1 00:00:38,600 --> 00:00:41,640 David Attenborough: In the far north of our planet 2 00:00:41,760 --> 00:00:44,480 lie vast frozen lands... 3 00:00:46,960 --> 00:00:49,120 Of snow-covered forests... 4 00:00:50,360 --> 00:00:52,400 And open tundra. 5 00:00:55,400 --> 00:00:57,000 During the months to come, 6 00:00:57,120 --> 00:00:58,920 they will be transformed 7 00:00:59,040 --> 00:01:02,840 by the greatest seasonal changes on earth. 8 00:01:05,880 --> 00:01:07,840 But now, in midwinter, 9 00:01:07,960 --> 00:01:12,800 conditions are so hostile that life seems all but impossible. 10 00:01:19,040 --> 00:01:20,360 But... 11 00:01:20,480 --> 00:01:22,240 Not so. 12 00:01:25,560 --> 00:01:28,800 In this world of extremes, animals must go 13 00:01:28,920 --> 00:01:31,720 to extraordinary lengths to survive. 14 00:02:01,160 --> 00:02:03,800 February, northern Canada. 15 00:02:06,600 --> 00:02:07,640 The harsh winter 16 00:02:07,760 --> 00:02:11,400 has brought together an extended family of wolves. 17 00:02:13,600 --> 00:02:16,600 But this is no ordinary pack. 18 00:02:21,160 --> 00:02:24,440 There are 25 of them. 19 00:02:27,120 --> 00:02:29,240 A super-pack, 20 00:02:29,360 --> 00:02:32,120 one of the largest ever recorded. 21 00:02:35,000 --> 00:02:37,280 They're ravenously hungry. 22 00:02:38,560 --> 00:02:41,720 They may have walked over 150 miles 23 00:02:41,840 --> 00:02:44,240 since they last had a meal. 24 00:02:45,760 --> 00:02:49,680 But now, at last, the lead male and female 25 00:02:49,800 --> 00:02:51,920 have picked up a trail. 26 00:02:55,160 --> 00:02:59,200 It's been left by the only substantial prey there is here 27 00:02:59,320 --> 00:03:00,920 at this time of year... 28 00:03:05,440 --> 00:03:07,440 Bison. 29 00:03:11,040 --> 00:03:12,920 They're formidable animals, 30 00:03:13,040 --> 00:03:15,200 not easy to attack. 31 00:03:17,800 --> 00:03:21,680 The bulls are ten times the size of a wolf. 32 00:03:23,720 --> 00:03:25,200 And they have horns 33 00:03:25,320 --> 00:03:29,040 with which they could rip any attacker to pieces. 34 00:03:36,480 --> 00:03:39,200 Gathered together and on guard, 35 00:03:39,320 --> 00:03:41,800 they appear invulnerable. 36 00:03:47,320 --> 00:03:49,200 The wolf pack's only chance... 37 00:03:50,360 --> 00:03:52,200 Is to try and break up the group 38 00:03:52,320 --> 00:03:54,360 and isolate one of them. 39 00:04:03,760 --> 00:04:04,960 To do that, 40 00:04:05,080 --> 00:04:08,480 they will have to work as a team 41 00:04:08,600 --> 00:04:11,600 and try to start a stampede. 42 00:04:31,720 --> 00:04:37,640 Even in thick snow, bison can run at up to 35mph. 43 00:04:39,800 --> 00:04:43,040 The lead female wolf leads the chase. 44 00:04:45,120 --> 00:04:49,160 A kick from a bison's hind leg could shatter her jaws. 45 00:04:59,040 --> 00:05:03,440 But the pack must feed, and they take turns to attack. 46 00:05:08,640 --> 00:05:11,280 The bison head for cover. 47 00:05:24,840 --> 00:05:27,800 The deep snow slows down both attacked... 48 00:05:27,920 --> 00:05:29,760 And attacker. 49 00:05:36,600 --> 00:05:38,920 The herd splits into two. 50 00:05:43,200 --> 00:05:46,120 But the wolves are far from giving up. 51 00:05:50,600 --> 00:05:52,200 Hours pass. 52 00:05:55,840 --> 00:05:58,600 The thicker vegetation has turned 53 00:05:58,720 --> 00:05:59,760 a straightfonnard chase... 54 00:06:00,840 --> 00:06:02,960 Into a deadly form... 55 00:06:03,080 --> 00:06:04,880 Of hide... 56 00:06:06,520 --> 00:06:08,280 And seek. 57 00:06:25,880 --> 00:06:27,080 Discovered. 58 00:06:32,720 --> 00:06:36,000 The lead female manages to chase the smaller group 59 00:06:36,120 --> 00:06:37,680 into the open. 60 00:06:56,640 --> 00:07:00,880 But here the bison are able to close ranks once again. 61 00:07:07,600 --> 00:07:09,520 The leading wolves wait 62 00:07:09,640 --> 00:07:11,920 for the rest of the pack to catch up. 63 00:07:27,520 --> 00:07:31,720 The super-pack is once again at full strength. 64 00:07:36,160 --> 00:07:39,080 Suddenly, two of the bison panic. 65 00:07:40,280 --> 00:07:43,280 It's just what the wolves have been waiting for. 66 00:07:58,200 --> 00:08:00,880 One of the bison is tiring. 67 00:08:04,360 --> 00:08:07,080 The lead female gets a grip on its flanks. 68 00:08:21,000 --> 00:08:22,760 The male joins her. 69 00:08:22,880 --> 00:08:26,120 Together, they might be able to bring it down. 70 00:08:35,680 --> 00:08:38,640 The rest of the wolves catch up and help. 71 00:08:52,640 --> 00:08:58,120 After eight long, hard hours, the hunt is coming to an end. 72 00:09:10,120 --> 00:09:13,160 Victory is sounded to summon the rest of the pack. 73 00:09:17,920 --> 00:09:21,560 A single wolf wouldn't stand a chance 74 00:09:21,680 --> 00:09:23,800 of making such a kill by itself. 75 00:09:26,000 --> 00:09:29,040 The only way they have of surviving the winter 76 00:09:29,160 --> 00:09:31,840 is as a super-pack. 77 00:09:47,560 --> 00:09:51,360 These snow-covered forests encircle the arctic 78 00:09:51,480 --> 00:09:54,240 from scandinavia, through Russia, 79 00:09:54,360 --> 00:09:58,120 to Alaska and the rest of North America. 80 00:10:01,120 --> 00:10:03,120 But close to the north pole, 81 00:10:03,240 --> 00:10:05,760 the winters are too long and too cold 82 00:10:05,880 --> 00:10:08,480 for even the hardiest of trees. 83 00:10:10,520 --> 00:10:14,080 This is the tundra, and it stretches 84 00:10:14,200 --> 00:10:17,320 all the way to the shores of the arctic ocean. 85 00:10:26,240 --> 00:10:30,560 Here, conditions are even more extreme than in the forests. 86 00:10:35,120 --> 00:10:37,960 During the two months of winter darkness, 87 00:10:38,080 --> 00:10:42,560 temperatures may fall to minus 50 degrees celsius. 88 00:10:45,640 --> 00:10:47,720 The ground deep beneath the snow 89 00:10:47,840 --> 00:10:52,000 has been frozen solid since the last ice age. 90 00:10:57,800 --> 00:11:00,400 There is no shelter of any kind. 91 00:11:00,520 --> 00:11:03,240 Very few animals can survive here. 92 00:11:08,040 --> 00:11:10,160 But this is one which does. 93 00:11:13,080 --> 00:11:15,000 An arctic fox. 94 00:11:17,960 --> 00:11:20,680 It has the warmest fur of any mammal. 95 00:11:21,680 --> 00:11:25,640 And it can survive blizzards that may rage for days on end. 96 00:11:30,120 --> 00:11:34,240 It must nonetheless eventually eat something. 97 00:11:35,600 --> 00:11:37,640 But how is that something to be found 98 00:11:37,760 --> 00:11:41,760 when you're all by yourself in this desolation? 99 00:11:55,200 --> 00:11:58,040 Arctic foxes are wanderers. 100 00:12:00,160 --> 00:12:05,120 And they can travel over 2,000 miles, from Norway to Canada, 101 00:12:05,240 --> 00:12:08,040 in a constant search for food. 102 00:12:24,960 --> 00:12:27,800 There might be something here. 103 00:12:29,080 --> 00:12:32,240 A patch of grass, kept clear of the snow 104 00:12:32,360 --> 00:12:34,960 by the near-constant wind. 105 00:12:35,080 --> 00:12:37,320 The slightest hint of scent 106 00:12:37,440 --> 00:12:40,080 might indicate the presence of prey. 107 00:12:47,320 --> 00:12:49,720 Less than a metre below the surface 108 00:12:49,840 --> 00:12:53,000 may lie a hidden network of tunnels, 109 00:12:53,120 --> 00:12:56,880 shown here using a special filming burrow. 110 00:13:14,360 --> 00:13:16,720 Tiny arctic lemmings. 111 00:13:19,520 --> 00:13:22,880 With a carpet of edible moss beneath 112 00:13:23,000 --> 00:13:25,480 and a thick blanket of snow above... 113 00:13:25,600 --> 00:13:28,800 The lemmings spend their entire winter 114 00:13:28,920 --> 00:13:30,440 hidden below the surface. 115 00:13:32,000 --> 00:13:34,360 And here they breed. 116 00:13:42,880 --> 00:13:45,000 For a hungry fox, 117 00:13:45,120 --> 00:13:49,120 a group of lemmings could be a life-saving discovery... 118 00:13:51,200 --> 00:13:53,240 If it can catch one. 119 00:13:56,760 --> 00:14:01,320 Lemming Burrows may extend for up to 15 metres. 120 00:14:09,160 --> 00:14:12,280 Pinpointing the position of one of the inhabitants... 121 00:14:13,560 --> 00:14:15,520 Is not easy. 122 00:14:18,760 --> 00:14:21,880 An acute sense of hearing is essential. 123 00:14:26,200 --> 00:14:27,760 And the arctic fox 124 00:14:27,880 --> 00:14:30,120 has a special trick. 125 00:14:43,320 --> 00:14:46,520 It doesn't always work first time. 126 00:14:51,760 --> 00:14:54,600 And it does require dedication. 127 00:15:15,480 --> 00:15:19,520 With less than 25 lemmings per square mile of tundra... 128 00:15:20,560 --> 00:15:24,040 You have to persevere. 129 00:15:32,560 --> 00:15:33,920 And at last... 130 00:15:35,200 --> 00:15:37,040 One plump lemming. 131 00:15:40,360 --> 00:15:44,200 The foxes' tenacity and unique hunting skills 132 00:15:44,320 --> 00:15:49,280 enable them to find prey which few others could catch. 133 00:16:05,440 --> 00:16:08,400 On the tundra's southern fringes, 134 00:16:08,520 --> 00:16:12,400 winter is significantly less severe. 135 00:16:16,000 --> 00:16:19,240 The slight increase in annual sunlight 136 00:16:19,360 --> 00:16:23,160 has enabled a stunted forest to develop. 137 00:16:40,960 --> 00:16:45,200 It's the northern edge of the world's largest woodland... 138 00:16:46,200 --> 00:16:48,720 The boreal forest. 139 00:16:55,400 --> 00:16:59,240 750 billion trees. 140 00:17:01,480 --> 00:17:04,400 A quarter of all the trees on earth. 141 00:17:07,400 --> 00:17:09,960 And it encircles the globe. 142 00:17:12,280 --> 00:17:15,560 These forests store twice as much carbon 143 00:17:15,680 --> 00:17:17,480 as a tropical forest, 144 00:17:17,600 --> 00:17:19,960 and they play a crucial part 145 00:17:20,080 --> 00:17:23,680 in regulating the climate of the entire planet. 146 00:17:29,800 --> 00:17:31,920 One of the most remote tracts 147 00:17:32,040 --> 00:17:35,160 stands in the far east of Siberia. 148 00:17:40,520 --> 00:17:44,480 It's cut off from the rest of the world by towering peaks... 149 00:17:45,640 --> 00:17:48,440 And precipitous valleys. 150 00:17:52,360 --> 00:17:55,200 And it is the last stronghold 151 00:17:55,320 --> 00:17:58,480 of the world's rarest big cat. 152 00:18:10,920 --> 00:18:13,160 The amur leopard. 153 00:18:19,360 --> 00:18:22,640 Hunting has brought it close to extinction. 154 00:18:22,760 --> 00:18:26,600 Only 120 are left in the wild. 155 00:18:29,800 --> 00:18:34,680 And this is one of the very few ever to be caught on film. 156 00:18:47,280 --> 00:18:51,920 Each must patrol a territory of over 100 square miles 157 00:18:52,040 --> 00:18:54,160 to find enough to eat. 158 00:18:59,760 --> 00:19:01,720 In the cold of march, 159 00:19:01,840 --> 00:19:05,080 prey is at its most scarce. 160 00:19:17,320 --> 00:19:20,280 But leopards are clever opportunists 161 00:19:20,400 --> 00:19:22,920 and watch for clues. 162 00:19:26,760 --> 00:19:28,000 Crows. 163 00:19:29,040 --> 00:19:31,440 They, too, are looking for food. 164 00:19:34,320 --> 00:19:38,440 And their calls tell him that they've found something. 165 00:19:54,640 --> 00:19:58,680 But he is not the only predator here. 166 00:20:00,000 --> 00:20:03,920 On one of the trees, the marks of huge claws, 167 00:20:04,040 --> 00:20:05,720 ten centimetres long. 168 00:20:09,840 --> 00:20:13,600 They've been made by a hunter twice his size... 169 00:20:20,720 --> 00:20:23,600 A siberian tiger. 170 00:20:26,320 --> 00:20:29,800 Fewer than 500 remain in the wild. 171 00:20:36,120 --> 00:20:41,440 These two rare big cats are sharing the same territory. 172 00:20:46,560 --> 00:20:48,440 And fixed remote cameras 173 00:20:48,560 --> 00:20:52,320 show that they even use exactly the same trails. 174 00:20:57,560 --> 00:21:01,000 But leopards know they must be careful. 175 00:21:06,400 --> 00:21:10,640 Siberian tigers are the biggest of all the big cats, 176 00:21:10,760 --> 00:21:13,280 and could kill a leopard... 177 00:21:16,080 --> 00:21:18,120 Should they ever meet. 178 00:21:29,440 --> 00:21:30,440 In winter, 179 00:21:30,560 --> 00:21:34,720 many forest animals rely on carrion for food. 180 00:21:39,560 --> 00:21:41,760 And that includes leopards. 181 00:21:52,000 --> 00:21:55,080 But he can't let down his guard. 182 00:22:06,840 --> 00:22:08,640 The crows that led him here... 183 00:22:08,760 --> 00:22:11,840 May also have alerted the tiger. 184 00:22:42,800 --> 00:22:44,240 The crows are disturbed. 185 00:22:45,960 --> 00:22:48,760 Another mouthful might be risky. 186 00:23:04,520 --> 00:23:08,080 Survival sometimes depends on knowing 187 00:23:08,200 --> 00:23:09,680 when to leave. 188 00:23:17,720 --> 00:23:20,840 Only a few choose to take their chances here 189 00:23:20,960 --> 00:23:23,400 in the depths of winter. 190 00:23:24,800 --> 00:23:30,160 Elsewhere, vast swathes of the forest remain eerily empty. 191 00:23:34,480 --> 00:23:38,800 Above, there is an othennorldly light show... 192 00:23:43,720 --> 00:23:46,120 The Aurora borealis. 193 00:23:52,760 --> 00:23:54,440 High in the sky, 194 00:23:54,560 --> 00:23:58,080 electrically charged solar particles from space 195 00:23:58,200 --> 00:24:00,720 collide with the earth's atmosphere 196 00:24:00,840 --> 00:24:03,720 and create this ethereal display. 197 00:24:16,000 --> 00:24:21,800 Meanwhile, in Canada, through the six long months of winter, 198 00:24:21,920 --> 00:24:26,760 life below ground is biding its time. 199 00:24:32,520 --> 00:24:36,080 The world's most northerly turtle... 200 00:24:37,880 --> 00:24:39,200 The painted turtle... 201 00:24:39,320 --> 00:24:43,040 Seen here in a special filming chamber. 202 00:24:44,400 --> 00:24:47,160 They hatched last Autumn, but have remained 203 00:24:47,280 --> 00:24:50,760 in a state of suspended animation ever since. 204 00:24:53,720 --> 00:24:56,320 Their hearts have stopped beating... 205 00:24:57,720 --> 00:25:00,120 And only their brains have remained active, 206 00:25:00,240 --> 00:25:02,640 and even then, only very faintly. 207 00:25:06,200 --> 00:25:09,520 Painted turtles wait underground 208 00:25:09,640 --> 00:25:12,080 for this most important of moments... 209 00:25:21,960 --> 00:25:25,240 The arrival of spring. 210 00:25:39,880 --> 00:25:43,160 In April, the strengthening sunshine 211 00:25:43,280 --> 00:25:47,240 triggers a miraculous transformation. 212 00:26:01,680 --> 00:26:05,880 The turtles' body temperature rises just above freezing... 213 00:26:11,600 --> 00:26:15,320 And their hearts start to beat once more. 214 00:26:30,560 --> 00:26:33,320 Slowly, they return to life. 215 00:26:35,320 --> 00:26:40,360 Thanks to this extraordinary adaptation, these young turtles 216 00:26:40,480 --> 00:26:44,200 get a valuable head start in spring... 217 00:26:54,240 --> 00:26:57,760 And are one of the first to emerge, ready to take 218 00:26:57,880 --> 00:27:01,520 full advantage of the forest's renewed abundance. 219 00:27:09,520 --> 00:27:13,200 In just a matter of weeks, the vast northern forests 220 00:27:13,320 --> 00:27:15,360 flush green. 221 00:27:30,760 --> 00:27:36,600 For Siberia's big cats, each spring could bring new hope. 222 00:27:40,000 --> 00:27:41,440 Cubs. 223 00:27:43,680 --> 00:27:46,440 Each of them increases the chance that, 224 00:27:46,560 --> 00:27:51,440 even at this very late stage, both species might recover. 225 00:28:03,920 --> 00:28:08,040 By June, the northern forests are full of life. 226 00:28:17,120 --> 00:28:21,680 But several thousands of miles further north, in the tundra, 227 00:28:21,800 --> 00:28:24,720 the spring thaw is only just beginning. 228 00:28:31,920 --> 00:28:34,960 When it does, under 24-hour daylight, 229 00:28:35,080 --> 00:28:38,240 its impact is even more extreme. 230 00:28:43,920 --> 00:28:46,560 Five million square miles of snow 231 00:28:46,680 --> 00:28:49,560 disappear in a matter of days. 232 00:29:00,200 --> 00:29:03,400 Ten centimetres beneath the surface of the ground, 233 00:29:03,520 --> 00:29:07,920 a snow queen is waiting to make her appearance. 234 00:29:13,280 --> 00:29:16,440 A lapland Bumblebee. 235 00:29:17,680 --> 00:29:19,960 She's barely alive. 236 00:29:22,040 --> 00:29:26,480 All the other members of her colony were killed by the cold. 237 00:29:28,880 --> 00:29:32,760 She survived, as Bumblebee queens do, 238 00:29:32,880 --> 00:29:37,720 thanks to her larger size, her particularly thick fur, 239 00:29:37,840 --> 00:29:42,320 and a natural antifreeze that she has in her body. 240 00:29:53,720 --> 00:29:56,320 As temperatures continue to rise, 241 00:29:56,440 --> 00:29:59,200 she begins to thaw. 242 00:30:10,520 --> 00:30:13,040 She vibrates her flight muscles, 243 00:30:13,160 --> 00:30:15,320 which raises her body temperature 244 00:30:15,440 --> 00:30:20,000 to over 30 degrees celsius in just six minutes. 245 00:30:22,520 --> 00:30:25,800 There is no time to lose. 246 00:30:29,120 --> 00:30:33,000 She must now create an entire colony. 247 00:30:41,400 --> 00:30:44,280 First, the queen must find a drink of nectar 248 00:30:44,400 --> 00:30:46,360 to regain her strength... 249 00:30:50,120 --> 00:30:52,360 Travelling as much as three miles a day 250 00:30:52,480 --> 00:30:55,520 to find the flowers from which to collect it. 251 00:31:04,960 --> 00:31:06,800 She works tirelessly. 252 00:31:09,560 --> 00:31:11,760 As well as high-energy nectar... 253 00:31:13,760 --> 00:31:16,040 There's pollen to be gathered. 254 00:31:29,600 --> 00:31:35,200 Back underground, she uses the pollen to build a waxy cocoon. 255 00:31:37,520 --> 00:31:40,800 And in it, she deposits tiny eggs. 256 00:31:44,600 --> 00:31:47,280 Had she laid them directly on the frozen ground, 257 00:31:47,400 --> 00:31:49,600 the cold would have killed them. 258 00:31:49,720 --> 00:31:51,760 And now she warms them 259 00:31:51,880 --> 00:31:54,240 by pulsating her body. 260 00:32:03,640 --> 00:32:06,040 She has also constructed a little pot 261 00:32:06,160 --> 00:32:08,120 in which she stores nectar 262 00:32:08,240 --> 00:32:11,120 to provide her with a drink when she needs it. 263 00:32:17,280 --> 00:32:19,200 For the next three weeks... 264 00:32:20,400 --> 00:32:21,880 This single mother 265 00:32:22,000 --> 00:32:25,080 works around the clock, gathering nectar 266 00:32:25,200 --> 00:32:26,920 to top up her pot... 267 00:32:35,600 --> 00:32:37,280 And vibrating her body 268 00:32:37,400 --> 00:32:40,840 to prevent her developing young from freezing to death. 269 00:32:52,600 --> 00:32:56,600 Eventually, a new generation of bees 270 00:32:56,720 --> 00:32:59,240 starts to emerge. 271 00:33:05,920 --> 00:33:09,920 She leads each young worker to her honey pot 272 00:33:10,040 --> 00:33:12,680 and encourages it to drink. 273 00:33:19,400 --> 00:33:22,760 By the end of the following week, 274 00:33:22,880 --> 00:33:26,440 the number in her little colony has increased to eight. 275 00:33:28,880 --> 00:33:31,840 Her timing has been perfect. 276 00:33:37,960 --> 00:33:41,000 The tundra is now in full bloom. 277 00:33:48,680 --> 00:33:51,880 And the Bumblebee families help to pollinate 278 00:33:52,000 --> 00:33:55,560 the largest wild-flower Meadow on earth. 279 00:34:10,400 --> 00:34:15,040 But the summer here is one of the shortest on the planet, 280 00:34:15,160 --> 00:34:17,880 and all of the tundra's residents 281 00:34:18,000 --> 00:34:20,400 are now racing to breed. 282 00:34:23,920 --> 00:34:28,480 Alaskan snowy owls have a brood of six fluffy chicks 283 00:34:28,600 --> 00:34:31,920 and only eight weeks in which to raise them. 284 00:34:40,600 --> 00:34:44,960 The parents provide them with 30 lemmings a day... 285 00:34:46,400 --> 00:34:48,880 For the chicks will need to triple their weight 286 00:34:49,000 --> 00:34:51,080 before they reach independence. 287 00:35:00,960 --> 00:35:05,520 Unusually for an owl, snowies hunt by day. 288 00:35:10,040 --> 00:35:12,040 And over the next two weeks, 289 00:35:12,160 --> 00:35:15,800 they take full advantage of the arctic's continuous light. 290 00:35:22,160 --> 00:35:28,280 But this morning, the female returns to an empty nest. 291 00:35:34,360 --> 00:35:36,960 Her chicks are nowhere to be seen. 292 00:35:46,960 --> 00:35:48,920 They're hiding. 293 00:35:54,160 --> 00:35:58,320 They're so big, the whole group might be spotted by predators, 294 00:35:58,440 --> 00:36:02,280 so they have scattered across the tundra. 295 00:36:08,520 --> 00:36:12,840 But that makes feeding them all much harder work. 296 00:36:24,560 --> 00:36:26,560 Over 600 meals later, 297 00:36:26,680 --> 00:36:29,280 the parents' labours are starting to pay off... 298 00:36:31,400 --> 00:36:35,480 As the chicks stretch their newly developed wings. 299 00:36:45,120 --> 00:36:49,400 Just a month is left before winter returns. 300 00:37:07,000 --> 00:37:08,360 Two weeks more, 301 00:37:08,480 --> 00:37:11,120 and their transformation is almost complete. 302 00:37:13,280 --> 00:37:15,640 The chicks' wings might at last be able 303 00:37:15,760 --> 00:37:18,920 to do more than just lift them from the ground. 304 00:37:24,840 --> 00:37:26,480 Getting there! 305 00:37:32,920 --> 00:37:34,840 Keep going! 306 00:37:38,840 --> 00:37:40,240 Airborne! 307 00:37:40,360 --> 00:37:44,000 The youngsters are ready for independence. 308 00:37:46,480 --> 00:37:50,320 And the exhausted parents can take a well-earned rest. 309 00:37:56,400 --> 00:37:59,400 The tundra has come to life once again. 310 00:38:01,600 --> 00:38:04,920 But in the longer term, its very foundations 311 00:38:05,040 --> 00:38:06,920 are now at risk. 312 00:38:21,400 --> 00:38:24,560 The ground itself is giving way. 313 00:38:37,520 --> 00:38:43,320 In some places, it's dropped by more than 60 metres. 314 00:38:47,400 --> 00:38:51,320 Grasslands that once supported thousands of different species 315 00:38:51,440 --> 00:38:54,320 have become wastelands. 316 00:39:01,520 --> 00:39:04,000 Arctic temperatures are rising 317 00:39:04,120 --> 00:39:07,240 as a consequence of climate change. 318 00:39:11,840 --> 00:39:14,680 The deep soil, which has been frozen solid 319 00:39:14,800 --> 00:39:18,120 for thousands of years, the permafrost, 320 00:39:18,240 --> 00:39:22,320 is now thawing at a rate never witnessed before. 321 00:39:28,440 --> 00:39:30,280 Without the ice to bind it together, 322 00:39:30,400 --> 00:39:33,040 the ground becomes unstable. 323 00:39:39,800 --> 00:39:43,360 In Canada, thousands of tonnes of the tundra 324 00:39:43,480 --> 00:39:46,000 have collapsed in a matter of weeks. 325 00:39:59,760 --> 00:40:04,000 And in Siberia, huge scars are appearing. 326 00:40:10,240 --> 00:40:14,160 By the end of the century, an area of arctic permafrost 327 00:40:14,280 --> 00:40:16,720 one third of the size of Europe 328 00:40:16,840 --> 00:40:18,880 could have thawed. 329 00:40:24,440 --> 00:40:25,800 The warming of the tundra 330 00:40:25,920 --> 00:40:29,400 is having a profound impact on its wildlife. 331 00:40:31,960 --> 00:40:37,240 For millennia, caribou have made annual migrations. 332 00:40:42,200 --> 00:40:43,400 Every summer, 333 00:40:43,520 --> 00:40:46,760 driven by the seasonal changes of the far north, 334 00:40:46,880 --> 00:40:50,440 and following long-established pathways, 335 00:40:50,560 --> 00:40:54,840 they have trekked almost 400 miles north. 336 00:41:11,920 --> 00:41:18,120 This herd alone in north-east Alaska numbers over 200,000. 337 00:41:26,920 --> 00:41:28,200 Their destination 338 00:41:28,320 --> 00:41:30,160 is a vast wilderness 339 00:41:30,280 --> 00:41:34,120 known as the arctic national wildlife refuge. 340 00:41:45,680 --> 00:41:49,280 These summer pastures provide rich grazing, 341 00:41:49,400 --> 00:41:53,480 just what's needed to raise newborn calves. 342 00:42:02,760 --> 00:42:05,680 This one, fattening up on its mother's milk, 343 00:42:05,800 --> 00:42:09,080 would normally double its weight in just a few weeks. 344 00:42:19,600 --> 00:42:23,320 But now grazing time is being disrupted. 345 00:42:29,920 --> 00:42:32,880 In summer, the tundra becomes waterlogged. 346 00:42:36,120 --> 00:42:39,280 These are excellent breeding conditions 347 00:42:39,400 --> 00:42:42,640 for mosquitoes and other biting insects. 348 00:42:51,080 --> 00:42:53,080 But as the climate warms, 349 00:42:53,200 --> 00:42:56,800 there are concerns that insects will breed earlier 350 00:42:56,920 --> 00:42:59,680 and eventually reach plague proportions 351 00:42:59,800 --> 00:43:02,240 just as the caribou need to feed. 352 00:43:06,480 --> 00:43:08,320 Individual animals could lose 353 00:43:08,440 --> 00:43:13,160 a quarter of a pint of blood a day to biting insects. 354 00:43:18,960 --> 00:43:21,960 So the caribou may end their grazing early 355 00:43:22,080 --> 00:43:26,200 and head for cooler, mosquito-free pastures. 356 00:43:34,320 --> 00:43:35,960 But to get to such places, 357 00:43:36,080 --> 00:43:40,120 they will have to cross rivers swollen by seasonal runoff. 358 00:43:55,040 --> 00:43:59,600 For a young calf, a deep river crossing is very dangerous. 359 00:44:05,800 --> 00:44:09,480 He does what he can to stay close to his mother. 360 00:44:19,280 --> 00:44:21,520 But he doesn't have the strength 361 00:44:21,640 --> 00:44:24,280 to resist the fast-moving current. 362 00:45:16,960 --> 00:45:20,200 He is one of the lucky ones. 363 00:45:24,400 --> 00:45:26,880 Reunited with his mother, 364 00:45:27,000 --> 00:45:30,640 he can continue on his journey with the herd. 365 00:45:39,800 --> 00:45:43,200 But other calves are less fortunate... 366 00:45:45,880 --> 00:45:49,800 And must now fend for themselves. 367 00:46:01,200 --> 00:46:05,320 Some are too exhausted to take another step. 368 00:46:13,400 --> 00:46:16,800 But this is not a safe place to take a rest. 369 00:46:42,200 --> 00:46:43,920 Grizzly bears. 370 00:46:48,080 --> 00:46:49,480 For the past few weeks, 371 00:46:49,600 --> 00:46:52,600 there has been little food for them on the tundra. 372 00:46:55,360 --> 00:46:58,120 And this one is extremely hungry. 373 00:47:14,600 --> 00:47:18,000 He's looking for the weak and weary. 374 00:47:27,720 --> 00:47:30,600 And he's found one... 375 00:47:42,640 --> 00:47:44,840 Too tired to flee... 376 00:47:48,040 --> 00:47:50,360 And too weak to resist. 377 00:48:02,040 --> 00:48:03,640 The herd's finally reached 378 00:48:03,760 --> 00:48:06,160 the northern limits of its range. 379 00:48:11,240 --> 00:48:14,560 These coastal pastures bordering the arctic ocean 380 00:48:14,680 --> 00:48:17,440 remain cool enough to provide relief 381 00:48:17,560 --> 00:48:19,640 from the swarms of insects. 382 00:48:24,560 --> 00:48:28,280 Mothers and calves can finally feed in peace. 383 00:48:35,440 --> 00:48:39,880 For now, this immense herd is stable. 384 00:48:42,080 --> 00:48:46,760 But in the long term, its survival is now uncertain. 385 00:48:52,520 --> 00:48:55,400 The seasonal extremes of the far north 386 00:48:55,520 --> 00:48:59,120 have always tested its inhabitants to the limits. 387 00:49:01,360 --> 00:49:04,040 But climate change could present them 388 00:49:04,160 --> 00:49:06,280 with one challenge too many. 389 00:49:08,240 --> 00:49:11,200 Only if we can mitigate its effects 390 00:49:11,320 --> 00:49:13,920 will the remarkable wildlife here 391 00:49:14,040 --> 00:49:17,040 stand a chance of survival. 392 00:49:36,240 --> 00:49:38,840 Filming in the extremes of the far north... 393 00:49:39,920 --> 00:49:42,800 The team's greatest challenge was to capture 394 00:49:42,920 --> 00:49:45,800 the epic showdown between super-packs of wolves 395 00:49:45,920 --> 00:49:48,400 and bison in midwinter, 396 00:49:52,120 --> 00:49:53,280 The crew travelled to 397 00:49:53,400 --> 00:49:55,920 wood buffalo national park in northern Canada, 398 00:49:56,040 --> 00:49:59,680 a remote wilderness the size of Switzerland. 399 00:50:03,240 --> 00:50:05,760 To stand a chance of filming this drama, 400 00:50:05,880 --> 00:50:07,640 they must take to the skies. 401 00:50:09,120 --> 00:50:10,360 Drawing on local knowledge, 402 00:50:10,480 --> 00:50:13,960 pilot Matt erhardt helps to pinpoint 403 00:50:14,080 --> 00:50:16,080 one of the last free-roaming herds of bison 404 00:50:16,200 --> 00:50:18,920 and the wolves that specialise in hunting them. 405 00:50:22,600 --> 00:50:24,400 Some of the wolves have run fonnards. 406 00:50:24,520 --> 00:50:26,600 Just have all your kit ready to go. 407 00:50:28,920 --> 00:50:30,240 With a positive sighting, 408 00:50:30,360 --> 00:50:32,360 it's time to mobilise the film crew. 409 00:50:35,080 --> 00:50:37,720 Cameraman Jamie mcpherson has rigged the helicopter 410 00:50:37,840 --> 00:50:40,480 with a gyrostabilised camera system, 411 00:50:40,600 --> 00:50:43,840 enabling him to capture rock-steady images 412 00:50:43,960 --> 00:50:45,560 from a safe distance. 413 00:50:45,680 --> 00:50:47,800 You'd think filming from a helicopter's easy, 414 00:50:47,920 --> 00:50:49,336 because you can just fly around and film stuff. 415 00:50:49,360 --> 00:50:50,920 But you've got to be incredibly careful, 416 00:50:51,040 --> 00:50:52,160 not influence the behaviour, 417 00:50:52,200 --> 00:50:53,840 not scare the wolves or the bison. 418 00:50:58,320 --> 00:51:00,640 There we go. Yeah, that is them. 419 00:51:01,800 --> 00:51:03,040 - It's a big pack. - Yeah. 420 00:51:05,200 --> 00:51:06,536 They're really chilled out with the helicopter. 421 00:51:06,560 --> 00:51:07,840 Really encouraging. 422 00:51:10,800 --> 00:51:12,640 But before Jamie can start filming, 423 00:51:12,760 --> 00:51:15,880 the chopper must first drop the accompanying ground crew. 424 00:51:16,000 --> 00:51:18,160 - Good luck. - Ok. 425 00:51:23,440 --> 00:51:25,080 We got put down 426 00:51:25,200 --> 00:51:26,920 in this vast open space, 427 00:51:27,040 --> 00:51:29,560 and now we're going to try and hike in and see 428 00:51:29,680 --> 00:51:30,920 if we can get close to them, 429 00:51:31,040 --> 00:51:32,680 or hopefully they'll get close to us. 430 00:51:34,440 --> 00:51:38,440 To intercept the pack, the team must scramble into position. 431 00:51:42,280 --> 00:51:44,800 But trudging through knee-deep snow 432 00:51:44,920 --> 00:51:46,680 is hard going. 433 00:51:51,280 --> 00:51:53,640 Every time I catch up with Justin, he just keeps on going. 434 00:51:53,760 --> 00:51:56,160 He's a machine! 435 00:52:01,840 --> 00:52:03,000 Yeah, go ahead, Matt. 436 00:52:03,120 --> 00:52:05,120 Over radio: They're starting to head 437 00:52:05,240 --> 00:52:06,616 a little bit towards the north-west, 438 00:52:06,640 --> 00:52:08,720 so they're starting to move away from you. 439 00:52:10,160 --> 00:52:11,480 Oh, goddamn it! 440 00:52:13,200 --> 00:52:15,480 David: The ground crew will have to dig deep 441 00:52:15,600 --> 00:52:18,280 if they're to film the fleet-footed wolves. 442 00:52:22,880 --> 00:52:24,280 Over the following week, 443 00:52:24,400 --> 00:52:26,920 Jamie manages to track the wolf pack 444 00:52:27,040 --> 00:52:28,840 from the comfort of the helicopter... 445 00:52:30,200 --> 00:52:32,080 While down on the ground, 446 00:52:32,200 --> 00:52:35,680 Justin and will are having a tougher time of it. 447 00:52:35,800 --> 00:52:37,680 - Ohhh! - It's really 448 00:52:37,800 --> 00:52:40,560 incredibly awkward getting around. 449 00:52:40,680 --> 00:52:43,400 Even lunch offers little consolation. 450 00:52:43,520 --> 00:52:44,640 It's frozen bread, 451 00:52:44,760 --> 00:52:47,680 frozen brie and frozen pickle. 452 00:52:49,040 --> 00:52:51,080 And with no wolf activity visible from the air, 453 00:52:51,200 --> 00:52:53,640 Jamie is soon grounded. 454 00:52:53,760 --> 00:52:55,800 Yeah, I'm just looking for an update. 455 00:53:04,720 --> 00:53:07,960 The winter weather takes a turn for the worse. 456 00:53:08,080 --> 00:53:11,080 It's snowing, and it's at a temperature where it could 457 00:53:11,200 --> 00:53:13,880 potentially stick to the blades and become really dangerous. 458 00:53:15,320 --> 00:53:19,680 For the next few days, the crew are forced to sit it out. 459 00:53:25,360 --> 00:53:27,600 Finally, the skies clear. 460 00:53:28,600 --> 00:53:30,960 But after nearly three weeks on location, 461 00:53:31,080 --> 00:53:34,400 there's precious little filming time left. 462 00:53:34,520 --> 00:53:36,800 We've got one last shot 463 00:53:36,920 --> 00:53:38,840 to get what we're looking for. 464 00:53:38,960 --> 00:53:42,280 And just hoping that it comes together at the last minute. 465 00:53:49,600 --> 00:53:50,880 There, there's the trail there, 466 00:53:51,000 --> 00:53:52,960 so they're on the West Side of that trail there. 467 00:53:56,520 --> 00:53:58,720 Soon enough, they find the bison, 468 00:53:58,840 --> 00:54:00,680 along with wolves 469 00:54:00,800 --> 00:54:02,440 who appear to be in hunting mode. 470 00:54:02,560 --> 00:54:06,440 The spotter plane just found the wolves with the bison, 471 00:54:06,560 --> 00:54:08,920 so we're scrambling to get there as quick as we can. 472 00:54:30,920 --> 00:54:32,800 There's something about 473 00:54:32,920 --> 00:54:36,280 being in the presence of prey and predator on the ground 474 00:54:36,400 --> 00:54:39,880 like this which is very special. 475 00:54:40,000 --> 00:54:45,240 Justin is in prime position to capture the showdown. 476 00:54:51,800 --> 00:54:53,080 As a chase begins, 477 00:54:53,200 --> 00:54:56,720 Jamie picks up the action from the air. 478 00:55:04,080 --> 00:55:05,760 It'd be amazing if we could get round that. 479 00:55:11,160 --> 00:55:13,920 In a stop-start pursuit lasting an entire day, 480 00:55:14,040 --> 00:55:18,560 Jamie manages to record the full jaw-dropping drama. 481 00:55:21,120 --> 00:55:22,456 They've definitely got that female. 482 00:55:22,480 --> 00:55:24,600 I think they're going to bring it down. 483 00:55:28,880 --> 00:55:31,960 Perfect, Jim. We got it. 484 00:55:33,320 --> 00:55:34,920 With the hunt nearly over, 485 00:55:35,040 --> 00:55:37,560 the crew reposition Justin once more. 486 00:55:47,480 --> 00:55:51,240 We got on the ground just in time to capture 487 00:55:51,360 --> 00:55:53,320 from a really far distance 488 00:55:53,440 --> 00:55:56,360 the last moments of the bison's life. 489 00:55:59,560 --> 00:56:01,760 There's a moment of confliction 490 00:56:01,880 --> 00:56:05,120 between your loyalty for each animal. 491 00:56:05,240 --> 00:56:10,480 One is filled with a mixture of both celebration for the wolves 492 00:56:10,600 --> 00:56:15,320 but a sadness. Both exist somehow simultaneously. 493 00:56:20,640 --> 00:56:23,640 Bearing witness to this rarely seen age-old battle 494 00:56:23,760 --> 00:56:27,040 between predator and prey leaves the crew 495 00:56:27,160 --> 00:56:30,160 with an appreciation of just how challenging life is 496 00:56:30,280 --> 00:56:33,320 in the frozen extremes of the far north.