0:00:08.620,0:00:13.050 In May of 1822, [br]Count Christian Ludwig von Bothmer 0:00:13.050,0:00:17.739 shot down a stork over his castle[br]grounds in North Germany. 0:00:17.739,0:00:23.024 However, he wasn’t the first person[br]to hunt that specific bird. 0:00:23.024,0:00:25.064 Upon recovering the stork, 0:00:25.064,0:00:30.213 von Bothmer found it impaled [br]by a yard long wooden spear. 0:00:30.213,0:00:34.464 A local professor determined [br]the weapon was African in origin, 0:00:34.464,0:00:38.652 suggesting that somehow, [br]this stork was speared in Africa 0:00:38.652,0:00:44.007 and then flew over 2,500 kilometers [br]to the count’s castle. 0:00:44.007,0:00:48.706 This astonishing flight wasn’t just[br]evidence of the stork’s resilience. 0:00:48.706,0:00:54.583 It was an essential clue in a mystery[br]that plagued scientists for centuries: 0:00:54.583,0:00:57.653 the seasonal disappearance of birds. 0:00:57.653,0:01:02.538 Ancient naturalists had various theories[br]to explain the annual vanishing act 0:01:02.538,0:01:05.608 we now know as migration. 0:01:05.608,0:01:11.044 Aristotle himself proposed [br]three particularly popular ideas. 0:01:11.044,0:01:16.749 One theory was that birds transformed into[br]different bodies that suited the season. 0:01:16.749,0:01:20.149 For example, summer time garden warblers 0:01:20.149,0:01:24.149 were believed to transform [br]into black caps every winter. 0:01:24.149,0:01:28.922 In reality these are two distinct species—[br]similar in shape and size, 0:01:28.922,0:01:31.912 but never appearing at the same time. 0:01:31.912,0:01:36.404 Over the following centuries, birds [br]were said to morph into humans, 0:01:36.404,0:01:40.074 plants, and even the timbers of ships. 0:01:40.074,0:01:45.437 This last transmutation was especially[br]popular with many Christian clergy. 0:01:45.437,0:01:48.477 If barnacle geese were truly made of wood, 0:01:48.477,0:01:54.408 they could be deemed vegetarian [br]and enjoyed during meatless fasts. 0:01:54.408,0:02:00.079 Aristotle’s second and even more enduring[br]hypothesis was that birds hibernate. 0:02:00.079,0:02:02.209 This isn’t so far-fetched. 0:02:02.209,0:02:04.549 Some species do enter short, 0:02:04.549,0:02:08.549 deep sleeps which lower their heart rates[br]and metabolisms. 0:02:08.549,0:02:12.329 And there’s at least one truly [br]hibernating bird: 0:02:12.329,0:02:16.937 the common poorwill sleeps out winters[br]in the deserts of North America. 0:02:16.937,0:02:21.341 But researchers were proposing much more[br]outlandish forms of hibernation 0:02:21.341,0:02:23.971 well into the 19th century. 0:02:23.971,0:02:29.019 Barn swallows were said to remove [br]their feathers and hibernate in holes, 0:02:29.019,0:02:33.588 or sleep through the winter at the bottom[br]of lakes and rivers. 0:02:33.588,0:02:36.948 Aristotle’s final theory [br]was much more reasonable, 0:02:36.948,0:02:40.368 and resembled something[br]like realistic migration. 0:02:40.368,0:02:44.504 However, this idea was also taken [br]to extremes. 0:02:44.504,0:02:50.762 In 1666, the leading migration advocate[br]was convinced that each winter, 0:02:50.762,0:02:52.892 birds flew to the moon. 0:02:52.892,0:02:58.081 It might seem strange that prominent [br]researchers considered such bizarre ideas. 0:02:58.081,0:03:01.138 But to be fair, the true story [br]of migration 0:03:01.138,0:03:05.178 may be even harder[br]to believe than their wildest theories. 0:03:05.178,0:03:09.309 Roughly 20% of all bird species [br]migrate each year, 0:03:09.309,0:03:12.989 following warm weather and fresh food[br]around the planet. 0:03:12.989,0:03:16.439 For birds who spend their summers[br]in the northern hemisphere, 0:03:16.439,0:03:22.214 this journey can span [br]from 700 to over 17,000 kilometers, 0:03:22.214,0:03:26.364 with some flights lasting as long[br]as four months. 0:03:26.364,0:03:32.995 Birds who migrate across oceans may soar[br]without stopping for over 100 hours. 0:03:32.995,0:03:37.445 Sleeping and eating on the fly, [br]they navigate the endless ocean 0:03:37.445,0:03:42.355 by the stars, wind currents, [br]and Earth’s magnetic field. 0:03:42.355,0:03:47.133 Tracking the specifics of these epic[br]expeditions is notoriously difficult. 0:03:47.133,0:03:51.133 And while birds often take [br]the most direct route possible, 0:03:51.133,0:03:54.733 storms and human development[br]can alter their paths, 0:03:54.733,0:03:58.573 further complicating our attempts[br]to chart migration. 0:03:58.573,0:04:02.986 Fortunately, Count von Bothmer’s stork[br]offered physical proof 0:04:02.986,0:04:06.986 not only that European storks were[br]migrating south for the winter, 0:04:06.986,0:04:10.186 but also where they were migrating to. 0:04:10.186,0:04:12.296 Ornithologists across the continent 0:04:12.296,0:04:15.436 were eager to map the trajectory[br]of this flight, 0:04:15.436,0:04:18.446 including Johannes Thienemann. 0:04:18.446,0:04:22.316 Owner of the world’s first permanent[br]bird observatory, 0:04:22.316,0:04:26.446 Thienemann was a major public advocate[br]for the study of birds. 0:04:26.446,0:04:28.866 And to solve the field’s biggest mystery, 0:04:28.866,0:04:32.866 he wrangled an army of volunteers[br]from across Germany. 0:04:32.866,0:04:38.823 His team used aluminum rings to tag[br]the legs of two thousand storks 0:04:38.823,0:04:42.823 with unique numbers and the address[br]of his offices. 0:04:42.823,0:04:47.452 Then he advertised the initiative [br]as widely as possible. 0:04:47.452,0:04:51.590 His hope was that word of the experiment[br]would find its way to Africa, 0:04:51.590,0:04:57.109 so people finding the tags would know[br]to mail them back with more information. 0:04:57.109,0:05:00.959 Sure enough, from 1908 to 1913, 0:05:00.959,0:05:07.998 Thienemann received 178 rings, [br]48 of which had been found in Africa. 0:05:07.998,0:05:13.013 Using this data, he plotted the first[br]migration route ever discovered, 0:05:13.013,0:05:18.033 and definitively established that storks[br]were not, in fact, flying to the moon.