1 00:00:05,200 --> 00:00:08,640 Every year, winter transforms our world, 2 00:00:08,640 --> 00:00:10,640 creating dazzling displays 3 00:00:10,640 --> 00:00:13,480 of frost, snow and ice. 4 00:00:22,560 --> 00:00:25,400 For us, it's a magical season, but for other animals, 5 00:00:25,400 --> 00:00:27,960 it's the toughest time of the year. 6 00:00:33,400 --> 00:00:35,880 I've been lucky enough to spend time 7 00:00:35,880 --> 00:00:39,040 in the company of some of the extraordinary animals 8 00:00:39,040 --> 00:00:41,880 that live through the wildest winters on Earth. 9 00:00:44,600 --> 00:00:47,840 I'm fascinated by the strategies they've developed 10 00:00:47,840 --> 00:00:50,280 to get them through those challenging months. 11 00:00:52,880 --> 00:00:54,200 SQUAWKING 12 00:00:54,200 --> 00:00:56,480 So now I'm finding out more about 13 00:00:56,480 --> 00:00:58,800 how animals prepare for winter... 14 00:01:01,240 --> 00:01:04,440 ..how they stay warm in some of the coldest temperatures 15 00:01:04,440 --> 00:01:05,840 on the planet... 16 00:01:08,200 --> 00:01:10,000 ..and manage to find food 17 00:01:10,000 --> 00:01:12,280 even in the deepest snow. 18 00:01:16,160 --> 00:01:18,880 I want to discover how their priorities 19 00:01:18,880 --> 00:01:20,800 and survival tactics change 20 00:01:20,800 --> 00:01:22,600 as winter comes to an end. 21 00:01:22,600 --> 00:01:24,080 SQUEALING 22 00:01:27,040 --> 00:01:29,880 I'm uncovering the fascinating stories behind 23 00:01:29,880 --> 00:01:33,480 how animals living in some of the most demanding places on Earth 24 00:01:33,480 --> 00:01:36,040 have evolved ingenious ways to survive, 25 00:01:36,040 --> 00:01:38,600 no matter what winter may bring. 26 00:01:59,920 --> 00:02:01,240 Winter, 27 00:02:01,240 --> 00:02:04,400 the season of sparkling, icy beauty. 28 00:02:09,840 --> 00:02:13,320 But this time of year poses a real challenge 29 00:02:13,320 --> 00:02:15,160 for the animals living through it. 30 00:02:23,320 --> 00:02:26,400 As winter arrives, temperatures start to drop. 31 00:02:26,400 --> 00:02:28,600 Here in the Alps they can plummet 32 00:02:28,600 --> 00:02:31,800 to a bone-chilling minus 33 degrees C. 33 00:02:33,320 --> 00:02:35,080 All around the world 34 00:02:35,080 --> 00:02:38,720 animals have to face these conditions day in, day out. 35 00:02:38,720 --> 00:02:40,760 BIRD CHIRPS 36 00:02:45,400 --> 00:02:47,680 And it's harder to find food. 37 00:02:47,680 --> 00:02:50,520 The vegetation has, for the most part, died out, 38 00:02:50,520 --> 00:02:53,160 and underneath all this ice and snow, 39 00:02:53,160 --> 00:02:55,000 it makes it so much harder to hunt. 40 00:03:01,800 --> 00:03:03,320 The days are also shorter. 41 00:03:03,320 --> 00:03:06,360 Here in the Alps, we're getting about eight hours of sun, 42 00:03:06,360 --> 00:03:08,360 But as you move closer to the North Pole, 43 00:03:08,360 --> 00:03:11,040 there's virtually no daylight, 44 00:03:11,040 --> 00:03:12,680 which ultimately means 45 00:03:12,680 --> 00:03:15,280 there's even less time to feed. 46 00:03:18,800 --> 00:03:21,760 Whether it's taking to the ice in the far north... 47 00:03:25,480 --> 00:03:28,080 ..or huddling up at the bottom of the world... 48 00:03:31,040 --> 00:03:33,200 ..every animal must find a way 49 00:03:33,200 --> 00:03:36,000 to get through the toughest season of all. 50 00:03:42,840 --> 00:03:46,600 The key to surviving winter for many animals is preparation, 51 00:03:46,600 --> 00:03:50,000 and the work must begin months in advance. 52 00:03:58,440 --> 00:04:01,000 On the island of Hokkaido in Japan, 53 00:04:01,000 --> 00:04:02,520 forests are alight 54 00:04:02,520 --> 00:04:04,680 with the blazing colours of autumn. 55 00:04:12,560 --> 00:04:14,680 This change is a sign 56 00:04:14,680 --> 00:04:17,040 that winter is fast approaching. 57 00:04:26,360 --> 00:04:28,480 And for the Siberian chipmunk, 58 00:04:28,480 --> 00:04:30,320 it's a critical moment. 59 00:04:32,280 --> 00:04:35,000 This male must gather as much food as possible 60 00:04:35,000 --> 00:04:37,480 to see him through what lies ahead. 61 00:04:40,960 --> 00:04:43,200 And it's a race against time. 62 00:04:47,760 --> 00:04:49,920 Chipmunks are one of the smallest members 63 00:04:49,920 --> 00:04:52,160 of the squirrel family. 64 00:04:52,160 --> 00:04:54,200 But to survive the winter, 65 00:04:54,200 --> 00:04:56,240 they need to find and safeguard 66 00:04:56,240 --> 00:04:58,120 up to four kilos of food 67 00:04:58,120 --> 00:05:00,200 in their underground burrows. 68 00:05:02,600 --> 00:05:04,720 And they have an ingenious technique 69 00:05:04,720 --> 00:05:06,640 for gathering supplies, 70 00:05:06,640 --> 00:05:09,640 using their very own built-in storage. 71 00:05:12,720 --> 00:05:15,000 These expandable cheek pouches 72 00:05:15,000 --> 00:05:17,360 can stretch to three times the size 73 00:05:17,360 --> 00:05:19,160 of the chipmunk's head... 74 00:05:22,080 --> 00:05:25,880 ..allowing them to gather up to 165 acorns 75 00:05:25,880 --> 00:05:27,480 every day. 76 00:05:29,480 --> 00:05:31,600 He needs as many as he can get his paws on 77 00:05:31,600 --> 00:05:33,800 before he goes into hibernation. 78 00:05:39,280 --> 00:05:41,480 He's been working hard for weeks 79 00:05:41,480 --> 00:05:43,600 to build up his winter larder. 80 00:05:46,320 --> 00:05:48,960 But it can be a struggle to get the goods 81 00:05:48,960 --> 00:05:50,280 before others do. 82 00:05:50,280 --> 00:05:52,760 SQUEAKING 83 00:06:00,000 --> 00:06:03,200 SQUEAKING 84 00:06:03,200 --> 00:06:05,480 The competition is fierce... 85 00:06:06,960 --> 00:06:09,560 ..especially when an animal three times your size 86 00:06:09,560 --> 00:06:11,400 appears in your territory. 87 00:06:17,400 --> 00:06:19,720 But this chipmunk won't let the red squirrel 88 00:06:19,720 --> 00:06:21,320 get the better of him, 89 00:06:21,320 --> 00:06:23,640 defending his patch ferociously. 90 00:06:23,640 --> 00:06:26,280 After all, his life depends upon it. 91 00:06:27,480 --> 00:06:29,360 SQUEAKING 92 00:06:39,880 --> 00:06:42,000 When the food gathering is complete, 93 00:06:42,000 --> 00:06:43,880 he collects leaves and grasses 94 00:06:43,880 --> 00:06:46,120 to create a cosy den to sleep in. 95 00:06:52,680 --> 00:06:54,040 Once settled in, 96 00:06:54,040 --> 00:06:55,880 he'll be waking up every few days, 97 00:06:55,880 --> 00:06:57,480 feeding on his stockpile 98 00:06:57,480 --> 00:06:58,920 to keep him going. 99 00:07:05,000 --> 00:07:07,280 Chipmunks are not the only species 100 00:07:07,280 --> 00:07:09,080 hard at work storing food. 101 00:07:10,120 --> 00:07:11,520 As winter approaches, 102 00:07:11,520 --> 00:07:13,280 animals all around the world 103 00:07:13,280 --> 00:07:15,120 are frantically gathering nuts 104 00:07:15,120 --> 00:07:16,600 and for very good reason. 105 00:07:20,720 --> 00:07:23,920 Nuts are the perfect packaged foods 106 00:07:23,920 --> 00:07:25,960 to see animals through winter. 107 00:07:25,960 --> 00:07:27,560 Their hard shells preserve 108 00:07:27,560 --> 00:07:29,440 all the goodness inside. 109 00:07:29,440 --> 00:07:31,560 Acorns, for example, are packed full of 110 00:07:31,560 --> 00:07:33,840 vitamins and calcium and fats. 111 00:07:33,840 --> 00:07:36,120 They're a high-energy food. 112 00:07:36,120 --> 00:07:39,200 In fact, this many acorns, about 100g, 113 00:07:39,200 --> 00:07:41,800 is equivalent to 400 calories. 114 00:07:41,800 --> 00:07:43,640 Now, that's the same as about 115 00:07:43,640 --> 00:07:46,120 ten chocolate biscuits, 116 00:07:46,120 --> 00:07:47,280 or... 117 00:07:48,840 --> 00:07:51,920 ..this many raspberries. 118 00:07:51,920 --> 00:07:54,840 Now, the fact that nuts are so highly nutritious 119 00:07:54,840 --> 00:07:57,640 and key to the survival of so many animals during winter 120 00:07:57,640 --> 00:08:00,800 has led to some pretty remarkable adaptations. 121 00:08:02,360 --> 00:08:04,520 The fox squirrel can hide anything between 122 00:08:04,520 --> 00:08:06,720 3 to 10,000 nuts 123 00:08:06,720 --> 00:08:09,400 in different places every season. 124 00:08:09,400 --> 00:08:11,880 To remember where it's hidden those stashes, 125 00:08:11,880 --> 00:08:14,480 it builds up a mental map of its surroundings. 126 00:08:14,480 --> 00:08:17,000 This requires so much brainpower, 127 00:08:17,000 --> 00:08:18,920 it's thought it actually causes 128 00:08:18,920 --> 00:08:21,200 the squirrel's brain to grow in size 129 00:08:21,200 --> 00:08:23,840 during prime, nut-hoarding season. 130 00:08:29,920 --> 00:08:31,960 The ability to store food 131 00:08:31,960 --> 00:08:34,360 has created a virtual lifeline 132 00:08:34,360 --> 00:08:36,200 for so many animals, 133 00:08:36,200 --> 00:08:38,240 but for others, that strategy 134 00:08:38,240 --> 00:08:40,320 simply isn't an option. 135 00:08:40,320 --> 00:08:42,640 They've got to approach it 136 00:08:42,640 --> 00:08:44,600 in an entirely different way, 137 00:08:44,600 --> 00:08:46,760 and that's resulted in some of the greatest 138 00:08:46,760 --> 00:08:48,800 natural spectacles on Earth. 139 00:08:52,760 --> 00:08:54,480 BIRDS SQUAWK 140 00:08:58,440 --> 00:09:00,120 As winter closes in, 141 00:09:00,120 --> 00:09:02,800 millions of animals are on the move... 142 00:09:06,480 --> 00:09:08,040 ..in the air... 143 00:09:09,520 --> 00:09:10,800 ..the sea... 144 00:09:12,640 --> 00:09:14,440 ..and on land. 145 00:09:18,280 --> 00:09:20,640 They embark on these epic migrations 146 00:09:20,640 --> 00:09:23,120 in search of new food sources, 147 00:09:23,120 --> 00:09:25,360 or to escape the harsh weather. 148 00:09:30,920 --> 00:09:33,920 Caribou, known in Europe as reindeer. 149 00:09:39,400 --> 00:09:40,800 In North America, 150 00:09:40,800 --> 00:09:43,240 these incredibly resilient animals 151 00:09:43,240 --> 00:09:44,920 travel to their wintering grounds 152 00:09:44,920 --> 00:09:46,960 in huge numbers. 153 00:09:46,960 --> 00:09:50,960 There can be close to 200,000 in one herd. 154 00:09:55,200 --> 00:09:57,760 Majestic narwhals spend their summers 155 00:09:57,760 --> 00:10:00,320 in the coastal waters of the Arctic, 156 00:10:00,320 --> 00:10:01,800 but when winter approaches, 157 00:10:01,800 --> 00:10:04,000 the whales head far out to sea. 158 00:10:06,840 --> 00:10:10,280 Here, these almost-mythical creatures find food 159 00:10:10,280 --> 00:10:11,920 deep beneath the surface, 160 00:10:11,920 --> 00:10:14,120 coming up to breathe through holes in the ice. 161 00:10:19,000 --> 00:10:20,480 And in Alaska, 162 00:10:20,480 --> 00:10:23,880 hundreds of thousands of sandhill cranes head south 163 00:10:23,880 --> 00:10:26,600 to Mexico, over 3,000 miles away. 164 00:10:31,200 --> 00:10:34,920 Cranes are one of the oldest bird families on Earth 165 00:10:34,920 --> 00:10:37,480 and it's thought that they've been making journeys like this 166 00:10:37,480 --> 00:10:38,920 for millions of years. 167 00:10:44,480 --> 00:10:47,600 It's an arduous flight, but they must persevere 168 00:10:47,600 --> 00:10:48,840 in order to survive. 169 00:10:50,160 --> 00:10:52,200 CRANE CALLS 170 00:10:58,120 --> 00:10:59,920 Not all animals flee 171 00:10:59,920 --> 00:11:02,280 the tightening grasp of winter, however. 172 00:11:02,280 --> 00:11:04,800 In fact, one Arctic specialist 173 00:11:04,800 --> 00:11:07,120 is eagerly awaiting its arrival... 174 00:11:14,640 --> 00:11:16,280 ..the polar bear... 175 00:11:18,960 --> 00:11:21,800 ..basking in the last rays of autumn sunshine. 176 00:11:25,200 --> 00:11:27,280 Here in the Canadian Arctic, 177 00:11:27,280 --> 00:11:29,360 the bears are gathering at the coast, 178 00:11:29,360 --> 00:11:31,120 waiting for the sea to freeze 179 00:11:31,120 --> 00:11:32,840 so that they can hunt on the ice. 180 00:11:36,040 --> 00:11:39,280 Their main prey is ringed and bearded seals, 181 00:11:39,280 --> 00:11:42,080 but they spend much of their time out at sea 182 00:11:42,080 --> 00:11:44,960 and the bears need the ice as a platform to reach them. 183 00:11:49,440 --> 00:11:52,440 The bears must bide their time on the land. 184 00:11:55,680 --> 00:11:58,680 Over the summer, they live off their fat reserves, 185 00:11:58,680 --> 00:12:00,760 but now these are dwindling. 186 00:12:03,400 --> 00:12:06,080 Many bears turn to eating plants, 187 00:12:06,080 --> 00:12:07,800 roots and berries, 188 00:12:07,800 --> 00:12:09,560 but it's not enough to sustain them. 189 00:12:15,680 --> 00:12:17,680 And as our climate changes, 190 00:12:17,680 --> 00:12:20,480 winter sea ice forms later in the year 191 00:12:20,480 --> 00:12:21,920 and is reducing, 192 00:12:21,920 --> 00:12:24,760 leaving the bears to survive on these meagre rations 193 00:12:24,760 --> 00:12:25,960 for even longer. 194 00:12:32,920 --> 00:12:35,760 Polar bears are usually solitary animals, 195 00:12:35,760 --> 00:12:37,960 so seeing them together like this is rare. 196 00:12:41,640 --> 00:12:45,280 For them, it's a chance to size up future rivals, 197 00:12:45,280 --> 00:12:47,880 but it also uses up valuable energy reserves. 198 00:13:05,840 --> 00:13:07,800 At last, the wait is over... 199 00:13:08,840 --> 00:13:10,440 ..the ice is on its way. 200 00:13:33,120 --> 00:13:35,400 With the arrival of deep winter, 201 00:13:35,400 --> 00:13:37,280 much of the planet undergoes 202 00:13:37,280 --> 00:13:39,160 a magical transformation. 203 00:13:40,480 --> 00:13:41,760 As temperatures plummet... 204 00:13:43,360 --> 00:13:45,000 ..lakes and rivers freeze... 205 00:13:52,080 --> 00:13:54,480 ..and snowflakes dance in the air. 206 00:14:00,840 --> 00:14:03,560 Landscapes become winter wonderlands. 207 00:14:20,520 --> 00:14:23,360 But now, life is much tougher. 208 00:14:27,280 --> 00:14:31,320 And one of the biggest challenges animals face is finding food. 209 00:14:39,680 --> 00:14:42,280 Snow acts as an obvious barrier 210 00:14:42,280 --> 00:14:44,520 to the food lying beneath it 211 00:14:44,520 --> 00:14:48,400 and it's often much deeper than this, many metres in depth, 212 00:14:48,400 --> 00:14:50,600 so any animals looking for vegetation 213 00:14:50,600 --> 00:14:52,840 or any small rodents beneath it all 214 00:14:52,840 --> 00:14:54,680 are going to have a very hard time reaching it. 215 00:14:56,280 --> 00:14:57,520 Not only that, 216 00:14:57,520 --> 00:15:00,320 but snow is excellent at absorbing sound waves... 217 00:15:01,520 --> 00:15:04,440 ..effectively acting as a layer of sound proofing 218 00:15:04,440 --> 00:15:07,280 and stopping any animals that rely on their hearing 219 00:15:07,280 --> 00:15:09,160 from detecting their prey. 220 00:15:09,160 --> 00:15:11,360 Now, in the Rocky Mountains of North America 221 00:15:11,360 --> 00:15:14,520 is an animal that is harnessing all of its skills 222 00:15:14,520 --> 00:15:16,040 to overcome these challenges. 223 00:15:22,920 --> 00:15:25,320 In this imposing mountain range, 224 00:15:25,320 --> 00:15:27,960 the snow can lie in huge drifts. 225 00:15:33,680 --> 00:15:36,720 This is home to a particularly elusive cat... 226 00:15:39,960 --> 00:15:42,400 ..the bobcat, a species of lynx. 227 00:15:45,440 --> 00:15:47,240 To survive in these conditions, 228 00:15:47,240 --> 00:15:49,080 it's always on the lookout 229 00:15:49,080 --> 00:15:50,360 for its next meal. 230 00:15:55,960 --> 00:15:58,800 Bobcats have evolved excellent hearing 231 00:15:58,800 --> 00:16:01,280 with ears that can swivel back and forth 232 00:16:01,280 --> 00:16:03,200 independently of one another 233 00:16:03,200 --> 00:16:06,280 in order to pinpoint any noise coming from their prey. 234 00:16:07,400 --> 00:16:09,960 And those characteristic ear tufts 235 00:16:09,960 --> 00:16:11,720 are thought to amplify the sound. 236 00:16:15,680 --> 00:16:17,720 But the deeper the snow, 237 00:16:17,720 --> 00:16:19,480 the harder this task is. 238 00:16:24,080 --> 00:16:27,160 Even the experts don't always get it quite right. 239 00:16:34,560 --> 00:16:37,120 Perhaps the river can provide an opportunity. 240 00:16:38,840 --> 00:16:41,080 It's fed by volcanic hot springs, 241 00:16:41,080 --> 00:16:43,400 so it never freezes over. 242 00:16:43,400 --> 00:16:47,600 It's a refuge of warmth, which draws in animals from miles around. 243 00:16:52,600 --> 00:16:56,360 The bobcat's preferred diet is rabbit and hare, 244 00:16:56,360 --> 00:16:58,000 but it's a resourceful cat 245 00:16:58,000 --> 00:17:00,000 and will try its luck with almost anything. 246 00:17:06,720 --> 00:17:09,000 Although this one doesn't seem to be very keen 247 00:17:09,000 --> 00:17:10,320 on getting its paws wet. 248 00:17:13,400 --> 00:17:16,040 It needs to find a suitable target. 249 00:17:40,360 --> 00:17:42,440 DUCKS QUACK 250 00:17:47,680 --> 00:17:48,960 No luck this time. 251 00:17:50,680 --> 00:17:52,600 But these determined cats 252 00:17:52,600 --> 00:17:54,640 are masters of perseverance. 253 00:18:00,360 --> 00:18:02,800 With those finely-tuned ears, 254 00:18:02,800 --> 00:18:06,240 perhaps this bobcat has caught the faintest of sounds 255 00:18:06,240 --> 00:18:07,440 beneath the snow. 256 00:18:14,320 --> 00:18:17,800 Its paws are soft and well-padded. 257 00:18:17,800 --> 00:18:20,200 Using the boulders as stepping stones, 258 00:18:20,200 --> 00:18:22,240 it can move without making a sound. 259 00:18:35,160 --> 00:18:37,680 In this particular game of cat and mouse, 260 00:18:37,680 --> 00:18:39,760 there's a clear winner. 261 00:18:45,640 --> 00:18:49,400 To overcome the problem of finding food in deep snow, 262 00:18:49,400 --> 00:18:52,360 one group of animals is using a different strategy - 263 00:18:52,360 --> 00:18:54,480 changing its diet in winter. 264 00:18:56,760 --> 00:18:58,240 As herbivores, 265 00:18:58,240 --> 00:19:00,680 deer feed on grasses and other vegetation on the ground 266 00:19:00,680 --> 00:19:04,520 and then browse the leaves of trees and shrubs, so when winter arrives, 267 00:19:04,520 --> 00:19:08,240 their food is often hidden deep beneath the snow or has died back. 268 00:19:08,240 --> 00:19:09,920 Now, in this wildlife park, 269 00:19:09,920 --> 00:19:12,640 these deer are being given supplementary food, 270 00:19:12,640 --> 00:19:15,680 but in the wild, deer have to become much more resourceful. 271 00:19:24,200 --> 00:19:26,640 This is the Shiretoko Peninsula 272 00:19:26,640 --> 00:19:28,640 in the far north of Japan, 273 00:19:28,640 --> 00:19:31,920 where snow covers the mountain peaks for eight months of the year. 274 00:19:38,800 --> 00:19:42,320 It's home to an incredibly tenacious animal - 275 00:19:42,320 --> 00:19:43,480 the sika deer. 276 00:19:50,400 --> 00:19:51,880 At this time of year, 277 00:19:51,880 --> 00:19:54,280 there's little to eat in these snowbound forests. 278 00:19:57,560 --> 00:19:59,600 Just getting around in these conditions 279 00:19:59,600 --> 00:20:01,560 is difficult enough 280 00:20:01,560 --> 00:20:03,160 and to add to the challenge, 281 00:20:03,160 --> 00:20:05,640 many of the females are pregnant, 282 00:20:05,640 --> 00:20:07,400 due to give birth in the spring. 283 00:20:14,640 --> 00:20:16,000 To find food, 284 00:20:16,000 --> 00:20:17,840 the deer dig down through the snow 285 00:20:17,840 --> 00:20:22,120 using their hooves, looking for any vegetation that might be available. 286 00:20:29,000 --> 00:20:30,760 But during harsh winters, 287 00:20:30,760 --> 00:20:33,560 sika deer are able to adapt their diets 288 00:20:33,560 --> 00:20:35,400 to add another food source 289 00:20:35,400 --> 00:20:37,120 that can be found more easily... 290 00:20:38,080 --> 00:20:39,480 ..tree bark. 291 00:20:50,760 --> 00:20:54,920 Perhaps surprisingly, tree bark does have some nutritional value. 292 00:20:58,760 --> 00:21:01,520 But deer are only able to survive on bark 293 00:21:01,520 --> 00:21:03,960 because of how their digestive system has evolved. 294 00:21:16,320 --> 00:21:19,160 Deer stomachs are made up of four compartments 295 00:21:19,160 --> 00:21:20,840 containing special enzymes 296 00:21:20,840 --> 00:21:24,200 that allow them to digest plants and twigs and bark 297 00:21:24,200 --> 00:21:26,920 and to break down cellulose, 298 00:21:26,920 --> 00:21:28,720 a tough material that stands in the way 299 00:21:28,720 --> 00:21:30,640 of all the nutritious stuff. 300 00:21:33,800 --> 00:21:36,800 But not only is bark especially difficult to digest, 301 00:21:36,800 --> 00:21:38,520 it also contains tannins, 302 00:21:38,520 --> 00:21:40,160 which can be toxic. 303 00:21:40,160 --> 00:21:44,880 Deer have overcome this by producing a special protein in their saliva 304 00:21:44,880 --> 00:21:46,600 that neutralises the tannins, 305 00:21:46,600 --> 00:21:48,480 rendering them harmless - 306 00:21:48,480 --> 00:21:50,680 a remarkable adaptation that allows them 307 00:21:50,680 --> 00:21:52,680 to make the most of the scant food available. 308 00:21:57,160 --> 00:21:59,200 WOLF HOWLS 309 00:22:04,080 --> 00:22:06,440 WOLVES HOWL 310 00:22:09,680 --> 00:22:11,320 All around the world, 311 00:22:11,320 --> 00:22:14,440 animals must be resourceful and creative 312 00:22:14,440 --> 00:22:17,200 to secure the food they need in winter. 313 00:22:22,440 --> 00:22:24,080 Wolves work together 314 00:22:24,080 --> 00:22:26,240 to hunt large prey like bison 315 00:22:26,240 --> 00:22:28,480 that could keep the whole pack going for weeks. 316 00:22:36,360 --> 00:22:38,600 Voles burrow under the snow 317 00:22:38,600 --> 00:22:40,600 to reach the vegetation they need. 318 00:22:42,600 --> 00:22:46,920 And bald eagles will fiercely fight off any competition. 319 00:22:46,920 --> 00:22:48,960 EAGLE SCREECHES 320 00:22:58,040 --> 00:23:00,520 It's not easy staying well-fed in winter... 321 00:23:05,200 --> 00:23:08,240 ..and animals that can adapt to new circumstances 322 00:23:08,240 --> 00:23:10,680 will be the ones to come out on top. 323 00:23:22,920 --> 00:23:26,800 The Arctic fox can cope with sub-zero winter temperatures 324 00:23:26,800 --> 00:23:28,600 in the extreme north 325 00:23:28,600 --> 00:23:30,920 thanks to its thick white fur coat. 326 00:23:35,680 --> 00:23:37,600 It's an accomplished hunter, 327 00:23:37,600 --> 00:23:39,680 feeding mostly on lemmings and voles. 328 00:23:44,840 --> 00:23:47,000 But it's a constant struggle to get enough food. 329 00:23:54,400 --> 00:23:58,640 Here in Alaska, new opportunities are presenting themselves. 330 00:24:02,680 --> 00:24:04,720 TRUCK HORN BLASTS 331 00:24:05,720 --> 00:24:07,040 The town of Deadhorse 332 00:24:07,040 --> 00:24:09,920 is one of the most remote settlements on Earth, 333 00:24:09,920 --> 00:24:11,880 more than 200 miles north 334 00:24:11,880 --> 00:24:13,360 of the Arctic Circle. 335 00:24:17,360 --> 00:24:20,120 The Arctic fox knows there's food to be found here. 336 00:24:28,840 --> 00:24:30,320 But it will need to be careful. 337 00:24:33,000 --> 00:24:36,200 Not only does it have to avoid humans and machinery... 338 00:24:39,600 --> 00:24:41,680 ..but red foxes live here too. 339 00:24:44,040 --> 00:24:46,040 They've also been lured into town 340 00:24:46,040 --> 00:24:47,760 by the promise of sustenance. 341 00:24:53,880 --> 00:24:56,160 The Arctic fox's sense of smell 342 00:24:56,160 --> 00:24:58,440 is leading it towards much-needed food. 343 00:25:00,960 --> 00:25:03,400 But the red fox is twice its size 344 00:25:03,400 --> 00:25:04,880 and could easily kill it. 345 00:25:21,440 --> 00:25:24,120 The Arctic fox has found what it was looking for. 346 00:25:29,000 --> 00:25:30,800 This frozen meal of scraps 347 00:25:30,800 --> 00:25:32,280 is enough to keep him going. 348 00:25:39,680 --> 00:25:41,640 This intrepid little mammal 349 00:25:41,640 --> 00:25:44,920 is successfully exploiting a new world to survive. 350 00:26:07,400 --> 00:26:10,240 And it also has the uncanny ability 351 00:26:10,240 --> 00:26:12,880 to vanish into the Arctic landscape 352 00:26:12,880 --> 00:26:14,240 thanks to its white coat. 353 00:26:17,960 --> 00:26:20,240 But he's not the only winter animal 354 00:26:20,240 --> 00:26:21,840 to use this disappearing act. 355 00:26:27,160 --> 00:26:30,720 The Yukon is the coldest place in North America. 356 00:26:33,400 --> 00:26:37,240 Temperatures can fall to minus 63 degrees Celsius 357 00:26:37,240 --> 00:26:38,960 and snow covers the ground 358 00:26:38,960 --> 00:26:40,480 for five months a year. 359 00:26:44,000 --> 00:26:47,640 This provides a distinct advantage for one of its residents, 360 00:26:47,640 --> 00:26:49,240 if you can find it... 361 00:27:04,320 --> 00:27:05,920 ..the snowshoe hare. 362 00:27:11,840 --> 00:27:14,960 It's fur perfectly matches this white world. 363 00:27:22,360 --> 00:27:25,400 But the hare doesn't look like this all year round. 364 00:27:27,360 --> 00:27:29,480 Throughout the spring and summer months, 365 00:27:29,480 --> 00:27:31,440 its fur is reddish brown 366 00:27:31,440 --> 00:27:34,640 to match its habitat at this time of year, 367 00:27:34,640 --> 00:27:38,600 but as winter approaches and the snow starts to fall, 368 00:27:38,600 --> 00:27:41,040 it transforms from brown 369 00:27:41,040 --> 00:27:42,680 to purest white. 370 00:27:48,560 --> 00:27:51,640 Snowshoe hares have many predators, 371 00:27:51,640 --> 00:27:54,480 from coyotes to golden eagles... 372 00:27:56,680 --> 00:27:58,760 ..and lynx. 373 00:27:58,760 --> 00:28:01,080 LYNX GROWLS 374 00:28:01,080 --> 00:28:03,520 So the hare's winter white coat 375 00:28:03,520 --> 00:28:05,280 makes for an excellent camouflage. 376 00:28:08,680 --> 00:28:10,520 With its perfect disguise, 377 00:28:10,520 --> 00:28:12,360 even out in the open, 378 00:28:12,360 --> 00:28:14,960 it can still remain hidden from the sharpest eyes. 379 00:28:18,040 --> 00:28:20,760 And if it thinks it's been spotted, 380 00:28:20,760 --> 00:28:22,280 it has a getaway plan. 381 00:28:24,520 --> 00:28:26,960 The aptly-named snowshoe hare 382 00:28:26,960 --> 00:28:29,600 has especially large furry paws, 383 00:28:29,600 --> 00:28:31,760 which stop it from sinking into the snow... 384 00:28:33,280 --> 00:28:36,320 ..and help it to be fast and nimble 385 00:28:36,320 --> 00:28:39,160 and leap three metres in a single bound. 386 00:28:45,280 --> 00:28:47,880 With all these impressive adaptations 387 00:28:47,880 --> 00:28:49,640 and a little bit of luck, 388 00:28:49,640 --> 00:28:52,000 the snowshoe hare will live to see another day. 389 00:29:02,280 --> 00:29:04,080 Only a few species, 390 00:29:04,080 --> 00:29:05,840 like this least weasel, 391 00:29:05,840 --> 00:29:08,200 have this special ability to turn white in winter. 392 00:29:11,440 --> 00:29:13,080 But how does this changing colour work? 393 00:29:16,040 --> 00:29:18,600 Colour in the fur and feathers of animals 394 00:29:18,600 --> 00:29:20,960 is all down to a pigment called melanin 395 00:29:20,960 --> 00:29:24,080 that's produced by specialised cells in the skin 396 00:29:24,080 --> 00:29:26,400 and a combination of different types of this pigment 397 00:29:26,400 --> 00:29:28,720 creates a whole range of colours. 398 00:29:28,720 --> 00:29:30,960 Now, white fur and feathers 399 00:29:30,960 --> 00:29:32,920 don't contain this melanin pigment. 400 00:29:35,240 --> 00:29:38,840 And the really clever bit is that animals that can change colour 401 00:29:38,840 --> 00:29:40,720 switch off melanin production 402 00:29:40,720 --> 00:29:44,160 as they grow their glorious white winter coats. 403 00:29:46,360 --> 00:29:49,800 This remarkable change is triggered by day length. 404 00:29:49,800 --> 00:29:52,520 As the days shorten before winter, 405 00:29:52,520 --> 00:29:54,920 these animals shed their darker coats 406 00:29:54,920 --> 00:29:57,040 and gradually grow their new winter ones. 407 00:29:58,520 --> 00:30:00,840 It's also thought that white fur 408 00:30:00,840 --> 00:30:03,000 might be more insulating than dark fur. 409 00:30:04,440 --> 00:30:06,200 Because it doesn't have any melanin, 410 00:30:06,200 --> 00:30:09,360 it's hollow and contains more trapped air in it. 411 00:30:09,360 --> 00:30:12,840 Trapped air equals greater insulation and warmth... 412 00:30:16,400 --> 00:30:19,480 ..making this transformation a vital adaptation 413 00:30:19,480 --> 00:30:21,520 for surviving winter. 414 00:30:33,800 --> 00:30:35,760 Polar bears, on the other hand, 415 00:30:35,760 --> 00:30:38,880 keep their magnificent white coats all year round. 416 00:30:45,280 --> 00:30:46,720 Out on the ice, 417 00:30:46,720 --> 00:30:49,080 conditions are some of the harshest on Earth. 418 00:30:51,160 --> 00:30:53,240 The bears face high winds 419 00:30:53,240 --> 00:30:56,080 and temperatures of minus 50 degrees Celsius. 420 00:31:02,880 --> 00:31:04,760 Their insulating white fur 421 00:31:04,760 --> 00:31:06,400 provides their main protection. 422 00:31:13,000 --> 00:31:14,720 But in this frozen world, 423 00:31:14,720 --> 00:31:17,360 even these coats aren't enough to keep them warm... 424 00:31:25,720 --> 00:31:28,440 ..so polar bears have a dense layer of blubber 425 00:31:28,440 --> 00:31:31,800 beneath their fur that can be up to ten centimetres thick. 426 00:31:35,040 --> 00:31:37,920 This also protects them as they hunt for seals... 427 00:31:39,160 --> 00:31:42,000 ..often having to swim between the ice floes... 428 00:31:43,200 --> 00:31:45,920 ..their huge paws acting as paddles. 429 00:31:56,160 --> 00:31:59,640 The combination of this layer of fat and thick white fur 430 00:31:59,640 --> 00:32:03,520 means that polar bears lose very little heat to the environment. 431 00:32:03,520 --> 00:32:06,560 Now, we have a thermal imaging camera trained on me at the moment 432 00:32:06,560 --> 00:32:08,120 to show you what I mean. 433 00:32:08,120 --> 00:32:10,200 Now, these cameras show up hot objects 434 00:32:10,200 --> 00:32:12,080 as white or yellow or orange, 435 00:32:12,080 --> 00:32:13,880 and then cold objects 436 00:32:13,880 --> 00:32:16,320 as purples and dark blues and even blacks. 437 00:32:16,320 --> 00:32:19,160 Now you can see, even though I've got loads of layers on, 438 00:32:19,160 --> 00:32:20,680 I'm mostly orange 439 00:32:20,680 --> 00:32:23,440 and then my face is really yellow, 440 00:32:23,440 --> 00:32:26,920 as are my hands, because I've got hand warmers in my gloves, 441 00:32:26,920 --> 00:32:31,440 but it goes to show how much heat I am losing to the air around me. 442 00:32:31,440 --> 00:32:34,200 Now, if we look at a thermal image of a polar bear, 443 00:32:34,200 --> 00:32:36,800 it's a very different picture altogether. 444 00:32:36,800 --> 00:32:38,680 The polar bear is mostly dark blues 445 00:32:38,680 --> 00:32:40,920 with just a little bit of light at its extremities 446 00:32:40,920 --> 00:32:44,360 like its nose, where it's losing a tiny bit of heat, 447 00:32:44,360 --> 00:32:48,400 but that just goes to show polar bears lose hardly any heat at all, 448 00:32:48,400 --> 00:32:51,560 making it one of the most resilient animals on the planet. 449 00:32:58,200 --> 00:33:01,560 This is Valdez Harbour in Alaska, 450 00:33:01,560 --> 00:33:04,400 a winter refuge for a charismatic little creature. 451 00:33:12,800 --> 00:33:16,840 Sea otters spend nearly their whole lives on the water. 452 00:33:19,920 --> 00:33:23,320 But unlike polar bears and other marine mammals, 453 00:33:23,320 --> 00:33:25,840 they don't have a layer of blubber for insulation... 454 00:33:31,080 --> 00:33:35,120 ..so they have evolved the thickest fur coat of any animal. 455 00:33:39,840 --> 00:33:43,400 The outer layer is made up of long waterproof hairs... 456 00:33:45,320 --> 00:33:48,640 ..while underneath, there's a short, dense underfur layer. 457 00:33:50,800 --> 00:33:53,640 This keeps cold water completely away from the skin. 458 00:34:00,720 --> 00:34:03,760 This female has an extra challenge on her hands. 459 00:34:03,760 --> 00:34:05,840 PUP MEWLS 460 00:34:07,040 --> 00:34:10,200 Sea otters can give birth all year round 461 00:34:10,200 --> 00:34:12,280 and this is not ideal timing. 462 00:34:14,600 --> 00:34:16,160 To keep her pup warm, 463 00:34:16,160 --> 00:34:17,760 she has to groom it constantly. 464 00:34:20,400 --> 00:34:23,280 She also blows air into its fur - 465 00:34:23,280 --> 00:34:25,640 the fluffier it is, the warmer it will be. 466 00:34:32,400 --> 00:34:34,000 When it's a little older, 467 00:34:34,000 --> 00:34:36,200 she takes it out to sea to hunt. 468 00:34:36,200 --> 00:34:39,680 To find food, she has to leave it at the surface. 469 00:34:47,640 --> 00:34:50,480 PUP MEWLS 470 00:34:50,480 --> 00:34:52,480 But thanks to its fluffy coat 471 00:34:52,480 --> 00:34:54,960 and especially large lung capacity, 472 00:34:54,960 --> 00:34:57,040 it's so buoyant, it just won't sink. 473 00:34:59,880 --> 00:35:02,000 PUP MEWLS 474 00:35:02,000 --> 00:35:03,320 When she surfaces, 475 00:35:03,320 --> 00:35:06,400 its cries lead her back so she can feed it too. 476 00:35:13,960 --> 00:35:15,880 The evolution of thick winter coats 477 00:35:15,880 --> 00:35:18,560 is yet another exquisite adaptation 478 00:35:18,560 --> 00:35:22,040 that allows animals to withstand the coldest temperatures, 479 00:35:22,040 --> 00:35:25,000 but even then, that may not be quite enough. 480 00:35:25,000 --> 00:35:27,480 But nature always finds a way, 481 00:35:27,480 --> 00:35:30,480 and some species have developed a very different, 482 00:35:30,480 --> 00:35:33,000 but equally effective, survival strategy. 483 00:35:40,680 --> 00:35:43,840 In the frozen mountain forests of southern China, 484 00:35:43,840 --> 00:35:46,920 2,500 metres above sea level, 485 00:35:46,920 --> 00:35:48,960 lives an astonishing animal. 486 00:35:54,080 --> 00:35:55,480 Rarely seen, 487 00:35:55,480 --> 00:35:58,720 this is the highest-living monkey in the world - 488 00:35:58,720 --> 00:36:00,720 the Yunnan snub-nosed monkey. 489 00:36:04,680 --> 00:36:08,800 These monkeys have developed some remarkable adaptations to cope with 490 00:36:08,800 --> 00:36:11,720 the freezing temperatures of their Himalayan home. 491 00:36:17,600 --> 00:36:20,480 Their noses are almost completely flat 492 00:36:20,480 --> 00:36:22,320 to avoid getting frostbite... 493 00:36:24,920 --> 00:36:27,400 ..and they're covered in dense fur 494 00:36:27,400 --> 00:36:29,600 that can be up to 15 centimetres long. 495 00:36:34,880 --> 00:36:36,720 But in this heavy snowfall, 496 00:36:36,720 --> 00:36:38,600 even this isn't enough... 497 00:36:40,360 --> 00:36:42,800 ..so they do something very clever. 498 00:36:46,080 --> 00:36:48,680 Snub-nosed monkeys are social animals 499 00:36:48,680 --> 00:36:50,760 who live in large family groups. 500 00:36:52,600 --> 00:36:54,080 As night approaches, 501 00:36:54,080 --> 00:36:56,560 they gather together amongst the branches of trees. 502 00:37:00,480 --> 00:37:03,960 Mothers and babies are usually at the centre 503 00:37:03,960 --> 00:37:06,400 with all the other members of the family surrounding them. 504 00:37:11,040 --> 00:37:13,480 They'll stay huddled like this until morning. 505 00:37:15,720 --> 00:37:17,360 In this bitter cold, 506 00:37:17,360 --> 00:37:19,800 they simply wouldn't survive the night on their own. 507 00:37:27,920 --> 00:37:30,320 So what's the science behind huddling? 508 00:37:30,320 --> 00:37:32,000 Exactly how does it work? 509 00:37:32,000 --> 00:37:35,240 Well, we have a thermal imaging camera trained on me 510 00:37:35,240 --> 00:37:37,840 to help explain exactly what's going on. 511 00:37:37,840 --> 00:37:40,440 Now, heat is a thermal energy 512 00:37:40,440 --> 00:37:43,480 that's constantly flowing around us 513 00:37:43,480 --> 00:37:47,160 and as it flows, it naturally moves from hotter objects 514 00:37:47,160 --> 00:37:48,440 to colder objects. 515 00:37:48,440 --> 00:37:49,880 To show you what I mean, 516 00:37:49,880 --> 00:37:52,560 I'm going to fill this solitary mug 517 00:37:52,560 --> 00:37:54,520 in the snow 518 00:37:54,520 --> 00:37:56,320 with some hot chocolate. 519 00:37:57,960 --> 00:38:00,040 Now, you can see it's hot - 520 00:38:00,040 --> 00:38:03,120 white or yellow in the centre - but very quickly, 521 00:38:03,120 --> 00:38:04,680 it's losing that heat 522 00:38:04,680 --> 00:38:07,080 to the colder air around it, 523 00:38:07,080 --> 00:38:08,200 but if I fill... 524 00:38:09,640 --> 00:38:12,120 ..all of these mugs of chocolate 525 00:38:12,120 --> 00:38:14,760 huddled together like our monkeys... 526 00:38:16,280 --> 00:38:18,480 ..we should be able to see something 527 00:38:18,480 --> 00:38:20,520 very different is happening. 528 00:38:20,520 --> 00:38:23,760 All of the mugs are losing their heat much less quickly, 529 00:38:23,760 --> 00:38:26,960 particularly the one in the centre 530 00:38:26,960 --> 00:38:30,520 and that's because it's protected by the hot mugs around it, 531 00:38:30,520 --> 00:38:34,600 but also, it's gaining some heat from the collective huddle 532 00:38:34,600 --> 00:38:36,760 that's hotter than it is. 533 00:38:36,760 --> 00:38:38,360 Therefore, the heat is transferring 534 00:38:38,360 --> 00:38:39,800 to that mug in the centre. 535 00:38:41,640 --> 00:38:42,880 In just a few minutes, 536 00:38:42,880 --> 00:38:44,960 you can clearly see the difference, can't you? 537 00:38:44,960 --> 00:38:47,360 This cup is now completely cold, 538 00:38:47,360 --> 00:38:49,560 having lost all its heat to the elements, 539 00:38:49,560 --> 00:38:52,760 while this one is nice and cosy and warm 540 00:38:52,760 --> 00:38:54,000 in the centre. 541 00:38:56,440 --> 00:38:58,120 Now, in the Antarctic, 542 00:38:58,120 --> 00:39:01,320 one particular species is using this huddling strategy 543 00:39:01,320 --> 00:39:03,480 in such a beautifully complex way 544 00:39:03,480 --> 00:39:07,120 that scientists are only just beginning to fully understand it. 545 00:39:10,880 --> 00:39:14,240 Emperor penguins are one of nature's great survivors. 546 00:39:19,440 --> 00:39:22,840 They can endure the extreme cold of an Antarctic winter 547 00:39:22,840 --> 00:39:24,520 where temperatures can plummet 548 00:39:24,520 --> 00:39:26,480 to minus 40 degrees Celsius. 549 00:39:30,360 --> 00:39:32,080 And the key to their survival 550 00:39:32,080 --> 00:39:33,960 is how they huddle together. 551 00:39:38,720 --> 00:39:42,800 One by one, the male emperor penguins lock themselves together 552 00:39:42,800 --> 00:39:44,440 in a tightly-packed group 553 00:39:44,440 --> 00:39:47,240 to keep warm and shelter from the intense winds. 554 00:39:49,240 --> 00:39:50,760 These huddles can contain 555 00:39:50,760 --> 00:39:52,920 as many as 4,000 penguins. 556 00:39:56,800 --> 00:39:59,360 And they are constantly moving - 557 00:39:59,360 --> 00:40:01,560 those on the outside push forward 558 00:40:01,560 --> 00:40:04,520 to get closer to the warmth in the centre of the group 559 00:40:04,520 --> 00:40:07,560 and away from the full force of the Antarctic storms. 560 00:40:10,560 --> 00:40:12,800 But the penguins on the inside of the huddle 561 00:40:12,800 --> 00:40:14,280 also move around 562 00:40:14,280 --> 00:40:17,320 to stop themselves from getting too warm. 563 00:40:17,320 --> 00:40:20,520 Recent studies have shown that temperatures at the centre 564 00:40:20,520 --> 00:40:23,400 can reach an incredible 37 degrees Celsius... 565 00:40:25,640 --> 00:40:28,680 ..so the penguins move away to avoid overheating, 566 00:40:28,680 --> 00:40:30,120 with others replacing them. 567 00:40:34,200 --> 00:40:36,400 It's one of the most phenomenal examples 568 00:40:36,400 --> 00:40:38,440 of cooperation in nature 569 00:40:38,440 --> 00:40:41,280 and a vital strategy for the emperor penguins' survival. 570 00:40:45,040 --> 00:40:48,720 Bracing yourself against everything that winter throws at you 571 00:40:48,720 --> 00:40:50,600 in such a sophisticated way 572 00:40:50,600 --> 00:40:53,080 is testament to just how resilient 573 00:40:53,080 --> 00:40:55,520 and awe-inspiring nature is, 574 00:40:55,520 --> 00:40:58,640 but nature is also incredibly versatile 575 00:40:58,640 --> 00:41:02,440 and other animals are avoiding the onslaught of winter altogether. 576 00:41:06,840 --> 00:41:10,120 To save energy when food is in short supply, 577 00:41:10,120 --> 00:41:12,560 some animals go into hibernation. 578 00:41:15,800 --> 00:41:18,120 After feeding up in the autumn, 579 00:41:18,120 --> 00:41:20,080 hedgehogs find a cosy den. 580 00:41:24,360 --> 00:41:27,160 Here, they fall into a state of inactivity, 581 00:41:27,160 --> 00:41:28,760 which can last all winter. 582 00:41:31,600 --> 00:41:33,680 Their body temperature drops, 583 00:41:33,680 --> 00:41:35,480 their heart rate slows 584 00:41:35,480 --> 00:41:37,720 and they live off their fat reserves 585 00:41:37,720 --> 00:41:38,920 for about four months. 586 00:41:48,800 --> 00:41:51,200 When winter arrives in North America, 587 00:41:51,200 --> 00:41:54,240 the Arctic ground squirrel retreats beneath the frozen ground... 588 00:41:59,120 --> 00:42:02,120 ..where it will sleep for an astounding eight months. 589 00:42:04,360 --> 00:42:07,240 A thermal camera inside a filming burrow 590 00:42:07,240 --> 00:42:10,240 shows how the squirrel's body temperature cools. 591 00:42:10,240 --> 00:42:11,840 It can drop to a staggering 592 00:42:11,840 --> 00:42:14,040 three degrees below freezing. 593 00:42:18,280 --> 00:42:22,160 Its major organs shut down almost entirely, 594 00:42:22,160 --> 00:42:23,720 but every few weeks, 595 00:42:23,720 --> 00:42:27,320 it shivers and its muscles send a flow of warm blood 596 00:42:27,320 --> 00:42:30,160 around its body, rebooting its brain. 597 00:42:34,440 --> 00:42:37,880 It will do this about a dozen times during the winter 598 00:42:37,880 --> 00:42:40,800 until finally, it's time to wake up again. 599 00:42:53,640 --> 00:42:56,960 Bats are another group of animals that are known to hibernate 600 00:42:56,960 --> 00:43:00,040 and new research has revealed that one particular species - 601 00:43:00,040 --> 00:43:03,200 the Ussurian tube-nosed bat from Japan, 602 00:43:03,200 --> 00:43:05,640 no bigger than the size of my palm - 603 00:43:05,640 --> 00:43:07,520 may hibernate in the snow. 604 00:43:09,800 --> 00:43:12,440 For many years, their whereabouts during the harsh winters 605 00:43:12,440 --> 00:43:15,840 remained a mystery, but now it's thought that when temperatures drop 606 00:43:15,840 --> 00:43:17,400 and the first snows fall, 607 00:43:17,400 --> 00:43:19,520 they leave their roosts in the cavities of trees 608 00:43:19,520 --> 00:43:21,320 and the crevices of rocks 609 00:43:21,320 --> 00:43:23,200 and settle onto that snow. 610 00:43:24,400 --> 00:43:25,680 As more snow falls, 611 00:43:25,680 --> 00:43:28,280 they become covered and surrounded, 612 00:43:28,280 --> 00:43:30,920 their tiny movements creating a cavity 613 00:43:30,920 --> 00:43:34,320 with much more stable temperatures than their tree roosts, 614 00:43:34,320 --> 00:43:36,000 exposed to the elements, 615 00:43:36,000 --> 00:43:39,920 and there they'll remain in what's called a super-cooled torpor 616 00:43:39,920 --> 00:43:41,880 or deep sleep. 617 00:43:41,880 --> 00:43:45,760 It's believed they'll stay there until the snow melts, 618 00:43:45,760 --> 00:43:48,240 potentially hibernating in their cavities 619 00:43:48,240 --> 00:43:50,600 all the way through to the spring. 620 00:44:06,160 --> 00:44:09,400 The shortest day of the year occurs at the end of December 621 00:44:09,400 --> 00:44:10,720 in the Northern Hemisphere. 622 00:44:10,720 --> 00:44:13,000 It's known as the winter solstice. 623 00:44:14,960 --> 00:44:17,520 Gradually, days begin to lengthen 624 00:44:17,520 --> 00:44:20,040 and some animals start planning for the future. 625 00:44:28,480 --> 00:44:30,240 The Himalayas, 626 00:44:30,240 --> 00:44:32,920 home to one of the planet's most majestic 627 00:44:32,920 --> 00:44:34,680 and elusive creatures... 628 00:44:43,400 --> 00:44:45,040 ..the snow leopard. 629 00:44:50,600 --> 00:44:53,200 Living in the world's highest mountains, 630 00:44:53,200 --> 00:44:55,800 this big cat's home range can be as large 631 00:44:55,800 --> 00:44:57,600 as 400 square miles. 632 00:45:03,760 --> 00:45:06,160 These cats are endangered. 633 00:45:06,160 --> 00:45:08,120 Scientists estimate there may be as few 634 00:45:08,120 --> 00:45:10,440 as 4,000 left in the wild. 635 00:45:13,080 --> 00:45:15,960 So the odds are well and truly stacked against them 636 00:45:15,960 --> 00:45:18,320 when it comes to finding a potential mate 637 00:45:18,320 --> 00:45:19,760 in this winter landscape. 638 00:45:23,040 --> 00:45:25,960 But this snow leopard doesn't seem to be too fazed 639 00:45:25,960 --> 00:45:27,560 by the challenge. 640 00:45:27,560 --> 00:45:29,920 He has a tried-and-tested strategy. 641 00:45:36,720 --> 00:45:40,760 First, he patrols the well-worn tracks of his territory 642 00:45:40,760 --> 00:45:42,720 over and over again. 643 00:45:45,680 --> 00:45:47,360 This is his patch, 644 00:45:47,360 --> 00:45:50,640 but it might overlap with the territory of a female 645 00:45:50,640 --> 00:45:52,880 and, with any luck, their paths will cross. 646 00:45:55,920 --> 00:45:58,160 Next, he uses scent marking 647 00:45:58,160 --> 00:45:59,760 to advertise his presence. 648 00:46:06,520 --> 00:46:10,360 Snow leopards scent mark their territory by spraying urine 649 00:46:10,360 --> 00:46:13,800 and scent chemicals and rubbing scent glands against rocks 650 00:46:13,800 --> 00:46:15,360 or patches of earth. 651 00:46:16,480 --> 00:46:19,400 He also checks for the scent of any potential mates 652 00:46:19,400 --> 00:46:20,680 who may have passed by. 653 00:46:22,120 --> 00:46:23,560 He's very diligent, 654 00:46:23,560 --> 00:46:26,520 sometimes spraying as many as 20 times an hour. 655 00:46:28,840 --> 00:46:30,640 He wouldn't want to miss his chance. 656 00:46:34,960 --> 00:46:38,400 Scent marking and detecting is a crucial part 657 00:46:38,400 --> 00:46:40,360 of the lives of snow leopards. 658 00:46:40,360 --> 00:46:42,880 It's how they communicate as solitary animals 659 00:46:42,880 --> 00:46:45,920 and it's incredibly important when it's time to breed. 660 00:46:45,920 --> 00:46:49,560 Snow leopards may have tens of millions of scent receptors. 661 00:46:49,560 --> 00:46:52,320 We humans only have a paltry five million. 662 00:46:52,320 --> 00:46:55,320 Their ability to detect different chemicals in a scent mark 663 00:46:55,320 --> 00:46:57,240 is nothing short of extraordinary. 664 00:47:01,800 --> 00:47:03,960 It can take a snow leopard over a week 665 00:47:03,960 --> 00:47:06,640 to cover his entire territory, 666 00:47:06,640 --> 00:47:09,040 walking hundreds of miles in search of a mate. 667 00:47:11,560 --> 00:47:13,840 Not even the deepest snow will stop him. 668 00:47:24,280 --> 00:47:27,320 At last, his determination pays off, 669 00:47:27,320 --> 00:47:29,400 he picks up the scent of a female. 670 00:47:34,960 --> 00:47:37,440 Eagerly, he rubs his own scent 671 00:47:37,440 --> 00:47:41,560 over the scent she has left to declare his presence and interest. 672 00:47:48,680 --> 00:47:51,840 He may be able to smell the marks of the female, 673 00:47:51,840 --> 00:47:54,000 but now he needs to find her. 674 00:47:56,320 --> 00:47:58,760 Then, across the mountains, 675 00:47:58,760 --> 00:48:01,400 comes the cry of a female snow leopard. 676 00:48:02,440 --> 00:48:04,480 SNOW LEOPARD CALLS IN DISTANCE 677 00:48:12,720 --> 00:48:14,280 He returns the call. 678 00:48:33,160 --> 00:48:35,200 If they do finally meet, 679 00:48:35,200 --> 00:48:37,320 these rare leopards will have a chance 680 00:48:37,320 --> 00:48:39,040 to add to the next generation... 681 00:48:44,760 --> 00:48:47,400 ..and with such low population numbers, 682 00:48:47,400 --> 00:48:50,000 every new litter of cubs is precious. 683 00:48:51,760 --> 00:48:53,720 SNOW LEOPARD CALLS 684 00:49:03,880 --> 00:49:05,440 As the snow begins to melt... 685 00:49:09,200 --> 00:49:11,720 ..and the sun's rays become stronger, 686 00:49:11,720 --> 00:49:13,560 spring will soon be on its way. 687 00:49:15,840 --> 00:49:19,440 But what causes these dramatic changes between the seasons? 688 00:49:21,720 --> 00:49:25,520 It's all down to the fact that planet Earth is tilted 689 00:49:25,520 --> 00:49:29,040 23.5 degrees off its axis. 690 00:49:29,040 --> 00:49:32,080 So when it's winter in the northern hemisphere, 691 00:49:32,080 --> 00:49:35,520 where we are in the UK and where I am here in Austria, 692 00:49:35,520 --> 00:49:37,640 the planet is in this position 693 00:49:37,640 --> 00:49:39,640 and it's tilted away from the sun, 694 00:49:39,640 --> 00:49:42,000 which means in the northern hemisphere, 695 00:49:42,000 --> 00:49:45,240 days are shorter and it's colder, 696 00:49:45,240 --> 00:49:47,280 but as the Earth moves around the sun... 697 00:49:49,000 --> 00:49:50,960 ..over 365 days, 698 00:49:50,960 --> 00:49:54,000 spinning on its own axis every 24 hours, obviously, 699 00:49:54,000 --> 00:49:56,000 as it hits spring around here 700 00:49:56,000 --> 00:49:57,880 and then summer here, 701 00:49:57,880 --> 00:50:02,120 you can see the northern hemisphere is tilted towards the sun, 702 00:50:02,120 --> 00:50:05,480 which means days are longer and warmer. 703 00:50:05,480 --> 00:50:08,000 Now, if our planet wasn't tilted at all, 704 00:50:08,000 --> 00:50:10,680 we simply wouldn't have any seasons 705 00:50:10,680 --> 00:50:13,480 and the Earth would be a very different place indeed. 706 00:50:24,640 --> 00:50:26,920 High in the northern hemisphere, 707 00:50:26,920 --> 00:50:28,920 with the arrival of spring, 708 00:50:28,920 --> 00:50:31,520 Arctic ground squirrels are beginning to stir 709 00:50:31,520 --> 00:50:32,960 from their very deep sleep. 710 00:50:35,280 --> 00:50:38,040 It takes three hours for them to heat up 711 00:50:38,040 --> 00:50:40,360 and a full day for their entire bodies 712 00:50:40,360 --> 00:50:41,920 to be fully functional again. 713 00:50:47,760 --> 00:50:49,600 As soon as they're up and about, 714 00:50:49,600 --> 00:50:51,680 males spring straight into action. 715 00:50:55,120 --> 00:50:57,160 SQUIRREL CHIRPS 716 00:51:03,280 --> 00:51:06,280 First, this male needs to reclaim his territory. 717 00:51:10,560 --> 00:51:12,600 SQUIRREL CHIRPS 718 00:51:16,640 --> 00:51:18,280 He sees off any rivals. 719 00:51:24,360 --> 00:51:27,080 He's ready for the most important day of his year. 720 00:51:34,320 --> 00:51:36,560 Female Arctic ground squirrels 721 00:51:36,560 --> 00:51:38,800 emerge a few days after the males. 722 00:51:43,040 --> 00:51:44,480 He needs to look his best... 723 00:51:47,720 --> 00:51:49,560 ..but he mustn't miss his chance. 724 00:51:52,880 --> 00:51:55,440 Females are only fertile 725 00:51:55,440 --> 00:51:57,720 for 12 hours each year. 726 00:51:57,720 --> 00:51:59,800 SQUIRREL CHIRPS 727 00:52:09,000 --> 00:52:11,280 He approaches her cautiously. 728 00:52:11,280 --> 00:52:13,320 He doesn't want to scare her off. 729 00:52:14,360 --> 00:52:16,160 But what will she make of him? 730 00:52:28,480 --> 00:52:30,200 He politely taps a greeting... 731 00:52:31,600 --> 00:52:34,040 ..and she returns the gesture. 732 00:52:34,040 --> 00:52:36,200 THEY CHIRP 733 00:52:36,200 --> 00:52:38,360 He can't afford to be complacent. 734 00:52:38,360 --> 00:52:41,800 She could go in search of another partner at any time, 735 00:52:41,800 --> 00:52:44,840 so he won't leave her side for 24 hours. 736 00:52:49,320 --> 00:52:53,280 And with any luck, the circle of life will start all over again. 737 00:52:58,800 --> 00:53:01,520 While some animals are beginning to pair up, 738 00:53:01,520 --> 00:53:04,120 others are already a few steps ahead. 739 00:53:05,360 --> 00:53:07,280 CALF BLEATS 740 00:53:13,720 --> 00:53:15,680 CUB GRUNTS 741 00:53:20,760 --> 00:53:22,800 CHICK CALLS 742 00:53:29,120 --> 00:53:31,600 Arctic fox cubs emerge from their den 743 00:53:31,600 --> 00:53:33,440 at just over three weeks old. 744 00:53:34,600 --> 00:53:36,960 Their mother has her work cut out with six... 745 00:53:38,280 --> 00:53:41,640 ..but they can have up to 14 cubs in a single litter, 746 00:53:41,640 --> 00:53:44,080 the most of any of the fox family. 747 00:53:46,480 --> 00:53:50,120 Weddell seal pups are born straight onto the ice. 748 00:53:50,120 --> 00:53:52,680 They'll double in weight in just the first week 749 00:53:52,680 --> 00:53:55,080 and soon after, they'll take their first swim. 750 00:53:58,680 --> 00:54:01,920 Young wild goats make the journey to their spring pastures 751 00:54:01,920 --> 00:54:03,400 when they're only a few weeks old... 752 00:54:05,720 --> 00:54:07,120 ..following their mothers, 753 00:54:07,120 --> 00:54:09,360 who'll protect them for the first year of their life. 754 00:54:15,400 --> 00:54:17,040 Young animals everywhere 755 00:54:17,040 --> 00:54:19,920 are out exploring their new world 756 00:54:19,920 --> 00:54:22,920 and the rising temperatures are enough to put a spring 757 00:54:22,920 --> 00:54:23,960 in everyone's step. 758 00:54:37,760 --> 00:54:42,440 The last places to feel the full effects of spring are the poles 759 00:54:42,440 --> 00:54:46,400 and beneath the snow in the Arctic, new life is emerging. 760 00:54:47,720 --> 00:54:49,760 CUB GRIZZLES 761 00:54:51,560 --> 00:54:54,840 These polar bear cubs are just two months old. 762 00:54:57,640 --> 00:54:59,520 They were born beneath the snow 763 00:54:59,520 --> 00:55:01,840 while their mother lay in her deep winter sleep. 764 00:55:08,240 --> 00:55:11,040 They're seeing the world for the first time. 765 00:55:11,040 --> 00:55:12,960 CUB GRUNTS 766 00:55:14,200 --> 00:55:15,600 They need to find their feet... 767 00:55:18,960 --> 00:55:20,880 ..and mum is on hand to help. 768 00:55:25,080 --> 00:55:27,160 CUB GRIZZLES 769 00:55:29,360 --> 00:55:31,880 After five months in hibernation, 770 00:55:31,880 --> 00:55:34,040 this is a chance to stretch her legs. 771 00:55:46,760 --> 00:55:48,880 Following the long winter, 772 00:55:48,880 --> 00:55:51,680 a mother bear's first task is to find food. 773 00:55:53,200 --> 00:55:55,640 She's headed for the sea ice to hunt, 774 00:55:55,640 --> 00:55:58,000 before it melts fully in a few months' time. 775 00:56:06,360 --> 00:56:09,880 Polar bears are dedicated and protective mothers. 776 00:56:14,800 --> 00:56:16,840 CUB CALLS 777 00:56:18,920 --> 00:56:20,760 They keep their cubs close 778 00:56:20,760 --> 00:56:23,640 and call to them when they wander too far. 779 00:56:23,640 --> 00:56:25,600 POLAR BEAR ROARS 780 00:56:25,600 --> 00:56:27,720 CUBS CALL 781 00:56:31,960 --> 00:56:33,720 Over the next two years, 782 00:56:33,720 --> 00:56:36,800 she will teach her cubs to swim and to hunt 783 00:56:36,800 --> 00:56:41,120 and how to survive the challenging Arctic winters by themselves. 784 00:56:50,960 --> 00:56:54,320 Until then, as they step out into a new year, 785 00:56:54,320 --> 00:56:57,120 she will always be at their side. 786 00:56:57,120 --> 00:56:59,160 POLAR BEAR GROWLS 787 00:57:06,160 --> 00:57:08,480 CUB GRIZZLES 788 00:57:08,480 --> 00:57:10,400 MOTHER BEAR GROWLS 789 00:57:12,360 --> 00:57:15,360 From the first frosts to the first thaws, 790 00:57:15,360 --> 00:57:18,240 our animals have developed remarkable adaptations... 791 00:57:24,680 --> 00:57:26,840 ..from making sure they have enough food... 792 00:57:31,320 --> 00:57:34,480 ..to staying as warm as possible in the coldest months. 793 00:57:41,640 --> 00:57:45,080 The strategies they've evolved to survive and thrive 794 00:57:45,080 --> 00:57:48,440 in our winter wonderlands make for some of the most inspirational 795 00:57:48,440 --> 00:57:50,160 stories from the natural world.