BBC Wild Down Under

In the seas around Australia, cataclysmic forces have formed thousands of islands -

of all shapes and sizes,

from tiny tropical ones to giants with huge snow capped peaks.

They stretch from Australia in a great arc,

from New Guinea in the north, right out into the Pacific

and down to New Zealand.

If Australia itself seems strange,

its island relatives and their unique creatures are stranger still.

No other continent has given birth

to such an explosion of fabulous island landscapes and their weird wildlife.

So how did the dry, old giant, Australia,

end up surrounded by such a glittering necklace of wild ocean jewels?

Just a few thousand years ago, the tip of Northern Australia

oozed out into a vast swampy plain that stretched all the way to New Guinea.

Today, in Australia's Top End,

you can still get an idea of that great swamp

in a watery landscape called Kakadu.

It's an oasis for water birds, including huge flocks of magpie geese.

Kakadu's swamps are created every year by monsoon floods.

They transform the parched landscape into a rich,

living broth and millions of water birds find it irresistible.

And something else finds them irresistible too...

...the salt-water crocodile.

Muddy water provides the perfect camouflage for these huge,

six metre long reptiles.

A magpie goose makes a nice bite-sized snack.

It will probably last him a week.

Kakadu may be full of life,

but it can give us only a tiny glimpse of

what those enormous swamps of thousands of years ago must have been like.

In those days, sea levels were much lower.

But about 10,000 years ago, world sea levels rose

and the swamp was drowned by the ocean,

completely cutting off New Guinea from Australia.

The tops of a few hills survived the flooding,

and today, like stepping stones,

they lead a path from Australia to the giant new island of New Guinea.

It was connected to the mainland for millions of years -

but now, it couldn't look more different.

While much of Australia is dusty and dry,

most of New Guinea is covered in lush tropical rainforest.

The landscape may look very different,

but the wildlife still has

that eccentric Australian blend of the improbable and the ingenious...

This is the long beaked echidna.

It's about twice the size of its Australian cousin.

It's also called the giant spiny anteater, but it doesn't eat ants.

Instead, it uses its long nose to probe for worms,

sniffing for them as it wanders through the forest.

When it catches the merest whiff of a worm, it uses its nose like a dibber,

poking it in and out of the ground until it finds a snack.

To haul the worm in, it spears it on a special barbed tongue...

...then up it goes, like a piece of spaghetti.

Because New Guinea was connected to Australia for so long,

it has a lot of familiar Australian animals,

like kangaroos.

But these are not your typical roos - they live up in the forest canopy.

Although they spend most of their time in trees,

they don't look very sure-footed.

But it's worth the effort.

There are no monkeys or squirrels to compete with here,

so if the kangaroos can reach it,

the entire canopy of leaves is there for the taking.

This baby will learn from its mother about which leaves to eat...

...and which fruit or lichen to round off the meal.

It's not an easy world for Joeys to learn to move about in

and they'll stick by their mothers for up to two years

before they're ready to live on their own.

New Guinea is covered in dramatic mountains and it has Australia,

one of the flattest continents on earth, to thank.

Over millions of years, Australia has been drifting northwards

and New Guinea has buckled up under the pressure.

Some of these rise as high as 5000 metres, into peaks of ice and snow.

These huge mountains have divided

the island into hundreds of ridges and valleys.

Within these, an endless variety of different landscapes have been created,

many with isolated pockets of extraordinary and unique wildlife.

And you don't get much more extraordinary than the birds of paradise.

Like animated neon signs,

these fabulously adorned males advertise to females

in an explosion of colour and sound.

And in case this isn't eye catching enough, they dance as well.

38 of the world's 42 species of bird of paradise live only here.

Of all of these, the Raggiana must be amongst the most dazzling.

Males dance together on a specially prepared stage,

which they've completely cleared of leaves.

And this is who they're desperate to please.

When these drab females arrive, the males give it everything they've got.

Females are hard to satisfy

and they'll only mate with the male who impresses them the most.

When a female flies in for a closer look, it sends the males into a frenzy.

And when she finally makes her choice - he's unstoppable.

He's laying it on a bit thick here...

...but she seems to like it.

These beautiful feathers

also make fabulous costumes for the people of New Guinea.

Each year, tribes from all over the highlands gather in displays

that almost outdo the showmanship of the birds themselves.

Hundreds of isolated cultures have evolved here,

with as many different languages -

more than any other place on earth.

The dry landscape of Australia couldn't support great numbers of Aborigines,

but the fertile mountains of New Guinea

allowed the development of settled agriculture

and a huge explosion of peoples and cultures.

On this one island,

there are as many different ways of life as there are valleys and mountainsides.

Many of these tribes were so isolated,

they weren't discovered by Europeans until the middle of the 20th century.

While Australia was a harsh, unpredictable place to survive in,

these mountain slopes could not be more hospitable.

Over 9,000 years ago, people started gardens here.

From plots like this, of sweet potato,

they've now manicured entire hillsides into a patchwork of allotments.

Even so, large parts of the island are too steep to cultivate.

Rugged cliffs and a lot of rain keep these areas thick with forest.

Where there are gaps, waterfalls plummet down to join streams below.

With so much rainfall, these streams very quickly swell into rivers.

It's such a wet place; the rivers are huge, twisting across vast floodplains.

The largest of them

has more water in it than all the rivers in Australia put together.

Eventually, they flow through extensive deltas until they meet the ocean.

In these seas around New Guinea, hundreds of smaller island stretch out -

to the west, towards Indonesia, and eastwards, into the Pacific.

Almost all of them are highly volcanic.

Violent eruptions literally blasted new islands out of the sea.

These are some of the most volcanically active islands on earth -

Vanuatu, the Solomons, New Ireland and New Britain.

The volcanoes are on a sort of geological conveyor belt -

new ones are continually being born, and then worn away -

creating thousands of miles of coastline for coral to grow on.

And as these islands begin to die and sink back beneath the waves,

the tips of extinct volcanoes form more coral reefs.

In just a single bay on any of these reefs,

you could find as many coral species and different kinds of fish

as there are on the whole of the Great Barrier Reef.

It's a kaleidoscope of life and colour, with layer upon layer of species,

like an intricately constructed Russian doll.

Barrel sponges live on the corals...

...feather stars live on the barrel sponges...

...and tiny fish live on the feather stars.

Anemones here have anemone fish and tiny little transparent shrimps.

And on some parts of the reef, creatures move about in costume.

This little prawn masquerades as a sea whip.

This tadpole sized pygmy sea horse is disguised as a piece of coral.

From a distance, it's virtually invisible.

Some animals take this deception even further.

These razor fish already wear beautiful striped costumes to look like sea whips,

but they add to the disguise by swimming vertically,

like a weird piece of performance art.

They only swim horizontally to dash from one group of whips, to another.

It's safer to move about in disguise,

because this busy neighbourhood attracts plenty of predators -

like these jacks.

They work the reef in gangs, trying to flush out smaller fry.

But as they muscle in on a patch, the neighbourhood dives for cover.

One bully heads underneath, scaring all the fish out through the top,

while the other members of the gang wait above... mouths open.

The gang does well with these tactics,

but they're just a bunch of small time thugs -

not even in the same league as some of the predators here...

Huge saltwater crocodiles roam these seas.

They are capable of swimming great distances to find new territories -

large ones have been seen several hundred kilometres out to sea.

With this sort of range,

it's been easy for them to colonise many of the volcanic islands of the pacific.

But while these islands have attracted all sorts of marine life,

including crocodiles,

land creatures like mammals have found it harder to get here.

Unless they can raft across or swim,

they're too far out.

But there has been one exception...

An invasion by air.

Squadrons of bats, especially the larger fruit bats.

In fact, New Guinea and the islands

that surround it are probably the fruit bat capital of the world.

There are more species here than anywhere else on earth.

These large fruit bats are strong travellers -

they can fly fifty kilometres in an evening in search of food.

Island hopping across the pacific is all in a night's work.

It's well worth the journey

because the island forests are full of all sorts of fruit.

With such a wide selection, there's room for lots of different fruit specialists -

this tube nosed bat is a professional fig eater.

As these bats move about from island to island,

they can also act as seed couriers.

They make unorthodox postmen though,

opening their parcels with strong teeth

and either dropping their contents

where they eat, or swallowing and depositing them,

perhaps on another island.

Beyond this chain of islands, the explosive activity begins to die away.

And further out in the Pacific, there's a graveyard of extinct volcanoes.

One of these is Lord Howe Island.

It retired from life as an active volcano about 6 million years ago.

A small speck in a vast expanse of ocean,

it's become a valuable service station for thousands of sea birds.

Each Spring, it transforms into seabird city.

Fourteen different species stop here to nest and breed,

like this booby...