1 00:00:01,600 --> 00:00:04,250 When winter descends upon Europe, 2 00:00:04,250 --> 00:00:07,093 many animals have no choice but to leave. 3 00:00:09,110 --> 00:00:11,040 The migrations of many creatures 4 00:00:11,040 --> 00:00:13,313 have been a mystery until now. 5 00:00:15,890 --> 00:00:20,700 And yet they cross oceans and deserts, brave intense weather 6 00:00:20,700 --> 00:00:24,023 and travel thousands of kilometers unabated. 7 00:00:26,360 --> 00:00:28,860 Thanks to recent scientific progress 8 00:00:28,860 --> 00:00:31,540 we are finally able to follow their journey 9 00:00:31,540 --> 00:00:35,573 and discover the secrets behind their incredible migrations. 10 00:00:42,810 --> 00:00:46,183 Gray plumage, a dark colored cap. 11 00:00:47,510 --> 00:00:50,853 Some 20 grams of feathers fluttering in the bushes, 12 00:00:52,330 --> 00:00:53,423 always alert. 13 00:00:54,910 --> 00:00:56,263 It's the blackcap. 14 00:00:58,640 --> 00:01:00,490 A common European bird 15 00:01:00,490 --> 00:01:02,893 that is also one of the most intriguing. 16 00:01:05,420 --> 00:01:06,470 Every autumn, 17 00:01:06,470 --> 00:01:09,690 millions of these birds cross the continent by night 18 00:01:09,690 --> 00:01:13,170 in search of more welcoming breeding grounds. 19 00:01:13,170 --> 00:01:15,430 How do they navigate in the dark? 20 00:01:15,430 --> 00:01:18,153 How do they find their way to their winter homes? 21 00:01:21,320 --> 00:01:23,190 Even more mysteriously, 22 00:01:23,190 --> 00:01:26,113 they seem to be taking new migratory routes. 23 00:01:33,573 --> 00:01:35,570 Thanks to new technologies, 24 00:01:35,570 --> 00:01:37,660 We are finally starting to understand 25 00:01:37,660 --> 00:01:39,503 the secrets of their migration. 26 00:01:40,697 --> 00:01:43,280 (lively music) 27 00:02:12,555 --> 00:02:15,138 (serene music) 28 00:02:16,730 --> 00:02:18,143 In southern Sweden, 29 00:02:19,270 --> 00:02:22,563 nature begins transforming in early September. 30 00:02:24,492 --> 00:02:27,242 (birds chirping) 31 00:02:28,450 --> 00:02:31,010 Autumn approaches and the bushes are teeming 32 00:02:31,010 --> 00:02:33,883 with small birds searching for sweet berries. 33 00:02:36,480 --> 00:02:39,683 Sparrows, robins, 34 00:02:41,000 --> 00:02:45,073 chickadees and also an abundance of blackcap warblers. 35 00:02:50,530 --> 00:02:53,140 Only the male is really worthy of the name 36 00:02:53,140 --> 00:02:56,950 as the female actually sports a brownish red cap on her head 37 00:03:01,040 --> 00:03:04,230 This is Northern European Warbler territory 38 00:03:04,230 --> 00:03:06,753 and this is where it all begins. 39 00:03:08,180 --> 00:03:10,763 These are migratory perching birds. 40 00:03:11,680 --> 00:03:13,820 They spent the summer in Sweden 41 00:03:13,820 --> 00:03:16,303 actively preparing for their great journey. 42 00:03:17,330 --> 00:03:21,200 In a few months, Sweden will be nothing but ice. 43 00:03:21,200 --> 00:03:22,700 In order to survive, 44 00:03:22,700 --> 00:03:27,392 the blackcaps only have one solution, migrating south. 45 00:03:27,392 --> 00:03:30,710 (lively music) 46 00:03:30,710 --> 00:03:33,570 With a wingspan around 23 centimeters 47 00:03:33,570 --> 00:03:36,450 and weighing an average of only 20 grams, 48 00:03:36,450 --> 00:03:39,340 blackcaps are surprisingly athletic creatures 49 00:03:39,340 --> 00:03:43,063 capable of traveling thousands of kilometers every year. 50 00:03:46,720 --> 00:03:50,293 As autumn approaches, the birds behavior changes. 51 00:03:53,570 --> 00:03:54,940 Suzanne Akesson, 52 00:03:54,940 --> 00:03:57,900 who studies animal mobility at Lund University, 53 00:03:57,900 --> 00:04:02,270 is very familiar with these biological transformations. 54 00:04:02,270 --> 00:04:04,563 They're the precursors to migration. 55 00:04:06,460 --> 00:04:09,020 They have an internal time program 56 00:04:09,020 --> 00:04:13,500 that will help them to time various important events 57 00:04:13,500 --> 00:04:16,960 in the life cycle for example the migration. 58 00:04:16,960 --> 00:04:19,900 The mechanism is everywhere in the body. 59 00:04:19,900 --> 00:04:23,727 Every cell is sort of having their timekeeper. 60 00:04:23,727 --> 00:04:26,310 (lively music) 61 00:04:28,940 --> 00:04:31,300 When it's biological clock commands it, 62 00:04:31,300 --> 00:04:34,393 the blackcaps behavior changes drastically. 63 00:04:38,670 --> 00:04:41,573 First is a radical switch in diet. 64 00:04:44,960 --> 00:04:46,860 In the summer they are insectivores, 65 00:04:47,700 --> 00:04:50,560 so they feed on the insects they can find in the bushes 66 00:04:50,560 --> 00:04:54,880 and then slowly they will start to forage on these berries 67 00:04:54,880 --> 00:04:57,140 and other fruit. 68 00:04:57,140 --> 00:04:58,750 This is elderberries. 69 00:04:58,750 --> 00:05:01,990 So this is the various types of black camps are feeding on 70 00:05:01,990 --> 00:05:02,890 at this time of year 71 00:05:02,890 --> 00:05:05,993 and they will try to find them along the migration routes. 72 00:05:09,110 --> 00:05:09,943 Sweet? 73 00:05:11,853 --> 00:05:14,293 It's also some extra, I'm not sure. 74 00:05:19,910 --> 00:05:22,860 In the weeks preceding migration, 75 00:05:22,860 --> 00:05:25,023 the blackcap begins overeating. 76 00:05:26,350 --> 00:05:30,823 An intentional fattening that leads to a 30 % weight gain. 77 00:05:30,823 --> 00:05:34,070 (lively music) 78 00:05:34,070 --> 00:05:37,830 These sugar-rich fruits allow the bird to rapidly accumulate 79 00:05:37,830 --> 00:05:41,303 the body fat it needs for its first migratory flight. 80 00:05:43,710 --> 00:05:46,550 Another important change takes place. 81 00:05:46,550 --> 00:05:49,163 The blackcap begins to molt its feathers. 82 00:05:52,144 --> 00:05:56,540 This is a blackcap and a young bird. 83 00:05:56,540 --> 00:05:58,500 There are some feathers 84 00:05:58,500 --> 00:06:03,500 that still have the cover around the base. 85 00:06:05,970 --> 00:06:09,040 So it's molting actually. 86 00:06:09,040 --> 00:06:12,530 This is very important to have a top flight apprentice 87 00:06:12,530 --> 00:06:15,763 when you depart a long migration flights. 88 00:06:20,170 --> 00:06:22,420 With new feathers in a new diet, 89 00:06:24,140 --> 00:06:26,493 one essential change remains. 90 00:06:27,570 --> 00:06:31,110 It's a transformation that ornithologists can only see 91 00:06:31,110 --> 00:06:33,273 with help from special technology. 92 00:06:35,710 --> 00:06:39,160 In these cages, we feel the activity from above 93 00:06:39,160 --> 00:06:43,080 and we can see how they become restless. 94 00:06:43,080 --> 00:06:44,860 A songbird like the blackcaps 95 00:06:44,860 --> 00:06:46,610 during the other time of year, 96 00:06:46,610 --> 00:06:49,280 it's mainly sleeping at nighttime 97 00:06:49,280 --> 00:06:54,280 but the migration season they will suddenly become awake 98 00:06:54,330 --> 00:06:58,613 and active at night because they use the night to migrate. 99 00:07:00,470 --> 00:07:02,770 The blackcap which is active during the day 100 00:07:02,770 --> 00:07:04,040 for most of the year, 101 00:07:04,040 --> 00:07:07,393 gradually transforms into a nocturnal creature. 102 00:07:09,500 --> 00:07:11,713 That's because they migrate at night. 103 00:07:13,510 --> 00:07:15,750 Flying in the dark allows the blackcap 104 00:07:15,750 --> 00:07:17,630 to limit hot sun exposure 105 00:07:17,630 --> 00:07:22,229 while also avoiding its primary predators, birds of prey. 106 00:07:22,229 --> 00:07:24,729 (light music) 107 00:07:25,760 --> 00:07:28,910 The juvenile birds migrating for the first time, 108 00:07:28,910 --> 00:07:31,623 make the journey alone without their parents. 109 00:07:33,510 --> 00:07:36,920 How can they possibly know as they fly away in the dark 110 00:07:36,920 --> 00:07:38,373 which direction to go? 111 00:07:40,100 --> 00:07:41,840 To answer this question, 112 00:07:41,840 --> 00:07:44,943 scientists have developed this peculiar device. 113 00:07:46,440 --> 00:07:47,570 As night falls, 114 00:07:47,570 --> 00:07:51,060 the device is placed in the center of a funnel-shaped cage 115 00:07:51,060 --> 00:07:54,730 and the birds are exposed to the night sky for several hours 116 00:07:56,900 --> 00:07:58,260 The birds start fluttering 117 00:07:58,260 --> 00:08:00,243 in the direction they wish to migrate. 118 00:08:02,310 --> 00:08:04,930 The traces left by their claws on the paper 119 00:08:04,930 --> 00:08:07,900 indicate that each bird is innately programmed 120 00:08:07,900 --> 00:08:10,063 to navigate in a certain direction. 121 00:08:11,590 --> 00:08:13,480 The blackcap is very interesting 122 00:08:13,480 --> 00:08:17,400 because they have to rely on their internal genetic program 123 00:08:17,400 --> 00:08:19,500 that will tell them what direction to go 124 00:08:19,500 --> 00:08:21,003 and how far to migrate. 125 00:08:22,900 --> 00:08:25,110 The experiment has also shown 126 00:08:25,110 --> 00:08:27,453 that new behaviors are emerging. 127 00:08:29,530 --> 00:08:33,050 We have have preferred migration directions 128 00:08:33,050 --> 00:08:35,610 more to south and southeast 129 00:08:35,610 --> 00:08:39,940 but nowadays we also find birds that have other preferences 130 00:08:39,940 --> 00:08:43,110 like in this case, a more westerly orientation. 131 00:08:43,110 --> 00:08:45,720 There's some large variation between individuals 132 00:08:45,720 --> 00:08:49,259 but it's also recent evolution of migration. 133 00:08:49,259 --> 00:08:51,723 That's very exciting with the blackcaps. 134 00:08:53,720 --> 00:08:55,360 The direction the blackcap takes 135 00:08:55,360 --> 00:08:59,070 for its migration differs from one bird to another 136 00:08:59,070 --> 00:09:02,623 yet each of them instinctively knows which course to set. 137 00:09:08,900 --> 00:09:12,410 Historically, they used to leave Sweden and head south 138 00:09:12,410 --> 00:09:14,130 but for the past few years 139 00:09:14,130 --> 00:09:16,840 more blackcaps are choosing new directions 140 00:09:16,840 --> 00:09:19,093 some of which seemed unusual. 141 00:09:22,480 --> 00:09:24,420 Before being released, 142 00:09:24,420 --> 00:09:26,690 these birds are tagged with a small ring 143 00:09:26,690 --> 00:09:29,623 displaying a unique number for each individual. 144 00:09:34,220 --> 00:09:37,630 If this blackcap is recaptured elsewhere in Europe, 145 00:09:37,630 --> 00:09:40,477 its ring will record the path that it took. 146 00:09:40,477 --> 00:09:43,060 (lively music) 147 00:09:50,100 --> 00:09:53,463 The time has finally come for the blackcaps to depart. 148 00:09:55,940 --> 00:09:59,063 This evening, thousands of them will fly south. 149 00:10:10,410 --> 00:10:11,870 As they leave Sweden, 150 00:10:11,870 --> 00:10:15,160 the birds crossed Denmark in a single stretch. 151 00:10:15,160 --> 00:10:19,830 400 kilometers later after eight long hours of traveling, 152 00:10:19,830 --> 00:10:21,523 they finally reached Germany. 153 00:10:23,320 --> 00:10:27,140 This first leg seems to follow an almost perfect trajectory 154 00:10:28,730 --> 00:10:31,543 but how did they orient themselves so precisely? 155 00:10:33,010 --> 00:10:36,010 Researchers have proven that blackcaps navigate 156 00:10:36,010 --> 00:10:39,223 by observing the rotation of the celestial hemisphere. 157 00:10:41,320 --> 00:10:44,350 The stars trace concentric circles in the sky 158 00:10:44,350 --> 00:10:48,550 that are precisely centered around the geographic North Pole 159 00:10:48,550 --> 00:10:50,510 It is this stationary reference 160 00:10:50,510 --> 00:10:54,160 that allows the blackcaps to orient themselves. 161 00:10:54,160 --> 00:10:55,140 But they aren't born 162 00:10:55,140 --> 00:10:58,020 with a fully functioning internal compass. 163 00:10:58,020 --> 00:11:01,650 Young birds need at least 21 nights of studying the stars 164 00:11:01,650 --> 00:11:04,973 before being able to correctly orient themselves. 165 00:11:06,960 --> 00:11:09,550 So what happens if a cloudy night sky 166 00:11:09,550 --> 00:11:11,893 interferes with their celestial compass? 167 00:11:15,760 --> 00:11:19,010 One scientist has spent years working on a device 168 00:11:19,010 --> 00:11:21,693 to help the birds fine-tune their navigation. 169 00:11:23,790 --> 00:11:26,350 At the University of Oldenburg in Germany, 170 00:11:26,350 --> 00:11:29,710 Henrik Mouritsen and his team have built an apparatus 171 00:11:29,710 --> 00:11:32,643 that allows them to alter the magnetic field. 172 00:11:34,840 --> 00:11:36,780 Well, this is a (mumbles) system 173 00:11:36,780 --> 00:11:39,090 which can be used to change the direction 174 00:11:39,090 --> 00:11:41,120 and intensity of the Earth's magnetic field. 175 00:11:41,120 --> 00:11:43,050 Out here, the magnetic nose is pointing north 176 00:11:43,050 --> 00:11:45,350 and this is actual north 177 00:11:45,350 --> 00:11:49,350 and if I put this compass inside the coil system here 178 00:11:49,350 --> 00:11:53,010 where I have set it to change the north-south component, 179 00:11:53,010 --> 00:11:56,890 you will see now the red arrow points towards South. 180 00:11:56,890 --> 00:12:00,200 So you can put these birds a little orientation cages, 181 00:12:00,200 --> 00:12:02,920 they will jump in the direction which they wanna fly 182 00:12:02,920 --> 00:12:04,610 and then when you turn the direction of the field, 183 00:12:04,610 --> 00:12:06,150 they started jumping on different directions. 184 00:12:06,150 --> 00:12:08,593 So they they directly show you but they have now detected 185 00:12:08,593 --> 00:12:10,393 that the magnetic field has changed. 186 00:12:15,520 --> 00:12:18,320 The iron core found at the center of the earth 187 00:12:18,320 --> 00:12:19,990 generates a magnetic field 188 00:12:19,990 --> 00:12:22,593 that goes from the South Pole to the North Pole. 189 00:12:25,130 --> 00:12:26,890 The birds don't learn direction 190 00:12:26,890 --> 00:12:29,800 based on the orientation of this magnetic field 191 00:12:29,800 --> 00:12:34,023 but rather on another of its characteristics, its tilt. 192 00:12:36,650 --> 00:12:38,910 The lines of the Earth's magnetic field 193 00:12:38,910 --> 00:12:41,630 form an angle in relation to its surface 194 00:12:41,630 --> 00:12:43,853 which varies according to latitude. 195 00:12:48,050 --> 00:12:52,460 That angle was 74 degrees at their departure point in Sweden 196 00:12:52,460 --> 00:12:55,723 but it is only 65 degrees at their arrival point. 197 00:12:58,490 --> 00:13:01,190 The nine degree difference between the two angles 198 00:13:01,190 --> 00:13:05,163 tells the birds they are now 350 kilometers further south. 199 00:13:09,090 --> 00:13:11,100 But which part of the bird's body 200 00:13:11,100 --> 00:13:14,870 contains this particularly efficient GPS? 201 00:13:14,870 --> 00:13:18,500 Henrik Mouritsen thinks it's based on a visual perception 202 00:13:18,500 --> 00:13:20,463 of the magnetic field lines. 203 00:13:22,930 --> 00:13:24,320 Basically the idea is 204 00:13:24,320 --> 00:13:27,660 that you have a light-sensitive molecule in the bird's eye, 205 00:13:27,660 --> 00:13:29,260 this absorbs light 206 00:13:29,260 --> 00:13:33,010 and due to complicated quantum mechanical phenomenon, 207 00:13:33,010 --> 00:13:35,250 you can generate a chemical composts. 208 00:13:35,250 --> 00:13:38,380 And to the birds, it would mean that they would actually see 209 00:13:38,380 --> 00:13:39,930 the magnetic field. 210 00:13:39,930 --> 00:13:41,350 This chemical compass 211 00:13:41,350 --> 00:13:43,810 is apparently generated by proteins 212 00:13:43,810 --> 00:13:46,000 located on the bird's retina. 213 00:13:46,000 --> 00:13:49,080 On this model which seems like a torture device, 214 00:13:49,080 --> 00:13:52,190 imagine each nail as one of these proteins 215 00:13:52,190 --> 00:13:54,190 and the basketball as the retina. 216 00:13:54,190 --> 00:13:56,680 This is the half ball shape 217 00:13:56,680 --> 00:13:59,870 would mean that there would be molecules oriented 218 00:13:59,870 --> 00:14:02,360 in all possible axial directions. 219 00:14:02,360 --> 00:14:05,140 Then imagine you look along the magnetic field lines 220 00:14:05,140 --> 00:14:07,550 and let's say the magnetic field lines are running here, 221 00:14:07,550 --> 00:14:10,990 then this molecule here would be parallel to the field lines 222 00:14:10,990 --> 00:14:13,920 and let's say that you would see a light pixels 223 00:14:13,920 --> 00:14:16,780 around the edge of the eye, you would get dark pixels 224 00:14:16,780 --> 00:14:18,370 and you can now imagine that 225 00:14:18,370 --> 00:14:20,340 if you now move your eye like this 226 00:14:20,340 --> 00:14:21,690 you would maybe do a head scan. 227 00:14:21,690 --> 00:14:23,840 You would scan your head 90 degrees to this side, 228 00:14:23,840 --> 00:14:25,330 90 degrees to that side. 229 00:14:25,330 --> 00:14:30,110 Now that light point will kind of move over the retina, 230 00:14:30,110 --> 00:14:33,520 and this would tell you where the magnetic field lines are 231 00:14:33,520 --> 00:14:35,873 so that maybe how they could perceive it. 232 00:14:37,590 --> 00:14:40,120 This mechanism is the very first 233 00:14:40,120 --> 00:14:44,223 to highlight a quantum physics phenomenon in animal biology. 234 00:14:45,640 --> 00:14:48,810 It opens up an entirely new investigative field, 235 00:14:48,810 --> 00:14:51,000 quantum biology. 236 00:14:51,000 --> 00:14:53,290 Simultaneously guided by the stars 237 00:14:53,290 --> 00:14:55,760 and the angle of the Earth's magnetic field, 238 00:14:55,760 --> 00:14:59,350 the blackcaps begin the next leg of their journey Southwest 239 00:14:59,350 --> 00:15:01,423 along the shore of the North Sea. 240 00:15:04,520 --> 00:15:06,250 After a long night of flying, 241 00:15:06,250 --> 00:15:10,333 the exhausted birds must imperatively rest and recuperate. 242 00:15:12,780 --> 00:15:15,400 The Sun rises over the Flemish coast, 243 00:15:15,400 --> 00:15:18,860 slowly revealing a green oasis in the distance. 244 00:15:18,860 --> 00:15:21,092 The Zwin Nature Park. 245 00:15:21,092 --> 00:15:23,675 (lively music) 246 00:15:28,290 --> 00:15:31,810 Last night was quite favorable for migration 247 00:15:31,810 --> 00:15:34,970 and a great number of blackcap are landing here this morning 248 00:15:39,290 --> 00:15:42,340 This forest is lush with protective shrubbery 249 00:15:42,340 --> 00:15:44,470 and an abundance of elderberries 250 00:15:44,470 --> 00:15:47,692 making it an ideal place for a layover. 251 00:15:47,692 --> 00:15:50,275 (serene music) 252 00:15:57,100 --> 00:16:00,002 All is going well until. 253 00:16:00,002 --> 00:16:03,490 (dramatic music) 254 00:16:03,490 --> 00:16:07,083 Luckily the birds time in this net won't be very long. 255 00:16:09,710 --> 00:16:13,200 Didier Vangeluwe and his fellow Zwin Park Rangers 256 00:16:13,200 --> 00:16:14,493 quickly free them up. 257 00:16:17,890 --> 00:16:19,610 Every year this scientist 258 00:16:19,610 --> 00:16:22,970 from the Royal Belgian Institute of Natural Sciences 259 00:16:22,970 --> 00:16:26,413 tags thousands of blackcaps with identification rings. 260 00:16:31,980 --> 00:16:34,500 Here's another blackcap. 261 00:16:34,500 --> 00:16:36,430 It's been mostly blackcaps today 262 00:16:36,430 --> 00:16:38,090 but this one's already tagged. 263 00:16:38,090 --> 00:16:40,732 It says Rix Museum, Stockholm 264 00:16:40,732 --> 00:16:42,933 which is the Swedish Royal Museum. 265 00:16:44,280 --> 00:16:47,460 So this bird was tagged by our Swedish colleagues a few days 266 00:16:47,460 --> 00:16:49,463 or possibly even a few years ago. 267 00:16:50,690 --> 00:16:53,290 Today we'll measure him, determine his age 268 00:16:53,290 --> 00:16:54,653 and update his fact sheet. 269 00:16:55,670 --> 00:16:59,310 That document is how little by little, we tracked the bird 270 00:16:59,310 --> 00:17:01,440 and try to understand how their migration patterns 271 00:17:01,440 --> 00:17:02,563 evolve over time. 272 00:17:03,460 --> 00:17:06,460 Let's put him in this bag so we can take a look at him later 273 00:17:08,160 --> 00:17:10,870 To raise the number of successful catches, 274 00:17:10,870 --> 00:17:13,610 Didier Vangeluwe uses a sonar trap 275 00:17:13,610 --> 00:17:15,863 to lure the birds into the net. 276 00:17:17,240 --> 00:17:19,640 Sonar emits bird calls and songs. 277 00:17:21,280 --> 00:17:22,830 It boosts a natural stimulus 278 00:17:22,830 --> 00:17:25,180 that may be a little surprising to many people. 279 00:17:26,849 --> 00:17:28,210 But it pertains to the fact that 280 00:17:28,210 --> 00:17:30,440 the birds usually sing at autumn 281 00:17:30,440 --> 00:17:33,390 even though we are well outside of the reproductive period. 282 00:17:35,310 --> 00:17:37,340 We think the songs are a natural mechanism 283 00:17:37,340 --> 00:17:38,600 that helps migrating birds 284 00:17:38,600 --> 00:17:42,090 understand if the area they fly over is appropriate. 285 00:17:42,090 --> 00:17:44,340 It can offer them enough food for a few days. 286 00:17:45,520 --> 00:17:48,280 So we imitate nature in order to increase our odds 287 00:17:48,280 --> 00:17:49,823 of catching more birds. 288 00:17:51,397 --> 00:17:54,040 To avoid subjecting the captured birds 289 00:17:54,040 --> 00:17:57,293 to too much stress, they must be tagged quickly. 290 00:17:59,140 --> 00:18:01,330 The researchers take advantage of the moment 291 00:18:01,330 --> 00:18:03,040 to measure and weigh them. 292 00:18:03,040 --> 00:18:05,303 Male wing length, 76. 293 00:18:06,840 --> 00:18:09,090 Their weight is a precious clue. 294 00:18:12,410 --> 00:18:14,710 This one weighs 17.8 grams 295 00:18:14,710 --> 00:18:17,410 which tells us that it arrived last night. 296 00:18:17,410 --> 00:18:18,330 Such light weight 297 00:18:18,330 --> 00:18:21,300 means this bird used up all of its fat reserves. 298 00:18:21,300 --> 00:18:23,030 Now it will take a break for a few days 299 00:18:23,030 --> 00:18:24,573 to replenish its energy. 300 00:18:25,760 --> 00:18:28,080 It will likely give back up to 22 grams 301 00:18:28,080 --> 00:18:30,680 which means it will gain about five grams here Zwin. 302 00:18:31,600 --> 00:18:32,770 That's why it's so important 303 00:18:32,770 --> 00:18:34,780 to manage the natural areas efficiently 304 00:18:34,780 --> 00:18:36,980 and why it's essential to limit pesticides 305 00:18:36,980 --> 00:18:38,493 and encourage biodiversity. 306 00:18:39,400 --> 00:18:40,570 These birds have to eat 307 00:18:41,830 --> 00:18:43,920 and if they don't have a varied biotope 308 00:18:43,920 --> 00:18:45,733 with fruit bushes like they do here, 309 00:18:46,760 --> 00:18:49,410 they won't be able to replenish their energy reserves 310 00:18:50,500 --> 00:18:53,870 which in turn mean they won't be able to migrate efficiently 311 00:18:53,870 --> 00:18:55,970 or might not even survive their migration. 312 00:18:57,780 --> 00:19:00,810 You have to understand that young blackcaps like this one 313 00:19:00,810 --> 00:19:05,063 typically have an annual mortality rate that's around 70%. 314 00:19:07,030 --> 00:19:09,680 The law of the jungle makes it clear. 315 00:19:09,680 --> 00:19:12,160 If the birds are not in the best shape possible, 316 00:19:12,160 --> 00:19:14,303 they will die, there's no other way. 317 00:19:15,730 --> 00:19:17,130 On the other hand, 318 00:19:17,130 --> 00:19:20,440 the survivors will be those that are fully developed, 319 00:19:20,440 --> 00:19:24,470 know how to feed efficiently, understand the weather 320 00:19:24,470 --> 00:19:27,200 and know when they've reached peak physical fitness 321 00:19:27,200 --> 00:19:28,680 so they can choose the right night 322 00:19:28,680 --> 00:19:31,603 to travel those 200, 250 kilometers. 323 00:19:33,140 --> 00:19:35,560 This is what affects population numbers. 324 00:19:35,560 --> 00:19:37,360 Where is this one from? 325 00:19:38,730 --> 00:19:40,520 No come on, 326 00:19:40,520 --> 00:19:43,513 I'm listening but alas, I don't speak Swedish. 327 00:19:45,010 --> 00:19:46,460 As soon as they are freed, 328 00:19:46,460 --> 00:19:49,343 the blackcaps resumed their elderberry feast. 329 00:19:50,450 --> 00:19:51,720 They only have a few days 330 00:19:51,720 --> 00:19:54,093 to replenish their body fat reserves. 331 00:19:55,630 --> 00:19:57,780 For a human weighing 70 kilos, 332 00:19:57,780 --> 00:20:00,280 that's the equivalent of gaining 21 kilos 333 00:20:00,280 --> 00:20:01,503 in less than a week. 334 00:20:03,580 --> 00:20:06,310 The tagging team is happy with their results, 335 00:20:06,310 --> 00:20:09,163 they've tagged 85 blackcaps today. 336 00:20:11,740 --> 00:20:14,860 Each time a tagged bird is recaptured, 337 00:20:14,860 --> 00:20:19,050 that data is meticulously entered in an open database. 338 00:20:19,050 --> 00:20:21,730 Decade's worth of information is stored here 339 00:20:21,730 --> 00:20:24,070 and it's the foundation of everything we know 340 00:20:24,070 --> 00:20:25,823 about blackcap migration. 341 00:20:28,420 --> 00:20:30,520 This is the recapture data map 342 00:20:30,520 --> 00:20:34,343 which shows every blackcap capture in Belgium since 1927. 343 00:20:38,840 --> 00:20:41,580 Each purple dot corresponds to a place in Belgium 344 00:20:41,580 --> 00:20:42,963 where a blackcap was found. 345 00:20:44,730 --> 00:20:47,100 We see that most blackcaps crossing over Belgium 346 00:20:47,100 --> 00:20:49,683 hibernate around the western Mediterranean basin. 347 00:20:51,470 --> 00:20:52,550 While most of the birds 348 00:20:52,550 --> 00:20:55,610 follow a logical path heading south, 349 00:20:55,610 --> 00:20:57,830 some of them migrate in another direction 350 00:20:57,830 --> 00:21:00,403 that may seem absurd, north. 351 00:21:01,720 --> 00:21:04,690 For example, here's a blackcap 352 00:21:05,740 --> 00:21:09,410 that was ringed in Greenburgh in Belgium on September 9th 353 00:21:10,540 --> 00:21:12,060 and this bird was found in Iceland 354 00:21:12,060 --> 00:21:13,733 on November 8th the same year. 355 00:21:14,630 --> 00:21:18,720 So instead of going south east, it went northeast. 356 00:21:18,720 --> 00:21:20,630 It's likely this bird won't survive 357 00:21:20,630 --> 00:21:22,820 but this is an example of the type of mistake 358 00:21:22,820 --> 00:21:24,900 a migrating bird can make. 359 00:21:24,900 --> 00:21:25,990 It can be fatal 360 00:21:25,990 --> 00:21:28,743 but it also allows them to discover new territories. 361 00:21:30,710 --> 00:21:31,870 The tagged blackcaps 362 00:21:31,870 --> 00:21:35,143 now have all the energy they'll need to resume their trip. 363 00:21:38,070 --> 00:21:39,540 As soon as night falls, 364 00:21:39,540 --> 00:21:42,420 they'll begin their journey to their next destination, 365 00:21:42,420 --> 00:21:43,253 France. 366 00:21:46,760 --> 00:21:49,120 Over a million blackcaps have been tagged 367 00:21:49,120 --> 00:21:53,880 in the past century and thanks to the numerous recaptures, 368 00:21:53,880 --> 00:21:57,902 we know there are two primary groups of migratory blackcaps. 369 00:21:57,902 --> 00:22:00,090 Those born in Western Europe 370 00:22:00,090 --> 00:22:03,933 that migrate west around the Alps and head toward Spain, 371 00:22:05,960 --> 00:22:08,820 those born in Eastern Europe avoid the Alps 372 00:22:08,820 --> 00:22:11,773 and migrate east towards the eastern Mediterranean. 373 00:22:14,110 --> 00:22:16,710 These two population groups are separated 374 00:22:16,710 --> 00:22:18,220 by an invisible barrier 375 00:22:18,220 --> 00:22:21,453 that ornithologist call the migration divide. 376 00:22:25,810 --> 00:22:29,220 Although we've known about migration divides for a long time 377 00:22:29,220 --> 00:22:31,420 it was only in the 1970s 378 00:22:31,420 --> 00:22:34,750 that work by Peter Berthold and Andreas Helbig 379 00:22:34,750 --> 00:22:37,373 gave us of better understanding of the phenomenon. 380 00:22:43,330 --> 00:22:45,310 It is at the Max Planck Institute 381 00:22:45,310 --> 00:22:47,570 in Radolfzell, Southern Germany 382 00:22:47,570 --> 00:22:51,950 that Peter Berthold now 78 years old carries out his studies 383 00:22:51,950 --> 00:22:54,260 after the astonishing discovery he made 384 00:22:54,260 --> 00:22:55,693 thanks to the blackcap. 385 00:22:59,503 --> 00:23:01,530 We went to collect blackcaps 386 00:23:01,530 --> 00:23:03,660 at Lake Neusiedl in Austria. 387 00:23:03,660 --> 00:23:06,190 And then we tested them in emmalin funnels 388 00:23:06,190 --> 00:23:07,660 right here in our lab. 389 00:23:07,660 --> 00:23:09,500 Where did the birds want to go? 390 00:23:09,500 --> 00:23:12,890 Obviously east towards Israel in Eastern Africa 391 00:23:12,890 --> 00:23:15,640 and then we took our own birds from around here 392 00:23:15,640 --> 00:23:17,700 that normally want to fly towards Burgundy 393 00:23:17,700 --> 00:23:20,563 and France and Spain, which is what they did. 394 00:23:21,520 --> 00:23:24,170 The next step was to place the birds in an aviary 395 00:23:24,170 --> 00:23:26,633 as mixed couples and then to observe them. 396 00:23:27,580 --> 00:23:30,200 The mixed couples produced hybrid birds 397 00:23:30,200 --> 00:23:33,343 that wanted to migrate south the perfect in-between. 398 00:23:34,220 --> 00:23:36,030 It was incredible. 399 00:23:36,030 --> 00:23:38,470 That's how we proved that migration orientation 400 00:23:38,470 --> 00:23:41,760 is genetically determined or in other words innate 401 00:23:41,760 --> 00:23:43,723 and inherited from the parents. 402 00:23:47,690 --> 00:23:49,680 When migratory directions combine 403 00:23:49,680 --> 00:23:51,540 from two different parent birds, 404 00:23:51,540 --> 00:23:55,223 it leads their offspring to an entirely new destination. 405 00:23:57,230 --> 00:24:00,160 The experiment proved that the birds migratory routes 406 00:24:00,160 --> 00:24:02,090 are clearly based on genetics 407 00:24:02,090 --> 00:24:04,613 and could also change very quickly. 408 00:24:07,500 --> 00:24:09,683 Yet several questions remain. 409 00:24:11,710 --> 00:24:14,703 Do the hybrids survived their migration heading south? 410 00:24:15,810 --> 00:24:18,320 And what happens to the innumerable blackcaps 411 00:24:18,320 --> 00:24:20,363 that follow new migratory routes? 412 00:24:22,860 --> 00:24:24,150 In the heart of Vienna 413 00:24:24,150 --> 00:24:26,810 on a protected island of the Danube River, 414 00:24:26,810 --> 00:24:29,550 Miriam Liedvogel from the Max Planck Institute 415 00:24:29,550 --> 00:24:31,860 For Evolutionary Biology in Plon 416 00:24:31,860 --> 00:24:34,913 is carrying out a large international study. 417 00:24:36,330 --> 00:24:38,450 Her goal is to precisely understand 418 00:24:38,450 --> 00:24:40,570 the blackcaps migratory routes 419 00:24:40,570 --> 00:24:43,083 by following each of them individually. 420 00:24:50,780 --> 00:24:52,280 We walk around on site 421 00:24:52,280 --> 00:24:54,480 and listen carefully for the blackcaps call. 422 00:24:57,200 --> 00:25:00,460 Once we have a general idea of where they're located, 423 00:25:00,460 --> 00:25:01,910 that's where we hang our net. 424 00:25:10,180 --> 00:25:12,000 We're really in the heart of Vienna 425 00:25:12,000 --> 00:25:13,950 in the very center of the city. 426 00:25:13,950 --> 00:25:16,360 The number of blackcaps found on this island 427 00:25:16,360 --> 00:25:18,783 in the middle of the Danube is incredible. 428 00:25:20,080 --> 00:25:23,570 If you walk along that path, you'll hear them everywhere. 429 00:25:23,570 --> 00:25:25,323 They nest very close to here. 430 00:25:26,320 --> 00:25:28,343 Our experiments take advantage of that. 431 00:25:30,380 --> 00:25:32,530 We've already caught a blackcap in our net. 432 00:25:33,860 --> 00:25:34,860 Let's go pick it up. 433 00:25:43,380 --> 00:25:44,770 There. 434 00:25:44,770 --> 00:25:47,083 Hey you, hello. 435 00:25:50,740 --> 00:25:51,573 A blackcap 436 00:25:51,573 --> 00:25:54,053 only weighs about 20 grams on average. 437 00:25:55,360 --> 00:25:57,450 Scientists must hence used tools 438 00:25:57,450 --> 00:25:59,233 adapted to that body weight. 439 00:26:01,520 --> 00:26:03,250 Miriam Liedvogel and her team 440 00:26:03,250 --> 00:26:07,893 have embraced a new piece of technology, a geo locator. 441 00:26:09,360 --> 00:26:13,030 This ultra lightweight receptor only does one thing, 442 00:26:13,030 --> 00:26:16,033 record the date and intensity of sunlight. 443 00:26:19,988 --> 00:26:22,690 That's the light sensor. 444 00:26:22,690 --> 00:26:24,053 It's outside the feathers. 445 00:26:25,200 --> 00:26:27,610 It records the length of the day 446 00:26:27,610 --> 00:26:29,900 and the maximum height of the sun. 447 00:26:29,900 --> 00:26:32,040 Using those two coordinates, 448 00:26:32,040 --> 00:26:34,653 we can calculate the longitude and latitude. 449 00:26:38,470 --> 00:26:41,870 That information allows us to follow their entire journey. 450 00:26:41,870 --> 00:26:43,610 We know when the bird has left here, 451 00:26:43,610 --> 00:26:46,293 where it makes it stops, where it spends the winter. 452 00:26:47,820 --> 00:26:49,610 The device will tell us all of that 453 00:26:49,610 --> 00:26:52,493 when we recaptured the bird and download its data. 454 00:26:54,620 --> 00:26:56,780 The downside of the Geo locator 455 00:26:56,780 --> 00:26:59,530 is that it doesn't transmit data remotely. 456 00:26:59,530 --> 00:27:02,330 The device will have to be retrieved the following year 457 00:27:02,330 --> 00:27:05,640 when this blackcap comes back to Austria. 458 00:27:05,640 --> 00:27:07,830 Luckily, the males are territorial 459 00:27:07,830 --> 00:27:09,550 so they have a tendency to nest 460 00:27:09,550 --> 00:27:12,630 in the same location year after year. 461 00:27:12,630 --> 00:27:14,110 But before any of that, 462 00:27:14,110 --> 00:27:17,060 they first need to survive their journey. 463 00:27:17,060 --> 00:27:20,070 The mini backpack must be precisely placed 464 00:27:20,070 --> 00:27:23,033 so as to not encumber the bird in any way. 465 00:27:24,180 --> 00:27:25,240 So our main objective 466 00:27:25,240 --> 00:27:26,800 is to attach these backpacks 467 00:27:26,800 --> 00:27:28,260 so that they're comfortable for the birds 468 00:27:28,260 --> 00:27:30,690 so that they have enough space to move around 469 00:27:30,690 --> 00:27:33,330 and they're gonna put some body mass on to migrate 470 00:27:33,330 --> 00:27:35,480 and we want to make sure that there's enough leeway 471 00:27:35,480 --> 00:27:38,630 for them to fly comfortably with these backpacks. 472 00:27:38,630 --> 00:27:40,370 One of the goals of this experiment 473 00:27:40,370 --> 00:27:42,270 is to prove that the hybrid birds 474 00:27:42,270 --> 00:27:45,050 which are born in the heart of the migratory divide 475 00:27:45,050 --> 00:27:49,040 are able to migrate south and return to their birthplace. 476 00:27:49,040 --> 00:27:50,960 This is why Austria was chosen 477 00:27:50,960 --> 00:27:52,733 as the site for the experiment. 478 00:27:54,676 --> 00:27:57,453 Austria is ideal for this research. 479 00:27:59,370 --> 00:28:01,230 This is where most of the geo locators 480 00:28:01,230 --> 00:28:02,693 are placed on the birds. 481 00:28:04,670 --> 00:28:08,838 The first year we installed about 200 geo locators in total, 482 00:28:08,838 --> 00:28:12,983 the following year we must have placed another 150 or so. 483 00:28:16,240 --> 00:28:17,290 In Austria, 484 00:28:17,290 --> 00:28:20,513 two groups of blackcap populations intermingle. 485 00:28:21,820 --> 00:28:26,040 Those who migrated West and of those heading east. 486 00:28:26,040 --> 00:28:28,420 To ensure a well-rounded experiment, 487 00:28:28,420 --> 00:28:33,420 the 350 geo locators were set in distinct geographic areas. 488 00:28:34,090 --> 00:28:35,550 Some were placed in the area 489 00:28:35,550 --> 00:28:38,730 that's home to blackcaps migrating West, 490 00:28:38,730 --> 00:28:42,030 others on easterly migrating blackcaps 491 00:28:42,030 --> 00:28:43,650 and others still were placed 492 00:28:43,650 --> 00:28:45,730 in the heart of the migration divide 493 00:28:45,730 --> 00:28:48,433 where the hybrid blackcaps migrate south. 494 00:28:52,540 --> 00:28:55,633 But the southern migration route is highly dangerous. 495 00:28:57,930 --> 00:29:00,263 The birds are forced to brave the Alps, 496 00:29:01,150 --> 00:29:04,490 cross the Mediterranean Sea at its widest part 497 00:29:04,490 --> 00:29:09,263 and tackle the ultimate obstacle, the Sahara Desert. 498 00:29:11,400 --> 00:29:13,960 Are the hybrid blackcaps capable of surviving 499 00:29:13,960 --> 00:29:15,740 such a trying ordeal? 500 00:29:15,740 --> 00:29:18,230 Most scientists wonder. 501 00:29:18,230 --> 00:29:20,790 But Miriam Liedvogel is the only one 502 00:29:20,790 --> 00:29:23,273 who actually has a way to find out. 503 00:29:26,730 --> 00:29:31,003 This young male is ready and his geo locator is in place. 504 00:29:34,340 --> 00:29:36,520 But before beginning the great journey 505 00:29:36,520 --> 00:29:40,063 males and females gather for one last grooming session. 506 00:29:41,510 --> 00:29:43,840 Their feathers need to be in optimal condition 507 00:29:43,840 --> 00:29:46,093 for the upcoming long-distance flight. 508 00:29:53,600 --> 00:29:56,280 This small pond on the edges of the Danube 509 00:29:56,280 --> 00:30:00,320 serves as a peaceful place where many different bird species 510 00:30:00,320 --> 00:30:03,463 that normally keep their distance gather for a bath. 511 00:30:07,770 --> 00:30:09,340 As the Sun sets 512 00:30:09,340 --> 00:30:12,403 the blackcaps embark on their long night of flying. 513 00:30:14,010 --> 00:30:17,263 They join the immense cohort of nocturnal migrants, 514 00:30:18,260 --> 00:30:21,340 a gathering of hundreds of thousands of other blackcaps 515 00:30:21,340 --> 00:30:24,403 already on their way to their winter destination. 516 00:30:26,770 --> 00:30:29,300 After migrating for a month and a half, 517 00:30:29,300 --> 00:30:32,020 the Scandinavian blackcaps heading west 518 00:30:32,020 --> 00:30:33,423 enter the Rhine Valley. 519 00:30:39,945 --> 00:30:43,170 (light music) 520 00:30:43,170 --> 00:30:46,283 Today's pit stop treat, grapes. 521 00:30:50,120 --> 00:30:52,193 Tomorrow, it will be apples. 522 00:30:53,550 --> 00:30:55,770 These sugar heavy fruits are key 523 00:30:55,770 --> 00:30:58,450 as the blackcaps remarkable metabolism 524 00:30:58,450 --> 00:31:01,803 transforms sugar into fat in record time. 525 00:31:05,120 --> 00:31:09,120 A few days later, the migrating birds come face-to-face 526 00:31:09,120 --> 00:31:11,930 with an immense mountain chain blocking their path, 527 00:31:11,930 --> 00:31:12,763 the Pyrenees. 528 00:31:15,520 --> 00:31:17,820 After flying overnight for nine hours, 529 00:31:17,820 --> 00:31:20,093 they once again need to refuel. 530 00:31:22,540 --> 00:31:25,630 How do the blackcaps keep up such an intense effort 531 00:31:25,630 --> 00:31:26,803 week after week? 532 00:31:28,780 --> 00:31:30,930 In the matter of long-distance runners, 533 00:31:30,930 --> 00:31:33,340 the blackcaps dig deep into their reserves 534 00:31:33,340 --> 00:31:35,233 on each leg of their migration. 535 00:31:40,080 --> 00:31:43,183 But they do so much more efficiently than mankind. 536 00:31:50,270 --> 00:31:52,700 The blackcaps remarkable metabolism 537 00:31:52,700 --> 00:31:56,930 allows it to transform lipids into energy ten times faster 538 00:31:56,930 --> 00:31:58,713 than most other vertebrates. 539 00:32:01,240 --> 00:32:05,400 During its journey it powers its strong pectoral muscles 540 00:32:05,400 --> 00:32:09,123 with a constant flow of energy from its body fat reserves. 541 00:32:10,470 --> 00:32:12,810 This is how the blackcap is able to fly 542 00:32:12,810 --> 00:32:15,113 for hours on end without foraging. 543 00:32:17,780 --> 00:32:18,833 Unlike this runner. 544 00:32:28,740 --> 00:32:30,260 It's late November 545 00:32:30,260 --> 00:32:32,510 and the first winter sleet hits the Pyrenees. 546 00:32:33,630 --> 00:32:35,900 The blackcaps make their way across 547 00:32:35,900 --> 00:32:38,513 either by going around or over the top. 548 00:32:40,910 --> 00:32:44,860 In two weeks, these passerines cover 1200 kilometers 549 00:32:44,860 --> 00:32:46,563 to get to southern Spain. 550 00:32:49,220 --> 00:32:52,310 For most of the blackcaps coming from Western Europe 551 00:32:52,310 --> 00:32:56,321 arriving in Andalusia, marks the end of their journey. 552 00:32:56,321 --> 00:32:58,821 (light music) 553 00:33:03,560 --> 00:33:06,530 Having left Northern Europe more than two months ago, 554 00:33:06,530 --> 00:33:09,483 the birds finally reached their winter destination. 555 00:33:12,390 --> 00:33:16,050 Located on the southernmost tip of the Iberian Peninsula, 556 00:33:16,050 --> 00:33:18,140 the Lowes Alcornocolles massive 557 00:33:18,140 --> 00:33:21,314 is in El Dorado for migrating blackcaps. 558 00:33:21,314 --> 00:33:23,897 (serene music) 559 00:33:26,800 --> 00:33:29,410 The young birds that survived their first journey, 560 00:33:29,410 --> 00:33:31,810 discover their new surroundings. 561 00:33:31,810 --> 00:33:33,950 A world of abundant food 562 00:33:33,950 --> 00:33:35,820 and where the temperature rarely drops 563 00:33:35,820 --> 00:33:37,653 below 10 degrees Celsius. 564 00:33:42,400 --> 00:33:43,770 If blackcaps could speak 565 00:33:43,770 --> 00:33:45,960 the native languages of their homelands, 566 00:33:45,960 --> 00:33:48,883 this forest would sound like the Tower of Babel. 567 00:33:53,170 --> 00:33:56,640 One would hear English, German, 568 00:33:56,640 --> 00:33:59,363 French and Scandinavian languages. 569 00:34:00,470 --> 00:34:04,323 But another language would also be present, Spanish. 570 00:34:07,320 --> 00:34:09,320 That's because these mountains are home 571 00:34:09,320 --> 00:34:12,823 to another group of blackcaps that haven't moved all year. 572 00:34:13,730 --> 00:34:16,793 These blackcaps don't migrate at all. 573 00:34:21,630 --> 00:34:25,130 A researcher at the Complutense University of Madrid, 574 00:34:25,130 --> 00:34:27,920 Javier Perez Tris studies the relationship 575 00:34:27,920 --> 00:34:29,870 between these sedentary blackcaps 576 00:34:29,870 --> 00:34:31,670 and the thousands of migrating birds 577 00:34:31,670 --> 00:34:33,223 that meet here each winter. 578 00:34:34,950 --> 00:34:37,510 Even though they're all part of the same species, 579 00:34:37,510 --> 00:34:41,026 their cohabitation is not always peaceful. 580 00:34:41,026 --> 00:34:43,359 (mumbles) 581 00:34:45,940 --> 00:34:47,373 So they arrived already. 582 00:34:49,360 --> 00:34:51,020 This must be the migratory blackcaps 583 00:34:51,020 --> 00:34:53,670 because they serve it at seldom use by the residents. 584 00:34:54,820 --> 00:34:56,110 If you look at the forest, 585 00:34:56,110 --> 00:34:59,147 this is the habitat of the resident population of blackcaps 586 00:34:59,147 --> 00:35:01,653 in the Jakarta area. 587 00:35:02,940 --> 00:35:06,520 The migrants are arriving to the place like in high numbers 588 00:35:06,520 --> 00:35:09,580 so the amount of blackcaps is 20 times as much 589 00:35:09,580 --> 00:35:11,833 as they are in Summer. 590 00:35:13,200 --> 00:35:15,640 The interesting thing is that the juvenile migrants 591 00:35:15,640 --> 00:35:18,040 they are apparently pushed outside the forest 592 00:35:18,040 --> 00:35:21,150 to the shrub lands like these ones that you see here. 593 00:35:21,150 --> 00:35:24,530 So this is an open habitat and they have to move in the open 594 00:35:24,530 --> 00:35:26,600 between the bushes and this is risky for them. 595 00:35:26,600 --> 00:35:29,850 So they get exposed to (mumbles) and all the radiators 596 00:35:29,850 --> 00:35:30,900 that can attack them. 597 00:35:35,060 --> 00:35:36,858 While the youngest migratory blackcaps 598 00:35:36,858 --> 00:35:39,440 are pushed to the edge of the forest, 599 00:35:39,440 --> 00:35:42,803 the adults claimed territory beneath the cork oaks. 600 00:35:48,720 --> 00:35:52,350 Javier Perez Tris can spot morphological differences 601 00:35:52,350 --> 00:35:54,930 that exist between the migratory birds 602 00:35:54,930 --> 00:35:57,667 and the sedentary ones in a single glance. 603 00:36:04,580 --> 00:36:05,830 12.5, 1.5, 5. 604 00:36:10,730 --> 00:36:12,660 This is a migrant for sure. 605 00:36:12,660 --> 00:36:14,960 So the main difference between the two birds, 606 00:36:14,960 --> 00:36:17,290 between the migrant and and the resident 607 00:36:17,290 --> 00:36:20,880 is the wings of the migrants are much longer, 608 00:36:20,880 --> 00:36:25,550 they are more pointy and the tail is comparatively shorter. 609 00:36:27,000 --> 00:36:29,180 The legs are typically shorter also. 610 00:36:29,180 --> 00:36:31,970 I mean this is very good at migrating 611 00:36:31,970 --> 00:36:35,640 and then the migrants typically have a lighter structure 612 00:36:35,640 --> 00:36:38,980 so you don't carry so much load. 613 00:36:38,980 --> 00:36:43,850 The residents, they have long legs, bigger bills, 614 00:36:43,850 --> 00:36:48,020 rounded wings better for maneuvering in those vegetation. 615 00:36:48,020 --> 00:36:50,000 At the same time by being bigger, 616 00:36:50,000 --> 00:36:54,050 we think that they can afford confrontation (mumbles) 617 00:36:54,050 --> 00:36:55,380 with the migrants that come from the north 618 00:36:55,380 --> 00:36:57,080 and exploit the same territories, 619 00:36:57,080 --> 00:36:59,640 they use for the whole year. 620 00:36:59,640 --> 00:37:03,910 Probably they are not very (laughing) 621 00:37:03,910 --> 00:37:05,460 I mean very fond of each other. 622 00:37:08,880 --> 00:37:10,539 The birds that coexist 623 00:37:10,539 --> 00:37:12,480 in this Andalusian forest 624 00:37:12,480 --> 00:37:14,830 prove that different behaviors can be present 625 00:37:14,830 --> 00:37:18,023 in creatures that are technically the same species. 626 00:37:25,620 --> 00:37:28,503 Some of the blackcaps decide to go a lot further. 627 00:37:29,640 --> 00:37:33,200 These tireless travelers cross the Strait of Gibraltar 628 00:37:33,200 --> 00:37:36,100 and continue until they reach the Magreb countries 629 00:37:36,100 --> 00:37:37,783 or even Western Africa. 630 00:37:39,800 --> 00:37:42,800 All these birds chose to leave at the right time 631 00:37:42,800 --> 00:37:46,313 as winter has now taken over all of northern Europe. 632 00:37:51,618 --> 00:37:54,940 (lively music) 633 00:37:54,940 --> 00:37:56,990 In southern England, 634 00:37:56,990 --> 00:37:59,223 morning frost or more and more frequent. 635 00:38:02,650 --> 00:38:05,290 The forests and hedges now have little to offer 636 00:38:05,290 --> 00:38:06,173 to passerines. 637 00:38:08,500 --> 00:38:11,400 A blackcaps chances of survival are very low 638 00:38:11,400 --> 00:38:13,423 in such hostile environments. 639 00:38:16,670 --> 00:38:21,200 Yet against all logic, some blackcaps take the risk 640 00:38:21,200 --> 00:38:23,293 of hibernating in these latitudes. 641 00:38:27,130 --> 00:38:29,160 In Chilbolton in Hampshire, 642 00:38:29,160 --> 00:38:32,193 one man is lucky enough to have witnessed this himself. 643 00:38:34,570 --> 00:38:36,930 A bird lover since he was a boy, 644 00:38:36,930 --> 00:38:40,010 Glynne Evans has noticed this mysterious phenomenon 645 00:38:40,010 --> 00:38:42,083 growing in scale over the years. 646 00:38:46,760 --> 00:38:51,070 50 years ago we never used to see blackcaps in gardens 647 00:38:51,070 --> 00:38:56,070 in winter in England and that's comparing with 25 blackcaps 648 00:38:58,220 --> 00:39:02,260 that I've encountered in the garden this winter. 649 00:39:02,260 --> 00:39:05,300 I mean always these things are very fascinating. 650 00:39:05,300 --> 00:39:07,770 You get these strange changes that take place 651 00:39:07,770 --> 00:39:09,063 and one wonders why. 652 00:39:14,380 --> 00:39:16,540 The presence of these wintering blackcaps 653 00:39:16,540 --> 00:39:17,493 is a mystery. 654 00:39:19,090 --> 00:39:20,823 Why are there numbers rising? 655 00:39:22,170 --> 00:39:24,003 How did they survive the winter? 656 00:39:25,960 --> 00:39:29,270 Glynne is part of a vast network of voluntary observers 657 00:39:29,270 --> 00:39:33,210 that work in collaboration with scientists from the BTO, 658 00:39:33,210 --> 00:39:35,483 the British Trust for Ornithology. 659 00:39:36,370 --> 00:39:38,840 Greg Conway is the Program Coordinator 660 00:39:38,840 --> 00:39:42,510 and he has several explanations for the birds behavior. 661 00:39:42,510 --> 00:39:44,310 The wings distribution of blackcap 662 00:39:44,310 --> 00:39:47,720 is increased by it was 77%. 663 00:39:47,720 --> 00:39:49,800 We know that the climate has changed 664 00:39:49,800 --> 00:39:51,940 quite considerably since the 1980s. 665 00:39:51,940 --> 00:39:53,890 We've got substantial warming 666 00:39:53,890 --> 00:39:56,360 across pretty much the whole the British Isles. 667 00:39:56,360 --> 00:39:57,550 That could be at a point now 668 00:39:57,550 --> 00:39:59,940 where that makes it more suitable for the birds. 669 00:39:59,940 --> 00:40:01,970 They can survive better in these areas 670 00:40:01,970 --> 00:40:03,600 but there are other factors as well. 671 00:40:03,600 --> 00:40:06,150 I mean in the British Isles people really love the birds 672 00:40:06,150 --> 00:40:10,420 so we find between 48 maybe 55 percent of households 673 00:40:10,420 --> 00:40:11,720 actually put food out for birds 674 00:40:11,720 --> 00:40:13,320 during the course of the winter. 675 00:40:13,320 --> 00:40:17,330 So that's a substantial resource for many wintering birds. 676 00:40:17,330 --> 00:40:19,913 (lively music) 677 00:40:21,710 --> 00:40:22,550 Great Britain 678 00:40:22,550 --> 00:40:25,873 is currently Europe's biggest bird food consumer by far. 679 00:40:38,740 --> 00:40:39,980 The sale of bird food 680 00:40:39,980 --> 00:40:42,620 is a multi-million Euro annual business 681 00:40:42,620 --> 00:40:44,673 that shows no signs of slowing. 682 00:40:46,420 --> 00:40:48,790 It's encouraged by the country's garden stores 683 00:40:48,790 --> 00:40:49,983 and supermarkets. 684 00:40:52,160 --> 00:40:56,720 This winter, some 60, 000 tons of seeds, fat balls, 685 00:40:56,720 --> 00:41:00,133 dried insects and fruit were offered to the birds. 686 00:41:02,130 --> 00:41:04,370 But while these industrial food products 687 00:41:04,370 --> 00:41:06,290 are a joy for the passerines. 688 00:41:06,290 --> 00:41:08,040 Ornithologist wishing to observe 689 00:41:08,040 --> 00:41:10,340 specific types of birds in their gardens 690 00:41:10,340 --> 00:41:12,603 are forced to cook up something of their own. 691 00:41:14,690 --> 00:41:17,040 That's just what Glyne Evans does, 692 00:41:17,040 --> 00:41:21,250 having perfected his very own recipe for blackcaps. 693 00:41:21,250 --> 00:41:23,730 Blackcaps are insectivores birds 694 00:41:23,730 --> 00:41:27,050 and the commercial fat balls are rather hard for them. 695 00:41:27,050 --> 00:41:30,020 So I try and make a match of it a bit softer. 696 00:41:30,020 --> 00:41:33,120 Rather like this which appears quite hard. 697 00:41:33,120 --> 00:41:35,760 But if I stick a spoon in 698 00:41:35,760 --> 00:41:40,260 you see that it's much softer than the hard things 699 00:41:40,260 --> 00:41:43,843 that we get from commercial suppliers. 700 00:41:46,600 --> 00:41:48,620 With an increasingly mild weather 701 00:41:48,620 --> 00:41:51,210 and an abundance of available food, 702 00:41:51,210 --> 00:41:54,883 the blackcap is now able to survive the English winter. 703 00:42:00,180 --> 00:42:03,040 Yet one question remains, 704 00:42:03,040 --> 00:42:04,940 are these blackcaps the same ones 705 00:42:04,940 --> 00:42:06,880 we see in England in summer? 706 00:42:06,880 --> 00:42:09,713 Or as some believe, are they from somewhere else? 707 00:42:11,090 --> 00:42:13,900 Benjamin Van Doren from Oxford University 708 00:42:13,900 --> 00:42:16,973 hopes to have the answer to that question soon. 709 00:42:18,780 --> 00:42:23,090 Last winter, he fit about 30 blackcaps with geo locators 710 00:42:23,090 --> 00:42:25,153 to find out where they spend the summer. 711 00:42:26,240 --> 00:42:28,200 It's crucial that the young scientist 712 00:42:28,200 --> 00:42:31,333 retrieves as many of his geo locators as possible. 713 00:42:33,850 --> 00:42:35,580 He meets up with Glyne Evans, 714 00:42:35,580 --> 00:42:38,513 who rigged his garden with capture nets for the occasion. 715 00:42:39,750 --> 00:42:42,320 You have information from ringing blackcaps 716 00:42:42,320 --> 00:42:45,070 but there have only been a handful of recoveries 717 00:42:45,070 --> 00:42:48,860 of these birds that have spent the winter in Britain 718 00:42:48,860 --> 00:42:50,360 and have been captured elsewhere. 719 00:42:50,360 --> 00:42:52,730 So these blackcaps could be going elsewhere 720 00:42:52,730 --> 00:42:54,560 or could be staying in the UK 721 00:42:54,560 --> 00:42:57,750 or could be doing other things that we would have no idea 722 00:42:57,750 --> 00:43:00,930 without tracking them individually with geo locators. 723 00:43:00,930 --> 00:43:04,050 Last winter we deployed 36 geo locators 724 00:43:04,050 --> 00:43:08,113 we'll hope to get back at least 12%, 15% if we can. 725 00:43:11,080 --> 00:43:12,950 Of the 36 blackcaps ringed 726 00:43:12,950 --> 00:43:14,950 with geo locators in this garden, 727 00:43:14,950 --> 00:43:17,053 only three have returned this winter. 728 00:43:20,610 --> 00:43:23,363 But Benjamin Van Doren can finally smile. 729 00:43:25,070 --> 00:43:28,773 The data he's collected reveals something extraordinary. 730 00:43:30,310 --> 00:43:34,740 The first bird that we captured left the UK on March 29 731 00:43:34,740 --> 00:43:36,808 and then we can see it spent the summer months 732 00:43:36,808 --> 00:43:40,870 in eastern France and worked its way back to the UK 733 00:43:40,870 --> 00:43:42,393 by early November. 734 00:43:43,300 --> 00:43:45,380 Is very weird for a bird to do. 735 00:43:45,380 --> 00:43:46,930 I don't know any other examples of birds 736 00:43:46,930 --> 00:43:50,910 that in the northern hemisphere migrated south 737 00:43:50,910 --> 00:43:53,260 for the summer and north for the winter. 738 00:43:53,260 --> 00:43:56,780 The second bird, it went all the way to southern Germany 739 00:43:56,780 --> 00:43:59,260 potentially the Western Czech Republic. 740 00:43:59,260 --> 00:44:00,450 The third bird we caught 741 00:44:00,450 --> 00:44:02,500 it seems to have gone to a similar location, 742 00:44:02,500 --> 00:44:05,150 potentially a little bit further south towards Italy. 743 00:44:07,260 --> 00:44:09,170 The data collected from the three birds 744 00:44:09,170 --> 00:44:10,173 is baffling. 745 00:44:12,830 --> 00:44:16,620 In autumn when the majority of birds headed south, 746 00:44:16,620 --> 00:44:20,620 these three blackcaps migrated towards the Northwest. 747 00:44:20,620 --> 00:44:23,900 Global warming and an abundance of food from humans 748 00:44:23,900 --> 00:44:26,593 allowed them to survive the English winter. 749 00:44:31,520 --> 00:44:32,830 It seems as though England 750 00:44:32,830 --> 00:44:35,123 is becoming a new migratory destination. 751 00:44:49,376 --> 00:44:52,126 (dramatic music) 752 00:44:53,120 --> 00:44:54,690 As soon as winter ends, 753 00:44:54,690 --> 00:44:57,303 the blackcaps prepare for the return trip. 754 00:44:59,711 --> 00:45:02,420 The first to go are those that spent winter 755 00:45:02,420 --> 00:45:03,703 in the United Kingdom. 756 00:45:07,420 --> 00:45:08,460 In early March, 757 00:45:08,460 --> 00:45:11,240 the blackcaps that spent winter in western Africa 758 00:45:11,240 --> 00:45:13,810 rejoin the birds from the Iberian Peninsula 759 00:45:13,810 --> 00:45:16,053 that are already in route towards the north. 760 00:45:20,437 --> 00:45:21,660 Three weeks later, 761 00:45:21,660 --> 00:45:25,013 these birds reach the foothills of the Pyrenees Mountains. 762 00:45:30,230 --> 00:45:31,660 Their arrival coincides 763 00:45:31,660 --> 00:45:34,863 with the flowering of the willow trees and wild cherries. 764 00:45:37,620 --> 00:45:39,430 With few insects around, 765 00:45:39,430 --> 00:45:43,323 the blackcaps adapt once again filling up on nectar. 766 00:45:45,160 --> 00:45:47,480 Less than six weeks after leaving Andalusia, 767 00:45:47,480 --> 00:45:52,200 the first migratory birds arrive at their destination. 768 00:45:52,200 --> 00:45:55,740 The blackcaps that nest in France, Belgium and Switzerland 769 00:45:55,740 --> 00:45:56,943 are already home. 770 00:46:01,690 --> 00:46:05,010 In the (mumbles) Valley in the heart of the Austrian Alps, 771 00:46:05,010 --> 00:46:08,463 blackcaps returned from every possible direction. 772 00:46:17,390 --> 00:46:21,123 Miriam Leidvogel is waiting for them here in the forest. 773 00:46:23,200 --> 00:46:26,130 This valley is in the heart of the migratory divide 774 00:46:26,130 --> 00:46:30,193 making it a great location for recapturing hybrid blackcaps. 775 00:46:34,220 --> 00:46:36,920 Birds from the southwest, the southeast 776 00:46:36,920 --> 00:46:41,325 and maybe even from England all come here for mating season. 777 00:46:41,325 --> 00:46:44,750 (birds chirping) 778 00:46:44,750 --> 00:46:47,369 It's now the male's turn to sing. 779 00:46:47,369 --> 00:46:50,119 (birds chirping) 780 00:46:51,590 --> 00:46:53,943 New couples form every day. 781 00:46:56,900 --> 00:46:59,333 Soon the first eggs will appear. 782 00:47:01,510 --> 00:47:05,740 Since returning the blackcaps have once again become diurnal 783 00:47:05,740 --> 00:47:08,793 and taken up a high protein insect based diet. 784 00:47:14,430 --> 00:47:17,573 This is exactly what their fledglings need to grow quickly. 785 00:47:25,390 --> 00:47:28,150 Males and females must also regularly remove 786 00:47:28,150 --> 00:47:30,560 the excrements produced by their chicks 787 00:47:30,560 --> 00:47:33,953 which is conveniently wrapped in small airtight packets. 788 00:47:37,168 --> 00:47:39,668 (light music) 789 00:47:51,300 --> 00:47:54,890 Joseph Hemburger, the valleys leading ornithologist, 790 00:47:54,890 --> 00:47:56,253 is already hard at work. 791 00:48:03,250 --> 00:48:06,760 The night before Miriam Leidvogel spotted a male 792 00:48:06,760 --> 00:48:08,913 that seemed to have a Geo locator. 793 00:48:10,520 --> 00:48:12,590 Capturing the bird and retrieving the data 794 00:48:12,590 --> 00:48:15,883 from its geo locator is crucial for the ornithologists. 795 00:48:17,840 --> 00:48:21,610 To be successful, they'll need every bit of their know-how 796 00:48:21,610 --> 00:48:23,383 and also a little luck. 797 00:48:26,017 --> 00:48:26,873 [Female translator] How's it going? 798 00:48:26,873 --> 00:48:28,560 There's a male in the net, 799 00:48:28,560 --> 00:48:29,393 I'll go, get him. 800 00:48:29,393 --> 00:48:30,713 [Female Translator] Wonderful. 801 00:48:34,581 --> 00:48:38,450 Yes, this one was ringed with this geo locator a year ago. 802 00:48:38,450 --> 00:48:40,570 Maybe he went to Africa or something, 803 00:48:40,570 --> 00:48:41,770 we're about to find out. 804 00:48:42,630 --> 00:48:44,323 Let's remove the geo locator. 805 00:48:50,600 --> 00:48:55,570 The bird is okay. 806 00:48:55,570 --> 00:48:56,573 We can release him. 807 00:49:01,350 --> 00:49:04,150 Now to visualize exactly where he was located, 808 00:49:04,150 --> 00:49:06,400 we need to download the data to the computer. 809 00:49:09,020 --> 00:49:11,830 This data, the very latest of the season, 810 00:49:11,830 --> 00:49:16,193 is being added to 66 other findings taken all over Europe. 811 00:49:19,890 --> 00:49:23,693 The blackcaps migratory map is slowly starting to change. 812 00:49:30,917 --> 00:49:34,330 [Female Translator] The data seems okay. 813 00:49:34,330 --> 00:49:35,390 The information we need 814 00:49:35,390 --> 00:49:38,813 to trace this migratory blackcaps itinerary is all here. 815 00:49:41,320 --> 00:49:43,780 What we can see is exactly what we wanted to know 816 00:49:46,040 --> 00:49:47,550 which is that the hybrid birds 817 00:49:47,550 --> 00:49:50,233 do indeed follow intermediate itineraries. 818 00:49:52,800 --> 00:49:55,160 They don't follow the east or west trajectories 819 00:49:55,160 --> 00:49:56,823 around the Mediterranean Sea, 820 00:49:58,070 --> 00:49:59,720 they go straight down the middle. 821 00:50:01,690 --> 00:50:03,610 What the data proves with certainty 822 00:50:03,610 --> 00:50:06,830 is that it's possible for a bird to fly over the Alps, 823 00:50:06,830 --> 00:50:09,970 the Mediterranean Sea and the Sahara Desert 824 00:50:10,870 --> 00:50:12,870 before returning unharmed. 825 00:50:12,870 --> 00:50:15,423 That was not obvious before we had this data. 826 00:50:16,330 --> 00:50:19,480 So for us, the blackcap is particularly interesting 827 00:50:19,480 --> 00:50:21,290 because it has an immense repertoire 828 00:50:21,290 --> 00:50:23,540 of possible migratory routes. 829 00:50:23,540 --> 00:50:26,630 It easily adapts to different environmental conditions 830 00:50:26,630 --> 00:50:29,150 and it can overcome numerous barriers. 831 00:50:29,150 --> 00:50:30,740 This is a very robust bird 832 00:50:30,740 --> 00:50:34,010 that quickly adapts to any new territory for example, 833 00:50:34,010 --> 00:50:36,750 those that survive winter on the British Isles. 834 00:50:36,750 --> 00:50:39,803 I wholeheartedly believe this is the bird of the future. 835 00:50:43,270 --> 00:50:45,090 These dedicated researchers 836 00:50:45,090 --> 00:50:48,210 have learned that the blackcap shows complex behavior 837 00:50:48,210 --> 00:50:50,853 and evolving migratory skills. 838 00:50:53,800 --> 00:50:56,160 Its incredible ability to adapt 839 00:50:56,160 --> 00:51:00,900 allows it to modify its itinerary, change its diet 840 00:51:00,900 --> 00:51:04,033 and succeed where many other species are failing. 841 00:51:06,510 --> 00:51:08,900 It's one of the few migratory passerines 842 00:51:08,900 --> 00:51:10,753 whose population is growing. 843 00:51:13,450 --> 00:51:15,910 By migrating in the opposite direction 844 00:51:15,910 --> 00:51:17,700 and spending winter in England, 845 00:51:17,700 --> 00:51:20,020 it demonstrates an amazing defiance 846 00:51:20,020 --> 00:51:22,003 in the face of human activity. 847 00:51:24,750 --> 00:51:28,210 If the future of biodiversity belongs to the animals 848 00:51:28,210 --> 00:51:30,940 with the best capacity for adaptation, 849 00:51:30,940 --> 00:51:33,813 the blackcap is certain to be among them. 850 00:51:35,710 --> 00:51:38,293 (lively music)