0:00:03 > 0:00:05Planet Earth.
0:00:06 > 0:00:09Millions of species...
0:00:10 > 0:00:13..but a few are special...
0:00:17 > 0:00:19..thriving,
0:00:19 > 0:00:21dominating.
0:00:25 > 0:00:29The key to their success lies in their opportunism.
0:00:31 > 0:00:35For others, it's down to their ability to collaborate.
0:00:38 > 0:00:42And for some, it's all about surviving where others can't.
0:00:44 > 0:00:46So, what is their secret?
0:00:48 > 0:00:53In this series, we'll delve deep beneath the skin to reveal
0:00:53 > 0:00:56the unique features that set some species apart.
0:01:00 > 0:01:05New behaviour and the very latest scientific discoveries
0:01:05 > 0:01:09will offer fresh insight into the wonder of animals.
0:01:23 > 0:01:27One group of animals dominate the skies...
0:01:30 > 0:01:32..winged predators.
0:01:34 > 0:01:38They've conquered every environment on the planet...
0:01:43 > 0:01:46..outdoing even their fellow birds...
0:01:49 > 0:01:51..because they don't just fly.
0:01:54 > 0:01:57They hunt in ways that
0:01:57 > 0:01:59no other animal on Earth can.
0:02:12 > 0:02:17What sets raptors apart from other birds is their strength...
0:02:19 > 0:02:21..their manoeuvrability...
0:02:23 > 0:02:24..and their speed.
0:02:29 > 0:02:32In this episode, we're going to explore
0:02:32 > 0:02:36the anatomical and physiological adaptations
0:02:36 > 0:02:39that allow these birds to rule the aerial roost.
0:02:41 > 0:02:44So, let's start with their strength.
0:02:49 > 0:02:53Raptors are distinguished from other birds by their choice of prey...
0:02:54 > 0:02:57..big, heavy vertebrates...
0:02:59 > 0:03:01..that can weigh more than the bird itself.
0:03:05 > 0:03:07They need strength both to catch their prey...
0:03:12 > 0:03:13..and to carry it.
0:03:17 > 0:03:20To capture it, raptors must channel their strength
0:03:20 > 0:03:22to one part of their body...
0:03:24 > 0:03:26..their talons.
0:03:30 > 0:03:32Four claws,
0:03:32 > 0:03:34three facing forward, and one back.
0:03:36 > 0:03:39They're made of keratin,
0:03:39 > 0:03:43similar to that found in human fingernails,
0:03:43 > 0:03:47but with a structure that makes it considerably stronger.
0:03:47 > 0:03:49BIRD CALL
0:03:49 > 0:03:52The largest can be nearly seven centimetres long.
0:03:54 > 0:03:57That's as long as a bear's claws.
0:04:03 > 0:04:06The talons of each species are tailored for their prey.
0:04:08 > 0:04:12The bald eagle's are perfect for catching fish.
0:04:14 > 0:04:18Each year on North America's Pacific coast,
0:04:18 > 0:04:21millions of salmon return to spawn.
0:04:26 > 0:04:29The bald eagle is waiting.
0:04:40 > 0:04:43It can catch fish weighing 6kg...
0:04:50 > 0:04:53..but keeping hold of it requires gripping power.
0:05:03 > 0:05:06Its curved talons function like fish hooks.
0:05:13 > 0:05:17Pressure-sensitive pads on the feet tell them when to close.
0:05:22 > 0:05:25Spicules, tiny spikes on the bottom of those feet,
0:05:25 > 0:05:28help them grasp their slippery prey.
0:05:30 > 0:05:33And once the grip is firm,
0:05:33 > 0:05:35the talons actually lock shut.
0:05:38 > 0:05:41To do THAT, they use tendons in their legs.
0:05:44 > 0:05:46These are contained in sheaths.
0:05:48 > 0:05:52Both tendons and sheaths have tiny ridges along their surface.
0:05:54 > 0:05:56When the muscles contract,
0:05:56 > 0:06:00two sets of teeth interlock, like a ratchet...
0:06:02 > 0:06:04..clamping the talons shut.
0:06:05 > 0:06:08The eagle can now maintain
0:06:08 > 0:06:10huge pressure on its claws...
0:06:11 > 0:06:15..even when its leg muscles are relaxed.
0:06:21 > 0:06:24Ratchet talons are just as crucial
0:06:24 > 0:06:27for birds of prey hunting on dry land.
0:06:42 > 0:06:46Once this Galapagos hawk gets hold of the marine iguana,
0:06:46 > 0:06:48it's unlikely to get away.
0:07:01 > 0:07:02Researchers have found
0:07:02 > 0:07:05that the talons are not always used as daggers.
0:07:06 > 0:07:11Raptors sometimes use their feet to suffocate their prey.
0:07:16 > 0:07:20Not all prey, though, can be eaten where it falls.
0:07:41 > 0:07:43To carry their kill...
0:07:45 > 0:07:47..and stay airborne,
0:07:47 > 0:07:49raptors must summon...
0:07:49 > 0:07:52a different form of strength.
0:07:52 > 0:07:56This time, channelled through their wings.
0:08:01 > 0:08:03The amount of power a bird needs to fly
0:08:03 > 0:08:05is governed by its "wing loading".
0:08:07 > 0:08:10That's the relationship between the area of the wings
0:08:10 > 0:08:13and the weight of the raptor.
0:08:16 > 0:08:20Big, powerful wings and a light body
0:08:20 > 0:08:24mean that a bird can carry heavier loads.
0:08:26 > 0:08:30The most powerful birds of prey are the eagles.
0:08:42 > 0:08:46Anatomy and physiology work together to keep their weight down.
0:08:53 > 0:08:57Some eagles have over 7,000 feathers
0:08:57 > 0:09:00that together weigh less than a kilo
0:09:00 > 0:09:03and their skeleton is even lighter
0:09:03 > 0:09:06because it's full of air.
0:09:09 > 0:09:11Their respiratory system
0:09:11 > 0:09:14is directly connected to their skeleton.
0:09:17 > 0:09:18When they breathe in,
0:09:18 > 0:09:22air floods into hollow spaces in the bones,
0:09:22 > 0:09:23keeping their weight down.
0:09:29 > 0:09:33Their wings, too, are designed for maximum lift.
0:09:34 > 0:09:37The golden eagle's are broad and long.
0:09:40 > 0:09:43Its wingspan can reach over two metres...
0:09:46 > 0:09:51..perfect for soaring and gliding on air currents...
0:09:53 > 0:09:56..both of which use far less energy than powered flight.
0:10:01 > 0:10:04Gaps between the feathers at their wingtips
0:10:04 > 0:10:08allow air to rush through, increasing lift.
0:10:19 > 0:10:23These long, broad wings, and lightweight structure
0:10:23 > 0:10:25mean that eagles can support
0:10:25 > 0:10:27a lot of extra weight when airborne...
0:10:35 > 0:10:40..enabling them to carry the biggest prey of all the raptors.
0:10:45 > 0:10:47In mountains across Europe,
0:10:47 > 0:10:50golden eagles scour the cliffs for a meal...
0:10:52 > 0:10:54..like young ibex and chamois.
0:10:56 > 0:10:59BLEATING
0:11:21 > 0:11:24A young chamois can weigh considerably more than
0:11:24 > 0:11:26the eagle's own body weight.
0:11:33 > 0:11:37But some birds of prey don't just rely on strength to get a meal.
0:11:40 > 0:11:44They employ supreme wing control to catch their prey...
0:11:50 > 0:11:53..especially when hunting in dense woodland.
0:11:59 > 0:12:01Navigating through trees,
0:12:01 > 0:12:04in pursuit of fast, evasive prey
0:12:04 > 0:12:08takes manoeuvrability and agility.
0:12:22 > 0:12:25The goshawk has both.
0:12:31 > 0:12:34It uses the forest to conceal its approach.
0:12:49 > 0:12:52Its ability to dodge obstacles at high speed
0:12:52 > 0:12:55is down to its wing design.
0:13:08 > 0:13:12Goshawks have a relatively short wingspan,
0:13:12 > 0:13:14averaging just one metre...
0:13:17 > 0:13:19..perfect for small spaces
0:13:19 > 0:13:22and for fast responses...
0:13:24 > 0:13:27..because short wings can be flapped quicker.
0:13:37 > 0:13:39What the wings lose in length,
0:13:39 > 0:13:42they make up for in breadth,
0:13:42 > 0:13:44generating a lot of lift with each flap...
0:13:47 > 0:13:51..and a long tail that acts like a rudder...
0:13:54 > 0:13:57..enabling the goshawk to change direction fast.
0:14:00 > 0:14:03But to cut through a space like THIS...
0:14:05 > 0:14:09..the goshawk must actually fold away its wings...
0:14:13 > 0:14:15..and stay airborne.
0:14:23 > 0:14:27Viewed in a lab and shot in slow motion,
0:14:27 > 0:14:29it becomes clear how it does it.
0:14:31 > 0:14:34Its feet lead the way
0:14:34 > 0:14:37and its wings fold neatly behind.
0:14:39 > 0:14:43What keeps it flying is its tail.
0:14:44 > 0:14:48As it clears the gap, the tail fans out,
0:14:48 > 0:14:50like a third wing...
0:14:51 > 0:14:53..giving it lift
0:14:53 > 0:14:57in even the tightest of spaces.
0:15:00 > 0:15:04Incredibly, as the goshawk makes these manoeuvres,
0:15:04 > 0:15:06it manages to keep sight of its quarry.
0:15:09 > 0:15:13No mean feat in dense woodland like this...
0:15:14 > 0:15:18..following fast, evasive prey.
0:15:22 > 0:15:27That's because raptors have the clearest vision of all birds.
0:15:29 > 0:15:32It's difficult to imagine how a raptor sees the world,
0:15:32 > 0:15:36but if our eyes were the same size as theirs,
0:15:36 > 0:15:39relative to our skull, then we would have eyes
0:15:39 > 0:15:41the size of oranges.
0:15:41 > 0:15:45But it's not just size that's important, it's sharpness, too.
0:15:48 > 0:15:50The resolution of raptor eyes
0:15:50 > 0:15:52is higher than ours
0:15:52 > 0:15:55because they have more receptors.
0:16:00 > 0:16:05Many birds of prey have over half a million, per square millimetre,
0:16:05 > 0:16:08in areas known as the foveae.
0:16:12 > 0:16:16That's over twice the density found in the human eye.
0:16:19 > 0:16:22And whereas we have one fovea per eye...
0:16:26 > 0:16:29..birds of prey have two.
0:16:32 > 0:16:36These are the areas of the eye where the image is most sharply focused.
0:16:38 > 0:16:42In birds, the forward-facing foveae
0:16:42 > 0:16:44are used for short-range vision.
0:16:44 > 0:16:48These fields overlap to give birds
0:16:48 > 0:16:50binocular vision, just like our own.
0:16:54 > 0:16:58The other pair of foveae, set at 45 degrees from the front,
0:16:58 > 0:17:00are used for long-range vision.
0:17:02 > 0:17:05These three fields of vision
0:17:05 > 0:17:08enable a raptor to focus on three things at once.
0:17:13 > 0:17:15It's thought this adaptation
0:17:15 > 0:17:18enables the goshawk to keep its eyes fixed,
0:17:18 > 0:17:20both firmly on its prey...
0:17:23 > 0:17:26..and firmly on the obstacles in its path...
0:17:28 > 0:17:31..as it tears through the undergrowth.
0:17:50 > 0:17:54But flying fast through sharp branches
0:17:54 > 0:17:58leaves the goshawk's eyes vulnerable to injury.
0:17:58 > 0:18:02So, to protect them, they are shielded by a third eyelid.
0:18:04 > 0:18:07The nictitating membrane.
0:18:08 > 0:18:10All birds have them.
0:18:12 > 0:18:15They keep the eye moist and protect it from the elements...
0:18:20 > 0:18:23..and from sharp branches.
0:18:25 > 0:18:29But whilst most birds' membranes are opaque...
0:18:33 > 0:18:37..the goshawk's are almost transparent.
0:18:43 > 0:18:46So, even when its membrane is shut,
0:18:46 > 0:18:50it may still be able to see the obstacles in its path.
0:18:51 > 0:18:55But being able to keep their eyes locked onto prey
0:18:55 > 0:18:57takes an extra adaptation.
0:19:02 > 0:19:04Keeping the eyes steady when manoeuvring
0:19:04 > 0:19:07is crucial to these high-speed hunters.
0:19:12 > 0:19:15So much so, that raptors have an adaptation
0:19:15 > 0:19:17that keeps their head motionless
0:19:17 > 0:19:20whilst their body is moving.
0:19:21 > 0:19:25In most vertebrates, when the body and head move,
0:19:25 > 0:19:27the eyes roll in their sockets to stay level.
0:19:29 > 0:19:33But raptors' eyes are relatively fixed in their sockets.
0:19:36 > 0:19:40So, the only way to keep their eyes level
0:19:40 > 0:19:42is to keep their head level, too.
0:19:43 > 0:19:49If you look at this goshawk flying, its eyes stay horizontal,
0:19:49 > 0:19:52no matter what the position of its wings.
0:19:54 > 0:19:56They can do this
0:19:56 > 0:20:00because birds' necks have more vertebrae than mammals
0:20:00 > 0:20:03and are packed with over 200 muscles.
0:20:04 > 0:20:06These enable fast reflexes
0:20:06 > 0:20:10to isolate the head from the vibrations of the body,
0:20:10 > 0:20:15keeping their eye-line completely horizontal.
0:20:20 > 0:20:25Being able to maintain a steady pin-sharp focus
0:20:25 > 0:20:30allows birds to function at speeds we can only dream of.
0:20:32 > 0:20:36Imagine sticking your head out of the car window,
0:20:36 > 0:20:38facing into the wind
0:20:38 > 0:20:42and then trying to breathe normally whilst travelling
0:20:42 > 0:20:46at speeds of over 200 miles an hour.
0:20:47 > 0:20:51Let's face it, you simply couldn't do it
0:20:51 > 0:20:53but birds of prey can.
0:20:56 > 0:21:01For raptors, speed is crucial for catching prey unaware.
0:21:11 > 0:21:16But flying rapidly requires huge amounts of energy
0:21:16 > 0:21:18and, therefore, more oxygen.
0:21:21 > 0:21:27What allows them to cope is their unusual respiratory system.
0:21:29 > 0:21:34It takes up over one-fifth of a bird's body.
0:21:34 > 0:21:38And is over seven times more efficient than ours
0:21:38 > 0:21:41at getting oxygen into the bloodstream.
0:21:43 > 0:21:47Because oxygen is extracted from air in their lungs
0:21:47 > 0:21:53both when they breathe in and when they breathe out.
0:21:55 > 0:22:00When a bird breathes in, air floods, not just into the lungs,
0:22:00 > 0:22:03but into a chain of air sacs around its body.
0:22:05 > 0:22:10These act as reservoirs, storing fresh, oxygenated air.
0:22:12 > 0:22:18When the bird breathes out, this stored air is sent to the lungs,
0:22:18 > 0:22:22supplying the blood with a second hit of oxygen.
0:22:23 > 0:22:28These air sacs mean that air flows in one direction around the body...
0:22:30 > 0:22:33..so inhaled air doesn't get polluted
0:22:33 > 0:22:36by exhaled air, as it does in mammals.
0:22:42 > 0:22:47This efficient system means that birds of prey are supplied
0:22:47 > 0:22:49with a near constant flow of oxygen...
0:22:51 > 0:22:55And more oxygen means more energy.
0:23:05 > 0:23:11When it comes to moving fast, one bird of prey outdoes
0:23:11 > 0:23:13every single animal on Earth.
0:23:21 > 0:23:23The peregrine falcon.
0:23:24 > 0:23:29Top speed - 220 miles an hour.
0:23:35 > 0:23:39On the face of it, it looks like any other bird of prey.
0:23:41 > 0:23:43Research by American ornithologists,
0:23:43 > 0:23:48however, found that falcons come from an entirely different branch
0:23:48 > 0:23:51of the family tree to their other raptor cousins.
0:23:54 > 0:23:59Their closest relative is, in fact, the parrot.
0:24:05 > 0:24:11This different evolutionary path has led to some novel adaptations,
0:24:11 > 0:24:16which allow the falcon to fly faster than all other birds.
0:24:16 > 0:24:20For a start, it has "baffles",
0:24:20 > 0:24:23cone-shaped bones just inside the nostrils,
0:24:23 > 0:24:27that moderate the air pressure as it enters the body,
0:24:27 > 0:24:30helping it to breathe at high speed.
0:24:30 > 0:24:32Its small intestine is, proportionally,
0:24:32 > 0:24:3650% shorter than those of other birds of prey,
0:24:36 > 0:24:41reducing its weight so it can accelerate faster.
0:24:41 > 0:24:46But most important is how it uses its wings.
0:24:49 > 0:24:52Unlike their eagle and hawk cousins,
0:24:52 > 0:24:55falcons have long, thin, pointed wings.
0:24:59 > 0:25:05This streamlined silhouette means less drag and faster flight.
0:25:10 > 0:25:15But fast, horizontal flight is not enough to keep up
0:25:15 > 0:25:17with some of its prey.
0:25:19 > 0:25:21The humble pigeon is no easy meal.
0:25:22 > 0:25:26It flies faster than the falcon on the flat
0:25:26 > 0:25:29and has more stamina.
0:25:30 > 0:25:35So, to catch it, the falcon has a trick up its sleeve...
0:25:35 > 0:25:36Gravity.
0:25:38 > 0:25:42In a dive or "stoop", it can reach its top speed.
0:25:49 > 0:25:52To dive like this, falcons need to reduce drag.
0:25:56 > 0:25:59They do this by adjusting their wing position...
0:26:01 > 0:26:03..moving them closer and closer to their body.
0:26:06 > 0:26:10For the final push, they fold their wings completely
0:26:10 > 0:26:15against their body, like a vacuum pack,
0:26:15 > 0:26:19preventing any air entering between the feathers.
0:26:25 > 0:26:29But airflow is controlled by more than just wing shape.
0:26:31 > 0:26:35The positioning of individual feathers is crucial.
0:26:37 > 0:26:40When a solid object moves through air,
0:26:40 > 0:26:45the flow of air around its surface forms regions of swirling eddies.
0:26:46 > 0:26:48These create drag...
0:26:50 > 0:26:52..but sometimes, drag can be decreased
0:26:52 > 0:26:56by creating an uneven surface.
0:26:59 > 0:27:02It's why golf balls are designed with dimples.
0:27:05 > 0:27:09And aeroplane wings have small fins on their surface.
0:27:11 > 0:27:14Falcons, however, have had their own
0:27:14 > 0:27:17natural solution for millions of years.
0:27:20 > 0:27:23New research from Germany has found that
0:27:23 > 0:27:25at the point the peregrine's dive,
0:27:25 > 0:27:28where drag should be a problem,
0:27:28 > 0:27:30feathers change position
0:27:30 > 0:27:32in the exact location of the drag.
0:27:36 > 0:27:42The feathers react to the flow of air over the wing's surface.
0:27:42 > 0:27:47If drag starts to develop, wing feathers will automatically pop up,
0:27:47 > 0:27:50adjusting the flow of air on their wing
0:27:50 > 0:27:54to enable the maximum speed needed...
0:27:55 > 0:27:57..to capture its prey.
0:28:04 > 0:28:09Giving the peregrine falcon the edge over its prey
0:28:09 > 0:28:11and its raptor relatives.
0:28:16 > 0:28:18From ratchet talons
0:28:18 > 0:28:22to the highest resolution sight...
0:28:22 > 0:28:25to drag-reducing feathers.
0:28:27 > 0:28:28Birds of prey have a range
0:28:28 > 0:28:32of anatomical and physiological adaptations
0:28:32 > 0:28:36that give them strength, manoeuvrability and speed.
0:28:38 > 0:28:41Essential attributes in their hunting armoury,
0:28:41 > 0:28:46which make them the ultimate aerial assassins.
0:28:47 > 0:28:51And THAT is the wonder of birds of prey.