Original subtitles

The gigantic giraffe...

..boasts some impressive stats.

It's the tallest mammal on Earth.

Nearly three times the height of a professional basketball player.

And as heavy as a car.

But have you ever considered what it takes to feed such a massive frame?

Or how this giant overcomes

the rather difficult problem of drinking?

Being one of Earth's big beasts has its advantages,

but also comes with sizeable challenges.

How they overcome life's big problems...

..can be truly jaw-dropping.

Whether it involves a total meltdown...

..a brutal battle...

..or maintaining their own air-conditioning,

it seems they've got it licked.

It's time to meet a remarkable group of animals.

Nature's Biggest Beasts.

From the behemoths of a bygone age...

..to the leviathans of our modern world...

..it's the biggest beasts that capture our imagination.

But size is relative.

And there are surprising giants

lurking in places you might not expect.

Animals whose claim to fame is simply being amongst

the biggest of their kind.

But whether they are a titan in a tiny world or a giant among

other giants, they all share the same basic challenges.

Moving their massive bodies.

Surviving extreme temperatures.

Having huge babies.

And, not least, the need to eat.

A lot.

Let's begin with an incontestable big beast.

Those giraffes.

Nearly six metres of mostly leg and neck,

perched on feet the size of dinner plates.

Being head and shoulders above the rest does have its perks.

Seeing for miles around.

Reaching 35mph, with its ground-eating strides.

And, of course, 1.8 metres of neck

and an extra 50cm of tongue means

it can reach the food its competitors can't.

Just as well, because a giraffe has a supersized appetite...

..which it needs to satisfy by eating foliage.

To get enough nutrients from just a few leaves per bite,

a large male must consume up to 65kg daily.

To eat through that many leaves a day can take up to 18 hours.

But never mind feeding...

..in dry times, a giraffe can need up to 38 litres of water

every few days.

But how to get it when it's seemingly so hard to come by?

Well, it has a neat trick.

By eating at dawn when condensation is high,

it can absorb most of its moisture from leaves.

It also wastes no water sweating or panting.

Instead, its temperature fluctuates with the surrounding air.

But when beaten by the heat,

giraffes must join their fellow beasts at the watering hole.

Being tall, it's tricky.

In this pose, the pressure is quite literally on.

Pumping blood against gravity up to the head takes a powerful heart.

It beats up to 170 times a minute.

That's twice as fast as ours.

This huge blood pressure, the highest of any mammal,

should give a drinking giraffe a bad head rush.

But instead, a clever system of valves regulates

blood flow to the brain.

The giraffe controls blood pressure so well that Nasa has taken

inspiration from these humble goliaths

for the design of its spacesuits.

It seems this big beast can even teach us a thing or two.

The unique physical characteristics of a giraffe allow it to feed with

relative ease.

Many big beasts, though, have to fight for their food.

This remote Indonesian island is home to an illustrious lizard.

It owes its prehistoric good looks to its age.

It's one of the few living species

to have been around for over three million years.

The Komodo dragon.

Earth's largest lizard.

Big enough to hog a king-sized bed

and then some.

Despite their intimidating credentials,

these dragons don't have it easy.

Around 6,000 remain, making them vulnerable to extinction.

To add to their woes, these ferocious beasts

have, for their size, a bite that is weaker

than that of the average house cat.

Their survival, though, relies on satisfying their insatiable hunger.

These dragons have set their sights

on this buffalo.

At ten times a dragon's size, it's a very dangerous dinner option.

One well aimed kick, and a dragon could die hungry.

So, how does a Komodo, with its measly nip,

take on such a formidable adversary?

Its bite may be weak,

but it's bolstered by around 60 backward facing, serrated teeth.

The grip and rip bite.

On prey this size, it just draws a bit of blood.

It's more deadly than it looks, though.

The bite has set the dragon's next weapon in motion.

Tucked either side of this lizard's weak jaw are venom glands.

A bite releases the poison,

preventing the prey's blood from clotting.

Stage two takes days and days of patience.

The buffalo's wound is not healing.

Three weeks later, and it's finally time to eat.

These ravenous reptiles can polish off 80% of their body weight in

a single sitting.

No energy gets wasted on chewing, either.

A tube running from the base of the tongue to the lungs

means a dragon can breathe while it swallows each mouthful...

..in one.

This combination of clever adaptations means this big beast can

take down even bigger beasts to satisfy its need to eat

and ensure its survival.

THUNDER RUMBLES

Enormous appetites have led many sizeable species to target prey

that should be out of their league.

And the big bugs of the undergrowth are no exception.

Imagine an insect that's big enough to take on a bird.

Meet the Kalahari's armoured ground cricket.

This hulk of the insect world puts its tiny European cousins to shame.

As an omnivore, it eats plants, insects, and crops.

But there's one more thing it really needs.

Red-billed quelea follow the rain,

gorging on crops that spring up in the now fertile ground.

They're feeding not just themselves,

but another million tiny mouths back at their nests.

And that is precisely where these immense vertebrates are headed too.

You see, life as a giant cricket is tough.

Protein is crucial for these goliaths

to sustain their huge frames.

So they must seize any opportunity to eat meat.

It's hard to slip under the radar, though, when you're massive.

So they've evolved some nifty defences.

A spiny, beak-proof armoured shell protects its insides.

And it can fire blood from pores in its exoskeleton...

..temporarily blinding its assailant.

With the security out of the way,

the meat feast is finally within reach.

This big beast has evolved to use its brawn and its weapons to get

the meal it needs to stay alive.

The leaf litter is rife with oversized invertebrates,

with appetites to match.

The Kinabalu giant red leech

would span the whole length

of a grown man's thigh.

It maintains its full figure by eating its next-door neighbour.

The Bornean blue earthworm.

It's even bigger than the leech...

..stretching to below a grown man's knee.

In this battle of the titans, though, it's the smallest that wins.

The leech's muscular mouth crushes the worm,

taking the phrase "down in one" to the extreme.

New Zealand's carnivorous Powelliphanta is the sumo wrestler

of the snail world.

The largest can grow to the size of a fist, and that is just the shell.

Their unfortunate prey is scraped into the gullet by a rasp-like

structure embellished with 6,000 teeth.

Japan's finger-length giant hornet

is one of the largest, heaviest,

and deadliest insects in the world.

It feeds on the larvae of the humble honeybee.

To get to its meal, it must fight its way into the hive.

A team of 30 can decimate a 30,000-strong hive in

just three hours.

BUZZING

Our big beasts may have got their dining options sorted, but for some,

size poses another challenge,

when nature turns up the thermostat.

The Australian outback.

Temperatures here can hit 50 degrees Celsius.

The red kangaroo is the world's largest marsupial.

It can grow to a towering height of almost two metres.

A single leap can cover seven metres,

allowing them to hit a top speed of 35mph.

But any exercise generates heat.

Big bodies like these have comparatively small surface areas,

making it hard for heat to escape.

As the temperature soars, they head for shade.

To cool their overheating bulk,

they paste themselves in their own refreshing saliva.

Their forearms are covered in a cobweb of capillaries.

As the saliva evaporates, their blood cools.

The blue parts of this thermal image are the coldest,

showing just how effective their saliva bath can be.

They also dig down beneath the scorching earth

to the cooler soil below,

to sit out the worst of the day's heat.

Sometimes, the simplest solutions are the cleverest.

In Australia's Northern Territory,

a famously sun-averse mammal is also wrestling with the temperature.

Staying cool just requires escaping the jaws of death.

The little red flying fox is not so little.

It's a species of mega bat...

..with a body as big as a rat, and heavier....

..and a wingspan of a metre.

If temperatures hit a tipping point of 40 degrees Celsius,

hundreds of these big bats can die.

It's 38 degrees.

Dangerously near the death zone.

300,000 bats are dehydrating.

Their burly bodies are producing more heat than they can release.

What they really need is water.

Skimming the river's surface with their chests is refreshing.

But more importantly,

it collects water in the hairs to lick off back at the roost

and quench their thirst.

But they are not the only ones making the most of the river.

This is the Australian freshwater crocodile.

Or freshie, to the locals.

The sun makes these cold-blooded reptiles alert,

and ready to hunt.

This deadly game of tag is non-negotiable.

If they don't risk becoming fodder for a freshie

they'll die in the heat.

Fortune favours these brave bats.

Most of the time.

So, being big is not so great when it's hot.

But can a bulky frame help stave off the cold?

Well, if you're warm-blooded the answer is yes.

Mammals tend to be beefier in cooler climes.

Take the biggest bear on earth, the polar bear.

Its huge volume stores the heat in temperatures as low as -37 Celsius.

And their 10cm blubber layer is such an effective insulator,

these mighty mammals sometimes need a good rub in the snow to cool down.

But, if you're cold-blooded,

you rely on a daily dose of sun to warm up your insides.

So reptiles and insects generally fare better in the cold

when they're small.

Some species, though, just can't help but defy convention.

Remember the gargantuan bird-eating cricket of the Kalahari?

Well, it has a distant cousin,

that beats it hands down in the size stakes.

This colossal beast is the mountain stone weta...

..an insect that's grown as big as a mouse...

..for one simple reason.

Wetas evolved back when there were no native mammals.

So they took the ecological niche normally reserved for small rodents

and matched them for size.

Being a massive insect is fine when it's warm...

..but this monster species lives high in New Zealand's Southern Alps.

It had to evolve a way to survive being big in the cold...

..by doing something no other insect this large can.

Even in the shelter of a cave, it can be below zero.

When ice sets in around it,

this ingenious hulk of an insect does something very strange indeed.

It freezes itself to death...

..nearly.

This weta species

actually encourages ice to form in its body.

Ice crystals are sharp.

If they form inside a cell, they tear through the membrane,

like razor blades in a balloon.

So the key to survival is to ensure ice only forms outside its cells.

First the weta dehydrates the cells, drawing water out.

There, the combination of water and special proteins

trigger the formation of ice crystals.

In this state of suspended animation a mountain stone weta can survive

temperatures as low as -10 Celsius.

An extraordinary 80% of its body can be frozen solid.

When temperatures rise and the ice thaws...

..a weta can gradually re-enter the land of the living.

Having got their temperature under control,

our big beasts can go about their day.

But the simple act of moving can be challenging in itself.

Generally, the bigger the beast, the more it weighs.

And the heavier the beast,

the harder it finds lifting its weight against

the downward pull of gravity.

Take Earth's largest land animal, the six-tonne African elephant.

Tracking down food in the Namibian desert

can mean lugging its eye-watering load for 25 miles a day.

Two thirds of an elephant's weight is channelled

through its front legs.

The solution?

Fatty pads in its dustbin-sized feet to absorb the shock.

With each step, they spread the load,

protecting the skeleton from the impact of its monumental weight.

Even with the help of ingenious evolutionary adaptation, though,

the fact remains that gravity limits how big a land animal can get.

So, how do big beasts fare...

..beneath the waves?

Down here, water's buoyancy helps support nature's heavyweights.

Which is why this is the domain of the most enormous animal...

..ever to have existed.

The 150-tonne blue whale outdoes even the biggest dinosaurs for size.

Its tongue alone weighs as much as its largest land rival,

the elephant.

Its heart is almost as big as a golf buggy.

Its major artery is as wide as a human head.

And it's thought they're still growing.

As long as the blue whale has enough food,

this species may just keep on getting bigger.

Despite its eye-popping stats, the blue whale can move with ease.

Which is more than can be said for excessively heavy beasts that want

to get airborne.

Some birds have found benefits to growing big, but in the process,

they've lost the ability to fly.

Take the kakapo,

the world's heaviest parrot.

To reach the fruit and leaves that maintain its full figure,

it has no choice but to climb.

The ostrich has a similar problem.

It's the largest living bird.

Nearly three metres tall...

..with a vast two-metre wingspan that is useless for flying.

Instead, it's perfected the art of running away from predators.

With a top speed of over 40mph,

it's the fastest two-legged animal on Earth.

It could complete a marathon in 45 minutes.

Being big, though, doesn't have to make air travel impossible.

Over 65 million years ago,

a beast far larger and heavier than an ostrich proudly displayed its

aerial skills in the skies above what is now Europe.

Hatzegopteryx may well be the largest flying animal ever known.

If it were alive today,

it would be tall enough peer into a first-floor window.

And they could take off from a standing start,

owing to the sheer power of their wing muscles.

Despite their impressive aerial antics,

it seems they didn't hunt on the wing, but fed on the ground...

..supporting their great weight with extra feet on each wing.

Back in the 21st century, the bird that comes closest to a Hatze,

is the albatross.

At 3.5 metres, the wandering albatross

has the longest wingspan of any bird alive today.

And the albatross can do something Hatze apparently couldn't.

Hunt from the air.

These big birds spend most of their lives at sea,

scouring the ocean's surface for food.

They only come in to land to breed.

This royal albatross has made a pit stop

on New Zealand's South Island,

where her two-month-old chick is waiting for food.

This big baby can polish off half a kilo of fish in a single sitting.

To find its next meal, Mum will have to scour a mere 600 miles of ocean.

So, given she weighs as much as a small dog,

how does she manage to fly?

Her enormous wings get her big body airborne.

The secret to the albatross staying up there, though,

is in its nostrils.

Special sensory organs measure the speed of the surrounding air.

What they're searching for are changes in airspeed.

At the water's surface, the air is almost still,

slowed as it hits the waves.

Ten metres up, it's windier.

As an albatross climbs into the faster air it gets free lift.

Then, turning sharply, it plunges down into the slower air.

Gravity has helped it accelerate to over 70mph.

Downward momentum catapults it back up again like a roller-coaster

into the lift of the faster air.

It's called dynamic soaring.

And, crucially, it means they can fly without flapping their wings.

By exploiting the energy of the wind,

they expend almost none of their own.

This aerial efficiency is what makes such a big body capable of flying

nonstop for over 10,000 miles

without the need to set foot on dry land for years at a time.

For a mother, though, it's straight back to the nest,

to satisfy the big appetite of her chunky chick.

The demands of rearing massive offspring

is something many a big beast can appreciate.

The challenges often begin at birth.

Because of her size, a hippo keeps cool in water.

It's here that she'll usually deliver her 45kg, metre-long baby.

Which leaves her with a problem.

Her little one can't breathe underwater...

..giving Mum just 40 seconds to get her newborn to the surface

for its first gulp of air.

Elephant babies spend nearly two years in the womb to reach

their record-breaking 100kg birth weight.

They take so long to grow, that Mum has to nurse them

for up to four years.

For some big beasts, though,

the trials of the mating game begin long before the birth.

It's the breeding season on the beaches of northern Patagonia.

Over 15,000 female southern elephant seals have flocked here to find

themselves a truly massive mate.

A bull seal can be a staggering eight times his suitor's size.

He can weigh as much as six dairy cows.

And yet, she's not the one in danger of getting injured in this game.

He is.

To secure his legacy, a male must mate

with as many lucky ladies as possible.

These females are all under the watchful eye of one bull.

He's the beach master of a harem that can number 150.

To protect his exclusive mating rites,

he has to stay on his beach territory 24/7 without food or drink

for three months.

Luckily for him, he's really fat.

His 15cm blubber, born of a diet of just seafood,

provides him with energy and water.

For an extra boost while napping,

he holds his breath for minutes at a time.

Every ounce of energy must be saved.

Competitors are always nearby.

It's a battle of bulk and teeth.

His fat suit can't protect him from his rival's 8cm canines.

But even after months of fasting,

the beach master defeats his challenger.

His prize - to father most of the pups this season.

For the loser, it's game over.

Three quarters of bulls each year never get to mate.

It's the bigger the better in the elephant seal mating game.

Securing the next generation is a risky business.

Not just for males.

One beast has grown so big,

that having babies means gambling with her life.

The humble hermit crab.

Harmless and, traditionally, small.

Except for this member of the family.

The coconut crab.

Or robber crab. The largest land crab on earth.

The South Pacific islands of Vanuatu are pretty hard to reach.

So having the place mostly to themselves,

it seems that these critters have taken the opportunity

to grow as big as medium-sized mammals.

Their legs can span a metre.

And they're strong enough to lift the equivalent of ten house bricks.

Being big has allowed them to cultivate some rare talents.

True to their name, they can crack a coconut.

And they've been known to kill and eat rats.

But there's one thing these crabs simply can't do.

And that is swim.

This crab lives its adult life entirely on land,

so you'd think this wouldn't be too much of a problem.

And for most of their days, it isn't.

But once a year, the females of these colossal crustaceans have

no choice but to brave the waves in order to pass on their genes.

This female has been nursing her fertilised eggs on her abdomen,

having mated some weeks ago.

But tonight is the night to release her precious cargo.

And, like all crabs, that's done in water.

She must tread carefully.

She's so well adapted to land

that she's evolved a form of lung that

can no longer breathe underwater.

And her great weight means if she gets out of her depth,

she'll sink...

..and drown.

Clinging for life, she releases her eggs into the waves.

They'll hatch into swimming larva.

But in a month's time, they'll be back on land...

..where they too will grow into terrestrial giants.

Across the coral sea from the coconut crab's paradise isle is

an immense sea beast that also reproduces just once a year.

When it does, it gets even bigger.

This springtime full moon is the trigger for a submarine spectacular.

When the perfect tide height, day length,

and sea temperature all align...

..this happens.

400 species of coral across 3,000 reefs reproduce

over a series of nights.

Tucked inside their limestone armour,

millions of coral polyps release their eggs and sperm simultaneously.

You may be wondering what's big about these tiny floating jewels.

Well, together are responsible for growing

the world's largest single living structure.

The Great Barrier Reef.

At 1,400 miles long, it's over twice the length of Great Britain...

..making it the only living thing visible from space.

Each time the reef reproduces, its gigantic scale increases.

The resulting coral larvae travel back down

to make their home on the reef.

This monumental structure once grew by several centimetres each year.

Of course, there's a twist to this tale.

In recent years,

it's thought that half the coral in this big beast has died.

It's believed rising sea temperatures are responsible

for driving away the colourful algae that live inside coral.

Without nutrients and its distinctive hues,

it's left bleached white.

It appears our modern world is taking its toll on this great beast.

We may not be amongst nature's biggest beasts,

but we do so often have the biggest impact on our planet and on

the animals we share it with.

Our fascination with the goliaths of our world can prove

catastrophic for them.

And nature's giants can't survive without ample space to roam,

plenty to eat, and prime habitat.

Half the remarkable titans featured here are threatened with extinction.

When you consider the astonishing solutions nature's biggest beasts

have come up with to life's big problems...

..ingenious ways to find food, to keep warm or stay cool,

to move around, and to reproduce...

..we should not only celebrate their success,

but also do what we can to ensure they stick around for generations to come.