"Birds of prey are the hunters of the sky powerfully equipped carnivores whose roots reach back to the age of the dinosaurs" "Most, like eagles and falcons hunt during the day" "But the owl can detect its prey at night with a body designed to home in on a kill even in complete darkness" "Vultures are hunters, too though they prey on the dead" "These voracious scavengers work together to strip the carcasses of large animals" "For all their variety, birds of prey are savage and graceful nature's monarchs of the air" "BIRDS OF PREY" "Scotland in April, and a late snow covers the ground" "A male golden eagle is hunting for food" "Like other birds of prey all the parts of his anatomy combine to create a highly efficient predator" "strong talons for grasping prey a muscular chest and powerful wings which help him lift it" "And a sharp beak for tearing it open" "These are the defining features of birds known as raptors" "The golden eagle feeds mainly on rabbits, hares and grouse though it's strong enough to kill a deer calf" "Golden eagles are among the largest birds of prey" "They can measure three feet from beak to tail with a wingspan of seven feet" "As in most birds of prey the female is larger than the male" "Along with hawks, falcons kites and buzzards they are diurnal raptors which means they hunt by day" "High up on the sides of a Scottish cliff golden eagles nest in an aerie" "The female is feeding her young" "She tears the meat into small strips to make it easier for them to digest" "However, the mother is unable to leave the nest to hunt" "The thin down on newborn chicks provides little insulation and they are vulnerable to the cold" "So the mother must keep them warm by brooding" "For the next ten days the whole family will rely on the hunting skills of the male" "Birds of prey need patience stealth and above all, keen senses" "Eagles rely on their sight" "Unlike many birds, raptors have eyes which point forward giving them binocular vision" "By using both eyes to view the same object they can see depth and are able to judge distances with great accuracy" "They also have a third eyelid called a nictitating membrane which protects their eyes particularly when they attack" "For centuries, people have known that birds of prey have good eyesight hence the expression "eagle-eyed"" "But until twenty years ago no one had tested their vision scientifically" "Liz Raymond, an Australian research scientist was the first to develop an eye test for eagles" "The biggest difficulty with testing any animal's, ah vision is that you can't talk to them directly" "So it all has to be done by indirect means" "Liz solved this problem with a simple but ingenious experiment" "In the first stage she trained an eagle to distinguish between images... projected onto two screens" ""They have two choices" "One is the black and white line of equal widths and the other one is, um a projection of a homogenous gray field" "Uh, and what you ask the eagle to do after a lot of training is to fly to the black and white lines" "And if the bird does that then he would receive a food reward."" "Liz then made the black and white lines progressively thinner" "The idea was to determine when the eagle could no longer distinguish the screen with the lines from the gray screen" "At this point, the eagle wouldn't know which screen to fly to" ""When he starts making the mistakes or he's got fifty percent right and fifty percent wrong then you can say that that's the actual limit of his resolving power."" "Liz was then able to compare the eagle's eyesight with that of humans" ""The results were quite surprising" "If you hold your finger out your thumbnail out about that distance and if across your thumbnail you draw ah, sixty black lines of equal widths and interdispersed with white lines of the same width that's about the amount of detail that humans can resolve."" "Ah, but the eagle could see up to about a hundred and thirty-two black lines about two and a half time as well as humans can see" "One of the reasons for their powerful vision is their large eyes" "If our eyes were in the same ratio to our body size they'll be as big as oranges" "A big eye allows a larger image to be projected onto the retina at the back of the eye" "This image is decoded for color and detail by light-sensitive receptors called cones" "An eagle's retina has six hundred thousand cones per square millimeter four times as many as in humans" "But eagles' eyes are practically fixed in their sockets and can only be turned a few degrees" "To compensate for this the eagle's neck is incredibly flexible and can twist all the way around" "Not all birds of prey have such powerful eyesight" "Smaller raptors like the kestrel have smaller eyes" "And their visual acuity is little better than ours" "Despite this, kestrels can see things we can't" "This is because they have specialized cones that can detect ultraviolet light" "These help them find their favorite food, voles" "Voles feed during the day" "Hidden in the grass they are difficult to see" "But they have one weakness their bladder" "They leave a trail of urine wherever they go" "Urine reflects ultraviolet light" "And to a kestrel searching for food these trails are perfectly visible from the air" "This time, the vole escapes" "As the light fades at the end of the day diurnal raptors like the golden eagle give up the hunt" "Their eyesight is adapted to work best in bright light" "In low light, their vision is worse than ours and they are unable to see their prey" "When the moon rises... the nocturnal birds of prey come out to hunt" "Barn owls are completely at home in the dark" "They have all the features of the diurnal birds of prey from their sharp talons to their strong beaks" "But their eyes are different" "In low-light conditions they are one hundred times more sensitive than ours" "Still, there are times when even a barn owl's eyes are not sensitive enough for hunting" "The film in these canisters was the first photographic evidence that owls could hunt without any light at all" "In 1957" "Roger Payne of Cornell University carried out an unusual experiment" ""I knew that owls had asymmetrical ears" "The ears weren't the same on the two sides of the head" "And that was curious" "That meant ears were important to owls" "They had to be doing something with them" "So I put an owl on a perch in a darkened room and I then released a mouse into leaves on the floor of the room" "And the mouse as it moved around made noise banging into the leaves and crushing them" "And suddenly in the darkness the owl struck" "And I turned on the lights and it was holding the mouse" "I just couldn't believe it" "And later on I got hold of an infrared viewing device which makes it possible to look in infrared which the owl can't see and we can't see" "And then I could watch what was going on" "And it was just fascinating."" "Throughout the winter in a small shed on the campus he used infrared light to watch barn owls hunt" "He recorded what he saw on infrared film" "What we got to remember is that throughout this whole time the owl can't see a thing" "There's enough infrared to expose the film but the owl can't see in infrared" "And here he goes" "He's flying along" "He brings his feet into a pattern right there which is exactly lined up with the mouse's body" "He then closes his eyes as, 'cause he knows he's about to hit something" "He lands and he's missed" "The mouse is sitting right next to him not two inches from his foot" "But he can't see it" "So he folds his wings" "Ooh, and then he looks at the mouse because the mouse has just made a sound" "And now he leans way forward" "He's six inches from it" "And at this moment he does a curious thing" "He brings his feet from the floor all the way up and puts them out like that 'cause it's the only way he can line them up with what he's hearing" "Here he goes." "Wham!" "He nails it right there" ""Make sure that it wasn't what he was homing on the smell of the mouse or that it had actually seen the mouse somehow or that maybe it was looking at the mouse in the infrared heat that a mouse gives off" "I took a small wad of paper dragged that through leaves and the owl struck the paper" "Paper doesn't smell" "It doesn't have any infrared coming off it" "It doesn't look like a mouse to anybody, not even an owl" "And the result is, it had to be sound" "Sound was what they were using" "At first sight, the barn owl doesn't appear to have ears at all unlike its cousin, the long-eared owl" "Looks, however, can be deceiving" "The tufts are only for display its real ears, like the barn owls are hidden under the feathers alongside its eyes" ""Everything about the way an owl looks the reason an owl looks like an owl is all to do with acoustic adaptations in other words, adaptations for hearing" "One of the most obvious ones is this circle of feathers around both sides of the head" "Actually, this is one parabola to collect sound for this ear and this is another parabola to collect sound for that ear which is actually very much like cupping your hand behind your ears a means of collecting more sound" "And you can also see another peculiar thing" "Owls sit with their bills pointed down like this looking at the world" "And the reason they do is to maximize the surface area over which they can collect sound" "If this was a, a robin or some other bird, songbird the bill would be held roughly horizontally like that" "But no." "They tilt it way down" "And the reason they do that is because this dimension of the head is greater than that dimension of the head" "That whole posture is part of why an owl looks like an owl."" "The barn owl locates the direction of a sound in two ways" "When the mouse makes a noise the sound reaches one ear a fraction of a second before it arrives at the other" "This minute time difference enables the owl to work out the left-right direction of the mouse" "When the mouse is directly in front of the owl the sound arrives at both ears at exactly the same time" "Now it has to calculate if the mouse is above or below" ""And if you cut just that collection of feathers in the very center here that help the air flow by smoothly then you get what we've done here to this owl which is a stuffed owl that's had just those feathers removed nothing else" "So right here you can see that there are two flaps of skin" "And those flaps are directly in front of the ear opening" "The ear opening is back here" "But they're asymmetrically placed" "One is higher than the other one" "This one is actually lower than that one" "These asymmetric flaps... gather the sound from the mouse in different ways" "The noise of rustling leaves come from below the owl" "The sound passes under the high flap which is on the left side of the owl's head and is reflected by the ruff into the ear" "The low flap on the right side deflects the sound coming from below" "When the sound is louder in the left than the right ear the owl knows it's coming from below" "By combining the up-down with the left-right information it pinpoints the mouse with great precision" "The mouse, however has ears of its own" "If it hears the owl coming it can simply run away" ""Well, here's a fight between owls and mice" "Mice have ways to avoid owls" "Owls have ways to improve their chances of catching a mouse and this is one of them" "The very leading edge of the feather that is in the front on the wing has a little series of tiny little spikes that stick out on it."" "No other bird of prey has these spikes" "The leading edge of an eagle's wing is smooth" "As the eagle flies its wings cut through the air creating turbulence" "This turbulence creates large sound waves making it noisy in flight" "When an owl flies the tiny spike on its wings break down the air into smaller spirals called microturbulence" "This makes the flight of the owl quieter" "Sharp hearing also helps an owl hunting in daylight" "The great gray owl lives in northern latitudes and in the winter months its prey is hidden beneath a blanket of snow" "But the snow offers no real protection" "Even through this covering the owl can detect the sound of a mouse eating" "The great gray owl like all birds of prey has senses finely adapted to its environment" "Turkey vultures ranging over the rain forests of South America can't see their food either" "The dense canopy of trees covering the ground hides animal carcasses from view" "So how these scavengers were able to locate food remained a mystery until the late 1930s" "In California, the Union Oil Company was plagued by a leak in a forty-two mile long natural gas pipeline" "The leak proved impossible to find in difficult terrain" "But company engineers had noticed that vultures often gathered while they were repairing holes in other pipelines" "So on a hunch, the engineers from the gas company traveled along the pipeline" "Eventually they saw turkey vultures circling in the distance" "When they reached the spot they started digging" "To help find pipeline leaks a gas with a distinctive smell of rotting meat is always added to natural gas" "It was this that attracted the vultures" "At the bottom of the hole the engineers found the broken pipe" "They had also discovered that turkey vultures could hunt just by smell" "Turkey vultures have nostrils so large you can see right through them" "Smells are processed by a very large olfactory bulb at the front of the brain" "The bulb is so sensitive it enables the bird to detect the direction a smell is coming from" "The turkey vulture follows the concentration of odors in the air to the source of the smell" "This acute sense provides a service to other vultures" "While the turkey vulture flies low over the forest canopy the other vultures soar high above waiting and watching" "These birds have a less-developed sense of smell and rely on the turkey vulture to guide them to the food" "When it descends, they follow" "Although first to the prey the turkey vulture isn't strong enough to rip through the skin of this large rodent" "It is soon joined by black vultures which are also unable to pierce the hide" "They must wait for the arrival of the king vulture" "Like the black vultures the king vulture has a weaker sense of smell" "But it does have a strong, sharp beak" "It repays the favor of being led to the meal by tearing through the skin of the carcass to provide food for all" "Back in Scotland, it is May" "The newborn golden eagle chicks are now seven weeks old" "They still need feeding twice a day" "But now they can be left alone on the aerie" "They've now acquired a thick layer of downy feathers and no longer depend on their mother for warmth" "The feathers to come, however will take them much further" "A typical bird of prey has over seven thousand feathers each with its own role" "Some insulate the bird from the cold" "Others waterproof it from the rain" "And then there are those that provide lift for flying" "Before a bird flies it raises and untangles its feathers putting each one into place ready for flight" "Flight is a bird's ultimate evolutionary achievement" "The evolution of birds is still the subject of fierce scientific debate" "The earliest ancestors of birds probably emerged two hundred million years ago as reptiles" "Some that climbed trees grew elongated scales to form primitive wings" "These allowed them to glide from the treetops" "Fifty million years later archaeopteryx appeared" "It still had teeth and solid bones just like a reptile" "But what made this animal so different was that it had feathers" "Like scales, feathers are made from keratin" "But they are light and flexible" "Archaeopteryx did more than glide It could fly" "Flight improved over the next seventy-five million years as every possible ounce was trimmed from what were now the birds" "To save weight they even lost their teeth" "Bones became hollow, strengthened with a honeycomb of trusses" "About fifty million years ago as the number of rodents and small mammals began to increase birds appeared that could hunt this rich food supply" "The modern bird of prey was born" "Eagle zero-one" "Wind one-six-zero-five Cleared for takeoff" "Change to your departure" "Eagle zero-one, cleared for takeoff Changing to departure" "Air bases throughout the world have a problem" "The short grass around an airfield attracts flocks of hungry birds" "Just one bird flying into the engine of a jet can cause it to crash" "The most dangerous time is when planes are coming in to land" ""Wart hog three-one clear to land runway two-four Wheels down."" ""And wart hog three-one expect possible go-round short final" "We have a small flock of birds crossing the runway left to right approach end" "Bird control one I'd like you to leave ground."" ""Control squadron, go ahead, please."" "The US 48th fighter wing based in England keeps peregrines and other falcons on stand by" ""Bird control one we need you to proceed out to runway two-four at the approach end" "We have a small flock of birds sitting on the runway approach end."" "Peregrines are the natural enemy of the rooks and pigeons that feed near the runways" "A tape recording of a distressed bird is often not enough to scare the flock" "But the release of peregrine has a dramatic effect" "First it climbs to gain altitude then it launches its attack with a steep dive called a stoop" "A peregrine falcon in a stoop is the fastest animal in the world" "A team in Germany has measured its speed at two hundred seventeen miles per hour" "The point is only to scare the birds" "But this time it catches a passing pheasant" "A peregrine's strong wings are designed for maneuverability" "But it depends on speed to catch its prey in the air" "The wings power the bird forward at over four beats a second" "An eagle's wings are not designed for speed" "Their shape and seven-foot span enable them to soar over vast areas in search of prey on the ground" "But one thing the eagle and the peregrine have in common with other birds of prey... is that they strike with their feet" "Each foot is armed with four talons which pierce skin like daggers" "On the eagle, they can be over two inches long" "When they grasp their prey or a branch raptors have a special locking mechanism in their legs that prevents their grip from slipping" "It works like a ratchet As their toes grasp ridges on the tendons lock the talons into place" "When it wants to let go the bird pulls the outer sheath away from the tendon and the grip is released" "In New Mexico the talons of the red-tailed hawk will find an easy target" "As the sun goes down" "Mexican free-tail bats stream out of their cave to start a night of feeding" "The red-tailed hawk normally hunts rabbits" "But it will also take bats" "And it doesn't pay to be choosy" "Raptors eating their prey have the skills of an experienced butcher" "A hungry eagle can strip the bones of a rabbit in fifteen minutes" "Birds of prey are fast eaters" "On the ground, the peregrine is vulnerable to predators so it needs to eat quickly" "It swiftly plucks the feathers of this pheasant to get at the flesh below" "Each species has a beak that is specialized and finely adapted to the prey it feeds on" "An eagle's beak has a sharp hook at the end able to cut into meat like a knife point" "And the sides of the beak have razor-sharp edges to tear flesh away from the carcass" "In the Florida Everglades one species of kite has a beak adapted to only one food source" "The snail kite feeds on apple snails" "lts thin, curved beak is so well-designed to prize a small snail out of its shell." "That a snail kite doesn't eat anything else" "While larger birds of prey eat their food where they find it smaller raptors like owls carry their catch to somewhere safe" "A raptor's digestive system with its specialized gastric juices is designed to deal with its exclusive diet of meat" "Even as young chicks barn owls swallow their prey whole" "Then the owls use an internal organ to separate the meat from the bones and fur" "Instead of teeth to break up the food owls have a gizzard a muscular stomach that grinds up the food" "The meat is digested by acids and the bones and fur are molded into pellets and regurgitated" "Dissecting a pellet reveals the owl's diet" "In a typical week it will eat twelve voles fourteen mice and eight shrews" "In Scotland, it is now eleven weeks since the young eagles hatched" "This down feather is all that's left of the bird's juvenile coat" "Their black and white flight feathers have grown and the birds are just mature enough to fly" "The parents are starting to leave the young birds to fend for themselves" "If they don't fly soon they'll starve" "These first flaps are essential preparation for flight" "They build up muscles and strengthen the wings" "The eldest chick finally gets up the courage to take to the air" "This maiden flight ends with an ungainly landing." "For any bird of prey the first year is the toughest in its life" "Over half will die in their first twelve months mainly due to starvation" "To survive, these birds will now need to find sites where they can hunt and breed" "Zoologist Mike McGrady has spent five years studying eagles in the western highlands of Scotland" "He's used tracking techniques to build the most detailed picture yet of the movements a young eagle makes once it has left the nest" "For the first few months after it leaves the nest it's, it, ah, is resident on its its natal territory" "But after, in usually, well November through January they they move on and start to wander quite widely" "These, these wanderings can be over hundreds of, of kilometers" "And they don't seem to have any direction" "To follow these wanderings" "Mike fits the eagles with radio transmitters" "But he has to catch one first" "Eighty yards from the hide" "Mike has baited the trap with a dead rabbit" "Trapping requires endless patience" ""lt, it's kind of a dynamic tension between being comfortable and being uncomfortable because you have to be you have to be awake all the time pretty much but you, you, and ready to move" "But you also, um, you're gonna ha." "Have to spend eleven hours in this hide when it's cold or raining or something like that" "And it, you're also trying to make yourself comfortable."" "This is the sixth day of watching and waiting" "When he does spot an eagle flying overhead there's no guarantee it will be tempted by the bait" "And even if it is, Mike's problems may have just begun" ""We then have to wait until the eagle's... uh exactly in the right position because one is always concerned that the the eagle will be injured by our trapping methods" "Um, but once the eagle is in, in, in position we just fire the trap by, ah radio control" "Unfortunately, sometimes the eagles spend half an hour in the wrong position but in the trap and we never catch them."" "Although the bird is in position, it isn't safe to spring the trap while its wings are open" "Finally, it folds its wings" ""Okay, the green number is ZZ 0832."" ""Oh-eight-three-two."" ""Yeah." "Let, let me just get a bill length on it."" "The first job is to tag the bird and measure it" "The beak and talon lengths will tell Mike whether this is a male or a female" ""Okay." "Forty-three-point two?"" "Although trapped, it is sill a formidable animal" ""Forty-nine point four."" "This bird has a short beak and talons and so Mike knows it's a male" ""All right." "We're ready to put the the tag on?"" "He fits the lightweight radio transmitter that will eventually detach itself from the bird" ""Um, this is a tail-monitor transmitter so it's life expectancy is really dependent, um upon where the, the tails, uh how long that tail feather going to stay in" "I've tried to choose a feather that's that's relatively new because eagle don't don't molt through all their feathers in one particular year" "So hopefully this bird will be able to to keep the transmitter on at least as long as the life of the transmitter which might be about two years."" "There are about four hundred fifty breeding pairs of eagles in Scotland" "To be successful, a young golden eagle needs to claim a territory" "But what if all the good sites are already taken?" "Today, Mike's picked up the signal of a young male eagle and followed it to its source" "The territory of this golden eagle is seven miles long and five miles wide" "The eagle has defended it against all comers" ""Just like any other territorial animal they, they maintain this territory um, at great, ah, energetic expense" "And the reason they have to do that is because the resources within that that territory are quite important to it breeding" "Those resources include food resources but also might include nesting resources or a mate" "They're maintaining an area which they can survive and and reproduce in" "The other eagles are are also interested in the same thing" "And you, if you have an eagle that's, um non-territorial and is looking to enter the breeding pop... population it has to, um, establish itself on a on a territory" "And at least from our work some of these eagles are, are ah, seem to be aggressive about that that, uh, territory establishment."" "Mike has recently discovered just how aggressive eagles can be" "In 1992, he tagged the male of a pair of breeding eagles" "He tracked the bird for a year and half until he eventually lost contact" ""Some months later we we picked up a very strong signal of the on this bird and followed the signal in to to find the bird dead and, and quite decomposed."" "What he discovered next came as a complete surprise" ""Once we cleaned up the, the skull and the whole skeleton we, we, we sort of realized what what had caused this this bird to die" "Um, it had, ah, obviously received a wound from probably another eagle" "It must be another eagle" "I can imagine anything else inflicting a wound like that on a adult, ah golden eagle."" "This eagle was killed for its territory" "How often this occurs no one knows" "But a young male eagle has now taken over the territory" "Chances are, this was the killer" "The new young male will mate with a resident female" "He will learn from her where the best... hunting sites are and benefit from her experience" "When she dies, he will stay in the territory and acquire a new mate" "In this way, territories have been handed down in an unbroken lineage stretching back centuries" "All birds of prey share an evolutionary legacy" "Whether they're hunting or scavenging flying or gliding they are the ultimate aerial predators" "THE END"