0:00:02 > 0:00:07*
0:00:38 > 0:00:41BIRDSONG
0:00:41 > 0:00:44It's spring in Sweden.
0:00:44 > 0:00:49Fieldfares are ferrying meals of worms to their ravenous chicks.
0:00:55 > 0:01:02They nest in colonies, up to 30 or 40 in a group, and that helps a lot with defence.
0:01:02 > 0:01:05 There are plenty of raiders around.
0:01:09 > 0:01:11This is one.
0:01:17 > 0:01:21It's a young raven. He's after a nestling.
0:01:27 > 0:01:33A fieldfare has spotted him and sounds the alarm. STRIDENT CHIRPING
0:01:38 > 0:01:43Others take up the call, and the defence force assembles.
0:01:43 > 0:01:48The raven now knows that he's been spotted, but he's hungry.
0:01:52 > 0:01:58The fieldfares, screaming with anger, converge on their enemy.
0:02:10 > 0:02:13Now threat turns into direct action.
0:02:13 > 0:02:17They mob him.
0:02:20 > 0:02:25Intimidated by the commotion, the raven retreats.
0:02:26 > 0:02:32But the fighters press home their attack. The raven is brought down.
0:02:32 > 0:02:35They bomb him with their droppings.
0:02:37 > 0:02:40RAVEN CAWS
0:02:45 > 0:02:49Soiled feathers soon become waterlogged.
0:02:49 > 0:02:52That could be crippling, even fatal.
0:02:52 > 0:02:55Thoroughly cowed, the raven retreats.
0:02:55 > 0:03:02The colony is saved, thanks to its members' highly effective system of communication
0:03:02 > 0:03:05between themselves AND with their enemy.
0:03:08 > 0:03:16The messages proclaimed by those Scandinavian fieldfares could hardly be misunderstood, even by us.
0:03:16 > 0:03:19The first were calls to arms.
0:03:19 > 0:03:24The second were battle cries designed to intimidate the enemy.
0:03:24 > 0:03:29But alarm calls aren't always so easily recognised by outsiders.
0:03:29 > 0:03:34Sometimes it's better to sound the alarm more surreptitiously.
0:03:37 > 0:03:41And that is something that birds in an English wood do very well.
0:03:43 > 0:03:48HIGH-PITCHED, SINGLE CHEEPS
0:03:48 > 0:03:53That sound is a general alarm call. It's short and very high-pitched.
0:03:53 > 0:03:58That makes it difficult to locate the bird that makes it.
0:04:06 > 0:04:12It's a great tit. Half-hidden among the leaves, he continues sending furtive signals to his family.
0:04:12 > 0:04:16But all the birds around get the message.
0:04:18 > 0:04:22An enemy would find it very hard
0:04:22 > 0:04:26to detect where that sound is coming from.
0:04:29 > 0:04:34Another warning. HIGH-PITCHED, QUIET, SINGLE CHIRPS
0:04:34 > 0:04:37This time it's from a robin.
0:04:41 > 0:04:46He's telling his mate to stay still until the danger has passed.
0:04:51 > 0:04:56And that's the blackbird's version. HIGH-PITCHED, GENTLE CHIRP
0:04:59 > 0:05:04The begging cries of nestlings could put them in danger.
0:05:09 > 0:05:15A male chaffinch tells them to keep quiet. REPEATED, SHRILL CHIRP
0:05:15 > 0:05:18They do as they're told.
0:05:19 > 0:05:26So this surreptitious call is like an international distress signal understood by everyone.
0:05:26 > 0:05:30SERIES OF REPEATED, STRIDENT CHIRPS
0:05:33 > 0:05:36That's a different kind of message.
0:05:36 > 0:05:42That's not one that's sent surreptitiously to others. It's aimed directly at me.
0:05:42 > 0:05:46It's a warning to tell me that I've been spotted.
0:05:49 > 0:05:54I'm too near this blackbird's mate who is sitting on her nest.
0:05:54 > 0:05:58His calls are almost continuous and much lower pitched
0:05:58 > 0:06:04because he wants to be located so as to distract me away from her.
0:06:09 > 0:06:15Sound is not the only way to spread the alarm or intimidate an intruder.
0:06:15 > 0:06:18Some birds do the same thing visually.
0:06:33 > 0:06:40Most of the time, this sun bittern is well camouflaged and unobtrusive,
0:06:40 > 0:06:47even less conspicuous than the jacanas and cayman that also haunt the river's edge, here, in Venezuela.
0:06:47 > 0:06:52The river is continually bringing edible bits and pieces within range,
0:06:52 > 0:06:57and the sun bittern lives on them. But it has competitors.
0:06:57 > 0:07:01A hawk in the branches above has spotted something.
0:07:02 > 0:07:07So has the sun bittern. But the hawk gets there first...
0:07:13 > 0:07:16..and collects it.
0:07:18 > 0:07:26A second hawk arrives. If the sun bittern is to get anything, it will have to frighten the others off.
0:07:28 > 0:07:30So it transforms itself.
0:07:30 > 0:07:37A ferocious, hissing, two-eyed monster that doesn't exist is saving the day.
0:07:52 > 0:07:54The hawk tries again.
0:07:59 > 0:08:06But this startling display convinces the hawks that the bird down there is dangerous. They give up.
0:08:10 > 0:08:14There is, of course, an alternative signal.
0:08:14 > 0:08:21Instead of saying, "I am here and extremely formidable," you could say, "I'm not here at all."
0:08:21 > 0:08:24That, of course, is a straightforward lie,
0:08:24 > 0:08:31but there's a bird in these Brazilian forests that tells the most convincing of lies.
0:08:32 > 0:08:40Finding it is not easy. Indeed, I'm sure I've walked past one many times. But this time, we're lucky.
0:08:41 > 0:08:45It's sitting on the tree trunk. It's a potoo,
0:08:45 > 0:08:48a kind of nightjar.
0:08:48 > 0:08:52It hunts for insects at night so it needs to rest during the day.
0:08:52 > 0:09:00It relies on the visual match between its feathers and the tree trunk to protect it from disturbance.
0:09:01 > 0:09:06The only thing that could give it away are its beak and its eyes.
0:09:13 > 0:09:16Now I'm getting quite close,
0:09:16 > 0:09:21so it decides to improve its disguise even further.
0:09:21 > 0:09:26It does that by changing its posture and closing those giveaway eyes.
0:09:26 > 0:09:30Now it's no more than the stump of a broken branch.
0:09:33 > 0:09:38You might think it would be a dangerous thing to do -
0:09:38 > 0:09:42to shut your eyes just when danger approaches.
0:09:42 > 0:09:47But, in fact, although its eyes are shut, it can still see me.
0:09:47 > 0:09:54There are two hitches in its eyelid. Its night-vision eyes are so sensitive that it can still see.
0:09:57 > 0:10:02As it watches me going away, it relaxes and returns to its doze.
0:10:05 > 0:10:11Most birds, of course, rely on their ability to fly to keep them out of trouble.
0:10:11 > 0:10:16So, as you walk through an English wood, they, too, vanish.
0:10:16 > 0:10:21But establish their confidence, and they will soon come back.
0:10:21 > 0:10:27And then you can see that they use their plumage to send very different messages.
0:10:30 > 0:10:35One finch meeting another needs to know whether it's the same species.
0:10:35 > 0:10:42If it is, it could be a rival, either for a mate or for territory. If it isn't, it can be ignored.
0:10:43 > 0:10:46So finches, with such similar body shapes,
0:10:46 > 0:10:51wear uniforms that make plain who they are.
0:10:51 > 0:10:54And what works for other birds
0:10:54 > 0:10:59will also work with us, provided we know the code.
0:10:59 > 0:11:02Most bird-watchers do.
0:11:03 > 0:11:08A grey-blue cap and reddish cheeks identify a chaffinch.
0:11:11 > 0:11:15A brown head and grey collar - a hawfinch.
0:11:16 > 0:11:20A completely green head - a greenfinch.
0:11:21 > 0:11:25A black cap and red cheeks - a bullfinch.
0:11:29 > 0:11:32And a red face and forehead - a goldfinch.
0:11:34 > 0:11:39So every finch knows whether another is a rival or not,
0:11:39 > 0:11:42and there are no pointless quarrels.
0:11:45 > 0:11:51In the forests of Indonesia, hornbills also use colour codes.
0:11:51 > 0:11:56Several species have predominantly black and white plumage.
0:12:00 > 0:12:03This one, however, the pied hornbill,
0:12:03 > 0:12:06has yellowish areas on its white wing patches.
0:12:09 > 0:12:12These are not accidental smudges.
0:12:12 > 0:12:14This bird uses make-up.
0:12:21 > 0:12:28With its beak, it squeezes a yellow oil from a giant preen gland on its rump.
0:12:32 > 0:12:37It uses that oil to paint on those yellow blotches.
0:12:39 > 0:12:46And not just on its wings. It adds yellow patches to its neck, though they are more difficult to put on.
0:12:47 > 0:12:53Even its huge bill owes its yellow colour to the preen oil.
0:12:57 > 0:13:01Different kinds of hornbills paint themselves different colours.
0:13:01 > 0:13:04Whether these cosmetics are used
0:13:04 > 0:13:11just for appearances' sake, or whether they have an additional purpose, we don't know.
0:13:13 > 0:13:15But one thing is quite certain -
0:13:15 > 0:13:19birds take a lot of care over their appearance.
0:13:21 > 0:13:26All birds have to have good eyesight to navigate at speed through the air,
0:13:26 > 0:13:31but, in particular, they have excellent colour vision.
0:13:31 > 0:13:35That enables some species to have the most gorgeous uniforms.
0:13:35 > 0:13:40This bottle of artificial nectar can attract some of the most spectacular.
0:13:42 > 0:13:45The particular glory of hummingbirds
0:13:45 > 0:13:48are their bibs and breast-shields.
0:13:53 > 0:14:00Their colour is not pigment, but an optical effect created by refraction, like the colours of oil on water.
0:14:18 > 0:14:25They're particularly attracted by red, which is why I've got red artificial flowers on this bottle.
0:14:25 > 0:14:28They can also see in ultraviolet,
0:14:28 > 0:14:33and that's a colour that lies beyond the range of the human eye.
0:14:33 > 0:14:38It's been discovered that many of their feathers reflect ultraviolet,
0:14:38 > 0:14:45so it's likely that these brilliant costumes are even more vivid in their eyes than they are in ours.
0:14:46 > 0:14:51Many birds that seem plain are almost gaudy in ultraviolet light.
0:14:51 > 0:14:55Starlings, for example, have a sheen to their plumage,
0:14:55 > 0:15:02but that has an ultraviolet component that makes them appear much more vivid to one another.
0:15:05 > 0:15:10Blue tits, in our eyes, are one of the more colourful garden birds.
0:15:10 > 0:15:15But in ultraviolet, they're much brighter still.
0:15:15 > 0:15:21Their crests are particularly vivid and much brighter in males than females.
0:15:21 > 0:15:26To them, the sexes look different. To us, blue tits all look the same.
0:15:29 > 0:15:34Most of us think that budgerigars are unusually colourful birds.
0:15:34 > 0:15:40But ultraviolet radically changes the character of their costume.
0:15:40 > 0:15:43Their feet glow.
0:15:44 > 0:15:51And the spots on their cheeks, which are not particularly prominent to our eyes, positively blaze.
0:15:57 > 0:16:02Indeed, a budgerigar's full-dress uniform is dramatic in the extreme.
0:16:05 > 0:16:09Uniforms not only indicate an individual's regiment,
0:16:09 > 0:16:12but his rank within that regiment.
0:16:13 > 0:16:16Male sparrows have black bibs,
0:16:16 > 0:16:21but the size varies. The more vigorous birds have bigger bibs
0:16:21 > 0:16:24and, therefore, higher ranks.
0:16:24 > 0:16:29Sparrows forage in flocks. When there's lots of food in a small area,
0:16:29 > 0:16:33you might expect lots of quarrels. But there aren't.
0:16:33 > 0:16:36This is a private with no badges.
0:16:37 > 0:16:41This one is somewhat senior - a sergeant, perhaps.
0:16:41 > 0:16:44A captain.
0:16:47 > 0:16:50And the colonel.
0:16:53 > 0:16:57There could be disputes, not only over food,
0:16:57 > 0:17:00but over amenities like dust baths.
0:17:08 > 0:17:12The privates are squabbling among themselves.
0:17:12 > 0:17:16But watch what happens when a corporal steps in.
0:17:19 > 0:17:22Junior ranks retreat.
0:17:22 > 0:17:26Or when a corporal gets too close to a sergeant.
0:17:30 > 0:17:34A sergeant, however, gives way to a captain.
0:17:34 > 0:17:38And no-one should think of parting a colonel from his lunch.
0:17:40 > 0:17:45A quick flourish of his insignia is quite enough.
0:17:47 > 0:17:51Among birds that don't live in flocks,
0:17:51 > 0:17:55there is no need for the ranking system to be so multi-layered.
0:17:56 > 0:17:59Moorhens may mingle,
0:17:59 > 0:18:02but each pair has its own territory.
0:18:02 > 0:18:08Their badges are the red beak and head shield, and white tail patches.
0:18:08 > 0:18:15Rivals assess one another's strength by the size and brilliance of those head shields.
0:18:25 > 0:18:29If they feel their ranks are equal,
0:18:29 > 0:18:32they may not want to contest the boundary,
0:18:32 > 0:18:40and they display the white tail patches to indicate that the confrontation is being broken off.
0:18:40 > 0:18:44But here, the male on the right is standing upright.
0:18:44 > 0:18:49He reckons he's the senior and he wants to enlarge his territory.
0:18:49 > 0:18:55The time for sending messages is over. This quarrel can only be settled by physical violence.
0:19:03 > 0:19:09Birds can get badly injured in these battles, but they have to be fought
0:19:09 > 0:19:13if a senior bird is to establish and retain his rank.
0:19:51 > 0:19:55Eventually, the junior bird surrenders.
0:19:55 > 0:20:01A new line has been drawn. They won't need to fight again as long as it's not overstepped.
0:20:03 > 0:20:08Communication by visual signals, however, has one major limitation.
0:20:08 > 0:20:10Except in completely open country,
0:20:10 > 0:20:16they only work at close range. In forests, sound signals travel much further.
0:20:16 > 0:20:21So if a bird, in order to get enough food, needs a large territory,
0:20:21 > 0:20:24it's likely to declare its claims with sound.
0:20:29 > 0:20:34There are, of course, many different ways of making a noise,
0:20:34 > 0:20:38and knocking on a resonant tree trunk is one of them.
0:20:38 > 0:20:45Here, in Patagonia in South America, two knocks on a tree trunk has a very particular meaning -
0:20:45 > 0:20:51at least among birds. If I do it, I might even get an answer.
0:21:01 > 0:21:04TWO, DISTANT, RAPID KNOCKS
0:21:09 > 0:21:12TWO KNOCKS IN REPLY
0:21:25 > 0:21:31It's a Magellanic woodpecker, one of the largest of all woodpeckers,
0:21:31 > 0:21:34and he thinks he's heard a rival.
0:21:44 > 0:21:47He comes in for a closer look.
0:22:07 > 0:22:10And here's his mate to support him.
0:22:15 > 0:22:18Now she joins in the dispute.
0:22:39 > 0:22:43He's now on my tree.
0:22:43 > 0:22:46His mate is even closer.
0:22:56 > 0:23:02I've stopped knocking, so it seems to them that their rival has gone.
0:23:02 > 0:23:04All is well.
0:23:06 > 0:23:09There's another drummer in the bird world -
0:23:09 > 0:23:12Australia's palm cockatoo.
0:23:12 > 0:23:17His beak is no good as a drumstick so he uses a wooden one.
0:23:19 > 0:23:22HOLLOW KNOCKING
0:23:31 > 0:23:36HARSH BUZZING
0:23:36 > 0:23:43And that noise, too, is made mechanically - by an African broadbill.
0:23:45 > 0:23:52It makes its call in the same way as children do when they blow across a blade of grass.
0:23:52 > 0:23:59But, instead of grass, the broadbill has specially strengthened and shaped wing feathers.
0:24:04 > 0:24:09Of course, most of the sounds made by birds come from their throats.
0:24:09 > 0:24:14The calls and songs that you hear in a tropical rainforest, however,
0:24:14 > 0:24:22are very different from those you might hear in a European woodland. And there's a reason for that.
0:24:22 > 0:24:27The leaves in a rainforest have shiny surfaces that reflect sound.
0:24:27 > 0:24:33So a complex call up here would have its notes slurred and confused.
0:24:33 > 0:24:36As a result, birds that live up here
0:24:36 > 0:24:41tend to have calls that are simple, short and, often, very, very loud.
0:24:42 > 0:24:46CLEAR, PIERCING CALL
0:24:46 > 0:24:50That's the loudest of all from a bare-throated bellbird.
0:25:00 > 0:25:06HIGH-PITCHED WHISTLES This is a close rival - a screaming piha.
0:25:13 > 0:25:17Toucans must also be close to the top ten.
0:25:17 > 0:25:21REPETITIVE, HIGH-PITCHED CALL
0:25:21 > 0:25:25All these birds call from high up in the canopy.
0:25:25 > 0:25:30Lower down, where foliage is less dense, the calls can be different.
0:25:30 > 0:25:33For one thing, they can be longer.
0:25:33 > 0:25:38ONE LONG CALL ON A FALLING NOTE
0:25:45 > 0:25:47That's a curassow.
0:25:52 > 0:25:55And this - a wattled guan.
0:25:58 > 0:26:02LONG, WHIRRING CALL
0:26:02 > 0:26:06A longer call, of course, can contain more notes.
0:26:06 > 0:26:13PIPING, MELODIC CALL A kagu in New Caledonia. This is a female.
0:26:16 > 0:26:19Her mate, some distance away, is listening.
0:26:23 > 0:26:28The family wandered apart as they foraged. They want to get together.
0:26:52 > 0:26:55Her son has also heard the message.
0:27:07 > 0:27:13So the adult pair are reunited and they greet one another, as usual,
0:27:13 > 0:27:16with a visual display.
0:27:25 > 0:27:29But their son is still out there somewhere.
0:27:54 > 0:27:58And, once again, the family group is complete.
0:28:09 > 0:28:14The calls of the kagu can be heard half a mile away.
0:28:14 > 0:28:19But some birds need to communicate over even greater distances.
0:28:19 > 0:28:23The best way to do that is with very low-pitched notes.
0:28:23 > 0:28:27THROATY, FROG-LIKE CALL
0:28:29 > 0:28:32An American bittern.
0:28:39 > 0:28:43LOW-PITCHED, HOLLOW GULPING
0:28:47 > 0:28:55An air sac in his chest acts as a resonator, so he starts by gulping in air and pumping it up.
0:29:01 > 0:29:04CALL ECHOES IN DISTANCE
0:29:04 > 0:29:09This call carries for over two miles, even through the thickets of reeds.
0:29:26 > 0:29:31When the performance is over, the air sac slowly deflates.
0:29:43 > 0:29:48If you can get out of the reeds, then your calls are less impeded.
0:29:48 > 0:29:55The Australian musk duck does just that in order to broadcast his messages.
0:29:55 > 0:30:01The smooth surface of the water also helps to reflect the sound far across the lake.
0:30:03 > 0:30:07HOLLOW, TAPPING CALL
0:30:15 > 0:30:21The flap on his chin is a visual signal for any birds that come over for a closer look.
0:30:28 > 0:30:33However, if calls are directed to neighbours nearby,
0:30:33 > 0:30:36then they can become very elaborate.
0:30:37 > 0:30:44This red bishop makes an almost constant stream of high-pitched notes as he hops around.
0:30:49 > 0:30:53You can't get much more elaborate than this.
0:30:53 > 0:30:56RAUCOUS, SQUEAKY TRILLING
0:30:57 > 0:31:04The extraordinary display of the oropendula includes one of the strangest songs of all.
0:31:04 > 0:31:07So how do birds do it?
0:31:12 > 0:31:18How, for example, can canaries sing continuously for minutes on end?
0:31:20 > 0:31:27Slowing the singer down, which also lowers the pitch of the notes, allows us to see what's happening.
0:31:29 > 0:31:34Between notes, it takes mini-breaths to replenish its air supply.
0:31:34 > 0:31:38In full song, it may do so 30 times a second,
0:31:47 > 0:31:52A bird's voice box can also produce two different notes simultaneously.
0:31:53 > 0:31:57It's not high in the throat like ours, but deep in its chest.
0:31:58 > 0:32:01Low notes come from one side,
0:32:01 > 0:32:04high from the other.
0:32:20 > 0:32:27By alternating between high and low notes, even short songs can carry very complex messages.
0:32:29 > 0:32:32And this is the champion.
0:32:32 > 0:32:35RAPID, MUSICAL TRILL
0:32:35 > 0:32:40The cowbird uses over 40 different notes in his songs.
0:32:40 > 0:32:47Some of them are so high that they are beyond the hearing of many of us. Again, if we slow the action down,
0:32:47 > 0:32:50 we can hear what's going on.
0:32:52 > 0:32:57The left side is producing the low notes...
0:32:57 > 0:33:00MELLOW WARBLE
0:33:00 > 0:33:02..and the right, the high.
0:33:02 > 0:33:05HIGH-PITCHED PEEPS
0:33:05 > 0:33:11Others are made by combining the sounds higher up in the throat.
0:33:11 > 0:33:15It may take a cowbird two years to learn his song properly.
0:33:21 > 0:33:27It's important that birds should get their calls exactly right
0:33:27 > 0:33:32for they can be as significant in proclaiming identity as a uniform.
0:33:32 > 0:33:36Indeed, if a bird has a shy and retiring disposition
0:33:36 > 0:33:40and lives in a secluded place like this English woodland,
0:33:40 > 0:33:48then its voice may be the only way that it can be recognised by another bird or, indeed, by a bird-watcher.
0:33:51 > 0:33:55There are two kinds of warblers here. This is a chiffchaff,
0:33:55 > 0:33:59fuelling up after its long flight from Africa.
0:34:03 > 0:34:09And this is a willow warbler. To me, it looks virtually identical.
0:34:11 > 0:34:14But wait until they sing.
0:34:15 > 0:34:21This is a chiffchaff. BRIEF, TWO-NOTED PEEPS
0:34:21 > 0:34:27MELODIOUS SONG WITH LONGER NOTES And this, a willow warbler.
0:34:44 > 0:34:49There's no mistaking who's who as long as you can hear their calls.
0:34:53 > 0:34:57But a bird's call can tell another bird
0:34:57 > 0:35:02more than just what kind of bird it is that's singing.
0:35:02 > 0:35:09This patch of bush on a small, offshore, New Zealand island belongs to a male saddleback.
0:35:09 > 0:35:16He's held it throughout the year and he knows who his neighbours are because their calls vary slightly
0:35:16 > 0:35:21and he can recognise each one individually. And there he is.
0:35:21 > 0:35:26Throughout the day, he keeps in regular contact with his neighbours.
0:35:26 > 0:35:30HIGH-PITCHED CHEEPS AND CHATTERING
0:35:33 > 0:35:36They each answer his call,
0:35:36 > 0:35:39and he can distinguish between them
0:35:39 > 0:35:44in the same way that we distinguish between regional dialects.
0:35:46 > 0:35:48A northerner.
0:35:48 > 0:35:51A southerner.
0:35:53 > 0:35:56And someone from the east coast.
0:36:00 > 0:36:04If the right call comes from the right place,
0:36:04 > 0:36:11then he knows that his territory is safe from intruders and he can go back to feeding.
0:36:14 > 0:36:19But if the call is from a saddleback that he doesn't recognise,
0:36:19 > 0:36:27and if, as well as that, it comes from a completely new place, then he will react in a very different way.
0:36:27 > 0:36:31And, of course, it's quite easy for me to make that happen.
0:36:36 > 0:36:41I'm going to play him a recording of a saddleback from a different island.
0:36:45 > 0:36:51His response is swift and very aggressive. STACCATO CHIRPING
0:36:54 > 0:36:56He comes down for a closer look.
0:36:59 > 0:37:02He gives another warning.
0:37:09 > 0:37:14This is a serious challenge to his territory. It can't be tolerated.
0:37:25 > 0:37:29Now, since his rival seems to be somewhere close by,
0:37:29 > 0:37:34he makes a visual threat, displaying the brown patch on his back.
0:37:34 > 0:37:39He's ready to fight, if only he could find who it is he has to fight.
0:37:41 > 0:37:45That's enough. We'll leave him in peace.
0:37:53 > 0:37:57MUTED, SWEET BIRDSONG
0:37:59 > 0:38:05To many of us, however, this is the most delectable of natural sounds.
0:38:07 > 0:38:14It's an hour before dawn. It's spring. This is an English woodland. And all around - the dawn chorus.
0:38:14 > 0:38:19It's so familiar that, perhaps, we take it for granted.
0:38:19 > 0:38:23But there's a lot we don't know about it still.
0:38:33 > 0:38:40As first light brightens, different kinds of birds, one by one, join the choir.
0:38:41 > 0:38:47CALLS MINGLE AND ECHO
0:39:04 > 0:39:08Why should they all sing together at this time?
0:39:08 > 0:39:12Wouldn't it be better for some to sing later by themselves?
0:39:12 > 0:39:15And that's not the only puzzle.
0:39:15 > 0:39:19Why should it happen at this time of day?
0:39:19 > 0:39:22Well, at dawn, it's still quite cold.
0:39:22 > 0:39:25Insects are not yet up and about.
0:39:25 > 0:39:30For many birds, there's nothing to eat. So they might as well sing.
0:39:32 > 0:39:35PROLONGED, RAPID TRILL
0:39:39 > 0:39:44 WELL-ARTICULATED MELODIOUS SONG
0:39:44 > 0:39:48DRAWN-OUT, HISSING CALL
0:39:48 > 0:39:52SWEET, FLUTE-LIKE CALL
0:40:01 > 0:40:03There's another possible reason.
0:40:03 > 0:40:08It's usually quite calm at dawn and, with no wind,
0:40:08 > 0:40:12these messages will travel far and still be recognisable.
0:40:16 > 0:40:23The chorus is the equivalent of our early morning news - only broadcast in 50 different languages at once.
0:40:36 > 0:40:38By listening to it,
0:40:38 > 0:40:43this wren knows which of his neighbours is still alive.
0:40:44 > 0:40:46He knows where they are.
0:40:50 > 0:40:53And if there are any new males on the scene.
0:40:59 > 0:41:05Each kind of bird listens to its own particular section of the sound spectrum.
0:41:07 > 0:41:11The song thrush broadcasts in the mid-range.
0:41:27 > 0:41:30The wood pigeon's calls are somewhat lower.
0:41:34 > 0:41:39Smaller birds, like the firecrest, use the higher frequencies.
0:41:40 > 0:41:44These springtime messages from male birds not only say,
0:41:44 > 0:41:50"This is my patch." They also say to passing females, "Come and join me."
0:41:50 > 0:41:53HIGH-PITCHED, RAPID TRILL
0:41:53 > 0:42:00Robins have now extended their usual songs to carry this additional message.
0:42:18 > 0:42:23The male chaffinch has done the same. CLEAR, MELODIOUS CALL
0:42:26 > 0:42:31He may sing this song over 500,000 times in a season.
0:42:41 > 0:42:49By late spring, migrants have arrived from southern Europe and Africa and are adding to the chorus.
0:42:57 > 0:43:00RAPID, METALLIC TRILL
0:43:02 > 0:43:05A wood warbler.
0:43:05 > 0:43:10CLEAR, RINGING CALL A pied flycatcher.
0:43:10 > 0:43:13And a redstart.
0:43:13 > 0:43:16SWEET, MELANCHOLY SONG
0:43:23 > 0:43:30His mate, like many, will be impressed by the originality and complexity of his song.
0:43:33 > 0:43:39The male sedge warbler can produce 50 different notes and never sings the same song twice.
0:43:55 > 0:43:59He's like a jazz singer - continually improvising.
0:43:59 > 0:44:03Different males develop different singing styles.
0:44:17 > 0:44:21And this is, perhaps, the most lyrical of all European songsters.
0:44:21 > 0:44:27COMPLEX, MELLOW SONG A nightingale.
0:44:32 > 0:44:37He may have 300 different love songs in his repertoire.
0:44:45 > 0:44:49And he will sing for a mate all through the night.
0:45:12 > 0:45:19What bird has the most elaborate, the most complex, the most beautiful song in the world?
0:45:19 > 0:45:25I guess there are lots of contenders, but this bird must be one of them -
0:45:25 > 0:45:28the superb lyrebird of southern Australia.
0:45:35 > 0:45:39MELODIOUS CHIRRUPING
0:45:40 > 0:45:42WHOOPS AND WHISTLES
0:45:42 > 0:45:47He clears a space in the forest to serve as his concert platform.
0:45:59 > 0:46:05To persuade females to come close and admire his plumes, he sings the most complex song he can manage.
0:46:05 > 0:46:13He does that by copying the songs of all the other birds he hears around him, such as the kookaburra.
0:46:13 > 0:46:16RAUCOUS CACKLING
0:46:16 > 0:46:19It's a very convincing impersonation.
0:46:25 > 0:46:28Even the original is fooled.
0:46:36 > 0:46:41He can imitate the calls of at least 20 different species.
0:46:44 > 0:46:50He also, in his attempt to outsing his rivals, incorporates other sounds that he hears in the forest.
0:46:50 > 0:46:54CLICK That was a camera shutter.
0:46:58 > 0:47:01CLICK And again.
0:47:06 > 0:47:10And now a camera with a motor drive. CLICK, WHIRR
0:47:10 > 0:47:14WHOOPING, WAILING CALL
0:47:14 > 0:47:16 And that's a car alarm.
0:47:25 > 0:47:30And now the sounds of foresters and their chain saws working nearby.
0:47:30 > 0:47:37WOOD CRACKLES AND CHAIN SAW BUZZES
0:47:39 > 0:47:42SAW CUTTING THROUGH WOOD
0:47:49 > 0:47:53That wonderful performance is only one example
0:47:53 > 0:47:58of the extent to which male birds will go in order to attract a female.
0:47:58 > 0:48:05The range and sheer extravagance of their courtship displays can be quite astonishing.
0:48:09 > 0:48:15And the range of relationships between male and female that these displays lead to
0:48:15 > 0:48:19is also much more varied than you might suppose.
0:48:19 > 0:48:24And it's that, the most crucial stage in the life of any bird,
0:48:24 > 0:48:27that we'll be looking at in the next programme.
0:48:27 > 0:48:30CLICK, WHIRR
0:49:03 > 0:49:08Subtitles by Mary Easton BBC Scotland - 1998