1 00:00:17,600 --> 00:00:20,280 Birds are masters of the skies. 2 00:00:23,120 --> 00:00:26,360 There are more than 10,000 species 3 00:00:26,360 --> 00:00:30,040 and they behave in a huge variety of different ways. 4 00:00:34,000 --> 00:00:36,520 But of all the birds I've filmed over the years, 5 00:00:36,520 --> 00:00:40,240 there's nothing that can really compare with these comic characters. 6 00:00:42,840 --> 00:00:45,920 That's not just because of their great size. 7 00:00:45,920 --> 00:00:48,560 But because they can't do the one thing 8 00:00:48,560 --> 00:00:50,880 that birds are famous for doing. 9 00:00:50,880 --> 00:00:52,600 They can't fly. 10 00:00:54,800 --> 00:00:58,800 The ostrich, the emu and the rhea, together with two other birds, 11 00:00:58,800 --> 00:01:00,920 the kiwi and the cassowary, 12 00:01:00,920 --> 00:01:03,440 are the court jesters of the avian world. 13 00:01:05,880 --> 00:01:09,440 They're a family with a remarkable success story, 14 00:01:09,440 --> 00:01:13,080 despite having never flown a day in their lives. 15 00:01:17,800 --> 00:01:21,880 But exactly how and why did these birds abandon flight? 16 00:01:23,680 --> 00:01:26,320 It's one of the natural world's great mysteries 17 00:01:26,320 --> 00:01:29,560 and it's taxed some of the finest minds in science 18 00:01:29,560 --> 00:01:33,000 from Darwin's time right through to the present day. 19 00:01:36,880 --> 00:01:40,160 And now, DNA is promising to give us the answer. 20 00:01:42,400 --> 00:01:44,080 But what is even more exciting 21 00:01:44,080 --> 00:01:47,600 than the remarkable evolutionary history of these birds 22 00:01:47,600 --> 00:01:49,240 is their behaviour - 23 00:01:49,240 --> 00:01:51,920 because if you're a bird that can't fly, 24 00:01:51,920 --> 00:01:54,960 you have to find other ways of surviving. 25 00:02:02,840 --> 00:02:05,200 BIRDSONG 26 00:02:06,800 --> 00:02:09,760 It's said that a bird is three things - 27 00:02:11,000 --> 00:02:13,960 feathers, 28 00:02:13,960 --> 00:02:16,480 flight 29 00:02:16,480 --> 00:02:19,120 and song. 30 00:02:19,120 --> 00:02:21,360 BIRDS CHIRP 31 00:02:23,600 --> 00:02:26,440 But what happens if you are a bird which can't fly, 32 00:02:26,440 --> 00:02:28,880 which doesn't sing... 33 00:02:28,880 --> 00:02:31,120 HISSING 34 00:02:32,320 --> 00:02:34,840 ..and whose feathers are closer to fluff? 35 00:02:37,000 --> 00:02:38,800 Well, then you have to come up with 36 00:02:38,800 --> 00:02:42,000 some pretty unusual ways of surviving. 37 00:02:46,320 --> 00:02:49,680 This small group of birds are real oddballs, 38 00:02:49,680 --> 00:02:52,080 with a rag bag of characteristics 39 00:02:52,080 --> 00:02:54,560 that help them with life on the ground. 40 00:02:57,880 --> 00:03:01,560 Among their number is the fastest bird on land. 41 00:03:03,680 --> 00:03:07,360 A bird with the biggest eyes on Earth. 42 00:03:07,360 --> 00:03:11,360 One has dagger-sharp talons. 43 00:03:11,360 --> 00:03:13,480 Another, killer thighs. 44 00:03:16,200 --> 00:03:18,120 OSTRICH HISSES 45 00:03:21,520 --> 00:03:25,320 Their chicks hatch, ready to run. 46 00:03:25,320 --> 00:03:27,520 CHICKS GRUNT SOFTLY 47 00:03:29,840 --> 00:03:32,840 And they all have crazy hair. 48 00:03:37,520 --> 00:03:39,760 And useless wings. 49 00:03:42,360 --> 00:03:45,080 This lot couldn't fly even if they wanted to 50 00:03:45,080 --> 00:03:49,120 because their feathers aren't like those of other birds. 51 00:03:49,120 --> 00:03:52,960 They don't have barbs that link together into air-cutting vanes, 52 00:03:52,960 --> 00:03:55,040 like normal wing feathers. 53 00:03:56,880 --> 00:03:59,880 Nor can they be held neatly and tightly together. 54 00:03:59,880 --> 00:04:02,280 They are more like a fluffy feather boa. 55 00:04:05,840 --> 00:04:09,360 Without a role in flight, these feathers act instead 56 00:04:09,360 --> 00:04:13,680 as warm blankets or insect repellers 57 00:04:13,680 --> 00:04:16,720 or props in an exotic dance. 58 00:04:20,800 --> 00:04:24,480 But if you are a bird that hasn't flown a day in its life, 59 00:04:24,480 --> 00:04:27,320 then beauty isn't enough to survive. 60 00:04:31,040 --> 00:04:35,200 The first, the fastest and the biggest of all our birds 61 00:04:35,200 --> 00:04:36,640 is the ostrich. 62 00:04:36,640 --> 00:04:40,960 OSTRICH BOOMS 63 00:04:40,960 --> 00:04:44,960 Indeed, it's the largest bird in the world. 64 00:04:46,960 --> 00:04:51,240 Standing up to 3 metres tall, it weighs up to 150 kilos. 65 00:04:57,960 --> 00:05:00,400 On the African plains, it lives alongside 66 00:05:00,400 --> 00:05:03,440 some of the world's most dangerous predators... 67 00:05:08,120 --> 00:05:09,560 ..hyenas... 68 00:05:11,640 --> 00:05:13,200 ..lions... 69 00:05:15,520 --> 00:05:17,080 ..and cheetahs. 70 00:05:20,040 --> 00:05:22,360 BIRDS CHIRP 71 00:05:28,640 --> 00:05:32,040 DRAMATIC MUSIC 72 00:05:33,120 --> 00:05:35,120 Pounding across the plains, 73 00:05:35,120 --> 00:05:38,800 it uses its powerful legs to run for its life. 74 00:05:45,080 --> 00:05:47,320 DRAMATIC MUSIC 75 00:05:47,320 --> 00:05:49,560 Adult birds can run at speeds 76 00:05:49,560 --> 00:05:53,360 of up to 70km - over 40 miles - an hour, 77 00:05:53,360 --> 00:05:56,480 covering almost 5 metres in a single stride. 78 00:06:04,080 --> 00:06:07,240 DRAMATIC MUSIC 79 00:06:26,920 --> 00:06:29,760 DRAMATIC MUSIC CLIMAXES 80 00:06:32,840 --> 00:06:35,680 This young ostrich hadn't quite developed 81 00:06:35,680 --> 00:06:37,720 the power or agility needed 82 00:06:37,720 --> 00:06:40,760 to escape these speediest of predators. 83 00:06:44,440 --> 00:06:47,440 But it still took the combined skill and experience 84 00:06:47,440 --> 00:06:50,480 of a team of cheetahs, working together, 85 00:06:50,480 --> 00:06:53,440 to bring the young ostrich down. 86 00:06:53,440 --> 00:06:54,960 CHEETAH GROWLS 87 00:06:56,880 --> 00:07:00,640 This is, nonetheless, a remarkable and very rare sight. 88 00:07:00,640 --> 00:07:02,280 CHEETAH PANTS 89 00:07:02,280 --> 00:07:06,120 Most ostriches escape from such attacks. 90 00:07:10,720 --> 00:07:14,760 Adult ostriches are powerhouses of strength and agility 91 00:07:14,760 --> 00:07:17,120 and are seldom caught by predators. 92 00:07:22,160 --> 00:07:25,040 BIRDS CHIRP AND WHOOP 93 00:07:25,040 --> 00:07:29,080 The second of our birds also has size and speed on its side. 94 00:07:31,560 --> 00:07:34,560 But for the biggest bird in South America, 95 00:07:34,560 --> 00:07:36,640 there is danger of a different kind. 96 00:07:42,920 --> 00:07:45,520 LATIN GUITAR MUSIC 97 00:07:51,040 --> 00:07:54,720 This Argentinian rhea has grown big - 98 00:07:54,720 --> 00:07:57,920 indeed, bigger than most of the mammals that live here. 99 00:08:06,480 --> 00:08:10,040 But this male has nonetheless to remain alert... 100 00:08:12,160 --> 00:08:14,600 ..from attacks from one of his own kind. 101 00:08:21,720 --> 00:08:24,120 It's the beginning of the breeding season 102 00:08:24,120 --> 00:08:29,200 and males are starting to spar, sizing up their rivals' strength 103 00:08:29,200 --> 00:08:31,760 before the real battle to breed begins. 104 00:08:36,120 --> 00:08:38,760 RHEAS GRUNT 105 00:08:40,800 --> 00:08:43,640 MUSIC CONTINUES 106 00:08:52,000 --> 00:08:55,640 To the winner, TWO females. 107 00:08:55,640 --> 00:08:58,280 But although this fight has been won, 108 00:08:58,280 --> 00:09:02,720 the coming war will doubtless see him forced to defend his gains. 109 00:09:07,400 --> 00:09:10,240 CRICKETS CHIRP, INSECTS BUZZ 110 00:09:12,480 --> 00:09:14,840 DIDGERIDOO PLAYS 111 00:09:15,920 --> 00:09:18,160 Here in the Australian outback 112 00:09:18,160 --> 00:09:22,080 roams the second-largest of our big birds, 113 00:09:22,080 --> 00:09:23,440 the emu. 114 00:09:34,560 --> 00:09:39,280 A nomadic character, he uses his spectacularly elongated legs 115 00:09:39,280 --> 00:09:42,560 and ferocious-looking feet to go walkabout... 116 00:09:46,200 --> 00:09:49,160 ..meaning he can cover vast distances 117 00:09:49,160 --> 00:09:51,280 in search of food and water. 118 00:09:53,720 --> 00:09:56,360 BANJO PLAYS 119 00:10:06,320 --> 00:10:09,480 Emu truly are wanderers - 120 00:10:09,480 --> 00:10:12,400 always on the move, following the rains, 121 00:10:12,400 --> 00:10:14,360 they walk hundreds of kilometres. 122 00:10:26,720 --> 00:10:31,080 And when they find water, they take on board all they can. 123 00:10:33,120 --> 00:10:35,880 BIRDS CHIRP, INSECTS BUZZ 124 00:10:39,200 --> 00:10:42,040 But flightless birds in Australia 125 00:10:42,040 --> 00:10:44,520 aren't restricted to the parched outback. 126 00:10:50,520 --> 00:10:53,840 In the tropical rainforests in the north of the country 127 00:10:53,840 --> 00:10:55,560 lives another one. 128 00:11:02,960 --> 00:11:07,680 It stands almost 2 metres tall and has a dinosaur-like crest 129 00:11:07,680 --> 00:11:11,320 and dagger-sharp claws that give it a lethal kick. 130 00:11:11,320 --> 00:11:14,040 DRAMATIC MUSIC 131 00:11:21,640 --> 00:11:23,680 Cassowaries are fiercely territorial. 132 00:11:25,360 --> 00:11:29,200 And one will fight to the death to defend itself 133 00:11:29,200 --> 00:11:32,240 or its magnificent emerald-green eggs. 134 00:11:58,960 --> 00:12:00,480 Like the rest of his family 135 00:12:00,480 --> 00:12:03,120 in Africa, South America and Australia, 136 00:12:03,120 --> 00:12:06,560 it's a bird which has taken an evolutionary route 137 00:12:06,560 --> 00:12:10,400 very different from that of its aeronautical relatives. 138 00:12:18,360 --> 00:12:21,200 Cassowaries vary greatly in colouration. 139 00:12:21,200 --> 00:12:24,840 So, it's debatable how many species there are. 140 00:12:24,840 --> 00:12:27,280 Probably three. 141 00:12:30,320 --> 00:12:33,040 Another flightless bird lives in New Zealand, 142 00:12:33,040 --> 00:12:35,880 hidden in the forests and only active at night. 143 00:12:37,520 --> 00:12:39,880 It could be called the runt of the litter. 144 00:12:46,400 --> 00:12:49,320 Standing only a half a metre or so tall, 145 00:12:49,320 --> 00:12:51,440 this is a kiwi. 146 00:12:55,720 --> 00:13:00,480 More like a mammal than a bird, it has dense, hair-like plumage 147 00:13:00,480 --> 00:13:03,440 and a very long, very sensitive beak, 148 00:13:03,440 --> 00:13:06,880 which makes up for its tiny and all but useless eyes. 149 00:13:10,960 --> 00:13:14,800 It walks along like a little hobbit, with its arms behind its back. 150 00:13:19,920 --> 00:13:21,480 When, in the 19th century, 151 00:13:21,480 --> 00:13:24,760 tales of the kiwi reached naturalists in England, 152 00:13:24,760 --> 00:13:28,800 they thought them merely figments of early travellers' imaginations. 153 00:13:36,280 --> 00:13:40,120 One of the largest collections of this weird walking family 154 00:13:40,120 --> 00:13:44,080 was amassed by a Victorian English eccentric, Walter Rothschild. 155 00:13:52,600 --> 00:13:57,480 Collectively, these extraordinary birds are known as the ratites, 156 00:13:57,480 --> 00:14:00,920 flightless birds that just grew and grew, 157 00:14:00,920 --> 00:14:03,160 from the smallest - that's the kiwi - 158 00:14:03,160 --> 00:14:07,920 to the largest alive today, the ostrich. 159 00:14:07,920 --> 00:14:11,400 But their ancient relatives were even more impressive. 160 00:14:15,760 --> 00:14:19,000 Enormous birds that would have towered over me, 161 00:14:19,000 --> 00:14:22,400 like the moa from New Zealand 162 00:14:22,400 --> 00:14:24,480 or the elephant bird from Madagascar. 163 00:14:29,640 --> 00:14:33,760 But exactly why did these birds abandon flight? 164 00:14:33,760 --> 00:14:36,960 Well, flying is a very energetic business, 165 00:14:36,960 --> 00:14:39,920 much more so than walking or running, 166 00:14:39,920 --> 00:14:43,840 and birds don't fly unless they have to. 167 00:14:43,840 --> 00:14:47,360 WAVES CRASH Some, like penguins, 168 00:14:47,360 --> 00:14:49,480 gave up flight relatively recently 169 00:14:49,480 --> 00:14:51,480 and took to the water. 170 00:14:51,480 --> 00:14:53,920 But they still have strong wings, 171 00:14:53,920 --> 00:14:56,560 which they use like paddles for swimming. 172 00:15:00,840 --> 00:15:04,480 The ratites are different. 173 00:15:04,480 --> 00:15:08,360 They are the original flightless birds. 174 00:15:08,360 --> 00:15:11,200 And they're the only birds whose skeletons 175 00:15:11,200 --> 00:15:14,040 make them incapable of flight. 176 00:15:14,040 --> 00:15:16,920 Hidden beneath their mass of feathery fluff 177 00:15:16,920 --> 00:15:19,520 is a flat, raft-like breastbone 178 00:15:19,520 --> 00:15:23,880 that lacks the ridge onto which flight muscles can be attached. 179 00:15:23,880 --> 00:15:26,840 In fact, it's this which gives them their name, 180 00:15:26,840 --> 00:15:29,880 from the Latin word, "ratis", meaning "raft". 181 00:15:31,400 --> 00:15:34,360 So, whilst there are other birds which don't fly, 182 00:15:34,360 --> 00:15:37,240 our very special family, the ratites, 183 00:15:37,240 --> 00:15:39,760 stand entirely apart from all the others. 184 00:15:41,280 --> 00:15:44,280 They are the Flintstones of the bird world, 185 00:15:44,280 --> 00:15:47,760 a group whose lineage can be traced back to the time 186 00:15:47,760 --> 00:15:50,000 when dinosaurs walked the Earth. 187 00:15:55,680 --> 00:15:57,880 The dinosaurs once dominated the land, 188 00:15:57,880 --> 00:16:01,600 just as their relatives, the pterosaurs, ruled the skies. 189 00:16:03,440 --> 00:16:07,880 But when, 66 million years ago, both groups were wiped out, 190 00:16:07,880 --> 00:16:10,520 some of the ancient birds seized their moment 191 00:16:10,520 --> 00:16:13,560 and made a bid to dominate the land themselves. 192 00:16:18,120 --> 00:16:23,120 Some, the ancestral ratites, grew big and fat, 193 00:16:23,120 --> 00:16:27,040 with long, strong legs, until one day, 194 00:16:27,040 --> 00:16:29,520 they were too heavy to fly. 195 00:16:32,960 --> 00:16:35,880 Since then, of course, the mammals have fought back 196 00:16:35,880 --> 00:16:38,760 and in most places, THEY won. 197 00:16:40,160 --> 00:16:42,960 But the elephant bird and the moa, now extinct, 198 00:16:42,960 --> 00:16:45,240 survived until a few centuries ago 199 00:16:45,240 --> 00:16:49,320 and five others still flourish across the southern hemisphere. 200 00:16:49,320 --> 00:16:51,320 The ostrich, the emu, 201 00:16:51,320 --> 00:16:53,760 the cassowary, the rhea 202 00:16:53,760 --> 00:16:56,200 and the kiwi. 203 00:17:02,400 --> 00:17:04,880 BIRDS CHIRP, INSECTS BUZZ 204 00:17:09,440 --> 00:17:13,080 The success of the ratites today is largely due to 205 00:17:13,080 --> 00:17:16,880 some bizarre breeding and very complicated relationships. 206 00:17:18,480 --> 00:17:21,200 Males mating with multiple females, 207 00:17:21,200 --> 00:17:24,480 females mating with multiple males, 208 00:17:24,480 --> 00:17:27,280 fathers raising chicks which aren't theirs. 209 00:17:29,760 --> 00:17:33,800 The tenacity and endurance of these dedicated dads 210 00:17:33,800 --> 00:17:37,640 has helped raise generations of walking giants. 211 00:17:39,920 --> 00:17:44,240 So, how do our motley crew ensure the survival of their offspring 212 00:17:44,240 --> 00:17:47,600 when safe tree-top nests are out of the question? 213 00:17:49,640 --> 00:17:51,680 Well, it takes a lot of work. 214 00:18:01,520 --> 00:18:04,680 For the emu in the Australian outback, 215 00:18:04,680 --> 00:18:06,840 the breeding season starts in the winter. 216 00:18:10,960 --> 00:18:14,640 This is when a male needs to be at his heaviest. 217 00:18:14,640 --> 00:18:16,960 DIDGERIDOO PLAYS 218 00:18:16,960 --> 00:18:20,800 Large bodies enable ratites to develop large guts, 219 00:18:20,800 --> 00:18:22,840 so unlike small flying birds, 220 00:18:22,840 --> 00:18:26,200 they can stock up on plenty of plants and seeds. 221 00:18:32,520 --> 00:18:37,360 Soon, he will mate and he will be the one who will incubate the eggs. 222 00:18:43,760 --> 00:18:47,320 During his time on the nest, he won't eat or drink. 223 00:18:47,320 --> 00:18:50,600 So, he's preparing for that by fattening up. 224 00:18:55,240 --> 00:18:58,320 This time of the year is all about finding food 225 00:18:58,320 --> 00:19:00,240 and some enterprising males 226 00:19:00,240 --> 00:19:02,960 even go into town to pick up dinner. 227 00:19:02,960 --> 00:19:05,000 CAR HORN BEEPS 228 00:19:08,080 --> 00:19:10,400 BANJO PLAYS 229 00:19:24,480 --> 00:19:26,920 TRUCK HORN BEEPS 230 00:19:32,160 --> 00:19:36,680 A strange sight - but the locals are used to it. 231 00:19:36,680 --> 00:19:38,920 TRUCK HORN BEEPS 232 00:19:51,120 --> 00:19:53,160 When they are ready to breed, 233 00:19:53,160 --> 00:19:56,600 male ratites start to try and impress females 234 00:19:56,600 --> 00:20:00,600 and they do so with some pretty flamboyant dance moves. 235 00:20:10,200 --> 00:20:13,880 Ratites might not be strong contenders in a beauty contest 236 00:20:13,880 --> 00:20:16,960 but these males certainly know how to move and groove. 237 00:20:20,760 --> 00:20:23,000 From the ostrich to the cassowary, 238 00:20:23,000 --> 00:20:26,040 the males all work hard to show off their best features. 239 00:20:34,800 --> 00:20:39,520 Just HOW hard can be seen on the grasslands of Argentina. 240 00:20:46,560 --> 00:20:50,640 It's spring and the rheas are preparing for the breeding season. 241 00:21:07,160 --> 00:21:11,160 Male rheas, with their distinctive black markings, have broken away 242 00:21:11,160 --> 00:21:14,280 from the flocks in which they spend the rest of the year. 243 00:21:16,000 --> 00:21:18,240 Now is the time for courtship, 244 00:21:18,240 --> 00:21:21,680 when their feathers will be shown off in all their splendour. 245 00:21:25,520 --> 00:21:30,040 As ratites no longer fly, they have no gland to produce the oil 246 00:21:30,040 --> 00:21:33,680 needed to preen their feathers into continuous air-catching services. 247 00:21:38,800 --> 00:21:40,600 But with a little grooming, 248 00:21:40,600 --> 00:21:42,920 their plumage can be very impressive. 249 00:21:50,800 --> 00:21:54,800 This male has managed to secure several females for himself. 250 00:22:03,720 --> 00:22:06,600 Herding them with his outstretched wings, 251 00:22:06,600 --> 00:22:12,480 a male can maintain a harem of anything from two to ten females, 252 00:22:12,480 --> 00:22:14,840 as long as he can keep them close. 253 00:22:22,040 --> 00:22:24,080 He doesn't let them out of his sight, 254 00:22:24,080 --> 00:22:27,000 courting each one in turn. 255 00:22:40,120 --> 00:22:43,560 And the grand finale of his mating ritual... 256 00:22:49,880 --> 00:22:53,160 ..this curious head-bobbing dance. 257 00:23:01,920 --> 00:23:04,480 It's hardly a tango. 258 00:23:09,040 --> 00:23:13,840 And the object of his affections doesn't seem particularly impressed. 259 00:23:23,400 --> 00:23:25,920 But despite the lack of encouragement, 260 00:23:25,920 --> 00:23:28,480 he will spend most of the breeding season 261 00:23:28,480 --> 00:23:32,520 herding and head-bobbing to his females, 262 00:23:32,520 --> 00:23:34,360 until they are ready to mate. 263 00:23:39,840 --> 00:23:42,000 Unless, of course... 264 00:23:43,480 --> 00:23:48,280 ..this rival male can rob him of his hard-won harem. 265 00:24:27,680 --> 00:24:29,600 Rising up as high as he can, 266 00:24:29,600 --> 00:24:32,280 he puts on a show of size and strength. 267 00:24:34,280 --> 00:24:37,120 This performance has rarely been filmed. 268 00:24:37,120 --> 00:24:40,600 It's a tango of a different, aggressive kind 269 00:24:40,600 --> 00:24:43,200 with plenty of Latin American spirit. 270 00:25:26,680 --> 00:25:30,120 Today, there is someone better than he. 271 00:25:39,000 --> 00:25:42,760 He retreats, leaving the rival male 272 00:25:42,760 --> 00:25:44,800 to take his place on the dance floor. 273 00:25:54,720 --> 00:25:58,960 This male is, it seems, a little more persuasive. 274 00:26:26,640 --> 00:26:28,920 Exactly how ratites mate 275 00:26:28,920 --> 00:26:31,800 was a mystery only solved by scientists 276 00:26:31,800 --> 00:26:33,920 in the last few years. 277 00:26:37,000 --> 00:26:40,200 Most birds don't have a penis. 278 00:26:40,200 --> 00:26:42,360 Instead, both the male and female birds 279 00:26:42,360 --> 00:26:44,680 have an opening called a cloaca. 280 00:26:52,200 --> 00:26:56,760 That certainly helps to streamline the body of a flying bird. 281 00:27:01,120 --> 00:27:04,200 The male ratite, however, is different. 282 00:27:04,200 --> 00:27:05,800 He does have a penis, 283 00:27:05,800 --> 00:27:08,120 and it was once assumed that these large birds 284 00:27:08,120 --> 00:27:10,800 would have blood-based erection systems, 285 00:27:10,800 --> 00:27:12,400 similar to humans. 286 00:27:16,360 --> 00:27:19,520 But in fact the ostrich, emu and rhea 287 00:27:19,520 --> 00:27:23,040 enlarge their penises with lymph fluid. 288 00:27:27,120 --> 00:27:31,600 They also have a few additional muscles to keep everything in place. 289 00:27:46,040 --> 00:27:49,080 While it's known that male and female rheas will mate 290 00:27:49,080 --> 00:27:53,160 with several different partners over the course of the breeding season, 291 00:27:53,160 --> 00:27:57,000 there is much less certainty with another of our ratite family. 292 00:28:14,640 --> 00:28:18,640 On the islands of New Zealand lives an enigma. 293 00:28:20,840 --> 00:28:23,320 The most secretive of our flightless birds. 294 00:28:26,640 --> 00:28:29,920 Hidden in these ancient and mysterious forests, 295 00:28:29,920 --> 00:28:32,520 it only emerges after dusk. 296 00:28:51,040 --> 00:28:53,400 HIGH-PITCHED BIRD CALL 297 00:29:03,000 --> 00:29:06,440 Only in the pitch-black dead of night does it call. 298 00:29:06,440 --> 00:29:09,080 HIGH-PITCHED CALLING 299 00:29:15,920 --> 00:29:18,080 Ratites might not sing, 300 00:29:18,080 --> 00:29:20,920 but their mating calls are certainly piercing. 301 00:29:23,680 --> 00:29:27,560 This is a bird which is heard but seldom seen. 302 00:29:27,560 --> 00:29:30,640 Scientists have to struggle to catch sight of the kiwi, 303 00:29:30,640 --> 00:29:33,080 let alone to understand its behaviour, 304 00:29:33,080 --> 00:29:35,120 even when they work around the clock. 305 00:29:40,000 --> 00:29:43,640 But using infrared light, which the kiwis can't see, 306 00:29:43,640 --> 00:29:47,240 and radio transmitters to track them in the darkness, 307 00:29:47,240 --> 00:29:49,920 the researchers here are slowly piecing together 308 00:29:49,920 --> 00:29:52,280 a picture of this shy bird. 309 00:29:57,160 --> 00:29:59,640 For the last 11 years, 310 00:29:59,640 --> 00:30:03,120 I have been looking at the breeding behaviour of Kiwi 311 00:30:03,120 --> 00:30:05,760 and everything that is associated with it. 312 00:30:07,400 --> 00:30:11,600 Dr Isabel Castro is a Colombian expert on kiwis 313 00:30:11,600 --> 00:30:14,720 who has lived in New Zealand for the past 25 years. 314 00:30:16,320 --> 00:30:18,200 This environment where they are 315 00:30:18,200 --> 00:30:20,800 is completely different than our environment. 316 00:30:20,800 --> 00:30:22,640 They are nocturnal where we are diurnal, 317 00:30:22,640 --> 00:30:25,800 and for many years before we started this research, 318 00:30:25,800 --> 00:30:29,120 people thought that they had this relatively boring life 319 00:30:29,120 --> 00:30:31,760 and yet as soon as we started this project, 320 00:30:31,760 --> 00:30:35,400 we started finding out these fantastic things 321 00:30:35,400 --> 00:30:37,480 about their intimate life. 322 00:30:38,800 --> 00:30:40,840 There have been all sorts of things 323 00:30:40,840 --> 00:30:42,800 that were completely unexpected, 324 00:30:42,800 --> 00:30:47,240 and that made now these birds very extraordinary, 325 00:30:47,240 --> 00:30:50,360 because we didn't know those things before. 326 00:30:54,440 --> 00:30:56,560 Living in complete darkness, 327 00:30:56,560 --> 00:31:00,240 unable to see virtually anything, the eyes of the kiwi 328 00:31:00,240 --> 00:31:02,040 are all but useless, 329 00:31:02,040 --> 00:31:04,240 but - unusually for a bird - 330 00:31:04,240 --> 00:31:06,520 it's got a great sense of smell, 331 00:31:06,520 --> 00:31:08,560 which it uses to find its way around. 332 00:31:17,400 --> 00:31:19,600 By setting up remote cameras, 333 00:31:19,600 --> 00:31:22,680 the scientists have been able to capture behaviour 334 00:31:22,680 --> 00:31:24,400 never filmed before in the wild. 335 00:31:26,200 --> 00:31:27,840 Two males fighting. 336 00:31:27,840 --> 00:31:29,880 KIWIS RASP 337 00:31:55,680 --> 00:31:58,720 A female calling for her mate. 338 00:31:58,720 --> 00:32:01,600 REPETITIVE GUTTURAL CALL 339 00:32:11,320 --> 00:32:13,560 Males and females have different calls. 340 00:32:13,560 --> 00:32:17,960 The females have this very coarse, grunty call, 341 00:32:17,960 --> 00:32:20,480 as all females should have, you know! 342 00:32:20,480 --> 00:32:24,400 The males have these whistles, beautiful and piercing. 343 00:32:24,400 --> 00:32:27,360 REPETITIVE SHRILL CALL 344 00:32:35,840 --> 00:32:40,360 Isabel and her team even managed to film a kiwi family 345 00:32:40,360 --> 00:32:41,720 with a tiny chick. 346 00:32:58,400 --> 00:33:01,320 Kiwis are the only nocturnal ratites 347 00:33:01,320 --> 00:33:03,320 and by far the smallest. 348 00:33:15,480 --> 00:33:18,520 This big bird isn't big at all. 349 00:33:18,520 --> 00:33:21,200 It only weighs about two kilos. 350 00:33:24,640 --> 00:33:26,480 Kiwis never grew big 351 00:33:26,480 --> 00:33:29,840 because they lived alongside the now-extinct moas. 352 00:33:33,760 --> 00:33:37,400 With those giant herbivores already roaming New Zealand, 353 00:33:37,400 --> 00:33:40,320 the kiwi's evolution took an alternative path. 354 00:33:42,080 --> 00:33:46,440 It remained small, became nocturnal and omnivorous. 355 00:33:53,880 --> 00:33:56,120 With nostrils at the end of its beak, 356 00:33:56,120 --> 00:33:59,960 the kiwi sniffs out insects and worms at night... 357 00:34:02,840 --> 00:34:06,280 ..and then stays in the safety of its burrow for the day. 358 00:34:14,640 --> 00:34:18,280 Unlike the other ratites, it nests underground. 359 00:34:26,360 --> 00:34:31,280 Until recently, it was thought that kiwis bred in monogamous pairs, 360 00:34:31,280 --> 00:34:36,560 but now DNA analysis has painted a much more complicated picture. 361 00:34:40,200 --> 00:34:42,240 They are very naughty, kiwi. 362 00:34:42,240 --> 00:34:45,160 For a long time, we thought that they were really good birds, 363 00:34:45,160 --> 00:34:48,120 and mated with one another, one male, one female, 364 00:34:48,120 --> 00:34:50,600 but they are not like that at all. 365 00:34:50,600 --> 00:34:52,320 They do stray a little bit. 366 00:34:52,320 --> 00:34:53,720 They do stray. 367 00:34:57,040 --> 00:35:02,760 It seems that breeding is a little more flexible than just one-on-one. 368 00:35:02,760 --> 00:35:06,440 Some birds seem to breed in family groups. 369 00:35:06,440 --> 00:35:08,600 Others may raise young as a pair 370 00:35:08,600 --> 00:35:11,680 even though the chicks might not belong to Dad. 371 00:35:15,760 --> 00:35:20,440 However, it's the males who shoulder the burden of incubation. 372 00:35:20,440 --> 00:35:23,880 The eggs in their care are among the oddest on earth. 373 00:35:25,920 --> 00:35:29,160 This is a kiwi's egg. 374 00:35:29,160 --> 00:35:33,640 It's the biggest in proportion to body size of any bird's egg. 375 00:35:33,640 --> 00:35:35,040 It weighs about a fifth 376 00:35:35,040 --> 00:35:38,520 as much as the adult bird. 377 00:35:38,520 --> 00:35:42,560 It's so big, it takes 80 days to incubate. 378 00:35:42,560 --> 00:35:43,880 The Maoris used to say 379 00:35:43,880 --> 00:35:48,840 that tree routes would grow over a kiwi's nest. 380 00:35:48,840 --> 00:35:53,520 This is the egg of another ratite, an ostrich, 381 00:35:53,520 --> 00:35:59,200 and curiously, it is the smallest egg in terms of body weight 382 00:35:59,200 --> 00:36:01,240 for any bird in the world. 383 00:36:04,120 --> 00:36:07,760 These ostrich eggs are unusual in other ways. 384 00:36:07,760 --> 00:36:12,000 They too are part of an elaborate game of pick and mix... 385 00:36:14,880 --> 00:36:18,120 ..because ostriches are almost like cuckoos. 386 00:36:18,120 --> 00:36:22,280 Females will lay in the nests of other ostriches, 387 00:36:22,280 --> 00:36:24,120 but unlike the cuckoo, 388 00:36:24,120 --> 00:36:26,240 the owners of the nest know about it 389 00:36:26,240 --> 00:36:28,240 and they don't seem to mind. 390 00:36:34,640 --> 00:36:37,240 It may help to have a few spare eggs. 391 00:36:41,280 --> 00:36:45,160 The female seems to be able to recognise her own eggs, 392 00:36:45,160 --> 00:36:49,200 keeping them at the centre of the nest while rolling out others 393 00:36:49,200 --> 00:36:53,440 as sacrifices to any predator brave enough to make an attack. 394 00:36:58,280 --> 00:37:02,480 Up to six female ostriches may lay in a single nest. 395 00:37:07,200 --> 00:37:09,760 For most members of the ratite family, 396 00:37:09,760 --> 00:37:11,920 the rhea, the emu and the cassowary, 397 00:37:11,920 --> 00:37:15,680 incubation is something of a gentleman's club - 398 00:37:15,680 --> 00:37:17,200 females aren't welcome. 399 00:37:18,520 --> 00:37:20,880 But the ostrich does things a little differently. 400 00:37:23,120 --> 00:37:27,400 The male and female take turns at caring for the clutch, 401 00:37:27,400 --> 00:37:30,000 keeping watch by day and night to make sure 402 00:37:30,000 --> 00:37:32,800 nothing has a chance to steal the eggs. 403 00:37:37,760 --> 00:37:41,800 This father-to-be is carefully rolling the eggs to make sure 404 00:37:41,800 --> 00:37:44,240 the embryo inside gets evenly warmed. 405 00:37:48,840 --> 00:37:50,240 In the cold of the night, 406 00:37:50,240 --> 00:37:53,800 he uses his feathers as a blanket to cover his charges. 407 00:38:06,960 --> 00:38:09,600 Communicating by clacking their beaks, 408 00:38:09,600 --> 00:38:12,280 this couple share the parental burden. 409 00:38:20,440 --> 00:38:23,040 They take turns to sit on the eggs, 410 00:38:23,040 --> 00:38:26,080 which, although small compared to the ostrich itself, 411 00:38:26,080 --> 00:38:29,120 weigh in fact almost two kilos each, 412 00:38:29,120 --> 00:38:31,960 the largest eggs laid by any living animal. 413 00:38:44,680 --> 00:38:49,000 Left unattended, such large eggs soon attract attention. 414 00:38:53,120 --> 00:38:56,240 These ostrich eggs are giant ready meals 415 00:38:56,240 --> 00:38:59,000 for a variety of African animals. 416 00:39:01,480 --> 00:39:04,280 You can't make an omelette without breaking eggs, 417 00:39:04,280 --> 00:39:08,480 and this jackal has worked out just how to crack one against another 418 00:39:08,480 --> 00:39:09,960 and so release his lunch. 419 00:39:32,920 --> 00:39:37,360 The Egyptian vulture has its own ingenious version of smash and grab. 420 00:39:58,440 --> 00:40:00,320 It's perhaps not surprising 421 00:40:00,320 --> 00:40:03,280 that up to 90% of ostrich clutches 422 00:40:03,280 --> 00:40:05,600 are totally destroyed. 423 00:40:19,600 --> 00:40:24,880 In South America, rheas nest in a similar way to the ostrich. 424 00:40:31,400 --> 00:40:37,680 For two weeks, females lay their eggs in one shallow, communal nest. 425 00:40:39,720 --> 00:40:44,200 Each egg is 12 times the size of that of a chicken. 426 00:40:45,440 --> 00:40:47,080 But unlike the ostrich, 427 00:40:47,080 --> 00:40:50,480 it's the male who settles down to do all the hard work. 428 00:40:53,880 --> 00:40:56,600 He alone will incubate these eggs, 429 00:40:56,600 --> 00:41:01,280 and he does so for more than five weeks, whatever the weather. 430 00:41:01,280 --> 00:41:05,360 THUNDER CRACKS, HEAVY RAIN 431 00:41:31,920 --> 00:41:34,360 It's an arduous task. 432 00:41:34,360 --> 00:41:38,200 65% of males abandon their nests, 433 00:41:38,200 --> 00:41:41,680 many because they don't have the energy to sustain themselves 434 00:41:41,680 --> 00:41:43,720 without going away to feed. 435 00:41:54,920 --> 00:41:59,560 The females, however, never put all their eggs in one basket. 436 00:42:01,680 --> 00:42:04,520 Once they've mated with this one male, 437 00:42:04,520 --> 00:42:07,680 they move on to another, so increasing the chance 438 00:42:07,680 --> 00:42:10,480 that at least some of their young will survive. 439 00:42:25,960 --> 00:42:28,560 Nesting on the ground out in the open 440 00:42:28,560 --> 00:42:32,080 means that, inevitably, the eggs are vulnerable. 441 00:42:38,680 --> 00:42:42,240 From the enormous eggs of the ostrich... 442 00:42:45,480 --> 00:42:48,120 ..to the green eggs of the emu. 443 00:42:57,480 --> 00:43:01,920 But for one of the relatives, the battle to keep their clutches safe 444 00:43:01,920 --> 00:43:05,160 was, in the end, lost. 445 00:43:08,640 --> 00:43:11,480 These are the leg bones of the elephant bird. 446 00:43:11,480 --> 00:43:13,400 It was the largest of the ratites. 447 00:43:13,400 --> 00:43:16,560 Indeed, it was one of the biggest birds ever known. 448 00:43:16,560 --> 00:43:20,440 It stood over 3m tall and weighed half a tonne. 449 00:43:22,520 --> 00:43:26,600 It lived on the ancient island of Madagascar, 450 00:43:26,600 --> 00:43:29,440 which I visited over 50 years ago. 451 00:43:46,200 --> 00:43:49,040 Before Europeans ever went to the island, 452 00:43:49,040 --> 00:43:50,880 it had a reputation for being the home 453 00:43:50,880 --> 00:43:53,000 of really strange, fabulous beasts, 454 00:43:53,000 --> 00:43:55,960 and Marco Polo, 700 years ago, 455 00:43:55,960 --> 00:43:58,800 believed that it was the home of the fabulous bird, the rukh. 456 00:43:58,800 --> 00:44:02,880 The rukh, which carried off Sinbad the Sailor, and which was reputed 457 00:44:02,880 --> 00:44:05,720 to be able to carry off elephants in its talons, 458 00:44:05,720 --> 00:44:08,200 as this one is doing. 459 00:44:08,200 --> 00:44:12,640 But Marco Polo had very good reason for thinking that it lived in Madagascar, 460 00:44:12,640 --> 00:44:16,440 because he heard stories that in Madagascar were found gigantic eggs, 461 00:44:16,440 --> 00:44:22,000 over two feet long. What else could have laid them but the rukh? 462 00:44:22,000 --> 00:44:24,080 Well, I was lucky enough to find 463 00:44:24,080 --> 00:44:27,880 some pieces of the rukh, or elephant bird's egg. 464 00:44:36,080 --> 00:44:40,080 And even luckier to be given some pieces that looked like 465 00:44:40,080 --> 00:44:41,840 they might belong to one egg. 466 00:44:46,640 --> 00:44:48,400 Now, would they fit together? 467 00:44:55,480 --> 00:44:57,600 These two certainly did. 468 00:45:05,360 --> 00:45:08,160 At the end of an hour, I had two halves. 469 00:45:18,120 --> 00:45:21,800 And to my joy, they fitted together perfectly. 470 00:45:24,920 --> 00:45:28,600 There was a place for even such a tiny fragment as this. 471 00:45:31,440 --> 00:45:35,920 The egg was well nigh perfect. 472 00:45:35,920 --> 00:45:40,480 As I held it, I had little difficulty in imagining the country 473 00:45:40,480 --> 00:45:44,520 as it must have been when great numbers of gigantic birds, 474 00:45:44,520 --> 00:45:48,680 over ten feet tall, strode majestically through the swamps. 475 00:45:51,560 --> 00:45:56,600 This is the egg that I brought back from Madagascar all those years ago. 476 00:45:56,600 --> 00:46:00,560 It's the biggest egg ever laid by anything. 477 00:46:00,560 --> 00:46:05,080 Bigger by far than even the egg of the biggest dinosaur. 478 00:46:05,080 --> 00:46:08,400 As you might imagine, it could have made a meal 479 00:46:08,400 --> 00:46:10,640 for quite a lot of people, 480 00:46:10,640 --> 00:46:13,560 and that may well be, some people think, 481 00:46:13,560 --> 00:46:17,200 the reason why the elephant bird became extinct. 482 00:46:17,200 --> 00:46:21,200 If it wasn't for human beings, the elephant bird might still 483 00:46:21,200 --> 00:46:22,960 be walking around on Madagascar. 484 00:46:30,920 --> 00:46:34,200 The same fate met the moas of New Zealand, 485 00:46:34,200 --> 00:46:38,360 some kinds of which weighed over 200 kilos. 486 00:46:38,360 --> 00:46:42,120 The elephant bird might have been the biggest bird ever to exist, 487 00:46:42,120 --> 00:46:46,160 but some think that one species of moa was the tallest. 488 00:46:47,800 --> 00:46:51,440 Moas, too, were hunted and had their eggs eaten by humans 489 00:46:51,440 --> 00:46:54,520 until there were none left. 490 00:46:54,520 --> 00:46:58,360 We know this because of the careful detective work scientists 491 00:46:58,360 --> 00:47:00,200 have done on their bones. 492 00:47:02,800 --> 00:47:04,760 It's not the only puzzle 493 00:47:04,760 --> 00:47:08,320 that fragments of extinct bird like these, of the moa, 494 00:47:08,320 --> 00:47:10,400 might be able to solve. 495 00:47:10,400 --> 00:47:14,120 If these birds were flightless, how did they manage to spread 496 00:47:14,120 --> 00:47:16,760 round the world, from the deserts of Africa 497 00:47:16,760 --> 00:47:18,880 to the rainforests of Australia? 498 00:47:18,880 --> 00:47:22,160 It's a conundrum that has puzzled minds for centuries. 499 00:47:27,000 --> 00:47:31,360 Not that long ago, scientists thought they had the answer. 500 00:47:31,360 --> 00:47:34,320 All the places in which the ratites lived 501 00:47:34,320 --> 00:47:38,080 had once been part of a supercontinent called Gondwanaland. 502 00:47:40,920 --> 00:47:45,120 Perhaps our birds came from one common ancestor, which was 503 00:47:45,120 --> 00:47:48,520 also flightless, that roamed all over that land. 504 00:47:50,760 --> 00:47:54,000 Then, millions of years ago, when the continents split up, 505 00:47:54,000 --> 00:47:57,360 populations of this bird were separated. 506 00:47:57,360 --> 00:47:59,920 As their homes drifted into new positions, 507 00:47:59,920 --> 00:48:03,960 the isolated birds adapted and evolved in different ways, 508 00:48:03,960 --> 00:48:06,600 producing everything from the tiny kiwi 509 00:48:06,600 --> 00:48:09,360 to the huge extinct elephant bird. 510 00:48:12,200 --> 00:48:15,840 But ancient bones are telling a different story. 511 00:48:15,840 --> 00:48:19,400 Scientists have recently been sequencing DNA 512 00:48:19,400 --> 00:48:21,960 from the bones of extinct ratites 513 00:48:21,960 --> 00:48:25,600 and compared them with living flightless birds, 514 00:48:25,600 --> 00:48:28,480 and the results have come as a huge surprise. 515 00:48:32,760 --> 00:48:35,680 The mighty elephant bird, which should be most closely 516 00:48:35,680 --> 00:48:39,800 related to the ostrich, turns out to be most similar to the tiny kiwi. 517 00:48:40,840 --> 00:48:44,520 Not what was expected at all. 518 00:48:44,520 --> 00:48:46,840 So how could this possibly be? 519 00:48:49,160 --> 00:48:53,480 Well, an unexpected character is providing some answers. 520 00:48:57,280 --> 00:49:00,120 A little-known ratite relative, the tinamou, 521 00:49:00,120 --> 00:49:02,640 that lives in Central and South America. 522 00:49:07,560 --> 00:49:12,240 DNA has recently revealed that it isn't a distant relative, 523 00:49:12,240 --> 00:49:14,640 a cousin, say, but instead a sibling, 524 00:49:14,640 --> 00:49:17,920 smack in the middle of the ratite family tree. 525 00:49:20,240 --> 00:49:24,680 Which is remarkable, because tinamous can fly. 526 00:49:26,920 --> 00:49:29,680 Now, if all the ratites and the tinamous evolved 527 00:49:29,680 --> 00:49:31,320 from one flightless ancestor, 528 00:49:31,320 --> 00:49:34,720 then the tinamous must have relearned how to fly. 529 00:49:36,600 --> 00:49:41,080 But there are no known examples of a species of flightless bird 530 00:49:41,080 --> 00:49:43,800 regaining flight, so this suggests 531 00:49:43,800 --> 00:49:46,960 that the common ancestor of the ratites and the tinamous 532 00:49:46,960 --> 00:49:51,200 wasn't flightless at all. He could fly. 533 00:49:56,920 --> 00:49:59,960 Our birds might not have drifted away from one another 534 00:49:59,960 --> 00:50:03,000 on the lands in which they live today. 535 00:50:03,000 --> 00:50:07,080 Instead, their ancestors must have flown across miles of ocean 536 00:50:07,080 --> 00:50:10,760 to reach the far corners of the world, and only then 537 00:50:10,760 --> 00:50:13,360 did they independently lose the ability to fly. 538 00:50:24,320 --> 00:50:26,280 It's an amazing thought, 539 00:50:26,280 --> 00:50:30,320 but the ratites lost their ability to fly independently 540 00:50:30,320 --> 00:50:33,160 and on several different occasions. 541 00:50:36,120 --> 00:50:40,360 Thousands of miles apart from each other on their separate continents, 542 00:50:40,360 --> 00:50:44,680 each kind of ratite developed into its own flightless form. 543 00:50:48,680 --> 00:50:51,560 The ostrich and the rhea kept their wings 544 00:50:51,560 --> 00:50:54,240 and evolved elaborate uses for their feathers. 545 00:50:57,440 --> 00:51:01,720 The wings of the emu and cassowary became short and tiny... 546 00:51:03,760 --> 00:51:07,800 ..and the kiwi, well, its wings are now all but invisible. 547 00:51:14,360 --> 00:51:16,760 Although the details are different, 548 00:51:16,760 --> 00:51:20,560 the demands of living on the ground meant that all the ratites 549 00:51:20,560 --> 00:51:23,040 evolved in their own way into flightlessness. 550 00:51:26,200 --> 00:51:30,160 And there's one survival strategy which they all share, 551 00:51:30,160 --> 00:51:32,400 and which begins when they hatch. 552 00:51:40,480 --> 00:51:42,720 In the Australian outback, 553 00:51:42,720 --> 00:51:48,400 this male emu's hard work over the past 56 days is about to pay off. 554 00:51:59,400 --> 00:52:01,560 He is a father. 555 00:52:05,960 --> 00:52:10,160 His chicks, like all newly hatched ratites, are able to get up and go 556 00:52:10,160 --> 00:52:13,920 almost from the moment they break free from their eggs. 557 00:52:24,760 --> 00:52:27,560 This is an invaluable ability for a chick, 558 00:52:27,560 --> 00:52:29,040 which is, after all, 559 00:52:29,040 --> 00:52:32,680 a very succulent mouthful for almost any predator. 560 00:52:40,440 --> 00:52:44,480 Emu chicks, with their tawny markings, are known to Australians 561 00:52:44,480 --> 00:52:46,520 as stripeys. 562 00:53:05,400 --> 00:53:10,520 Their dedicated dad will spend the next six months caring for them, 563 00:53:10,520 --> 00:53:15,760 by which time they will already have grown to at least half his height. 564 00:53:15,760 --> 00:53:18,200 That is, if they ever hurry up and hatch. 565 00:53:34,200 --> 00:53:38,040 The chicks had to work hard to free themselves from the egg shells. 566 00:53:38,040 --> 00:53:40,280 Now they need a drink. 567 00:53:45,240 --> 00:53:48,480 Their father must face a tough decision. 568 00:54:01,480 --> 00:54:04,760 One egg still hasn't hatched. 569 00:54:04,760 --> 00:54:09,400 If he stays and waits for it to do so, the older chicks may die. 570 00:54:21,240 --> 00:54:25,240 It's likely that he can hear sounds coming from within 571 00:54:25,240 --> 00:54:26,440 the unhatched egg. 572 00:54:31,520 --> 00:54:35,680 Meanwhile, the harsh Australian sun scorches down on those 573 00:54:35,680 --> 00:54:39,320 of his offspring desperately waiting for their first drink. 574 00:55:15,480 --> 00:55:19,520 After many agonising hours, he makes his choice. 575 00:55:34,520 --> 00:55:36,760 Leading the brood to find water, 576 00:55:36,760 --> 00:55:42,640 this father helps a new generation of big birds take their first steps. 577 00:56:14,800 --> 00:56:18,600 From South Africa to South America, 578 00:56:18,600 --> 00:56:22,240 an extraordinary combination of mating behaviour 579 00:56:22,240 --> 00:56:26,200 and parental care has produced birds which are very special indeed. 580 00:56:27,920 --> 00:56:29,960 CHIRPING 581 00:56:39,680 --> 00:56:45,120 These young ostriches will soon grow into the biggest birds in the world. 582 00:56:49,520 --> 00:56:54,440 Although today, as they take tiny steps across this vast landscape, 583 00:56:54,440 --> 00:56:56,400 that day seems a long way off. 584 00:57:00,160 --> 00:57:02,680 The next generation of ratites. 585 00:57:04,680 --> 00:57:08,960 A reminder of how one remarkable group of birds independently 586 00:57:08,960 --> 00:57:12,920 seized a moment when there were no predators around to hunt them down 587 00:57:12,920 --> 00:57:16,880 and set off down various but similar evolutionary paths. 588 00:57:21,440 --> 00:57:25,640 The only group of birds to have become massive and flightless. 589 00:57:29,240 --> 00:57:34,360 It wasn't long before some mammals also became big and dominant, 590 00:57:34,360 --> 00:57:35,800 and when they did, 591 00:57:35,800 --> 00:57:39,480 the window of opportunity for more birds to do so closed. 592 00:57:39,480 --> 00:57:43,320 But what an opportunity it was, 593 00:57:43,320 --> 00:57:47,400 and those birds which took advantage of it are truly remarkable. 594 00:57:54,680 --> 00:57:58,760 Scientists are currently working to gather still more clues, 595 00:57:58,760 --> 00:58:03,000 from birds both extinct and living, to add even more detail 596 00:58:03,000 --> 00:58:06,240 to their amazing evolutionary history. 597 00:58:06,240 --> 00:58:09,880 We can only hope this will help us to better understand 598 00:58:09,880 --> 00:58:14,560 this family of birds, which are surely flightless wonders.