Original subtitles

Dawn over a silent forest

a few hundred miles from the South Pole

It is the end of months of total darkness

and as the sun's rays filter down through the trees,

they reveal a cold, harsh world

Polar dinosaurs are adapted to cope with extreme conditions,

but even they struggle to stay alive

This far south, the first day of spring

lasts only a few minutes,

but it triggers the start of an astonishing story

of survival through the polar year

It is the mid-Cretaceous period

and dinosaurs are more widespread than ever,

reaching every part of the globe

But one place is a special challenge - the South Pole

Here, a giant continent made up of South America,

Australia and Antarctica

is kept warm by ocean currents

that are forced down from the equator to encircle it

Instead of ice caps, there are lush forests

But unlike the unchanging tropical climate elsewhere,

Antarctica has seasons - from hot summers under midnight sun

to cold winters of total darkness

(Cheeping cry)

Leaellynasaura is a dinosaur

that has adapted to this extreme climate

Throughout winter, they survive in the heart of the forest,

but now, in spring,

they emerge to feed on the fresh plant growth

They are just two metres long

and their most distinctive feature is their large eyes,

which help them find food in the dark winter

They are sociable little animals that live in small clans,

enabling them to make the most of scarce resources

The clan is dominated by one breeding pair,

and the hierarchy ensures

that one of them is always on lookout duty

He issues reassuring clicks as long as the coast is clear

(Whirring clicks)

(Squeaking)

The sentry has spotted a giant amphibian, Koolasuchus

He has massively powerful jaws,

weighs about half a tonne and is a carnivore

In the water, Koolasuchus is lethal,

but on land, his legs have trouble dragging his bulk around

and he is no threat to the lithe little dinosaurs

He has been hibernating over winter in the forest,

and now faces what for him is an arduous journey of 200m

to get back to the river for the summer

This bizarre-looking creature

is a relic from a time before dinosaurs

In most parts of the world,

competition from crocodiles drove them to extinction

Here, the waters get too cold for crocodiles,

and the last Koolasuchus survive,

still patrolling the waterways,

just as their ancestors did

150 million years before them

As spring takes hold and the days grow longer,

a forest bursts into life

Many of the plants in these unique conifer and fern forests

have specially adapted to lie dormant during the dark of winter

Only with the spring light

do they start to photosynthesize again

For the clan, it is also a time of feverish activity

Having mated with the spring sunrise, they now build nests

The dominant pair builds in the centre

and other subordinate animals work around them

Many of these piles of leaves act as decoys

to help protect the main nest

But no matter how busy they are,

they always have to remain alert to danger

A polar allosaur -

a summer visitor from warmer lands to the north

He is a one-tonne ambush predator

(Rumbling growl)

(Squawking)

(Ferocious roar)

The allosaur is the largest and fiercest killer in the forest,

but he was spotted by the sentry

As the clan melt into the undergrowth,

he is no match for their speed and agility

Spring across the polar forests brings the movement of many animals

In the sky, lines of pterosaurs head south

for their summer roosts

And among the trees, there is the echo of unfamiliar sounds

(Booming call)

The largest of all the summer migrants

is coming to the forest

These unusual calls herald the arrival

of huge herds of Muttaburrasaurus from the north

For the last two months,

they have been migrating 800 km down the coast of Australia,

following the sun to the south

They do this every year to strip the lush vegetation

and find secure sites to lay their eggs

The herds have a major impact on the forest

Each adult weighs about 3 tonnes

and can pluck food from branches several metres off the ground

While feeding, they keep in touch

using their specially adapted noses to produce trumpeting calls

(Horn-like call)

As the forest gets more crowded,

the clan's nests need constant attention

The lead female treats her pile of leaves like an incubator

and uses her sensitive beak to monitor the temperature

Then she adds and removes vegetation

to keep the eggs at about 30 degrees centigrade

Already, the baby Leaellynasaura can be heard inside,

responding to their mother's clicks

(Faint cheeps)

The nests also have to be protected round the clock

Fur-coated mammals thrive in these Antarctic forests,

and some are easily large enough to steal an egg

But the Leaellynasaura has an unusual defence

It is enough to see off this egg thief,

but the little dinosaur knows there will be others

The Muttaburrasaurus continue to arrive on the flood plains

and are watched from the forest edges by hungry eyes

The allosaur is testing the herd,

probing for sick or old animals

These herbivores are slow, but find safety in size and numbers

(Booming roars)

The allosaur is no match for a healthy bull Muttaburrasaurus,

and he is forced to back down

By late spring, the tree ferns and conifers are in full flush

and have formed a thick canopy,

soaking up every bit of sunlight

Many of the nests have now fallen victim to predators,

but the clan has ensured that the dominant pair's has survived

Secure within are three hatchlings

For the first two weeks of their lives, they will stay in the nest

while the adults take turns collecting food

and bringing it back to them

(Squeaking)

The lead female takes great care to maintain the nest

To stop predators sniffing out her brood,

she removes the old eggshells and eats the unhatched eggs

This also recycles the nutrients

At this stage, the hatchlings are vulnerable

and can easily become lost on the forest floor if they stray

All the adults watch out for wanderers,

in case a predator moves in

Within weeks, this little hatchling will be strong enough to keep up,

but for now, he is returned to the safety of the nest

It is now summer and permanently light

The sun will not set for another five months

At this time, the forest floor comes alive

with polar insects, like this weta,

out hunting for food among the leaf litter

They themselves are food for larger animals, like the tuatara

It is a reptile,

but one surviving from a time long before the dinosaurs

It will remain long after them, too,

clinging on in the land that will become New Zealand

The Muttaburrasaurus herd

is being tormented by bloodsuckers

Summer brings out swarms of biting flies,

and although dinosaurs are covered in tough, scaly skin,

they do have softer parts

The insects concentrate on areas like the inside of the ear,

where they can pierce the skin and suck out a meal

These swarms can drive their gigantic hosts wild,

and soon the herd has to move away from the river

In the forest, the Leaellynasaura enjoy the summer bounty

and, despite the dangers around them, sleep

During these long months of sun,

they rely heavily on their patterned skin

to camouflage them among the ferns

Sleep is the last thing on the minds

of the hatchlings playing nearby

They have grown and are now practising the sort of agile moves

which may one day save their lives

Wherever the young are, their mother is not far away,

acting as lookout for her increasingly active brood

On the banks of the river,

an old Muttaburrasaurus has been brought down,

and a male allosaur feeds off the rotting flesh

The polar allosaur is a descendant

of the carnivores of the Jurassic, 50 million years before

His type are rare in the Cretaceous,

but they survive at the South Pole

(Rumbling growls)

Although there is enough meat for 20 allosaurs,

it is unlikely this rival female will be tolerated

(Roaring)

(Roaring)

She is driven away by the hungry male

A fully-grown polar allosaur

needs about 100 kilos of meat a week

She will need to come back

once the male has eaten his fill

Later, under the light of the midnight sun,

one of the young Leaellynasaura

ventures down to the river alone

(Squeaks)

Saved by his lightning reactions

But the young Leaellynasaura has much to learn

about the dangers of his forest home

(Thunderclap)

In the time of dinosaurs,

Antarctica suffers summer storms that cause widespread flooding

These floods drive forest creatures together,

and this can lead to confrontation

(Squealing cry)

The Leaellynasaura have spotted a rival clan

and it triggers an aggressive response

Each clan must defend its area of forest,

so it does not face competition for food

The interlopers must be put off

by a convincing show of strength

It has worked

The rivals retreat and, for the moment,

the clan's territory is safe

After the rains, the floodwaters quickly subside

and dinosaurs can return to the riverbanks to feed

When there is plenty of food,

herbivores can be very tolerant of each other

As the Muttaburrasaurus tear at the podocarp trees,

the Leaellynasaura gather up the fruit

that gets scattered on the ground

Although a risky harvest,

the clan must take every opportunity the forest offers,

because time is running out

The seasons draw on,

and for the first time in four months, the sun sets

Autumn has arrived

and the forest prepares for a polar winter

Up and down the river valleys,

the Muttaburrasaurus sense the change,

and begin their long trek north

(Booming grunts)

Occasionally, some of these giant migrants

get lost in the forest

But what for them is a minor problem

can mean life or death for the Leaellynasaura clan

The noise these huge herbivores make

prevents the Leaellynasaura sentry

from hearing more threatening sounds

(Squealing and roaring)

The giant carnivore has killed the dominant female

It is a bitter blow

Winter is coming, and without a lead female,

there will be tension in the clan

In the gathering gloom,

the Koolasuchus senses the drop in temperature

and reluctantly leaves his summer home

Once again, he lumbers into the forest

in search of a suitable shelter

to hibernate through the cold, dark months that lie ahead

The low light also triggers a change in the forest plants

They stop growing

and photosynthesis halts

Some will shed their leaves,

others will just lie dormant

(Chirruping cry)

The Leaellynasaura have to work extra hard to find food,

searching for fungus

and nutritious roots beneath the forest floor

At this time of year, their survival strategy

is to move to the heart of the forest, where it rarely freezes

and to keep active to maintain their body temperature

But it is clear that the summer predators have taken their toll

Only one hatchling has survived

and they still have no lead female

Towards the end of autumn,

the last day passes in a few minutes

and the long twilight begins

Life in the polar forest faces its biggest killer -

freezing temperatures

Some polar creatures, like the weta,

have learned to cope with cold

by allowing themselves to become frozen

In the winter sky,

the Southern Lights whip and flicker over the silent forest

Under the sleeping trees, it is almost pitch-black,

but with image-enhancement,

we get a Leaellynasaura's-eye view of the clan

The dinosaurs are still active, but the ground has frozen

and it has become almost impossible

to scrape a living out of the soil

Even pond water is frozen,

and the Leaellynasaura resort to using their hard beaks

Temperatures this low don't usually last long in the forest,

but with their strict social order in tatters,

the fate of this clan hangs in the balance

They push deeper into the forest

There has been no light for two months

and another cold snap forces the clan to take drastic action

They have evolved one further adaptation to the cold

They huddle together and drift into torpor

In suspended animation,

they can resist the effects of the cold,

but they cannot stay like this for more than a couple of days

The first hints of salvation are small

Under his rock, the weta is revived from his deep freeze

by a slight rise in temperature

On the horizon, the sun's rays grow stronger

and there is the promise of spring

(Squeaking cries)

The forest silence is shattered by an agitated clan

Two males are fighting

This is the mating season for the Leaellynasaura,

and the males are competing for dominance

These fights are short but can sometimes be vicious

Having asserted his authority,

the victorious male chooses a mate and, at last,

the clan can start to re-establish round a dominant pair

Their annual struggle to survive can begin again

Life at the poles

is a remarkable evolutionary achievement for the dinosaurs

But eventually, a slight cooling in the world's climate

will spell doom for these lush Antarctic forests

And, without them,

all these unique dinosaurs will also disappear

Away from the poles, the dinosaurs continue to thrive

for another 40 million years before extinction

In the final programme,

we see how, just before the end of their reign,

they evolved the most terrifying predator of all

(Ferocious roar)

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