1 00:00:39,960 --> 00:00:43,710 A third of the land on our planet is desert. 2 00:00:52,680 --> 00:00:57,510 These great scars on the face of the earth appear to be lifeless. 3 00:00:57,600 --> 00:01:00,270 But surprisingly, none are. 4 00:01:06,960 --> 00:01:12,230 In all of them life manages, somehow, to keep a precarious hold. 5 00:01:32,920 --> 00:01:35,110 Not all deserts are hot. 6 00:01:35,720 --> 00:01:39,110 Fifty-mile-an-hour winds blowing in from Siberia 7 00:01:39,200 --> 00:01:42,550 bring snow to the Gobi Desert in Mongolia. 8 00:02:08,040 --> 00:02:11,390 From a summer high of 50 degrees centigrade, 9 00:02:11,480 --> 00:02:15,510 the temperature in mid-winter can drop to minus 40, 10 00:02:15,600 --> 00:02:19,110 making this one of the harshest deserts of all. 11 00:02:28,040 --> 00:02:32,750 Few animals can survive these extreme changes. 12 00:02:38,960 --> 00:02:43,590 Wild Bactrian camels, one of the rarest mammals on the planet, 13 00:02:44,160 --> 00:02:46,510 and perhaps the hardiest. 14 00:02:47,880 --> 00:02:50,350 Their biggest problem is the lack of water, 15 00:02:50,480 --> 00:02:54,990 particularly now in winter when the little there is is locked up as ice. 16 00:03:02,240 --> 00:03:05,790 Surprisingly, snow here never melts. 17 00:03:06,440 --> 00:03:10,870 The air is just too cold and too dry for it to do so. 18 00:03:16,040 --> 00:03:19,270 The sun's rays turn it straight into vapour. 19 00:03:19,680 --> 00:03:21,430 It evaporates. 20 00:03:29,280 --> 00:03:32,470 But it is the only source of water 21 00:03:32,560 --> 00:03:35,230 so Bactrian camels eat it. 22 00:03:36,200 --> 00:03:37,510 Elsewhere in the world, 23 00:03:37,640 --> 00:03:43,030 a camel at a waterhole can drink as much as 200 litres during a single visit. 24 00:03:45,840 --> 00:03:50,790 Here, the strategy is to take little and often, and with good reason 25 00:03:50,880 --> 00:03:54,270 for filling the stomach with snow could be fatal. 26 00:03:59,920 --> 00:04:05,150 The camels must limit themselves to the equivalent of just 10 litres a day. 27 00:04:21,560 --> 00:04:24,230 Winter is the time for breeding. 28 00:04:28,880 --> 00:04:33,110 This extraordinary performance is a male Bactrian camel's way 29 00:04:33,200 --> 00:04:36,070 of attracting the attention of a passing female. 30 00:04:38,400 --> 00:04:42,470 In summer, the camels can't stray far from waterholes. 31 00:04:43,240 --> 00:04:46,470 But now, with mouthfuls of snow lying everywhere, 32 00:04:46,560 --> 00:04:49,670 they can travel widely in search of mates. 33 00:04:53,760 --> 00:04:59,230 Today, less than 1,000 of these desert specialists remain in the wild. 34 00:05:00,000 --> 00:05:04,670 The Gobi, hostile though it is, is their last stronghold. 35 00:05:11,280 --> 00:05:14,550 There is no other desert quite like the Gobi. 36 00:05:14,640 --> 00:05:17,070 But why is this place a desert? 37 00:05:18,800 --> 00:05:21,830 There is one simple and massive cause. 38 00:05:21,920 --> 00:05:23,550 The Himalayas. 39 00:05:27,800 --> 00:05:31,870 Clouds blowing from the south hit this gigantic barrier. 40 00:05:31,960 --> 00:05:33,510 As they're forced upwards, 41 00:05:33,600 --> 00:05:36,670 so they empty their moisture on the mountain slopes, 42 00:05:36,760 --> 00:05:39,830 leaving little for the land on the other side. 43 00:05:44,840 --> 00:05:48,510 From space, deserts are very conspicuous. 44 00:05:51,240 --> 00:05:55,710 Dunes of sand hundreds of miles long streak their surface. 45 00:06:00,560 --> 00:06:03,630 With no cloak of vegetation to conceal them, 46 00:06:03,720 --> 00:06:07,590 strange formations are exposed in the naked rock. 47 00:06:13,720 --> 00:06:17,390 Africa's Sahara is the largest desert of all. 48 00:06:17,480 --> 00:06:19,750 It's the size of the United States 49 00:06:19,840 --> 00:06:23,950 and the biggest source of sand and dust in the entire world. 50 00:07:03,080 --> 00:07:06,350 Sandstorms like these appear without warning 51 00:07:06,440 --> 00:07:10,710 and reduce visibility for days over areas the size of Britain. 52 00:07:19,880 --> 00:07:24,670 Dromedaries, single-humped camels, take these storms in their stride. 53 00:07:28,400 --> 00:07:32,630 The heavy sand rises only a few metres above the ground. 54 00:07:32,720 --> 00:07:37,430 But the dust can be blown 5, 000 metres up into the sky. 55 00:07:43,000 --> 00:07:46,550 The ferocious wind, armed with grains of sand, 56 00:07:46,640 --> 00:07:49,670 is the agent that shapes all deserts. 57 00:07:59,120 --> 00:08:04,990 Reptiles have armoured, scaly skins that protect them from the stinging grains. 58 00:08:07,960 --> 00:08:12,190 For insects, the bombardment can be very severe indeed. 59 00:08:14,560 --> 00:08:17,630 The only escape is below the surface. 60 00:08:33,920 --> 00:08:38,030 As the winds rise and fall, swirl and eddy, 61 00:08:38,120 --> 00:08:41,030 so they pile the sand into dunes. 62 00:08:45,000 --> 00:08:48,550 These sand seas can be hundreds of miles across. 63 00:08:53,080 --> 00:08:57,230 In Namibia, the winds have built some of the biggest dunes in the world. 64 00:09:05,280 --> 00:09:09,110 Star dunes like these can be 300 metres high. 65 00:09:09,480 --> 00:09:13,950 Grains swept up the flanks are blown off the crests of the ridges 66 00:09:14,040 --> 00:09:16,310 so it's only the tops that are moving. 67 00:09:23,360 --> 00:09:28,430 The main body of these dunes may not have shifted for 5, 000 years. 68 00:09:40,320 --> 00:09:45,950 Few rocks can resist the continuous blast of the sand-carrying wind. 69 00:09:46,640 --> 00:09:50,510 These outcrops are standing in Egypt's White Desert. 70 00:09:51,600 --> 00:09:54,590 But they will not do so for much longer. 71 00:09:56,080 --> 00:10:01,110 They are being inexorably chiselled away and turned into more sand. 72 00:10:39,080 --> 00:10:45,590 Now lumps of heavily eroded rocks have been marooned in a sea of sand. 73 00:11:02,440 --> 00:11:06,110 These jagged pyramids, 100 metres tall, 74 00:11:06,200 --> 00:11:09,670 were once part of a continuous rocky plateau. 75 00:11:09,760 --> 00:11:13,790 The blasting sand will eventually eliminate them altogether. 76 00:11:22,160 --> 00:11:24,310 The relentless power of the wind 77 00:11:24,400 --> 00:11:28,390 ensures that the face of a desert is continually changing. 78 00:11:28,480 --> 00:11:31,110 But there is one constant presence. 79 00:11:39,080 --> 00:11:40,870 The desert sun. 80 00:11:55,240 --> 00:11:58,590 The sun's heat and the power to evaporate water 81 00:11:58,680 --> 00:12:03,670 has had a profound effect on the bodies and habits of everything that lives here. 82 00:12:08,240 --> 00:12:11,270 This sun, potentially, is a killer. 83 00:12:12,880 --> 00:12:16,430 And the red kangaroos must acknowledge that. 84 00:12:17,920 --> 00:12:22,590 Right now, while the sun is low, there's no immediate cause for concern. 85 00:12:23,840 --> 00:12:26,630 But this situation won't last long. 86 00:12:27,760 --> 00:12:33,310 Australia is the world's most arid continent with blistering daytime temperatures. 87 00:12:40,640 --> 00:12:45,350 Every hour, the temperature rises by five degrees centigrade. 88 00:12:52,880 --> 00:12:56,270 Soon the heat will reach a critical point. 89 00:13:06,120 --> 00:13:11,230 Any kangaroo out in the open is in serious danger of overheating. 90 00:13:17,200 --> 00:13:22,670 In the full sun, the temperature on the ground soars to 70 degrees. 91 00:13:27,560 --> 00:13:32,870 By midday, the radiation is so intense they must take shelter. 92 00:13:52,600 --> 00:13:56,070 In the shade, they are shielded from much of the sun's energy 93 00:13:56,160 --> 00:13:58,830 but their body temperature can still rise. 94 00:14:01,640 --> 00:14:05,070 So they lick saliva onto their forearms 95 00:14:05,160 --> 00:14:09,110 where there is a network of blood vessels close to the surface of the skin, 96 00:14:09,200 --> 00:14:13,430 and as the saliva evaporates, their blood is cooled. 97 00:14:16,280 --> 00:14:20,790 This thermal image shows just how effective the process is. 98 00:14:20,920 --> 00:14:24,310 The blue areas on the body are the cooler parts. 99 00:14:33,280 --> 00:14:36,910 As the saliva dries, it has to be replaced. 100 00:14:37,000 --> 00:14:41,030 And this is a real drain on the kangaroo's body fluids. 101 00:14:51,120 --> 00:14:54,510 Even in the shade, the earth is baking hot. 102 00:14:55,480 --> 00:15:01,110 So the kangaroos dig away the warmed topsoil to get at the cooler ground beneath. 103 00:15:23,720 --> 00:15:28,110 By staying in the shade and licking to control their body temperature, 104 00:15:28,240 --> 00:15:32,830 kangaroos manage to get through the hottest part of the day without heatstroke. 105 00:15:34,080 --> 00:15:39,430 But for the majority of desert animals, this strategy would not be enough for survival. 106 00:16:02,040 --> 00:16:06,790 The extraordinary ears of the fennec foxes of Africa radiate heat, 107 00:16:06,880 --> 00:16:10,150 but the animals have another way of keeping cool. 108 00:16:19,560 --> 00:16:24,550 They spend their days underground and only emerge at sunset. 109 00:16:36,440 --> 00:16:39,390 Darkness brings huge changes. 110 00:16:39,800 --> 00:16:44,430 In the Sahara, the temperature can drop as much as 30 degrees during the night. 111 00:16:44,640 --> 00:16:48,630 So it's cool enough to allow these desert fox cubs to play. 112 00:16:56,440 --> 00:17:01,830 All sorts of creatures now appear, including some really unexpected ones. 113 00:17:05,120 --> 00:17:07,230 Toads have permeable skins 114 00:17:07,320 --> 00:17:11,150 and would quickly die from desiccation out in the daytime heat. 115 00:17:11,240 --> 00:17:13,710 It's only now that they can leave shelter. 116 00:17:16,680 --> 00:17:21,550 The same is true for scorpions, even though their shells are actually watertight. 117 00:17:33,840 --> 00:17:37,470 In fact, most small desert creatures are nocturnal. 118 00:17:37,640 --> 00:17:42,990 So it's only now that you can judge just how much life there can be in a desert. 119 00:17:43,920 --> 00:17:46,390 But moisture lost, even at night, 120 00:17:46,480 --> 00:17:49,510 has to be replaced sometime, somehow. 121 00:17:49,600 --> 00:17:53,630 And that problem dominates the lives of all desert dwellers. 122 00:18:01,920 --> 00:18:07,190 The Atacama in Chile. This is the driest desert in the world. 123 00:18:09,240 --> 00:18:13,590 Some parts may not see rain for 50 years, and with such a record, 124 00:18:13,680 --> 00:18:16,550 you would expect the place to be completely barren. 125 00:18:22,120 --> 00:18:25,910 These are South America's camels, guanacos. 126 00:18:27,760 --> 00:18:30,030 They are very good at conserving moisture 127 00:18:30,120 --> 00:18:33,110 but they, nonetheless, need a regular supply of water. 128 00:18:45,840 --> 00:18:48,910 They get it partly from cactus flowers. 129 00:18:49,000 --> 00:18:52,270 But that explanation raises another question. 130 00:18:54,720 --> 00:18:58,070 How do the cacti survive without rain? 131 00:19:04,680 --> 00:19:09,230 Hot winds suck all the moisture from the surface of the land. 132 00:19:11,120 --> 00:19:15,830 Clearly, there must be something else that takes the place of rain. 133 00:19:17,240 --> 00:19:22,470 The secret is a cold sea current that runs parallel to the land. 134 00:19:39,360 --> 00:19:45,230 The cold water cools the moist, warm air above it and that produces banks of fog. 135 00:20:08,080 --> 00:20:13,830 At the same time, wind blowing onto the shore sweeps the fog inland. 136 00:20:29,040 --> 00:20:33,110 Before long, the cacti are dripping with dew. 137 00:20:42,000 --> 00:20:43,790 The fog is so regular 138 00:20:43,880 --> 00:20:47,310 that moisture-loving lichens are able to grow on the cacti 139 00:20:47,400 --> 00:20:50,390 and they absorb liquid like a sponge. 140 00:20:53,080 --> 00:20:55,670 In the land of almost no rain, 141 00:20:55,760 --> 00:21:00,550 these precious drops are lifesavers for many different creatures. 142 00:21:09,560 --> 00:21:15,190 Further inland, the air remains so warm that its moisture does not condense. 143 00:21:15,280 --> 00:21:19,950 So this slender strip of desert is virtually the only part of the Atacama 144 00:21:20,040 --> 00:21:21,710 where life can exist. 145 00:21:25,960 --> 00:21:30,150 And without the fog, this land, too, would be empty. 146 00:21:43,720 --> 00:21:46,790 The guanacos make the most of the dew. 147 00:21:47,280 --> 00:21:49,390 But it will not remain for long. 148 00:21:50,400 --> 00:21:55,470 In an hour or two, the sun will have burnt it off and dried the surface of the cacti. 149 00:22:04,360 --> 00:22:09,550 The Sonoran Desert in Arizona is not quite so dry as the Atacama. 150 00:22:09,640 --> 00:22:11,510 Some rain does fall. 151 00:22:12,680 --> 00:22:14,230 But it is infrequent, 152 00:22:14,360 --> 00:22:19,230 and when it does arrive, animals and plants have to be ready to make the most of it. 153 00:22:21,040 --> 00:22:22,350 And it's coming. 154 00:22:30,960 --> 00:22:33,070 When the summer monsoon blows in, 155 00:22:33,160 --> 00:22:36,510 the giant saguaros, one of the biggest of all cacti, 156 00:22:36,600 --> 00:22:39,030 are ready to take full advantage of it. 157 00:23:12,080 --> 00:23:13,950 After a rainstorm, 158 00:23:14,040 --> 00:23:18,110 the saguaro's long, shallow root system sucks up the water 159 00:23:18,760 --> 00:23:22,950 and the pleats on its trunk enable it to expand rapidly. 160 00:23:31,040 --> 00:23:36,270 When full, a saguaro stem can store up to five tonnes of water, 161 00:23:36,360 --> 00:23:40,070 and that's enough to see it through many months of drought. 162 00:23:44,800 --> 00:23:49,670 The trunks of these huge plants provide homes for the Gila woodpecker. 163 00:23:52,240 --> 00:23:57,790 But birds are not the only animals to benefit from the presence of the cacti. 164 00:24:14,240 --> 00:24:20,870 During four weeks of the summer, the saguaros bloom at night to attract visitors. 165 00:24:24,640 --> 00:24:27,830 The pollen and nectar with which these flowers are loaded 166 00:24:27,920 --> 00:24:31,630 attract long-nosed and long-tongued bats. 167 00:24:46,600 --> 00:24:51,590 The bats left Mexico a few days earlier to escape the heat of summer 168 00:24:51,680 --> 00:24:55,470 and are on their way north to the southern United States. 169 00:24:57,640 --> 00:25:01,110 To get there, they have to cross the Sonoran Desert. 170 00:25:07,080 --> 00:25:12,630 But the desert is so big that for most of the year they would be unable to cross it. 171 00:25:12,720 --> 00:25:17,430 Now, with the saguaro in bloom, they can refuel on the way. 172 00:25:27,360 --> 00:25:31,230 So the saguaro's success in developing a way to store water 173 00:25:31,320 --> 00:25:37,150 is now crucial to most of the animals that live or even travel through this land. 174 00:26:16,040 --> 00:26:20,430 The scarcity of rain determined the shape of this icon of the desert. 175 00:26:20,560 --> 00:26:26,510 But water, scarce though it is, has also, like the wind, shaped the land itself. 176 00:26:43,200 --> 00:26:48,070 In the deserts of Utah, ancient rivers flowing across sandstone country 177 00:26:48,160 --> 00:26:50,550 steadily widened their canyons 178 00:26:50,640 --> 00:26:56,230 until now, the land between them has been reduced to spires and pinnacles. 179 00:27:25,240 --> 00:27:30,190 With little or no soil to retain the water on the surface of the land, 180 00:27:30,360 --> 00:27:33,030 life here is scarce indeed. 181 00:27:35,000 --> 00:27:39,190 And when resources are limited, conflict is never far away. 182 00:27:49,680 --> 00:27:54,590 These are Nubian ibex and they are squaring up for a duel. 183 00:28:01,080 --> 00:28:07,310 And when trouble starts, a smart ibex knows that the best thing to do is to gain higher ground. 184 00:28:24,480 --> 00:28:30,230 These are actually subordinate male ibex, but their fights are, nonetheless, serious. 185 00:28:30,320 --> 00:28:34,710 Losing one might mean never getting the chance to breed, ever. 186 00:28:56,800 --> 00:29:00,230 When competitors are evenly matched, as they are here, 187 00:29:00,320 --> 00:29:02,510 duels can last for an hour. 188 00:29:22,080 --> 00:29:26,110 In this heat, the effort is truly exhausting. 189 00:29:28,160 --> 00:29:33,430 But victory here will gain important ranking points on a male's way to the top. 190 00:30:04,440 --> 00:30:07,950 There's so much at stake that not all play fair. 191 00:30:22,960 --> 00:30:25,230 The battle has produced a winner. 192 00:30:25,320 --> 00:30:28,750 But the ultimate prize is not his yet. 193 00:30:32,560 --> 00:30:36,550 That currently belongs to the dominant male ibex. 194 00:30:38,880 --> 00:30:42,630 His rank earns him the loyalty of a harem of females 195 00:30:42,720 --> 00:30:44,150 and they follow him closely 196 00:30:44,240 --> 00:30:48,150 as he travels across this desert searching for food and water. 197 00:30:50,640 --> 00:30:55,150 He doesn't have to waste time looking for mates, they're his for the taking. 198 00:30:55,240 --> 00:30:59,550 So he can concentrate with them on keeping fit and healthy. 199 00:31:14,640 --> 00:31:17,790 Lizards are desert specialists. 200 00:31:20,680 --> 00:31:23,910 But here, their numbers are extraordinary. 201 00:31:29,480 --> 00:31:31,550 These crevices in South Africa 202 00:31:31,640 --> 00:31:34,830 contain the highest density of lizards in the world. 203 00:31:44,920 --> 00:31:48,470 They're called flat lizards, for obvious reasons, 204 00:31:48,600 --> 00:31:53,150 and they flaunt their multicoloured bellies in territorial disputes. 205 00:31:55,720 --> 00:31:59,990 He's made his point and now it's time to find some food. 206 00:32:01,880 --> 00:32:05,590 As the day warms up, the lizards move away from their cracks 207 00:32:05,680 --> 00:32:08,110 and head down to the bottom of the gorge. 208 00:32:09,480 --> 00:32:11,670 Their goal is the river. 209 00:32:14,040 --> 00:32:19,350 There is no food at the edge, but this desert river holds a secret. 210 00:32:26,040 --> 00:32:30,910 Each day, black fly rise from turbulent stretches of the river. 211 00:32:31,520 --> 00:32:34,110 This is what the lizards have come for. 212 00:32:48,920 --> 00:32:50,750 The black fly never land 213 00:32:50,840 --> 00:32:54,070 so the lizards have to leap for their food. 214 00:33:06,320 --> 00:33:11,910 In one day, each of these acrobatic little lizards may catch 50 flies. 215 00:33:22,240 --> 00:33:27,270 There are plenty of flies to go around, even with hundreds of lizards competing for them. 216 00:33:41,280 --> 00:33:42,950 Away from these rapids, 217 00:33:43,040 --> 00:33:47,190 flat lizard populations are found in much smaller numbers. 218 00:33:47,280 --> 00:33:51,350 But here, one unusual abundance has produced another. 219 00:34:02,720 --> 00:34:05,630 Deserts are created by the lack of water 220 00:34:05,720 --> 00:34:11,390 but what actually kills animals here is not heat or thirst, but lack of food. 221 00:34:29,560 --> 00:34:33,470 So how on earth does a plant-eater this size 222 00:34:33,560 --> 00:34:38,550 survive in a place apparently totally devoid of vegetation? 223 00:34:45,120 --> 00:34:49,070 Elephants in Namibia are the toughest in Africa. 224 00:34:49,160 --> 00:34:50,990 And they need to be. 225 00:35:07,400 --> 00:35:10,630 What little food exists is so dispersed 226 00:35:10,720 --> 00:35:13,790 that these elephants walk up to 50 miles a day 227 00:35:13,880 --> 00:35:18,790 as they travel up the dry river channels searching for something to eat. 228 00:35:33,520 --> 00:35:37,350 At times, the task looks truly hopeless. 229 00:36:10,840 --> 00:36:14,550 Elephants may seem out of place in this landscape, 230 00:36:14,640 --> 00:36:16,790 but they're not the only ones. 231 00:36:32,840 --> 00:36:35,950 Amazingly, lions live here, too. 232 00:36:40,720 --> 00:36:46,990 In savannah country, huge herds of game support prides containing 20 lions or more. 233 00:36:47,480 --> 00:36:51,270 But to live here, lions have had to change their habits. 234 00:36:51,400 --> 00:36:55,550 Prides are much smaller and their home ranges are very much bigger. 235 00:36:56,880 --> 00:36:58,950 And there's an added problem. 236 00:37:00,560 --> 00:37:03,630 Their food is always on the move. 237 00:37:12,280 --> 00:37:13,870 Like the elephants, 238 00:37:13,960 --> 00:37:18,310 the lions must travel great distances to find enough to live on. 239 00:37:33,120 --> 00:37:35,750 But lions can't go everywhere. 240 00:37:35,880 --> 00:37:40,070 They won't attempt to cross this field of sand dunes, 241 00:37:40,160 --> 00:37:41,910 and the oryx know it. 242 00:38:39,480 --> 00:38:43,470 The lions must wait for the oryx to leave the safety of the dunes, 243 00:38:43,560 --> 00:38:46,430 which eventually they must to find food and water, 244 00:38:46,520 --> 00:38:48,990 and then the lions will ambush them. 245 00:39:51,880 --> 00:39:55,630 The elephants have found some of their favourite food. 246 00:40:02,440 --> 00:40:05,390 Grasses are the staple diet of all elephants, 247 00:40:05,480 --> 00:40:08,750 but this herd concentrates on digging up the roots, 248 00:40:08,840 --> 00:40:12,390 which have more nutrition and moisture than the stems. 249 00:40:12,880 --> 00:40:14,390 It's the sort of behaviour 250 00:40:14,480 --> 00:40:18,110 that can make all the difference in a place of serious shortages. 251 00:40:19,160 --> 00:40:22,710 Yet all this can change in an instant. 252 00:40:39,280 --> 00:40:43,870 The fortunes of many deserts are ruled by distant rains. 253 00:40:43,960 --> 00:40:48,630 This water fell as rain in mountains more than 100 miles away. 254 00:40:54,400 --> 00:40:56,230 It's known as a flash flood 255 00:40:56,360 --> 00:41:00,510 and called that because the water may run for just a single day. 256 00:41:00,600 --> 00:41:04,590 It's an event that only happens once or twice a year at the most. 257 00:41:25,080 --> 00:41:29,310 The sandy riverbed acts like a giant strip of blotting paper, 258 00:41:29,400 --> 00:41:32,150 sucking up the water as soon as it appears. 259 00:41:41,840 --> 00:41:45,070 But every square metre of soil moistened by this river 260 00:41:45,160 --> 00:41:49,190 will increase the chances of survival for those that live here. 261 00:41:54,760 --> 00:41:57,910 Waterholes are filled temporarily. 262 00:42:02,560 --> 00:42:05,950 Elsewhere in Africa elephants drink everyday 263 00:42:06,080 --> 00:42:10,870 but the lack of water here means that desert elephants can only refill their tanks 264 00:42:10,960 --> 00:42:13,590 once every four or five days. 265 00:42:15,160 --> 00:42:19,350 Within a week, the flash flood has produced a flush of green, 266 00:42:19,440 --> 00:42:22,910 more than enough to draw the oryx out of the dunes. 267 00:42:25,400 --> 00:42:29,190 It's a rare chance for them to build up their food reserves. 268 00:42:37,520 --> 00:42:41,230 The flood has made life easier for the lions, too. 269 00:42:44,120 --> 00:42:48,750 The flesh of this oryx will keep the family going for a week at the most. 270 00:42:49,160 --> 00:42:54,150 But for a while, the hunting will be easier now that the river channel has turned green. 271 00:42:58,480 --> 00:43:01,350 The good times for lions and oryx are brief. 272 00:43:01,440 --> 00:43:03,310 But these are the short moments 273 00:43:03,400 --> 00:43:06,990 that make it possible to live in deserts the year round. 274 00:43:12,840 --> 00:43:15,950 Death Valley is the hottest place on Earth. 275 00:43:16,040 --> 00:43:19,710 Yet even this furnace can be transformed by water. 276 00:43:30,320 --> 00:43:35,030 A single shower can enable seeds that have lain dormant for 30 years or more 277 00:43:35,120 --> 00:43:36,910 to burst into life. 278 00:43:45,280 --> 00:43:49,070 And there hasn't been a bloom like this one for a century. 279 00:44:01,240 --> 00:44:04,630 The periods of boom in Death Valley are short 280 00:44:04,720 --> 00:44:08,510 but they're just frequent enough to keep life ticking over. 281 00:44:17,120 --> 00:44:21,630 A sudden flush of vegetation is what every desert dweller waits for 282 00:44:21,720 --> 00:44:25,070 and when it happens, they must make the most of it. 283 00:44:44,480 --> 00:44:46,830 There is no other species on the planet 284 00:44:46,960 --> 00:44:50,750 that responds as quickly and as dramatically to the good times 285 00:44:50,840 --> 00:44:52,910 as the desert locust. 286 00:44:53,800 --> 00:44:58,470 Eggs that have remained in the ground for 20 years begin to hatch. 287 00:45:10,840 --> 00:45:15,470 The young locusts are known as hoppers, for at this stage they're flightless. 288 00:45:15,560 --> 00:45:21,310 They find new feeding grounds by following the smell of sprouting grass. 289 00:45:27,400 --> 00:45:31,310 Normally it takes four weeks for hoppers to become adults. 290 00:45:31,400 --> 00:45:33,790 But when the conditions are right, as now, 291 00:45:33,880 --> 00:45:37,070 their development switches to the fast track. 292 00:45:42,320 --> 00:45:45,430 As the vegetation in one place begins to run out, 293 00:45:45,520 --> 00:45:48,870 the winged adults release pheromones, scent messages, 294 00:45:48,960 --> 00:45:52,430 which tell others in the group that they must move on. 295 00:46:03,840 --> 00:46:07,630 And when groups merge, they form a swarm. 296 00:46:29,400 --> 00:46:33,310 An adult locust eats its entire body weight every day. 297 00:46:33,400 --> 00:46:38,150 And a whole swarm can consume literally hundreds of tonnes of vegetation. 298 00:46:40,280 --> 00:46:42,510 They have to keep on moving. 299 00:46:43,880 --> 00:46:45,990 The swarm travels with the wind. 300 00:46:46,080 --> 00:46:48,910 It's the most energy-saving way of flying. 301 00:46:52,760 --> 00:46:54,470 Following the flow of wind 302 00:46:54,560 --> 00:46:58,230 means that they're always heading toward areas of low pressure. 303 00:46:58,320 --> 00:47:02,990 Places where wind meets rain and vegetation starts to grow. 304 00:47:05,200 --> 00:47:10,870 As they fly, swarms join up with other swarms to form gigantic plagues 305 00:47:10,960 --> 00:47:14,870 several billion strong and as much as 40 miles wide. 306 00:47:17,280 --> 00:47:21,190 They will consume every edible thing that lies in their path. 307 00:47:34,480 --> 00:47:38,390 This is one of planet Earth's greatest spectacles. 308 00:47:38,520 --> 00:47:42,190 It's rarely seen on this scale and it won't last long. 309 00:47:42,680 --> 00:47:44,310 Once the food has gone, 310 00:47:44,400 --> 00:47:48,150 the steady roar of a billion beating locust wings 311 00:47:48,240 --> 00:47:53,990 will once again be replaced by nothing more than the sound of the desert wind.