Natural World (1983–…): Season 38, Episode 2 - Natural World - full transcript

Size matters in wildlife, for species and individuals. As relative skin surface versus mass decreases exponentially with size, large animals have an advantage in the cold, hence Arctic species tend to be larger, like the polar bea...

Are you wondering how healthy the food you are eating is? Check it -
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

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

but also comes with sizeable

How they overcome life's
big problems...

..can be truly jaw-dropping.

Whether it involves a total

..a brutal battle...

..or maintaining their own

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... the leviathans of
our modern world...'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... 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

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

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,

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

Stage two takes days and days of

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,

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

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


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

Protein is crucial for these

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

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

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

..temporarily blinding its

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.


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

Or freshie, to the locals.

The sun makes these cold-blooded
reptiles alert,

and ready to hunt.

This deadly game of tag is

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... 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... 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...


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

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

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

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

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... 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

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

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

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

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.