1 00:00:31,563 --> 00:00:33,003 The Arctic. 2 00:00:34,963 --> 00:00:37,843 It is intensely cold 3 00:00:37,843 --> 00:00:40,963 yet, nonetheless, mammals live here. 4 00:00:45,003 --> 00:00:50,203 This icy territory is ruled by polar bears. 5 00:00:52,363 --> 00:00:55,203 And for this young, inquisitive bear, 6 00:00:55,203 --> 00:01:01,443 these frozen seas are both its home 7 00:01:01,443 --> 00:01:04,683 and its playground. 8 00:01:11,883 --> 00:01:15,483 This might appear to be a game with a walrus... 9 00:01:17,043 --> 00:01:20,363 ...but, if so, it's the walrus who's winning. 10 00:01:49,203 --> 00:01:52,523 The young bear still has much to learn, 11 00:01:52,523 --> 00:01:55,523 as it starts to find its way around 12 00:01:55,523 --> 00:01:57,563 in this freezing world. 13 00:02:01,643 --> 00:02:05,123 From frozen seas to snowcapped mountains, 14 00:02:05,123 --> 00:02:07,883 specialised and hardy mammals 15 00:02:07,883 --> 00:02:11,323 have found many ways of flourishing 16 00:02:11,323 --> 00:02:14,523 in the coldest places on Earth. 17 00:02:35,923 --> 00:02:39,763 Many polar bears spend most of their time on the coast, 18 00:02:39,763 --> 00:02:41,483 hunting seals... 19 00:02:43,483 --> 00:02:45,683 ...but this young female 20 00:02:45,683 --> 00:02:47,843 is heading inland. 21 00:03:03,523 --> 00:03:07,243 Guided by her keen sense of smell, 22 00:03:07,243 --> 00:03:09,843 she's making for the mountains. 23 00:03:25,883 --> 00:03:29,443 It's 20 degrees below zero... 24 00:03:31,163 --> 00:03:34,443 ...but she's well adapted to these temperatures. 25 00:03:35,923 --> 00:03:38,403 She has two layers of fur 26 00:03:38,403 --> 00:03:41,803 and, beneath them, insulating fat, 27 00:03:41,803 --> 00:03:45,483 so she loses little body heat. 28 00:03:57,443 --> 00:03:59,403 After walking for hours... 29 00:04:01,763 --> 00:04:05,523 ...she at last finds what she has come for. 30 00:04:09,563 --> 00:04:12,123 Svalbard reindeer. 31 00:04:13,203 --> 00:04:16,043 The smallest reindeer in the world. 32 00:04:24,083 --> 00:04:27,323 Inland, they rarely encounter polar bears... 33 00:04:35,403 --> 00:04:40,363 ...but now, they are about to do so. 34 00:05:00,963 --> 00:05:05,123 Polar bears are not built for high-speed pursuits. 35 00:05:57,363 --> 00:05:59,683 She has been outrun. 36 00:06:08,763 --> 00:06:11,203 It's unusual for a polar bear 37 00:06:11,203 --> 00:06:13,403 to chase prey for so long... 38 00:06:16,443 --> 00:06:20,443 ...but even so, she doesn't give up. 39 00:06:25,323 --> 00:06:27,683 Her progress is hardly graceful. 40 00:06:43,163 --> 00:06:46,083 Soon, she's back on their trail... 41 00:06:49,923 --> 00:06:51,723 ...and she catches them up. 42 00:07:03,443 --> 00:07:06,443 This time, she chases the reindeer 43 00:07:06,443 --> 00:07:09,163 towards deeper snow. 44 00:07:09,163 --> 00:07:12,163 Perhaps this will slow them down. 45 00:07:14,763 --> 00:07:16,603 The group splits. 46 00:07:17,803 --> 00:07:21,403 For a moment, she is unsure which way to go. 47 00:07:45,523 --> 00:07:49,283 Both prey and predator are now exhausted. 48 00:07:51,643 --> 00:07:53,643 But she's not giving up. 49 00:07:58,403 --> 00:08:00,683 The two reindeer separate. 50 00:08:05,043 --> 00:08:07,443 She follows one downhill... 51 00:08:10,283 --> 00:08:12,243 ...back into the deep snow. 52 00:08:22,923 --> 00:08:25,923 Here, her great strength and longer legs 53 00:08:25,923 --> 00:08:28,003 help her to plough through it. 54 00:08:58,163 --> 00:09:01,923 This astonishing behaviour is rarely seen. 55 00:09:16,363 --> 00:09:19,283 However, in this part of the Arctic, 56 00:09:19,283 --> 00:09:22,483 several bears have been seen hunting in this way. 57 00:09:23,923 --> 00:09:28,723 But it's too early to know whether, as the world warms, 58 00:09:28,723 --> 00:09:31,243 a diet of reindeer alone 59 00:09:31,243 --> 00:09:33,483 could be enough to sustain them. 60 00:09:40,643 --> 00:09:43,003 Mammals like the polar bear 61 00:09:43,003 --> 00:09:47,163 have had millennia to find ways to survive in the cold. 62 00:09:48,523 --> 00:09:51,083 Since the extinction of the dinosaur, 63 00:09:51,083 --> 00:09:54,443 there have been over 50 glacial periods. 64 00:09:56,043 --> 00:09:59,963 During the coldest, ice sheets over half a mile thick 65 00:09:59,963 --> 00:10:03,483 lay where Edinburgh and New York now stand. 66 00:10:10,403 --> 00:10:13,563 Today, Alaska's northern wildernesses 67 00:10:13,563 --> 00:10:17,443 are still much as they were during those colder times. 68 00:10:31,923 --> 00:10:35,643 One particularly hardy and resourceful mammal 69 00:10:35,643 --> 00:10:39,763 has survived here for tens of thousands of years. 70 00:10:45,243 --> 00:10:46,843 A wolverine. 71 00:10:59,603 --> 00:11:03,403 Like all mammals, he's warm-blooded, 72 00:11:03,403 --> 00:11:06,723 and to maintain his body temperature, 73 00:11:06,723 --> 00:11:08,483 he must eat a lot. 74 00:11:10,803 --> 00:11:13,123 But it's not easy to find food 75 00:11:13,123 --> 00:11:15,883 in this vast, empty wilderness. 76 00:11:18,043 --> 00:11:20,123 Wolverines have to travel 77 00:11:20,123 --> 00:11:21,603 up to 50 miles 78 00:11:21,603 --> 00:11:23,563 a day in search of it. 79 00:11:36,283 --> 00:11:40,403 But his feet, like snowshoes, are broad 80 00:11:40,403 --> 00:11:43,763 and help him cross snowfields without sinking in. 81 00:11:50,243 --> 00:11:53,643 {\an8}And he has an extremely sensitive nose. 82 00:11:53,643 --> 00:11:56,203 {\an8}SNIFFS 83 00:11:58,723 --> 00:12:01,243 It's so sensitive, 84 00:12:01,243 --> 00:12:05,483 he can locate a carcass 85 00:12:05,483 --> 00:12:08,563 even though it's frozen solid. 86 00:12:13,763 --> 00:12:17,563 A caribou that has been killed by the cold. 87 00:12:26,083 --> 00:12:28,563 The wolverine's powerful jaws 88 00:12:28,563 --> 00:12:30,523 enable him to strip off 89 00:12:30,523 --> 00:12:32,083 the frozen flesh. 90 00:12:39,883 --> 00:12:41,723 He can even crunch 91 00:12:41,723 --> 00:12:43,843 through solid bone. 92 00:12:49,683 --> 00:12:52,923 But he doesn't finish his meal. 93 00:13:00,043 --> 00:13:02,363 Some of it, he carries away. 94 00:13:10,323 --> 00:13:13,443 {\an8}Surprisingly, perhaps, this male drops his food 95 00:13:13,443 --> 00:13:17,283 {\an8}in the middle of nowhere and then leaves. 96 00:13:27,043 --> 00:13:29,043 And this is why. 97 00:13:29,043 --> 00:13:31,203 A female wolverine. 98 00:13:33,443 --> 00:13:36,363 The food is a gift for his mate. 99 00:13:44,683 --> 00:13:48,283 {\an8}It will stave off her hunger for several days. 100 00:13:49,643 --> 00:13:52,603 {\an8}Wolverines are very secretive animals, 101 00:13:52,603 --> 00:13:57,403 {\an8}and very few people have ever seen this caring behaviour. 102 00:14:00,003 --> 00:14:04,283 Several days later, it becomes clear how important 103 00:14:04,283 --> 00:14:07,043 these deliveries of food have been. 104 00:14:11,443 --> 00:14:14,243 The female emerges from her den, 105 00:14:14,243 --> 00:14:15,963 beneath the snow. 106 00:14:19,683 --> 00:14:20,843 And... 107 00:14:21,923 --> 00:14:24,523 ...another head appears. 108 00:14:25,923 --> 00:14:28,043 Their three-month-old kit. 109 00:14:29,643 --> 00:14:32,323 It was born and has been nurtured 110 00:14:32,323 --> 00:14:35,163 two metres below the surface. 111 00:14:39,643 --> 00:14:42,083 This may well be the first time 112 00:14:42,083 --> 00:14:44,883 it has seen the world above the snow. 113 00:14:49,363 --> 00:14:52,923 The kit is strong enough to accompany its mother, 114 00:14:52,923 --> 00:14:55,443 and they look for a meal together. 115 00:15:11,203 --> 00:15:14,843 {\an8}90% of mammal males 116 00:15:14,843 --> 00:15:18,163 {\an8}take little or no part in raising their young... 117 00:15:22,803 --> 00:15:26,083 {\an8}...but fatherly devotion helps wolverines 118 00:15:26,083 --> 00:15:28,243 {\an8}to raise a family during this, 119 00:15:28,243 --> 00:15:30,363 {\an8}the coldest time of the year. 120 00:15:42,963 --> 00:15:46,243 Not all mammals have to travel huge distances 121 00:15:46,243 --> 00:15:49,723 to find their food, if they know where to look. 122 00:15:52,083 --> 00:15:55,883 Winter in Canada's northerly forests. 123 00:16:09,243 --> 00:16:12,003 It's minus 25 degrees. 124 00:16:22,363 --> 00:16:25,163 Most rivers are frozen over... 125 00:16:27,283 --> 00:16:29,963 ...but this one is kept ice-free 126 00:16:29,963 --> 00:16:31,963 by constant springs 127 00:16:31,963 --> 00:16:33,803 bubbling up from its bed... 128 00:16:35,083 --> 00:16:37,763 {\an8}...and that allows chum salmon 129 00:16:37,763 --> 00:16:40,443 {\an8}to spawn late in the season. 130 00:16:45,763 --> 00:16:50,123 {\an8}And they attract hungry brown bears. 131 00:17:02,923 --> 00:17:04,563 While most other bears 132 00:17:04,563 --> 00:17:06,803 are already hibernating, 133 00:17:06,803 --> 00:17:09,603 these few that know about 134 00:17:09,603 --> 00:17:12,763 this special place continue 135 00:17:12,763 --> 00:17:15,643 to fatten up deep into winter. 136 00:17:19,723 --> 00:17:22,683 And these fish, each containing 137 00:17:22,683 --> 00:17:24,723 over 4,000 calories, 138 00:17:24,723 --> 00:17:27,003 are well worth staying awake for. 139 00:17:29,803 --> 00:17:32,083 But not all of the bears 140 00:17:32,083 --> 00:17:34,163 are equally skilled at fishing. 141 00:17:46,523 --> 00:17:49,083 Some do little more than put 142 00:17:49,083 --> 00:17:51,323 their head under the water 143 00:17:51,323 --> 00:17:53,283 {\an8}and hope for the best. 144 00:18:00,043 --> 00:18:03,003 But their underwater vision 145 00:18:03,003 --> 00:18:05,803 is much like our own, 146 00:18:05,803 --> 00:18:08,283 and it's clearly a struggle. 147 00:18:11,963 --> 00:18:14,523 An elevated view might help... 148 00:18:33,123 --> 00:18:34,443 ...but it didn't. 149 00:18:38,643 --> 00:18:42,123 {\an8}Upstream, in a secluded part of the river, 150 00:18:42,123 --> 00:18:46,363 a mother is fishing with her two young cubs. 151 00:18:55,003 --> 00:18:59,283 {\an8}They both will rely on her milk during hibernation, 152 00:18:59,283 --> 00:19:01,403 so she puts on as much weight 153 00:19:01,403 --> 00:19:02,923 as she can. 154 00:19:02,923 --> 00:19:05,523 Up to 2kg a day. 155 00:19:09,843 --> 00:19:13,323 {\an8}In the months to come, the fat she gains now 156 00:19:13,323 --> 00:19:16,603 {\an8}will keep her alive during her long winter sleep. 157 00:19:29,283 --> 00:19:33,283 {\an8}By passing on her knowledge of this special place... 158 00:19:35,683 --> 00:19:37,883 ...and teaching her young cubs 159 00:19:37,883 --> 00:19:41,403 the skills they need to survive, 160 00:19:41,403 --> 00:19:46,723 {\an8}their mother has given them a good start in this icy world. 161 00:19:51,523 --> 00:19:53,603 Full of fish, the family 162 00:19:53,603 --> 00:19:55,843 is now ready to hibernate... 163 00:19:59,003 --> 00:20:02,523 ...and so avoid the hardships of winter. 164 00:20:11,043 --> 00:20:15,963 Old disused mines are excellent winter shelters for mammals. 165 00:20:20,083 --> 00:20:22,083 By sleeping down here, 166 00:20:22,083 --> 00:20:25,203 they can avoid the worst of the winter. 167 00:20:35,523 --> 00:20:40,203 And some use their time here in unexpected ways. 168 00:20:42,643 --> 00:20:44,963 {\an8}A colony of both little 169 00:20:44,963 --> 00:20:47,163 {\an8}and big brown bats. 170 00:20:48,723 --> 00:20:52,243 {\an8}The smallest weighs just 6g, 171 00:20:52,243 --> 00:20:54,843 {\an8}and what little body fat they have 172 00:20:54,843 --> 00:20:56,923 will last them six months. 173 00:20:59,803 --> 00:21:02,683 To do so, they change their bodily functions 174 00:21:02,683 --> 00:21:04,323 in a remarkable way. 175 00:21:06,363 --> 00:21:08,803 Their heartrate drops to just 176 00:21:08,803 --> 00:21:10,283 ten beats a minute 177 00:21:10,283 --> 00:21:12,403 and, at times, they take only 178 00:21:12,403 --> 00:21:14,723 two breaths an hour. 179 00:21:18,683 --> 00:21:20,763 Thermal images reveal 180 00:21:20,763 --> 00:21:24,363 that their body temperatures in midwinter 181 00:21:24,363 --> 00:21:26,443 are only just above freezing. 182 00:21:29,443 --> 00:21:33,683 They are now using only 2% of the energy they would do 183 00:21:33,683 --> 00:21:35,363 were they awake. 184 00:21:37,123 --> 00:21:40,803 The whole colony has put life on hold. 185 00:21:46,763 --> 00:21:50,323 Except for some solitary males. 186 00:21:54,203 --> 00:21:56,963 This one is shivering... 187 00:22:01,203 --> 00:22:03,843 ...not from the cold... 188 00:22:05,163 --> 00:22:06,763 ...but to wake up. 189 00:22:12,883 --> 00:22:17,083 {\an8}Vibrating his muscles rewarms his blood... 190 00:22:20,683 --> 00:22:24,563 ...and his heart is now beating ten times faster than it was. 191 00:22:25,963 --> 00:22:28,723 This awakening consumes as much fat 192 00:22:28,723 --> 00:22:30,763 as he would need for the next two months 193 00:22:30,763 --> 00:22:33,083 were he to continue to hibernate. 194 00:22:35,843 --> 00:22:38,483 So this is a risky thing to do. 195 00:22:43,483 --> 00:22:45,123 But there's a reason. 196 00:22:48,643 --> 00:22:52,723 {\an8}Before hibernation, some males failed to mate. 197 00:22:53,883 --> 00:22:56,443 {\an8}Now they have a chance to try again. 198 00:22:58,643 --> 00:23:02,603 Every step costs precious body heat. 199 00:23:06,083 --> 00:23:10,163 He's searching for a small cluster of females. 200 00:23:12,083 --> 00:23:14,883 He must be careful not to wake them 201 00:23:14,883 --> 00:23:17,483 or they too would expend the precious calories 202 00:23:17,483 --> 00:23:20,603 they will need if they are to survive the winter. 203 00:23:26,443 --> 00:23:28,163 He mates with one... 204 00:23:31,683 --> 00:23:34,883 ...and then quietly leaves 205 00:23:34,883 --> 00:23:37,003 and goes back to sleep. 206 00:23:45,003 --> 00:23:48,683 Five months later, the females wake. 207 00:23:52,443 --> 00:23:54,643 When they mated in the autumn, 208 00:23:54,643 --> 00:23:58,723 the sperm they acquired was not used, but stored. 209 00:24:00,363 --> 00:24:03,363 Only now will it fertilise an egg. 210 00:24:06,363 --> 00:24:09,323 {\an8}So a male who mates during hibernation 211 00:24:09,323 --> 00:24:12,883 {\an8}still has the chance of being a father. 212 00:24:18,883 --> 00:24:22,723 But bringing babies into a cold world of snow and ice 213 00:24:22,723 --> 00:24:24,403 is not easy. 214 00:24:45,083 --> 00:24:47,603 Each February in the Arctic, 215 00:24:47,603 --> 00:24:50,163 thousands of female harp seals 216 00:24:50,163 --> 00:24:53,323 haul out onto unstable pack ice 217 00:24:53,323 --> 00:24:54,963 and give birth. 218 00:24:56,163 --> 00:24:58,603 {\an8}A newborn pup doesn't have enough fat 219 00:24:58,603 --> 00:25:01,323 {\an8}to survive in the cold water... 220 00:25:04,523 --> 00:25:06,843 ...so mothers have to feed them 221 00:25:06,843 --> 00:25:09,603 as quickly and intensively as they can. 222 00:25:15,043 --> 00:25:16,803 And harp seals have 223 00:25:16,803 --> 00:25:19,443 a special way of doing that. 224 00:25:20,883 --> 00:25:22,483 The females produce 225 00:25:22,483 --> 00:25:24,723 {\an8}supercharged milk. 226 00:25:26,963 --> 00:25:31,363 {\an8}It contains ten times more fat than human milk. 227 00:25:33,923 --> 00:25:38,083 This enables each mother to rear her young faster than 228 00:25:38,083 --> 00:25:42,123 {\an8}almost any other mammal - just 12 days. 229 00:25:48,363 --> 00:25:50,003 For the young that appeared 230 00:25:50,003 --> 00:25:52,683 early in the season, 231 00:25:52,683 --> 00:25:55,363 the value of doing so is already visible. 232 00:25:59,443 --> 00:26:02,203 This one is fattening up nicely... 233 00:26:08,403 --> 00:26:10,683 ...but it's still very demanding... 234 00:26:15,323 --> 00:26:17,523 ...and its mother sometimes 235 00:26:17,523 --> 00:26:19,043 slips away. 236 00:26:44,283 --> 00:26:46,523 As the pups accumulate fat... 237 00:26:49,083 --> 00:26:52,043 ...they need to be fed less often... 238 00:26:57,643 --> 00:26:59,523 ...and this allows a mother 239 00:26:59,523 --> 00:27:02,083 to spend longer under the ice, 240 00:27:02,083 --> 00:27:05,123 in a more tranquil world. 241 00:27:14,043 --> 00:27:17,163 As the ice melts, it drifts - 242 00:27:17,163 --> 00:27:19,963 sometimes, over six miles in a day. 243 00:27:22,763 --> 00:27:25,883 So, after a lengthy swim, 244 00:27:25,883 --> 00:27:30,363 it's not always easy for a female to locate her pup. 245 00:27:49,563 --> 00:27:52,323 She flares her nostrils, 246 00:27:52,323 --> 00:27:55,243 in an attempt to pick up its scent. 247 00:28:00,683 --> 00:28:02,563 No, not that one. 248 00:28:06,883 --> 00:28:09,283 Definitely not. 249 00:28:24,563 --> 00:28:26,003 A sniff... 250 00:28:27,123 --> 00:28:30,923 ...and a kiss confirms this pup is hers. 251 00:28:42,963 --> 00:28:45,963 But, sadly, not all mothers get it right. 252 00:28:47,523 --> 00:28:51,403 Some never find their pups again. 253 00:28:55,763 --> 00:29:00,163 Alone and hungry, an abandoned pup 254 00:29:00,163 --> 00:29:03,003 understandably seeks comfort. 255 00:29:18,763 --> 00:29:21,443 But this nearby mother 256 00:29:21,443 --> 00:29:23,723 won't share her milk. 257 00:29:26,643 --> 00:29:30,163 Her priority is her own pup. 258 00:29:53,883 --> 00:29:56,883 The nursery continues to drift... 259 00:29:58,563 --> 00:30:03,363 {\an8}...but most mothers do eventually find their own pups again. 260 00:30:09,163 --> 00:30:12,083 {\an8}During their 12 short days together, 261 00:30:12,083 --> 00:30:15,123 {\an8}each mother tries to provide her pup 262 00:30:15,123 --> 00:30:19,043 with nearly 15kg of fat, 263 00:30:19,043 --> 00:30:20,963 which is enough to keep it warm, 264 00:30:20,963 --> 00:30:23,203 no matter how cold the water. 265 00:30:27,323 --> 00:30:31,083 So the mammalian ability to produce rich milk 266 00:30:31,083 --> 00:30:35,843 enables harp seals to breed on the sea ice. 267 00:30:44,603 --> 00:30:46,403 High above the sea, 268 00:30:46,403 --> 00:30:49,523 there are other icy worlds. 269 00:30:57,443 --> 00:31:01,683 These are the Kluane mountains of North America... 270 00:31:03,723 --> 00:31:07,203 ...and they carry the world's largest ice field, 271 00:31:07,203 --> 00:31:09,643 other than those around the Poles. 272 00:31:11,923 --> 00:31:16,283 Summer here is shorter than almost anywhere else on Earth. 273 00:31:18,323 --> 00:31:22,643 {\an8}But it has been colonised by diminutive relatives 274 00:31:22,643 --> 00:31:26,203 of rabbits - pikas. 275 00:31:27,723 --> 00:31:31,923 This young male has been awake all winter, 276 00:31:31,923 --> 00:31:34,123 {\an8}living on the food reserves 277 00:31:34,123 --> 00:31:36,483 {\an8}he built up last year. 278 00:31:37,803 --> 00:31:40,163 For him, summer 279 00:31:40,163 --> 00:31:42,243 can't come soon enough. 280 00:31:45,163 --> 00:31:47,363 As the sun's warmth returns, 281 00:31:47,363 --> 00:31:49,163 for just a few weeks, 282 00:31:49,163 --> 00:31:51,963 this harsh world is transformed 283 00:31:51,963 --> 00:31:55,123 into a rich high-altitude meadow. 284 00:31:58,243 --> 00:32:02,603 It's what all the pikas here have been waiting for, 285 00:32:02,603 --> 00:32:05,483 for almost ten months. 286 00:32:07,323 --> 00:32:09,323 There's no time to waste. 287 00:32:13,283 --> 00:32:16,643 Ready, steady... 288 00:32:19,123 --> 00:32:21,123 Now they must collect as much food 289 00:32:21,123 --> 00:32:23,123 as quickly as they possibly can. 290 00:32:30,683 --> 00:32:33,363 But some of them seem in less of a hurry. 291 00:32:41,923 --> 00:32:44,443 Clearly biding their time. 292 00:32:46,963 --> 00:32:48,843 The others 293 00:32:48,843 --> 00:32:50,963 are gathering leaves nonstop. 294 00:33:05,643 --> 00:33:07,163 Except this one. 295 00:33:12,963 --> 00:33:16,363 They build haystacks, and that takes a lot of work. 296 00:33:17,603 --> 00:33:19,443 Each mouthful has to be 297 00:33:19,443 --> 00:33:21,123 carefully placed to allow 298 00:33:21,123 --> 00:33:22,763 the sunlight to dry it. 299 00:33:25,643 --> 00:33:28,203 They also add a few leaves from other plants 300 00:33:28,203 --> 00:33:30,403 that contain chemicals which will help 301 00:33:30,403 --> 00:33:32,603 preserve the hay during the winter. 302 00:33:40,523 --> 00:33:45,203 As many as 11,000 return journeys may be needed... 303 00:33:47,163 --> 00:33:51,363 ...to build a reasonably large haystack. 304 00:33:56,083 --> 00:33:58,403 And then it has to be guarded 305 00:33:58,403 --> 00:34:01,243 against opportunistic neighbours. 306 00:34:08,963 --> 00:34:11,963 The weather is showing signs of changing. 307 00:34:13,803 --> 00:34:16,203 It's time to make a move. 308 00:34:25,963 --> 00:34:29,323 This pika specialises 309 00:34:29,323 --> 00:34:31,403 in stealing from its neighbours. 310 00:34:53,163 --> 00:34:56,763 Got away with it, again. 311 00:34:58,963 --> 00:35:01,523 Pika are one of the few mammals 312 00:35:01,523 --> 00:35:04,203 that prepare for winter in this way. 313 00:35:05,963 --> 00:35:08,563 With their food successfully stored, 314 00:35:08,563 --> 00:35:11,083 they're ready for the winter lockdown. 315 00:35:25,803 --> 00:35:28,043 The Qinghai-Tibet Plateau 316 00:35:28,043 --> 00:35:31,883 is around 4,000 metres above sea level. 317 00:35:36,123 --> 00:35:39,803 It's the largest and highest plateau in the world. 318 00:35:43,763 --> 00:35:48,843 The air here is so thin that it hardly retains any heat. 319 00:35:55,843 --> 00:35:59,323 Here, it's almost always very cold. 320 00:36:05,283 --> 00:36:07,203 A snow leopard. 321 00:36:07,203 --> 00:36:09,763 A female. Her dappled coat 322 00:36:09,763 --> 00:36:13,123 making her hardly noticeable against the broken rocks. 323 00:36:17,123 --> 00:36:19,803 The plateau's top predator. 324 00:36:30,003 --> 00:36:33,403 Her ancestors have lived and hunted here 325 00:36:33,403 --> 00:36:35,963 for over two million years. 326 00:36:47,003 --> 00:36:51,563 But recently, people have also come to live up here. 327 00:37:00,563 --> 00:37:02,363 A Tibetan homestead. 328 00:37:08,443 --> 00:37:11,483 The settlers have brought domesticated yak... 329 00:37:17,563 --> 00:37:21,363 ...and protect them with fences and dogs. 330 00:37:25,363 --> 00:37:27,163 Tibetan mastiffs. 331 00:37:29,043 --> 00:37:30,883 They were bred originally 332 00:37:30,883 --> 00:37:33,803 to protect the livestock kept by 333 00:37:33,803 --> 00:37:35,563 {\an8}Buddhist monks, and now 334 00:37:35,563 --> 00:37:38,243 {\an8}they are guarding the herders' yak. 335 00:37:45,403 --> 00:37:47,363 A yak is tempting prey 336 00:37:47,363 --> 00:37:49,643 for a hungry snow leopard in winter. 337 00:37:57,923 --> 00:38:00,443 But this female has been seen. 338 00:38:14,083 --> 00:38:15,803 The mastiffs outweigh 339 00:38:15,803 --> 00:38:17,763 even the biggest snow leopard. 340 00:38:35,403 --> 00:38:37,403 She's also outnumbered, 341 00:38:37,403 --> 00:38:39,963 so she retreats. 342 00:38:44,523 --> 00:38:46,643 She'll have to change her plan. 343 00:38:56,883 --> 00:38:59,683 This herd is unguarded... 344 00:39:04,523 --> 00:39:07,123 ...but they would not be easy prey. 345 00:39:12,883 --> 00:39:16,643 An adult yak weighs over half a ton 346 00:39:16,643 --> 00:39:19,323 and has horns up to a metre long. 347 00:39:21,963 --> 00:39:26,843 Even a calf is about twice the weight of a snow leopard. 348 00:39:36,923 --> 00:39:39,083 The leopard edges closer. 349 00:40:27,923 --> 00:40:32,163 As the calf disappears behind the slope, she follows. 350 00:40:35,363 --> 00:40:38,963 {\an8}Her impact takes them both careering downwards. 351 00:40:45,163 --> 00:40:46,803 But she holds on. 352 00:41:15,963 --> 00:41:18,483 It was a risk worth taking. 353 00:41:32,563 --> 00:41:36,283 The people here may lose ten yaks a year 354 00:41:36,283 --> 00:41:38,523 to predators like snow leopards. 355 00:41:39,643 --> 00:41:44,243 {\an8}But the local community aims to live alongside snow leopards 356 00:41:44,243 --> 00:41:47,443 {\an8}and compensate herders who lose yak... 357 00:41:50,123 --> 00:41:52,723 ...so they are not hunted here. 358 00:41:56,923 --> 00:41:59,203 Thanks to these decisions, 359 00:41:59,203 --> 00:42:02,003 this once-persecuted mammal 360 00:42:02,003 --> 00:42:04,243 is now thriving here. 361 00:42:30,963 --> 00:42:33,283 Today, for many mammals, 362 00:42:33,283 --> 00:42:36,763 the cold is not their biggest challenge. 363 00:42:38,083 --> 00:42:39,603 A far greater threat 364 00:42:39,603 --> 00:42:42,723 comes from changes in the climate. 365 00:42:48,283 --> 00:42:52,003 Here, along the coast of Canada's Hudson Bay, 366 00:42:52,003 --> 00:42:55,523 there is open water where there should be ice. 367 00:43:00,643 --> 00:43:02,243 An Arctic fox. 368 00:43:05,003 --> 00:43:06,843 At the beginning of each winter, 369 00:43:06,843 --> 00:43:10,323 foxes here form unlikely alliances 370 00:43:10,323 --> 00:43:12,283 with polar bears. 371 00:43:14,643 --> 00:43:16,243 It's late in the year 372 00:43:16,243 --> 00:43:19,563 and both species are waiting for the sea to freeze. 373 00:43:21,203 --> 00:43:23,523 Once it does, polar bears 374 00:43:23,523 --> 00:43:27,123 will once again be able to hunt seals out on the ice... 375 00:43:31,643 --> 00:43:33,923 ...and Arctic foxes will scavenge 376 00:43:33,923 --> 00:43:35,603 from their leftovers. 377 00:43:37,403 --> 00:43:40,323 But right now, both are hungry, 378 00:43:40,323 --> 00:43:43,243 and both must wait. 379 00:43:50,563 --> 00:43:53,803 She needs to be careful not to push her luck. 380 00:43:56,283 --> 00:44:00,643 Polar bears are not sociable creatures. 381 00:44:11,563 --> 00:44:16,283 Ten days pass, but there is still no sea ice in sight. 382 00:44:21,123 --> 00:44:24,803 {\an8}For the foxes, the situation is becoming desperate. 383 00:44:31,363 --> 00:44:33,683 A few edible morsels in the seaweed 384 00:44:33,683 --> 00:44:35,963 are all that she can find. 385 00:44:46,883 --> 00:44:49,483 {\an8}The wait, for one Arctic fox, 386 00:44:49,483 --> 00:44:51,643 {\an8}has been too long. 387 00:44:55,043 --> 00:44:56,723 {\an8}The starving survivors 388 00:44:56,723 --> 00:44:59,323 {\an8}cannot ignore this opportunity. 389 00:45:06,603 --> 00:45:10,883 {\an8}Desperation has led to cannibalism. 390 00:45:15,603 --> 00:45:19,803 {\an8}Something being seen more and more in the Arctic. 391 00:45:25,523 --> 00:45:27,323 Others begin to gather. 392 00:45:38,643 --> 00:45:41,563 As each tries to see off the competition... 393 00:45:43,083 --> 00:45:44,763 ...the sound of the quarrel 394 00:45:44,763 --> 00:45:47,683 attracts even more starving foxes. 395 00:45:52,163 --> 00:45:54,923 None are willing to surrender this meal... 396 00:46:10,643 --> 00:46:14,803 {\an8}...but each is unable to keep the others at bay. 397 00:46:17,523 --> 00:46:20,403 The commotion hasn't gone unnoticed. 398 00:46:24,203 --> 00:46:26,043 A cross fox. 399 00:46:26,043 --> 00:46:29,523 This stronger, more aggressive cousin from the south 400 00:46:29,523 --> 00:46:31,243 has been moving north 401 00:46:31,243 --> 00:46:34,403 as the winters have become steadily milder. 402 00:46:39,603 --> 00:46:42,403 It is now the top dog here. 403 00:46:59,483 --> 00:47:02,323 With the arrival of this newcomer, 404 00:47:02,323 --> 00:47:05,243 life for the long-time residents 405 00:47:05,243 --> 00:47:07,163 will only get harder. 406 00:47:24,723 --> 00:47:28,323 At last, the sea ice has formed. 407 00:47:31,283 --> 00:47:34,603 And for one Arctic fox, with luck, 408 00:47:34,603 --> 00:47:37,083 a meal is not far away. 409 00:47:41,243 --> 00:47:44,403 Mammals living in the coldest parts of the world 410 00:47:44,403 --> 00:47:47,603 have found remarkable ways to succeed 411 00:47:47,603 --> 00:47:49,883 where others could not do so. 412 00:47:58,523 --> 00:48:01,963 But as global temperatures continue to rise... 413 00:48:03,843 --> 00:48:06,203 ...only time will tell 414 00:48:06,203 --> 00:48:08,203 if they will be able to survive 415 00:48:08,203 --> 00:48:10,483 in this warming world. 416 00:48:25,603 --> 00:48:27,843 To capture one of the cold's 417 00:48:27,843 --> 00:48:30,443 most elusive mammals, the crew travelled 418 00:48:30,443 --> 00:48:32,563 to the tundra of northern Alaska. 419 00:48:34,323 --> 00:48:37,163 Home to the legendary wolverine. 420 00:48:41,243 --> 00:48:44,123 The ambition was not just to film wolverines 421 00:48:44,123 --> 00:48:46,163 in this vast landscape, but to record 422 00:48:46,163 --> 00:48:49,683 the emergence of their kits for the first time. 423 00:48:51,803 --> 00:48:54,803 The crew joined forces with a crack team 424 00:48:54,803 --> 00:48:58,083 of wolverine scientists and experts. 425 00:49:02,443 --> 00:49:05,083 {\an8}Everything's working and, um... 426 00:49:06,323 --> 00:49:08,723 ...yeah, we just need some wolverines now. 427 00:49:08,723 --> 00:49:11,083 Wolverine biologist Tom Glass 428 00:49:11,083 --> 00:49:14,003 has an early report of activity. 429 00:49:14,003 --> 00:49:16,203 There are some pretty old tracks and then there are 430 00:49:16,203 --> 00:49:19,083 some fresher ones. It looks like a promising one. 431 00:49:19,083 --> 00:49:21,403 With a wolverine in the area, 432 00:49:21,403 --> 00:49:25,843 producer Will Lawson leads the team to investigate. 433 00:49:25,843 --> 00:49:27,643 As a wolverine can cover 434 00:49:27,643 --> 00:49:30,003 up to 600 square miles, 435 00:49:30,003 --> 00:49:32,883 they will need to roam far and wide. 436 00:49:37,603 --> 00:49:40,523 To build a picture of the wolverines' movements, 437 00:49:40,523 --> 00:49:43,483 they set cameras along travel corridors 438 00:49:43,483 --> 00:49:45,443 and potential hot spots. 439 00:49:49,163 --> 00:49:51,203 But as the days pass, 440 00:49:51,203 --> 00:49:54,283 it becomes clear it's going to be a challenge. 441 00:49:54,283 --> 00:49:57,243 It's, like, corrupted or something. 442 00:49:58,603 --> 00:50:01,043 The lens has really frosted up. 443 00:50:01,043 --> 00:50:03,043 Disappointing. 444 00:50:03,043 --> 00:50:05,643 After weeks of frustrations, 445 00:50:05,643 --> 00:50:08,803 {\an8}finally, the team gets a reassuring sign. 446 00:50:08,803 --> 00:50:10,003 What have we got? 447 00:50:10,003 --> 00:50:13,403 {\an8}Wolverine came and checked our camera here. 448 00:50:13,403 --> 00:50:14,643 Yes! 449 00:50:14,643 --> 00:50:16,203 This is encouraging. 450 00:50:18,363 --> 00:50:20,043 I'm not sure what's happened here, 451 00:50:20,043 --> 00:50:21,723 but I don't think it's worked. 452 00:50:23,283 --> 00:50:25,763 This is the heartbreak of camera traps. 453 00:50:28,203 --> 00:50:30,723 How annoying! 454 00:50:30,723 --> 00:50:33,843 At least we know a wolverine has definitely been here. 455 00:50:33,843 --> 00:50:37,683 Though the camera traps haven't recorded the behaviour, 456 00:50:37,683 --> 00:50:40,683 they have confirmed it's a wolverine hot spot. 457 00:50:41,883 --> 00:50:44,323 So specialist pilot Mark Keech 458 00:50:44,323 --> 00:50:47,563 takes Will up for an aerial view... 459 00:50:52,803 --> 00:50:56,283 ...with the hope of locating a potential den. 460 00:50:58,643 --> 00:51:01,203 With thousands of hours and many years 461 00:51:01,203 --> 00:51:02,963 spent surveying wildlife from the air, 462 00:51:02,963 --> 00:51:05,723 Mark knows exactly what to look for. 463 00:51:08,043 --> 00:51:11,403 That's probably a wolverine track there our shadow is just about 464 00:51:11,403 --> 00:51:12,923 to go across, right now. 465 00:51:14,243 --> 00:51:16,083 There, you can see that is 466 00:51:16,083 --> 00:51:18,203 definitely a wolverine track there. 467 00:51:18,203 --> 00:51:21,603 This could be actually a den here. 468 00:51:21,603 --> 00:51:23,443 That would be great. Yeah. 469 00:51:23,443 --> 00:51:25,923 I think there's a very good chance, 470 00:51:25,923 --> 00:51:27,763 cos there is multiple tracks. 471 00:51:28,803 --> 00:51:30,683 So would you say that this site looks like 472 00:51:30,683 --> 00:51:33,203 a promising option? Absolutely. Great. 473 00:51:38,003 --> 00:51:40,483 With this exciting discovery, 474 00:51:40,483 --> 00:51:44,043 the crew decides to set up a remote camp near the den, 475 00:51:44,043 --> 00:51:46,763 30 miles from the nearest road. 476 00:51:46,763 --> 00:51:48,963 {\an8}Here's where the den is. Oh, I see. This is the route 477 00:51:48,963 --> 00:51:51,603 {\an8}we took in, so we can connect to that route really easily. 478 00:51:51,603 --> 00:51:53,163 All right, I think we've got a plan. 479 00:51:55,403 --> 00:51:58,563 The film crew heads out over the vast tundra, 480 00:51:58,563 --> 00:52:01,563 deep into the wolverines' territory, 481 00:52:01,563 --> 00:52:03,803 hauling everything they need 482 00:52:03,803 --> 00:52:05,883 to be self-sufficient in the field. 483 00:52:13,083 --> 00:52:14,523 We are exactly 484 00:52:14,523 --> 00:52:17,003 1.5 miles from this den. 485 00:52:17,003 --> 00:52:20,883 It looks like it's in that drainage we can see ahead, 486 00:52:20,883 --> 00:52:24,363 but on this side of it. 487 00:52:24,363 --> 00:52:28,283 Pretty cool to actually be here, standing so close. 488 00:52:38,363 --> 00:52:40,483 The camp established, 489 00:52:40,483 --> 00:52:42,163 the crew devises a strategy 490 00:52:42,163 --> 00:52:44,283 to watch the potential den 491 00:52:44,283 --> 00:52:45,963 around the clock. 492 00:52:47,723 --> 00:52:50,523 With Will and Matt working the perimeter, 493 00:52:50,523 --> 00:52:53,003 Neil sets up his filming hide, 494 00:52:53,003 --> 00:52:55,803 his home for the foreseeable future. 495 00:52:58,883 --> 00:53:01,203 It's hard to tell from the ground, 496 00:53:01,203 --> 00:53:03,763 one, exactly where the den is, 497 00:53:03,763 --> 00:53:06,683 and, two, how active it's been. 498 00:53:08,083 --> 00:53:10,483 {\an8}All Neil can do now is wait. 499 00:53:29,803 --> 00:53:32,043 My sandwiches are frozen solid. 500 00:53:36,083 --> 00:53:38,123 {\an8}Is there a wolverine in the hole? 501 00:53:38,123 --> 00:53:39,603 {\an8}We've done 200 hours in the hide 502 00:53:39,603 --> 00:53:40,803 {\an8}without seeing one yet. 503 00:53:40,803 --> 00:53:43,403 That's more of the question. 504 00:53:52,523 --> 00:53:54,203 Oh! There's one, there. 505 00:53:56,723 --> 00:53:58,923 I'm not joking, it's an actual... 506 00:53:58,923 --> 00:54:01,083 Come on, come on, come on. 507 00:54:14,723 --> 00:54:16,283 Beautiful to see. 508 00:54:16,283 --> 00:54:17,843 Finally get to see it. 509 00:54:17,843 --> 00:54:19,723 Thank goodness. 510 00:54:19,723 --> 00:54:23,283 With a female at the den finally confirmed, 511 00:54:23,283 --> 00:54:27,123 Matt and Will head in to resupply Neil. 512 00:54:28,203 --> 00:54:31,243 On the way, they make an exciting discovery. 513 00:54:31,243 --> 00:54:33,083 So we've got these wolverine tracks 514 00:54:33,083 --> 00:54:35,083 coming this way down the valley, 515 00:54:35,083 --> 00:54:37,483 and there's more than one set of tracks. 516 00:54:37,483 --> 00:54:39,643 So they come together right there 517 00:54:39,643 --> 00:54:41,523 and follow the same path. 518 00:54:41,523 --> 00:54:44,203 They look to be about the same age, 519 00:54:44,203 --> 00:54:46,163 which is pretty, pretty cool. 520 00:54:46,163 --> 00:54:49,323 {\an8}With signs of two adult wolverines in the area, 521 00:54:49,323 --> 00:54:53,683 {\an8}they meet Neil and find he's already filmed them both. 522 00:54:53,683 --> 00:54:55,123 So, this is what we have. 523 00:54:55,123 --> 00:54:58,203 The blonde one, and then that's the other one. 524 00:54:58,203 --> 00:55:00,483 {\an8}Oh, wow! There's quite a marked difference in... 525 00:55:00,483 --> 00:55:02,243 {\an8}Oh, wow! Yeah. 526 00:55:02,243 --> 00:55:03,563 That's the male. Really? 527 00:55:03,563 --> 00:55:04,923 Yeah. Guys! 528 00:55:06,243 --> 00:55:08,483 There's that wolverine. 529 00:55:08,483 --> 00:55:11,083 I mean, I could try and get back in the hide. Shall I? 530 00:55:11,083 --> 00:55:12,763 I think you should. OK, boys. 531 00:55:19,563 --> 00:55:22,283 Neil's managed to make it back to his filming hide. 532 00:55:22,283 --> 00:55:24,603 I'm just hoping that the wolverine didn't see him. 533 00:55:26,003 --> 00:55:28,523 Not only did he make it back, 534 00:55:28,523 --> 00:55:33,403 {\an8}but Neil manages to film the larger, darker male 535 00:55:33,403 --> 00:55:35,603 {\an8}delivering an edible gift. 536 00:55:38,803 --> 00:55:41,003 The male brought some food in. 537 00:55:41,003 --> 00:55:43,803 He's a bit bigger, because he actually got his bum stuck. 538 00:55:43,803 --> 00:55:46,683 {\an8}His wee legs were sticking out of the top of the hole for a minute. 539 00:55:53,763 --> 00:55:56,323 With the mating pair using the den, 540 00:55:56,323 --> 00:55:58,083 the team has high hopes 541 00:55:58,083 --> 00:56:00,083 that the female has kits. 542 00:56:01,843 --> 00:56:03,483 All the signs are pointing 543 00:56:03,483 --> 00:56:04,883 towards her having young. 544 00:56:08,443 --> 00:56:11,483 But as days pass, there's no sign of kits, 545 00:56:11,483 --> 00:56:15,563 and the team's time with the wolverines has run out. 546 00:56:15,563 --> 00:56:19,043 Feeling quite, yeah, quite disappointed. 547 00:56:19,043 --> 00:56:21,923 I don't want to be going, cos it feels so close. 548 00:56:22,963 --> 00:56:26,763 On their final day, under the cover of freezing fog, 549 00:56:26,763 --> 00:56:29,003 Will and Neil take the opportunity 550 00:56:29,003 --> 00:56:31,923 to leave camera traps behind. 551 00:56:31,923 --> 00:56:35,203 It will be their last roll of the dice to get the vital shots 552 00:56:35,203 --> 00:56:37,403 and finish the wolverines' story. 553 00:56:41,203 --> 00:56:42,443 That's done. 554 00:56:47,403 --> 00:56:50,243 Days after the crew's departure, 555 00:56:50,243 --> 00:56:52,643 the cameras finally start recording... 556 00:56:58,763 --> 00:57:01,163 ...and, against the odds, 557 00:57:01,163 --> 00:57:03,563 record the wolverines' kit emerging 558 00:57:03,563 --> 00:57:05,443 for the very first time. 559 00:57:09,523 --> 00:57:12,763 Mammals like the wolverine have colonised 560 00:57:12,763 --> 00:57:15,003 the coldest parts of the planet. 561 00:57:16,803 --> 00:57:19,843 We can only marvel at their ability to survive 562 00:57:19,843 --> 00:57:22,283 in these unforgiving landscapes. 563 00:57:31,723 --> 00:57:35,283 Next time, we journey to the hottest places on Earth 564 00:57:35,283 --> 00:57:39,683 to discover how mammals overcome 565 00:57:39,683 --> 00:57:41,483 challenges and adversity... 566 00:57:43,723 --> 00:57:45,603 ...and use heat in the most 567 00:57:45,603 --> 00:57:47,923 surprising and unexpected ways.