Original subtitles

(LOW GROWL)

(TRUMPETS)

Across the planet...

(GROWLS)

..there are giants.

Creatures that have pushed their bodies...

(LOW ROAR)

..to the limits.

(BELLOWS)

In this series, I'm on a mission to find some of the biggest animals on the planet,

and discover why, in the natural world, size really matters!

Travelling to Asia...

Just look at the size of that thing!

..the Americas...

..and Africa.

Wow! Look at that power!

I'll show the surprising ways animals use bulk

to survive.

And stepping back in time...

..I'll also meet the prehistoric monsters...

..that once roamed the Earth.

Today, many of our big animals are in trouble.

From plastics in our oceans

to climate change...

..it's often the biggest creatures...

..that are hardest hit.

In this episode,

I'm searching for the giants of Australia and Asia...

..to reveal how different habitats...

..have driven some species to become supersized.

Prepare to meet the big beasts, the last of the giants.

Our story starts in the ocean...

..with a true giant.

Weighing over 20 tonnes...

..and growing to the length of a bus...

..this is the biggest fish on the planet.

The whale shark.

Much of their lives are spent deep down.

But every year, they gather in a few special places

to feed close to the surface.

I'm joining a team of marine experts

who are monitoring the sharks in one of those seasonal hot-spots.

Ningaloo Reef, Western Australia.

The word "ningaloo" means deep water

and as its name suggests, beyond the reef,

the sea-bed drops into an abyss 1,000 metres deep.

And those waters are full of nutrients.

The ocean currents drive them upwards

making these waters some of the richest in the world.

These up-wellings create huge plankton blooms.

And that's what the whale sharks are here to feed on.

He's just come out of our glare now, right on at three o'clock

and he's heading south. Oh, yeah! There he is!

I've just spotted a whale shark!

And the ocean just seems like this vast expanse of blue

and just in the middle is this tiny - what looks like a tadpole.

What incredible animals.

RADIO:'Hey, guys, I just picked up a whale shark...'

Once a shark is spotted, the team can track it from the water.

Wonderful. Thanks. We're heading on over.

First, we're going to measure the length of the shark,

to see whether it's an adult or a juvenile.

There are many ways of measuring a whale shark.

But the simplest is to compare them to a human swimmer.

'At six feet tall, I've offered to be a human ruler!'

She's gonna mark the shark for us...

'Diving specialist David Dunstan gives me some cautionary advice.'

..and when you see that mouth coming towards you, enjoy that moment -

it's a very cool moment!

But then we're gonna move to the side.OK.

Biggest thing in the ocean always wins! It's not a game of chicken here!

50 metres away.

'But it's not the mouth I need to worry about.

'It's the powerful tail fin.'

Whoa, whoa, whoa, whoa, whoa!

At first, it's hard to make anything out.

Its mouth is the width of a car!

And its tail fin is taller than I am.

But to estimate its length,

I've got to get alongside.

These gentle giants swim at a speed of five kilometres an hour.

From the air, the size difference is clear to see.

That's awesome!

I think it was probably about three times my body length.

So around seven metres. And that tells me it was a juvenile.

The amazing thing is they can get even bigger.

The largest ever-recorded whale shark

came in at just under 20 metres.

To put that into perspective,

imagine going to your local swimming pool

and seeing one fish, one fish,

take up the entire length

and you've got yourself a whale shark!

Like most big animals,

whale sharks have long life spans.

They can live for up to 70 years

and continue to grow throughout their lives.

But why has a fish evolved to be so huge?

The last I saw of that whale shark, it was diving and disappearing off into the deep.

But that action gives us a clue as to why they're so big.

As well as feeding at the surface,

whale sharks also dive deep to find food.

They've been recorded at depths of over 1,000 metres,

where the water is just three degrees above freezing.

To feed at this depth, you need to stay warm.

And big bodies retain heat better than small ones.

So it's this combination of having a large size

and a very special body shape

that allows these animals to survive in these waters.

It's a strategy known as gigantothermy.

For whale sharks,

gigantothermy allows them to dive to some of the deepest, coldest waters

in search of food.

Ningaloo's plankton-rich waters

are home to another ocean giant.

The manta ray.

Their wing span can reach seven metres.

Like whale sharks,

they are filter feeders...

..sieving out microscopic plankton from the water.

But today, tiny fragments of degraded plastic,

the same size and weight as plankton,

are turning areas of our oceans into a plastic soup.

And these huge filter feeders

have no way of distinguishing microplankton from microplastic.

Scientists fear it will cause a build-up of toxins

affecting their growth and reproduction.

These giants have been gliding through our oceans

for millions of years.

But today, due to our impact,

their future is uncertain.

Across the planet, animals use size as a strategy

to survive in many different landscapes.

Strangely, on islands,

creatures have often evolved to be bigger

than similar species found on the mainland.

I'm travelling to a distant corner of the Indonesian archipelago

to track down a legendary island giant.

This remote volcanic island

is home to a prehistoric-looking creature.

A gigantic venomous lizard

that can hunt prey weighing more than half a tonne.

It's been described in the past as a primeval monster

in a primeval setting.

And I can't wait to meet one!

The Komodo dragon.

The largest and heaviest lizard in the world.

These carnivorous reptiles

are a type of varanid, or monitor lizard.

But those on Komodo Island...

..are giants.

Nearly five times bigger than other monitors.

To show why they've become supersized...

..I want to get close to one of these big beasts.

But these are powerful predators.

A forked stick should stop them getting too close.

When you're sat face-to-face with the top predator of these islands,

something really comes over you.

Right now, my skin is alive with goosebumps.

This thing has a deadly bite.

60 serrated teeth that can really do some serious damage.

And if you don't die from the initial bite,

then...

..its venom will do the rest.

Because it's been recently found

that that venom...

..is an anticoagulant so it stops its intended victim

from being able to heal.

And if you can't sense it right now,

the entire crew are on tenterhooks!

(HE CHUCKLES)

Thankfully, Komodo dragons rarely hunt on beaches.

Despite their bulky appearance,

they are, in fact, stealth predators.

Using long grass and the surrounding forests to ambush prey.

They hunt deer and wild boar.

But their biggest prize is almost three metres long

and weighs half a tonne.

Water buffalo.

When it comes to hunting a prey item of this magnitude,

it's only when the Komodo dragons reach about 50 kilograms

that they're big enough to take it down.

Dragons grow throughout their lives

and can live for up to 30 years.

Only the oldest, biggest individuals can hunt buffalo.

Hiding in the grass, they ambush them, biting one of their legs.

Toxic proteins in the dragon's saliva

stop its victims blood from clotting

and cause muscle paralysis.

This water buffalo was bitten two weeks ago.

It's now just moments from the end.

(LOW BELLOW)

What happens next shows why for these lizards,

big is best.

Numerous dragons have picked up the buffalo scent.

Their long, forked tongues

can detect a carcass from four kilometres away.

A small, younger dragon chances it.

(BUFFALO GRUNTS)

The bigger dragons bide their time.

From experience,

they know this is a waiting game.

The next morning, the feast begins.

The biggest individuals are first in.

Komodo dragons can eat 80% of their body weight in one go.

The smaller juvenile is back.

But big dragons are cannibalistic.

So he's not taking any chances.

It's left to the largest lizard to finish up.

An entire leg, hoof and all,

swallowed in one go.

This primal scene

shows why these lizards became so massive.

With an abundance of huge prey on these islands,

and no competition from other predators,

they were able to evolve into giants.

But there was a time when even bigger lizards roamed the Earth.

Megalania prisca was the largest lizard to have ever lived.

Its powerful skull was 2.5 times the size of a Komodo dragon's.

Megalania prowled the Australian outback two million years ago,

hunting giant marsupials.

It died out around the same time the first humans arrived.

Some believe we hunted them to extinction.

Today, the Komodo dragon is the closest living relative

of megalania.

They only exist on five remote Indonesian islands.

Their isolation may be the only reason

these lizard kings have survived.

The jungles of south-east Asia.

The oldest rainforests on Earth.

To survive high in the treetops...

..most animals have evolved to be small.

Light-weight.

And nimble.

But there's one notable exception.

The orangutan.

The biggest tree-dwelling animal on the planet.

Males can weigh almost 100 kilograms.

And have an arm span of two metres.

Up to 95% of their lives are spent in the canopy.

But they're surprisingly clumsy climbers!

It looks to me like this is an animal too big for its treetop home.

To reveal the secret behind their size,

I'm travelling to a research centre

in the heart of the Bornean jungle.

Here, wild living orangutans have their diets supplemented with fresh fruit.

And alongside several mothers and babies...

..there's one massive male.

What's really impressive about this guy is his size.

It's just mind-blowing to think that

he can just with one arm haul himself up a tree.

Just look at those hands. They are gigantic!

But not only does he have incredible power,

he also has a fine dexterity to handle fruit

and those bananas he's eating over there.

But what's most striking is how this male differs from the other orangutans.

The difference between this male and the females

is clearly visible.

He's at least twice their size.

And his hair looks like a magnificent cloak.

You can see that throat sac and those cheek pads

on the side of his face.

He is clearly the dominant male in this area.

The flirty cheek pads are known as flanges.

Only the males develop them.

And they make their heads appear almost twice the size.

This difference in size and body shape

is known as sexual dimorphism.

At the feeding station, the male uses his bulk

to try and bully others off the food.

But it doesn't always go to plan!

But size is also about impressing the opposite sex.

To win a mate, male orangutans undergo a bizarre transformation.

Until around ten years old,

the males look similar to the females.

Then they turn from this...

..to this.

They experience a 50% increase

in growth hormones similar to testosterone.

It triggers them to double in size

and develop those fleshy cheek pads

in just one year.

It's the most impressive-looking males that the females choose as their mates.

A female orangutan

only gives birth to four or five offspring

over the course of her entire lifespan.

So for males, the bigger they are,

the better their chance of passing on their genes

to the next generation.

The orangutan is the largest ape in Asia.

But even they would have been dwarfed by their prehistoric primate cousins.

Gigantopithecus blacki...

..was the largest ape ever to have lived.

Too big to climb, it walked on all fours.

A large, robust skull suggests it munched fibrous plants, like bamboo.

Some believe its oversized feet were the origins of the mythical Bigfoot.

Gigantopithecus died out 100,000 years ago

when an ice age turned its forests to grasslands.

These giant apes couldn't adapt quickly enough to their new environment.

Today, it's not an ice age that threatens the orangutan.

It's deforestation.

Critically endangered,

the orangutan is at risk of going the same way

as its colossal prehistoric cousin.

The frozen wilds of northern Asia.

Temperatures here can drop to minus 40 degrees.

Snow covers the ground for seven months of the year.

It's a challenging landscape for any animal.

Especially a giant predator.

The Amur tiger.

The biggest cat on Earth.

There are less than 600 of these giant felines left in the wild.

Weighing up to 250 kilograms,

they've been known to kill and even eat grizzly bears.

The Amul tiger is twice the size of its tropical cousin, the Malayan tiger.

And that comes down to its cold environment.

Bigger bodies retain heat better than smaller ones

because they can maintain warmth in their core.

This principle is known as Bergmann's Rule.

And it explains why the Amur tiger

can survive in one of the coldest places on Earth.

But the wilds of northern Asia

were once home to an even bigger feline.

Amphimachairodus, a giant saber-toothed cat,

prowled the Earth around ten million years ago,

hunting prehistoric horses.

With a jaw gape of 60 degrees

and enormous fangs,

it's thought to have ambushed its quarry,

slashing the neck.

But this bulky cat wasn't built for speed.

And as its fleet-footed prey got faster,

it was no longer able to catch them.

And this gigantic feline eventually disappeared.

It's not just giant predators

that use size to survive in the wilderness of northern Asia.

In the remote mountains of China's Sichuan province,

another rare giant uses its bulk for a far gentler purpose.

The Giant Panda.

Pandas are a species of bear.

They are three times the weight of other Asian bears, like the sun bear.

But unlike any of their cousins,

they are strict vegetarians.

To show why their size is so important,

I've come to this panda sanctuary.

And I hear my first panda before I see it.

(BLEATING)

Aw!

It makes such an adorable sound!

Here it comes. Look.

(BLEATING CONTINUES)

What an amazing creature!

I can't believe that I'm stood just a stone's throw away from a Giant Panda!

It's really quite extraordinary

to think that there are only 2,000

of these animals left in the wild.

They look like a big ball of fur,

and that comes down to those thick layers of fur and fat.

They look so cute,

but it's that same stocky, round build

that helps pandas to keep warm.

Temperatures here can plummet to well below freezing.

Until around two million years ago,

pandas were smaller and ate meat,

just like other bears.

But a random change to their DNA

meant that they lost their umami taste receptors -

the receptors that allow carnivores to taste flesh.

And it was around this time

that they switched to a purely vegetarian diet,

specialising in one type of plant.

Giant pandas are very fussy eaters.

99% of their diet is made out of this stuff, bamboo,

and never mind eating it, just trying to break it apart!

Look at that. It's very difficult and requires huge amounts of energy.

This new fibrous diet

changed the way pandas looked.

They developed huge, robust skulls...

..for maximum bite strength.

Size for size, the panda's bite is stronger than a polar bear's.

It allows them to pulverise the bamboo.

But the panda's specialised diet comes at a cost.

In the 1980s,

huge swathes of bamboo forest died out...

..killing more than ten per cent of the entire species

in a matter of years.

It's a stark reminder

of how vulnerable big animals can be.

All the animal giants I've encountered

have a number of things in common.

They all grow slowly, they all reproduce much later,

and they give birth to fewer offspring.

And that means that when there's a rapid change in the conditions within their environment,

they're unable to adapt as quickly

as smaller creatures that reproduce much faster.

And this is one of the fundamental reasons

why big animals are prone to extinction.

Today, many of our "giants"

are living through a period of unrivalled change.

Whale shark are ingesting harmful microplastics.

Due to a loss of their forest home,

orangutans are now critically endangered.

And we still don't know how climate change

will affect big predators like the Amur tiger.

But there is some hope.

In recent years,

nearly four million square kilometres of ocean

has been given protected status.

And in China, the plight of the Giant Panda is on the turn.

In recent decades, huge conservation efforts

and the protection of 1.4 million hectares of panda territory

has resulted in an increase in their numbers.

Although they're still listed as vulnerable,

it shows that it is possible to bring big animals back from the brink of extinction.

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