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00:00:29,320 --> 00:00:35,120
The polar regions are the coldest,
most extreme places on our planet.


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00:00:36,800 --> 00:00:39,320
Winds reach 200 miles an hour


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00:00:39,320 --> 00:00:43,080
and temperatures drop as low as
minus 70 degrees centigrade.


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00:00:47,040 --> 00:00:49,960
Only the toughest can survive here.


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00:00:54,520 --> 00:00:57,960
Over the course of a year,
polar animals must overcome


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00:00:57,960 --> 00:01:04,000
not just the cold, but the most
extreme seasonal changes on Earth.


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00:01:11,960 --> 00:01:17,000
In the High Arctic, winter is one
long night that lasts for months.


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00:01:18,760 --> 00:01:25,520
On lee-side slopes, beneath
the snow, new lives are beginning.


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00:01:40,280 --> 00:01:43,560
The cubs are born blind and tiny.


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00:01:56,400 --> 00:02:00,520
An early birth is easier on
the mother, who is barely awake.


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00:02:09,400 --> 00:02:12,280
Despite her sleepiness, her instinct


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to nurse is overwhelming.


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00:02:26,520 --> 00:02:29,240
CUBS SQUEAK


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The cubs' clucking calls


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stimulate her to produce milk.


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00:02:34,480 --> 00:02:35,880
And what milk!


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It's nine times richer than our own,


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and enables her to double


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00:02:39,840 --> 00:02:41,960
their weight every few weeks.


20
00:03:04,640 --> 00:03:10,240
The sun is returning after
an absence of nearly four months.


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And its warmth starts to transform
this magical ice world.


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00:03:17,200 --> 00:03:18,960
Spring has arrived.


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00:03:33,680 --> 00:03:38,560
The greatest seasonal change
on our planet is now under way.


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00:03:45,720 --> 00:03:48,200
Antarctica is still locked in ice,


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00:03:48,200 --> 00:03:51,120
and surrounded by a frozen ocean.


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00:03:52,280 --> 00:03:54,960
Nonetheless,
there are signs of spring.


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00:04:02,320 --> 00:04:06,480
Adelie penguins are arriving.
Just the males.


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00:04:06,480 --> 00:04:08,480
They've spent five months at sea,


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where it's warmer than it is
on land,


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00:04:10,640 --> 00:04:12,800
and now they're in a hurry,


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for spring will be short.


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00:04:22,080 --> 00:04:25,480
They have travelled 6,000 miles
across the ocean


33
00:04:25,480 --> 00:04:30,600
since leaving their colony last year
and now, they're returning to breed.


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00:04:30,600 --> 00:04:33,920
They cannot lay their eggs on ice
for they would freeze.


35
00:04:33,920 --> 00:04:37,400
So they have to come here,
where there is bare rock.


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00:04:41,720 --> 00:04:43,040
Over the coming months,


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the few parts of Antarctica
that are ice-free will be the stage


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on which five million Adelies will
build their nests.


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00:04:57,480 --> 00:05:00,160
To construct one, they need pebbles.


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00:05:00,160 --> 00:05:02,280
And without a good-looking nest,


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00:05:02,280 --> 00:05:06,160
a male will be unable to
attract a female.


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00:05:06,160 --> 00:05:08,560
When they at last arrive.


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An impressive property demonstrates
your worth as a mate.


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00:05:15,640 --> 00:05:19,800
It takes stones of all shapes
and sizes to build a decent nest


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and finding ones that are
just right is not easy.


46
00:05:28,400 --> 00:05:32,960
So, some penguins turn
to a life of crime.


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00:06:10,320 --> 00:06:13,160
The one who has been robbed
seems unaware


48
00:06:13,160 --> 00:06:17,480
that the thief is just over his
shoulder and looking for more.


49
00:06:27,120 --> 00:06:31,840
The thief's nest is coming along
nicely, probably because


50
00:06:31,840 --> 00:06:35,720
he keeps a particularly
sharp lookout for robbers.


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00:06:35,720 --> 00:06:38,160
After all, it takes one to know one.


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00:06:46,000 --> 00:06:50,440
By fair means or foul, the males
must finish their nests quickly


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if they're to raise a family
over the short Antarctic summer.


54
00:07:08,680 --> 00:07:10,840
In the north of our planet,


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00:07:10,840 --> 00:07:15,760
the weak sunshine is a welcome
relief after the months of darkness.


56
00:07:20,640 --> 00:07:26,480
Finally, it's time for polar bear
families to emerge from their dens.


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This is not the easiest place


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to take your first steps.


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00:07:36,000 --> 00:07:37,960
And the little ones will need plenty


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of encouragement from their mother.


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00:07:48,280 --> 00:07:50,800
If she can raise all three
to independence,


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it will be a rare achievement.


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00:08:07,600 --> 00:08:11,360
During the months underground,
all they've known is their mother.


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00:08:11,360 --> 00:08:15,480
Now, the big, wide world holds
all sorts of challenges


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for these brave, young explorers.


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00:08:26,680 --> 00:08:31,040
The mother leads her new family out
over the frozen sea


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00:08:31,040 --> 00:08:32,480
to hunt for seals.


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00:08:37,240 --> 00:08:40,200
But the spring melt
is already under way.


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00:08:44,040 --> 00:08:48,840
All across the Arctic, the sun's
warming effect is increasing.


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00:08:48,840 --> 00:08:52,240
Sea ice is showing
the first signs of weakening.


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00:08:55,760 --> 00:08:59,320
Inland, the northern rivers are
still locked in ice.


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00:09:03,080 --> 00:09:06,960
The frozen waterfalls are like dams,
holding back billions of tonnes


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00:09:06,960 --> 00:09:11,720
of fresh water that has not moved
for almost six months.


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00:09:11,720 --> 00:09:14,040
CREAKING


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The vast watershed lies motionless.


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00:09:17,880 --> 00:09:19,800
But as spring advances,


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it begins to stir.


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The frozen waterfalls start
to weaken.


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Above them,
the pressure is mounting.


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00:09:38,200 --> 00:09:42,560
Now, from high above, whole sections
can be seen to be on the move.


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00:09:51,080 --> 00:09:54,760
The waterfalls are straining
to hold back the force


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00:09:54,760 --> 00:09:56,680
that is building up above them.


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00:10:04,440 --> 00:10:06,200
The dam bursts...


84
00:10:07,440 --> 00:10:09,360
..and the river is unleashed.


85
00:10:35,040 --> 00:10:37,960
These vast floods accelerate
the breakup.


86
00:10:39,920 --> 00:10:43,720
Soon, an area of sea ice
the size of Australia


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will vanish from the Arctic Ocean.


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The spring melt breaks the ice
for visitors.


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00:11:00,120 --> 00:11:01,280
Narwhals.


90
00:11:06,120 --> 00:11:10,240
The unicorns of the North are on
a mission to reach


91
00:11:10,240 --> 00:11:13,360
the new fishing grounds in the bays
that have been frozen up all winter,


92
00:11:13,360 --> 00:11:14,680
but are now opening up.


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00:11:23,760 --> 00:11:27,200
To get to them,
the narwhals must travel down leads,


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00:11:27,200 --> 00:11:29,160
temporary cracks in the ice.


95
00:11:30,360 --> 00:11:33,640
But these new roads could close
at any time,


96
00:11:33,640 --> 00:11:36,360
cutting off the air
that they need to breathe.


97
00:11:39,640 --> 00:11:43,120
The road narrows, until there's
barely room for one-way traffic.


98
00:11:45,040 --> 00:11:49,160
Then, a surprise. Narwhals
coming from the other direction.


99
00:11:54,680 --> 00:12:00,720
It's a stand-off. Each team faces
an armoury of sharp tusks.


100
00:12:18,760 --> 00:12:21,760
Finally, one side concedes.


101
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And everyone continues
in the same direction.


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00:12:31,960 --> 00:12:35,760
The melting sea ice reveals
open ocean.


103
00:12:35,760 --> 00:12:38,960
And the changes on land are
no less dramatic.


104
00:12:44,760 --> 00:12:47,800
Beneath the snow,
life is already stirring.


105
00:12:49,720 --> 00:12:53,280
The Arctic tundra is unveiled.


106
00:13:00,520 --> 00:13:02,880
Water that has been locked in ice
all winter


107
00:13:02,880 --> 00:13:05,040
once again flows freely.


108
00:13:28,160 --> 00:13:31,400
A landscape that was only white
now bursts with colour.


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Migrants begin arriving
from the south


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00:13:53,080 --> 00:13:57,040
and, suddenly, the tundra is alive
with new families.


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00:14:04,200 --> 00:14:08,040
These Arctic wolf cubs are
just over a month old


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00:14:08,040 --> 00:14:11,440
and always looking out
for their next meal.


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Their parents have been hunting.


114
00:14:23,720 --> 00:14:28,080
Their offerings are devoured
instantly.


115
00:14:29,680 --> 00:14:33,920
Arctic hare is a mainstay
of the tundra diet


116
00:14:33,920 --> 00:14:36,360
and one the cubs seem
particularly keen on.


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Uneaten food is usually hidden
for leaner times,


118
00:14:43,840 --> 00:14:46,800
but there will be no leftovers
today.


119
00:14:46,800 --> 00:14:50,280
The cubs are growing fast
and are always hungry.


120
00:15:01,040 --> 00:15:05,840
The good times are certainly back,
but these white wolves remind us


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00:15:05,840 --> 00:15:09,160
of the Arctic's less welcoming side.


122
00:15:10,800 --> 00:15:12,960
Their coats are pale to conceal them


123
00:15:12,960 --> 00:15:14,800
during the long, snowy winter.


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00:15:16,680 --> 00:15:19,760
It's easy to forget
that one month ago,


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00:15:19,760 --> 00:15:22,760
this land was
a barren, white desert.


126
00:15:22,760 --> 00:15:27,320
But finding a decent meal here
is never easy.


127
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The parents travel up to 80 miles
in a day in search of


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00:15:34,400 --> 00:15:37,360
more substantial prey
for their growing family.


129
00:15:50,520 --> 00:15:53,200
Musk oxen are immensely powerful.


130
00:15:53,200 --> 00:15:56,160
And their sharp horns can kill.


131
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But a calf is more vulnerable.


132
00:16:22,240 --> 00:16:25,040
The two wolves work together
to split the herd


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00:16:25,040 --> 00:16:26,880
and isolate their victim.


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00:16:47,640 --> 00:16:51,200
It seems that the wolf cubs will,
at last, eat well.


135
00:16:56,040 --> 00:16:57,920
But the herd regroups.


136
00:17:06,520 --> 00:17:09,120
The cattle ride to the rescue.


137
00:17:22,880 --> 00:17:25,960
The wolves cannot penetrate
the wall of horns.


138
00:17:28,640 --> 00:17:30,720
The herd are protecting their calf.


139
00:17:33,720 --> 00:17:36,400
For the musk oxen, it's all for one


140
00:17:36,400 --> 00:17:38,360
and one for all.


141
00:17:44,120 --> 00:17:47,600
It's a struggle for all polar
animals to feed themselves


142
00:17:47,600 --> 00:17:51,000
and their families
in the brief Arctic summer.


143
00:17:53,640 --> 00:17:57,360
But there is one tiny creature
of the tundra that has found


144
00:17:57,360 --> 00:18:02,120
an astounding solution
to the shortness of the season.


145
00:18:02,120 --> 00:18:04,960
The woolly bear caterpillar.


146
00:18:05,960 --> 00:18:10,320
It's always the first insect
to appear after the snow's retreat.


147
00:18:12,240 --> 00:18:15,960
The caterpillar then eats as fast as
it can and, indeed it must,


148
00:18:15,960 --> 00:18:19,000
for this far north,
summer only lasts a few weeks.


149
00:18:27,040 --> 00:18:32,160
The days shorten only too soon,
but the caterpillar has not yet


150
00:18:32,160 --> 00:18:36,600
got enough reserves
to transform itself into a moth.


151
00:18:36,600 --> 00:18:40,080
It can't leave the Arctic,
for it can't fly.


152
00:18:40,080 --> 00:18:42,360
So, it settles down beneath a rock.


153
00:18:43,720 --> 00:18:46,960
The sun's warmth rapidly dwindles.


154
00:18:52,960 --> 00:18:55,840
Beneath the rock,
the caterpillar is out of the wind,


155
00:18:55,840 --> 00:18:58,920
but the cold penetrates
deep into the ground.


156
00:19:01,480 --> 00:19:03,440
Soon, its heart stops beating.


157
00:19:03,440 --> 00:19:07,520
It ceases to breathe
and its body starts to freeze.


158
00:19:08,760 --> 00:19:11,240
First, its gut. Then, its blood.


159
00:19:35,920 --> 00:19:38,200
After four months of darkness,


160
00:19:38,200 --> 00:19:40,200
the Arctic begins to thaw.


161
00:19:45,640 --> 00:19:48,400
And the caterpillar rises
from the dead.


162
00:19:55,080 --> 00:19:58,440
By the time the first shoots of
willow appear in the early spring,


163
00:19:58,440 --> 00:20:00,360
the woolly bear is already eating.


164
00:20:02,360 --> 00:20:05,280
But no matter how fast
the woolly bear eats,


165
00:20:05,280 --> 00:20:09,160
it will not have time to gather
enough food this year either,


166
00:20:09,160 --> 00:20:12,720
and the cold closes in once again.


167
00:20:31,960 --> 00:20:35,800
Year after year, the caterpillar
slows down in the autumn


168
00:20:35,800 --> 00:20:37,640
and then freezes solid.


169
00:20:46,040 --> 00:20:49,400
But, eventually,
a very special summer arrives.


170
00:20:54,320 --> 00:20:56,040
This one will be its last.


171
00:21:01,920 --> 00:21:03,120
It's now 14 years old.


172
00:21:03,120 --> 00:21:07,280
The world's oldest caterpillar.


173
00:21:07,280 --> 00:21:10,280
Its remaining days
now become frantic.


174
00:21:10,280 --> 00:21:12,760
It starts to weave a silk cocoon.


175
00:21:16,040 --> 00:21:18,920
Inside, its body is changing


176
00:21:18,920 --> 00:21:21,920
into one that can fly and search.


177
00:21:21,920 --> 00:21:23,960
Abilities that will be crucial
in the days ahead.


178
00:21:38,360 --> 00:21:42,120
All across the Arctic,
moths are emerging.


179
00:21:42,120 --> 00:21:46,080
After completing
their 14-year preparation,


180
00:21:46,080 --> 00:21:49,040
they now have just a few days
to find a partner and mate.


181
00:21:55,040 --> 00:21:58,760
No life illustrates more vividly
the struggle to survive


182
00:21:58,760 --> 00:22:01,360
in this most seasonal of places.


183
00:22:07,360 --> 00:22:11,280
In a matter of weeks, the north
will be frozen over once again.


184
00:22:14,600 --> 00:22:16,840
At the southern end of our planet,


185
00:22:16,840 --> 00:22:19,760
Antarctica is still surrounded
by sea ice.


186
00:22:29,760 --> 00:22:34,040
The Antarctic spring arrives first
at the outer islands.


187
00:22:36,360 --> 00:22:39,640
Although the beaches
of South Georgia are now ice-free,


188
00:22:39,640 --> 00:22:41,480
the King Penguins face
a new challenge.


189
00:22:42,880 --> 00:22:48,320
Their peaceful waterfront has turned
into an obstacle course of blubber.


190
00:22:50,640 --> 00:22:52,920
The elephant seals have arrived.


191
00:22:56,200 --> 00:22:59,600
The beachmaster's authority is
being challenged.


192
00:23:05,240 --> 00:23:07,760
This rival means business.


193
00:23:09,720 --> 00:23:13,680
The beachmaster owns the females
here and must to fight keep them.


194
00:23:26,720 --> 00:23:33,440
The beachmaster himself weighs four
tonnes, but this rival is his equal.


195
00:24:30,280 --> 00:24:33,240
The beachmaster has won
the first battle,


196
00:24:33,240 --> 00:24:38,160
but he may have to defend his harem
every hour for the next month.


197
00:24:38,160 --> 00:24:41,520
If he can stay master of his beach
for this period,


198
00:24:41,520 --> 00:24:44,880
many of the young born here
next year will be his.


199
00:25:01,360 --> 00:25:04,600
In summer,
the Southern Ocean bursts with life.


200
00:25:33,880 --> 00:25:38,240
No bird is more at home in water,
and they are masterful surfers.


201
00:25:43,600 --> 00:25:48,760
Penguins are found only
in the Southern Hemisphere.


202
00:25:50,360 --> 00:25:55,040
They can't fly, but they don't need
to. There are no polar bears here.


203
00:26:03,640 --> 00:26:06,160
These are Gentoo Penguins.


204
00:26:06,160 --> 00:26:11,040
Each spring, they come ashore to lay
their eggs and rear their young.


205
00:26:11,040 --> 00:26:12,440
Their hungry chicks demand


206
00:26:12,440 --> 00:26:15,720
so much seafood that
both parents have to go fishing.


207
00:26:22,840 --> 00:26:24,800
And fishing can be dangerous.


208
00:26:40,080 --> 00:26:42,680
A southern sea lion.


209
00:26:46,640 --> 00:26:51,160
It uses the speed of a breaking wave
to catch up with the Gentoos.


210
00:27:06,720 --> 00:27:08,640
Sea lions normally eat fish,


211
00:27:08,640 --> 00:27:12,680
so he's used to catching
streamline swimmers.


212
00:27:12,680 --> 00:27:15,880
But the Gentoos seem more
than his match out at sea.


213
00:27:15,880 --> 00:27:17,520
He must change tactics.


214
00:27:21,800 --> 00:27:25,400
Perhaps it would be easier
in the shallows.


215
00:27:48,200 --> 00:27:51,520
But, no, it seems
penguins are uncatchable in water.


216
00:27:57,840 --> 00:27:59,080
How about on land?


217
00:28:00,840 --> 00:28:04,000
The penguin's wings,
so powerful for swimming,


218
00:28:04,000 --> 00:28:06,760
are of no help
when it comes to running.


219
00:28:06,760 --> 00:28:09,280
Now, surely,
the sea lion has a chance?


220
00:28:14,960 --> 00:28:18,200
But on the beach,
both are like fish out of water.


221
00:28:40,840 --> 00:28:45,400
Rarely do hunter and hunted play
their roles with so little skill.


222
00:28:45,400 --> 00:28:47,520
The outcome is anyone's guess.


223
00:29:17,360 --> 00:29:20,320
Every summer,
over 40 million penguins


224
00:29:20,320 --> 00:29:23,080
take to the Southern Ocean to feed.


225
00:29:29,240 --> 00:29:31,720
They're joined
by thousands of whales.


226
00:29:31,720 --> 00:29:33,760
Minkes are the most numerous.


227
00:29:40,400 --> 00:29:44,200
They all come here to harvest
the richest ocean on Earth.


228
00:29:50,800 --> 00:29:55,040
Southern humpbacks have travelled
4,000 miles from the equator


229
00:29:55,040 --> 00:29:58,040
to get here in time
for the Antarctic summer.


230
00:30:03,200 --> 00:30:07,400
Each year, the sea ice
that surrounds Antarctica melts,


231
00:30:07,400 --> 00:30:10,120
effectively halving the size
of the continent


232
00:30:10,120 --> 00:30:12,960
and exposing rich waters
around its coastline.


233
00:30:15,880 --> 00:30:19,080
It's the most spectacular
seasonal change occurring


234
00:30:19,080 --> 00:30:21,680
anywhere on our planet.


235
00:30:24,840 --> 00:30:27,960
The remnants of the sea ice are
occupied by sunbathing seals


236
00:30:27,960 --> 00:30:30,920
that have been here all winter.


237
00:30:33,320 --> 00:30:37,720
But new arrivals are following
the retreating ice edge.


238
00:30:38,880 --> 00:30:41,720
And they have come here to hunt.


239
00:30:48,040 --> 00:30:50,880
Killer whales.
The ocean's top predator.


240
00:30:52,760 --> 00:30:54,720
Killers are like wolves,


241
00:30:54,720 --> 00:30:57,880
for they will hunt animals
far larger than themselves.


242
00:30:57,880 --> 00:30:59,840
But even smaller prey are a problem


243
00:30:59,840 --> 00:31:01,600
if you can't reach them.


244
00:31:08,280 --> 00:31:10,880
The solution is teamwork.


245
00:31:12,160 --> 00:31:15,280
Swimming in perfect formation,
they flick their tails in unison


246
00:31:15,280 --> 00:31:18,320
and create a wave
that cracks the ice.


247
00:31:27,200 --> 00:31:30,080
They regroup and assess the damage.


248
00:31:30,080 --> 00:31:32,240
A more powerful wave is needed.


249
00:31:37,800 --> 00:31:40,800
The ice floe is breaking up.


250
00:31:42,160 --> 00:31:45,960
Now, they are close enough to get
a good look at their target.


251
00:31:45,960 --> 00:31:50,120
The seal is a crabeater,
sharp-toothed and feisty.


252
00:31:50,120 --> 00:31:51,560
Not their favourite.


253
00:31:55,560 --> 00:31:57,600
The wolves of the sea move on


254
00:31:57,600 --> 00:31:59,480
in search of easier quarry.


255
00:32:04,640 --> 00:32:06,600
A Weddell seal, that's better.


256
00:32:07,720 --> 00:32:11,040
These are more docile
and easier to tackle.


257
00:32:14,120 --> 00:32:17,600
The pod stays close together
and travels silently.


258
00:32:19,840 --> 00:32:23,240
This time, they unleash
a far more powerful wave,


259
00:32:23,240 --> 00:32:25,360
and with astonishing accuracy.


260
00:32:32,040 --> 00:32:35,880
These big waves are not intended
to break the ice,


261
00:32:35,880 --> 00:32:38,400
but to knock the prey into
the water,


262
00:32:38,400 --> 00:32:40,000
and they rarely fail.


263
00:33:25,720 --> 00:33:28,480
The seal is now where
the killers wanted.


264
00:33:30,480 --> 00:33:32,360
But the hunt is far from over.


265
00:33:35,120 --> 00:33:36,800
They need to grab their prey
by the tail,


266
00:33:36,800 --> 00:33:39,240
while avoiding its snapping jaws.


267
00:33:40,560 --> 00:33:43,400
Only then will they be able
to pull it down and drown it.


268
00:33:47,800 --> 00:33:52,240
Side swipes create violent,
underwater turbulence, a new tactic.


269
00:33:59,040 --> 00:34:02,520
Blowing bubbles gives cover for
others to lunge at the seal's tail.


270
00:34:12,400 --> 00:34:15,720
Somehow, the seal manages
to reach a tiny ice floe.


271
00:34:21,040 --> 00:34:22,680
The killers could easily grab it,


272
00:34:22,680 --> 00:34:25,360
but now, this seems
to have become a game.


273
00:34:27,800 --> 00:34:31,440
The seal's life hangs
on a roll of the ice.


274
00:34:44,040 --> 00:34:47,600
Yet again, the pod joins forces
to dislodge the seal.


275
00:35:06,440 --> 00:35:08,160
The seal sees a chance to escape.


276
00:35:12,440 --> 00:35:17,480
Exhausted, it no longer has
the energy to pull itself to safety.


277
00:35:17,480 --> 00:35:19,520
And the killers are moving in.


278
00:35:28,440 --> 00:35:29,480
Game over.


279
00:35:42,120 --> 00:35:46,280
As the Antarctic summer draws to an
end, visitors that rely on the brief


280
00:35:46,280 --> 00:35:52,080
flush of food will soon be forced
north by the return of the sea ice.


281
00:35:56,920 --> 00:36:02,200
For the largest land predator, the
sea ice cannot return soon enough.


282
00:36:06,080 --> 00:36:11,440
The end of the Arctic summer and
the sun hasn't set for three months.


283
00:36:14,040 --> 00:36:17,640
It's hard to imagine the bitter cold
will soon return.


284
00:36:28,240 --> 00:36:32,080
Some will welcome the chills
of autumn but, for most,


285
00:36:32,080 --> 00:36:36,440
time is running out before they will
have to retreat to the south.


286
00:36:43,080 --> 00:36:46,200
The shorter days
and colder nights trigger


287
00:36:46,200 --> 00:36:50,200
a dramatic change in the willows
and blueberry bushes.


288
00:36:50,200 --> 00:36:53,160
They stop producing
the green pigment that harnesses


289
00:36:53,160 --> 00:36:58,280
the sun's energy, and red and yellow
pigments build up in their leaves.


290
00:37:07,840 --> 00:37:10,840
The tundra blazes with colour


291
00:37:10,840 --> 00:37:12,920
and the whole landscape is
transformed.


292
00:37:33,160 --> 00:37:35,240
The sound of autumn.


293
00:37:35,240 --> 00:37:37,800
The musk ox rut has begun.


294
00:37:45,040 --> 00:37:48,840
This clash of polar titans could
easily become a fight


295
00:37:48,840 --> 00:37:52,040
to the death, as males battle
over females.


296
00:37:55,080 --> 00:37:58,120
A heavy skull and helmet of horn,
four inches thick,


297
00:37:58,120 --> 00:38:02,040
provide some protection
for the musk ox's brain.


298
00:38:12,880 --> 00:38:15,960
The impact is like a car crash
at 30 miles an hour.


299
00:38:34,560 --> 00:38:36,080
Over the next half hour,


300
00:38:36,080 --> 00:38:40,800
the advantage ebbs and flows,
as each tries to finish the duel.


301
00:38:40,800 --> 00:38:42,240
If one can turn the other


302
00:38:42,240 --> 00:38:44,840
and gore its flank,
the fight will be over.


303
00:38:57,400 --> 00:39:00,920
The stakes rise as the risk of
injury, or even death, increases.


304
00:39:14,360 --> 00:39:16,320
This male is outmanoeuvred.


305
00:39:18,080 --> 00:39:20,680
And the champion returns
to claim his females.


306
00:39:25,880 --> 00:39:29,280
By now,
most animals have migrated south.


307
00:39:29,280 --> 00:39:31,840
But the musk ox,
with their thick coats,


308
00:39:31,840 --> 00:39:34,720
will stay
and face the approaching winter.


309
00:39:43,760 --> 00:39:47,720
The moisture in the air freezes
and hoarfrost decorates the leaves.


310
00:39:51,400 --> 00:39:56,000
Ice crystals grow like shards
of glass on every twig.


311
00:40:11,600 --> 00:40:16,040
As the sun's influence continues
o dwindle here in the north,


312
00:40:16,040 --> 00:40:19,200
the freeze pushes
into the tree line,


313
00:40:19,200 --> 00:40:21,880
spreading over
one fifth of the planet.


314
00:40:31,320 --> 00:40:34,240
The northern forests
lock down for winter.


315
00:40:45,320 --> 00:40:49,400
The last running water freezes
and cathedrals of ice are formed.


316
00:40:56,440 --> 00:41:00,280
The great waterfalls of the north
shut down.


317
00:41:07,160 --> 00:41:11,360
The stage is now set
for a magical event.


318
00:41:12,480 --> 00:41:15,360
The formation of snowflakes.


319
00:41:17,480 --> 00:41:20,640
Cold air meets warm air
from the south


320
00:41:20,640 --> 00:41:23,560
and the moisture it carries
crystallises.


321
00:41:31,040 --> 00:41:33,200
All have a six-fold symmetry,


322
00:41:33,200 --> 00:41:36,960
but no two have ever been found
with exactly the same shape.


323
00:41:44,880 --> 00:41:49,680
Each snowflake is water waiting
to be released in spring.


324
00:41:49,680 --> 00:41:54,560
For this reason, snow is the
life blood of these silent forests


325
00:41:54,560 --> 00:41:58,200
and all that live here depend on it
in one way or another.


326
00:42:05,160 --> 00:42:08,160
Some, like the Great Grey Owl,


327
00:42:08,160 --> 00:42:13,680
appear in spring for the boom times,
then vanish like phantoms.


328
00:42:57,920 --> 00:43:02,280
Stooped, shrouded figures bear
the weight of winter's heavy snows.


329
00:43:40,120 --> 00:43:41,560
The heavy snows make it


330
00:43:41,560 --> 00:43:42,800
hard to get around,


331
00:43:42,800 --> 00:43:44,360
even for the largest and


332
00:43:44,360 --> 00:43:46,720
most powerful wolves in the world.


333
00:43:48,960 --> 00:43:51,760
Today, they are setting out to hunt.


334
00:43:51,760 --> 00:43:53,880
The pack is 25-strong,


335
00:43:53,880 --> 00:43:57,280
a sign that the prey
they are seeking is formidable.


336
00:43:57,280 --> 00:43:59,760
The largest land animal
in North America.


337
00:44:00,880 --> 00:44:02,080
Bison.


338
00:44:13,440 --> 00:44:16,640
The bison form a defensive circle
around their young,


339
00:44:16,640 --> 00:44:17,960
horns pointing outwards.


340
00:44:25,600 --> 00:44:28,040
The wolves need a bison
to break rank.


341
00:44:34,480 --> 00:44:38,200
But the tables are turning
and now the wolves have to retreat.


342
00:44:41,840 --> 00:44:44,800
The pack focus their attention
on the rear of the herd


343
00:44:44,800 --> 00:44:46,760
and the bison begin to panic.


344
00:45:21,800 --> 00:45:23,880
A young bison falls behind.


345
00:45:30,120 --> 00:45:32,640
Even this yearling dwarfs
the wolves.


346
00:45:40,880 --> 00:45:42,240
Running head down,


347
00:45:42,240 --> 00:45:44,600
the herd's only thought is escape.


348
00:45:49,760 --> 00:45:51,880
A stroke of luck for the wolves.


349
00:46:05,520 --> 00:46:08,800
The kill will feed the pack
for several days.


350
00:46:08,800 --> 00:46:12,320
But then,
they will have to resume the chase.


351
00:46:12,320 --> 00:46:14,400
At the frozen ends of our planet,


352
00:46:14,400 --> 00:46:17,240
the struggle for survival
never eases.


353
00:46:28,000 --> 00:46:30,040
For a few, the snow is an ally.


354
00:46:38,680 --> 00:46:43,400
Voles stay active throughout
the winter, moving between pockets


355
00:46:43,400 --> 00:46:48,200
of perfectly refrigerated food
in a network of tunnels.


356
00:46:48,200 --> 00:46:51,320
These tunnels are a sanctuary
from predators.


357
00:46:54,600 --> 00:46:56,080
Except one.


358
00:47:00,360 --> 00:47:02,480
The least weasel is a tiny hunter


359
00:47:02,480 --> 00:47:04,760
and the vole's nemesis.


360
00:47:11,400 --> 00:47:13,120
Its body is exactly


361
00:47:13,120 --> 00:47:15,520
the same width as a vole's,


362
00:47:15,520 --> 00:47:18,040
so there's nowhere a vole can go
that a weasel can't follow.


363
00:47:46,360 --> 00:47:50,840
The weasel's long slender shape is
perfect for hunting in tunnels,


364
00:47:50,840 --> 00:47:53,960
but the worst possible shape
for staying warm.


365
00:47:53,960 --> 00:47:56,280
So, they need a special way
of doing that.


366
00:47:58,080 --> 00:48:01,720
She plucks the fur from its body,
tuft by tuft.


367
00:48:11,400 --> 00:48:15,400
And now, she puts it all together
to make a cosy blanket,


368
00:48:15,400 --> 00:48:17,480
under which to sleep in her den.


369
00:48:34,960 --> 00:48:39,680
100 miles above the Earth,
the aurora lights up the sky.


370
00:48:51,360 --> 00:48:55,920
After travelling millions of miles
across space, solar winds, attracted


371
00:48:55,920 --> 00:49:00,640
by the magnetic pull of the Poles,
collide with the Earth's atmosphere.


372
00:49:02,800 --> 00:49:06,440
Trillions of charged particles
dance across the sky.


373
00:49:13,280 --> 00:49:18,440
Above the Arctic, the aurora
borealis, the northern lights.


374
00:49:18,440 --> 00:49:22,040
In the south,
it's the aurora australis,


375
00:49:22,040 --> 00:49:26,400
the southern lights, that bring
light to Antarctica's long winter.


376
00:49:35,320 --> 00:49:40,000
These spectacular light shows
are only a tease.


377
00:49:40,000 --> 00:49:44,320
Solar energy maybe, but no warmth
that will help the Emperor Penguins.


378
00:50:05,480 --> 00:50:09,560
The male penguins have not eaten
for months and have only each other


379
00:50:09,560 --> 00:50:12,480
for protection
from hurricane-force winds.


380
00:50:17,520 --> 00:50:21,240
They have been deserted
by the females, left to incubate


381
00:50:21,240 --> 00:50:24,560
their eggs throughout
the worst winter on Earth.


382
00:50:36,400 --> 00:50:39,080
The Emperors are not entirely alone.


383
00:50:43,280 --> 00:50:44,760
The Weddell seal.


384
00:50:44,760 --> 00:50:49,160
The only mammal to remain here
throughout the winter.


385
00:50:55,480 --> 00:51:00,160
Beneath the ice, they are beyond the
reach of the bitter winter winds.


386
00:51:08,880 --> 00:51:12,000
The sea is minus two degrees
centigrade.


387
00:51:12,000 --> 00:51:15,800
A warm bath compared
to the conditions overhead.


388
00:51:23,000 --> 00:51:25,440
The roof of ice insulates this world


389
00:51:25,440 --> 00:51:27,840
from the wild fluctuations above.


390
00:51:29,760 --> 00:51:34,880
The temperature down here has barely
changed for 25 million years.


391
00:51:46,760 --> 00:51:49,760
There could hardly be
a greater contrast


392
00:51:49,760 --> 00:51:52,880
to the bleak, windswept world
just above.


393
00:52:05,200 --> 00:52:08,040
But there is a constant danger here.


394
00:52:12,320 --> 00:52:16,600
Swirling patterns in the water
reveal its presence.


395
00:52:18,280 --> 00:52:23,120
They're made by brine,
super-concentrated salt water.


396
00:52:23,120 --> 00:52:24,960
It's a warning.


397
00:52:29,120 --> 00:52:32,760
New sea ice forming above
leaves behind brine


398
00:52:32,760 --> 00:52:36,160
that is so extremely salty,
it sinks rapidly.


399
00:52:42,280 --> 00:52:46,240
As it descends, the sea water
around it freezes instantly


400
00:52:46,240 --> 00:52:48,640
and forms a sheath of ice.


401
00:52:48,640 --> 00:52:52,520
A brinicle that grows downwards
towards the sea floor.


402
00:52:59,280 --> 00:53:02,840
Winter is reaching down
from the cold world above.


403
00:53:23,280 --> 00:53:26,480
As it touches the sea floor,
it kills whatever living thing


404
00:53:26,480 --> 00:53:29,840
it contacts by encasing it
in a tomb of ice.


405
00:53:43,000 --> 00:53:45,920
As calm returns beneath the ice,


406
00:53:45,920 --> 00:53:49,680
a dramatic change is coming
to the world above.


407
00:54:16,040 --> 00:54:18,440
The sun returns to Antarctica.


408
00:54:21,640 --> 00:54:24,040
The longest night on Earth has ended


409
00:54:24,040 --> 00:54:26,720
and winter begins to give way
to spring.


410
00:54:47,840 --> 00:54:50,040
Female Emperor Penguins.


411
00:54:50,040 --> 00:54:55,080
After four months feeding at sea,
they're returning sleek and fat.


412
00:55:25,880 --> 00:55:28,120
Penguins, it seems,
can fly after all.


413
00:55:32,000 --> 00:55:35,800
But a winter at sea has left them
a little out of practice.


414
00:56:28,560 --> 00:56:34,360
There is no time to waste.
Faraway, the males are waiting.


415
00:56:47,680 --> 00:56:50,960
Reunited after three months apart.


416
00:56:56,720 --> 00:56:59,880
The reward for the female's return,


417
00:56:59,880 --> 00:57:02,440
a first glimpse of her chick.


418
00:57:08,480 --> 00:57:12,040
A task that began in autumn
has been completed.


419
00:57:15,120 --> 00:57:17,360
Despite the huge odds against it,


420
00:57:17,360 --> 00:57:21,520
the precious chick has survived the
winter and is now with its mother.


421
00:57:22,680 --> 00:57:24,640
And she has food.


422
00:57:30,200 --> 00:57:32,480
The chick's first fresh meal.


423
00:57:34,360 --> 00:57:36,760
The female's mission is complete.


424
00:57:44,440 --> 00:57:47,040
For those Emperor Penguins
that survive,


425
00:57:47,040 --> 00:57:48,760
the worst is over for this year.


426
00:57:56,160 --> 00:57:59,200
There will soon be abundant food
for everyone.


427
00:58:05,080 --> 00:58:10,080
The Emperors have taken on
the polar winter and won.


428
00:58:10,080 --> 00:58:11,600
The gamble has paid off.


429
00:58:13,560 --> 00:58:15,040
All other animals escaped.


430
00:58:15,040 --> 00:58:17,120
Only they remained with their eggs,


431
00:58:17,120 --> 00:58:23,520
and it's they who will benefit most
from the rich southern spring.


432
00:58:23,520 --> 00:58:25,560
Their epic journey is complete.


433
00:58:35,840 --> 00:58:39,360
Subtitles by Red Bee Media Ltd


434
00:58:39,360 --> 00:58:43,080
E-mail subtitling@bbc.co.uk