(SLOW, INTERWEAVING ORCHESTRAL MUSIC)
(RIPPLING PIANO AND STRINGS MUSIC)
(DISTANT HARSH SCREECHING)
50 million years ago,
all of Australia was covered by a mantle of dense rainforest.
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.
(BIRDS CALL, DISTANT WATERFALL THUNDERS)
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.
(PARROTS SCREECH)
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.
(BIRD CAROLS)
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 art 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.
(Trills rapidly)
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.
(Male flutters wings) (Cheeps piercingly)
As well as disperse seeds,
birds play another important 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 honeyeaters.
A rich flow of nectar rewards them for taking pollen between trees
and fertilising the flowers.
(HAUNTING MUSIC)
(INSECTS CHIRP)
When night falls, the mammals emerge.
Among them are tree kangaroos.
Despite their name, they spend as much time on the ground as aloft.
(Huffs)
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 honeyeaters,
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 ringtail relishes the flowers
as a welcome break from its usual fare of leaves.
Possums first evolved in the rainforests.
And over time, 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.
(SONOROUS MUSIC)
Australia started to dry out.
And most of the rainforests 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.
(SOARING MUSIC)
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 rainforest 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.
(VARIETY OF BIRD CALLS IN SUCCESSION)
In fact, all the songs have but one singer, the lyrebird,
a uniquely Australian master of both mimicry and display.
(Cries shrilly)
(Calls piercingly)
The aim is to persuade females nearby
that the cock bird is a fine and healthy specimen,
well worthy of fathering their chicks.
(Mimics several birds)
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.
(ENCHANTING MUSIC)
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.
(GENTLE DESCENDING MUSIC)
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.
(TRANQUIL SOARING MUSIC)
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.
(Gliders sniff deeply)
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.
(Squeaks)
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 rainforest 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.
(WATER RUSHES)
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.
Caddis-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 caddis 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 rainforest 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 rainforest.
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 rainforest ancestors, gums don't make fleshy fruit.
Instead, seeds are packed in woody cases to stop them drying out.
(PARROTS CHATTER AND TRILL)
A colourful company of cockatoos, parakeets and lorikeets
feeds on gumnuts 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.
(FIRE ROARS)
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.
(BELLBIRDS SING)
(INCREASING CHORUS OF BIRDSONG)
(TRIPPING BASSOON AND OBOE)
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.
(TRIPPING BASSOON AND OBOE CONTINUE)
Because the eucalypts can put out new growth repeatedly,
they seem to suffer more insect attack than many other trees.
(PLAYFUL WOODWIND MELOD Y)
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 for that 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.
(GENTLE CLASSICAL MUSIC)
(BIRDSONG)
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.
(GENTLE CLASSICAL MUSIC CONTINUES)
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 partnership with a parasitic plant - the mistletoe.
(Chicks chirp)
The mistletoe taps into the eucalypts for its own growth
and it employs the mistletoe bird to spread its seeds and gain a roothold.
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.
(GENTLE WOODWIND MUSIC)
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 rainforest ringtail possums,
only the common ringtail 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 for this antechinus.
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 antechinus -
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 antechinus, 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.
(KOOKABURRAS LAUGH)
The challenge of procreation in these woodlands
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 a way 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.
(Squawks)
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.
(GENTLE CLASSICAL MUSIC)
Beneath the eucalypts live banksias -
ancient plants going back to the primeval rainforest.
(FLIGHTY OBOE MUSIC)
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.
(GENTLE CLASSICAL MUSIC)
In these ancient leached soils, so poor they're almost pure sand,
climatic hardships created an evolutionary nursery without parallel.
(BIRDSONG)
So many flowers eager to attract pollinators
have fostered a matching diversity 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.
(Wasp buzzes)
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 honeyeaters 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 honeyeaters,
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 honeyeating birds,
it has a long tongue fitted with a brush at the end.
The partnership began in the ancestral rainforests,
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 numbat.
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 numbat
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.
(Koalas snarl and growl)
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.
(Both snarl and growl)
(Growls and howls deeply)
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 of fathering a royal cub.
(Growls repeatedly)
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 gumleaves -
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.
(KOOKABURRAS LAUGH)