The Frozen World The Living Planet

Water - hundreds of thousands of tons of it,

lying frozen on the mountains of the world.

It covers not only the poles, but caps great peaks on the equator.

Water molecules, distilled from the sea by the heat of the sun,

condense in the sky.

As they fall gently through the air, they pack together into shapes

that echo their six-fold symmetry and form infinitely varied crystals of ice.

They settle on the high mountains and compact into snow and ice

that is, chemically, almost pure water,

much purer than the sea from which most of it came.

On Mount Rainier in the western United States,

permanent snow begins at 7,000 feet.

You might think that this was one of the most inhospitable places on Earth for life.

After all, no vegetation grows on these snowfields,

so there can be no animals that feed on it, like marmots or mice or rabbits,

and if there are no herbivores, there can't be any carnivores, any predators

like hawks or weasels.

But in fact, there is a surprising amount of life here.

There is some life actually within this snowfield itself,

because this snow is not white, but red.

The colour comes from microscopic plants - algae.

The redness is produced by light reflected from their cell walls,

and is almost invisible when, under the microscope, light shines through them.

Internally, they're green with chlorophyll.

With its aid, they use the sun's energy to convert carbon dioxide and water

into sugars.

And these, together with the minerals dissolved in the melt water,

are all the algae need to grow and reproduce.

The heavy falls of winter snow will bury them feet deep,

but in spring, when the surface melts, they divide, develop tiny beating hairs,

and swim up to the surface in the sunshine.

As they age, and the minerals are used up, they change colour,

forming huge smears of red in snowfields all over the world.

Eventually, the snow algae produce spores as fine as dust

and in that form they are blown from one snowfield to another.

But other, bigger animals, also brought up by the wind,

and blow across the snows of Mount Rainier.

Ladybirds. Thousands of them.

Nobody knows why they come up in such numbers and assemble like this.

But in late summer they fly up from the valleys up to these high peaks

and here assemble in the rocks.

When the winter snows come, the ladybirds remain underneath

the snow in the rocks,

and then in the spring, as now, the snow melts and the sun warms the ladybirds,

and they become active and fly off back to the valley to feed on aphids.

The ladybirds are only temporary residents of the Mount Rainier snowfields.

Other insects manage, almost unbelievably,

to live all their lives in this seemingly inhospitable snow.

The best time to find them is at night.

A whole community lives here,

feeding on pollen grains and the bodies of dead insects blown up on the wind.

Some, like this primitive relation of the cockroach, a grylloblattid,

have a body chemistry so well adjusted to function at low temperatures

that if you pick them up, your hand's warmth will kill them.

Permanent snow lies directly on bare rock,

but lower down, where it comes and goes, there can be a little vegetation

to be grazed.

Mountain sheep. These on Mount McKinley are the kind

known as Dall sheep.

Little ground squirrels live up here too.

Unlike the sheep, which retreat to lower altitudes in winter,

the squirrels are permanent residents,

insulated in their burrows from the frosts by the cover of snow.

There are sheep like these in mountains all through North America,

Asia and Europe.

They all carry big horns, and all the senior males, in autumn,

indulge in the most alarming courtship battles.

It's net easy for plants to grow on steep, high slopes

The warming by day and freezing by night makes the gravelly soil slip

downwards, so it's difficult for plants to keep a hold.

With few plants, grazing animals are rare,

though there may be more than there appear to be at first sight.

These, in the Himalayas, are blue sheep,

so nimble and sure-footed they simply able to reach almost any vegetation on

the steep slopes.

But if these are rare, rarer still is the animal that preys on them,

the snow leopard.

During the summer it stays high, at between 12,000 and 15,000 feet,

hunting small rodents and birds as well as mountain sheep.

Snow leopards have been seen as high as 18,000 feet in summer.

But when winter comes and there are heavy falls of snow, it retreats to the valleys.

Game is now so scarce that there's barely enough in even a large valley

to support more than one leopard,

so this animal hunts alone.

Its thick, dense fur is now paler.

It has a thick, woolly undercoat and cushions of hair under its paws

which prevent it from sinking in the snow.

The mountains of Africa, even though they so close to the equator,

are permanently capped by snow.

Kilimanjaro, 19,000 feet high, is a volcano.

Mount Kenya, also volcanic, is 2,000 feet lower but still has its own glaciers

Each has its own animals and plants

specially adapted to life at low temperatures.

And here, at about 13,000 feet, grow some most beautiful and dramatic plants.

Giant groundsels and giant lobelias.

At these altitudes, plants like these

have to face two totally conflicting problems every 24 hours.

Every night the temperature falls so low that they're in danger of freezing solid.

And every day the sun rises and beats down so strongly in this very thin air

that it threatens to warm them up and rob them of their moisture by evaporation.

But look how this lobelia deals with those problems.

This little pond of water in the leaf rosette freezes over every night,

and this shield of ice prevents the water beneath from freezing,

so that it acts as a liquid jacket, preventing the frost from reaching

the heart of the plant.

But then, as the day wears on, there comes the other problem.

As it gets warmer, this water is in danger of

evaporating and the plant of losing its night-time insulation.

But it isn't just rainwater that's accumulated in this rosette of the plant.

It's been secreted by the plant itself and it's slightly slimy.

It contains pectin, a colloidal substance which greatly reduces evaporation.

But there's another kind of lobelia

which deals with these two problems in a quite different way.

This one grows very tall and has extremely long leaves,

each fringed with tiny hairs which acting much the same way as the fur

of an animal, trapping air between them, so that they insulate the stem from chills.

They also prevent the wind from robbing the plants of moisture.

Each group of lobelias is owned by a pair of sunbirds

which collect the small insects the plants attract.

They keep themselves warm with fluffed-up feathers.

And among the rocks are hyrax.

The reason these little creatures are so tame and I can get so close to them

as I am, is just because they're living so high up.

Up here, there are very few creatures to prey on them.

An occasional leopard may come up and hunt them, but apart from that, nothing.

And so they can come out during the few brief hours of sunshine

and bask on the rocks without any fear,

just as they're doing now.

Hyrax also live down on the hot plains below,

but these, in response to the cold, have developed particularly long fur.

Though you might not think it from their shape, they often climb trees to crop leaves.

But at these altitudes, there's only grass and lobelias,

and they share it with the little furry-eared rat.

Mount Kenya, like its neighbours Kilimanjaro and Ruwenzori,

is an isolated patch of snow and ice surrounded by the baking hot

African plains.

But the great mountains of South America,

like Cotopaxi, 19,000 feet high, are very different.

These volcanoes, some active, some dormant, are not isolated peaks

but part of a continuous range that runs the whole length of the continent

and is surrounded by the high, cold plains of the Altiplano,

so their flanks support a large and varied population of animals,

all adapted to life at high altitudes and low temperatures.

Here lives a wild South American camel, the vicuna.

Its coat is fine and silky and protected so effectively from the cold,

that it has, paradoxically, led to its near-extinction.

Men have recognised that vicuna wool has an unexcelled softness and warmth

and hunted the animal for it until it's close to extinction.

The people of the Andes have domesticated another wild camel,

the guanaco,

to produce heavy-fleeced versions which not only produce excellent wool

but serve as beasts of burden.

Here, in Ecuador and Peru, close to the equator, wild camels live at

around 14,000 feet.

But as you travel south down the range of the Andes, the snowline gets lower.

Half-way down, 2,000 miles south of Cotopaxi,

the line of permanent snow has dropped from 16,000 feet to 13,000 feet.

A thousand miles farther south still, the mountains are not nearly so high

but are almost completely covered with snow, which comes down to

within a few hundred feet of the sea.

So, on the southernmost tip of South America,

in Patagonia and Tierra del Fuego,

the guanaco doesn't live at great altitudes, but almost at sea level.

Yet it needs its warm coat just as much, for here, even in summer, it's very cold,

and during the winter the whole land is snowbound.

The reason that it gets colder as we get closer to the pole is not complicated.

Rays from the sun strike the Earth at the equator at right angles.

But as you travel round the curve of the Earth,

the rays become more and more glancing.

So a given amount of heat falling on the equator

is distributed over a very much greater area in the polar regions

and has to travel through more of the Earth's atmosphere,

which weakens it still further.

So down in Patagonia, the sun's rays are very much less intense and carry

much less heat, and the glaciers flow right down to the sea.

Farther south still, across the near-frozen seas off Cape Horn,

you reach chains of small volcanic islands

that run down towards the Antarctic continent itself.

Remote, little-known archipelagos

such as the South Sandwich and, here, the South Orkneys.

There are only two flowering plants that can manage to survive

in this bleak, icy country.

One is a kind of thrift and the other is a small, stunted grass.

And apparently, no land-living animals of any kind.

But when the snows melt in summer, they reveal that the rocks and

the boulders are covered with more than 100 different kinds of mosses and lichens,

some of them rounded green cushions, others like miniature trees.

The capacity of these simple plants to endure cold is phenomenal.

Some species can even survive being frozen solid for weeks on end.

Within this miniature tangled jungle lives a whole menagerie of tiny animals.

Primitive creatures little bigger than pinheads

manage to survive by slowly chewing away at the lichens and mosses

during summer.

In winter they almost grind to a halt,

yet they survive unfrozen because their blood contains a kind of antifreeze

and remains liquid even when the temperature falls well below zero.

The majority are vegetarians, but there are also carnivorous mites among them

which clamber around the grazing herds,

picking off individuals as they fancy.

In this extreme cold, the processes of life are greatly slowed down,

not only those of growth, but those that lead to old age and death.

So such tiny creatures as these, which elsewhere might live for merely months,

survive for two or three years within the green mossy carpets.

The seas around these Antarctic islands are strewn with ice.

The pack ice that litters the surface is frozen sea water,

and in winter forms a solid cover to the sea.

The icebergs are different.

They're made of fresh water and have broken away from glaciers flowing

into the sea.

And this is the source of those bergs - the edge of a glacier.

Beyond it, the continent of Antarctica.

It's huge, bigger than the whole of Europe,

and, for the most part, it seems totally devoid of life.

But not all of Antarctica is covered by snow and ice.

In parts of the interior there are valleys where almost no snow ever falls.

This is as desolate a part of the Earth as exists.

The cold is extreme, it's drier even than the centre of the Sahara,

it's dark for half the year

and it's scoured by a never-ending, howling wind.

And the wind is responsible for these carvings in the solid granite.

Crystals of salt form beneath tiny flakes on the surface,

and grow slowly, but so powerfully that particles are broken loose.

The wind then sweeps them up and hurls them at the rock face,

eroding it still further.

Desolate though this waste of shattered rocks may seem, there is life even here.

Algae. Beneath the stone, the wind doesn't dry it out,

and it's protected from the worst of the cold.

It gets the light it needs to grow through the translucent rock.

There are also green patches actually within the rock.

Algae have penetrated the microscopic spaces between the rock's constituent particles

and there managed to grow.

Glaciers flow down these dry valleys,

fed by the ice cap that covers the centre of the continent.

They're among the world's fastest moving, advancing as much as

300 feet in a year.

As they surge downwards, their surface is torn into thousands of crevasses.

During the summer, even though the winds are bitterly cold,

the sun is sufficiently strong to melt a little of the glacier's surface.

Where it accumulates in pools, blue-green algae grows vigorously,

its dark colour enabling it to absorb a high proportion of the sun's feeble heat.

These pools and streams are the only places in all of Antarctica's interior

where life flourishes in any abundance.

The Earth, right at the beginning of the history of life

before any higher plants or any animals had appeared,

must have looked something like this.

Yet here, mysteriously, lie the corpses of large animals.

A crab-eater seal. It looks comparatively fresh,

but examination of its tissues show that it is about 300 years old.

This extreme climate has freeze-dried it.

It must have lost its way, perhaps because of sickness,

and misguidedly crawled up here from the coast, 25 miles away.

Although the land of the Antarctic is almost sterile,

its waters are extremely fertile,

so its margins, particularly the beaches of its off-shore islands, are rich in life.

These fur seals in South Georgia flourish in great numbers

because the surface waters of the seas

are thick with shoals of floating shrimp - krill, which is their main food.

Every year they come ashore to the beaches to pup and mate.

They're not true seals but are technically called eared seals,

for they have small external ears.

They also have hind flippers that can be brought forward, which enables

them to move quite fast on land, something that true seals can't do.

These fur seals retained the fur of their land-living ancestors,

and indeed they thickened it.

So that now some of these big males have manes on them which give them

that other name of sea lion.

This fur lies in two layers.

There's an outer guard hair and then there is a very thick layer close to the skin,

and that traps air in it, so it acts as an insulator and keeps the animals warm

when they go swimming.

But the trouble with fur as an insulator

is that if you dive too deep,

the pressure of the water will squeeze out the air,

and then it's no use.

So fur seals, for the most part, fish in the surface waters.

True seals, like these pups of the elephant seal, have a different kind

of insulation. Their fur on their body is sparse,

but beneath the skin they have a thick layer of oily fat, blubber,

which surrounds their entire body.

Elephant seals dive to great depths to hunt squid,

finding their way in the dark with sonar helping their huge eyes,

but they don't get chilled, for pressure has no effect on the insulating qualities of blubber.

With every year, the blubber which kept them so warm

in the freezing seas loses its power.

Because every year the sea elephants have to moult,

and in order to grow new skin they have to bring

a blood supply close to the surface.

So blood vessels open up through the blubber

and the skin is flushed with blood just below the surface.

If they stayed in the sea in that condition, they'd chill very quickly.

But they don't. Instead...

SEAL GRUNTS

..they haul themselves up onto the beaches and come up into mud wallows

like this one. And there, the big old bulls like that one have to

suppress the feelings of antagonism they felt only a few months ago

and lie close together with their fellows in the interests of keeping warm.

These are the biggest of all seals.

The huge adult males develop a bladder on top of their noses,

like a kind of trunk.

But they also justify their name of sea elephant by their immense size.

The bulls may grow to 20 feet long and weigh three tons.

If you wanted to pick a creature to symbolise the frozen wastes of the Antarctic,

you might well choose a creature like this.

These are macaroni penguins on the island of South Georgia,

halfway between the southern end of South America and the Antarctic.

But it seems the original penguins evolved

not so much in cold climates as in relatively warm ones.

Even today, there are species of penguins that live on the equator,

in the Galapagos islands.

So this dense coat of insulating feathers with a layer of fat beneath it

was probably originally developed simply to keep them warm in the seas anywhere,

but it serves them just as well in the freezing Antarctic winds,

standing on land or on a surging iceberg.

And they are superb swimmers.

Not only are they swift and agile through the water,

when they come in to land through breakers that would smash any boat

they seem to have the resilience of rubber balls.

These chinstrap penguins are only a couple of feet high.

King penguins are half as tall again.

Large size can be an advantage in cold climates.

The bigger a body,

the smaller the surface area of its skin in proportion to its volume.

So a big penguin retains it's heat better than a smaller one.

But their great size causes considerable problems in breeding.

They lay just one egg, which they keep off the freezing ground

by the ingenious if rather inconvenient method of holding it on top of their feet,

covered by a fold of feathered skin.

They keep it here for eight long weeks.

When it does at last hatch, the chick takes so long to grow to it's full size and independence,

that they have to feed it for a further ten months

These king penguins aren't the biggest of all penguins.

They have a cousin, living farther south, which grows even bigger.

It, too, has fearsome problems in raising its chicks

and it solves them in the most dramatic way imaginable.

They lay their eggs not in spring, but at the end of summer.

Their breeding grounds are on the permanent sea ice near the coast.

The females return to the sea after laying to feed,

and now, as winter sets in, the males are left with the eggs.

They shuffle back and forth, each with an egg on his feet,

held carefully above the ice.

The gales intensify as the winter advances

and the sun sinks lower.

In the skies above, the aurora plays.

The male emperors stoically sit out the months of winter darkness.

The sea ice can offer them no nest. Not even a scrape of a few pebbles.

They have nothing to eat, and nothing to do except protect the precious egg

and prevent it from freezing while the chick slowly forms inside it.

As the gales intensify, the males huddle together to give one another shelter.

Then, 65 days after it was laid, the chick begins to hatch.

The newly-emerged chicks are hungry.

All the male can provide is a little secretion from his throat and

long-empty stomach. He's close to starving himself,

having been sustained only by the layer of fat beneath his skin.

He's lost a third of his weight.

But soon after, the female reappears with a full stomach

and takes the chick onto her feet and gives it its first proper feed.

From now on the parents will take turns to trek back and forth to the sea,

bringing food for their youngsters.

But now, at the end of winter,

the sea ice has extended far off from the coast,

and the penguins may have to walk 50 miles to reach open water.

The adults have a powerful urge to cherish a chick.

Those that have lost one will try and adopt any that wanders by.

Others will even incubate pieces of ice.

Repeatedly, the parent in charge

manages to find something from the pit of its stomach

to feed the ever-hungry chick.

Until the chicks lose their down and get their adult plumage,

they can't swim and so can't feed for themselves.

But being so big, they, like the king penguins, take a long time to grow to

full size, and week after week their parents must make the long march

to the sea to collect food for them.

Though the winter is almost over, there is still bad weather.

Blizzards rage over the ice,

and the young, who are becoming independent, huddle together in

groups of their own amongst the parent birds.

Many of the youngsters haven't got the strength to withstand the cold.

Many die.

As the sun rises higher each day,

the adults guarding the chicks suffer in a different fashion.

On sunny days they get uncomfortably hot in their insulating blanket of feathers,

and eat snow in order to cool themselves.

The chicks still have their downy feathers and still can't swim.

But ten months after the eggs were first laid the chicks fledge,

and over the next few weeks, the whole community makes it way down

to the sea, which now, once more, with the spring break-up of the ice, is close at hand.

Now, at last, the adults can feed entirely for themselves.

They've got two months in which to restore their weight

before they start the whole process over again.

These birds, at first sight so penguin-like,

live not near the south pole, but near the north.

They're not penguins but guillemots, members of the auk family.

All auks, like penguins, are excellent underwater swimmers.

They use their wings like flippers, like penguins do.

But they have not become such specialised swimmers as the penguins,

for they can still fly.

These are the guillemots' smaller cousins, the little auk.

Auks and penguins, similar though they are, are not closely related.

They've come to resemble one another by adopting a similar lifestyle

at opposite ends of the Earth.

Unlike Antarctica, that isolated continent surrounded by sea,

the Arctic is connected by land to more temperate parts of the world.

So the land animals of Europe and North America have been able

to reach it, colonise it, and become adapted to its particular demands.

Foxes have moved up here.

The coat of the Arctic fox is lighter than its cousin down south,

and in winter becomes completely white.

On land, it feeds on small rodents,

and on ice floes, it may hope to catch a few birds.

It's just as well the little auks have kept their powers of flight.

The ice floes are also the hunting ground of one of the biggest of all carnivores.

The polar bear.

This one has killed a bearded seal.

A young bear is eager to take a share of the kill, but it has to be cautious.

Adults sometimes kill youngsters in squabbles.

The polar bear is clearly a close relative of the bears

that live farther south in Europe and America.

Its whiteness is an obvious adaptation to the snow and ice,

but so is its huge size.

The principle of a big body retaining heat better than a small one,

applies to bears just as it does to penguins,

and polar bears are very much bigger

than their cousins in temperate lands farther south.

Polar bears, if forced to, will eat all kinds of things

but their preferred food is flesh, particularly that of seals.

They especially like the blubber just below the skin of the seal,

and often leave the meat for the scavenging gulls and foxes.

GRUNTING

BIRDS SQUAWK

LOW GRUNT

Among the glaucous gulls is the much rarer and pure-white ivory gull.

The polar bear's white coat and great size are not its only adaptations to

life in the Arctic.

It gets a good grip on the ice with long, sharp claws

and thick hair on the soles, which also makes them excellent paddles

in the water.

For the polar bear spends a lot of time swimming during the summer.

Ringed seals are much hunted by polar bears,

and when they haul themselves out on the ice,

they must be constantly on the alert.

They have to have regular holes in the ice through which they can leave the water,

or at least stick up their heads in order to breathe.

A polar bear will wait for many hours, motionless, beside such a hole.

They also stalk seals that are rash enough to lie out on the ice.

The polar bear has lost, but about once in every five hunting days,

it does kill, and that is enough.

The most powerful and effective hunter of all, however, on the northern ice, is man.

Eskimo, or Inuit, as they prefer to call themselves,

came up to the Arctic in very early times.

Superb hunters, they were able to live for many months in the winter

on nothing whatever but raw meat.

THEY SPEAK IN THEIR NATIVE TONGUE

They were so skilled in the techniques of living out on the ice

that with nothing more than a knife of bone

they could make a waterproof house from snow in an hour or so.

A slab of sea ice made a window.

CHILD CRIES

LAUGHTER

Inside, the igloo was lit with lamps fed by seal blubber.

Heat from the flame and from their own bodies

could raise the temperature sufficiently for them

to remove their heavy clothing and relax.

It was a life of extraordinary rigour and privation.

These pictures were taken 20 years ago.

No Eskimo lives in this way today.

The poles have not always been so cold.

One explanation of why they've become so concerns

the warming effect of ocean currents.

If they can circulate the waters of the polar seas down towards the equator,

they would keep them relatively warm.

And maybe they did so 100 million years ago, when the continents were

distributed like this.

But since then, the continents have shifted, the polar seas become more

enclosed and any such currents interrupted.

At the other end of the world, during the same period,

the Antarctic continent drifted south until it came to rest over the south pole.

There was no way now that ocean currents there could keep that part of the world warm either,

and so an ice cap formed.

Once that happened, the whiteness reflected back 90% of the heat

in the already feeble rays of the sun.

So ice now covers the whole of Antarctica and the seas of the north pole.

Over the past million years, there have been other variations,

probably connected with the varying strength the sun

and the ice cover has waxed and waned.

At the moment, fortunately for us, we're in one of the warmer phases,

but even so, Antarctica is still buried beneath ice a mile thick,

and in the north, ice and snow extend for 1,000 miles away from the pole.

Eventually, as you come down the mountain or away from the pole,

the land becomes warm enough to prevent it being covered by ice and snow throughout the entire year.

Beyond, the country is bleak enough. Boulders and gravel, rocks

that have been ground to fragments by the glaciers and pushed in front of them.

This is the tundra, and it's a land full of strange shapes and patterns.

Fine muds and sands retain more moisture than coarse gravel,

so when they freeze, they expand more

and push the gravel away from the centre to produce

these geometric shapes.

A foot or so down, the soil is still frozen, permafrost,

so the melted water the summer can't soak away and the land is

covered with bogs and ponds that often lie within the polygonal ridges,

so that the land looks almost as though it's been cultivated by man.

In places, the underground ice pushes upwards

into a mountain called a pingo.

It looks like a small volcano,

but instead of hot lava in its heart,

it has cold, blue ice.

Even though the ice relaxes its grip for only a mere six or eight weeks in summer,

a surprising number of plants and animals manage to find

a permanent home here.

Small flowering plants keep low,

for within a few inches of the ground there is little wind

and the sun's rays can be quite warm.

One kind of tree manages to live up here in surprisingly large numbers

by adopting exactly the same policy.

This is the Arctic willow and it lies flat.

It grows extremely slowly in these cold temperatures,

and this one may well be a century or so old,

as the rings in its tiny trunk would show.

In shallow burrows in the topsoil

live the harvesters of this meagre crop of leaves and grass - lemmings.

During the summer, when there's food about, they breed with astounding speed.

One female produces five or six babies in a litter, and does so four or five times

in a single season. So in a few months she may produce 30 young.

And what is more, the babies grow so quickly that the first to be born in the spring

can themselves produce young before the winter returns.

At the peak of summer, all the tundra plants put out their leaves

and there's lots to eat.

The swarming hordes of lemmings attract hunters.

Snowy owls.

During the summer, lemmings are the owl's main food.

Abundant though the lemmings are,

the hunting has not been sufficiently good for this owl.

She may have laid as many as eight eggs,

but only one chick has survived.

As the days lengthen, herds of caribou migrate up from the south.

Their calves were born early in the season and the herd moves as much as

15 miles a day.

They have to keep travelling in order to find enough food to sustain them all.

They follow the same route each year.

In places, paths have been worn 18 inches deep

where the animals have passed, century after century.

Snow geese fly up, too.

They've come from as far away as Mexico, 3,000 miles distant,

to claim a share in summer's brief crop and to breed.

They exist in two forms.

Ones with dark feathers on the body, as well as pure-white ones.

But they're all the same species, and mixed couples are common.

Soon the tundra is thick with their nests.

Ptarmigan, now in their dark summer plumage, feed on the willow scrub.

The caribou take not only willow, but grasses and lichen.

The first snow geese to arrive and go to nest already have goslings,

and are foraging as a family.

Later arrivals are still on the nest,

and can't leave until the last of their eggs have hatched.

While they stay there, the first goslings to emerge and their parents

are plagued by hordes of voracious blood-hungry mosquitoes.

BUZZING

From the warming pools, more and more mosquitoes hatch.

They in turn provide food for the red-necked phalarope,

and there are plenty to gather.

A square yard of fresh water here can produce 100,000 insects in a season.

Now the blackfly larvae,

that have spent the winter as eggs attached to stones in the shallow pools,

are also beginning to emerge.

Activity now is intense,

for it is light for almost the whole 24 hours of the day.

But by late August, the snow geese begin to sense the imminence of winter

and start to head southwards again.

The caribou, too, come to the end of their grazing,

and start to plod back across the tundra.

As they go, they continue to feed,

building up the reserves of fat they will need

to sustain themselves through the winter.

HONKING

As the weather gets colder and colder, the need to find shelter

becomes more urgent and the herds may cover 25 miles in a day.

And then, at last, the returning travellers

reach the first tall trees.

It's the beginning of the great coniferous forest

that lies south of the tundra right round the globe.

The snow geese will fly on for thousands of miles yet,

but the caribou have reached their wintering grounds.

The forest is a sanctuary

which will protect them from the bitter cold of the coming winter

and it's here that we shall be coming in the next programme.