1 00:00:34,284 --> 00:00:36,328 A Perfect Planet. 2 00:00:52,511 --> 00:00:56,682 We live in a world with a violent atmosphere. 3 00:00:59,893 --> 00:01:06,525 Rain clouds form, and powerful winds carry their fresh water around the globe. 4 00:01:08,819 --> 00:01:13,574 Without this, our perfect planet simply couldn't function... 5 00:01:14,783 --> 00:01:19,121 for all life on land depends on the weather. 6 00:01:32,759 --> 00:01:38,348 We all know that the weather can change on a daily, even hourly, basis. 7 00:01:40,392 --> 00:01:45,022 But annual weather patterns have been stable for millennia... 8 00:01:46,607 --> 00:01:51,486 and it's this reliability on which life depends. 9 00:01:57,492 --> 00:02:01,913 Every year in October, the weather brings a dramatic transformation 10 00:02:02,039 --> 00:02:06,001 to this tiny patch of forest in Zambia. 11 00:02:11,298 --> 00:02:13,800 Storm clouds begin to build. 12 00:02:21,850 --> 00:02:24,561 And right on cue, 13 00:02:24,686 --> 00:02:28,732 straw-coloured fruit bats start to appear. 14 00:02:34,696 --> 00:02:39,785 They've travelled hundreds, if not thousands, of miles to be here. 15 00:02:47,542 --> 00:02:51,755 And they always arrive at exactly the same time. 16 00:02:55,092 --> 00:02:58,929 They know that these rains will transform this forest, 17 00:02:59,054 --> 00:03:02,724 allowing countless fruit trees to ripen. 18 00:03:07,229 --> 00:03:11,858 And the bats gorge on the new-found abundance. 19 00:03:31,753 --> 00:03:34,172 For just 12 weeks every year, 20 00:03:34,297 --> 00:03:40,178 this forest becomes home to ten million fruit bats. 21 00:03:44,266 --> 00:03:48,061 One of the greatest gatherings of mammals on Earth, 22 00:03:48,186 --> 00:03:53,358 all crowding into an area no bigger than a dozen football pitches. 23 00:03:57,112 --> 00:03:59,865 From this hub, the bats fan out, 24 00:03:59,990 --> 00:04:04,077 consuming more than 300,000 tonnes of fruit, 25 00:04:04,202 --> 00:04:08,123 spreading the seeds and regenerating the forests. 26 00:04:28,477 --> 00:04:34,441 Africa's largest wildlife migration - entirely dependent on the rain 27 00:04:34,566 --> 00:04:37,778 that comes to this small corner of Zambia 28 00:04:37,903 --> 00:04:41,573 at the same time each year. 29 00:04:57,756 --> 00:05:02,135 Every second, over 13 million tonnes of water 30 00:05:02,260 --> 00:05:07,265 evaporate from our oceans, forming clouds. 31 00:05:13,855 --> 00:05:17,150 The spin of the Earth and the prevailing winds 32 00:05:17,275 --> 00:05:20,070 determine where these clouds blow. 33 00:05:21,947 --> 00:05:25,408 As a consequence, some places get less rain... 34 00:05:27,410 --> 00:05:29,162 and others much more. 35 00:05:32,123 --> 00:05:34,334 The Amazon rainforest... 36 00:05:37,420 --> 00:05:40,507 one of the wettest places on Earth. 37 00:05:51,101 --> 00:05:53,728 It gets three metres of rain a year... 38 00:05:55,021 --> 00:06:01,319 so life has learned to deal with the near-daily downpours. 39 00:06:06,867 --> 00:06:11,246 Every year, for thousands of years, the persistent rains 40 00:06:11,371 --> 00:06:15,083 have flooded vast tracts of the Amazon... 41 00:06:17,127 --> 00:06:21,798 turning the jungle into a seasonal wetland. 42 00:06:24,009 --> 00:06:28,889 Anything living here must either climb or swim. 43 00:06:33,977 --> 00:06:38,231 But there's one extraordinary animal that has turned this deluge 44 00:06:38,356 --> 00:06:42,027 from a disaster into an opportunity. 45 00:06:48,366 --> 00:06:53,330 This fire ant has reached the edge of her known world. 46 00:06:57,083 --> 00:07:01,755 Her way forward has now become blocked by the rising waters. 47 00:07:07,844 --> 00:07:11,556 She's one of many, and in a few minutes 48 00:07:11,681 --> 00:07:14,976 their underground home will be submerged. 49 00:07:21,858 --> 00:07:28,615 Forced to evacuate, workers and soldiers try to save the larval young. 50 00:07:30,241 --> 00:07:35,205 As their nest floods, the colony seems to be doomed. 51 00:07:43,588 --> 00:07:47,384 But from chaos comes order. 52 00:07:49,427 --> 00:07:53,890 The fire ants band together, each locking legs with its neighbours. 53 00:07:57,227 --> 00:07:59,813 They're building a living raft. 54 00:08:02,816 --> 00:08:08,697 Each ant is covered in fine hairs that trap air against its body. 55 00:08:13,034 --> 00:08:19,040 As the raft forms, this air creates a cushion for them all to float on. 56 00:08:22,252 --> 00:08:24,671 This is the power of the colony. 57 00:08:26,506 --> 00:08:29,884 By working together, they've become unsinkable. 58 00:08:34,597 --> 00:08:36,933 And no-one gets left behind. 59 00:08:50,363 --> 00:08:55,493 Pulled from the shallows, the colony is now at the mercy of the flood. 60 00:09:01,541 --> 00:09:03,585 Holding tight to the larvae 61 00:09:03,710 --> 00:09:06,838 and keeping their queen hidden at the centre of the raft, 62 00:09:06,963 --> 00:09:10,717 the colony drifts into deeper water... 63 00:09:16,598 --> 00:09:22,270 where they're vulnerable to fish that now swim through the flooded forest. 64 00:09:28,359 --> 00:09:34,199 Those that lose their grip must get back to the safety of the raft. 65 00:09:46,169 --> 00:09:50,173 With jaws that join to become a surgical needle, 66 00:09:50,298 --> 00:09:54,094 this pond skater could suck an ant dry. 67 00:10:05,814 --> 00:10:12,237 But together, the colony is strong, and it's time to repel boarders. 68 00:10:24,165 --> 00:10:27,752 The ants can travel like this for weeks. 69 00:10:30,839 --> 00:10:34,342 They've even come to depend on the flood to carry them 70 00:10:34,467 --> 00:10:36,803 to new feeding grounds. 71 00:10:50,400 --> 00:10:54,529 At last, the ants can make their raft secure. 72 00:11:00,618 --> 00:11:03,955 Surging forward, they claim their new home... 73 00:11:05,165 --> 00:11:08,626 evicting current tenants without hesitation. 74 00:11:12,797 --> 00:11:16,259 One of the first to safety is their larval queen, 75 00:11:16,384 --> 00:11:18,928 carried from the heart of the raft. 76 00:11:26,019 --> 00:11:30,023 This palm will be their home for the next three months, 77 00:11:30,148 --> 00:11:35,111 until the floodwaters recede and they can head back underground. 78 00:11:49,125 --> 00:11:52,462 The average temperature of our planet hasn't varied 79 00:11:52,587 --> 00:11:57,383 by more than a single degree Celsius in 10,000 years. 80 00:11:59,135 --> 00:12:02,013 This has made our climate stable, 81 00:12:02,138 --> 00:12:05,558 allowing animals to fine-tune their behaviour 82 00:12:05,683 --> 00:12:09,062 around predictable weather patterns. 83 00:12:12,148 --> 00:12:14,192 October in the Amazon. 84 00:12:16,319 --> 00:12:18,655 The heaviest rains have come to an end, 85 00:12:18,780 --> 00:12:23,660 and the falling river level exposes a new landscape. 86 00:12:26,329 --> 00:12:31,876 Three weeks ago, these mile-wide sandbars didn't exist. 87 00:12:34,337 --> 00:12:38,758 In another three months, they'll be back under water. 88 00:12:41,344 --> 00:12:47,767 But now they provide a crucial opportunity for giant river turtles. 89 00:12:50,561 --> 00:12:55,608 They've been coming here at precisely this time of year for generations. 90 00:13:00,822 --> 00:13:06,119 50,000 of them - a quarter of the world's population. 91 00:13:10,581 --> 00:13:12,542 They're all here for one reason. 92 00:13:14,335 --> 00:13:19,966 But their window of opportunity is short, so timing is everything. 93 00:13:25,054 --> 00:13:30,935 Scaling the three-metre-high banks will take this female higher and drier 94 00:13:31,060 --> 00:13:33,730 than she's been for months. 95 00:13:36,024 --> 00:13:39,736 She's come here to lay her eggs. 96 00:13:41,321 --> 00:13:43,364 But others have beaten her to it. 97 00:13:54,417 --> 00:14:00,381 The early arrivals have already claimed nearly every inch of the beach... 98 00:14:01,632 --> 00:14:04,177 and there are still many more turtles to come. 99 00:14:10,391 --> 00:14:14,354 Wherever she turns, the space is taken. 100 00:14:23,571 --> 00:14:27,575 But being fashionably late does have an advantage. 101 00:14:30,870 --> 00:14:32,622 Had she arrived earlier, 102 00:14:32,747 --> 00:14:38,294 her eggs might have been dug up by those searching for somewhere to lay. 103 00:14:43,633 --> 00:14:46,177 She's found her spot. 104 00:14:53,351 --> 00:14:57,939 Settling down, she lays nearly 100 eggs. 105 00:15:02,819 --> 00:15:06,531 Burying them keeps them safe from predators, 106 00:15:06,656 --> 00:15:10,284 and the warm sand incubates the clutch. 107 00:15:17,917 --> 00:15:23,548 They must hatch before the river rises again and floods the sandbar. 108 00:15:28,136 --> 00:15:32,223 Any turtles that lay after her may have left it too late. 109 00:15:39,730 --> 00:15:42,900 Hopefully, she has got her timing right. 110 00:15:57,039 --> 00:16:02,211 Two months on, and the hatchlings emerge into the world. 111 00:16:12,555 --> 00:16:16,350 They were laid at the perfect time. 112 00:16:16,476 --> 00:16:18,895 Hundreds scramble for the river 113 00:16:19,020 --> 00:16:21,355 just as the water starts to rise. 114 00:16:23,649 --> 00:16:26,527 Those still to hatch aren't so lucky. 115 00:16:33,326 --> 00:16:36,787 This year, the heavy rains have returned early. 116 00:16:59,310 --> 00:17:02,313 The nesting beach is beginning to flood. 117 00:17:10,905 --> 00:17:14,033 Most hatchlings can escape in time. 118 00:17:22,124 --> 00:17:24,502 Those still below ground... 119 00:17:25,878 --> 00:17:28,047 will drown in their nests. 120 00:17:33,553 --> 00:17:38,474 For thousands of years, giant river turtles have timed their breeding 121 00:17:38,599 --> 00:17:42,645 around the Amazon's reliable cycles of rain. 122 00:17:46,482 --> 00:17:49,819 But today, our weather is changing. 123 00:17:54,699 --> 00:18:01,247 Disastrous early floods like this used to happen once every 20 years. 124 00:18:01,372 --> 00:18:06,794 Now the turtles have to deal with them every four. 125 00:18:21,976 --> 00:18:25,980 Winds may carry huge amounts of rain to the Amazon, 126 00:18:26,105 --> 00:18:31,235 but they don't provide this service to every corner of the planet. 127 00:18:32,987 --> 00:18:39,493 A third of the land receives less than 25 centimetres of rain a year. 128 00:18:44,457 --> 00:18:49,879 Deserts are scarred by desiccating winds and baked by the sun. 129 00:18:53,049 --> 00:18:58,554 But even weather as challenging as this can be perfect for the locals. 130 00:19:04,310 --> 00:19:08,189 As darkness falls in the coastal deserts of South Africa, 131 00:19:08,314 --> 00:19:11,067 the dunes come alive... 132 00:19:12,818 --> 00:19:17,073 with the call of a surprising desert dweller. 133 00:19:38,135 --> 00:19:42,515 A rain frog - not what you'd expect 134 00:19:42,640 --> 00:19:47,853 in a place that gets just seven centimetres of rain a year. 135 00:19:52,775 --> 00:19:56,779 To survive here, she has to avoid the heat of the day 136 00:19:56,904 --> 00:19:58,906 buried in the sand. 137 00:20:01,617 --> 00:20:07,331 But each night, she heads out on her hunt for moisture. 138 00:20:11,293 --> 00:20:15,798 Short stumpy legs and a plump body are ideal for digging... 139 00:20:18,843 --> 00:20:21,929 but not so good for getting around. 140 00:20:25,975 --> 00:20:32,565 She can't hop, so she waddles across the dunes. 141 00:20:40,322 --> 00:20:44,744 The world's slowest steeplechaser. 142 00:20:49,123 --> 00:20:53,419 Obstacles are tackled with dogged perseverance. 143 00:21:00,718 --> 00:21:05,431 She can travel a whopping 38 metres a night, 144 00:21:05,556 --> 00:21:10,978 no mean feat when you're the same size and shape as a marshmallow. 145 00:21:16,984 --> 00:21:18,819 Termites. 146 00:21:18,944 --> 00:21:22,490 They are 75% water... 147 00:21:23,783 --> 00:21:26,869 a meal and a drink in one. 148 00:21:30,956 --> 00:21:34,794 But she's not the most agile predator. 149 00:21:37,129 --> 00:21:41,217 Maybe if they just came a little closer... 150 00:21:45,846 --> 00:21:47,306 Oh, dear. 151 00:21:49,892 --> 00:21:52,770 Perhaps if they stop moving... 152 00:22:14,667 --> 00:22:16,043 At last! 153 00:22:17,711 --> 00:22:21,590 But now she has another challenge. 154 00:22:21,715 --> 00:22:28,138 To swallow her food, she must squash in her eyeballs to push it down her throat. 155 00:22:37,481 --> 00:22:39,525 Termites may be juicy, 156 00:22:39,650 --> 00:22:43,529 but they don't provide her with quite enough water to survive. 157 00:22:47,449 --> 00:22:49,785 It rarely rains here, 158 00:22:49,910 --> 00:22:55,499 but coastal deserts do get another reliable source of moisture. 159 00:23:07,219 --> 00:23:08,220 At night, 160 00:23:08,345 --> 00:23:11,599 cool moist air is blown in from the ocean, 161 00:23:11,724 --> 00:23:16,061 forming fog banks that shroud the desert in mist. 162 00:23:28,407 --> 00:23:33,287 It condenses on vegetation, wetting the sand beneath. 163 00:23:33,412 --> 00:23:38,959 So it's here that she waits, absorbing moisture through her skin. 164 00:23:47,343 --> 00:23:50,763 Rain frogs are so dependent on this water 165 00:23:50,888 --> 00:23:57,519 that they can only survive in places with at least 100 days of fog a year. 166 00:23:59,897 --> 00:24:05,069 And on the foggiest nights, when other frogs have emerged onto the dunes, 167 00:24:05,194 --> 00:24:09,198 she takes her opportunity to find love. 168 00:24:16,914 --> 00:24:20,876 Male rain frogs are smaller than the females, 169 00:24:21,001 --> 00:24:26,131 and his stubby legs make it hard to hold on, 170 00:24:26,256 --> 00:24:30,636 so he glues himself onto her back. 171 00:24:42,439 --> 00:24:47,444 Still locked in their embrace, the pair head back beneath the sand, 172 00:24:47,569 --> 00:24:52,700 where they'll lay their eggs, safe from the heat of the desert sun. 173 00:25:01,500 --> 00:25:05,212 But there's one desert that gets so cold 174 00:25:05,337 --> 00:25:09,550 that liquid water simply can't exist. 175 00:25:12,469 --> 00:25:16,473 Winter in Mongolia's Gobi Desert... 176 00:25:18,100 --> 00:25:21,103 40 degrees below freezing. 177 00:25:23,939 --> 00:25:28,777 One of the driest and most extreme environments in the world. 178 00:25:35,659 --> 00:25:39,496 Most animals can't survive weather like this... 179 00:25:42,124 --> 00:25:48,047 but there's one unique mammal that manages to eke out a living here. 180 00:25:50,841 --> 00:25:52,843 The Gobi is home 181 00:25:52,968 --> 00:25:57,848 to the last 1,000 wild Bactrian camels on Earth... 182 00:26:00,100 --> 00:26:03,020 surviving at the very edge of what's possible. 183 00:26:06,815 --> 00:26:12,905 Even camels need moisture, but any water here is now frozen solid. 184 00:26:16,992 --> 00:26:20,162 It's down to the bull to find a solution. 185 00:26:27,377 --> 00:26:33,425 Setting off with his herd, his search could cover thousands of square miles. 186 00:26:39,765 --> 00:26:44,645 Driving them forward, he can keep going for days on end. 187 00:26:55,864 --> 00:26:59,243 Herds come together from across their vast range... 188 00:27:00,994 --> 00:27:03,288 all looking for the same thing. 189 00:27:12,214 --> 00:27:18,095 These long-distance specialists can smell moisture from 30 miles away... 190 00:27:19,179 --> 00:27:21,140 and they've picked up a scent. 191 00:27:26,478 --> 00:27:30,524 Even in the Gobi, one of the driest places on Earth, 192 00:27:30,649 --> 00:27:35,154 wind can provide a rare source of moisture. 193 00:27:37,406 --> 00:27:41,660 Snow is blown to this desert from Siberia. 194 00:27:43,704 --> 00:27:49,001 Where it settles is impossible to predict, and it may not last long. 195 00:27:56,508 --> 00:28:01,847 But for now, at least, this bull has found what he's been searching for. 196 00:28:12,566 --> 00:28:14,526 In the cold, dry air, 197 00:28:14,651 --> 00:28:16,737 snow doesn't melt... 198 00:28:18,864 --> 00:28:21,158 so it must be eaten. 199 00:28:30,709 --> 00:28:35,047 The Gobi's windblown snow is a lifeline 200 00:28:35,172 --> 00:28:38,425 that will sustain his herd throughout the winter. 201 00:28:46,767 --> 00:28:50,020 Even in this most hostile of places, 202 00:28:50,145 --> 00:28:54,608 weather still provides just enough for survival. 203 00:29:06,954 --> 00:29:11,250 The largest, most unpredictable weather on the planet 204 00:29:11,375 --> 00:29:14,419 starts far out at sea. 205 00:29:19,925 --> 00:29:24,471 Hurricanes, typhoons and tropical cyclones 206 00:29:24,596 --> 00:29:28,433 are violent, short-lived megastorms. 207 00:29:30,102 --> 00:29:33,188 But there's a far more reliable weather system 208 00:29:33,313 --> 00:29:35,524 that originates over the ocean... 209 00:29:36,733 --> 00:29:41,238 one that is eagerly anticipated by all in its path. 210 00:29:44,408 --> 00:29:51,164 Monsoons are seasonal winds that blow at the same time each year... 211 00:29:53,750 --> 00:29:58,714 and they carry colossal amounts of water from the ocean to the land. 212 00:30:06,596 --> 00:30:08,181 Christmas Island. 213 00:30:09,766 --> 00:30:13,186 A remote speck of rock in the Indian Ocean. 214 00:30:18,108 --> 00:30:24,448 For the last four months, its forest interior has remained dry and dusty. 215 00:30:27,617 --> 00:30:31,663 Life here is waiting for change. 216 00:30:35,042 --> 00:30:40,047 In November, the first storms of the monsoon reach the island. 217 00:30:58,440 --> 00:31:02,944 They're a welcome relief for those that have suffered through the dry. 218 00:31:07,783 --> 00:31:12,954 And they are vital for the island's most numerous residents. 219 00:31:27,469 --> 00:31:31,139 The red crabs of Christmas Island. 220 00:31:34,726 --> 00:31:39,272 They've spent the dry season sheltering in damp burrows 221 00:31:39,398 --> 00:31:40,899 beneath the leaf litter. 222 00:31:44,444 --> 00:31:48,490 Crabs breathe through gills that must be kept moist. 223 00:31:53,537 --> 00:31:56,832 So it's only with the return of the annual monsoon 224 00:31:56,957 --> 00:32:01,253 that these land crabs can finally emerge. 225 00:32:08,927 --> 00:32:15,225 With the humidity now high enough, they can begin an epic trek to the coast. 226 00:32:28,113 --> 00:32:33,326 Every red crab comes together from across the island, 227 00:32:33,452 --> 00:32:36,204 and they do so in their millions. 228 00:32:37,664 --> 00:32:41,209 50 million, to be precise. 229 00:32:55,891 --> 00:33:01,897 They've come to release their eggs that can only develop in the ocean. 230 00:33:03,356 --> 00:33:06,318 There's just one small problem. 231 00:33:07,402 --> 00:33:08,945 They may be crabs... 232 00:33:10,280 --> 00:33:12,449 but they can't swim. 233 00:33:16,411 --> 00:33:18,830 They're scared of the sea. 234 00:33:33,345 --> 00:33:35,388 But they don't have a choice. 235 00:33:37,057 --> 00:33:41,353 They must release their eggs on the highest tide. 236 00:33:48,026 --> 00:33:51,947 Each carries around 100,000 eggs, 237 00:33:52,072 --> 00:33:54,783 so over just two or three nights, 238 00:33:54,908 --> 00:33:58,161 trillions are released into the ocean... 239 00:34:00,705 --> 00:34:04,459 though some are more successful than others. 240 00:34:30,527 --> 00:34:35,448 Once their work is done, the crabs will return to the forest. 241 00:34:52,966 --> 00:34:55,885 Then, four weeks later, 242 00:34:56,011 --> 00:34:58,722 on the next highest tide... 243 00:35:03,977 --> 00:35:06,271 having hatched out to sea, 244 00:35:06,396 --> 00:35:11,860 a new generation of red crabs returns to the same beach. 245 00:35:13,403 --> 00:35:15,822 In good years like this one, 246 00:35:15,947 --> 00:35:20,118 countless millions arrive back on the shores of Christmas Island, 247 00:35:20,243 --> 00:35:22,787 turning the beaches red. 248 00:35:40,722 --> 00:35:45,560 Like their parents, they also need moisture in the air to breathe... 249 00:35:48,229 --> 00:35:50,482 so before the rains move on, 250 00:35:50,607 --> 00:35:56,738 the young crabs must undertake their own epic journey into the forest, 251 00:35:56,863 --> 00:36:00,367 where they'll wait out the next few months of dry. 252 00:36:21,554 --> 00:36:23,348 The Christmas Island crab - 253 00:36:23,473 --> 00:36:28,561 entirely reliant on the return of the monsoon. 254 00:36:39,864 --> 00:36:45,995 The annual rhythms of the weather shape life across our planet. 255 00:36:48,540 --> 00:36:50,792 In some parts of the world, 256 00:36:50,917 --> 00:36:53,545 seasonal cycles of wet and dry 257 00:36:53,670 --> 00:36:55,588 can bring dramatic change. 258 00:36:58,425 --> 00:37:03,346 And there are few places where this is more apparent than Southern Africa. 259 00:37:10,854 --> 00:37:12,856 The Zambezi River. 260 00:37:14,774 --> 00:37:21,281 It flows across six countries and drains half a million square miles. 261 00:37:35,754 --> 00:37:38,840 At the peak of the wet season, 262 00:37:38,965 --> 00:37:42,051 5,000 tonnes of water cascade 263 00:37:42,177 --> 00:37:45,388 over Victoria Falls every second. 264 00:37:48,349 --> 00:37:52,187 And yet, each year when the rains stop, 265 00:37:52,312 --> 00:37:55,398 these falls run dry. 266 00:38:03,573 --> 00:38:07,243 It's almost as if someone turns off the tap. 267 00:38:12,832 --> 00:38:14,083 May. 268 00:38:17,796 --> 00:38:19,506 December. 269 00:38:22,967 --> 00:38:24,469 Wet season. 270 00:38:28,556 --> 00:38:30,391 Dry season. 271 00:38:32,435 --> 00:38:37,148 It's happened like this for thousands of years. 272 00:38:42,904 --> 00:38:47,867 But there are signs that the weather here is changing. 273 00:38:48,993 --> 00:38:50,245 In recent years, 274 00:38:50,370 --> 00:38:56,167 the volume of water flowing over Victoria Falls has dropped by half... 275 00:39:01,005 --> 00:39:04,342 a concern for animals that have come to rely on 276 00:39:04,467 --> 00:39:08,179 the natural rhythms of wet and dry. 277 00:39:21,693 --> 00:39:27,949 Zambia's Luangwa River is a major tributary of the Zambezi. 278 00:39:29,784 --> 00:39:32,912 Every year, as the dry season takes hold, 279 00:39:33,037 --> 00:39:36,583 it dwindles into pools. 280 00:39:39,627 --> 00:39:43,423 Accommodation starts to get tight for the locals. 281 00:39:47,468 --> 00:39:52,432 With no other water around, the river becomes a magnet for visitors. 282 00:39:58,855 --> 00:40:03,359 Millions of red-billed quelea flock to the water's edge. 283 00:40:08,364 --> 00:40:12,327 These seed-eaters need to drink every day... 284 00:40:32,221 --> 00:40:34,933 and Nile crocodiles know it. 285 00:40:36,601 --> 00:40:38,978 They may not have eaten for six months. 286 00:40:40,396 --> 00:40:45,276 For them, the dry season is the start of the good times. 287 00:40:55,411 --> 00:41:00,083 And they are not the only ones to depend on this time of year. 288 00:41:05,797 --> 00:41:09,801 Carmine bee-eaters have flown hundreds of miles 289 00:41:09,926 --> 00:41:12,762 from the rainforests of the Congo... 290 00:41:14,013 --> 00:41:17,016 arriving at the peak of the dry season, 291 00:41:17,141 --> 00:41:22,480 when steep sandbanks are exposed by the falling water. 292 00:41:28,653 --> 00:41:34,367 They're a perfect place to nest, out of reach of predators from above. 293 00:41:44,711 --> 00:41:50,133 Bee-eater burrows can extend for two metres into the soft river sand. 294 00:41:51,384 --> 00:41:54,512 Already home to 6,000 nests, 295 00:41:54,637 --> 00:41:59,642 real estate at Bee-eater Towers is in high demand. 296 00:42:03,813 --> 00:42:07,567 But it pays not to build too close to the neighbours. 297 00:42:18,911 --> 00:42:23,708 As more birds arrive, competition for the best nesting sites heats up. 298 00:42:35,678 --> 00:42:37,513 It's thirsty work. 299 00:42:48,649 --> 00:42:52,945 In the sudden commotion, they're vulnerable from below... 300 00:42:55,156 --> 00:42:56,365 and above. 301 00:43:00,953 --> 00:43:03,372 African fish eagles. 302 00:43:12,048 --> 00:43:14,926 They are permanent residents here. 303 00:43:15,051 --> 00:43:20,098 But at this time of the year, they don't just eat fish. 304 00:43:24,644 --> 00:43:28,231 The safest place to be is inside a burrow. 305 00:43:30,191 --> 00:43:36,072 But an eagle fly-by sends shockwaves of panic through the colony. 306 00:43:48,543 --> 00:43:54,590 The eagle's strategy is to pin their prey against the river bank. 307 00:43:59,095 --> 00:44:04,016 With the colony in disarray, the predators have the advantage. 308 00:44:46,392 --> 00:44:50,396 These fish eagles also choose to breed in the dry season 309 00:44:50,521 --> 00:44:54,775 because they need the bee-eaters as food for their chicks. 310 00:45:02,658 --> 00:45:07,747 But this year's dry season shows no sign of letting up. 311 00:45:15,796 --> 00:45:18,841 Parts of the river are now bone dry, 312 00:45:18,966 --> 00:45:22,970 forcing huge male hippos from their home. 313 00:45:34,190 --> 00:45:35,983 With nowhere left to turn, 314 00:45:36,108 --> 00:45:40,112 they must converge on the few remaining patches of water. 315 00:45:41,864 --> 00:45:44,951 But these are already occupied. 316 00:45:57,421 --> 00:45:59,966 The resident bull here 317 00:46:00,091 --> 00:46:04,595 can't tolerate another big male in his shrinking pool. 318 00:46:36,210 --> 00:46:38,963 The newcomer is banished. 319 00:46:51,309 --> 00:46:54,186 Still, the sun bakes the land... 320 00:46:57,148 --> 00:47:01,068 with devastating consequences. 321 00:47:34,018 --> 00:47:37,146 Hundreds of nests are wiped out. 322 00:47:45,571 --> 00:47:49,658 Southern Africa has experienced dry seasons 323 00:47:49,784 --> 00:47:52,787 for thousands of years. 324 00:47:53,954 --> 00:47:56,707 But this is something different. 325 00:48:01,545 --> 00:48:07,968 Record high temperatures and the lowest rainfall in nearly 40 years 326 00:48:08,094 --> 00:48:14,141 have thrown parts of Africa into one of the worst droughts in a century. 327 00:48:29,448 --> 00:48:35,287 Across the planet, our once stable climate is changing. 328 00:48:40,835 --> 00:48:43,003 Weather is less reliable... 329 00:48:45,798 --> 00:48:48,926 and is getting more extreme. 330 00:48:52,930 --> 00:48:55,599 Wildfires are becoming more frequent. 331 00:49:12,616 --> 00:49:15,035 Droughts are more intense. 332 00:49:26,505 --> 00:49:30,968 And storms are more ferocious. 333 00:49:34,847 --> 00:49:40,311 All this from a recent rise in global temperatures 334 00:49:40,436 --> 00:49:43,439 of just a single degree Celsius. 335 00:49:45,065 --> 00:49:48,777 Yet if climate change continues unchecked, 336 00:49:48,903 --> 00:49:54,992 we may see a rise of almost five degrees by the end of the century. 337 00:49:57,036 --> 00:50:01,540 We can only imagine what this will do to our weather.