0:00:33 > 0:00:37In this driest of continents there's a vast green landscape
0:00:37 > 0:00:41that stretches for thousands of kilometres round Australia's edge.
0:00:41 > 0:00:47This is the Australian bush - its most characteristic landscape.
0:00:50 > 0:00:55The first European settlers, pushing through it 200 years ago,
0:00:55 > 0:00:57didn't like the bush.
0:00:57 > 0:01:01It was daunting and alien, and so big you could get lost and die.
0:01:02 > 0:01:07In these hot, endless forests, the very trees seemed to droop.
0:01:07 > 0:01:11These, they said, were "forests in rags".
0:01:11 > 0:01:14And from one end of the country to another,
0:01:14 > 0:01:16they all looked strangely alike...
0:01:18 > 0:01:23..because these thousands of kilometres of green
0:01:23 > 0:01:28are dominated by just one kind of tree - the eucalypt, or gumtree.
0:01:28 > 0:01:30And around these trees
0:01:30 > 0:01:34live Australia's oddest and most charismatic animals.
0:01:35 > 0:01:38The eucalypt has transformed itself
0:01:38 > 0:01:43into 700 different species - some growing monstrously tall.
0:01:45 > 0:01:48Some thrive in the baking north,
0:01:48 > 0:01:53some in the chilly south, and some even grow in the snow.
0:02:01 > 0:02:04Wherever they find a foothold,
0:02:04 > 0:02:07gumtrees attract a vast assortment of wildlife.
0:02:08 > 0:02:13Australia is the eucalypt's native home - it was born here.
0:02:13 > 0:02:15But how has this peculiar tree
0:02:15 > 0:02:19managed to spread itself over the entire continent?
0:02:19 > 0:02:22And why is it that so much lives around it?
0:02:28 > 0:02:33Fifty million years ago, when the climate was wetter,
0:02:33 > 0:02:36much of Australia was covered in rainforest.
0:02:38 > 0:02:42In this lush land eucalypts barely existed.
0:02:42 > 0:02:45But the continent was gradually drying out
0:02:45 > 0:02:48and the eucalypts seized their chance.
0:02:48 > 0:02:53Far better able to cope with the harsh new conditions,
0:02:53 > 0:02:55they rushed out and thrived.
0:02:58 > 0:03:02Now eucalypt bushland encircles Australia
0:03:02 > 0:03:05in an almost unbroken line.
0:03:11 > 0:03:15But in this vast land, every gumtree landscape is different.
0:03:20 > 0:03:25The tropical north is Crocodile Dundee country,
0:03:25 > 0:03:29where the year swings between months of dryness and weeks of rain.
0:03:34 > 0:03:38It's a hot and sultry place.
0:03:40 > 0:03:42But eucalypts thrive here.
0:03:42 > 0:03:47And up in these trees live big and watchful lizards.
0:03:48 > 0:03:52A frilled lizard can spot its prey from three metres up a tree.
0:03:52 > 0:03:56All it has to do then is jump down and catch it.
0:04:04 > 0:04:07For their size and big teeth,
0:04:07 > 0:04:10frilled lizards have moderate tastes.
0:04:10 > 0:04:13They eat almost nothing but insects.
0:04:18 > 0:04:22A good feeding area like this is worth hanging onto.
0:04:22 > 0:04:26A frilled lizard won't tolerate a rival in its territory.
0:04:35 > 0:04:40Competing males hiss and lash their tails, raising their frills
0:04:40 > 0:04:44to make themselves look bigger than they really are.
0:04:44 > 0:04:47But it's dangerous on the ground.
0:04:54 > 0:04:58Whistling kites eat frilled lizards round here.
0:05:06 > 0:05:10All that frill-waving and hissing forgotten,
0:05:10 > 0:05:14the lizards make a two-legged dash back to the safety of their trees.
0:05:23 > 0:05:27The eucalypt's rough bark helps them get a grip as they climb.
0:05:34 > 0:05:37Once safely back up there,
0:05:37 > 0:05:41they make themselves look as small and inconspicuous as possible.
0:05:48 > 0:05:52And for 90% of their lives, this is where they stay,
0:05:52 > 0:05:56using the gumtrees as lookout posts and bolt holes.
0:06:05 > 0:06:08In these tropical northern woodlands,
0:06:08 > 0:06:12the temperature most days can top 30 degrees Celsius.
0:06:13 > 0:06:17But Australia is a land of enormous contrasts.
0:06:17 > 0:06:21Move from the far north to the far south,
0:06:21 > 0:06:25at the same time of year, and the change couldn't be more extreme.
0:06:31 > 0:06:35Here it's mountainous and metres deep in snow.
0:06:35 > 0:06:39Australia is so big, it can have baking heat in one place
0:06:39 > 0:06:44and winter in another. And eucalypts can cope with both.
0:06:45 > 0:06:49On the ancient mountains of Australia's southern Alps
0:06:49 > 0:06:51grow woodlands of snow gums.
0:06:55 > 0:06:59They can tolerate temperatures as low as minus 20,
0:06:59 > 0:07:02twisted and dwarfed by the wind and the cold.
0:07:06 > 0:07:10And in these snowy uplands, among these hardy trees,
0:07:10 > 0:07:13there are parrots.
0:07:23 > 0:07:27Gang-gang cockatoos feast on the eucalypt's hard seed capsules,
0:07:27 > 0:07:31cracking them open with their strong beaks.
0:07:31 > 0:07:34Many birds move to lower ground in winter,
0:07:34 > 0:07:40but gang-gangs brave the cold to take advantage of this valuable food.
0:07:44 > 0:07:48Up here, the weather can quickly turn nasty.
0:07:48 > 0:07:51The mountains are snowbound for months of the year.
0:07:51 > 0:07:53This is no place for wimps.
0:07:57 > 0:08:00But wombats, with their thick fur,
0:08:00 > 0:08:04trudge out to dig for grass buried under the snow.
0:08:07 > 0:08:11And up in the trees, the gang-gangs keep on feeding,
0:08:11 > 0:08:15even with their jaunty feathers all caked in ice.
0:08:20 > 0:08:24The red-headed males, grey-headed females and blushing juveniles
0:08:24 > 0:08:27pick away together at the gumtree feast.
0:08:45 > 0:08:47Australia's south-eastern mountains
0:08:47 > 0:08:52trap the cold and soaking air that blows in from the southern seas.
0:08:52 > 0:08:54Moisture falls as snow and rain.
0:08:57 > 0:09:01Australia may be the driest inhabited continent on Earth,
0:09:01 > 0:09:03but here there's plenty of water.
0:09:10 > 0:09:13And on the lower slopes of these misty mountains,
0:09:13 > 0:09:16the trees grow monumentally tall.
0:09:21 > 0:09:24With wetter weather and slightly better soil,
0:09:24 > 0:09:27they reach a height of over 100m.
0:09:27 > 0:09:31Towering above the rest of the forest greenery,
0:09:31 > 0:09:35these trees can grow over a metre a year.
0:09:35 > 0:09:40These are the tallest hardwood trees in the world -
0:09:40 > 0:09:42and they're eucalypts.
0:09:47 > 0:09:50The first British settlers called them mountain ash,
0:09:50 > 0:09:54because they were homesick for the old country.
0:09:55 > 0:09:59And they do have the feeling of lush European forests -
0:09:59 > 0:10:02until the inhabitants turn up.
0:10:11 > 0:10:13VARIOUS CALLS
0:10:13 > 0:10:17From the dense, damp undergrowth comes a strange recital.
0:10:17 > 0:10:20Not a flock of different birds, but just one.
0:10:20 > 0:10:23The superb lyrebird is striking up.
0:10:28 > 0:10:31Male lyrebirds mimic the other birds around them,
0:10:31 > 0:10:35pulling their songs together into an impressive repertoire.
0:10:35 > 0:10:39Wattlebirds, honeyeaters, whip birds, kookaburras -
0:10:39 > 0:10:41he does them all!
0:10:41 > 0:10:43CROAKS AND WHISTLES
0:10:44 > 0:10:46WHIRRING CALL
0:10:46 > 0:10:49CACKLES
0:10:52 > 0:10:55WHISTLES
0:10:55 > 0:10:59His powerful voice can carry up to a kilometre through the forest.
0:11:01 > 0:11:05Clearing a stage for himself on a mound of earth,
0:11:05 > 0:11:07he belts out his performance.
0:11:07 > 0:11:11All this effort is to attract as many females as possible.
0:11:11 > 0:11:14He'll carry on like this for hours.
0:11:23 > 0:11:27When darkness falls and the lyrebirds are asleep in the trees,
0:11:27 > 0:11:30a different set of wildlife emerges.
0:11:32 > 0:11:37Mountain ash can live to be 300 years old. Many are full of holes.
0:11:37 > 0:11:41At night, these holes produce some curious animals.
0:11:44 > 0:11:49Australia has no monkeys - instead it has these.
0:11:49 > 0:11:53They're possums, and just after dark,
0:11:53 > 0:11:56they come out of their gumtree nests to feed.
0:11:58 > 0:12:02Tiny Leadbeater's possums zip through the lower trees
0:12:02 > 0:12:04looking for insects and sap.
0:12:10 > 0:12:14They're sociable animals, and eight or more may share a single hollow.
0:12:21 > 0:12:24Hollow eucalypts are desirable homes,
0:12:24 > 0:12:28but to live in these big trees, you have to be agile.
0:12:35 > 0:12:38Mountain brush-tailed possums are far bigger and slower,
0:12:38 > 0:12:41but they're competent climbers. They're tree-dwellers,
0:12:41 > 0:12:44but they spend a fair bit of time on the forest floor,
0:12:44 > 0:12:49coming down in the darkness to eat fungi and fallen seeds.
0:12:55 > 0:12:59It's tricky having to negotiate these dense trees by yourself,
0:12:59 > 0:13:04but imagine what it's like having to haul a baby around with you.
0:13:05 > 0:13:08This female has carried her baby in her pouch for six months,
0:13:08 > 0:13:12and it will ride on her back for another two.
0:13:21 > 0:13:24But alongside her, and safe from attack by owls,
0:13:24 > 0:13:28it learns all the skills it will need for a life on its own.
0:13:30 > 0:13:33For now it can feast on fallen seeds,
0:13:33 > 0:13:37and it might even have a quick suckle while Mum's grooming herself
0:13:37 > 0:13:40with her huge tree-climber's feet.
0:13:50 > 0:13:53And before daylight comes,
0:13:53 > 0:13:57mother and baby will vanish into the safety of their gumtree den.
0:14:11 > 0:14:15These giant eucalypts thrive here because there's more water
0:14:15 > 0:14:19and fractionally better soil than in other parts of Australia.
0:14:19 > 0:14:23But though eucalypts do well in the wetter fringes of the land,
0:14:23 > 0:14:25they don't just stop there.
0:14:37 > 0:14:41The further you move inland, the more arid the scenery becomes.
0:14:44 > 0:14:49The typical Australian landscape is hot, dry and sandy -
0:14:49 > 0:14:52not an easy place to put down roots.
0:14:52 > 0:14:55But gumtrees pop up almost everywhere.
0:14:55 > 0:14:58They grow alongside trickles of inland rivers,
0:14:58 > 0:15:02where there's barely any water flowing, putting down deep roots
0:15:02 > 0:15:04to suck what moisture there is.
0:15:06 > 0:15:09They grow in the outback,
0:15:09 > 0:15:13where conditions couldn't be more different from the misty highlands.
0:15:13 > 0:15:15There's a 10th of the rainfall,
0:15:15 > 0:15:19and the soil is thin, worn down by sheer age.
0:15:27 > 0:15:31A white trunk reflects the glare of the sun,
0:15:31 > 0:15:35and leaves hang down to avoid overheating.
0:15:35 > 0:15:40But when daytime temperatures climb to 40 plus,
0:15:40 > 0:15:44red kangaroos are grateful for even this thin shade.
0:16:00 > 0:16:05Once parked, a big red will spend its day under the trees,
0:16:05 > 0:16:09until the sun goes down and the land cools again.
0:16:16 > 0:16:20Even here, among the red rocks of the centre,
0:16:20 > 0:16:22gumtrees have a toehold.
0:16:25 > 0:16:28This most ethereal tree is a ghost gum,
0:16:28 > 0:16:31and it grows in Australia's heart.
0:16:31 > 0:16:35It clings to crumbling gorges, where water is scarce
0:16:35 > 0:16:37and only the hardiest survive.
0:16:42 > 0:16:45This is one tough tree.
0:16:48 > 0:16:51But even the scrawniest of eucalypts
0:16:51 > 0:16:54in the most desiccated places have a surprise.
0:16:56 > 0:17:00They produce the most beautiful nectar-filled flowers.
0:17:08 > 0:17:12The colours and shapes are as diverse as the trees themselves,
0:17:12 > 0:17:16each attractive to different animal visitors.
0:17:16 > 0:17:18Many flowers are cup-shaped,
0:17:18 > 0:17:22allowing insects inside to gather pollen and nectar.
0:17:26 > 0:17:31Blossoms appear on different trees at different times of year,
0:17:31 > 0:17:33providing an ever-moving feast.
0:17:33 > 0:17:36Lorikeets and honeyeaters are energetic nectar specialists -
0:17:36 > 0:17:40always on the lookout for new flowers to drink at.
0:17:56 > 0:17:58Eucalypts are such a draw
0:17:58 > 0:18:03that flying foxes in the tropics will fly 50 kilometres every night,
0:18:03 > 0:18:07moving from flowering tree to flowering tree to feed.
0:18:23 > 0:18:26In return for this feast of nectar,
0:18:26 > 0:18:30the trees use these big bats as couriers, covering them in pollen,
0:18:30 > 0:18:34which they'll leave at the flowers of the next tree they visit.
0:18:44 > 0:18:49Even if you can't fly, eucalypt flowers are worth the climb.
0:18:49 > 0:18:52The tiny western pygmy possum in southern Australia
0:18:52 > 0:18:55emerges at nightfall.
0:18:55 > 0:18:59It eats plenty of insects, but it's also very partial to nectar.
0:19:12 > 0:19:15Weighing little more than a boiled sweet,
0:19:15 > 0:19:17and not much bigger than the flowers themselves,
0:19:17 > 0:19:21it laps up the nectar with a tongue shaped like a brush.
0:19:30 > 0:19:33This possum is a strictly nocturnal animal.
0:19:33 > 0:19:38At dawn, it goes to its tree-hollow nest - made of gum leaves.
0:19:48 > 0:19:51Nectar is cheap for these trees to produce,
0:19:51 > 0:19:54and they give it away freely.
0:19:54 > 0:19:57But their leaves are another story.
0:19:59 > 0:20:03They're precious in a land where nutrients are in short supply,
0:20:03 > 0:20:07and the eucalypts do their best to hang on to them.
0:20:07 > 0:20:11They're hard and full of toxic chemicals, including the oils -
0:20:11 > 0:20:14which give them their distinctive smell.
0:20:14 > 0:20:19It's enough to stop most animals eating them, but not all.
0:20:22 > 0:20:25And this is the classic gum eater.
0:20:25 > 0:20:28In fact, it doesn't eat much else.
0:20:34 > 0:20:37Koalas evolved with the eucalypts,
0:20:37 > 0:20:40and they can just about cope with their leaves,
0:20:40 > 0:20:44thanks to a large and complicated digestive system.
0:20:45 > 0:20:47But it has to be careful -
0:20:47 > 0:20:52before it eats, it has a sniff to check the chemical strength.
0:20:53 > 0:20:56And those leaves are so hard,
0:20:56 > 0:21:00it has to chew more than 16,000 times a day to break them down.
0:21:00 > 0:21:04An old koala will eventually wear out its teeth completely.
0:21:14 > 0:21:17It's all such hard work for so little nutrients,
0:21:17 > 0:21:22that koalas have to sleep for 20 hours a day, just to save energy.
0:21:43 > 0:21:46This is a highly specialised way of life.
0:21:46 > 0:21:49A tiny baby koala, barely out of the pouch,
0:21:49 > 0:21:53won't be able to cope with eating gum leaves straightaway.
0:21:53 > 0:21:57First, it must have a snack of its mother's special droppings.
0:22:05 > 0:22:10Disgusting as it may seem, the baby koala wouldn't survive otherwise.
0:22:10 > 0:22:13By eating "pap", it's taking in vital bacteria
0:22:13 > 0:22:16passed from its mother's gut,
0:22:16 > 0:22:19which will later help it digest those leaves.
0:22:20 > 0:22:24It's a bit like eating live yoghurt.
0:22:38 > 0:22:40When you're this tiny,
0:22:40 > 0:22:44it's sometimes hard to work out which way is up,
0:22:44 > 0:22:48which is especially hazardous when you're ten metres above the ground.
0:23:00 > 0:23:04And koala mums are pretty laid-back when it comes to childcare.
0:23:04 > 0:23:09But at six months, this baby has to get used to a life in the trees.
0:23:09 > 0:23:13If it's lucky, it will live to be 15 years old.
0:23:17 > 0:23:21Young koalas stay dependent on their mothers for a whole year,
0:23:21 > 0:23:25but as they grow, they start to become more adventurous.
0:23:40 > 0:23:45In spite of the hazards, most koalas survive their childhood,
0:23:45 > 0:23:48and the bond with their mothers is usually broken
0:23:48 > 0:23:51only when she gives birth to her next baby.
0:23:53 > 0:23:55Koalas don't make dens,
0:23:55 > 0:24:00so a mother has nowhere that she can leave her offspring in safety.
0:24:00 > 0:24:04She has to carry it round with her as she moves from tree to tree.
0:24:17 > 0:24:21Most mothers carry their children on their back,
0:24:21 > 0:24:25but others have slightly more unconventional ways.
0:24:33 > 0:24:38And when your baby can be a quarter of your weight,
0:24:38 > 0:24:41that's a lot to heave around.
0:24:51 > 0:24:53It's all very hard work.
0:24:54 > 0:24:57Gumtrees tend to grow widely spaced apart,
0:24:57 > 0:25:02but other woodland dwellers have cracked the problem of travelling.
0:25:04 > 0:25:06They glide.
0:25:11 > 0:25:15A yellow-bellied glider can sail as far as 120 metres
0:25:15 > 0:25:18from tree to tree, making strange noises in the night.
0:25:25 > 0:25:27It spends its days inside hollow trees,
0:25:27 > 0:25:31only emerging when darkness falls.
0:25:39 > 0:25:43A cape of skin stretches from wrists to ankles,
0:25:43 > 0:25:46and this is what gives it lift.
0:25:46 > 0:25:50As it comes in to land, it swings its limbs forward, touching down
0:25:50 > 0:25:53with all four feet together.
0:25:53 > 0:25:56Gripping toes and big claws help it to hang on.
0:26:04 > 0:26:06It's out and about to feed.
0:26:06 > 0:26:11Yellow-bellied gliders are fond of insects and eucalypt nectar.
0:26:11 > 0:26:15But they also bite notches in the bark of trees
0:26:15 > 0:26:19and eat the oozing sap - often in the company of a few relatives.
0:26:29 > 0:26:33On such a meagre diet, gliding is a low-energy way to travel.
0:26:43 > 0:26:46This is an economical place.
0:26:48 > 0:26:51Eucalypts are almost all evergreen,
0:26:51 > 0:26:56and evergreen leaves are expensive to produce when nutrients are low.
0:26:56 > 0:27:00But they do last for a good long time.
0:27:03 > 0:27:08Eucalypts stand dusty and ragged, with leaves several years old.
0:27:08 > 0:27:11And even when they do fall,
0:27:11 > 0:27:14something is sure to want to put them to good use.
0:27:20 > 0:27:24In the arid gumtree shrublands of southern Australia,
0:27:24 > 0:27:26the mallee fowl is busy.
0:27:26 > 0:27:30The female has laid her eggs in a huge mound of soil and dead leaves
0:27:30 > 0:27:34that she and her mate have carefully scraped into shape.
0:27:39 > 0:27:44As this pile rots down, the heat generated incubates the eggs.
0:27:44 > 0:27:49Too much or too little heat and the eggs will die,
0:27:49 > 0:27:53so the birds keep on adjusting the mound to keep it at 34 degrees.
0:27:56 > 0:28:00Both birds have temperature sensors in their mouths -
0:28:00 > 0:28:03a quick taste keeps things monitored.
0:28:09 > 0:28:13Two months after they're laid, the eggs begin to hatch.
0:28:23 > 0:28:28The chick bursts out and starts its journey upwards.
0:28:28 > 0:28:31When you're buried a metre down, this is no picnic.
0:28:31 > 0:28:35It can take two days to get to the surface,
0:28:35 > 0:28:38and it gets no help at all from its parents.
0:28:47 > 0:28:50This is one tough little chick!
0:29:04 > 0:29:06When it finally gets out,
0:29:06 > 0:29:10it's able to walk immediately and it toddles off into the bush.
0:29:10 > 0:29:14It can even feed itself and it'll be able to fly within a day.
0:29:29 > 0:29:33It's just as well it's so self-sufficient,
0:29:33 > 0:29:36because from now on, it's on its own.
0:29:36 > 0:29:40And with all those dry, dead leaves around,
0:29:40 > 0:29:42the bush is a dangerous place to be.
0:29:47 > 0:29:50Of all that gumtrees have to endure,
0:29:50 > 0:29:54this surely seems the most devastating.
0:30:05 > 0:30:09Australia's landscape has been dramatically shaped by fires.
0:30:09 > 0:30:12They happen right across the country -
0:30:12 > 0:30:15and in some areas very frequently.
0:30:16 > 0:30:20Whether started by lightning or careless matches,
0:30:20 > 0:30:23bushfires are a fact of life.
0:30:23 > 0:30:27In dry conditions, the fires quickly take hold.
0:30:27 > 0:30:30Strips of bark peel away in flames,
0:30:30 > 0:30:35carried off in the wind to start new fires as much as 30km away.
0:30:46 > 0:30:51In eucalypt woodlands, the litter that collects round the trees
0:30:51 > 0:30:57is highly flammable, and can create a fire as hot as 1,000 degrees C.
0:31:06 > 0:31:10It may look like a disaster for the trees, but the bizarre truth is,
0:31:10 > 0:31:15eucalypts seem to encourage their surroundings to burst into flames.
0:31:20 > 0:31:23Many have thick and insulating bark,
0:31:23 > 0:31:27able to withstand all but the most ferocious fires.
0:31:29 > 0:31:34Some gums actually NEED a really good blaze to release their seeds,
0:31:34 > 0:31:38and provide a fertile bed of ash on which they'll later sprout.
0:31:44 > 0:31:49This dry old country has been burning like this for millennia.
0:31:53 > 0:31:56Although it may not look like it,
0:31:56 > 0:32:00the gumtrees have the situation well under control.
0:32:07 > 0:32:12And this devastation is a prelude to something quite remarkable.
0:32:12 > 0:32:16Within weeks of a fire that seems to have killed them,
0:32:16 > 0:32:20many gumtrees start popping out fresh green shoots.
0:32:20 > 0:32:22They grow from buds under the bark,
0:32:22 > 0:32:25where they'd been protected from the intense heat.
0:32:34 > 0:32:37Bare and blackened branches are green again,
0:32:37 > 0:32:42and the trees carry on as normal. It's almost like a magic trick.
0:32:47 > 0:32:53In this volatile country, eucalypts seem able to cope with anything.
0:32:53 > 0:32:56To add to the damage begun by fire and rain,
0:32:56 > 0:33:00they are chewed away by millions of termites.
0:33:05 > 0:33:09Australia's gumtrees are among the most termite-ridden in the world.
0:33:09 > 0:33:14Some are completely hollowed out by the activities of these insects.
0:33:15 > 0:33:18But with so many termites around,
0:33:18 > 0:33:21there are other animals ready to eat them.
0:33:22 > 0:33:25Including these. They're numbats...
0:33:25 > 0:33:29and they live in the woodlands of Australia's south-west.
0:33:36 > 0:33:41Numbats have tiny mouths and their teeth are not very effective.
0:33:41 > 0:33:46But as they only eat termites, all they need is a good sense of smell
0:33:46 > 0:33:51and the right tongue - sticky, manoeuvrable and very, very long.
0:33:56 > 0:34:00It can flick termites into its mouth and swallow them whole.
0:34:13 > 0:34:17Most of Australia's small mammals are nocturnal,
0:34:17 > 0:34:21but numbats don't get out of bed until the sun's warmed the ground,
0:34:21 > 0:34:24and the termites are active just below the surface.
0:34:42 > 0:34:45Numbats are solitary animals,
0:34:45 > 0:34:49but these are young ones - out and about together.
0:34:49 > 0:34:53When they're old enough, they'll feed alone, like their parents,
0:34:53 > 0:34:56eating 20,000 termites a day.
0:35:04 > 0:35:07These youngsters will stay together for a few months,
0:35:07 > 0:35:10learning to fend for themselves.
0:35:10 > 0:35:14Until then, the slightest danger - real or imaginary -
0:35:14 > 0:35:19will make them flee to the den in the safety of a gumtree hollow.
0:35:26 > 0:35:29Hollow trees are a real feature of the bush.
0:35:29 > 0:35:33There was once a man who lived inside a giant gumtree -
0:35:33 > 0:35:35and raised a family of four there.
0:35:35 > 0:35:38Tall trees, strange tales.
0:35:49 > 0:35:51There is a particular type of gum
0:35:51 > 0:35:56that thrives on the banks of the Murray River of southern Australia.
0:35:56 > 0:35:59The river red gum grows here in enormous forests,
0:35:59 > 0:36:03and some of the trees may be 500 years old.
0:36:06 > 0:36:11The oldest are full of holes and are very popular with parrots.
0:36:19 > 0:36:22Regent parrots make their homes here.
0:36:22 > 0:36:26In the breeding season, the male brings food to the female,
0:36:26 > 0:36:29who's never far away from the nest.
0:36:39 > 0:36:43And that nest may be more than five metres down inside the tree.
0:37:04 > 0:37:08It may seem like hard work to have to climb so far,
0:37:08 > 0:37:13but it's sensible - it protects the eggs and young from the elements,
0:37:13 > 0:37:15and from other hazards.
0:37:17 > 0:37:19There are thieves around.
0:37:28 > 0:37:30Given the chance,
0:37:30 > 0:37:34a lace monitor would easily make a meal of an egg or a chick.
0:37:42 > 0:37:46In the nesting season, they're a major part of its diet.
0:37:46 > 0:37:49And it knows where they live.
0:38:17 > 0:38:19The danger passes,
0:38:19 > 0:38:24and the lace monitor turns its attentions elsewhere.
0:38:28 > 0:38:33These gumtree forests flank the river for hundreds of kilometres,
0:38:33 > 0:38:35and they're full of wildlife.
0:38:35 > 0:38:38Some of it has the oddest behaviour.
0:38:39 > 0:38:41When night falls,
0:38:41 > 0:38:45a strange, savage little marsupial makes its appearance.
0:38:49 > 0:38:52It's a yellow-footed antechinus.
0:38:53 > 0:38:59The size of a mouse, it's a voracious, feisty little carnivore.
0:39:17 > 0:39:21Thus fortified, this male has a busy time ahead of him.
0:39:32 > 0:39:34It's a bizarre life cycle.
0:39:34 > 0:39:38These animals have just one short, sharp mating season,
0:39:38 > 0:39:42and competition for females during that time is so strong
0:39:42 > 0:39:44that the males even give up food.
0:39:49 > 0:39:53Each mating can last 12 hours, and it's a bit of a free-for-all,
0:39:53 > 0:39:57with the females having a pretty rough time of it.
0:40:23 > 0:40:26The stress is all so much
0:40:26 > 0:40:31that after two weeks of frantic activity, all the males drop dead.
0:40:31 > 0:40:35The pregnant females are left to carry on alone.
0:40:39 > 0:40:41But with the males out of the way,
0:40:41 > 0:40:46it does mean there will be more food left for mother and the kids.
0:40:47 > 0:40:52It's a perilous environment, this gumtree bushland -
0:40:52 > 0:40:55in more ways than one.
0:40:57 > 0:41:02These giant old red gums have been nicknamed "widow-makers".
0:41:02 > 0:41:05- And this is why. - CREAKING
0:41:05 > 0:41:09They have an alarming tendency to drop their branches,
0:41:09 > 0:41:13without warning, on the calmest of days.
0:41:23 > 0:41:27The wood is so heavy that if it falls into the river,
0:41:27 > 0:41:29it sinks like a stone.
0:41:33 > 0:41:36And so the river is full of snags -
0:41:36 > 0:41:40a tangle of fallen branches and collapsed trees.
0:41:44 > 0:41:48But even these drowned limbs have their uses.
0:41:48 > 0:41:51Water birds use them as lookout posts.
0:41:57 > 0:42:02These underwater woodlands are also the perfect hideout
0:42:02 > 0:42:05for Australia's biggest freshwater fish.
0:42:05 > 0:42:10The Murray cod can reach more than a metre long - even bigger,
0:42:10 > 0:42:14if fishermen's tales are true - and weigh more than a man.
0:42:16 > 0:42:20Under these snags it can hide from predators,
0:42:20 > 0:42:24rest from the flow of the river and shelter from the sun,
0:42:24 > 0:42:27while it lives to be 100 years old.
0:42:33 > 0:42:37In the Australian bush, even the fish live in trees.
0:43:16 > 0:43:20The Murray river is shallow and the banks are low.
0:43:20 > 0:43:25Once every few years, when spring rains are especially heavy,
0:43:25 > 0:43:29and snow melts fast in the mountains upstream,
0:43:29 > 0:43:31the big river breaks its banks
0:43:31 > 0:43:35and it moves into the surrounding forest.
0:44:00 > 0:44:03It looks like a beautiful disaster.
0:44:03 > 0:44:07But the bushland inhabitants are surprisingly adaptable.
0:44:13 > 0:44:16When put to it, a kangaroo can swim.
0:44:46 > 0:44:51And the gumtrees themselves are perfectly at home.
0:44:51 > 0:44:55In this dry place, where rainfall is generally so low,
0:44:55 > 0:44:59these big trees would die of thirst without floods from time to time.
0:44:59 > 0:45:04For now, they can drink deep and put on a spurt of green growth.
0:45:11 > 0:45:14For a while, the forest is transformed into a wetland -
0:45:14 > 0:45:17a maze of swamps and billabongs.
0:45:33 > 0:45:37Where, a few days ago, kangaroos browsed in grassy clearings,
0:45:37 > 0:45:42now there are spoonbills and egrets fishing among the trees.
0:45:58 > 0:46:02Floods like these are less frequent than they once were.
0:46:02 > 0:46:05The Murray's flow has been altered by people
0:46:05 > 0:46:08because the water was needed elsewhere.
0:46:08 > 0:46:13But when they do happen, the results are spectacular.
0:46:13 > 0:46:16The wildlife is tuned to events like these.
0:46:16 > 0:46:21Fish begin to breed, and thousands of water birds start nesting
0:46:21 > 0:46:23around the flooded trees.
0:46:51 > 0:46:55This is the driest inhabited continent in the world,
0:46:55 > 0:46:59and yet here are kangaroos up to their knees in water!
0:46:59 > 0:47:04The Australian bush is nothing if not contradictory.
0:47:47 > 0:47:52The first European settlers had dismissed these vast green swathes
0:47:52 > 0:47:55as just "forests in rags".
0:47:55 > 0:48:01But as they got to grips with the curious land, the bush, with its resilience and strange wildlife,
0:48:01 > 0:48:04became the essence of Australia.
0:48:04 > 0:48:06It's a land of pioneers,
0:48:06 > 0:48:10where adaptability and tenacity are the keys to survival.
0:48:10 > 0:48:13And gumtrees seem to suit it very well.
0:48:22 > 0:48:26Next week, Wild Down Under explores the exotic islands
0:48:26 > 0:48:29that surround Australia,
0:48:29 > 0:48:32from tropical New Guinea to icy New Zealand.
0:48:33 > 0:48:37Each of these islands has its own cargo
0:48:37 > 0:48:40of unique and extraordinary wildlife.
0:48:42 > 0:48:46This breathtaking journey reveals bizarre creatures
0:48:46 > 0:48:50in spectacular landscapes - island-hopping on an epic scale.
0:48:51 > 0:48:54E-mail us at subtitling@bbc.co.uk