:39:37 > 0:39:39Once the concrete was set,
0:39:39 > 0:39:43they dug away the earth to reveal an extraordinary secret city.
0:39:49 > 0:39:54There are subterranean highways connecting the main chambers,
0:39:54 > 0:39:58with side roads to fungus farms, huge rubbish pits
0:39:58 > 0:40:01and temperature-controlled nurseries.
0:40:08 > 0:40:12This is one house for 12 million inhabitants.
0:40:13 > 0:40:15That's more than London or New York.
0:40:18 > 0:40:22On our scale, it is a mile deep, and five miles across.
0:40:31 > 0:40:36The social insects are nature's finest architects.
0:40:40 > 0:40:45These three-metre-high termite mounds all point north to south.
0:40:50 > 0:40:54In the morning and evening they face the sun and are warmed,
0:40:54 > 0:40:58but at noon, they are sideways on and so don't overheat.
0:41:00 > 0:41:04Our large buildings could follow this simple trick.
0:41:04 > 0:41:08However, this is not the whole story.
0:41:08 > 0:41:13Half the year this is a swamp and the sail-like shape and larger
0:41:13 > 0:41:18surface areas are perfect for keeping the colony dry, as well as warm.
0:41:24 > 0:41:29Most termites avoid overheating by descending into lower levels
0:41:29 > 0:41:30during the hotter part of the day.
0:41:30 > 0:41:35But these termites have found an architectural solution
0:41:35 > 0:41:36to the problem.
0:41:45 > 0:41:50Finding an egg 1,000 times your size in your house must be puzzling.
0:41:50 > 0:41:53Terrifying, when it starts to hatch.
0:41:58 > 0:42:02The gigantic aliens are lace monitor lizards.
0:42:06 > 0:42:11Their exit is closed. The termites repaired the hole in the wall
0:42:11 > 0:42:14the monitor mother made to lay her eggs.
0:42:14 > 0:42:16They are trapped.
0:42:37 > 0:42:42It seems almost incredible that their mother would return to release them.
0:42:46 > 0:42:50These lizards could not have chosen a better nursery -
0:42:50 > 0:42:52protected from predators
0:42:52 > 0:42:55and incubated at the perfect temperature.
0:43:03 > 0:43:07The termites must repair the mound.
0:43:07 > 0:43:10They use mud and mortar out of their back end.
0:43:12 > 0:43:16The walls are essential to stay within half a degree centigrade
0:43:16 > 0:43:19of 30, whatever the weather outside.
0:43:23 > 0:43:27Far from the tropics, insects have resorted to central heating.
0:43:28 > 0:43:32In a hollow tree, a Japanese giant hornet
0:43:32 > 0:43:37starts to build a city with cavity walls and electric radiators.
0:43:39 > 0:43:41The queen first makes a few compartments.
0:43:41 > 0:43:44An egg in each hatches into a larva.
0:43:44 > 0:43:50It spins a silk cocoon for itself that has extraordinary properties.
0:43:50 > 0:43:54The silk is like a thermostatic electric blanket.
0:43:54 > 0:43:57It stores heat as electrical charge,
0:43:57 > 0:44:02which automatically turns back into heat if the nest cools.
0:44:04 > 0:44:09Her daughters pupate and emerge.
0:44:09 > 0:44:11They are the first battalion of builders.
0:44:11 > 0:44:15They add additional floors, suspended in the middle.
0:44:15 > 0:44:19Supporting columns are moulded.
0:44:19 > 0:44:23They build with chewed-up wood pulp, the same material as paper.
0:44:28 > 0:44:32As more of the queen's larvae hatch, they start demanding food,
0:44:32 > 0:44:35banging and scraping their heads on the walls.
0:44:40 > 0:44:45The workers collect insects and mash them into a paste for the larvae.
0:44:52 > 0:44:56The outside walls are extended downwards, with up to eight
0:44:56 > 0:45:01layers of cavity insulation, and built-in flues and ducts.
0:45:01 > 0:45:05Like the termites, a few simple instructions may come together
0:45:05 > 0:45:08to build a surprisingly complex design.
0:45:08 > 0:45:12Scientists call this an "emergent property".
0:45:12 > 0:45:15And what emerges, after four months,
0:45:15 > 0:45:18is a hornet's nest almost a metre tall.
0:45:29 > 0:45:36If it's cold, the nest is heated by the larvae and their silk blankets,
0:45:36 > 0:45:38but on hot days, cooling air is fanned in.
0:45:40 > 0:45:44This nest is held within two degrees of 30.
0:45:44 > 0:45:49The colony behaves as much like a warm-blooded animal as a house.
0:45:54 > 0:45:58Towards autumn, the queen turns to producing new queens for next year.
0:46:01 > 0:46:03She, and all her workers, will soon die here,
0:46:03 > 0:46:06exhausted and now expendable.
0:46:07 > 0:46:11The city will crumble, too, and can never be reused.
0:46:12 > 0:46:15In the final days of her life,
0:46:15 > 0:46:17the queen ensured that a few larvae were fed
0:46:17 > 0:46:20and fresh queen hornets emerge.
0:46:22 > 0:46:27Each faces a winter of hibernation and, in spring, starts building
0:46:27 > 0:46:31a brand new edifice 40,000 times her size.
0:46:33 > 0:46:38For every home, there comes a time to move on.
0:46:51 > 0:46:54There is one animal in the rainforest
0:46:54 > 0:46:57that builds the most extraordinary city of all.
0:46:59 > 0:47:02Army ants kill almost everything they can
0:47:02 > 0:47:04and carry it all back to their home.
0:47:05 > 0:47:10Their house is a living building entirely made of ants,
0:47:10 > 0:47:11called a bivouac.
0:47:14 > 0:47:17The legs carry the weight of the whole nest.
0:47:26 > 0:47:29Big cities have big problems.
0:47:29 > 0:47:33The ants generate so much waste that they need a rubbish tip.
0:47:34 > 0:47:37The carcasses of dead insects, and old cocoons are taken
0:47:37 > 0:47:40out of the city to the dump.
0:47:41 > 0:47:44Soon the colony sits in a sea of municipal waste
0:47:44 > 0:47:47and all the surrounding food has gone.
0:47:50 > 0:47:54So, they unhook themselves at night and set off.
0:47:56 > 0:47:59Pupae and larvae are carried, and the queen is protected
0:47:59 > 0:48:02behind a cavalcade of soldiers.
0:48:12 > 0:48:16A new site is chosen and living ropes become columns.
0:48:17 > 0:48:19They seem to build around a frame,
0:48:19 > 0:48:23but since every site is different, the design is never identical.
0:48:27 > 0:48:29The frame is filled in with walls,
0:48:29 > 0:48:33to create corridors and rooms, all made of ants.
0:48:34 > 0:48:38Their new neighbourhood will be stripped of prey in a few days.
0:48:40 > 0:48:44If the ants couldn't move their city,
0:48:44 > 0:48:47they'd quickly eat themselves into extinction.
0:48:50 > 0:48:52All houses face the same dilemma.
0:48:54 > 0:48:57The beavers have felled hundreds of tons of wood.
0:48:57 > 0:49:01After four or five years, there is nothing left but bushes.
0:49:02 > 0:49:05The ponds have silted up, and without logs for repair,
0:49:05 > 0:49:07things start to fall apart.
0:49:16 > 0:49:21The beavers make do for a while on shrubs, like willow herbs,
0:49:21 > 0:49:24but even these, they eat faster than can grow back.
0:49:27 > 0:49:31As their lake shrinks, they will abandon their home.
0:49:35 > 0:49:39Almost all homes become unsustainable, eventually.
0:49:40 > 0:49:45The rivers are littered with empty lodges and broken dams.
0:49:48 > 0:49:51Every construction is an attempt to tame nature...
0:49:51 > 0:49:55and nature will always win, in the end.
0:49:57 > 0:49:59Things are even tougher for prairie dogs.
0:50:01 > 0:50:04In summer, the land dries.
0:50:04 > 0:50:06The cattle and buffalo can move,
0:50:06 > 0:50:11but the dog towns can't and the families have nowhere else to go.
0:50:11 > 0:50:16The owl family can all fly now. They can come and go.
0:50:19 > 0:50:21The prairie dogs eat the remaining grass,
0:50:21 > 0:50:24until their neighbourhood becomes a dust bowl.
0:50:30 > 0:50:32They face starvation.
0:50:35 > 0:50:38The young are a few months old
0:50:38 > 0:50:40and now the colony turns against them.
0:50:40 > 0:50:43Neighbours start to hunt down cubs.
0:50:43 > 0:50:46Even cousins and aunts turn nasty.
0:50:48 > 0:50:52In a dry year, up to half of the young are killed.
0:51:05 > 0:51:11Stuck underground, out of sight, their home becomes a prison, a tomb.
0:51:17 > 0:51:21THUNDER RUMBLES
0:51:21 > 0:51:23Salvation does come in the end
0:51:23 > 0:51:26for the few survivors inside their houses.
0:51:38 > 0:51:42In autumn, the rains replenish the land
0:51:42 > 0:51:46and, in spring, the grass grows back.
0:51:53 > 0:51:56The prairie dogs have done no permanent damage.
0:51:58 > 0:52:00They help the grassland over the years,
0:52:00 > 0:52:03by mowing and fertilising their gardens.
0:52:07 > 0:52:10The neighbourhood returns to normal.
0:52:19 > 0:52:23The beavers have started a new life a couple of miles downstream.
0:52:25 > 0:52:28They have found ponds built generations ago,
0:52:28 > 0:52:30overgrown and abandoned.
0:52:30 > 0:52:35They have repaired the dams and re-opened the canals.
0:52:36 > 0:52:38The trees here have regenerated,
0:52:38 > 0:52:42thanks to the fertile silt clogging the old ponds.
0:52:46 > 0:52:50We can begin to see why not every animal makes a home.
0:52:50 > 0:52:54You can't rely on one place for long.
0:52:54 > 0:52:57For many, the risks are too great.
0:53:02 > 0:53:07The restless and the hungry follow the seasons in great migrations.
0:53:14 > 0:53:18The world is constantly changing
0:53:18 > 0:53:22and even the wisest animals struggle to keep up.
0:53:36 > 0:53:40These are the homeless of the Earth
0:53:40 > 0:53:43and, until recently, we were among them.
0:53:46 > 0:53:51So how did we become the greatest homemaker of all?
0:53:54 > 0:53:57Our closest animal relatives are still homeless,
0:53:57 > 0:54:00unable even to keep out of the rain.
0:54:01 > 0:54:03Apes and monkeys don't make shelters,
0:54:03 > 0:54:07though a gorilla's hands and brain are easily up to the job.
0:54:11 > 0:54:15The priority for these mountain gorillas is to find fresh food,
0:54:15 > 0:54:19so they keep moving. A house would only tie them down.
0:54:23 > 0:54:26The signs of an ability, however, are here.
0:54:27 > 0:54:30An improvised roof is better than none, while it lasts.
0:54:36 > 0:54:40Our ape cousins build beds, or even platforms, woven from branches.
0:54:40 > 0:54:42But they never sit under them, like a roof.
0:54:46 > 0:54:50We may have started with twisting branches into shelters,
0:54:50 > 0:54:52but there is another way to get out of the rain.
0:54:54 > 0:54:59In Kenya, on Mount Suswa, baboons use caves at night.
0:55:01 > 0:55:07Caves like these contain the earliest evidence of human habitation.
0:55:16 > 0:55:19The monkeys' fingers and sense of balance
0:55:19 > 0:55:22take them along ledges impossible for leopards and hyenas to follow.
0:55:26 > 0:55:30Many of our phobias may have originated here,
0:55:30 > 0:55:32with bats and snakes,
0:55:32 > 0:55:35and strange, ghostly noises in the dark.
0:55:52 > 0:55:55We probably became serious builders
0:55:55 > 0:55:58only a few hundred thousand years ago, at the most.
0:55:58 > 0:56:01It is extraordinary what we have achieved.
0:56:09 > 0:56:12We don't often realise how fragile all this is.
0:56:17 > 0:56:20Our cities have all the problems of animal cities -
0:56:20 > 0:56:25burglars and squatters, and getting the food in and the rubbish out.
0:56:26 > 0:56:30To feed the city, we eat up the wilderness.
0:56:30 > 0:56:34We forget that we kick animals out of their homes to do so.
0:56:37 > 0:56:42Maybe we can be reminded by the refugees,
0:56:42 > 0:56:45by an urban generation of peregrines and pigeons,
0:56:45 > 0:56:47gulls and bats and foxes.
0:56:52 > 0:56:55Animals will share our world, if we let them.
0:57:02 > 0:57:08We can make space and help with protection, food and warmth.
0:57:08 > 0:57:11We are homemakers, we understand.
0:57:12 > 0:57:18We can build a world, surely, where animals can have a home, too.
0:57:21 > 0:57:26# I'm coming home, I'm coming home
0:57:26 > 0:57:28# Tell the world I'm coming home
0:57:28 > 0:57:33# Let the rain wash away
0:57:33 > 0:57:36# All the pain of yesterday
0:57:36 > 0:57:41# I know my kingdom awaits
0:57:41 > 0:57:44# And they've forgiven my mistakes
0:57:44 > 0:57:48# I'm coming home, I'm coming home
0:57:48 > 0:57:51# Tell the world I'm coming. #
0:58:12 > 0:58:15Subtitles by Red Bee Media Ltd
0:58:15 > 0:58:18E-mail subtitling@bbc.co.uk