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For a quirky mix of creatures…

look no further…

…than the marsupials.

Those mammalian misfits

with the pouch.

They might seem a bit bizarre…

but don't underestimate them.

With unexpected superpowers

and amazing adaptability…

they have conquered a continent.

These high-altitude valleys

are home to an iconic marsupial.

The eastern grey kangaroo.

Today, a new roo
is being welcomed into the world.

All kangaroo babies
start out the same way.

Little more than an embryo.

Blind, with hind limbs barely grown,

he must scale a wall of fur
six times his height.

His goal?

Mum's pouch.

The pouch keeps the young joey warm,

fed,

and safe…

…until he's ready to emerge.

Fast forward six months.

The eastern grey joey
takes his first look at the world.

To learn he's part of a group,

known as a mob.

Mum and a handful of females,

jealously guarded by the boss.

That's his dad.

Joey is about to discover
the secret to his father's success.

A lot of muscle,

a lot of flexing.

A challenger has arrived

to contest Dad's mating rights.

It's an exhibition of power…

…urine…

and there's a bit of scratching as well.

Body language says, "I could fight you."

"But you don't want to go there."

"No, no, no."

It seems to do the job.

Until next time.

One day, the joey will make his bid

to be a kangaroo king.

If he makes it that far.

This valley is also home
to a pack of dingoes.

And catching kangaroos is their specialty.

At 25 miles an hour,
dingoes are pretty quick.

But roos can go 40!

The pack looks for stragglers.

But no luck this time.

For now, joey can relax
in the safety of Mum's pouch.

It's just a simple fold of skin,

but it's given marsupials a head start

for millions of years.

The marsupials first arose
alongside the dinosaurs

on an ancient supercontinent.

Today, in most places,

they're being outcompeted
by placental mammals.

But a number of opossums
still survive in the Americas.

Including the monito del monte,

the last remaining member of a family

that gave rise to three-quarters
of marsupials alive today.

It's thought that
as the supercontinent fragmented,

a close relative
of this living fossil was cast away.

Isolated in what is now Australia,

with little competition
from other mammals,

this pioneering possum's descendants
branched out across a land of opportunity.

Over time, 200 different species evolved.

Each with a fantastical name.

Each with a unique way of life.

Most are nocturnal…

insectivores,

or vegetarians.

But some grew larger,

fiercer,

and developed a taste for meat.

Filmed in 1936,

the thylacine,
also know as the Tasmanian tiger,

was once Australia's apex predator.

This is the last time it was documented

before human settlement
and bounty hunters wiped it out.

Today, only a few
marsupial carnivores survive.

The largest lurks in one
of the wildest corners of the continent.

A legendary beast…

…with a fearsome reputation.

The Tasmanian devil.

A young imp might act tough…

…but he's probably
more anxious than aggressive.

Like all devils, he prefers the dark.

He's just eight months old,
only recently left Mum,

and not had much to eat since.

If that doesn't change soon, chances
of making it to adulthood are slim.

His biggest problem?

Other devils.

The imp can't compete with the big boys.

Two full-grown adults
scrapping over a carcass.

But he could steal a quick snack…

while they fight it out.

He'd better eat fast…

…before trouble returns.

All he can do is hope for some leftovers.

But considering a devil can devour
almost half its body weight in a sitting,

it could be a long wait.

Come dawn, his patience has paid off.

Well… kind of.

Only skin and bone left,
but an imp can't afford to be picky.

Devils do hunt sometimes,

but they're just as happy to scavenge.

This ability to eat the uneatable

helped marsupials claim a continent.

Eucalyptus trees make up three-quarters
of Australia's native forest.

Their leaves are so toxic,

they're inedible
to almost every living thing.

But one famous marsupial

has found a way
to exploit this bountiful resource.

This koala mum may look a little dozy,

but she's feeding for two.

And her body's working overtime.

Her gut contains
a unique cocktail of microbes

which neutralize the poisons
that would put us into a coma.

But koalas aren't born
with such strong digestion.

It has to be acquired.

So baby is on a mix of milk and pap.

Slushy droppings
that pass on the bacteria he'll need.

Even with the toxins taken care of,
it takes almost all of the koala's energy

to break down these low-nutrient leaves.

It's no wonder
they spend 90% of their lives asleep.

But not all marsupials
lead such laid-back lives.

Meet nature's BASE jumper.

The sugar glider.

This palm-sized possum

can glide half the length
of a soccer field in a single leap.

His fast-paced lifestyle
is fueled by sugary sap.

But his teeth are too small
to cut through thick bark.

Time to drop in
on his heavyweight cousins.

The yellow-bellied gliders.

Their stronger jaws are quick
to slice through the toughest trees.

And when the yellow-bellies move on,

the little fella takes his chance.

But gliders are social animals.

More and more join the party.

This many uninvited guests
are hard to ignore.

The yellow-belly's had enough.

It's fight

or flight.

An easy choice for a sugar glider.

Back in the Australian Alps,
the joey is now one big baby.

Nine months old
and well on course to adulthood.

Well, almost.

He'll continue to hop in and out
of the pouch for the next few months.

Following in his father's footsteps,

he's working on his tough guy image.

And sparring with Mum.

Lucky she's long-suffering.

She'll put up with this
until he's a year and a half.

Then he'll be on his own,

fighting his way to the top.

Because only the mob boss
is allowed to mate…

and right now, that's Dad.

The rival male is back.

And now it's time. Time for a showdown.

Fights are brutal.

Sometimes fatal.

Rival defeated,

Dad claims his reward.

A little kangaroo courtship.

His caresses…

and sniffs

are well-received.

Seems joey will soon have a sibling.

But when it arrives,

he'll lose the security of Mum's pouch.

From then on, he'll have to count
on his own turn of speed.

The challenge of surviving
Australia's vast desert interior

has shaped the fastest marsupial of all.

The red kangaroo.

Named for the males' distinctive coat,

the red kangaroo is also
the largest marsupial in the world.

Food sources here are few and far between,

and water is even scarcer,

so red kangaroos
need to keep moving to stay alive.

They spend their lives chasing the rains.

They can cover eight meters
in a single leap.

Tendons in their hind legs
work like giant springs,

recycling up to 70%
of the energy in every hop.

And this rhythmic bounce also pumps
more oxygen through their lungs…

allowing them to cruise
at 30 miles an hour.

Fast and efficient,

red kangaroos migrate vast distances.

When they finally reach greener pastures…

they extract almost all the water
they need from the plants they eat…

and can go for weeks
without drinking at all.

With incredible specialization,

red roos can thrive
in Australia's arid regions.

But most marsupials
are tied to permanent water.

Agile wallabies
are smaller cousins of red kangaroos.

They graze around the billabongs
and creeks of Northern Australia…

and have to regularly
come down to the water to drink.

Saltwater crocodiles prey on the thirsty.

An ancient foe that's haunted these waters
since the time of the dinosaurs.

Collective vigilance and fast reactions

mean, more often than not,
the wallabies get away.

They've had millions of years
to adapt to this danger.

But now, marsupials face new threats,

and they're struggling to cope.

Two hundred years ago, humans introduced
new predators to Australia.

Feral cats kill
nearly 1.5 billion native animals a year.

And they've played a major part
in the extinction of 22 marsupial species.

The greater bilby
is in danger of going the same way.

These timid creatures rely on acute senses
to navigate the night.

Their elongated noses allow them
to sniff out seeds and fruit in the dark.

And oversized ears help detect danger.

But they don't have
the agility to outrun a cat.

Greater bilbies have disappeared
from 80% of their range.

Some wilderness areas
are now protected by cat-proof fences.

And here,

bilby numbers are on the rise.

But the greatest threat facing marsupials
is even harder to control.

In recent years,

Australia's natural bushfires have become
more destructive than ever before.

Climate change means occasional burns
have become regular firestorms.

Almost every year, thousands
of koalas and other marsupials die.

In the aftermath,

it seems nothing could survive.

But eucalyptus trees
are protected by thick bark.

Within weeks of a burn,
they spring back to life.

And soon, all across Australia,

the survivors are fighting back.

Come the koala breeding season,

the usually sleepy animals
are raring to go.

A male's bellow carries for miles…

…broadcasting his location…

showing off his size.

It's an invitation to females.

A response.

But not the one he wanted.

Disputes between males are rare…

and pretty quickly, they turn ugly.

Rival dispatched.

Time to get back to finding a female.

At long last, his love song is heard.

Well, she's in no rush to commit.

Mm-mm-mm.

But when it comes
to actually making babies,

koalas don't hang around.

In just 35 days, she'll give birth.

So long as he gets his way.

Such rapid reproduction
has helped marsupials

to exploit every corner of the continent,
no matter how extreme.

These are some of Australia's
tallest trees.

Now, you might wonder
what a kangaroo joey is doing up here.

But he's a tree kangaroo.

His ancestors evolved out on the plains,

but six million years ago,

one daring roo took to the trees.

Slowly but not so surely,

its descendants
are making the canopy their home.

They've developed stronger front limbs,

curvier claws

and shorter hind feet than a regular roo.

But evolution is a slow process.

Compared to other tree dwellers,
they're not the most graceful.

And that's just the adults.

After seven months in the pouch,

it's time for the joey to go it alone.

No experience,

under-equipped,

and seven floors up.

Ooh, Mum can only watch.

But the kangaroo gods
are smiling on this little joey.

So long as his luck holds,

he'll spend another year in Mum's care.

Though the day comes when all marsupials
have to leave the protection of the pouch.

Now 15 months old,
joey's taken a big leap forward.

He spends his days
sparring with his peers.

Mum's pouch has been taken over…

by a sister.

She's just six months old,
and hasn't set foot outside.

But roos aren't the only ones
in the valley with young.

The dingo pack
have left their pups to go hunting.

Early human settlers introduced dingoes
to Australia around 3,500 years ago.

Since then, they've become
the grey kangaroo's worst enemy.

Other youngsters head for safety.

But joey's got nowhere to go.

If he can't keep up with the mob,
he's in trouble.

The dingoes rush the roos…

…searching for the slow.

A heavily-laden Mum is lagging behind.

The hunters close in.

Fewer than half of all joeys
make it to adulthood.

But on the far side of the valley,

joey, Mum and his sister
have all survived.

With pioneering spirit,

amazing adaptability

and, let's face it, not much competition,

Australia's marsupials
have risen to the challenges

of this unforgiving land.

But this wonderful collection
of eccentric animals

is struggling to adapt
to the threat of new predators…

…and the chaos of climate change.

But there are some
who are fighting for their future.

Across Australia, people are devoting
their lives to rescuing…

releasing…

and protecting
the marsupials most in need.

And some species
are proving remarkably resilient.

Eastern grey kangaroos
still thrive in their millions.

Thanks to the might of the mob,

one seriously dedicated mum

and her amazing pouch,

joey's had a great start.

Now it's time to grow up.

And just maybe,

maybe one day,

become a kangaroo king.