1
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[ambient music fades in]

2
00:00:08,805 --> 00:00:10,223
[David Attenborough] Laysan.

3
00:00:10,306 --> 00:00:13,309
A remote island in the Pacific Ocean.

4
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[poignant music playing]

5
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Home to this Laysan albatross chick.

6
00:00:25,488 --> 00:00:29,325
He's ready to make
his maiden flight to the open ocean.

7
00:00:31,077 --> 00:00:34,080
But there can be no room for error.

8
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[cheeping softly]

9
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-[music becomes tense]
-[urgently] Tiger sharks.

10
00:00:44,382 --> 00:00:47,594
They've traveled a thousand kilometers
to get here,

11
00:00:48,178 --> 00:00:51,723
arriving just in time
for the fledging season.

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Leaving will be
the most dangerous journey of his life.

13
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[music intensifies]

14
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But it's his neighbors,
black-footed albatross chicks,

15
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that go first.

16
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[music intensifies]

17
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A splash landing.

18
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Just what the sharks are waiting for.

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[music abates]

20
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[music intensifies]

21
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[music becomes dramatic]

22
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Now, it's his turn.

23
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With the summer winds picking up,

24
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conditions are finally right
for him to spread his wings

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and fly.

26
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[music intensifies]

27
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He's airborne
for the first time in his life.

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But when the breeze suddenly drops…

29
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[music abates]

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…so too does the chick.

31
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[tense music playing]

32
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Without wind,

33
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he's helpless.

34
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[music intensifies]

35
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[squawks]

36
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A very lucky escape.

37
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[screeches]

38
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[music intensifies]

39
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[music becomes rousing]

40
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He's off!

41
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He may not touch land again for five years

42
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as he travels
hundreds of thousands of kilometers

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across the ocean searching for food.

44
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[music climaxes]

45
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[music fades out]

46
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[theme tune playing]

47
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[theme tune fades out]

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Our planet is solar-powered.

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[rousing music playing]

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The sun's rays take eight minutes
to reach us.

51
00:04:01,788 --> 00:04:06,584
But due to the Earth's tilt,
they don't strike its surface evenly.

52
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This solar energy
arrives in varying amounts

53
00:04:13,091 --> 00:04:17,053
at different times of the year,
depending on where it strikes.

54
00:04:18,471 --> 00:04:20,723
And in the Northern Hemisphere,

55
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the huge increase that comes with summer

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triggers countless journeys.

57
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[music fades out]

58
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[chorus of twittering birds]

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00:04:34,153 --> 00:04:35,863
In early July,

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the flower meadows of Europe
receive more sunlight

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than at any other time of the year.

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00:04:46,207 --> 00:04:50,420
And that makes it
a very busy time for honeybees.

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[whimsical guitar music playing]

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Few animals work harder
to exploit the summer's riches.

65
00:05:02,223 --> 00:05:04,976
To make just half a kilo of honey,

66
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a colony of bees
must fly 90,000 kilometers

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and visit over a million flowers.

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And we have taken advantage
of their labors for thousands of years.

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[music fades out]

70
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[loud thrumming]

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In this domestic hive in Germany,

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60,000 bees are working together
as one superorganism.

73
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[hypnotic electronic music playing]

74
00:05:44,015 --> 00:05:48,644
And with the larger queen
laying an egg every 30 seconds,

75
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it's a colony
that is now bursting at the seams.

76
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There could be another 40,000 bees
developing in this hive.

77
00:06:01,074 --> 00:06:04,535
And there just isn't enough room
for them all.

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The superorganism has to split.

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[music intensifies]

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[music abates]

81
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[music becomes dramatic]

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Those in the leaving party
gather at the entrance.

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[music becomes rousing]

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And when they reach a critical mass,
they begin to swarm.

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[music intensifies]

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They must find a new home.

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But the first stop
is just a staging post close to the hive.

88
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In a few minutes,
30,000 bees gather around the queen,

89
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who is now shielded by the swarm.

90
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[music gradually fades out]

91
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Out in the open,
they're vulnerable to the elements.

92
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So the race is on
to find somewhere else to live.

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Scouts set off
looking for a suitable home.

94
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[ethereal music playing]

95
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A tree hole that is just the right size,
height, and angle to the sun.

96
00:08:06,657 --> 00:08:08,117
This one looks possible.

97
00:08:09,327 --> 00:08:11,454
But… too shady.

98
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Too small.

99
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Already taken.

100
00:08:29,055 --> 00:08:31,182
Now, what about this one?

101
00:08:32,934 --> 00:08:34,060
[music abates]

102
00:08:34,143 --> 00:08:35,978
[optimistically] It looks promising.

103
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Yes, this will do nicely.

104
00:08:53,704 --> 00:08:56,916
So it's back to the staging post

105
00:08:56,999 --> 00:08:59,418
to convince the rest of the colony.

106
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[lively whimsical music playing]

107
00:09:03,339 --> 00:09:06,300
And she does that by dancing.

108
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[music becomes quirky]

109
00:09:09,387 --> 00:09:12,932
The angle of her waggle dance
relative to the sun

110
00:09:13,015 --> 00:09:16,561
tells them in which direction
the hole can be found,

111
00:09:17,812 --> 00:09:21,315
while the duration lets them know
how far away it is.

112
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And the better the spot,
the more intense her performance.

113
00:09:29,282 --> 00:09:32,451
Others return to advertise their finds.

114
00:09:33,494 --> 00:09:38,124
But their moves
just don't cut it compared to hers.

115
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[music intensifies]

116
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Interest grows around her.

117
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And more bees set out
to inspect the new hole.

118
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It's house hunting by committee.

119
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It seems they agree,

120
00:10:01,522 --> 00:10:05,234
and they return to spread the news
to the rest of the swarm.

121
00:10:09,363 --> 00:10:10,615
[music fades out]

122
00:10:11,198 --> 00:10:15,578
To do so,
the scouts must touch every bee in turn.

123
00:10:16,537 --> 00:10:18,205
[lively music playing]

124
00:10:18,289 --> 00:10:21,167
And, incredibly, in just half an hour,

125
00:10:21,250 --> 00:10:24,879
all 30,000 of them are ready to leave.

126
00:10:29,008 --> 00:10:30,176
[music becomes rousing]

127
00:10:43,022 --> 00:10:47,735
Upon arrival, each bee
fans a pheromone across the forest,

128
00:10:48,569 --> 00:10:51,822
helping others to find the new nest site.

129
00:10:54,367 --> 00:10:57,453
More and more arrive at the new location.

130
00:10:59,288 --> 00:11:02,833
All joining in
to spread the chemical message.

131
00:11:09,632 --> 00:11:14,428
Within a few hours,
the entire swarm has made the move.

132
00:11:20,351 --> 00:11:22,812
Bees are only able to move like this

133
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when the sun's energy
provides them with enough food

134
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to rebuild their colony from scratch.

135
00:11:30,569 --> 00:11:33,030
So for the next few weeks,

136
00:11:33,114 --> 00:11:35,741
they will need to be as busy as,

137
00:11:35,825 --> 00:11:37,410
well, a bee!

138
00:11:38,244 --> 00:11:39,453
[music climaxes]

139
00:11:39,537 --> 00:11:40,788
[music fades out]

140
00:11:44,291 --> 00:11:46,961
In July, the further north you go,

141
00:11:47,044 --> 00:11:48,921
the more daylight there is.

142
00:11:49,004 --> 00:11:50,798
[whimsical music fades in]

143
00:11:50,881 --> 00:11:53,008
And, for just a brief period,

144
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this increase in solar power

145
00:11:55,344 --> 00:11:59,223
turns the Arctic tundra
into a rich grassland,

146
00:12:00,307 --> 00:12:03,811
attracting more than a million snow geese.

147
00:12:04,520 --> 00:12:06,188
[music becomes rousing]

148
00:12:11,026 --> 00:12:13,654
They've traveled the length
of North America,

149
00:12:13,738 --> 00:12:16,782
a distance of 5,000 kilometers,

150
00:12:16,866 --> 00:12:19,827
and they've come here to breed.

151
00:12:24,248 --> 00:12:26,333
Arctic summers are short,

152
00:12:26,417 --> 00:12:29,044
so the geese start laying straightaway.

153
00:12:29,879 --> 00:12:32,757
The female sits tight on the nest.

154
00:12:35,342 --> 00:12:38,471
While the male
keeps an eye out for enemies.

155
00:12:38,971 --> 00:12:40,222
[music fades out]

156
00:12:40,306 --> 00:12:41,432
[quacks]

157
00:12:41,515 --> 00:12:42,600
[tense music playing]

158
00:12:42,683 --> 00:12:44,560
And he doesn't have long to wait.

159
00:12:46,854 --> 00:12:48,272
[quacking]

160
00:12:48,856 --> 00:12:51,776
Arctic foxes live here the year-round,

161
00:12:51,859 --> 00:12:54,987
and they eagerly await
the return of the geese.

162
00:12:55,070 --> 00:12:56,739
[shrieking]

163
00:12:58,741 --> 00:13:00,117
[music intensifies]

164
00:13:02,870 --> 00:13:07,625
The fox's survival
depends on a steady supply of eggs.

165
00:13:09,001 --> 00:13:10,586
-[shrieks]
-[squawking]

166
00:13:11,462 --> 00:13:12,838
[music intensifies]

167
00:13:15,800 --> 00:13:17,802
[geese shrieking]

168
00:13:24,016 --> 00:13:27,895
But snow geese only lay one clutch a year.

169
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[goose squawks]

170
00:13:30,981 --> 00:13:33,108
And they defend it with their lives.

171
00:13:38,280 --> 00:13:43,702
Nonetheless, a single fox may steal
over a thousand eggs in a season.

172
00:13:47,873 --> 00:13:48,999
[music intensifies]

173
00:13:54,797 --> 00:13:56,131
[music abruptly fades out]

174
00:13:59,635 --> 00:14:01,303
Despite these losses…

175
00:14:02,221 --> 00:14:03,722
[soft peeping]

176
00:14:03,806 --> 00:14:06,225
…plenty of eggs do hatch.

177
00:14:08,102 --> 00:14:09,395
[peeping]

178
00:14:13,148 --> 00:14:16,986
It may be the height of summer,
but it's still the Arctic.

179
00:14:17,528 --> 00:14:21,115
So the goslings stay with Mother
to keep warm.

180
00:14:29,832 --> 00:14:33,335
But there's only so much room
under one wing.

181
00:14:33,836 --> 00:14:35,212
[duckling screeches]

182
00:14:41,635 --> 00:14:44,305
Still, it's better to keep out of the way

183
00:14:45,180 --> 00:14:48,517
when the tundra's larger residents
pass through.

184
00:14:50,853 --> 00:14:53,522
Caribou themselves pose little risk.

185
00:14:54,398 --> 00:14:56,483
But they do bring problems.

186
00:14:57,359 --> 00:14:58,569
[somber music playing]

187
00:14:58,652 --> 00:15:02,781
Grizzly bears follow them
in the hope of an easy meal.

188
00:15:05,367 --> 00:15:06,493
[growls]

189
00:15:10,331 --> 00:15:14,501
And their presence
causes a stir within the colony.

190
00:15:15,711 --> 00:15:17,671
[music becomes suspenseful]

191
00:15:20,758 --> 00:15:23,010
[sniffing]

192
00:15:23,093 --> 00:15:24,011
[growls]

193
00:15:25,930 --> 00:15:26,847
[honks]

194
00:15:28,766 --> 00:15:32,144
Any chick in its path is hoovered up.

195
00:15:33,187 --> 00:15:34,313
[honking]

196
00:15:36,065 --> 00:15:37,358
[music fades out]

197
00:15:39,818 --> 00:15:41,195
[chicks peeping]

198
00:15:41,278 --> 00:15:43,280
With things getting dangerous,

199
00:15:43,364 --> 00:15:47,076
it's time for these chicks
to start their life on the move.

200
00:15:47,159 --> 00:15:49,161
[whimsical music playing]

201
00:15:54,041 --> 00:15:57,336
The family heads
for the safety of the water.

202
00:16:00,965 --> 00:16:02,841
[music becomes rousing]

203
00:16:02,925 --> 00:16:07,262
In just eight weeks,
when the sun's power starts to wane here,

204
00:16:09,098 --> 00:16:12,184
the goslings will make
their first flight south,

205
00:16:13,519 --> 00:16:16,146
all the way to the Gulf of Mexico.

206
00:16:23,570 --> 00:16:24,822
[music fades out]

207
00:16:28,784 --> 00:16:32,788
Not all animals migrate
as the seasons change.

208
00:16:34,999 --> 00:16:39,128
Lions control the same territory
year in, year out.

209
00:16:40,254 --> 00:16:46,468
So this pride in East Africa's Serengeti
relies on prey coming to them.

210
00:16:46,552 --> 00:16:48,053
[snorting]

211
00:16:48,137 --> 00:16:51,390
Right now,
it's the height of the dry season,

212
00:16:51,473 --> 00:16:54,393
and the long grass plains
where these lions live

213
00:16:54,476 --> 00:16:56,228
are relatively empty.

214
00:16:57,438 --> 00:16:58,439
[growls softly]

215
00:16:59,064 --> 00:17:01,692
But things are about to change.

216
00:17:01,775 --> 00:17:03,861
[rousing music fades in]

217
00:17:03,944 --> 00:17:08,323
Heading towards them
are hundreds of thousands of wildebeest.

218
00:17:14,663 --> 00:17:19,752
Together, they make up the biggest
terrestrial migration on Earth.

219
00:17:24,965 --> 00:17:30,512
The herd eats its way
through nearly 5,000 tons of grass a day,

220
00:17:31,221 --> 00:17:34,016
which means they have to keep on the move.

221
00:17:36,060 --> 00:17:39,104
Something the lions have been counting on.

222
00:17:39,605 --> 00:17:40,898
[music fades out]

223
00:17:41,940 --> 00:17:43,442
[wildebeest grunting]

224
00:17:44,985 --> 00:17:48,822
The long dry grass
is of little nutritional value,

225
00:17:49,531 --> 00:17:51,992
but the herd must pass through it.

226
00:17:52,076 --> 00:17:53,869
[distant thrum of hooves]

227
00:17:54,495 --> 00:17:56,371
And the lions know that.

228
00:17:56,455 --> 00:17:59,124
[unsettling music plays, fades out]

229
00:18:01,627 --> 00:18:06,256
The grass provides
a very effective cloak of invisibility.

230
00:18:12,346 --> 00:18:13,639
[insects buzzing]

231
00:18:18,227 --> 00:18:20,229
[wildebeest grunting softly]

232
00:18:21,605 --> 00:18:23,941
To prevent her scent being detected,

233
00:18:24,650 --> 00:18:27,820
the lioness approaches from downwind.

234
00:18:30,864 --> 00:18:32,741
[unsettling music playing]

235
00:18:33,826 --> 00:18:35,160
[in hushed tone] Stalking.

236
00:18:37,663 --> 00:18:38,705
And stopping.

237
00:18:40,582 --> 00:18:42,960
[wildebeest grunting, snorting]

238
00:18:43,710 --> 00:18:45,254
Every movement

239
00:18:46,505 --> 00:18:47,422
considered.

240
00:18:48,632 --> 00:18:52,553
One careless step
could reveal her presence.

241
00:18:56,807 --> 00:18:58,725
[snorting]

242
00:19:02,604 --> 00:19:03,772
[snuffling]

243
00:19:08,485 --> 00:19:10,404
[unsettling music playing]

244
00:19:12,906 --> 00:19:15,159
[in hushed tone]
Any disturbance in the grass

245
00:19:15,784 --> 00:19:18,745
could be a potential threat for the herd.

246
00:19:18,829 --> 00:19:20,831
[chirping]

247
00:19:22,791 --> 00:19:24,376
That's just a guinea fowl.

248
00:19:26,587 --> 00:19:27,588
A false alarm.

249
00:19:31,800 --> 00:19:34,386
[menacing music fades in and out]

250
00:19:34,469 --> 00:19:36,889
Or… perhaps not.

251
00:19:38,098 --> 00:19:39,850
[menacing music playing]

252
00:19:41,185 --> 00:19:43,478
She's almost perfectly placed.

253
00:19:45,814 --> 00:19:48,650
Just 20 meters from her target.

254
00:19:51,445 --> 00:19:53,238
[wildebeest grunting nearby]

255
00:19:53,322 --> 00:19:54,281
[lion sniffs]

256
00:20:09,254 --> 00:20:10,672
[music intensifies]

257
00:20:12,216 --> 00:20:14,009
[music becomes dramatic]

258
00:20:21,391 --> 00:20:22,768
[music intensifies]

259
00:20:29,775 --> 00:20:30,943
[wildebeest shrieks]

260
00:20:31,026 --> 00:20:31,902
[music fades out]

261
00:20:31,985 --> 00:20:32,945
[wildebeest groans]

262
00:20:34,363 --> 00:20:39,034
After months with little to eat,
this is a vital meal.

263
00:20:43,789 --> 00:20:46,875
The pride will need to make the most
of the migration

264
00:20:47,459 --> 00:20:49,086
while it's passing through.

265
00:20:50,629 --> 00:20:53,924
Soon, the herds
will have left the lions' territory,

266
00:20:54,675 --> 00:20:58,762
moving north in their never-ending search
for fresh grazing.

267
00:21:02,266 --> 00:21:04,017
[ambient music playing]

268
00:21:10,440 --> 00:21:14,736
In August, the Northern Hemisphere
is at its warmest.

269
00:21:15,946 --> 00:21:18,573
And on Canada's Vancouver Island,

270
00:21:18,657 --> 00:21:23,203
there's one animal whose life cycle
depends on these higher temperatures.

271
00:21:24,037 --> 00:21:25,789
[ethereal music playing]

272
00:21:26,790 --> 00:21:29,459
As day breaks over Cedar Lake,

273
00:21:29,543 --> 00:21:32,379
something is stirring in its depths.

274
00:21:32,462 --> 00:21:34,214
[music becomes hypnotic]

275
00:21:39,803 --> 00:21:44,975
Tadpoles here spend their nights
hiding in deep, cool water.

276
00:21:46,727 --> 00:21:50,272
Now, with the sun up,
they set off across the lake.

277
00:21:52,232 --> 00:21:53,400
[music intensifies]

278
00:21:55,027 --> 00:21:57,446
Initially, in hundreds.

279
00:21:59,531 --> 00:22:01,616
Then thousands.

280
00:22:05,370 --> 00:22:08,623
All are heading for the sunlit shallows.

281
00:22:13,295 --> 00:22:18,383
Here, the water is five degrees warmer
than in the lake's depths,

282
00:22:19,259 --> 00:22:22,554
and that will speed
their transformation into toads.

283
00:22:23,805 --> 00:22:24,848
[music intensifies]

284
00:22:25,932 --> 00:22:27,392
But when night falls,

285
00:22:28,310 --> 00:22:30,979
they head back to the safety of the deep.

286
00:22:31,063 --> 00:22:32,230
[music abates]

287
00:22:32,314 --> 00:22:34,358
Until the next morning.

288
00:22:35,567 --> 00:22:36,526
[music reprises]

289
00:22:36,610 --> 00:22:39,237
Every day they repeat the journey.

290
00:22:40,322 --> 00:22:41,156
Sun.

291
00:22:41,239 --> 00:22:42,282
[music intensifies]

292
00:22:42,366 --> 00:22:43,325
Swim.

293
00:22:44,701 --> 00:22:45,702
Feed.

294
00:22:46,703 --> 00:22:47,662
Repeat.

295
00:22:47,746 --> 00:22:48,663
[music abates]

296
00:22:48,747 --> 00:22:50,415
[music reprises]

297
00:22:52,250 --> 00:22:54,002
[music intensifies]

298
00:22:57,089 --> 00:22:58,590
It seems perfect.

299
00:22:59,758 --> 00:23:04,262
Except others take advantage
of their daily routine.

300
00:23:04,346 --> 00:23:06,098
[music becomes ambient]

301
00:23:07,516 --> 00:23:09,309
Dragonfly larvae.

302
00:23:14,356 --> 00:23:17,234
They are ambush predators

303
00:23:18,735 --> 00:23:21,238
with extendable jaws.

304
00:23:21,321 --> 00:23:23,573
[unsettling music playing]

305
00:23:23,657 --> 00:23:25,867
And they have voracious appetites.

306
00:23:33,250 --> 00:23:36,670
Blind leeches patrol the muddy bottom.

307
00:23:36,753 --> 00:23:38,588
[music becomes hypnotic]

308
00:23:46,304 --> 00:23:47,889
Once they catch something…

309
00:23:49,975 --> 00:23:52,310
they suck out its blood.

310
00:23:53,437 --> 00:23:54,563
[leech sucking]

311
00:24:00,527 --> 00:24:01,820
[music abates]

312
00:24:01,903 --> 00:24:03,113
[music becomes dramatic]

313
00:24:03,822 --> 00:24:05,157
Throughout the summer,

314
00:24:06,700 --> 00:24:10,036
the tadpoles continue their daily commute.

315
00:24:13,540 --> 00:24:15,167
[music intensifies]

316
00:24:17,794 --> 00:24:18,962
[music fades out]

317
00:24:19,045 --> 00:24:21,423
Until, after a few weeks…

318
00:24:21,506 --> 00:24:23,008
[ambient music playing]

319
00:24:23,675 --> 00:24:26,595
…they start to look like tiny toads.

320
00:24:29,973 --> 00:24:34,019
By harnessing the sun's energy,
they've grown quickly.

321
00:24:36,897 --> 00:24:39,566
Now, they stop their daily routines

322
00:24:39,649 --> 00:24:42,736
and prepare for their journey
into the forest.

323
00:24:45,530 --> 00:24:47,407
[unsettling music playing]

324
00:24:49,534 --> 00:24:50,577
Here too,

325
00:24:51,870 --> 00:24:53,330
predators await.

326
00:24:53,413 --> 00:24:55,207
[music becomes suspenseful]

327
00:24:59,294 --> 00:25:02,589
Garter snakes specialize
in eating amphibians.

328
00:25:03,298 --> 00:25:06,885
Though they rarely have
as much choice as this.

329
00:25:20,899 --> 00:25:22,150
[music fades out]

330
00:25:23,193 --> 00:25:29,115
Eventually, the sheer numbers
of young toads overwhelm the snakes.

331
00:25:29,199 --> 00:25:30,659
[music becomes rousing]

332
00:25:33,912 --> 00:25:36,414
The survivors spread out into the forest

333
00:25:36,498 --> 00:25:39,167
where they'll spend the next four years.

334
00:25:46,424 --> 00:25:51,888
Until it's time for them
to head back to the lake to breed.

335
00:25:56,059 --> 00:25:58,061
[music climaxes]

336
00:26:00,605 --> 00:26:01,856
[music fades out]

337
00:26:04,859 --> 00:26:10,115
By midsummer, there is little snow left
in America's Pacific Northwest.

338
00:26:12,450 --> 00:26:14,369
Meltwater fills the rivers,

339
00:26:14,452 --> 00:26:17,706
ready to carry travelers
who make what is perhaps

340
00:26:17,789 --> 00:26:20,625
the most extraordinary
and demanding journey

341
00:26:20,709 --> 00:26:22,460
tackled by any animal.

342
00:26:22,544 --> 00:26:24,296
[hypnotic music playing]

343
00:26:26,506 --> 00:26:27,757
Sockeye salmon.

344
00:26:28,258 --> 00:26:31,177
And they're heading upriver to breed.

345
00:26:41,730 --> 00:26:44,733
After three years
feeding in the Bering Sea,

346
00:26:44,816 --> 00:26:48,612
they find their way
across hundreds of kilometers of ocean,

347
00:26:48,695 --> 00:26:51,239
guided by the Earth's magnetic field

348
00:26:51,323 --> 00:26:55,577
and their astounding ability
to recognize the taste of the river

349
00:26:55,660 --> 00:26:57,203
in which they hatched.

350
00:26:59,539 --> 00:27:05,462
They are one of the few fish in the world
that can move from saltwater into fresh.

351
00:27:06,379 --> 00:27:08,006
And over the next month,

352
00:27:08,089 --> 00:27:11,259
they will travel 200 kilometers upstream,

353
00:27:11,343 --> 00:27:15,889
past Lake Iliamna,
to their spawning pools just beyond.

354
00:27:19,768 --> 00:27:24,230
It's the last journey
these salmon will ever make.

355
00:27:29,611 --> 00:27:32,530
As they enter the river, they stop eating…

356
00:27:35,367 --> 00:27:38,787
putting all their efforts
into battling the current.

357
00:27:46,544 --> 00:27:50,674
Swift rapids and high waterfalls
do not stop them.

358
00:27:53,218 --> 00:27:54,928
[music becomes rousing]

359
00:28:00,725 --> 00:28:01,726
[music abates]

360
00:28:01,810 --> 00:28:03,728
Four weeks into their journey,

361
00:28:03,812 --> 00:28:06,690
their bodies begin to change.

362
00:28:08,775 --> 00:28:11,653
Flashes of red appear in their flanks.

363
00:28:15,615 --> 00:28:17,909
These are their breeding colors.

364
00:28:18,618 --> 00:28:21,746
And the redder the fish,
the fitter they are.

365
00:28:22,372 --> 00:28:23,957
[optimistic music playing]

366
00:28:24,040 --> 00:28:27,293
A few more weeks,
and they're barely recognizable.

367
00:28:28,920 --> 00:28:32,674
The jaws of the males
have become hooked beaks,

368
00:28:32,757 --> 00:28:35,218
which they will use to fight for a mate.

369
00:28:37,429 --> 00:28:42,392
But their spawning pools
are still nearly 100 kilometers away.

370
00:28:43,810 --> 00:28:45,228
And just upriver,

371
00:28:45,895 --> 00:28:49,274
there are predators
ready to intercept them.

372
00:28:53,653 --> 00:28:55,238
[somber music playing]

373
00:28:58,867 --> 00:29:00,493
[music becomes dramatic]

374
00:29:00,577 --> 00:29:03,830
Bears depend on the annual salmon run

375
00:29:05,331 --> 00:29:07,959
to fatten up for the winter ahead.

376
00:29:15,759 --> 00:29:19,763
And right now, they're very, very hungry.

377
00:29:38,698 --> 00:29:39,657
[music intensifies]

378
00:29:41,117 --> 00:29:42,702
During the migration,

379
00:29:42,786 --> 00:29:46,498
an adult bear can eat 40 salmon a day.

380
00:29:50,752 --> 00:29:52,921
The salmon are quick and agile.

381
00:30:06,434 --> 00:30:07,435
[music abates]

382
00:30:07,936 --> 00:30:10,480
But, as the water gets shallower…

383
00:30:12,774 --> 00:30:16,361
the advantage swings
in favor of the bears.

384
00:30:27,789 --> 00:30:29,415
[music fades out]

385
00:30:34,754 --> 00:30:36,798
Several kilometers upstream,

386
00:30:36,881 --> 00:30:40,510
the fish finally reach Lake Iliamna.

387
00:30:40,593 --> 00:30:42,178
[poignant music playing]

388
00:30:42,262 --> 00:30:45,932
One of the last pristine waterways
in America.

389
00:30:50,436 --> 00:30:53,398
Their spawning pools lie just upstream.

390
00:30:53,982 --> 00:30:55,817
But, for now, the sockeye linger

391
00:30:55,900 --> 00:30:59,070
while the females' eggs
complete their development.

392
00:31:07,704 --> 00:31:10,415
[in hushed tone]
But their troubles are not yet over.

393
00:31:10,498 --> 00:31:12,500
[apprehensive music playing]

394
00:31:15,253 --> 00:31:20,675
These waters are the home
of the only freshwater seals in America.

395
00:31:35,481 --> 00:31:38,318
The salmon haven't eaten in eight weeks,

396
00:31:39,736 --> 00:31:42,155
but they can still outswim
these predators.

397
00:31:54,584 --> 00:31:55,668
[music abates]

398
00:31:57,337 --> 00:31:59,923
The seals switch strategy

399
00:32:00,006 --> 00:32:03,259
and start to hide in plain sight.

400
00:32:03,760 --> 00:32:05,428
[ominous music playing]

401
00:32:08,556 --> 00:32:10,767
In a rarely seen behavior,

402
00:32:11,476 --> 00:32:14,687
they wait for the salmon to come to them.

403
00:32:17,899 --> 00:32:21,778
Surprisingly, they ignore the males
right in front of them.

404
00:32:27,033 --> 00:32:28,701
And go for the females,

405
00:32:29,786 --> 00:32:32,497
who are laden with calorie-rich eggs.

406
00:32:45,134 --> 00:32:46,386
[music fades out]

407
00:32:46,469 --> 00:32:47,762
[optimistic music playing]

408
00:32:49,222 --> 00:32:51,599
But for every salmon that's taken,

409
00:32:53,309 --> 00:32:55,061
thousands get through.

410
00:33:04,278 --> 00:33:07,490
Battered and bruised
from their long journey,

411
00:33:07,573 --> 00:33:11,327
they have, at last,
reached their spawning pools.

412
00:33:13,663 --> 00:33:16,791
Once here, males and females pair up

413
00:33:16,874 --> 00:33:20,378
and, together,
fight for the best nest sites.

414
00:33:35,435 --> 00:33:37,937
Finally, they mate.

415
00:33:46,070 --> 00:33:49,574
It's the only time they will ever do so.

416
00:33:49,657 --> 00:33:51,576
[music becomes spiritual]

417
00:33:58,958 --> 00:34:03,629
They've given everything
to complete this epic migration.

418
00:34:05,840 --> 00:34:08,718
Their lives are over.

419
00:34:12,221 --> 00:34:16,476
The nutrients from their decaying bodies
fertilize the water.

420
00:34:18,186 --> 00:34:21,773
A sacrifice that ensures
the next generation

421
00:34:21,856 --> 00:34:24,442
will have the very best start in life.

422
00:34:31,616 --> 00:34:32,909
[music fades out]

423
00:34:33,659 --> 00:34:36,245
August in the High Arctic.

424
00:34:37,455 --> 00:34:40,124
After three months of continuous daylight,

425
00:34:40,208 --> 00:34:42,794
little is left of the sea ice.

426
00:34:44,337 --> 00:34:45,463
[chirruping]

427
00:34:45,963 --> 00:34:47,715
[poignant music playing]

428
00:34:48,883 --> 00:34:53,054
And that makes life
very hard for this ice bear

429
00:34:54,222 --> 00:34:56,724
and her eight-month-old cubs.

430
00:35:03,231 --> 00:35:07,860
Three months ago, they were hunting
blubber-rich seals out on the ice.

431
00:35:09,487 --> 00:35:13,199
Now they're forced to swim continuously
for days on end

432
00:35:14,367 --> 00:35:17,078
in search of whatever food they can find.

433
00:35:27,547 --> 00:35:32,218
Polar bears use five times more energy
when swimming than walking.

434
00:35:34,512 --> 00:35:39,183
And that is beginning to take its toll
on her smallest cub.

435
00:35:39,267 --> 00:35:40,143
[cub barking]

436
00:36:03,916 --> 00:36:05,668
[music becomes ethereal]

437
00:36:10,631 --> 00:36:12,800
He's finding it hard to keep up.

438
00:36:15,386 --> 00:36:18,472
But his mother
is too hungry to wait for long.

439
00:36:18,556 --> 00:36:21,559
She can smell food
somewhere on this island.

440
00:36:24,228 --> 00:36:25,521
[gulls squawking]

441
00:36:26,314 --> 00:36:30,943
And the dive-bombing gulls
are a sign that she's close.

442
00:36:32,778 --> 00:36:33,863
[gull squawking]

443
00:36:33,946 --> 00:36:36,866
For the largest land carnivore on Earth,

444
00:36:36,949 --> 00:36:38,784
these chicks are not much of a meal.

445
00:36:40,077 --> 00:36:43,998
Though they would be a much-needed boost
for the cubs…

446
00:36:48,628 --> 00:36:51,964
if they can get down to it
before it's gone.

447
00:36:55,468 --> 00:36:59,096
The weaker cub is not very sure-footed.

448
00:37:06,270 --> 00:37:07,313
[grunts softly]

449
00:37:07,396 --> 00:37:08,648
[gulls squawking]

450
00:37:12,860 --> 00:37:16,489
By the time he's caught up, it's too late.

451
00:37:17,990 --> 00:37:19,617
[snorting]

452
00:37:24,038 --> 00:37:25,039
[bear growls]

453
00:37:25,539 --> 00:37:27,291
With food so scarce,

454
00:37:28,334 --> 00:37:30,628
there is no time for rest.

455
00:37:31,504 --> 00:37:32,380
[shrieks]

456
00:37:34,715 --> 00:37:38,386
The climb back up should be easy.

457
00:37:38,469 --> 00:37:39,595
[sniffing]

458
00:37:41,973 --> 00:37:46,018
Certainly, his sibling seems to take it
in his stride.

459
00:37:48,312 --> 00:37:53,484
But after that long swim
the weaker cub has little energy left.

460
00:37:53,567 --> 00:37:54,735
[shrieks softly]

461
00:37:57,947 --> 00:38:00,783
Unable to follow, he panics

462
00:38:00,866 --> 00:38:03,119
and heads in the wrong direction.

463
00:38:03,202 --> 00:38:04,036
[soft thud]

464
00:38:04,704 --> 00:38:09,417
A slip here would mean
a 15-meter fall onto the rocks below.

465
00:38:09,500 --> 00:38:10,459
[cub shrieks]

466
00:38:11,127 --> 00:38:12,169
[sniffing]

467
00:38:15,339 --> 00:38:16,424
[cub shrieks]

468
00:38:18,134 --> 00:38:21,220
His mother takes no notice
of his problems,

469
00:38:21,304 --> 00:38:23,681
so desperate is she for another meal.

470
00:38:30,271 --> 00:38:31,188
[cub shrieks]

471
00:38:33,107 --> 00:38:36,777
His survival depends
on staying close to his mother.

472
00:38:36,861 --> 00:38:38,362
[shrieking softly]

473
00:38:39,322 --> 00:38:43,784
If he can't keep up,
she will be forced to abandon him.

474
00:38:43,868 --> 00:38:44,702
[soft thud]

475
00:38:45,286 --> 00:38:46,579
[shrieking softly]

476
00:38:57,465 --> 00:38:59,925
-[mother sniffing]
-[cub shrieking]

477
00:39:00,968 --> 00:39:02,053
[mother growls]

478
00:39:05,264 --> 00:39:06,766
-[cub crying]
-[mother growls]

479
00:39:13,606 --> 00:39:14,648
He's made it.

480
00:39:18,652 --> 00:39:22,490
Only to find
that he must still keep going.

481
00:39:24,784 --> 00:39:26,535
[poignant music playing]

482
00:39:27,661 --> 00:39:31,582
It's a journey
this young cub may not survive.

483
00:39:36,545 --> 00:39:40,216
With summer sea ice
melting earlier than we've ever known,

484
00:39:40,299 --> 00:39:44,136
polar bears are having to spend
more of their year swimming.

485
00:39:47,181 --> 00:39:50,393
For animals used to traveling across ice,

486
00:39:50,476 --> 00:39:53,771
these changes may well prove
to be too great.

487
00:39:53,854 --> 00:39:55,106
[music fades out]

488
00:39:56,607 --> 00:39:58,275
[ambient music playing]

489
00:40:06,826 --> 00:40:09,787
Six thousand kilometers
south of the Arctic,

490
00:40:09,870 --> 00:40:15,209
the summer sun is also heating
the shallow waters of the Persian Gulf,

491
00:40:15,292 --> 00:40:19,046
making the sea here
the hottest on the planet.

492
00:40:24,468 --> 00:40:28,180
And that attracts
the ocean's biggest fish.

493
00:40:31,100 --> 00:40:32,893
The whale shark.

494
00:40:39,400 --> 00:40:42,069
After a journey
of thousands of kilometers,

495
00:40:42,153 --> 00:40:47,116
it's arrived in time for one of
the best feeding events of its year…

496
00:40:49,535 --> 00:40:52,329
and is heading to a particular spot.

497
00:40:56,417 --> 00:41:00,087
The waters of the Al Shaheen Oil Fields.

498
00:41:04,550 --> 00:41:07,261
The platforms act as reefs,

499
00:41:07,344 --> 00:41:10,431
providing a home for hundreds of species.

500
00:41:12,808 --> 00:41:17,521
No vessels are allowed
within half a kilometer of each rig,

501
00:41:18,772 --> 00:41:23,736
so creating marine sanctuaries
where fish can spawn in safety.

502
00:41:27,490 --> 00:41:29,074
Tuna are among them.

503
00:41:29,992 --> 00:41:35,206
They can only breed when the water
is 25 degrees Celsius or more.

504
00:41:38,918 --> 00:41:42,630
So, in summer,
when the gulf is at its hottest,

505
00:41:42,713 --> 00:41:48,052
they gather together
and release hundreds of millions of eggs.

506
00:41:51,597 --> 00:41:54,975
The water's surface
becomes thick with spawn.

507
00:41:55,059 --> 00:41:56,769
[music becomes optimistic]

508
00:41:56,852 --> 00:42:01,023
And that is what the whale shark
has crossed oceans for.

509
00:42:14,203 --> 00:42:17,873
Taking in water
through its meter-wide mouth,

510
00:42:17,957 --> 00:42:19,792
it collects the eggs.

511
00:42:29,218 --> 00:42:32,346
More sharks arrive to join the feast.

512
00:42:36,058 --> 00:42:39,311
But this is the hottest sea on Earth.

513
00:42:41,647 --> 00:42:45,067
And after feeding
for a few hours each morning,

514
00:42:45,150 --> 00:42:48,904
the whale sharks
will have to return to the cooler depths.

515
00:42:56,912 --> 00:42:58,998
At the height of the spawning season,

516
00:42:59,081 --> 00:43:02,334
there may be over 100
per square kilometer.

517
00:43:05,796 --> 00:43:09,592
It's one of the largest gatherings
of whale sharks on the planet.

518
00:43:11,385 --> 00:43:17,433
And all the more remarkable that it was
only recorded for the first time in 2010.

519
00:43:26,358 --> 00:43:27,651
[music fades out]

520
00:43:31,113 --> 00:43:33,073
Back in the Serengeti,

521
00:43:33,157 --> 00:43:37,119
a million wildebeest and zebra
are still on the move,

522
00:43:37,202 --> 00:43:41,081
following the sun and rain
in search of fresh grazing.

523
00:43:42,833 --> 00:43:44,501
[rousing music playing]

524
00:43:45,836 --> 00:43:47,838
And in amongst the throng…

525
00:43:47,921 --> 00:43:49,256
[zebra grunting]

526
00:43:49,340 --> 00:43:50,549
…new life.

527
00:43:54,219 --> 00:43:59,058
This zebra foal and his family
travel amongst the wildebeest for safety.

528
00:44:02,519 --> 00:44:05,064
He is just four weeks old,

529
00:44:05,147 --> 00:44:08,734
and keeping pace with the herd
is a daily struggle.

530
00:44:13,197 --> 00:44:16,575
Yet his biggest hurdle lies just ahead.

531
00:44:16,659 --> 00:44:18,077
[suspenseful music playing]

532
00:44:19,036 --> 00:44:20,371
The Mara River.

533
00:44:25,042 --> 00:44:26,752
Its fast-flowing waters

534
00:44:26,835 --> 00:44:30,589
claim the lives of 6,000 animals a year.

535
00:44:33,217 --> 00:44:38,889
Crossing it will be a major trial
for a foal that has never swum before.

536
00:44:38,972 --> 00:44:40,432
[grunting]

537
00:44:42,184 --> 00:44:44,687
The herd nears the river's edge.

538
00:44:46,939 --> 00:44:49,566
None wants to be the first to cross.

539
00:44:51,151 --> 00:44:52,736
But as numbers increase,

540
00:44:53,362 --> 00:44:55,739
pressure mounts on those at the front.

541
00:44:56,782 --> 00:44:58,534
[music becomes dramatic]

542
00:44:59,201 --> 00:45:00,577
Once one commits,

543
00:45:00,661 --> 00:45:02,413
the floodgates open.

544
00:45:18,512 --> 00:45:21,140
But the foal and his family wait.

545
00:45:21,223 --> 00:45:22,474
[grunting]

546
00:45:29,648 --> 00:45:32,943
Many wildebeest drown in the crush.

547
00:45:44,538 --> 00:45:45,914
[music intensifies]

548
00:45:53,255 --> 00:45:54,590
[music abates]

549
00:45:54,673 --> 00:45:56,967
Still, the zebra hold back.

550
00:45:58,635 --> 00:46:00,053
[unsettling music playing]

551
00:46:00,137 --> 00:46:01,638
And with good reason.

552
00:46:03,599 --> 00:46:06,310
Five-meter-long Nile crocodiles.

553
00:46:07,227 --> 00:46:09,396
Amongst the biggest in Africa.

554
00:46:16,612 --> 00:46:21,492
These giant reptiles may not have eaten
since this time last year.

555
00:46:29,625 --> 00:46:32,336
With so many targets from which to choose,

556
00:46:32,419 --> 00:46:34,630
they can afford to take their time.

557
00:46:41,470 --> 00:46:43,472
[wildebeest groaning]

558
00:46:55,776 --> 00:46:57,402
Soon, perhaps,

559
00:46:57,486 --> 00:47:00,405
the crocodiles will have taken their fill.

560
00:47:02,574 --> 00:47:03,992
[music fades out]

561
00:47:04,076 --> 00:47:05,661
[somber music playing]

562
00:47:07,079 --> 00:47:09,122
-No such luck.
-[music becomes dramatic]

563
00:47:09,206 --> 00:47:10,332
[nickers]

564
00:47:14,169 --> 00:47:16,588
The zebra can wait no longer.

565
00:47:16,672 --> 00:47:19,174
They must stay with the herd.

566
00:47:20,217 --> 00:47:25,514
So, the young foal
must now swim for his life.

567
00:47:25,597 --> 00:47:27,391
[foal whimpering]

568
00:47:27,474 --> 00:47:28,851
[music intensifies]

569
00:47:31,520 --> 00:47:33,480
[music rapidly trails off]

570
00:47:33,564 --> 00:47:35,065
[theme tune playing]

571
00:49:00,609 --> 00:49:01,860
[music fades out]