Original subtitles

50 million years ago,

all of Australia was covered by a mantle of dense rain forest.

This green luxuriance was the cradle of evolution

for the unique plants and animals

that now give Australia such a distinctive character.

Today, three-quarters of the continent is arid.

But some fragments of that primeval jungle remain,

mostly here in the tropical north-east.

It's a living museum, where the very beginnings of the bush survive.

The canopy is so dense here

that in the cooler winter pythons emerge from the trees

to warm themselves in the sun.

Today, this is one of the few places on the arid continent

where the struggle for life is not for water but for light.

On the forest floor, where it's dark, the young plants have reddish foliage,

all the better to absorb the light.

Ingenious solutions

have been evolved by the plants in their race to the sky.

Vines send out tendrils or barbed hooks to claw their way swiftly to the top,

using existing trees for support.

Some figs get a head start

by germinating their seed high up in the canopy

then sending down roots which eventually strangle their host.

The fig itself grows on,

and pushes its massive crown high above the forest roof.

There's a constant jostle for light and space in the canopy,

and the crowns weave together in a dense and billowing layer.

Were they simply to drop, seeds might not grow in the gloom.

So they're packed in fruit

to entice birds into eating them and carrying the vital contents away.

Where there are birds, there are nests and eggs,

food for the green tree snakes that patrol the upper storey.

Only the flesh of the fruit is digested. The seeds simply pass through the gut.

The more birds eat, the more seeds get scattered around the forest.

Even the fruit that does fall to the ground may be picked up by cassowaries,

a flightless bird unique to Australasia.

They too void the seeds.

And because the birds tend to do so in clearings,

where there's more light,

the seeds have a better chance of developing.

Such a wealth of food within easy reach

gives certain birds more time to devote to breeding.

Male bowerbirds have become skilled artists and builders

in their quest for sex.

On the dim forest floor,

the decorated structures are marvels of arf and architecture,

designed solely to attract and impress females.

Among the golden bowerbirds,

these courtship theatres are passed down the generations

and freshly embellished with mosses and lichens.

The more brilliant the plumage, the less elaborate the bower.

This regent bowerbird has a fairly modest arena,

but he still can't afford to leave it for long,

because other males may try to take it over.

Male satin bowerbirds make an avenue -

twin rows of twigs are glued in place with a mixture of charcoal and saliva

and later painted with crushed plants.

It's impressive enough to lure a hen.

The sight of her excites the artist into a brilliant song and dance.

In a season's wooing, many will be won.

The male role ends with copulation

and the hen's left to build a nest and raise their chicks alone.

As well as disperse seeds,

birds play another imporfant part in the forest's procreation,

as pollinators.

Up in the canopy,

there's much competition for animals to carry pollen.

Perhaps that's why this bumpy satin ash grows its flowers directly from the trunk

to catch the passing traffic of honey eaters.

A rich flow of nectar rewards them for taking pollen between trees

and fertilising the flowers.

When nightfalls, the mammals emerge.

Among them are tree kangaroos.

Despite their name, they spend as much time on the ground as aloft.

Lemuroid possums prefer the canopy,

where they find some of their favourite foliage.

But it's flowers that are especially prized.

And their scent brings yet more visitors to the satin ash,

to harvest the nectar and collect the pollen.

Like the honey eaters,

the blossom bats have long tongues tipped with tiny brushes

to soak up the sweet liquid.

Flowers provide their only source of food.

And enough pollen sticks to their whiskers and fur

to make these tiny bats gentle and reliable go-betweens.

The trees derive no benefit from this possum.

The Herbert River ring tail relishes the flowers

as a welcome break from its usual fare of leaves.

Possums first evolved in the rain forests.

And overtime, they diversified into many specialised kinds.

For arboreal animals, lemuroid possums aren't all that agile.

While most of the larger species feed on leaves and other plant food,

this small and elusive striped possum prefers insects.

Searching along the rotting and dying trees,

it tears at the bark with sharp teeth and digs out wood-boring grubs.

Its hands tap along the wood

for the hollow sounds that betray the presence of borers.

The fourth finger on each hand is much longer than the others

and it's tipped with a sharp claw

to skewer fat and juicy grubs from deep inside the rotting timber.

Today, this pretty striped possum is hard to find.

Although the rot and decay that's so much part of this dense and wet forest

gives it a good living here,

its special way of life left it no match for a dramatic change

which began to gather pace 15 million years ago.

Australia star fed to dry out.

And most of the rain forests and their inhabitants vanished.

But among the plants were some that adapted -

plants that already had evolved features

to survive in places where the soil was poor.

And it was these marginal, hardier plants that took over

while the ancestral forests retreated to a few pockets.

From among the new plants

rose a group that spread around Australia in splendid variety-

the eucalypts, the gums.

They reach their most majestic form in the mountain ash.

Growing to 100 metres, it's the tallest flowering plant in the world.

And with its light and airy crown, it's the king of the eucalypts.

The open canopy

lets through much more light than the rain forest it replaced.

And in these higher, wetter areas,

it allows an understorey of tree ferns to flourish -

a backdrop of green lace for what sounds like a great chorus of birds.

In fact, all the songs have but one singer, the lyrebird,

a uniquely Australian master of both mimicry and display.

The aim is to persuade females nearby

that the cock bird is a fine and healthy specimen,

well worthy of fathering their chicks.

This hen seems to have heard it all before.

And she's more interested in the insects hiding in the litter.

But in time, the display will work its spell.

Eucalypt forests are spacious and uncluttered.

And that gave some of the possums added impetus

to turn leaping into gliding as a means of getting around.

Folds of skin

that stretch between the fore- and hindlimbs of the leaping possums

evolved into strong and supple membranes

to carry sugar gliders and their kin on long flights through the open forests.

Gliding doesn't use as much energy as climbing.

And it's an economical way for possums to harvest a special food

provided by some kinds of widely scattered gums.

In these uncommon trees,

a sugary sap flows so close to the outer skin

that a slash of sharp teeth has it oozing out

to become a rich and sustaining food.

The sap trees are few and far between.

And so sugar gliders band together to defend this precious resource.

As a result, they've become the most social of the possums.

It's a society where the chief language is not sound but smell,

and a complex idiom it is.

Whenever gliders meet,

they stop to sniff and refresh their communal scent.

The glands are in the most unlikely places -

under the chin, on the forehead, even under the feet.

As well as the tribal odour,

there are subtle blends that tell who's who in the social order

and details of sex-

for instance, whether this female is ready to mate.

The unfamiliar odour all around

warns this stranger that he's in the wrong place.

To warn all comers that this is occupied territory,

the resident males smear pungent trails around the tribal range.

A strong scent from glands around the vent is mixed with drops of urine.

Again, it's scent, or rather the lack of a familiar one,

that marks out an intruder.

His body odour declares him to be a male,

but a very young one and so no real threat.

Before dawn breaks,

the gliders make their way to the communal den.

Such a tight squeeze keeps out larger possums

and gives protection against whatever enemies might come prowling by.

Inside the eucalypt hollow, it's also a fairly snug fit.

Some colonies have as many as eight gliders bedding down together.

Sharing body warmth saves energy

and helps to pass around the all-important tribal scent.

The eucalypts' distinctive dull green foliage is much more open

than that of the rain forest trees from which they evolved,

with smaller, hardier leaves to withstand the climate.

The leaves hang angled away from the sun to keep water loss down.

And to make them unpalatable,

they're loaded with potent cocktails of toxins and oils.

Despite this,

some animals have found ways of breaching the eucalypts' defences.

And they form a web of life

that extends even to the streams flowing through the forest.

The leaves fall all year round.

And almost the moment they hit the water,

the first of a long line of insect shredders gets to work.

Caddie-fly larvae,

armoured in a suit of sand grains and plant fragments,

reduce the leaf to a skeleton,

carefully munching their way around the poisonous oil glands.

The bits of leaf get broken down further

and are swept downstream,

some to fetch up in a tiny net spun by another kind of caddis larva.

Instead of having a portable suit of armour,

this one builds a fortress out of tiny pebbles.

It's such a good spot

that another larva mounts an assault on the miniature castle and takes over.

The usurper's first task is to improve and strengthen the structure.

One side of the keep serves to anchor the net.

And with all the rebuilding, it's become rather tattered and torn.

When the last pebble is securely in place,

the caddie sets about reweaving its gossamer snare,

producing sticky threads much like a spider's.

The net is delicate but tough - only 5mm across,

yet sturdy enough to catch and hold

the bits of broken-down leaf swept into it by the strong current.

The creatures that inhabit these streams belong to very ancient families.

It's only the nature of the leaves on which all their lives depend

that's changed -

from rain forest to eucalypt.

The leaf-shredders and net-spinners

become food for larger insects and crustaceans.

And there are enough of those to help feed the platypus,

which lives much as it did

when these streams were still fed not by eucalypts but by rain forest.

Change becomes more apparent further downstream,

in the drier woodland of the lower rainfall country.

The soils are poorer here, and the gum trees don't grow as tall.

They're more gaunt and spare than the eucalypts of the higher ranges.

This is the characteristic bush.

Unlike their rain forest ancestors, gums don't make fleshy fruit.

Instead, seeds are packed in woody cases to stop them drying out.

A colourful company of cockatoos, parakeets and Iorikeets

feeds on gum nuts and berries,

deftly peeling them with tongue and beak.

The open canopy allows a lot of sun to reach the ground.

There's plenty of light and space for seeds to germinate and grow.

And the eucalypts have no need to bribe birds to carry the seeds away.

Though many are eaten by parrots, many more survive.

But sun also dries the litter as it builds up,

accumulating fuel

for another powerful force that moulded the nature of Australia -fire.

Astonishingly, the eucalypts came to thrive on fire.

Features that developed first to cope with poor soils and then with drought

now stand them in good stead in dealing with flames.

In the aftermath, the bush looks black and lifeless.

But it's far from dead.

Already, the wombats which hid from the flames in their burrows are out,

squabbling over bits of plant food left unburnt.

The eucalypts live on.

The reserve shoots and buds under the bark and the main branches

begin to sprout.

And within weeks, the gums are veiled in green again.

The fresh growth attracts armies of insects,

for leaves are best eaten when they're young and tender,

even though they're already loaded with defensive toxins.

A vast array of suckers, cutters, nibblers and munchers goes to work.

They're mostly the larvae of moths and butterflies.

And they consume great quantities of leaves.

Some simply nibble their way around the chemical defences.

Others are immune.

Because the eucalypts can put out new growth repeatedly,

they seem to suffer more insect attack than many other trees.

Fire, insects, and still the trees survive.

Indeed, they do attract some allies in the insect wars,

though even a legion of praying mantises

wouldn't take much of a bite out of the hosts of leaf eaters.

The intervention of this bell-miner actually works against the trees.

The reason forth at is its fondness of these small sugary domes

that form on the leaves of some eucalypts.

They're called lerps,

and they're made by the larvae of psyllid insects

to protect their soft bodies from the sun while they suck the sap from the leaves.

The psyllids digest what they need from the sap

and use the waste to build their sunshades.

At first, the material is soft and pliable, and the larva can work it into shape.

Eventually, the fruit of two hours patient labour

sets into a tiny house of sweet glass.

Bell-miners relish the stuff, and carefully remove the domes,

leaving the insects to manufacture more.

They chase other birds away-

birds that eat the insects as well as their shelters.

And that's a problem for the eucalypts,

for with the bell-miners protecting the psyllids and taking their domes,

the insects' appetite for leaf sap is constantly being stimulated

to become ever more voracious.

The eucalypts can't count this bird among their friends either.

It's gone into parfnership with a parasitic plant-the mistletoe.

The mistletoe taps into the eucalypts for its own growth

and it employs the mistletoe bird to spread its seeds and gain a root hold.

The bird and its chicks have the gut specially designed

so that the berries go directly into the intestine and bypass the stomach.

That way, they go through very quickly,

and when the partly digested berries emerge, they're still sticky.

The seeds are dropped high in another tree, and sprout.

One eucalypt may carry several mistletoes

and struggle to survive itself.

The mistletoe is at the centre of another even more remarkable relationship.

At the base of some host trees,

the caterpillars of azure butterflies are tended by sugar ants,

which give them shelter in their own nest.

Every night, the grubs go on a long and dangerous trek to the top of the tree

to feed on the mistletoe leaves.

The ants go with them,

and their presence guards against spiders and other enemies.

In return, the grubs supply the ants with a rich, sugary liquid

from their body glands.

In their rise to dominance over the last two million years,

the eucalypts formed a range of extraordinary associations,

but most involve birds and insects,

which either avoid or cope with the toxic leaves.

By contrast, only a few leaf-eating marsupials have been able to adapt.

Of all the rain forest ring tail possums,

only the common ring tail thrives in these drier woodlands.

It's successful because its digestion can cope with the oils and toxins

in the eucalypt foliage, which is the most abundant food here.

As soon as they're out of the pouch,

the baby possums start weaning on the tough plant food

that'll be their adult fare.

That grasping tail helps them reach the fragile outer branches

bearing the fresh new leaf growth

and it also makes a handy carrier for nesting material.

The leaves that pose the marsupials with such a digestive challenge

make a dry, hard litter which takes a long time to break down,

but enough insects and other invertebrates live amongst it

to provide a good living forth is an tech in us.

Its hunting skill is extraordinary.

Speed and a single-minded ferocity

enable it to tackle almost any kind of prey.

But it's the antechinus's sex life that's even more remarkable.

There too, ferocity is the hallmark.

With the advent of the mating season,

males competing for females fight each other to a standstill.

The male sex drive is especially urgent with an tech in us -

as well it might be, for they have only one season to reproduce.

It makes their couplings fairly brutal - more like a rape -

and lengthy they are too.

All this frantic breeding is lethal.

It takes tremendous energy and produces great tension,

and males hardly eat, their teeth fall out, they get gastric ulcers,

and their stress hormones rise to levels so high

that their immune system fails, like AIDS.

By the end of the season they're all dead,

leaving only the pregnant females.

It's a high price to pay for breeding success,

but there is sense in it.

Small mammals don't live long anyway,

and among the an tech in us, evolution has favoured males,

which put all their reproductive effort into their first and only mating season.

Success lies not in personal survival but in how many young are fathered,

to ensure that the line is carried on.

The challenge of procreation in these wood lands

has fashioned other, equally intriguing, strategies.

Many of the birds here form extended families

to share the task of rearing young.

Several generations of kookaburras -

older brothers, sisters, unattached uncles and aunts -

pitch in with feeding and even help to incubate the eggs.

Communal breeding is away of giving chicks a better chance

in an environment where food supplies aren't always reliable.

But animals don't usually do anything for nothing.

Perhaps the return comes later,

when the helpers get help with their own young.

The galah's strategy is to form a lifelong bond with one mate.

Pairs come back to nest in the same tree hollow year after year.

Hollows are fairly safe places

but no bond is strong enough to guard against lace monitors on the prowl.

Though they're only active for a short time each day,

their acutely sensitive taste and smell

make them the most feared predator in these parts.

It's just another meal for the lace monitor,

but for the galahs, it's the end of their chance

to rear a family this season.

Beneath the eucalypts live banksias -

ancient plants going back to the primeval rain forest.

They are inhabited by pygmy possums.

Vacant bird nests often provide a home,

and some of their food comes from insects.

Insects are relished, but the banksias themselves

provide their small guests with even more important nourishment.

The pygmy possums feed on the nectar

and in so doing help pollinate the flowers.

The possum babies soon get the hang of clambering around.

After all, the pygmy possums and banksias evolved together

over an immensely long time.

The shape of the flowers suits these nocturnal pollinators -

each spike has hundreds of tiny flowers,

densely packed together to provide support,

and plenty of nectar and pollen.

Banksias and their relatives

come splendidly into their own in the heathlands,

especially here in Western Australia.

In these ancient leached soils, so poor they're almost pure sand,

climatic hardships created an evolutionary nursery without parallel.

So many flowers eager to attract pollinators

have fostered a matching diversify of insects.

Many, like these jewel beetles, are rewarded with nectar,

but some plants show even greater entrepreneurial flair.

Honeyeaters make good go-betweens, and many plants employ them.

Even more recruit insects,

and the result is a wonderful assortment of shapes

designed to suit the various visitors.

Certain plants even resort to fraud to seduce insects.

One group of orchids

cunningly exploits the sexual habits of this wasp -

habits remarkable enough in themselves.

The female has no wings, and when she's ready to mate,

she rubs off chemical signals for a male to come and fly off with her.

The wasps mate on the wing, and, still coupled end to end,

he takes her to some nectar-rich flowers.

Now he feeds, dragging his partner behind him.

She can't feed herself,

but when he's had his fill, he rubs her abdomen,

which prompts her to curl forward and receive a few drops from his mouth.

Feeding her is his investment in the eggs now forming in her body.

The whole method hangs on the chemical signals she sends out,

and the orchids have evolved almost identical signals

to trick the male wasps into trying to copulate with them

and so become their pollen carriers.

This flower looks as well as smells like a sexy female wasp,

and he keeps on trying to mate

even when the orchid flips him onto its pollen-bearing part.

Such mimicry is an economic way of seducing pollinators

without having to supply nectar-

a great advantage in these poor soils.

The plants that use birds do give a reward,

but the flowers are shaped

so that the visitor has to collect a dab of pollen as well.

The honey eaters are also matched to the task.

Inside the long bill there's a long tongue

tipped with a brush to soak up the nectar.

Rather than opt for one particular kind of pollinator,

banksias play the field.

Their dense blooms are arranged to tempt various honey eaters,

reward them with nectar and ensure they carry away pollen.

But those same blooms also support a much more ancient partnership

with this extraordinary animal.

Much smaller than a mouse,

the marsupial honey possum is one of the very few mammals in the world

designed to feed exclusively on nectar and pollen.

Like the honey eating birds,

it has a long tongue fitted with a brush at the end.

The partnership began in the ancestral rain forests,

and while many other plants and animals vanished,

the honey possums stayed with the banksias

as they became transformed into these hardy plants of the bush.

In the eucalypts that fringe the heathlands

lives another very specialised marsupial -the numb at.

Its survival is linked closely to the termites

that became abundant as the Australian landscape dried out.

Uniquely among marsupials, they become active only by day,

because that's when the termites upon which they feed

move near the surface and into the fallen timber.

The stripes are good camouflage,

but having to step out in broad daylight still makes the numbats very cautious.

This kind of eucalypt woodland provides a plentiful supply

of the wood-eating termites that the numbats prefer.

And they're well-equipped to harvest them,

with a tongue that unrolls to half their body length.

It's a specialised way of life, and it's enabled the numb at

to live through the ever-drying climate that made the bush.

The rise of the eucalypts offered a secure place

for any marsupial that could stomach their foliage.

Some possums managed it,

but it's the koala that's come to typify the supreme gum specialist.

Its gut has special bacteria to extract all it needs

from just a few types of eucalypt leaves.

It means koala life revolves around a small range of gums -

that's where they fight, feed and mate.

Mating is what's on the mind of this old dominant bull right now.

The female is still carrying last year's young,

and she sees the approach as a threat to herself and her joey.

She's much lighter

and she can move out to the thinner branches where he daren't follow.

The awkward way they clamber around

suggests that they haven't been tree dwellers all that long.

In fact, their closest relatives are wombats.

The old bull is about to suffer more frustration.

A young rival has come into his range with designs on a virgin female.

The commotion sends the king koala hurrying to protect his mating rights.

If this intruder manages to impregnate one of his consorts,

there's one less chance off a the ring a royal cub.

The old male is an experienced campaigner.

His tactic is to drive the young rival far out on a slender limb.

Now the choice is to fall or risk an escape past the royal rage.

Peace returns, but the tension remains.

Sooner or later, the young male will try his luck again -

he may even displace the old bull and become the new ruler.

It'll make no difference to the females.

They'll continue to care for their young

and when the time is right, receive the seed for the next generation.

It's important for joey to stay close to mother,

not only for milk, but also to be fed with some of her faeces.

It's a pap that will prime the young

with the special bacteria to process gum leaves -

its sole food in adult life.

Of all the marsupials,

the koalas have tied their fortunes most closely to the eucalypts.

It's the quintessential partnership in the bush,

a partnership that could only have evolved in Australia.

Inland from the wooded margins,

the drying centre of the continent

posed animals and plants with an even greater challenge,

and that's the theme of our next program.

In the back of beyond lies a shimmering wilderness

where even the stones seem to burn.

It's been called the never-never, the dead heart of Australia.

Three quarters of the continent is arid now,

but once, this vast interior was a place of plentiful rain

with rivers flowing into great lakes.

Even today, huge rains occasionally transform the arid lands

into a semblance of that wetter past.

In these deep valleys,

run-off from the infrequent rains filters through the rock

long after the surrounding country has dried out again,

and the water preserves stands of ancient palms.

Permanent pools teem with fish.

They are now able to cope

with wild swings in water temperature and salinity,

and they breed into vast shoals

when the heavy rains flush them out into the desert rivers.

That happens perhaps only a few times each century now.

Most of the time the rivers are dry.

And yet they're far from dead.

For deep within their sandy beds,

there's moisture left behind by the last rains.

It's these hidden waters which support a rich mosaic of life

through even the driest times.

Millions of years of erosion

carved deep and wide through the shields of rock.

Pillars of harder stone remain,

while the rest of the plateau wore away

to form the deserts of Central Australia.

Ancient floods scattered the eroded rock into plains of stone -

the gibber deserts,

their bright sheen a film of iron oxide

left by evaporated moisture.

It seems that nothing could grow here amid this wilderness of rock.

Yet amazingly there's life.

The shingleback lizard seems a pattern of stone, until it moves.

There aren't many places to hide, and camouflage is a good defence.

Reptiles manage well here,

for they can do without regular food or water.

While there isn't enough to support many mammals or birds,

the gibber bird does thrive here.

There are sufficient insects to supply all its needs,

including the little moisture it requires.

It escapes the worst of the blistering heat

in what shade there is,

holding the wings out to keep air circulating close to its body.

The fierce winds that came

with the last great drying of Australia 20,000 years ago

sifted the sand from the gibber and swept it into vast dunes.

Row upon row of dunes arc halfway around the continent,

some running without a break for 300 kilometres.

The sand seems a meagre basis for life.

Yet life there is.

Its presence is written in the sand.

A moving ripple announces a most intriguing and secretive creature -

the marsupial mole.

The mole spends much of its life swimming through sand.

Its sturdy little claws are shaped like shovels.

Eyes would be useless beneath the surface,

and they've all but disappeared.

Instead, it relies on touch and smell

to find its subterranean meals of grubs.

But not all that ripples is a mole.

Some lizards have also become sand swimmers.

Several skinks have gradually lost their legs,

the easier to slip through the shifting granules

and sneak up on insects.

But this grasshopper's come up with a defence.

Already patterned like sand,

it completes the vanishing act with a flurry of shovelling legs.

In the swales between the dunes, a crust of clay and sand has formed.

And in the years between rains it lies sunbaked and cracked.

These miniature canyons are home to Australia's tiniest marsupials -

the planigales.

They weigh as little as six grams,

and their heads are flattened

to squeeze through the narrow spaces in search of insects.

But small mammals

also make attractive prey for the desert snakes.

At moments like this,

the cracks offer protection against more than the desert sun.

Reptiles are the major predators in these parts.

And the most formidable of them all is the perentie -

a giant goanna, two metres long.

Much of its prey hides from the sun,

but the forked tongue picks up even the faintest traces of scent.

The snake is extremely venomous.

Bashing it breaks the back and leaves it helpless.

A meal this size can last perenties a month or more.

Storing food in layers off at

enables them to thrive in this unpredictable region.

The desert dunes overlie and rechannel ancient river courses

that once drained into a huge inland lake.

What shimmers now is salt left by thousands of years of evaporation.

Today Lake Eyre is the driest place on the continent

and among the hottest.

It lies 15 metres below sea level

and temperatures can soar to a scorching 60 degrees.

Yet even at this harsh extreme some animals flourish.

Lake Eyre dragons survey their salty domain.

Their eyelids shaped like sun visors against the blinding glare.

They feed on ants which harvest insects blown onto the salt.

The ant mounds also serve as lookouts

to spot potential mates or rivals.

To avoid actual battle,

the dragons have evolved a most eloquent body language.

Head bobs, push ups and arm waves sort out the hierarchy

and signal readiness for mating, or reluctance.

This male has proved his dominance.

Now he can feed undisturbed,

walking on the heels so as to keep toes from getting burnt.

The dragons manage to thrive

in conditions that would defeat most other creatures.

And most of the time their domain remains undisturbed.

But a few times each century Lake Eyre becomes a sea again.

Most of Central Australia drains into Lake Eyre.

Usually, run-off from light rains

evaporates long before it reaches the lake.

But occasionally a tropical cyclone

dumps huge rains across the remote channel country.

It's these unpredictable heavy drenchings

that are the crucial events in the life of the arid country.

Waterfalls in such abundance

that it soaks deep into the parched earth

and replenishes the hidden stores

which keep the plants and animals going when the dry times return.

The downpour is a welcome chance

for the desert animals to drink their fill,

and for these galahs to wash the dust out of their feathers.

In this region of little and erratic rain,

the survivors are those who, like this spiny-tailed gecko,

make the most of every opportunify.

Normally it emerges only at night.

A praying mantis sips the droplets that gather on its arms.

The thorny devil drinks in a most ingenious fashion.

The sculpting of the scales creates fine channels

which draw the water to the corners of the mouth.

The rain is heavy enough to sink deep into the sand.

A metre or so down

it wakens a most surprising animal to find in the desert-

a frog.

Yet frogs live here in abundance,

for they cope with drought in a remarkable way.

They escape underground for years,

cocooned in a second skin to keep their body moist.

That shroud provides the first meal

when the kiss of water ends a sleep that may have lasted five years.

Then comes a brief but glorious spell of freedom -

feeding and breeding

until the returning dry sends the frogs back into their time capsule.

The desert plants have their own ways of making the most of the rain.

Many mulgas are shaped like inverted umbrellas.

The rain is funnelled down the leaves and branches,

then cascades down the trunk.

The water soaks in around the base of the tree

and recharges the underground stores.

The cracked clay between the sand dunes soon becomes saturated

and forces the planigale to seek higher ground.

There's been so much rain here in the channel country

that the run-off races hundreds of kilometres down the dry creek beds

towards the arid heart.

The waters replenish the subterranean reservoirs,

carrying the benefits of the rains

a long way from where they actually fell.

Once again, masses of water are surging towards Lake Eyre.

So suddenly did the rivers rise

that they caught this gecko unawares.

It's a marvellous transformation

from bone-dry sand to water churning with fish.

They're bred from stocks in isolated water holes

flushed out by the rains.

These cormorants are among the legions of water birds

which follow the newly flowing rivers into the flooding desert.

The rivers carry so much water,

they flood out across plains that are among the flattest on earth.

The warmth of the sun and the wealth of fresh nutrients

brings everything to life.

Dragonflies and insects of all kinds are in a frenzy to reproduce,

to make the most of the good times while they last.

The touch of water stirs dormant eggs into life

and the claypans soon teem with shield shrimps.

Theirs is a most fleeting existence,

forth is shallow water won't last long.

Two weeks after hatching, they mate

and lay eggs that may lie dormant for 25 years.

The budgerigars know the rain will produce a flush of food.

And they gather in trees lining the flooded rivers

to form pairs and start families.

These nomadic little birds

are well tuned to the shifting fortunes of the interior.

They mature quickly

and the males produce sperm when they're only a few months old.

The flooded rivers become flyways

for ever more invasions from the continent's wetter margins.

Long line of water birds follow the shining trails deep into the heart.

The wave of life reaches its crest in Lake Eyre,

transformed again into a mighty inland sea.

Water now stands metres deep

where the dragons perform their courtly dance.

They've fled to the shores, and the lake belongs to the birds.

Close to shore, red-necked avocets

sweep through the mud for brine shrimps.

Further out, pelicans flock together to round up the teeming fish.

The floods have turned the salty desert into a vast bowl of rich soup

that supports breeding colonies of enormous size.

Just in this one place alone, 15,000 pelicans gather to breed.

In their regular habitats, pelicans and gulls breed only once a year.

But here they'll keep producing clutches till the food runs out.

There are broods at all stages of growth,

from naked hatchlings to young pelicans ready to take wing.

With no predators to worry them,

the greatest threat comes from the relentless heat.

Inevitably some will perish.

But for a time Lake Eyre offers what counts most- an abundance of food.

Elsewhere the rains have painted the desert with glorious colour.

These are the ephemeral short-lived deserf plants.

They sit out the dry years in time capsules -

dormant seeds which only rain can unlock.

Like this Sturt's deserf pea, their flowering will be brief.

And in their urgent need to attract pollinators,

they provide copious nectar.

The plants set great quantities of seed,

so there'll be enough to last till the next rains.

The flowers vanish as swiftly as they bloomed.

Their abundant seeds will feed many creatures for a long time to come.

Most of the desert animals come out only in the cool of the night.

Avoiding the daytime heat is one way these hopping mice

have made themselves at home in the sandy desert.

They also get their moisture from seeds.

And they've evolved a speedy hop to escape their enemies.

The hopping mice almost vanish in the dry years.

But plentiful food stimulates them to multiply rapidly.

They're very social creatures.

As many as 10 live together.

And their communal burrows are marvels of design.

As well as a main entrance, there are several escape holes,

and the main living area is a metre or so down

to avoid the extremes of hot and cold.

Young are born about four weeks after mating,

and part of the burrow becomes a nursery.

There are usually four in a litter,

and mothers suckling one brood may already be pregnant with another,

to reproduce even more quickly in this time of plenty.

Long after the rains, the water that soaked into the sands

sustains the arid region's most characteristic plant.

Spinifex is a uniquely Australian grass,

and covers a third of the interior.

This grasshopper mimics the foliage -

one of many creatures thriving within the spiky ramparts.

Deep taproots reach the moisture metres down,

and surface roots seek what few nutrients the soil has to offer.

As a result, spin if ex grows outwards in ever-widening rings.

In some places, the tussocks are linked

by these intriguing tunnel-like structures.

The runways are built by ants,

using grains of sand glued together with drops of spin if ex resin.

The covered trails shield the ants from sun and predators

on the way to their food supply in the spin if ex.

The ants protect the source of that food

with more sand and resin shelters.

Within them, minute sap-sucking insects are at work.

And this is the purpose of the ants' striving.

Sugary drops that are the waste product

of the insects feeding on the spin if ex sap.

Together, these tiny droplets provide all the energy needed

to drive an entire ant colony.

Using some of that energy to build runways is a wise precaution.

Ants without that protection may fall victim to the thorny devil.

On higher ground, there's sufficient vegetation

to supporf one of Australia's creative artists -

the western bower bird.

It shapes stalks of grass into an elegant bower,

and decorates them with desert fruits and berries.

The calls lure a female to the bower.

It's sole purpose is to impress her

And to serve as the arena

for the male's seductive display of song and dance.

When evening comes and the sands cool,

the pace of life among the spin if ex quickens.

Scorpions and other creatures

that have spent the day shielded from the sun

come out to hunt.

There's much food about, but also danger from other hunters.

The stripe-faced dunnart, a ferocious marsupial carnivore,

tackles almost anything - even a venomous centipede.

Dunnarts belong to an ancient marsupial group.

Although females do have a pouch,

it's too small to hold six growing young for long,

and some occasionally lose their grip.

Hanging on to mother is vitally important,

for dunnarts are always moving their home range

to keep up with the shifting supplies of insect food.

There's no advantage for dunnarts in having a regular nest or burrow,

but forth is little creature, a permanent home makes much sense.

The pebble mound mouse has reliable food

of seeds and tubers nearby.

And making a shelter from heat and enemies

is well worth even this prodigious labour.

Some of the stones are bigger than itself.

The stones are piled in a circle around the entrance.

On dewy nights, they collect moisture to drink.

The arid landscapes are a patchwork

made by millions of years of shifting and leaching soil,

from sands to stony ground.

Some retain more of the recent rains, some less.

The variations shape an astonishing diversify of life.

The mulga is the characteristic desert tree.

In favoured places, it produces a nectar

that's promoted an extraordinary animal response.

The nectar flows from small leaf glands,

and the ants it attracts keep leaf-eaters away.

Many ants come to feed on this mulga honey,

but because the flow varies considerably,

certain species have evolved an ingenious way of storing it.

In these unusual colonies, a special caste never leaves the nest,

but serves as living stores, their bellies hugely distended

into translucent honey pots.

When the nectar flow dries up,

the colony taps into the storage ants.

Stroking stimulates them to release the sweet liquid,

a tiny drop at a time.

Nursing ants only digest a little themselves

and feed the rest to the larvae in their care.

These busy insects are the most numerous inhabitants

of the arid lands.

About half of Australia's 5,000 species of ants live here.

Through some remarkable interactions with the plant world,

ants play a major part in shaping the environment,

carrying vast amounts of plant material,

and turning over the desert's meagre stores of nutrients.

But ants also exploit seeds,

and so short-lived plants produce huge quantities.

Some, at least, will escape the columns of foragers.

Some of the permanent plants

actually turn the ants' appetite to their advantage.

Desert trees won't thrive too close together in these poor soils,

so the seeds need to be dispersed.

Birds sometimes help by distributing seeds in their droppings.

But not these galahs - what they eat, they digest.

The remainder drops close to the trees.

Were they to sprout here, they would compete with their parent

for nutrients and moisture.

So ants have been enticed to carry them away.

The seeds themselves are ant-proof,

but they're packaged with an attractive food -

oil-rich bodies called elaiosomes.

In the underground chambers, nurses and other workers

labour together to remove the elaiosomes

and distribute the food to the rest of the colony.

The seeds are just waste,

and dumped on a rubbish heap in a distant gallery,

there to await the germinating touch of the next rains.

Some trees use the wind to get their seeds away.

Dispersing seeds gives the saplings more space to grow extensive roots

and make the most of the little moisture in these soils.

While the desert rivers have long stopped flowing,

masses of water run deep within the sandy beds -

enough to sustain the mighty river redgums.

All that's left on the surface is a chain of pools,

and most of those will vanish soon.

But the moisture flowing in the hidden rivers

supports generous stands of the river reds

through even the driest times.

Clouds of corellas roost in the gums on their travels around the interior,

following the movable feast of seeds and fruits.

It's not hard to think of these antics as pure play,

a means of whiling away the long hours between feeds.

Come breeding time in late winter, the flocks break up,

and the corella couples start looking for nesting hollows.

In this season of plenty,

every suitable hollow is soon occupied.

This pink cockatoo already has chicks in the nest.

It approaches cautiously so as not to alert predators.

The parents take it in turn to feed their youngsters.

There's still an abundance of seeds and fruits to collect,

and the birds make many trips a day

to pump the mash into the ever-beckoning young beaks.

The chicks are now a fortnight old.

In another month,

they'll be strong enough to follow their parents and fly.

Cockatoos are hardy and resilient birds,

well-designed to cope with the rigours of a rid life.

But they can't do without water.

This deeper pool will remain filled well into the dry times,

and it becomes the focus for much of the animal life

of the surrounding plains.

Red kangaroos can go without water for months

while there's fresh growth.

But when that's gone,

they need to come in for a drink once or twice a week.

Those other large plains dwellers, the emus,

need water nearly every day, once it gets really hot.

With so many kangaroos crowding together,

tussles often break out among rival bucks.

When nightfalls,

the cockatoos find resting places in the trees nearby.

And the big reds start moving back to their home ranges,

to feed in the cool of the night.

Grasses that grew tall in the wake of the rains have dried out,

and the green pick that the kangaroos need for moisture is harder to find.

The rising sun swiftly sends the temperature soaring to 40 degrees,

and the kangaroos move to what meagre shade they can find.

Such large and warm-blooded animals

should have real problems in this kind of heat,

yet the kangaroos cope remarkably well.

Oneway they keep cool is to lick parts of their body

where the blood vessels run close to the surface.

While the reds shelter in the shade,

the emus carry their own heat shields.

A double layer of feathers insulates them very efficiently,

and they can keep foraging through the heat of the day.

As the dry tightens its grip, food and water start to run out,

and the big reds have to move on or perish.

The awkward shuffle of their feeding gait

shifts into an effortless, fluid bounce.

The energy of each hop is stored in the hind leg tendons,

like a spring, to provide the propulsive force for the next.

For those that leave too late, the end is inevitable.

The diminishing resources simply won't sustain the numbers

that flourished in the time of plenfy.

It won't be long before the mud in this pool is baked hard again,

too hard for the animals to penetrate to the moisture below.

Soon the females will stop producing milk,

and the joeys will die.

But if the does manage to survive till conditions improve,

they'll quickly breed again.

For a time, the great die-off provides a feast

for the hunters and scavengers of the arid country.

Soaring on wings spanning two-and-a-half metres,

the mighty wedgetailed eagle, Australia's largest bird of prey,

scans the drying country for dead and dying animals.

Eagles feed on carrion, as well as live prey.

But even carrion is becoming scarce,

and hunger drives the birds into fierce competition

for the little food that remains.

Two years after it began to fill,

Lake Eyre, the great sea at the heart of the continent,

has dried to salt again.

Rows of dead fish mark the receding shores.

The legions of birds that flourished here have vanished,

the last of their broods abandoned.

These cormorant chicks had the misfortune

to be at the end of the line when the food ran out.

Nothing can save them, or the pelican broods.

But though the images speak of death,

they belie the fact that this so-called dead heart

can also be a place of extraordinary ferfility.

Even while the flood of life that came with the rains ebbs away,

the underlying pulse continues to beat strongly,

and the permanent inhabitants reappear.

The Lake Eyre dragons are coming back

now that the country is returning to its normal state of drought.

Lack of food Ieft the last of the pelican flights

without the strength to make their escape.

The winds suck away the last traces of moisture

and leave the plains bone dry.

But deep beneath the waves of sand and dust,

the hidden aquifers still run -

the lifeblood that keeps the arid heart beating.

Even on the salt beds of Lake Eyre, seemingly so dead,

life continues to proclaim its vigorous existence.

The Lake Eyre dragons have reclaimed their dominion.

The males reassert their dominance

with inflated impressions of their size.

Soon the hierarchy will be sorted out.

Each dragon will have its place in which to feed and breed...

...to live and die.

The challenge in the arid centre is not so much lack of rain,

as its unpredictability.

Over millions of years, plants and animals

came to meet that challenge in remarkable ways.

More than 50,000 years ago,

man set foot on the continent for the first time.

And his response to its challenge changed,

dramatically and forever, the nature of Australia.

Human song first sounded in Australia at least 50,000 years ago.

It heralded great changes for the island continent.

The origins of the first Australians are lost in time.

They came from somewhere in Asia,

gradually drifting south over many generations.

A final voyage across a strait,

narrower than now because the sea was lower,

brought them to north Australia.

Here they found a mix of the known and the new-

swamps where crocodiles lurked, like those of South-East Asia,

but also much that was strange.

Like the regions of their forefathers,

tropical Australia was ruled by monsoons,

but here, the annual swing from flood to dry

was far less predictable, far more savage.

The newcomers had to learn new ways, interpret new patterns

and weave them into a system of beliefs to explain this new land.

They identified with certain animals...

...and made them powerful tribal totems.

The first Australians were coastal wanderers.

Their descendants on the northern shores

still call themselves saltwater people.

They never moved far from the familiar sea -

that never-failing provider of good things to eat.

Among the skills imported by the early people

was a practised use of fire.

Through wielding flames to clear the land and aid the hunt,

they went on to change the face of Australia.

Before people came here, lightning was the only source of fire.

They believed lightning was made by Namarrgon, the 'Lightning Man'.

Namarrgon's stone axes hit the clouds to make sparks and thunder.

These are the storms of the build-up, the time before the wet.

The Aborigines call it Gunumeleng -

one of the many seasons they came to recognise.

Gunumeleng is also signalled by fainter sounds,

calling freshwater crocodiles to their nest.

The cries come from inside eggs buried in the river bank

some three months earlier.

They summon the females to excavate the nests,

so helping to release their offspring.

Not all the eggs survive.

Some are dug up by human foragers, who find them delicious.

But enough are left to ensure there'll continue to be crocodiles

and supplies of eggs.

Though capable of making it to the water on their own,

it's much safer and quicker for Mother to carry them.

The sound of sand being scraped away and the calls of the newly hatched

stimulate the rest of the brood to break free.

As soon as the maternal jaws release them,

the young crocodiles launch their lifelong hunting career,

starting on insects and working their way up.

But they also make attractive morsels themselves,

and the mother keeps watch, especially for other crocodiles

coming to investigate with cannibalistic intent.

Northern Australia lies on the edge of the monsoonal belt,

and the build-up is a fickle time.

Dry spells alternate with drenching rains.

Early falls soak in, then the soils saturate,

pools fill, rivers flow.

They flow out of the great Kakadu escarpment looming over the plains -

the edge of a vast and ancient plateau.

Its worn and cragged roof makes an enormous catchment

that feeds permanent pools and rivers.

Millions of years of monsoonal rains scoured and sculpted the sandstone,

and rivers carved deep gorges.

It's Gudjewg now-

the wet season proper in January and February.

It's a barren and forbidding place where Aborigines rarely come,

but it's also the source of much ferfility,

for the waters wash sediments down to the lowlands.

The cascades feed broad rivers which meander across the northern plains,

and the rising waters set the rhythm of life for many animals.

Pig-nosed turtle is one of them.

As the river rises, it cues a new generation into the world.

They spend most of their time submerged,

but they have to come out to bury their eggs.

Three months earlier, they dug their nests in the river bank.

The eggs of reptiles like crocodiles drown if they're flooded,

but pig-nosed turtles actually wait until they're completely immersed

before breaking out.

The sudden drop in oxygen passing through the shell

gives them their cue.

Eager for air,

they emerge into conditions best suited to their survival -

fast-flowing water to aid dispersal, and a wealth of food.

The rising waters also stimulate the magpie geese to gather and breed

and tell the people there's an abundance of goose eggs to collect.

The spike rushes grow tall in the swamps,

and the geese trample them into floating nests.

Crops of wild rice shoot up,

and in the steaming heat, their seeds ripen swiftly

to provide rich nourishment for the goslings.

But it won't last.

Parents and chicks are racing against time,

for the youngsters need to grow strong enough to fly

before the swamps begin to dry out and they have to move elsewhere.

The breeding of these ancient birds

follows the rise and fall of the waters,

and their seasonal wanderings

became part of the knowledge that guided Aboriginal walkabouts.

The season rolls on.

The storms of Gudjewg sweep in almost daily now...

...and with ever-increasing force.

Hot winds, heavy with moisture, drive in from the north-west,

pile the clouds into mountains...

...and hurl sheets of water across the landscape.

Day after day, this is the pattern of Gudjewg.

The very sky turns to water.

As the plains became impassable

to all but water birds and aquatic creatures,

the people moved to higher ground,

into the shelter of the escarpment's caves and overhangs.

The long, wet days gave time to reflect on their place in this world.

In painting the rock walls,

the people celebrated their deep sense of affinity with the land.

The record goes back unbroken for tens of thousands of years.

The torrential downpour sends so much water rushing across the plains

that even higher ground disappears under the swirling floods.

The swiftly rising waters send creatures scrambling

for whatever precarious perch they can find.

This sand goanna will need to hang on for many hours

before the floods subside.

Even capable swimmers

like highly venomous king brown snakes, and water goannas,

may find the currents too strong.

A mass of termites.

Odd companions, a python shares its refuge with a water rat.

In this common crisis, normal predatory instincts are suspended.

The flood plains merge into one vast, shallow lake.

The spreading waters replenish their ferfility

with sediments washed down from the escarpment.

But while the rains recharge the Top End's biological power,

they also bring hardship to many animals.

Rocky outcrops become islands

and maroon the wallabies that normally graze down on the plains.

Until the floods subside,

these short-eared rock wallabies will have a lean time of it.

Overtime, the lives of animals and people

wove into a complex fabric of myth and custom.

The rock paintings became the icons of Aboriginal belief

as well as a practical inventory of their most important creatures.

The rainbow serpent,

mythical carver of rivers and gorges as it slid across the landscape,

intertwines with pictures of animals hunted for food.

The record also traces changing climate.

As sea levels rose and estuaries came closer,

images of barramundi fish featured more.

In 2,000 generations of human occupation,

the view from the escarpment changed

as flood plains extended and retreated,

but the relentless rhythm of the tropical monsoons

continued to rule all of life here.

The mating call of the green tree frog

adds to the cacophony that marks the height of the wet season.

They need standing water,

and there are now plenty of pools where the females can spawn.

She lifts her rear end to scatter the eggs.

The male, clasping her firmly from behind, covers them with sperm.

Of the hundreds of eggs, only a few will survive.

The rest will feed other creatures.

Deep within the escarpment, other animals breed.

The walls of some caves crawl with bats.

More than 100,000 bent wings crowd together,

all of them females and their young.

The females came here early in the wet to give birth.

Now their offspring are on the verge of flight.

But for the moment, they're still left behind in a creche

while the mothers make their evening exodus, streaming out to feed.

The creche is far from safe.

Below the bat-covered walls, green tree frogs lurk,

waiting for a baby to fall.

The young bats are only tiny.

Even so, they make quite a mouthful for the frog,

which is about the size of a man's fist.

The dense flow of bat flesh attracts other predators.

Pythons and venomous snakes cast around in the stream

like lethal fishing rods.

The snake throws a deadly coil around the victim,

then dislocates its jaws to swallow the bat whole.

The meal lasts the snake many weeks.

The streams of breeding bats are an endless source of food

at this time of Gudjewg.

Their comings and goings meld into the flow of the seasons -

part of the nature of Australia for 25 million years

when bats first flew in from Asia.

They're particularly abundant in the tropical north,

flying foxes especially.

At dawn, tens of thousands return to their tree camps

to roost for the day.

They're the largest of the bats,

very different from the small insect-hunters

that inhabit the caves.

Their flesh is as sweet and succulent

as the flowers and fruits upon which they feed,

and highly prized by human hunters.

Flying foxes, also called fruit bats, are found throughout South-East Asia,

and raiding their camps remained an important part of life

for the Aborigines of northern Australia.

The fruit bats have their own seasonal rhythms.

As the monsoonal rains fall away and the end of the wet draws near,

males begin to feel the urge to mate, and females respond...eventually.

Having to mate upside down

might seem to add an extra dimension of difficulty,

but for the fruit bats, there's no other way.

The pair may mate four times in half an hour

and several more times during the day.

During that time, the immediate space around them is inviolate territory.

Soon, the bats shift camp

to follow the move able feast of flowers and fruits

as the season turns.

With the heaviest rains passed,

the Aboriginal year moves to Banggerreng -

a time of brooding calm pierced by sudden storms.

The waterlilies flower in the paperbark swamps,

and on their broad leaves, jacana eggs are about to hatch.

While the cock bird broods the eggs,

his mate jealously keeps other hens away.

A few days later, the jacana chicks take their first tentative measure

of this floating, leafy world.

The father has a wonderful way of keeping his chicks safe.

At the first sign of danger, he calls and sweeps them under his wing.

Only their legs betray their presence,

already with the long toes that make jacanas seem to walk on water.

In these closing days of the wet,

the humid air is heavy with the scent of flowers, vibrant with insects.

In a final spurt, the spear grass shoots to twice a man's height.

But the storms of Banggerreng will soon knock it down.

For the early people and their descendants,

this was a good time of year to collect wild honey.

As the season turns to dry, fire begins to dominate the daily round.

The art of making it came with the ancestors.

Using it became an ever more important skill,

on the small scale and the large.

Though the native bees are small and have no sting,

flame and smoke help clear the way into the sweet heart of the nest.

Fire sticks were also put to larger use,

and the effects reached into the very essence of the landscape.

When the winds turn cool and blow from the south-east,

it's Yegge -the burning time.

Fire cleaned the country of the spear grass,

smashed into an impenetrable tangle by the storms of Banggerreng.

Natural fires, sparked by lightning,

mostly flared towards the end of the dry.

The Aborigines burnt early in the season and altered the landscape.

They lit their first fires when dew still fell.

It dampened the flames at night.

Over the years, Aboriginal burning created a mosaic of plant growth

that fostered a range of valuable game.

The smouldering aftermath

also brings immediate benefits to the hunter gatherers -

human and animal alike.

Fried insects make rich pickings

and bring game within a spear's throw.

Alert eyes spot barbecued meals of small lizards and snakes.

A scatter of fresh leaves protects the human feet.

The scavenging birds

have nothing between theirs and the glowing cinders.

The patterns of Aboriginal burning

brought lasting change to the nature of Australia,

evident on the small scale through the hunting birds

that prosper as fire-followers,

and on the larger scale through a shift in vegetation,

with fire-tolerant eucalypts thriving

where plants sensitive to scorching could not.

The wood lands seem dead after fire.

But within days, the gums green up again.

The spread of the eucalypts was aided by another force,

less obvious and dramatic than fire, but just as powerful.

These castles of clay conceal that hidden power.

They're the strongholds of the termites.

And it was fire that destroyed the bark's defences,

and opened the way for termites to enter the tree.

Deep within lies the colony's pulsating heart-

the termite queen.

She produces a ceaseless flow of eggs to keep the colony growing

and issues a stream of chemical commands to govern her subjects.

Workers stack the precious eggs in nurseries

and tend them till they hatch.

Other workers look after the larvae,

preparing them for their allotted task as workers, soldiers,

and once a year,

they tend a special brood of future kings and queens.

Workers form the largest class, labouring endlessly,

turning the eucalypt's structural heartwood

into energy that drives the entire colony.

Their sharp jaws slice into the tough fibres,

and the hindgut breaks it down into digestible nutrients.

Some goes to feed other termites - the queen, soldiers and juveniles.

The massed jaws of the worker brigades

swiftly excavate the heartwood,

chewing their way up inside the main trunk

and out into the branches.

The waste is moulded into more galleries and egg chambers.

Within a few years, the eucalypt is completely hollow.

In places, breaking branches open away to the outside,

branches that provide Aborigines with hollow wood

to craft into didgeridoos.

Now the legions move out,

digging tunnels to seek fresh supplies

in the surrounding trees.

They too are hollowed out and the colony grows ever larger.

Strange as it may seem,

not only do the eucalypts survive this attack on their very heart,

they actually benefit from it.

The termites might appear to be parasites,

but, in fact, the hollows they chew out

are a kind of payment for their board and lodging.

Hollows attract birds and other animals

to nest and shelter.

Their spillings and droppings make valuable fertiliser.

The trees absorb these bonus rations

and grow well in the soils of this higher ground,

which are otherwise extremely poor.

The dollar bird takes insects on the wing.

It migrates from New Guinea

and joins the local birds to take advantage of the nest holes

created by the termites.

Individually, the fragments don't amount to much.

Together, the leftovers and litter of nesting birds -

like this forest kingfisher-

add up to a feast when taken into the bowels of the tree.

Over time, it gives eucalypts a great competitive advantage

over trees that don't have this curious partnership with termites.

As well as birds,

half the local mammals use hollows as lairs,

turning the trees into a well-stocked larder.

Aboriginal hunters need only a fire stick

to smoke the game out.

Night reveals other hunters.

Some holes excavated by termites

make nurseries for quoits and their young.

When they're nearly full-grown,

the youngsters go piggyback when Mother goes hunting.

For the young quolls, catching insects and keeping them

are the first big steps on the road to independence.

The adult quoits tend to use the same hollow all year round,

and when they come home,

the waste they excrete helps to nourish their host-

an organic form of rent.

But eventually the termites weaken the tree so much

that fire or a storm sends it crashing.

The termite castle smashes open

and armies of green tree ants come racing in to devour the workers.

The sudden onslaught temporarily overwhelms the termite soldiers,

but soon they'll repel the invaders.

And if the queen survived, the colony will rebuild.

The season moves to Wurrgeng -

hot, still and no rain.

The flood plains are dry.

The streams stop flowing.

The waters withdraw to the deeper swamps and billabongs.

And the magpie geese follow.

For the first Australians, the sight of such vast flocks

meant more than abundance.

Watching them, stalking them,

inspired dances of a natural grace matched only by the birds themselves.

Trumpeting, tossing sprays of leaves, the brolgas dance around the year

as parf of the courtship at breeding time

and to enhance the bond between pairs wherever the birds flock together.

The dry tightens its grip,

but the mud around the swamps remains soft enough

for the brolgas' long beaks to spear up tubers.

In a week or so, it will be too hard, and the birds move on.

These stately waders breed in the wet season

when it's easier for growing chicks to find food.

By contrast, hunting birds like sea eagles

build their nests and have their chicks in the dry,

snatching up nesting material with the same easy swoop

used to catch fish.

Wurrgeng is a hard time for the water creatures.

The diminishing lagoons cram them together

and make them easy to catch.

The eagles hook up fish and turtles in plenty

and they keep their young well fed.

When the wet season returns,

it'll bring an abundance of other game,

especially newly hatched goslings,

and there'll be plentiful opportunity

for the young eagles to learn to hunt.

The season changes to Gurrung - the hottest time of the year.

The flying foxes prepare to give birth.

The baby's head has just emerged

and the mother arches upwards to clean it with her tongue.

The baby may stay like this for more than an hour.

It's a tense time for both mother and young.

Should the newborn fall, it'll be to its death,

for many predators lurk nearby.

When finally all of the baby emerges, Mother has to be ready to catch it.

And she does.

This youngster, at least, is safe.

She cleans off the last of the afterbirth

and helps the infant find her nipples located in the armpits

where it can cling in safety when Mother goes flying.

Barbed growths inside their claws

help young bats hook into their mother's fur

and their teeth curve inwards to hang on to the nipple.

Independence comes swiftly.

Even at two weeks,

it's already trying for its own grip on the tree.

Until the young bat's ready to fly, at around three months,

the maternal wings always remain ready to enfold it

and keep it safe.

The wings help the flying foxes to keep cool.

They fan the air and, folded, make an excellent heat shield.

The searing heat has sucked all the moisture

from the swamps and flood plains,

and the only water left

is in the permanent soaks and deeper billabongs.

Birds from all over the region converge on these precious oases.

Red-tailed black cockatoos wander from soak to billabong

in search of a drink.

Aborigines believed the flaming red of the tails was fire -

the means by which the birds carried it round the land.

While all around the plains lie parched,

these Iast wetlands provide rich bounfy.

Each billabong attracts its own progression of visitors.

Each bird's bill is designed to harvest different food

at different depths in different ways.

This jabiru has caught a water snake.

As the waters recede, the birds need to keep moving

to find the food that suits their particular way of feeding.

These royal spoonbills come to feast

on the rich broth of this shallow lagoon,

sweeping through the water

to sift out small fish and crustaceans.

Pelicans flock together on a deeper billabong

and round up shoals offish

and scoop them up with capacious beaks.

Cormorants patrol alongside ready to snatch any that escape.

There are as many fishing techniques as there are birds.

A pied heron takes extraordinary steps to secure a safe vantage point.

The waters fall ever further exposing new crops of food.

The plant-eating birds have their feast now.

And flocks grow by the thousands every day.

The sound of the whistling ducks is made by voices and wings together,

rising and falling as they move between grazing and resting.

The massed song is a spectacular celebration

of the great ferfility of these northern wetlands.

Clouds of birds darken the sky over these last waters.

Now's the time too

when magpie geese assemble in their hundreds of thousands,

a sure sign that the first storms of Gunumeleng are not far away,

that the season's coming full cycle.

The vanishing water leaves great stretches of soft mud

with abundant bulbs and tubers for the birds to rip up

with their hooked bills.

The massing of the magpie geese is one of the biological events

that mark the turning of the seasons in the Far North.

For the first Australians, they became part of the calendar

which set the rhythm of their own rounds and celebrations.

Knowing the nature of the land was basic to their survival.

But in learning to live with it,

the skills they acquired and practised over 2,000 generations

set profound changes in train.

Fire became the symbolic centre

of their spiritual and ceremonial life -

their tribal temple.

Far from being a timeless people in a timeless land,

their impact was as great as that of any people on earth.

And the chief instrument of that impact was fire.

Aboriginal burning altered the mix of plants in the landscape.

The fire-tolerant eucalypts extended their hold,

and the wood lands opened out.

As the Aboriginal people grew in numbers

and spread across the vastness of Australia,

the migrations were marked by trails of fire

and the hunting birds that followed them.

The fire skills perfected in the monsoonal north

were carried to new terrain and different climates.

The fire stick reached into every plant and animal community

in every part of the continent,

from the coastal regions to the dry interior.

Many animals profited from the changes.

Many others vanished for all time.

In all this vast land,

there were only ever less than 1 million people at any moment,

yet in their 50,000 years, the Aborigines' way with fire

changed the face of the continent.

Evil spirits they called these willy-willys.

But they were tornadoes of ash and dust

unleashed by the heat of their own fires.

Now a new storm was about to break-

the whirlwind of the European invasion

would race across the continent with unprecedented speed,

and pose the most severe challenge yet to the nature of Australia.