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.
0nly 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.
0n 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)
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 )
0ccasionally, 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.
0nce 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.
0nly 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.
0n 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)