生命之旅第三集:空中運(yùn)輸 Airborne

[00:00.00] [00:08.50] [00:11.50]Imagine the freedom... The excitement, of taking to the skies! [00:17.20] [00:20.20]To fly as free as a bird is something we humans can only dream of [00:25.07] [00:25.78]...but for two thirds of the animals alive today it's a reality. [00:29.94] [00:38.29]Flight is one of the greatest breakthroughs in the whole story of evolution. [00:42.75] [00:44.29]We're going to find out just how life achieved this miracle and took to the skies. [00:49.73] [00:54.04]A string of evolutionary accidents created wings in four very different ways [01:00.10] [01:03.25]Hundreds of millions of years apart. [01:05.65] [01:20.20]Flight is a unique weapon. [01:22.29] [01:25.04]Mastering the skies leaves earthbound creatures at your mercy... [01:28.87] [01:35.11]When there's a black eagle on the wing, [01:36.98] [01:37.18]rock hyrax need to be especially alert to aerial attack... [01:41.21] [02:20.26]But wings aren't just about extra strike power. [02:23.32] [02:25.03]Flying is also the fastest, most efficient way to travel... [02:28.46] [02:29.00]It allows you to find food, explore new territory or escape from danger. [02:33.99] [02:38.21]So there were lots of good reasons for life to get into the air... [02:41.64] [02:43.55]...but who would overcome gravity and get airborne first [02:47.07] [02:50.82]500 million years ago, animals took their first steps onto land. [02:55.88] [03:02.63]The pioneers included millipedes... scorpions... and spiders. [03:07.13] [03:11.38]While these creatures quickly spread over the earth... [03:14.37] [03:14.88]the skies remained empty and lifeless. [03:18.34] [03:24.42]Life stayed grounded for at least a hundred million years. [03:28.36] [03:28.56]Until one group of animals finally defied gravity [03:31.96] [03:32.16]and changed the course of evolutionary history for ever. [03:36.29] [03:42.41]The insects - the first animals ever to fly. [03:46.74] [03:48.41]But how did they sprout wings? [03:50.47] [03:52.75]One idea is that it's all because insects love to sunbathe... [03:56.31] [04:01.56]Insects are cold-blooded - they need heat from outside to warm up and move around. [04:06.96] [04:08.23]They often bask in the sun... and maybe in the past, [04:11.86] [04:12.07]one type of bug developed small flaps on its back to help soak up the rays [04:17.23] [04:17.44]- like mini solar panels. [04:18.97] [04:20.54]Purely by chance, these panels may also have helped the insect to be carried by the wind... [04:25.45] [04:34.12]Perhaps the panels then evolved into a more aerodynamic shape [04:38.29] [04:38.50]- eventually becoming wings. [04:40.33] [04:46.30]But there's a flaw in this theory. [04:48.10] [04:48.74]Insect wings have complex hinged joints, worked by muscles and tendons. [04:53.57] [04:55.15]Could they really have evolved from those simple fixed panels? [04:58.71] [05:02.89]There is another explanation as to how flight began... [05:06.12] [05:06.69]bizarrely it may have started in the water. [05:09.06] [05:16.00]Many insects spend the first part of their lives submerged... [05:20.20] [05:21.07]They breathe through gills, pumping them up and down to take in oxygen... [05:25.47] [05:26.04]Some scientists believe that in the past gills like these gradually turned into wings. [05:31.85] [05:34.35]What triggered such a dramatic change? [05:36.72] [05:38.76]One insect living in the rivers of North America holds a clue... [05:42.35] [05:46.03]Stonefly larvae spend almost their first year underwater, [05:49.97] [05:50.40]then emerge in late winter to start their adult lives. [05:53.86] [05:56.04]The adults live just a few days and their sole purpose is to breed... [05:59.94] [06:05.65]But to find a mate, they have to make a death-defying crossing to the shore... [06:10.11] [06:14.26]Their wings are far too weak to fly... [06:16.45] [06:20.03]But they do make good sails... perhaps this is how flight began... [06:25.59] [06:26.24]An ancient insect waved its gills to catch the breeze, [06:29.50] [06:29.71]and set sail, just like stoneflies do today. [06:33.01] [06:38.05]Gills already had the joints and muscles to flap up and down, [06:41.88] [06:42.09]and could then have evolved from sails to wings. [06:45.75] [06:48.33]And then - insects really took off!! [06:51.16] [07:01.14]Whatever that first flying insect was, [07:03.33] [07:03.54]it won the biggest evolutionary jackpot of all time... [07:06.91] [07:10.05]Its genes were now unstoppable... [07:12.17] [07:12.48]today its legacy is around 10 million flying insect species... [07:17.18] [07:17.55]the most successful type of animal on earth. [07:20.15] [07:52.92]We may never know exactly what that first aerial insect looked like, [07:56.76] [07:56.99]but fossils have shed light on some of its descendants [08:00.12] [08:06.07]Among them a design that's really stood the test of time. [08:09.37] [08:13.28]Dragonflies have been around for more than 300 million years. [08:17.34] [08:18.88]They were already on the wing when our ancestors crawled out of the swamps. [08:22.78] [08:34.16]Dragonflies are the fighter planes of the insect world... [08:37.46] [08:38.54]Fast, Agile, aerial Aces [08:41.00] [08:43.47]These are male emperor dragonflies, and they're fiercely territorial. [08:47.57] [08:48.91]When rivals meet, they test each other's flying skills to the limit [08:52.64] [09:08.27]These dogfights can be vicious, even deadly... [09:12.22] [09:20.21]Dragonflies are dazzling fliers. [09:22.24] [09:22.58]But the best insect stunt pilot of them all is smaller and much less glamorous. [09:27.38] [09:34.12]The fly. We all know how hard it is to swat one. [09:38.08] [09:48.00]Their maneuverability is unrivalled and their reactions are 12 times [09:52.13] [09:52.34]faster than our own... [09:53.74] [09:58.28]So what's their secret? [09:59.48] [10:00.98]Well, bizarrely, it's because the flies ancestors gave up a pair of wings. [10:06.01] [10:07.36]Like dragonflies, all early insects had two pairs. [10:10.76] [10:19.27]In one type though, the hind wings shrank, evolving into tiny rod [10:23.60] [10:23.81]and ball structures called halteres. [10:26.44] [10:27.71]They're high tech precision instruments... [10:29.94] [10:30.35]and work a bit like gyroscopic stabilizers on a modern helicopter or plane. [10:34.61] [10:38.96]Flies come in a great variety of shapes and sizes - [10:42.29] [10:42.53]they include the hoverfly, crane fly, mosquito and our friendly housefly. [10:48.73] [10:49.17]And they all have halteres. [10:50.96] [10:53.70]Halteres give the fly precise feedback on its position, [10:56.93] [10:57.14]helping it make split second adjustments without losing control... [11:01.01] [11:01.61]So it can dodge a swipe and instantly regain perfect poise... [11:05.74] [11:22.03]There are now more than a hundred thousand kinds of fly. [11:26.13] [11:29.31]Their duck & dive design has let them take over the world [11:33.00] [11:33.34]and though they're small, [11:34.54] [11:34.74]they have a massive impact on other life, including us. [11:39.15] [11:41.45]In fact, flies are the most dangerous animals on earth, [11:44.42] [11:44.75]responsible for more human deaths than any other creature. [11:48.21] [11:51.90]They carry and spread disease... [11:53.95] [11:54.46]and because they're so small and maneuverable they're impossible to avoid. [11:58.53] [12:15.39]But being a successful insect isn't just about having the top technology for flight. [12:20.05] [12:22.59]It's also about when to fly. [12:24.42] [12:25.09]It's hard to believe that this... [12:27.09] [12:27.66]...and this are the same kind of animal. [12:30.33] [12:37.01]Why does such a gorgeous creature have such weird and wingless offspring? [12:41.44] [12:46.22]Caterpillars are munching machines, their only purpose is to eat and grow... [12:51.18] [12:51.79]At this stage, having wings would just get in the way. [12:54.55] [13:02.13]A caterpillar can balloon to an incredible 2,000 times its starting weight. [13:07.33] [13:07.87]That's like a human baby gaining eight tons in a month - [13:11.43] [13:11.64]and becoming the size of a bus! [13:13.44] [13:17.35]Once it's finished gorging, though, [13:18.84] [13:19.05]the caterpillar uses all those calories to make a stunning transformation... [13:23.31] [13:31.06]From ugly bug... [13:32.25] [13:38.94]To winged beauty... [13:40.49] [13:43.77]The adult has a very different mission... to attract a mate and lay eggs far and wide. [13:49.21] [13:51.81]Now wings are a big help and one butterfly has taken air travel to extremes. [13:56.98] [14:00.36]This is the monarch butterfly, long haul operator of the insect world. [14:04.95] [14:09.10]It's late summer in Canada [14:10.66] [14:10.93]and these are great, great grandchildren of monarchs [14:13.63] [14:13.84]that had flown north in spring. [14:15.80] [14:20.88]Now they're ready to embark on one of nature's most miraculous journeys. [14:25.28] [14:36.06]Triggered by shorter, cooler nights, they head south, [14:39.43] [14:39.63]flying the entire length of North America, and beyond... [14:42.93] [14:59.02]Finally, up to five thousand kilometers away [15:02.11] [15:02.32]the monarchs reach their winter destination in the mountains of central Mexico. [15:06.72] [15:12.00]Somehow they find their way back to the same trees used by previous generations... [15:16.99] [15:17.53]Millions cluster together for safety and warmth, creating an amazing spectacle. [15:22.77] [15:50.37]Insects were the first creatures into the air, [15:52.93] [15:53.14]and flew unchallenged for about a hundred million years. [15:56.37] [15:56.94]Then another twist of evolution brought a second wave of flight... [16:01.21] [16:04.58]Down on the ground was the ancestor of a different group of animals [16:07.78] [16:07.98]that produced some of the most impressive flyers ever - [16:11.25] [16:19.36]The pterosaurs... [16:21.13] [16:32.54]Sadly no pterosaurs are left to help us tell their story. [16:36.34] [16:38.75]What we do know is that they evolved from an ancient kind of reptile. [16:42.78] [16:44.72]How did a four-legged reptile... [16:46.59] [16:46.89]turn into one of nature's most magnificent flyers. [16:50.02] [16:51.63]Today, tree dwelling reptiles offer a clue. [16:54.53] [16:57.03]For a green iguana cornered in the treetops, there's just one way out... [17:01.30] [17:01.70]straight down! [17:02.60] [17:04.27]They generally hang out over water, for a safer landing. [17:07.17] [17:17.22]A simple free fall isn't very stylish - but it's a start... [17:20.55] [17:30.73]If you can add some control to your descent then you're a step closer to taking flight. [17:35.40] [17:38.31]And in the forests of South East Asia lives an animal [17:41.17] [17:41.38]that's taken free fall that one stage further. [17:44.11] [18:02.33]This gecko has evolved a kind of onboard parachute. [18:05.63] [18:08.77]Webbed toes and flaps of skin along its sides act like air brakes, [18:12.73] [18:12.94]giving it some control over its fall. [18:15.38] [18:23.09]It can't go far but it's a leap in the right direction. [18:26.28] [18:31.63]And if you think that's impressive, watch what its neighbor can do! [18:35.43] [18:36.43]The draco looks like any other lizard - until it jumps... [18:40.60] [18:46.08]This simple wing is actually skin membrane stretched over its ribs. [18:50.48] [18:53.18]It lets this tiny lizard glide up to a hundred meters - [18:56.67] [18:57.92]still not strictly speaking flying - [18:59.98] [19:00.42]but it saves an awful lot of climbing up and down! [19:03.09] [19:06.43]At some point an ancient gliding reptile took the next crucial step. [19:11.37] [19:11.77]Turned its arms to wings and developed true powered flight. [19:16.00] [19:22.11]This second airborne breakthrough heralded the arrival of the pterosaurs. [19:27.95] [19:52.98]Fossils suggest that many lived like some birds do today. [19:57.07] [19:59.32]One had a mouth with a built -in sieve - to filter out small creatures from the water... [20:04.22] [20:05.66]much as a modern flamingo does. [20:07.85] [20:18.27]Another had sharp hooked teeth good for snagging slippery prey. [20:22.90] [20:23.61]It used its beak to trap fish just below the surface, [20:27.13] [20:27.48]like a skimmer does today. [20:28.94] [20:33.08]Another pterosaur had an expandable throat pouch, [20:36.02] [20:36.35]a built-in fishing net... it was a kind of prehistoric pelican. [20:40.69] [21:00.11]But there's one thing about the pterosaurs no modern bird can match - [21:04.34] [21:06.32]their size! [21:07.30] [21:09.09]Some got as big as a hang glider [21:11.25] [21:13.16]How did these giants take off and stay airborne? [21:17.09] [21:18.49]As for a hang glider a head wind would be vital to provide enough lift to get off the ground. [21:23.63] [21:29.04]The largest pterosaur, Quetzalcoatlus measured 12 meters across [21:33.81] [21:35.54]But how did the world's biggest ever flying animal stay up? [21:39.71] [21:43.92]Pterosaurs were built a bit like this glider - with massive long wings and a small body. [21:49.95] [21:51.16]Like the glider's hollow aluminum tubes [21:53.56] [21:53.76]their bones were also partly hollow to minimize weight. [21:57.29] [21:58.80]Once up in the air they'd have soared using updrafts [22:01.83] [22:02.04]and thermals just as a glider pilot does. [22:05.20] [22:28.30]Pterosaurs dominated the skies for 150 million years [22:32.26] [22:32.47]but they vanished along with the dinosaurs. [22:34.90] [22:37.47]By then a third airborne animal had arrived. [22:40.44] [22:41.41]Its success was down to a brand new structure - the feather. [22:45.64] [22:47.45]It led to perhaps the most beautiful of all flying animals. [22:50.91] [23:26.29]The surprising thing about feathers though is that [23:29.12] [23:29.33]they didn't even evolve for flight... [23:31.26] [23:33.06]in fact feathers didn't begin with birds at all. [23:35.90] [23:36.30]The birds inherited them. [23:37.89] [23:40.54]From dinosaurs. [23:41.73] [23:47.28]Birds are descended from small dinosaurs, [23:49.71] [23:49.91]a bit like this one preserved in rock from a 124 million years ago. [23:54.68] [23:57.22]Look closely and you'll notice some mysterious impressions - feathers. [24:02.09] [24:13.10]So what made these scaly hunters go all fluffy? [24:16.20] [24:21.34]Feathers are in fact modified scales... [24:23.94] [24:24.31]Over countless generations, some scales must have begun to thin and fray, [24:29.11] [24:29.32]evolving into fluffy down. [24:31.15] [24:35.16]But why did dinosaurs need feathers? [24:37.68] [24:42.23]Well they'd be perfect for keeping warm like those found on young birds [24:46.60] [24:48.50]In the Antarctic albatross chicks survive sub-zero temperatures for months on end. [24:53.41] [24:53.68]Thanks to their thick down. [24:55.47] [24:57.58]Downy feathers probably evolved to insulate small dinosaurs... [25:01.45] [25:01.68]But they're not much good for making a wing. [25:03.98] [25:06.32]So how did fluffy feathers turn into stiff ones like these used for flight. [25:11.78] [25:21.17]The latest theory is that evolution hijacked the feather [25:24.30] [25:24.51]for a completely different job long before it was used for flight... [25:28.17] [25:30.28]It's now thought that feathers might have been used for display, [25:33.51] [25:34.02]just like many birds use them today. [25:36.04] [25:53.07]And stiff display feathers are far more spectacular than fluffy down. [25:57.37] [26:00.38]Male birds flaunt themselves to win a female, and perhaps it was the same for dinosaurs. [26:05.54] [26:06.25]By choosing the most striking males, [26:08.15] [26:08.35]the females helped feathers evolve in a completely different way. [26:12.05] [26:15.29]As soft feathers became longer and stronger, [26:17.85] [26:18.13]they were much more suitable for building wings, as well as showing off. [26:22.46] [26:28.14]But how did that first leap into the skies actually happen? [26:32.07] [26:45.09]The most popular theory is that flight started up in the trees. [26:49.22] [26:51.26]Feathered arms would come in very handy for a tree-dwelling dinosaur. [26:55.16] [26:56.60]For a start they'd break a fall. [26:58.43] [27:00.24]And it's easy to imagine how a leap could then become a glide. [27:04.23] [27:05.94]Arms were slowly reshaped into wings... [27:08.74] [27:08.94]strong enough to flap their way into the air... [27:11.81] [27:14.72]Gliding became true powered flight. [27:17.85] [27:20.42]Enter the birds! [27:22.55] [27:38.04]The evolution of birds was a massive breakthrough. [27:41.17] [27:41.61]Their superb flying ability unlocked a way of life that has proved very successful. [27:47.05] [27:51.29]The dinosaurs died out, yet birds survived and more than that, [27:55.35] [27:55.56]went on to dominate the skies... [27:57.82] [28:13.68]All this, thanks to the fabulous feather! [28:16.47] [28:29.32]The conquest of the air began with insects then the pterosaurs came and went, [28:33.95] [28:35.56]but the arrival of the birds marked a new era in the history of life... [28:39.40] [28:39.80]and the beginning of an evolutionary battle between birds and insects [28:43.76] [28:43.97]that would push flight to extremes. [28:46.41] [28:48.18]Each spring mayflies have just a few hours to leave the water, find a mate, and breed. [28:54.08] [28:56.59]Many never make it... [28:58.49] [29:44.30]The mayfly feast only lasts a few days [29:47.23] [29:47.44]but there's lots more insect food on offer - if you can get to it. [29:52.00] [29:55.38]In an average British summer month, [29:57.11] [29:57.31]around three billion insects fly over each square kilometer, [30:01.37] [30:02.48]that's nearly three tons of insects. [30:04.95] [30:07.49]We can't see them up here because they're so small. [30:09.96] [30:10.49]But there are birds that can... [30:12.12] [30:12.53]that have evolved to reach this aerial banquet. [30:15.33] [30:16.83]And none are better at it than the swift. [30:19.30] [30:21.10]The ultimate high flyer. [30:22.73] [30:31.65]They fly to and from South Africa each year for summer's insect feast, [30:35.81] [30:36.02]a return trip of around 23 thousand kilometers. [30:39.55] [30:46.16]A long history of aerial pursuit has given swifts a streamlined body [30:50.12] [30:50.33]with long narrow wings to slice through the sky. [30:53.06] [31:03.21]Only at normal speed can you really appreciate how well they live up to their name... [31:07.48] [31:20.16]Swifts are so specialized for living on the wing, they can't even land on the ground. [31:25.23] [31:25.70]Their tiny legs and long wings would make it impossible for them to take off again. [31:29.97] [31:32.34]That's why they always nest up high... [31:34.31] [31:37.25]One mouthful like this may contain up to 500 insects, [31:40.61] [31:40.85]and when food is plentiful, the chick may get 10 meals - [31:44.11] [31:44.32]5000 insects - in a day. [31:46.55] [31:54.23]But in bad weather, most insects are grounded, [31:57.03] [31:57.23]which can mean the parents have a hard job finding food. [32:00.20] [32:06.88]Sometimes the adults have no choice [32:08.57] [32:08.78]but to desert their chicks and keep on flying ahead of the storm. [32:12.27] [32:25.13]A British swift will even cross the sea to Continental Europe... [32:28.39] [32:35.24]A trip to Holland is no big deal when you can cover nearly 300 kilometers in a day. [32:40.57] [32:48.25]Back at the nest, [32:49.11] [32:49.32]the helpless chick can only wait whilst adults feed in fair Continental skies... [32:54.22] [33:04.17]Another day and still the chick waits, living on its fat reserves... [33:08.47] [33:13.94]Swift chicks are tough... [33:15.47] [33:15.78]They can lose half their bodyweight, surviving even weeks without a meal. [33:20.01] [33:20.68]But now this chick needs to eat, and soon... [33:24.05] [33:28.12]The parent is in sight of home, [33:29.89] [33:30.09]after a round trip of perhaps sixteen hundred kilometers or more... [33:34.12] [33:37.27]Just in time to deliver a life-saving meal... [33:39.93] [33:51.21]Millions of years of chasing tiny winged insects have shaped swifts [33:55.58] [33:55.78]into true aerial aces... [33:57.65] [33:59.49]Amazing to think they started as feathered dinosaurs [34:02.32] [34:02.52]that clambered around in the trees. [34:04.39] [34:12.03]Central America is home to the swifts' closest living relatives - [34:16.33] [34:16.57]a group of birds that have pushed flight along a very different evolutionary track... [34:21.17] [34:28.15]Hummingbirds. [34:29.28] [34:30.59]Hummingbirds can fly forwards, up and down and backwards. [34:35.15] [34:35.62]And all with unbelievable precision. [34:37.59] [34:40.60]These aerobatics are unrivalled among birds. [34:43.46] [34:51.31]And it's all because of flowers. [34:52.77] [34:57.35]But how did flowers lead to such fancy flight? [35:00.68] [35:02.88]Over millions of years [35:03.98] [35:04.19]hummingbirds and plants have struck an evolutionary deal. [35:07.78] [35:08.06]The hummingbirds get to drink nectar in return for pollinating plants. [35:12.69] [35:14.30]And hovering has proved the most efficient way to get a meal... [35:17.49] [35:20.27]It's a relationship that's been perfected [35:22.13] [35:22.34]until bird and flower fit together like a key in a lock. [35:25.64] [35:28.18]Plants have forced hummingbirds to become more like feathered insects... [35:32.04] [35:32.28]which is why, at first glance, it's hard to tell a hummingbird... [35:35.58] [35:35.78]from a hummingbird hawkmoth. [35:37.65] [35:43.36]It's a great example of what's known as convergent evolution... [35:46.76] [35:47.03]where two entirely unrelated animals [35:49.26] [35:49.46]come up with almost identical solutions to the same problem. [35:53.13] [36:06.38]But the hummingbird's supreme flying ability comes at a great cost. [36:10.18] [36:14.19]Their high energy lifestyle means they need to eat [36:17.09] [36:17.29]half their weight in nectar every day. [36:19.69] [36:23.13]And they can only achieve such precision flying by staying very small. [36:26.90] [36:33.41]Swans have the opposite problem - [36:35.24] [36:37.08]they're so heavy that just getting into the air is a struggle. [36:40.28] [36:57.07]Swans are one of the heaviest of all flying birds. [36:59.93] [37:02.27]They're like the bird equivalent of a jumbojet, so they take a lot of energy to get into the air. [37:07.54] [37:09.74]Once they're up in the air [37:10.61] [37:10.81]it's all about saving energy and that's why they fly in this formation. [37:14.87] [37:17.39]By sticking close together, each bird gains a little extra lift [37:20.62] [37:20.82]from turbulence created by the bird in front. [37:23.35] [37:23.96]As a result they make a 50% energy saving. [37:27.09] [38:03.97]When you're this big, landing is a challenge too. [38:07.16] [38:33.70]Thanks to that first feathered dinosaur, [38:35.93] [38:36.16]today more than 9000 species of bird fill the air, across every continent. [38:41.50] [39:49.10]Despite their success most birds share a weakness... [39:52.90] [39:53.27]their eyes work best in daylight. [39:55.90] [40:00.98]That left the night sky up for grabs and another family of animals seized their chance. [40:06.58] [40:07.99]Bats... [40:08.98] [40:16.36]Creatures of the night that can find their way [40:18.42] [40:18.63]around in the pitch black and live secret lives in deep, dark places. [40:23.63] [40:29.54]But perhaps their biggest secret is how they evolved. [40:33.00] [40:35.05]Bats are thought to be descended from a small nocturnal mammal, [40:38.58] [40:39.62]at some point their ancestors took to the trees in search of prey. [40:43.79] [40:51.13]They probably began to glide on skin flaps stretched between their limbs, [40:55.13] [40:55.34]just like some modern mammals such as flying squirrels and sugar-gliders. [40:59.74] [41:26.17]It's a great way to get around but still not real flight - [41:29.66] [41:29.87]more like free-falling with style. [41:31.63] [41:40.15]But the colugo may provide a missing link to show how bats evolved true wings. [41:45.55] [41:49.19]The difference is in its hands - they're webbed. [41:52.65] [41:55.40]The bats' ancestor had these too... [41:57.52] [41:57.87]but its fingers got longer and the skin between them stretched to turn hands into wings. [42:03.90] [42:08.24]It flapped these wings and took off, making bats the fourth group after insects, [42:13.11] [42:13.31]pterosaurs and birds, to really fly! [42:16.81] [42:22.19]You might think that one bat is pretty much like another [42:25.18] [42:25.53]but in fact they're one of the most diverse and widespread of any mammal. [42:29.33] [42:32.57]Flying foxes are the biggest bats of all. [42:35.56] [42:49.28]They spend the day crowded together in their favorite trees - [42:52.25] [42:52.89]there can be millions in a single colony. [42:54.86] [43:07.07]As dusk falls they make a mass exodus in search of fruiting trees. [43:11.97] [43:13.27]The power of flight means they can cover up to 50 kilometers a night [43:17.40] [43:17.61]in search of the ripest fruit. [43:18.98] [43:21.88]No other mammal puts on a show quite like this. [43:25.25] [43:40.40]Bats are now one of the most successful mammal families. [43:43.70] [43:43.97]There are nearly a thousand species each with their own special habits. [43:48.07] [43:50.55]Like flying foxes many are fruit lovers... [43:53.11] [43:56.08]Others sip nectar [43:57.48] [44:10.13]Some have even learned to fish [44:11.96] [44:24.18]But a fat juicy insect is what most bats like to eat. [44:27.77] [44:33.52]Bats need more than wings though to track down food in the dark. [44:37.25] [44:37.89]These creatures of the night had to evolve a whole new way [44:40.52] [44:40.73]of mapping out their world... [44:42.29] [44:45.33]They listen to the echoes of their own calls and create an image of their surroundings. [44:50.43] [44:51.77]It's called echolocation... but how did such a complex system evolve? [44:56.77] [45:03.65]Bats probably began by using simple clicking sounds, [45:07.35] [45:07.56]giving a very rough picture of what's around... [45:09.89] [45:11.83]Detecting even basic shapes is still better than flying blind... [45:15.59] [45:17.70]Then, by developing a more complex range of sounds, echolocation was improved. [45:22.47] [45:24.67]Bats were gradually able to pick up more details of their surroundings... [45:28.77] [45:34.18]and of their prey. [45:35.55] [45:38.39]Insects filled the night sky long before bats existed. [45:42.12] [45:42.46]They were a meal waiting to happen - and the bats tucked in! [45:46.26] [46:03.11]Of course there are more than insects on the menu. [46:05.48] [46:23.46]Using its finely tuned echolocation skills, [46:26.19] [46:26.40]a tiny Natterer's bat can even pluck a spider from its web without getting entangled. [46:32.20] [46:42.48]Once it has its prize, the bat goes into reverse... [46:45.54] [46:45.99]keeping its wings clear of the sticky threads with just a hair's breadth to spare. [46:50.22] [46:54.20]This has to be the ultimate refinement to seeing with sound! [46:57.49] [47:04.24]Bats were the last group of animals to get airborne... [47:07.26] [47:07.61]they've used their wings to reach almost all parts of the earth. [47:10.60] [47:13.05]Their sheer numbers are testament to their success. [47:15.71] [47:33.13]The power of flight is one of evolution's biggest triumphs. [47:37.09] [47:42.18]It has shaped some of the most beautiful and successful animals that ever lived. [47:46.51] [48:01.23]Today's winged creatures make up around two thirds of all the species on Our planet. [48:06.17] [48:19.11]And to think they're all descended from just four ancestors, [48:23.07] [48:23.28]who managed to grow wings and take to the air! [48:26.91] [48:29.91]The End [49:19.91]

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