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[Wind whistling]

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SCOTT: The Arctic has always
been the toughest test,

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no more so than
in the far corner of Alaska

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called the Arctic National
Wildlife Refuge.

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Thousands of caribou face the cold...

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the terrain...

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and formidable predators
to reach one special place

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at just the right time...

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a vast, beautiful plain
on the edge of the Arctic Ocean.

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Here, they give birth.

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This is the story of the last
great land migration

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in North America.

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And of how every Arctic creature
is now on a daunting journey

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from a timeless past
into a vastly different future.

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♪

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♪

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♪

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♪

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SCOTT: On the top
of the world,

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it is still the ice age.

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♪

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♪

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It's northern Alaska in winter.

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The temperature drops to 50 below.

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♪

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♪

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Frozen rivers curl north
from the Brooks Range

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and down to a plain
stretching to the Beaufort Sea

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and the Arctic Ocean, now locked in ice.

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[Wind whistling]

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This vast stretch of white mountains,

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tundra, and icy rivers,

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forms one of the world's
most important wildernesses...

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the Arctic National Wildlife Refuge.

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It's a home for courageous
creatures from another time.

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This wildlife community will face a year

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of difficult decisions.

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Hundreds of miles southeast,
bravest of all perhaps,

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is a pregnant caribou.

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She's part of the Porcupine caribou herd

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and will undertake the longest
annual land migration

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on the planet.

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In her lifetime, she's likely
to walk the same distance

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as a complete circuit of the globe.

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It's December, and the caribou
are waiting,

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eating lichen in the twilight.

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The journey ahead needs precise timing.

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She'll march through forests,

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over mountains, across rivers,

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to the coastal plain.

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It's a round trip
of almost a thousand miles.

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♪

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Some 160,000 caribou

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will walk from their wintering grounds

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in the Yukon and Northwest Territories

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to their calving grounds
in the Wildlife Refuge.

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♪

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The Brooks Range stands in their way,

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running parallel to the coast.

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The sun sets for the last time
until the New Year.

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♪

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♪

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The only sunlight is reflected
by a wintry moon.

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♪

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Hundreds of miles above,

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solar radiation fires up the ionosphere,

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and the ghostly aurora.

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♪

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♪

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This is a world of huge planetary

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forces in constant flux.

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This is nature at its most
spectacular and extreme.

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♪

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[Wolf howls]

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A dawn twilight returns in January.

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♪

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Blizzards blast the tundra.

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Most animals have left or are
hibernating under the deep snow,

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but musk ox remain.

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[Growling]

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[Wind whistling]

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They are loyal to a home range
and won't leave.

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They rarely visit the valley.

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The snow is too deep,

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and they can't dig out the frozen grass.

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Even up here, it's hard work.

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Winters seem to be more erratic recently,

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on average more than eight degrees warmer

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than 50 years ago, which sounds better,

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but now there's freezing rain
on top of heavier snowfall.

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The caribou are becoming restless.

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♪

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Her belly is beginning to swell
with her unborn calf.

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♪

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She's searching for reindeer
lichen, her winter food.

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She's a reindeer as much as a caribou.

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They are the same species.

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♪

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She digs through snow like the musk ox.

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For a prospective mother,

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finding enough food
is her principal focus.

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But it's not her only worry.

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♪

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♪

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It's a lone wolf.

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♪

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♪

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The caribou's instinct
is to stay on the move.

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Somewhere has to be better than this.

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♪

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But migration is not blind instinct.

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It's a series of collective
decisions based on subtle clues

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to weather patterns and journey times.

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Every year is different.

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The wolf has choices to make, too.

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He can follow the caribou,
but they move fast,

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and the journey is too far.

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The first birth of spring.

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It's not a caribou,

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but a newborn musk ox, a 30-pound baby,

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delivered straight onto the snow.

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The family surrounds her,

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a protection from dangers
outside their circle.

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But within hours, the calf wants out.

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There's a beautiful new world to explore.

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Every calf is precious.

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Musk ox were hunted
to extinction in Alaska

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in the 1860s,

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but were brought back in the 1930s.

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There are now a few thousand
here in Alaska.

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A little river gully is a new
adventure for the calf.

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Once in, getting back out is harder.

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♪

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♪

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The mother won't follow.

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She doesn't know how deep the snow is

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and could easily get stuck.

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She tracks her calf from the bank.

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♪

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The calf discovers...

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ice.

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♪

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[Calf lowing]

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♪

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♪

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There's a physical urgency
to find your feet here...

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...but perhaps a greater
mental urgency for the calf

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to figure out her world.

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♪

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The patient mother waits...

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and her calf finds a way out.

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♪

157
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♪

158
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♪

159
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She's got maybe another two years

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looking after this youngster.

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The herd of about 15
will protect the calves

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and search for food around their
large home range until summer.

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The caribou have left
the winter woodland far behind,

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and are heading north.

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♪

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By April, the snow is starting to melt,

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and many rivers run earlier
than a decade ago.

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Spring is moving north faster,
and the caribou need to keep up.

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♪

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The herd heads on for about
a hundred miles,

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then will turn west

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towards the Arctic National
Wildlife Refuge.

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♪

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00:12:30,266 --> 00:12:34,167
It's the end of April.
They are over halfway.

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The mothers will all give birth

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within days of the third of June.

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Six weeks to go.

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[Birds chirping]

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Golden eagles nest along the route.

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They came up from the south

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and established territories in March,

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feeding on hares, ptarmigan, or marmots.

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The eagle pair returns to the
same spectacular nest each year.

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00:13:08,580 --> 00:13:13,551
They are loyal to a site
decided over a decade ago.

185
00:13:13,585 --> 00:13:16,347
But the calendar has changed
a lot since then.

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[Chirping continues]

187
00:13:28,221 --> 00:13:31,500
By early May, the chicks
are near fledging,

188
00:13:31,534 --> 00:13:34,572
and the caribou herd has already passed.

189
00:13:42,994 --> 00:13:45,617
A ground squirrel is breakfast.

190
00:13:51,727 --> 00:13:53,591
[Insects buzzing]

191
00:13:58,354 --> 00:14:00,701
It will take a new generation of eagles

192
00:14:00,736 --> 00:14:04,705
to make the huge adjustment
to the changes unfolding here.

193
00:14:08,330 --> 00:14:13,542
A lone wolf has stuck with
the herd for many miles.

194
00:14:13,576 --> 00:14:22,275
♪

195
00:14:22,309 --> 00:14:31,077
♪

196
00:14:31,111 --> 00:14:35,150
Caribou from a broad area either
side of the Canadian border

197
00:14:35,184 --> 00:14:37,807
are converging on the same route.

198
00:14:37,842 --> 00:14:41,466
They'll navigate around the
eastern end of the Brooks Range,

199
00:14:41,501 --> 00:14:44,400
about 40 miles from the Arctic shore.

200
00:14:44,435 --> 00:14:50,959
♪

201
00:14:50,993 --> 00:14:57,517
♪

202
00:14:57,551 --> 00:15:00,830
In a few places, the route has bottlenecks

203
00:15:00,865 --> 00:15:03,212
around rivers and lakes.

204
00:15:03,247 --> 00:15:10,771
♪

205
00:15:10,806 --> 00:15:18,331
♪

206
00:15:18,365 --> 00:15:22,542
This migration of Arctic caribou
is compared to wildebeest

207
00:15:22,576 --> 00:15:26,615
on the African savanna,
and so the coastal plain

208
00:15:26,649 --> 00:15:30,619
is sometimes called America's Serengeti.

209
00:15:30,653 --> 00:15:40,180
♪

210
00:15:42,872 --> 00:15:44,978
As the herd funnels through the foothills

211
00:15:45,013 --> 00:15:46,738
of the Brooks Range,

212
00:15:46,773 --> 00:15:49,741
the wolf briefly gains an advantage.

213
00:15:59,648 --> 00:16:03,997
The weaker calves from last year
are struggling to keep up.

214
00:16:04,032 --> 00:16:06,448
There's been little time to stop and eat.

215
00:16:06,482 --> 00:16:13,558
♪

216
00:16:13,593 --> 00:16:16,009
As long as the herd stays watchful

217
00:16:16,044 --> 00:16:19,116
and maintains a distance, they're safe.

218
00:16:19,150 --> 00:16:28,056
♪

219
00:16:28,090 --> 00:16:30,955
Caribou are faster.

220
00:16:30,990 --> 00:16:33,268
The wolf is a tactician,

221
00:16:33,302 --> 00:16:36,616
but tactics are hard if you work alone.

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00:16:36,650 --> 00:16:43,726
♪

223
00:16:43,761 --> 00:16:50,837
♪

224
00:16:50,871 --> 00:16:58,051
♪

225
00:16:58,086 --> 00:17:02,055
Here is an unparalleled amount
of food on the hoof,

226
00:17:02,090 --> 00:17:06,301
but to this lone wolf, it might
as well not be here at all.

227
00:17:06,335 --> 00:17:13,066
♪

228
00:17:13,101 --> 00:17:19,728
♪

229
00:17:19,762 --> 00:17:24,629
By May, spring has reached the
Arctic National Wildlife Refuge.

230
00:17:24,664 --> 00:17:26,528
[Buzzing]

231
00:17:26,562 --> 00:17:30,739
Life here has slept under snow
for eight months.

232
00:17:32,327 --> 00:17:35,675
[Chirps]

233
00:17:35,709 --> 00:17:39,334
Plovers and redpolls arrive to nest,

234
00:17:39,368 --> 00:17:41,991
part of a massive aerial migration.

235
00:17:46,272 --> 00:17:50,379
Millions of snow geese
leave California or Texas

236
00:17:50,414 --> 00:17:54,349
and are on their way
to the Arctic Islands of Canada.

237
00:17:54,383 --> 00:17:57,179
They'll stop off here on their way back.

238
00:17:57,214 --> 00:18:03,185
♪

239
00:18:03,220 --> 00:18:09,260
♪

240
00:18:09,295 --> 00:18:12,677
Sandpipers are part of
the worldwide event.

241
00:18:12,712 --> 00:18:18,683
♪

242
00:18:18,718 --> 00:18:22,480
Golden plovers set off from Argentina.

243
00:18:22,515 --> 00:18:26,898
Terns, loons, and songbirds
come from Antarctica

244
00:18:26,933 --> 00:18:30,005
or Africa or East Asia.

245
00:18:30,039 --> 00:18:33,042
Hundreds of species cross the planet

246
00:18:33,077 --> 00:18:35,493
on their way to the Arctic north.

247
00:18:35,528 --> 00:18:42,362
♪

248
00:18:42,397 --> 00:18:49,266
♪

249
00:18:49,300 --> 00:18:54,616
A world of birds is heading to
the summer paradise of Alaska.

250
00:18:54,650 --> 00:19:03,866
♪

251
00:19:03,901 --> 00:19:06,973
[Chirping]

252
00:19:07,007 --> 00:19:12,323
The golden plover couple have
arranged a nest on the ground,

253
00:19:12,358 --> 00:19:15,878
laid their eggs,
and are raising their chicks.

254
00:19:29,340 --> 00:19:33,068
The parents provide some
protection against Arctic foxes

255
00:19:33,102 --> 00:19:35,208
or predatory birds,

256
00:19:35,243 --> 00:19:38,763
but it's mainly just warmth
under a camouflaged wing.

257
00:19:49,636 --> 00:19:53,537
Once thawed out, the chicks have
to get back to finding food

258
00:19:53,571 --> 00:19:55,090
for themselves.

259
00:20:08,414 --> 00:20:11,382
The mother leaves after a couple of weeks,

260
00:20:11,417 --> 00:20:14,834
and the father follows a week or so later.

261
00:20:14,868 --> 00:20:17,146
But the chicks stay longer

262
00:20:17,181 --> 00:20:20,598
and have to find their own way
back to South America.

263
00:20:23,670 --> 00:20:26,190
In the meantime, the chicks catch insects

264
00:20:26,225 --> 00:20:28,261
for as long as they can,

265
00:20:28,296 --> 00:20:31,022
then come running back to warm up again.

266
00:20:36,200 --> 00:20:39,617
Their mother knows it's not just
the cold that will get them.

267
00:20:39,652 --> 00:20:40,894
[Chirps]

268
00:20:51,940 --> 00:20:56,738
Arctic foxes live in tunnels in
the layer above the permafrost.

269
00:21:02,157 --> 00:21:03,917
The parents returned a few months ago

270
00:21:03,952 --> 00:21:08,439
from their winter wanderings
in snowy white coats

271
00:21:08,474 --> 00:21:11,477
to give birth and turn brown for summer.

272
00:21:18,173 --> 00:21:21,659
♪

273
00:21:21,694 --> 00:21:25,422
The cubs were born here in early May.

274
00:21:25,456 --> 00:21:28,045
Now, a few weeks later,

275
00:21:28,079 --> 00:21:30,841
they enjoy the remarkably warm days.

276
00:21:30,875 --> 00:21:38,331
♪

277
00:21:38,366 --> 00:21:45,925
♪

278
00:21:45,959 --> 00:21:53,450
♪

279
00:21:53,484 --> 00:21:56,556
They need to grow up fast.

280
00:21:56,591 --> 00:21:59,007
The cubs are already eating meat

281
00:21:59,041 --> 00:22:02,079
and seem constantly hungry.

282
00:22:02,113 --> 00:22:04,668
Ground squirrels
and nesting birds are here

283
00:22:04,702 --> 00:22:07,360
in large numbers in May and June.

284
00:22:09,673 --> 00:22:12,331
One delivery is not enough for them all.

285
00:22:12,365 --> 00:22:17,750
♪

286
00:22:17,784 --> 00:22:20,408
The others don't notice
the mother's return

287
00:22:20,442 --> 00:22:22,444
until it's almost too late.

288
00:22:22,479 --> 00:22:29,520
♪

289
00:22:29,555 --> 00:22:36,562
♪

290
00:22:36,596 --> 00:22:43,603
♪

291
00:22:43,638 --> 00:22:45,156
Oh, well.

292
00:22:45,191 --> 00:22:47,193
Dad will be back soon with more.

293
00:22:47,227 --> 00:22:51,680
♪

294
00:22:54,096 --> 00:22:56,961
It's a constant meal service during days

295
00:22:56,996 --> 00:22:58,963
that never quite seem to end.

296
00:23:03,692 --> 00:23:06,937
Nesting on the ground is dangerous,

297
00:23:06,971 --> 00:23:12,874
but there is one bird that would
fight off any fox... the jaeger.

298
00:23:12,908 --> 00:23:15,463
Jaeger means hunter in German.

299
00:23:18,638 --> 00:23:21,814
The caribou are beginning to arrive.

300
00:23:21,848 --> 00:23:27,198
They are tired, hungry,
many are about to give birth,

301
00:23:27,233 --> 00:23:30,478
and they could so easily tread
on a bird's nest.

302
00:23:34,930 --> 00:23:38,313
The jaegers are not going
to let that happen.

303
00:23:38,347 --> 00:23:41,109
They start with some gentle warnings,

304
00:23:41,143 --> 00:23:43,456
but the caribou ignore them.

305
00:23:43,491 --> 00:23:47,598
♪

306
00:23:47,633 --> 00:23:50,636
Yet the jaegers are fearless.

307
00:23:50,670 --> 00:23:59,886
♪

308
00:23:59,921 --> 00:24:09,206
♪

309
00:24:09,240 --> 00:24:12,278
The caribou mother has come
hundreds of miles,

310
00:24:12,312 --> 00:24:14,349
faced raging torrents,

311
00:24:14,383 --> 00:24:17,973
been jammed by lakes, escaped wolves,

312
00:24:18,008 --> 00:24:20,493
and now there's a determined parent bird

313
00:24:20,528 --> 00:24:22,599
that doesn't want her here at all.

314
00:24:22,633 --> 00:24:31,780
♪

315
00:24:31,815 --> 00:24:35,819
The caribou respond to
the swooping bird ballet

316
00:24:35,853 --> 00:24:38,235
with strange dance moves of their own.

317
00:24:38,269 --> 00:24:47,002
♪

318
00:24:47,037 --> 00:24:55,735
♪

319
00:24:55,770 --> 00:25:04,537
♪

320
00:25:04,572 --> 00:25:13,373
♪

321
00:25:13,408 --> 00:25:15,514
As more of the herd arrives,

322
00:25:15,548 --> 00:25:19,138
the jaegers battle tirelessly
to keep their eggs safe.

323
00:25:21,416 --> 00:25:25,662
For the birds, and for all life
here, there's little rest.

324
00:25:28,181 --> 00:25:30,390
Even the sun keeps going,

325
00:25:30,425 --> 00:25:34,291
skimming above the horizon
for most of June.

326
00:25:34,325 --> 00:25:44,370
♪

327
00:25:44,404 --> 00:25:47,442
This midnight sun warms the caribou

328
00:25:47,476 --> 00:25:50,825
as they all finally reach
their destination.

329
00:25:50,859 --> 00:25:59,730
♪

330
00:25:59,765 --> 00:26:02,250
These are their calving grounds,

331
00:26:02,284 --> 00:26:06,047
in the heart of the Arctic
National Wildlife Refuge.

332
00:26:06,081 --> 00:26:11,397
♪

333
00:26:11,431 --> 00:26:15,884
She must arrive precisely,
so that she's in the right place

334
00:26:15,919 --> 00:26:18,611
when, a week to 10 days
after the snow melts,

335
00:26:18,646 --> 00:26:22,235
the sedges and grasses
are at their most nutritious.

336
00:26:24,859 --> 00:26:27,758
Somewhere is a mother giving birth...

337
00:26:27,793 --> 00:26:35,214
one new calf among 160,000,
anonymous to all but each other.

338
00:26:35,248 --> 00:26:39,390
Almost all the mothers
give birth within a few days.

339
00:26:39,425 --> 00:26:44,637
♪

340
00:26:44,672 --> 00:26:49,987
♪

341
00:26:50,022 --> 00:26:53,853
The calf doubles in size in two weeks.

342
00:26:53,888 --> 00:26:57,823
The first green flush of sedges
is briefly high in protein

343
00:26:57,857 --> 00:27:01,067
and sugars and coincides within a few days

344
00:27:01,102 --> 00:27:04,519
of when the calf needs most milk.

345
00:27:04,553 --> 00:27:08,005
A week or so later, the grass
will become coarser,

346
00:27:08,040 --> 00:27:11,112
bitter, and indigestible.

347
00:27:11,146 --> 00:27:18,637
♪

348
00:27:18,671 --> 00:27:20,846
The caribou slowly spread out,

349
00:27:20,880 --> 00:27:25,367
surfing a wave of melting snow
and growing grass.

350
00:27:25,402 --> 00:27:34,445
♪

351
00:27:34,480 --> 00:27:36,758
The successful flood of energy

352
00:27:36,793 --> 00:27:39,968
transforms the character of the caribou.

353
00:27:40,003 --> 00:27:45,318
♪

354
00:27:45,353 --> 00:27:48,528
The first people here feel part of it.

355
00:27:48,563 --> 00:27:52,981
Humans and caribou were created
as one, they believe,

356
00:27:53,016 --> 00:27:57,952
and each still contains
a piece of each other's heart.

357
00:27:57,986 --> 00:28:01,093
To the Gwich'in, this is the sacred place

358
00:28:01,127 --> 00:28:03,612
where life begins.

359
00:28:03,647 --> 00:28:12,311
♪

360
00:28:12,345 --> 00:28:20,975
♪

361
00:28:21,009 --> 00:28:26,912
It's late June, and paradise
suddenly closes in.

362
00:28:26,946 --> 00:28:30,639
A plague of mosquitoes emerges.

363
00:28:30,674 --> 00:28:32,331
[Mosquitoes buzzing]

364
00:28:32,365 --> 00:28:36,059
Each one may take just a drop of blood,

365
00:28:36,093 --> 00:28:40,063
but the warmer summers favor the insects.

366
00:28:40,097 --> 00:28:43,273
They emerge earlier and breed faster.

367
00:28:53,145 --> 00:28:55,388
The mosquitoes take so much blood

368
00:28:55,423 --> 00:28:58,391
and distress the caribou mothers so much

369
00:28:58,426 --> 00:29:00,773
that the herd spends
the rest of the summer

370
00:29:00,808 --> 00:29:02,775
attempting to avoid them

371
00:29:02,810 --> 00:29:06,020
by searching for somewhere cooler.

372
00:29:06,054 --> 00:29:09,437
Life becomes a daily
balancing act of finding

373
00:29:09,471 --> 00:29:11,473
food for yourself

374
00:29:11,508 --> 00:29:15,823
and not being food for mosquitoes.

375
00:29:15,857 --> 00:29:19,240
The consequences of the hotter
summers may be subtle

376
00:29:19,274 --> 00:29:22,001
and complex for the caribou,

377
00:29:22,036 --> 00:29:27,489
but the effects to the north
are much more obvious.

378
00:29:27,524 --> 00:29:30,665
Over the last 40 years,
the decline of sea ice

379
00:29:30,699 --> 00:29:32,356
in the Beaufort Sea

380
00:29:32,391 --> 00:29:35,670
is one of the most
dramatic changes anywhere.

381
00:29:35,704 --> 00:29:42,850
♪

382
00:29:42,884 --> 00:29:47,337
One of the animals affected most
is the polar bear.

383
00:29:47,371 --> 00:29:49,166
During the last ice age,

384
00:29:49,201 --> 00:29:54,413
they would probably spend
all year on the frozen sea.

385
00:29:54,447 --> 00:29:57,830
Since the ice age ended,
polar bears hunted seals

386
00:29:57,865 --> 00:30:00,902
on the Arctic ice in winter and spring,

387
00:30:00,937 --> 00:30:03,629
and in late summer, rested on land,

388
00:30:03,663 --> 00:30:06,770
snoozing and living off their fat.

389
00:30:06,805 --> 00:30:14,467
♪

390
00:30:14,502 --> 00:30:18,575
Nowadays the ice on
the Beaufort Sea is erratic.

391
00:30:18,609 --> 00:30:23,822
It melts faster, and the bears
arrive early and thinner.

392
00:30:23,856 --> 00:30:30,794
♪

393
00:30:30,829 --> 00:30:37,732
♪

394
00:30:37,766 --> 00:30:42,806
By July, they are hunting
for food along the shore.

395
00:30:42,841 --> 00:30:45,913
They're not a huge threat
to the caribou herd.

396
00:30:45,947 --> 00:30:49,468
They are lumbering on land,
and easily overheat.

397
00:30:49,502 --> 00:30:51,504
[Gulls crying]

398
00:30:59,547 --> 00:31:01,929
Years are more variable now,

399
00:31:01,963 --> 00:31:05,864
and polar bears are showing
unexpected flexibility.

400
00:31:05,898 --> 00:31:08,004
They search for smaller prey

401
00:31:08,038 --> 00:31:10,834
and scavenge or fight over scraps.

402
00:31:14,251 --> 00:31:16,909
The Arctic Refuge is a safe home,

403
00:31:16,944 --> 00:31:20,844
but there is no refuge
from the outside world.

404
00:31:20,879 --> 00:31:22,881
It's too hot for them.

405
00:31:22,915 --> 00:31:26,815
The July record here is now
85 degrees Fahrenheit.

406
00:31:30,302 --> 00:31:32,787
It's often hardest for a mother.

407
00:31:41,071 --> 00:31:45,041
Polar bear cubs are born in midwinter.

408
00:31:45,075 --> 00:31:49,183
This coast is one of the most
important onshore denning areas

409
00:31:49,217 --> 00:31:50,770
in North America.

410
00:31:56,466 --> 00:31:59,400
These cubs are almost two years old

411
00:31:59,434 --> 00:32:01,333
but still need their mother's milk.

412
00:32:20,490 --> 00:32:25,081
Polar bears have declined
in the southern Beaufort Sea.

413
00:32:25,115 --> 00:32:28,877
There are about half of how many
were here 35 years ago.

414
00:32:31,915 --> 00:32:34,745
♪

415
00:32:34,780 --> 00:32:37,472
These are desperate times.

416
00:32:37,507 --> 00:32:39,958
♪

417
00:32:39,992 --> 00:32:41,960
[Ship horn blares]

418
00:32:44,238 --> 00:32:49,001
North Alaska has the largest
oil field in America.

419
00:32:49,036 --> 00:32:54,213
♪

420
00:32:54,248 --> 00:32:59,494
♪

421
00:32:59,529 --> 00:33:02,463
The base at Prudhoe Bay is next to

422
00:33:02,497 --> 00:33:05,638
the Arctic National Wildlife Refuge.

423
00:33:05,673 --> 00:33:07,330
It's a stark reminder

424
00:33:07,364 --> 00:33:10,057
of the cause of the changing seasons.

425
00:33:10,091 --> 00:33:16,201
♪

426
00:33:16,235 --> 00:33:22,241
♪

427
00:33:22,276 --> 00:33:25,037
Pipelines extend south

428
00:33:25,072 --> 00:33:28,661
and cross several caribou
migration routes.

429
00:33:28,696 --> 00:33:37,222
♪

430
00:33:37,256 --> 00:33:40,466
The polar bears search for food
across land

431
00:33:40,501 --> 00:33:43,745
now scarred by oil exploration.

432
00:33:43,780 --> 00:33:50,649
♪

433
00:33:50,683 --> 00:33:53,065
[Woman vocalizing]

434
00:33:53,100 --> 00:34:02,385
♪

435
00:34:02,419 --> 00:34:06,078
For the caribou, the green surge is over,

436
00:34:06,113 --> 00:34:07,942
and they are eating willow shrub

437
00:34:07,976 --> 00:34:12,947
and searching for anywhere
cooler and mosquito free.

438
00:34:12,981 --> 00:34:16,226
For some, that means the coast.

439
00:34:16,261 --> 00:34:20,506
Others head south into the
foothills of the Brooks Range.

440
00:34:20,541 --> 00:34:28,342
♪

441
00:34:28,376 --> 00:34:33,209
After enduring the heat of July,
by late August, it's cooler.

442
00:34:41,113 --> 00:34:45,359
A mother and calf turn south,
with the protection of the herd.

443
00:34:48,327 --> 00:34:52,814
Waiting for them is a grizzly.

444
00:34:52,849 --> 00:34:55,541
Grizzlies and caribou meet each year.

445
00:34:58,303 --> 00:35:02,030
The herd is named after the
Porcupine River they must cross.

446
00:35:10,867 --> 00:35:15,182
The bear's journey here
is equally hazardous.

447
00:35:15,216 --> 00:35:19,531
In summer, grizzlies hunt
all the way to the Arctic Ocean.

448
00:35:51,218 --> 00:35:53,530
The Porcupine caribou herd

449
00:35:53,565 --> 00:35:56,119
is heading south into the Brooks Range.

450
00:36:02,021 --> 00:36:04,714
♪

451
00:36:04,748 --> 00:36:08,304
Away from the water,
the caribou start to relax.

452
00:36:12,618 --> 00:36:14,206
It's a mistake.

453
00:36:14,241 --> 00:36:20,661
♪

454
00:36:20,695 --> 00:36:27,185
♪

455
00:36:27,219 --> 00:36:31,119
Caribou may be faster than bears
on the open plain,

456
00:36:31,154 --> 00:36:33,950
but they must also rest the calves.

457
00:36:33,984 --> 00:36:39,887
♪

458
00:36:39,921 --> 00:36:43,615
Grizzlies and polar bears
are almost the same species

459
00:36:43,649 --> 00:36:46,997
and increasingly overlap and interbreed,

460
00:36:47,032 --> 00:36:50,449
but grizzlies are a more
serious threat to the herd.

461
00:36:52,831 --> 00:36:56,524
The bear has learned
to chase off the mothers

462
00:36:56,559 --> 00:36:59,872
and then search for calves
hiding in the scrub.

463
00:36:59,907 --> 00:37:07,535
♪

464
00:37:07,570 --> 00:37:15,267
♪

465
00:37:15,302 --> 00:37:16,889
He's found two.

466
00:37:19,375 --> 00:37:22,861
In a moment of indecision...

467
00:37:22,895 --> 00:37:24,311
he loses both.

468
00:37:28,867 --> 00:37:32,215
The calf's mother gallops to his side.

469
00:37:32,250 --> 00:37:36,012
It's a huge victory
after so much hardship.

470
00:37:36,046 --> 00:37:38,463
[Bear panting]

471
00:37:38,497 --> 00:37:43,468
♪

472
00:37:43,502 --> 00:37:45,055
Though not for the bear.

473
00:37:53,754 --> 00:37:58,103
The journey south crosses
the Brooks Range in fall.

474
00:37:58,137 --> 00:38:01,762
In spring, this route is blocked by snow,

475
00:38:01,796 --> 00:38:04,903
but now they can return
straight over the mountains.

476
00:38:04,937 --> 00:38:14,292
♪

477
00:38:14,326 --> 00:38:23,611
♪

478
00:38:23,646 --> 00:38:32,965
♪

479
00:38:33,000 --> 00:38:37,625
For the calf, this is his
first taste of the wider world,

480
00:38:37,660 --> 00:38:41,871
with some new characters...
Dall sheep.

481
00:38:41,905 --> 00:38:49,637
♪

482
00:38:49,672 --> 00:38:54,159
They are cousins of bighorns,
little bighorns,

483
00:38:54,193 --> 00:38:56,126
and mountain specialists.

484
00:38:59,958 --> 00:39:02,478
Like musk ox, they don't migrate,

485
00:39:02,512 --> 00:39:05,515
but they do move around
the mountains looking for grass

486
00:39:05,550 --> 00:39:09,105
and shrubs between the rocks.

487
00:39:09,139 --> 00:39:13,351
The ewes give birth to a single
lamb in late May.

488
00:39:13,385 --> 00:39:17,665
By September, they are all
enjoying the last of the summer.

489
00:39:17,700 --> 00:39:23,326
♪

490
00:39:23,361 --> 00:39:25,293
[Sheep bleats]

491
00:39:25,328 --> 00:39:34,751
♪

492
00:39:34,786 --> 00:39:40,930
The mothers gather in flocks
and watch for wolves and eagles.

493
00:39:40,964 --> 00:39:43,415
This is the migration route south,

494
00:39:43,450 --> 00:39:46,004
familiar to more than just caribou.

495
00:39:46,038 --> 00:39:49,663
♪

496
00:39:49,697 --> 00:39:52,286
[Bleating]

497
00:39:57,498 --> 00:40:07,439
♪

498
00:40:07,474 --> 00:40:09,476
The fledged golden eagle

499
00:40:09,510 --> 00:40:14,066
has been shadowing the caribou herd south.

500
00:40:14,101 --> 00:40:16,068
As the herd turns east,

501
00:40:16,103 --> 00:40:19,382
the caribou face the mountains' wolves.

502
00:40:19,417 --> 00:40:24,560
♪

503
00:40:24,594 --> 00:40:28,564
In a small valley, the herd slows to rest.

504
00:40:33,327 --> 00:40:36,330
A lone female plans her hunt.

505
00:40:42,509 --> 00:40:44,511
She doesn't try to hide.

506
00:40:44,545 --> 00:40:47,168
The mountains are on her side now.

507
00:40:47,203 --> 00:40:54,969
♪

508
00:40:55,004 --> 00:41:02,805
♪

509
00:41:02,839 --> 00:41:10,537
♪

510
00:41:10,571 --> 00:41:13,643
A calf becomes separated.

511
00:41:13,678 --> 00:41:22,341
♪

512
00:41:22,376 --> 00:41:31,005
♪

513
00:41:31,040 --> 00:41:32,455
To its mother,

514
00:41:32,490 --> 00:41:37,460
almost home, the trek has
lost its meaning, its purpose.

515
00:41:45,572 --> 00:41:51,543
The snow geese arrive here from
the northernmost Arctic islands.

516
00:41:51,578 --> 00:41:55,685
This is an important stopover
on their way back to California,

517
00:41:55,720 --> 00:41:58,308
Texas, and Mexico.

518
00:41:58,343 --> 00:42:00,241
[Squawking]

519
00:42:03,175 --> 00:42:07,697
Snow geese numbers have grown
over the last 20 years.

520
00:42:07,732 --> 00:42:09,837
There are now 20 million of them.

521
00:42:09,872 --> 00:42:15,463
♪

522
00:42:15,498 --> 00:42:17,845
In a world of so much decline,

523
00:42:17,880 --> 00:42:21,055
it's good to know
some species are doing well.

524
00:42:21,090 --> 00:42:29,685
♪

525
00:42:29,719 --> 00:42:38,314
♪

526
00:42:38,348 --> 00:42:46,943
♪

527
00:42:46,978 --> 00:42:51,258
The autumn storms are sweeping in.

528
00:42:51,292 --> 00:42:53,674
The weather changes very quickly.

529
00:42:53,709 --> 00:42:59,749
♪

530
00:42:59,784 --> 00:43:05,824
♪

531
00:43:05,859 --> 00:43:10,035
Ptarmigans have been caught
in their summer plumage.

532
00:43:10,070 --> 00:43:13,038
They'll turn white to
an out-of-date schedule.

533
00:43:17,318 --> 00:43:20,011
As long as the snow isn't too deep,

534
00:43:20,045 --> 00:43:23,186
they can feed on willow buds and birch.

535
00:43:23,221 --> 00:43:30,262
♪

536
00:43:30,297 --> 00:43:33,162
Ptarmigans are here all year.

537
00:43:33,196 --> 00:43:37,476
That makes them a reliable
target for a red fox.

538
00:43:37,511 --> 00:43:44,414
♪

539
00:43:44,449 --> 00:43:51,352
♪

540
00:43:51,387 --> 00:43:53,458
[Calling]

541
00:43:53,492 --> 00:43:56,841
The many eyes of a flock

542
00:43:56,875 --> 00:44:00,154
and their sharp calls
protect them for now.

543
00:44:02,640 --> 00:44:05,228
Red foxes are thriving in the Arctic

544
00:44:05,263 --> 00:44:09,577
and out-compete Arctic foxes
if the weather is milder.

545
00:44:09,612 --> 00:44:19,001
♪

546
00:44:25,732 --> 00:44:28,838
By October, the rivers are frozen

547
00:44:28,873 --> 00:44:30,598
and are buried under snow.

548
00:44:30,633 --> 00:44:38,089
♪

549
00:44:38,123 --> 00:44:41,713
The musk ox have to dig
for vegetation again.

550
00:44:41,748 --> 00:44:48,513
♪

551
00:44:48,547 --> 00:44:52,448
The male musk ox have other concerns.

552
00:44:52,482 --> 00:44:54,174
Before winter arrives,

553
00:44:54,208 --> 00:44:57,384
they must sort out mating rights
to the harem.

554
00:44:57,418 --> 00:44:59,593
The rut started in August

555
00:44:59,627 --> 00:45:02,251
and a clear victor has yet to emerge.

556
00:45:02,285 --> 00:45:10,052
♪

557
00:45:10,086 --> 00:45:17,887
♪

558
00:45:17,922 --> 00:45:20,994
[Growling]

559
00:45:21,028 --> 00:45:29,347
♪

560
00:45:29,381 --> 00:45:37,700
♪

561
00:45:37,735 --> 00:45:46,053
♪

562
00:45:46,088 --> 00:45:54,337
♪

563
00:45:54,372 --> 00:45:58,307
The musk ox are also related
to bighorn sheep,

564
00:45:58,341 --> 00:46:00,274
but are much bigger.

565
00:46:00,309 --> 00:46:03,105
Males weigh in at 800 pounds,

566
00:46:03,139 --> 00:46:07,765
and their closing speed
is close to 60 miles an hour.

567
00:46:07,799 --> 00:46:10,664
Their skulls are heavily reinforced

568
00:46:10,698 --> 00:46:13,391
and the brain protected by fluid.

569
00:46:13,425 --> 00:46:20,018
♪

570
00:46:20,053 --> 00:46:26,749
♪

571
00:46:26,784 --> 00:46:30,960
They back away,
but only to prepare for combat.

572
00:46:30,995 --> 00:46:37,449
♪

573
00:46:37,484 --> 00:46:40,832
On the right, the older waits,

574
00:46:40,867 --> 00:46:42,972
then charges.

575
00:46:43,007 --> 00:46:49,254
♪

576
00:46:49,289 --> 00:46:55,536
♪

577
00:46:55,571 --> 00:46:58,298
There's probably no other animal on Earth

578
00:46:58,332 --> 00:47:00,162
that could survive this battle.

579
00:47:03,579 --> 00:47:06,237
The winner will now mate with the herd.

580
00:47:06,271 --> 00:47:12,312
♪

581
00:47:12,346 --> 00:47:16,903
By October, the land is frozen solid.

582
00:47:16,937 --> 00:47:20,147
[Gulls crying]

583
00:47:20,182 --> 00:47:23,461
Two polar bear cubs
have survived the summer

584
00:47:23,495 --> 00:47:25,221
thanks to their mother.

585
00:47:25,256 --> 00:47:35,300
♪

586
00:47:35,335 --> 00:47:38,027
The sea won't freeze solid until November,

587
00:47:38,062 --> 00:47:43,377
but some coastal bays and river
estuaries freeze earlier.

588
00:47:43,412 --> 00:47:47,347
It's their playground while they wait.

589
00:47:50,626 --> 00:47:52,386
On warm days the surface

590
00:47:52,421 --> 00:47:55,942
starts to melt and becomes slippery

591
00:47:55,976 --> 00:47:59,324
and tides weaken the new ice.

592
00:47:59,359 --> 00:48:02,224
The surface is still fragile.

593
00:48:02,258 --> 00:48:09,231
♪

594
00:48:09,265 --> 00:48:16,341
♪

595
00:48:16,376 --> 00:48:23,348
♪

596
00:48:23,383 --> 00:48:26,938
By midwinter, they'll be
sniffing out seals

597
00:48:26,973 --> 00:48:30,252
in a freezing twilight far from land.

598
00:48:30,286 --> 00:48:36,258
♪

599
00:48:36,292 --> 00:48:40,227
This is their ice age home at last,

600
00:48:40,262 --> 00:48:44,887
a timeless scene that leaves
behind a world of change.

601
00:48:44,922 --> 00:48:52,999
♪

602
00:48:53,033 --> 00:48:57,279
Then the ice breaks, and reality returns.

603
00:49:10,637 --> 00:49:13,157
The sea melts and refreezes

604
00:49:13,191 --> 00:49:17,092
and will melt again
for two frustrating months.

605
00:49:17,126 --> 00:49:26,584
♪

606
00:49:26,618 --> 00:49:30,208
The polar bears of the southern
Beaufort Sea are doing better

607
00:49:30,243 --> 00:49:33,867
than many others around the Arctic.

608
00:49:33,901 --> 00:49:40,011
♪

609
00:49:40,046 --> 00:49:46,259
♪

610
00:49:46,293 --> 00:49:50,470
The Arctic National Wildlife
Refuge protects the dens,

611
00:49:50,504 --> 00:49:54,646
and mothers have become expert scavengers.

612
00:49:54,681 --> 00:49:59,720
Their sense of smell is probably
the best of all animals.

613
00:49:59,755 --> 00:50:08,936
♪

614
00:50:08,971 --> 00:50:18,118
♪

615
00:50:18,153 --> 00:50:20,293
And look what they've found.

616
00:50:20,327 --> 00:50:26,471
♪

617
00:50:26,506 --> 00:50:30,234
It's a bowhead whale...
what's left of it.

618
00:50:30,268 --> 00:50:32,512
[Gulls crying]

619
00:50:35,239 --> 00:50:38,138
With unpredictable winter ice ahead,

620
00:50:38,173 --> 00:50:42,073
this bowhead carcass is
a salvation for the family

621
00:50:42,108 --> 00:50:45,594
and for all the local polar bears.

622
00:50:45,628 --> 00:50:47,837
They will feed for weeks.

623
00:50:49,839 --> 00:50:55,466
Bowhead whales are increasing,
maybe thanks to longer summers.

624
00:50:55,500 --> 00:50:58,883
Everything is changing,
and everything is connected.

625
00:51:01,575 --> 00:51:04,233
There is regulated whale hunting here,

626
00:51:04,268 --> 00:51:06,201
and this carcass has actually been left

627
00:51:06,235 --> 00:51:08,651
on the beach for the wildlife.

628
00:51:11,033 --> 00:51:13,794
For the polar bears, it's a lifeline,

629
00:51:13,829 --> 00:51:15,313
but maybe little more.

630
00:51:17,798 --> 00:51:21,181
They are ice bears,
evolved in another world.

631
00:51:21,216 --> 00:51:27,049
♪

632
00:51:27,084 --> 00:51:31,433
Across millions of years,
the Earth has seen huge changes

633
00:51:31,467 --> 00:51:33,780
many times.

634
00:51:33,814 --> 00:51:38,785
The most recent was the end of
the Ice Age, 12,000 years ago.

635
00:51:38,819 --> 00:51:46,172
♪

636
00:51:46,206 --> 00:51:48,070
This extraordinary wilderness

637
00:51:48,105 --> 00:51:51,349
protects these Ice Age survivors...

638
00:51:51,384 --> 00:51:55,250
the polar bears, musk ox, arctic foxes,

639
00:51:55,284 --> 00:51:57,631
and the spectacular caribou,

640
00:51:57,666 --> 00:52:02,049
holding out on the top of the world.

641
00:52:02,084 --> 00:52:06,502
Now, even for them,
the ice age may, finally,

642
00:52:06,537 --> 00:52:08,366
be coming to an end.

643
00:52:08,401 --> 00:52:10,748
[Woman vocalizing]

644
00:52:10,782 --> 00:52:14,441
♪

645
00:52:17,134 --> 00:52:25,142
♪

646
00:52:25,176 --> 00:52:33,184
♪

647
00:52:33,219 --> 00:52:41,192
♪

648
00:52:41,227 --> 00:52:49,269
♪

649
00:52:49,304 --> 00:52:51,202
♪

650
00:52:51,237 --> 00:52:52,686
♪

651
00:52:52,721 --> 00:52:54,826
♪

652
00:52:54,861 --> 00:52:55,862
♪