1 00:00:01,070 --> 00:00:03,244 Viewers like you make this program possible. 2 00:00:02,000 --> 00:00:07,000 Downloaded from YTS.MX 3 00:00:03,279 --> 00:00:05,350 Support your local PBS station. 4 00:00:08,000 --> 00:00:13,000 Official YIFY movies site: YTS.MX 5 00:00:15,394 --> 00:00:20,848 The Arctic has always been the toughest test, 6 00:00:20,882 --> 00:00:24,300 no more so than in the far corner of Alaska 7 00:00:24,334 --> 00:00:28,235 called the Arctic National Wildlife Refuge. 8 00:00:28,269 --> 00:00:31,376 Thousands of caribou face the cold... 9 00:00:33,240 --> 00:00:36,036 the terrain... 10 00:00:36,070 --> 00:00:41,075 and formidable predators to reach one special place 11 00:00:41,110 --> 00:00:43,146 at just the right time... 12 00:00:43,181 --> 00:00:47,426 a vast, beautiful plain on the edge of the Arctic Ocean. 13 00:00:49,980 --> 00:00:52,259 Here, they give birth. 14 00:00:55,124 --> 00:00:58,575 This is the story of the last great land migration 15 00:00:58,610 --> 00:01:00,129 in North America. 16 00:01:02,441 --> 00:01:07,653 And of how every Arctic creature is now on a daunting journey 17 00:01:07,688 --> 00:01:11,899 from a timeless past into a vastly different future. 18 00:01:44,242 --> 00:01:46,140 On the top of the world, 19 00:01:46,175 --> 00:01:48,867 it is still the ice age. 20 00:02:01,121 --> 00:02:04,262 It's northern Alaska in winter. 21 00:02:04,296 --> 00:02:06,643 The temperature drops to 50 below. 22 00:02:18,207 --> 00:02:21,796 Frozen rivers curl north from the Brooks Range 23 00:02:21,831 --> 00:02:25,041 and down to a plain stretching to the Beaufort Sea 24 00:02:25,075 --> 00:02:28,113 and the Arctic Ocean, now locked in ice. 25 00:02:31,806 --> 00:02:34,326 This vast stretch of white mountains, 26 00:02:34,361 --> 00:02:36,501 tundra, and icy rivers, 27 00:02:36,535 --> 00:02:39,987 forms one of the world's most important wildernesses... 28 00:02:40,021 --> 00:02:43,680 the Arctic National Wildlife Refuge. 29 00:02:43,715 --> 00:02:46,890 It's a home for courageous creatures from another time. 30 00:02:51,240 --> 00:02:54,139 This wildlife community will face a year 31 00:02:54,174 --> 00:02:55,761 of difficult decisions. 32 00:02:59,213 --> 00:03:03,666 Hundreds of miles southeast, bravest of all perhaps, 33 00:03:03,700 --> 00:03:07,221 is a pregnant caribou. 34 00:03:07,256 --> 00:03:10,224 She's part of the Porcupine caribou herd 35 00:03:10,259 --> 00:03:13,434 and will undertake the longest annual land migration 36 00:03:13,469 --> 00:03:15,540 on the planet. 37 00:03:15,574 --> 00:03:19,233 In her lifetime, she's likely to walk the same distance 38 00:03:19,268 --> 00:03:23,306 as a complete circuit of the globe. 39 00:03:23,341 --> 00:03:26,344 It's December, and the caribou are waiting, 40 00:03:26,378 --> 00:03:29,174 eating lichen in the twilight. 41 00:03:29,209 --> 00:03:33,454 The journey ahead needs precise timing. 42 00:03:33,489 --> 00:03:35,663 She'll march through forests, 43 00:03:35,698 --> 00:03:37,941 over mountains, across rivers, 44 00:03:37,976 --> 00:03:39,633 to the coastal plain. 45 00:03:39,667 --> 00:03:43,464 It's a round trip of almost a thousand miles. 46 00:03:47,330 --> 00:03:49,988 Some 160,000 caribou 47 00:03:50,022 --> 00:03:51,886 will walk from their wintering grounds 48 00:03:51,921 --> 00:03:54,682 in the Yukon and Northwest Territories 49 00:03:54,717 --> 00:03:58,030 to their calving grounds in the Wildlife Refuge. 50 00:04:02,518 --> 00:04:05,037 The Brooks Range stands in their way, 51 00:04:05,072 --> 00:04:08,731 running parallel to the coast. 52 00:04:08,765 --> 00:04:12,390 The sun sets for the last time until the New Year. 53 00:04:23,435 --> 00:04:26,990 The only sunlight is reflected by a wintry moon. 54 00:04:35,447 --> 00:04:37,449 Hundreds of miles above, 55 00:04:37,484 --> 00:04:41,073 solar radiation fires up the ionosphere, 56 00:04:41,108 --> 00:04:42,696 and the ghostly aurora. 57 00:04:58,367 --> 00:05:00,576 This is a world of huge planetary 58 00:05:00,610 --> 00:05:04,131 forces in constant flux. 59 00:05:04,165 --> 00:05:08,687 This is nature at its most spectacular and extreme. 60 00:05:20,389 --> 00:05:24,462 A dawn twilight returns in January. 61 00:05:32,815 --> 00:05:35,680 Blizzards blast the tundra. 62 00:05:35,714 --> 00:05:40,098 Most animals have left or are hibernating under the deep snow, 63 00:05:40,132 --> 00:05:41,858 but musk ox remain. 64 00:05:47,795 --> 00:05:51,972 They are loyal to a home range and won't leave. 65 00:05:52,006 --> 00:05:54,215 They rarely visit the valley. 66 00:05:54,250 --> 00:05:55,872 The snow is too deep, 67 00:05:55,907 --> 00:05:59,117 and they can't dig out the frozen grass. 68 00:05:59,151 --> 00:06:01,844 Even up here, it's hard work. 69 00:06:07,574 --> 00:06:11,163 Winters seem to be more erratic recently, 70 00:06:11,198 --> 00:06:13,649 on average more than eight degrees warmer 71 00:06:13,683 --> 00:06:17,411 than 50 years ago, which sounds better, 72 00:06:17,446 --> 00:06:21,173 but now there's freezing rain on top of heavier snowfall. 73 00:06:24,453 --> 00:06:26,938 The caribou are becoming restless. 74 00:06:32,530 --> 00:06:36,430 Her belly is beginning to swell with her unborn calf. 75 00:06:41,918 --> 00:06:46,992 She's searching for reindeer lichen, her winter food. 76 00:06:47,027 --> 00:06:50,168 She's a reindeer as much as a caribou. 77 00:06:50,202 --> 00:06:52,239 They are the same species. 78 00:06:57,693 --> 00:07:01,766 She digs through snow like the musk ox. 79 00:07:01,800 --> 00:07:03,526 For a prospective mother, 80 00:07:03,561 --> 00:07:07,323 finding enough food is her principal focus. 81 00:07:07,357 --> 00:07:09,498 But it's not her only worry. 82 00:07:20,819 --> 00:07:23,166 It's a lone wolf. 83 00:07:35,834 --> 00:07:39,355 The caribou's instinct is to stay on the move. 84 00:07:39,389 --> 00:07:42,082 Somewhere has to be better than this. 85 00:07:47,881 --> 00:07:51,125 But migration is not blind instinct. 86 00:07:51,160 --> 00:07:55,095 It's a series of collective decisions based on subtle clues 87 00:07:55,129 --> 00:07:58,788 to weather patterns and journey times. 88 00:07:58,823 --> 00:08:00,894 Every year is different. 89 00:08:04,069 --> 00:08:06,727 The wolf has choices to make, too. 90 00:08:06,762 --> 00:08:10,248 He can follow the caribou, but they move fast, 91 00:08:10,282 --> 00:08:12,422 and the journey is too far. 92 00:08:18,152 --> 00:08:21,017 The first birth of spring. 93 00:08:21,052 --> 00:08:22,571 It's not a caribou, 94 00:08:22,605 --> 00:08:26,920 but a newborn musk ox, a 30-pound baby, 95 00:08:26,954 --> 00:08:30,786 delivered straight onto the snow. 96 00:08:30,820 --> 00:08:33,064 The family surrounds her, 97 00:08:33,098 --> 00:08:36,377 a protection from dangers outside their circle. 98 00:08:48,666 --> 00:08:53,636 But within hours, the calf wants out. 99 00:08:53,671 --> 00:08:56,190 There's a beautiful new world to explore. 100 00:09:04,440 --> 00:09:07,339 Every calf is precious. 101 00:09:07,374 --> 00:09:10,170 Musk ox were hunted to extinction in Alaska 102 00:09:10,204 --> 00:09:12,103 in the 1860s, 103 00:09:12,137 --> 00:09:15,934 but were brought back in the 1930s. 104 00:09:15,969 --> 00:09:19,075 There are now a few thousand here in Alaska. 105 00:09:24,011 --> 00:09:27,428 A little river gully is a new adventure for the calf. 106 00:09:33,055 --> 00:09:37,818 Once in, getting back out is harder. 107 00:09:49,692 --> 00:09:51,591 The mother won't follow. 108 00:09:51,625 --> 00:09:53,903 She doesn't know how deep the snow is 109 00:09:53,938 --> 00:09:55,664 and could easily get stuck. 110 00:09:59,806 --> 00:10:02,567 She tracks her calf from the bank. 111 00:10:11,576 --> 00:10:13,820 The calf discovers... 112 00:10:13,854 --> 00:10:15,649 ice. 113 00:10:35,462 --> 00:10:38,638 There's a physical urgency to find your feet here... 114 00:10:41,571 --> 00:10:44,920 ...but perhaps a greater mental urgency for the calf 115 00:10:44,954 --> 00:10:47,267 to figure out her world. 116 00:10:51,271 --> 00:10:54,101 The patient mother waits... 117 00:10:54,136 --> 00:10:56,690 and her calf finds a way out. 118 00:11:17,297 --> 00:11:19,368 She's got maybe another two years 119 00:11:19,402 --> 00:11:21,819 looking after this youngster. 120 00:11:21,853 --> 00:11:25,270 The herd of about 15 will protect the calves 121 00:11:25,305 --> 00:11:29,861 and search for food around their large home range until summer. 122 00:11:40,423 --> 00:11:44,600 The caribou have left the winter woodland far behind, 123 00:11:44,634 --> 00:11:46,844 and are heading north. 124 00:11:56,785 --> 00:11:59,649 By April, the snow is starting to melt, 125 00:11:59,684 --> 00:12:03,757 and many rivers run earlier than a decade ago. 126 00:12:03,792 --> 00:12:08,935 Spring is moving north faster, and the caribou need to keep up. 127 00:12:16,977 --> 00:12:20,291 The herd heads on for about a hundred miles, 128 00:12:20,325 --> 00:12:21,982 then will turn west 129 00:12:22,017 --> 00:12:24,985 towards the Arctic National Wildlife Refuge. 130 00:12:30,266 --> 00:12:34,167 It's the end of April. They are over halfway. 131 00:12:34,201 --> 00:12:35,789 The mothers will all give birth 132 00:12:35,824 --> 00:12:38,585 within days of the third of June. 133 00:12:38,619 --> 00:12:40,138 Six weeks to go. 134 00:12:48,768 --> 00:12:52,495 Golden eagles nest along the route. 135 00:12:52,530 --> 00:12:54,049 They came up from the south 136 00:12:54,083 --> 00:12:56,810 and established territories in March, 137 00:12:56,845 --> 00:13:00,469 feeding on hares, ptarmigan, or marmots. 138 00:13:02,851 --> 00:13:08,546 The eagle pair returns to the same spectacular nest each year. 139 00:13:08,580 --> 00:13:13,551 They are loyal to a site decided over a decade ago. 140 00:13:13,585 --> 00:13:16,347 But the calendar has changed a lot since then. 141 00:13:28,221 --> 00:13:31,500 By early May, the chicks are near fledging, 142 00:13:31,534 --> 00:13:34,572 and the caribou herd has already passed. 143 00:13:42,994 --> 00:13:45,617 A ground squirrel is breakfast. 144 00:13:58,354 --> 00:14:00,701 It will take a new generation of eagles 145 00:14:00,736 --> 00:14:04,705 to make the huge adjustment to the changes unfolding here. 146 00:14:08,330 --> 00:14:13,542 A lone wolf has stuck with the herd for many miles. 147 00:14:31,111 --> 00:14:35,150 Caribou from a broad area either side of the Canadian border 148 00:14:35,184 --> 00:14:37,807 are converging on the same route. 149 00:14:37,842 --> 00:14:41,466 They'll navigate around the eastern end of the Brooks Range, 150 00:14:41,501 --> 00:14:44,400 about 40 miles from the Arctic shore. 151 00:14:57,551 --> 00:15:00,830 In a few places, the route has bottlenecks 152 00:15:00,865 --> 00:15:03,212 around rivers and lakes. 153 00:15:18,365 --> 00:15:22,542 This migration of Arctic caribou is compared to wildebeest 154 00:15:22,576 --> 00:15:26,615 on the African savanna, and so the coastal plain 155 00:15:26,649 --> 00:15:30,619 is sometimes called America's Serengeti. 156 00:15:42,872 --> 00:15:44,978 As the herd funnels through the foothills 157 00:15:45,013 --> 00:15:46,738 of the Brooks Range, 158 00:15:46,773 --> 00:15:49,741 the wolf briefly gains an advantage. 159 00:15:59,648 --> 00:16:03,997 The weaker calves from last year are struggling to keep up. 160 00:16:04,032 --> 00:16:06,448 There's been little time to stop and eat. 161 00:16:13,593 --> 00:16:16,009 As long as the herd stays watchful 162 00:16:16,044 --> 00:16:19,116 and maintains a distance, they're safe. 163 00:16:28,090 --> 00:16:30,955 Caribou are faster. 164 00:16:30,990 --> 00:16:33,268 The wolf is a tactician, 165 00:16:33,302 --> 00:16:36,616 but tactics are hard if you work alone. 166 00:16:58,086 --> 00:17:02,055 Here is an unparalleled amount of food on the hoof, 167 00:17:02,090 --> 00:17:06,301 but to this lone wolf, it might as well not be here at all. 168 00:17:19,762 --> 00:17:24,629 By May, spring has reached the Arctic National Wildlife Refuge. 169 00:17:26,562 --> 00:17:30,739 Life here has slept under snow for eight months. 170 00:17:35,709 --> 00:17:39,334 Plovers and redpolls arrive to nest, 171 00:17:39,368 --> 00:17:41,991 part of a massive aerial migration. 172 00:17:46,272 --> 00:17:50,379 Millions of snow geese leave California or Texas 173 00:17:50,414 --> 00:17:54,349 and are on their way to the Arctic Islands of Canada. 174 00:17:54,383 --> 00:17:57,179 They'll stop off here on their way back. 175 00:18:09,295 --> 00:18:12,677 Sandpipers are part of the worldwide event. 176 00:18:18,718 --> 00:18:22,480 Golden plovers set off from Argentina. 177 00:18:22,515 --> 00:18:26,898 Terns, loons, and songbirds come from Antarctica 178 00:18:26,933 --> 00:18:30,005 or Africa or East Asia. 179 00:18:30,039 --> 00:18:33,042 Hundreds of species cross the planet 180 00:18:33,077 --> 00:18:35,493 on their way to the Arctic north. 181 00:18:49,300 --> 00:18:54,616 A world of birds is heading to the summer paradise of Alaska. 182 00:19:07,007 --> 00:19:12,323 The golden plover couple have arranged a nest on the ground, 183 00:19:12,358 --> 00:19:15,878 laid their eggs, and are raising their chicks. 184 00:19:29,340 --> 00:19:33,068 The parents provide some protection against Arctic foxes 185 00:19:33,102 --> 00:19:35,208 or predatory birds, 186 00:19:35,243 --> 00:19:38,763 but it's mainly just warmth under a camouflaged wing. 187 00:19:49,636 --> 00:19:53,537 Once thawed out, the chicks have to get back to finding food 188 00:19:53,571 --> 00:19:55,090 for themselves. 189 00:20:08,414 --> 00:20:11,382 The mother leaves after a couple of weeks, 190 00:20:11,417 --> 00:20:14,834 and the father follows a week or so later. 191 00:20:14,868 --> 00:20:17,146 But the chicks stay longer 192 00:20:17,181 --> 00:20:20,598 and have to find their own way back to South America. 193 00:20:23,670 --> 00:20:26,190 In the meantime, the chicks catch insects 194 00:20:26,225 --> 00:20:28,261 for as long as they can, 195 00:20:28,296 --> 00:20:31,022 then come running back to warm up again. 196 00:20:36,200 --> 00:20:39,617 Their mother knows it's not just the cold that will get them. 197 00:20:51,940 --> 00:20:56,738 Arctic foxes live in tunnels in the layer above the permafrost. 198 00:21:02,157 --> 00:21:03,917 The parents returned a few months ago 199 00:21:03,952 --> 00:21:08,439 from their winter wanderings in snowy white coats 200 00:21:08,474 --> 00:21:11,477 to give birth and turn brown for summer. 201 00:21:21,694 --> 00:21:25,422 The cubs were born here in early May. 202 00:21:25,456 --> 00:21:28,045 Now, a few weeks later, 203 00:21:28,079 --> 00:21:30,841 they enjoy the remarkably warm days. 204 00:21:53,484 --> 00:21:56,556 They need to grow up fast. 205 00:21:56,591 --> 00:21:59,007 The cubs are already eating meat 206 00:21:59,041 --> 00:22:02,079 and seem constantly hungry. 207 00:22:02,113 --> 00:22:04,668 Ground squirrels and nesting birds are here 208 00:22:04,702 --> 00:22:07,360 in large numbers in May and June. 209 00:22:09,673 --> 00:22:12,331 One delivery is not enough for them all. 210 00:22:17,784 --> 00:22:20,408 The others don't notice the mother's return 211 00:22:20,442 --> 00:22:22,444 until it's almost too late. 212 00:22:43,638 --> 00:22:45,156 Oh, well. 213 00:22:45,191 --> 00:22:47,193 Dad will be back soon with more. 214 00:22:54,096 --> 00:22:56,961 It's a constant meal service during days 215 00:22:56,996 --> 00:22:58,963 that never quite seem to end. 216 00:23:03,692 --> 00:23:06,937 Nesting on the ground is dangerous, 217 00:23:06,971 --> 00:23:12,874 but there is one bird that would fight off any fox... the jaeger. 218 00:23:12,908 --> 00:23:15,463 Jaeger means hunter in German. 219 00:23:18,638 --> 00:23:21,814 The caribou are beginning to arrive. 220 00:23:21,848 --> 00:23:27,198 They are tired, hungry, many are about to give birth, 221 00:23:27,233 --> 00:23:30,478 and they could so easily tread on a bird's nest. 222 00:23:34,930 --> 00:23:38,313 The jaegers are not going to let that happen. 223 00:23:38,347 --> 00:23:41,109 They start with some gentle warnings, 224 00:23:41,143 --> 00:23:43,456 but the caribou ignore them. 225 00:23:47,633 --> 00:23:50,636 Yet the jaegers are fearless. 226 00:24:09,240 --> 00:24:12,278 The caribou mother has come hundreds of miles, 227 00:24:12,312 --> 00:24:14,349 faced raging torrents, 228 00:24:14,383 --> 00:24:17,973 been jammed by lakes, escaped wolves, 229 00:24:18,008 --> 00:24:20,493 and now there's a determined parent bird 230 00:24:20,528 --> 00:24:22,599 that doesn't want her here at all. 231 00:24:31,815 --> 00:24:35,819 The caribou respond to the swooping bird ballet 232 00:24:35,853 --> 00:24:38,235 with strange dance moves of their own. 233 00:25:13,408 --> 00:25:15,514 As more of the herd arrives, 234 00:25:15,548 --> 00:25:19,138 the jaegers battle tirelessly to keep their eggs safe. 235 00:25:21,416 --> 00:25:25,662 For the birds, and for all life here, there's little rest. 236 00:25:28,181 --> 00:25:30,390 Even the sun keeps going, 237 00:25:30,425 --> 00:25:34,291 skimming above the horizon for most of June. 238 00:25:44,404 --> 00:25:47,442 This midnight sun warms the caribou 239 00:25:47,476 --> 00:25:50,825 as they all finally reach their destination. 240 00:25:59,765 --> 00:26:02,250 These are their calving grounds, 241 00:26:02,284 --> 00:26:06,047 in the heart of the Arctic National Wildlife Refuge. 242 00:26:11,431 --> 00:26:15,884 She must arrive precisely, so that she's in the right place 243 00:26:15,919 --> 00:26:18,611 when, a week to 10 days after the snow melts, 244 00:26:18,646 --> 00:26:22,235 the sedges and grasses are at their most nutritious. 245 00:26:24,859 --> 00:26:27,758 Somewhere is a mother giving birth... 246 00:26:27,793 --> 00:26:35,214 one new calf among 160,000, anonymous to all but each other. 247 00:26:35,248 --> 00:26:39,390 Almost all the mothers give birth within a few days. 248 00:26:50,022 --> 00:26:53,853 The calf doubles in size in two weeks. 249 00:26:53,888 --> 00:26:57,823 The first green flush of sedges is briefly high in protein 250 00:26:57,857 --> 00:27:01,067 and sugars and coincides within a few days 251 00:27:01,102 --> 00:27:04,519 of when the calf needs most milk. 252 00:27:04,553 --> 00:27:08,005 A week or so later, the grass will become coarser, 253 00:27:08,040 --> 00:27:11,112 bitter, and indigestible. 254 00:27:18,671 --> 00:27:20,846 The caribou slowly spread out, 255 00:27:20,880 --> 00:27:25,367 surfing a wave of melting snow and growing grass. 256 00:27:34,480 --> 00:27:36,758 The successful flood of energy 257 00:27:36,793 --> 00:27:39,968 transforms the character of the caribou. 258 00:27:45,353 --> 00:27:48,528 The first people here feel part of it. 259 00:27:48,563 --> 00:27:52,981 Humans and caribou were created as one, they believe, 260 00:27:53,016 --> 00:27:57,952 and each still contains a piece of each other's heart. 261 00:27:57,986 --> 00:28:01,093 To the Gwich'in, this is the sacred place 262 00:28:01,127 --> 00:28:03,612 where life begins. 263 00:28:21,009 --> 00:28:26,912 It's late June, and paradise suddenly closes in. 264 00:28:26,946 --> 00:28:30,639 A plague of mosquitoes emerges. 265 00:28:32,365 --> 00:28:36,059 Each one may take just a drop of blood, 266 00:28:36,093 --> 00:28:40,063 but the warmer summers favor the insects. 267 00:28:40,097 --> 00:28:43,273 They emerge earlier and breed faster. 268 00:28:53,145 --> 00:28:55,388 The mosquitoes take so much blood 269 00:28:55,423 --> 00:28:58,391 and distress the caribou mothers so much 270 00:28:58,426 --> 00:29:00,773 that the herd spends the rest of the summer 271 00:29:00,808 --> 00:29:02,775 attempting to avoid them 272 00:29:02,810 --> 00:29:06,020 by searching for somewhere cooler. 273 00:29:06,054 --> 00:29:09,437 Life becomes a daily balancing act of finding 274 00:29:09,471 --> 00:29:11,473 food for yourself 275 00:29:11,508 --> 00:29:15,823 and not being food for mosquitoes. 276 00:29:15,857 --> 00:29:19,240 The consequences of the hotter summers may be subtle 277 00:29:19,274 --> 00:29:22,001 and complex for the caribou, 278 00:29:22,036 --> 00:29:27,489 but the effects to the north are much more obvious. 279 00:29:27,524 --> 00:29:30,665 Over the last 40 years, the decline of sea ice 280 00:29:30,699 --> 00:29:32,356 in the Beaufort Sea 281 00:29:32,391 --> 00:29:35,670 is one of the most dramatic changes anywhere. 282 00:29:42,884 --> 00:29:47,337 One of the animals affected most is the polar bear. 283 00:29:47,371 --> 00:29:49,166 During the last ice age, 284 00:29:49,201 --> 00:29:54,413 they would probably spend all year on the frozen sea. 285 00:29:54,447 --> 00:29:57,830 Since the ice age ended, polar bears hunted seals 286 00:29:57,865 --> 00:30:00,902 on the Arctic ice in winter and spring, 287 00:30:00,937 --> 00:30:03,629 and in late summer, rested on land, 288 00:30:03,663 --> 00:30:06,770 snoozing and living off their fat. 289 00:30:14,502 --> 00:30:18,575 Nowadays the ice on the Beaufort Sea is erratic. 290 00:30:18,609 --> 00:30:23,822 It melts faster, and the bears arrive early and thinner. 291 00:30:37,766 --> 00:30:42,806 By July, they are hunting for food along the shore. 292 00:30:42,841 --> 00:30:45,913 They're not a huge threat to the caribou herd. 293 00:30:45,947 --> 00:30:49,468 They are lumbering on land, and easily overheat. 294 00:30:59,547 --> 00:31:01,929 Years are more variable now, 295 00:31:01,963 --> 00:31:05,864 and polar bears are showing unexpected flexibility. 296 00:31:05,898 --> 00:31:08,004 They search for smaller prey 297 00:31:08,038 --> 00:31:10,834 and scavenge or fight over scraps. 298 00:31:14,251 --> 00:31:16,909 The Arctic Refuge is a safe home, 299 00:31:16,944 --> 00:31:20,844 but there is no refuge from the outside world. 300 00:31:20,879 --> 00:31:22,881 It's too hot for them. 301 00:31:22,915 --> 00:31:26,815 The July record here is now 85 degrees Fahrenheit. 302 00:31:30,302 --> 00:31:32,787 It's often hardest for a mother. 303 00:31:41,071 --> 00:31:45,041 Polar bear cubs are born in midwinter. 304 00:31:45,075 --> 00:31:49,183 This coast is one of the most important onshore denning areas 305 00:31:49,217 --> 00:31:50,770 in North America. 306 00:31:56,466 --> 00:31:59,400 These cubs are almost two years old 307 00:31:59,434 --> 00:32:01,333 but still need their mother's milk. 308 00:32:20,490 --> 00:32:25,081 Polar bears have declined in the southern Beaufort Sea. 309 00:32:25,115 --> 00:32:28,877 There are about half of how many were here 35 years ago. 310 00:32:34,780 --> 00:32:37,472 These are desperate times. 311 00:32:44,238 --> 00:32:49,001 North Alaska has the largest oil field in America. 312 00:32:59,529 --> 00:33:02,463 The base at Prudhoe Bay is next to 313 00:33:02,497 --> 00:33:05,638 the Arctic National Wildlife Refuge. 314 00:33:05,673 --> 00:33:07,330 It's a stark reminder 315 00:33:07,364 --> 00:33:10,057 of the cause of the changing seasons. 316 00:33:22,276 --> 00:33:25,037 Pipelines extend south 317 00:33:25,072 --> 00:33:28,661 and cross several caribou migration routes. 318 00:33:37,256 --> 00:33:40,466 The polar bears search for food across land 319 00:33:40,501 --> 00:33:43,745 now scarred by oil exploration. 320 00:34:02,419 --> 00:34:06,078 For the caribou, the green surge is over, 321 00:34:06,113 --> 00:34:07,942 and they are eating willow shrub 322 00:34:07,976 --> 00:34:12,947 and searching for anywhere cooler and mosquito free. 323 00:34:12,981 --> 00:34:16,226 For some, that means the coast. 324 00:34:16,261 --> 00:34:20,506 Others head south into the foothills of the Brooks Range. 325 00:34:28,376 --> 00:34:33,209 After enduring the heat of July, by late August, it's cooler. 326 00:34:41,113 --> 00:34:45,359 A mother and calf turn south, with the protection of the herd. 327 00:34:48,327 --> 00:34:52,814 Waiting for them is a grizzly. 328 00:34:52,849 --> 00:34:55,541 Grizzlies and caribou meet each year. 329 00:34:58,303 --> 00:35:02,030 The herd is named after the Porcupine River they must cross. 330 00:35:10,867 --> 00:35:15,182 The bear's journey here is equally hazardous. 331 00:35:15,216 --> 00:35:19,531 In summer, grizzlies hunt all the way to the Arctic Ocean. 332 00:35:51,218 --> 00:35:53,530 The Porcupine caribou herd 333 00:35:53,565 --> 00:35:56,119 is heading south into the Brooks Range. 334 00:36:04,748 --> 00:36:08,304 Away from the water, the caribou start to relax. 335 00:36:12,618 --> 00:36:14,206 It's a mistake. 336 00:36:27,219 --> 00:36:31,119 Caribou may be faster than bears on the open plain, 337 00:36:31,154 --> 00:36:33,950 but they must also rest the calves. 338 00:36:39,921 --> 00:36:43,615 Grizzlies and polar bears are almost the same species 339 00:36:43,649 --> 00:36:46,997 and increasingly overlap and interbreed, 340 00:36:47,032 --> 00:36:50,449 but grizzlies are a more serious threat to the herd. 341 00:36:52,831 --> 00:36:56,524 The bear has learned to chase off the mothers 342 00:36:56,559 --> 00:36:59,872 and then search for calves hiding in the scrub. 343 00:37:15,302 --> 00:37:16,889 He's found two. 344 00:37:19,375 --> 00:37:22,861 In a moment of indecision... 345 00:37:22,895 --> 00:37:24,311 he loses both. 346 00:37:28,867 --> 00:37:32,215 The calf's mother gallops to his side. 347 00:37:32,250 --> 00:37:36,012 It's a huge victory after so much hardship. 348 00:37:43,502 --> 00:37:45,055 Though not for the bear. 349 00:37:53,754 --> 00:37:58,103 The journey south crosses the Brooks Range in fall. 350 00:37:58,137 --> 00:38:01,762 In spring, this route is blocked by snow, 351 00:38:01,796 --> 00:38:04,903 but now they can return straight over the mountains. 352 00:38:33,000 --> 00:38:37,625 For the calf, this is his first taste of the wider world, 353 00:38:37,660 --> 00:38:41,871 with some new characters... Dall sheep. 354 00:38:49,672 --> 00:38:54,159 They are cousins of bighorns, little bighorns, 355 00:38:54,193 --> 00:38:56,126 and mountain specialists. 356 00:38:59,958 --> 00:39:02,478 Like musk ox, they don't migrate, 357 00:39:02,512 --> 00:39:05,515 but they do move around the mountains looking for grass 358 00:39:05,550 --> 00:39:09,105 and shrubs between the rocks. 359 00:39:09,139 --> 00:39:13,351 The ewes give birth to a single lamb in late May. 360 00:39:13,385 --> 00:39:17,665 By September, they are all enjoying the last of the summer. 361 00:39:34,786 --> 00:39:40,930 The mothers gather in flocks and watch for wolves and eagles. 362 00:39:40,964 --> 00:39:43,415 This is the migration route south, 363 00:39:43,450 --> 00:39:46,004 familiar to more than just caribou. 364 00:40:07,474 --> 00:40:09,476 The fledged golden eagle 365 00:40:09,510 --> 00:40:14,066 has been shadowing the caribou herd south. 366 00:40:14,101 --> 00:40:16,068 As the herd turns east, 367 00:40:16,103 --> 00:40:19,382 the caribou face the mountains' wolves. 368 00:40:24,594 --> 00:40:28,564 In a small valley, the herd slows to rest. 369 00:40:33,327 --> 00:40:36,330 A lone female plans her hunt. 370 00:40:42,509 --> 00:40:44,511 She doesn't try to hide. 371 00:40:44,545 --> 00:40:47,168 The mountains are on her side now. 372 00:41:10,571 --> 00:41:13,643 A calf becomes separated. 373 00:41:31,040 --> 00:41:32,455 To its mother, 374 00:41:32,490 --> 00:41:37,460 almost home, the trek has lost its meaning, its purpose. 375 00:41:45,572 --> 00:41:51,543 The snow geese arrive here from the northernmost Arctic islands. 376 00:41:51,578 --> 00:41:55,685 This is an important stopover on their way back to California, 377 00:41:55,720 --> 00:41:58,308 Texas, and Mexico. 378 00:42:03,175 --> 00:42:07,697 Snow geese numbers have grown over the last 20 years. 379 00:42:07,732 --> 00:42:09,837 There are now 20 million of them. 380 00:42:15,498 --> 00:42:17,845 In a world of so much decline, 381 00:42:17,880 --> 00:42:21,055 it's good to know some species are doing well. 382 00:42:46,978 --> 00:42:51,258 The autumn storms are sweeping in. 383 00:42:51,292 --> 00:42:53,674 The weather changes very quickly. 384 00:43:05,859 --> 00:43:10,035 Ptarmigans have been caught in their summer plumage. 385 00:43:10,070 --> 00:43:13,038 They'll turn white to an out-of-date schedule. 386 00:43:17,318 --> 00:43:20,011 As long as the snow isn't too deep, 387 00:43:20,045 --> 00:43:23,186 they can feed on willow buds and birch. 388 00:43:30,297 --> 00:43:33,162 Ptarmigans are here all year. 389 00:43:33,196 --> 00:43:37,476 That makes them a reliable target for a red fox. 390 00:43:53,492 --> 00:43:56,841 The many eyes of a flock 391 00:43:56,875 --> 00:44:00,154 and their sharp calls protect them for now. 392 00:44:02,640 --> 00:44:05,228 Red foxes are thriving in the Arctic 393 00:44:05,263 --> 00:44:09,577 and out-compete Arctic foxes if the weather is milder. 394 00:44:25,732 --> 00:44:28,838 By October, the rivers are frozen 395 00:44:28,873 --> 00:44:30,598 and are buried under snow. 396 00:44:38,123 --> 00:44:41,713 The musk ox have to dig for vegetation again. 397 00:44:48,547 --> 00:44:52,448 The male musk ox have other concerns. 398 00:44:52,482 --> 00:44:54,174 Before winter arrives, 399 00:44:54,208 --> 00:44:57,384 they must sort out mating rights to the harem. 400 00:44:57,418 --> 00:44:59,593 The rut started in August 401 00:44:59,627 --> 00:45:02,251 and a clear victor has yet to emerge. 402 00:45:54,372 --> 00:45:58,307 The musk ox are also related to bighorn sheep, 403 00:45:58,341 --> 00:46:00,274 but are much bigger. 404 00:46:00,309 --> 00:46:03,105 Males weigh in at 800 pounds, 405 00:46:03,139 --> 00:46:07,765 and their closing speed is close to 60 miles an hour. 406 00:46:07,799 --> 00:46:10,664 Their skulls are heavily reinforced 407 00:46:10,698 --> 00:46:13,391 and the brain protected by fluid. 408 00:46:26,784 --> 00:46:30,960 They back away, but only to prepare for combat. 409 00:46:37,484 --> 00:46:40,832 On the right, the older waits, 410 00:46:40,867 --> 00:46:42,972 then charges. 411 00:46:55,571 --> 00:46:58,298 There's probably no other animal on Earth 412 00:46:58,332 --> 00:47:00,162 that could survive this battle. 413 00:47:03,579 --> 00:47:06,237 The winner will now mate with the herd. 414 00:47:12,346 --> 00:47:16,903 By October, the land is frozen solid. 415 00:47:20,182 --> 00:47:23,461 Two polar bear cubs have survived the summer 416 00:47:23,495 --> 00:47:25,221 thanks to their mother. 417 00:47:35,335 --> 00:47:38,027 The sea won't freeze solid until November, 418 00:47:38,062 --> 00:47:43,377 but some coastal bays and river estuaries freeze earlier. 419 00:47:43,412 --> 00:47:47,347 It's their playground while they wait. 420 00:47:50,626 --> 00:47:52,386 On warm days the surface 421 00:47:52,421 --> 00:47:55,942 starts to melt and becomes slippery 422 00:47:55,976 --> 00:47:59,324 and tides weaken the new ice. 423 00:47:59,359 --> 00:48:02,224 The surface is still fragile. 424 00:48:23,383 --> 00:48:26,938 By midwinter, they'll be sniffing out seals 425 00:48:26,973 --> 00:48:30,252 in a freezing twilight far from land. 426 00:48:36,292 --> 00:48:40,227 This is their ice age home at last, 427 00:48:40,262 --> 00:48:44,887 a timeless scene that leaves behind a world of change. 428 00:48:53,033 --> 00:48:57,279 Then the ice breaks, and reality returns. 429 00:49:10,637 --> 00:49:13,157 The sea melts and refreezes 430 00:49:13,191 --> 00:49:17,092 and will melt again for two frustrating months. 431 00:49:26,618 --> 00:49:30,208 The polar bears of the southern Beaufort Sea are doing better 432 00:49:30,243 --> 00:49:33,867 than many others around the Arctic. 433 00:49:46,293 --> 00:49:50,470 The Arctic National Wildlife Refuge protects the dens, 434 00:49:50,504 --> 00:49:54,646 and mothers have become expert scavengers. 435 00:49:54,681 --> 00:49:59,720 Their sense of smell is probably the best of all animals. 436 00:50:18,153 --> 00:50:20,293 And look what they've found. 437 00:50:26,506 --> 00:50:30,234 It's a bowhead whale... what's left of it. 438 00:50:35,239 --> 00:50:38,138 With unpredictable winter ice ahead, 439 00:50:38,173 --> 00:50:42,073 this bowhead carcass is a salvation for the family 440 00:50:42,108 --> 00:50:45,594 and for all the local polar bears. 441 00:50:45,628 --> 00:50:47,837 They will feed for weeks. 442 00:50:49,839 --> 00:50:55,466 Bowhead whales are increasing, maybe thanks to longer summers. 443 00:50:55,500 --> 00:50:58,883 Everything is changing, and everything is connected. 444 00:51:01,575 --> 00:51:04,233 There is regulated whale hunting here, 445 00:51:04,268 --> 00:51:06,201 and this carcass has actually been left 446 00:51:06,235 --> 00:51:08,651 on the beach for the wildlife. 447 00:51:11,033 --> 00:51:13,794 For the polar bears, it's a lifeline, 448 00:51:13,829 --> 00:51:15,313 but maybe little more. 449 00:51:17,798 --> 00:51:21,181 They are ice bears, evolved in another world. 450 00:51:27,084 --> 00:51:31,433 Across millions of years, the Earth has seen huge changes 451 00:51:31,467 --> 00:51:33,780 many times. 452 00:51:33,814 --> 00:51:38,785 The most recent was the end of the Ice Age, 12,000 years ago. 453 00:51:46,206 --> 00:51:48,070 This extraordinary wilderness 454 00:51:48,105 --> 00:51:51,349 protects these Ice Age survivors... 455 00:51:51,384 --> 00:51:55,250 the polar bears, musk ox, arctic foxes, 456 00:51:55,284 --> 00:51:57,631 and the spectacular caribou, 457 00:51:57,666 --> 00:52:02,049 holding out on the top of the world. 458 00:52:02,084 --> 00:52:06,502 Now, even for them, the ice age may, finally, 459 00:52:06,537 --> 00:52:08,366 be coming to an end.