0:01:06 > 0:01:09This lava gull in the Galapagos,
0:01:09 > 0:01:14like all the rest of those birds, it is sending a very clear message.
0:01:14 > 0:01:20It's saying, "I'm ready to mate and I've got a great place for a nest."
0:01:50 > 0:01:57Their visual signal is normally an inconspicuous patch of shrivelled skin on the throat.
0:01:57 > 0:02:01It takes about 20 minutes to blow one up.
0:02:11 > 0:02:18The females, who don't have a throat pouch, cruise by, assessing what is on offer.
0:02:20 > 0:02:27The size of the balloon gives an indication of a male's vigour and thus his desirability as a father.
0:02:57 > 0:03:00The female leaves
0:03:00 > 0:03:05and one of the homeless males decides to make a challenge.
0:03:13 > 0:03:16The throat pouch is an obvious target -
0:03:16 > 0:03:20tear that and its owner can't attract anyone.
0:03:26 > 0:03:31A new proprietor takes over the nest site and pumps up HIS balloon.
0:03:38 > 0:03:41Success is swift.
0:03:45 > 0:04:06She's found what she was looking for.
0:04:06 > 0:04:10he cements their relationship with a few judicious gifts.
0:04:16 > 0:04:19A little fruit.
0:04:19 > 0:04:25Males worldwide ingratiate themselves with females in this way.
0:04:25 > 0:04:30Wattled guans do in the tropics of Amazonia.
0:04:30 > 0:04:34And so do great tits in the suburban gardens of Europe.
0:04:34 > 0:04:38Sea birds, of course, like fish,
0:04:38 > 0:04:44though it's still the prerogative of the female to decline a gift the first time it's offered.
0:04:48 > 0:04:53Grebes like fish too - these are on a lake in North America.
0:04:53 > 0:04:56But for grebes in particular,
0:05:42 > 0:05:47Once they've got to know each other really well, however,
0:05:47 > 0:05:49they perform their pas-de-deux
0:05:49 > 0:05:52with immaculate timing.
0:06:31 > 0:06:36but the dancers make up for that with impressive footwork.
0:07:13 > 0:07:35After the dancing,
0:07:35 > 0:07:41A male swallow-tailed gull also declares his intentions
0:07:41 > 0:07:44with a down payment on the nest.
0:07:47 > 0:07:51As a pair get to know one another better,
0:07:51 > 0:07:56they become sufficiently trustful to indulge in mutual preening.
0:08:07 > 0:08:10Albatross behave in the same way.
0:08:18 > 0:08:26These bills are quite strong enough to injure anything or anyone that dares to interfere with them,
0:08:26 > 0:08:43but now, as the pair sit together on their nest site, they are used to deliver the most tender of caresses.
0:08:47 > 0:08:51What follows may seem like duelling,
0:08:51 > 0:08:56but actually, it is, once again, a kind of dancing.
0:08:58 > 0:09:01The sequence of movements
0:09:01 > 0:09:03is long and complicated.
0:09:32 > 0:09:57If both partners perform without mistakes and in harmony,
0:10:06 > 0:10:08So pairs are formed,
0:10:08 > 0:10:11and the union is consummated.
0:10:11 > 0:10:18For most birds, the pair will stay together for several weeks, if not for years.
0:10:18 > 0:10:24These waved albatross in the Galapagos will stay together for the rest of their lives,
0:10:24 > 0:10:27and that is very unusual.
0:10:27 > 0:10:35Insects don't stay together, frogs and toads don't, lizards and snakes don't. Why should birds?
0:10:35 > 0:10:38The answer is there.
0:10:38 > 0:10:45No female bird can manage to fly around with an egg inside her, let alone several,
0:10:45 > 0:11:05for the days or weeks it needs to develop.
0:11:05 > 0:11:08The evidence doesn't support that.
0:11:08 > 0:11:12It's not so much the mutual affection
0:11:12 > 0:11:17as the concern it has for its own genes which are in the egg.
0:11:17 > 0:11:20If, without jeopardising those,
0:11:20 > 0:11:25either bird could find a way of spreading its genes more widely,
0:11:25 > 0:11:27the evidence suggests
0:11:27 > 0:11:30they would take it.
0:11:30 > 0:11:32Here in Jamaica,
0:11:32 > 0:11:36some male birds are far from faithful.
0:11:36 > 0:11:41Flame trees, when in flower, produce delicious, sweet nectar.
0:11:41 > 0:11:45It is the staple diet for hummingbirds
0:11:45 > 0:11:49and Jamaica has many different species of them.
0:11:49 > 0:11:54The male streamer-tailed hummer is a vigorous and aggressive creature
0:11:54 > 0:12:18and a strong individual will take control of an entire tree.
0:12:18 > 0:12:21for everyone.
0:12:33 > 0:12:38But he's not fighting just because he wants to drink all the nectar.
0:12:38 > 0:12:41He is more devious than that.
0:12:41 > 0:12:46The tree is the most prolific source of nectar around.
0:12:46 > 0:12:51There are female streamer-tails in the neighbourhood,
0:12:51 > 0:12:54and they're busy building nests.
0:12:54 > 0:13:00They're relatively plain creatures, lacking the long streamer-like tails of the male.
0:13:03 > 0:13:29There's so much nectar that they'll be able to feed their chicks alone.
0:13:32 > 0:13:36He erects little tufts like ears on either side of his head.
0:13:40 > 0:13:43She accepts him.
0:13:47 > 0:13:50He goes back to wait for the next diner...
0:13:52 > 0:13:58..while she pulls herself together and prepares for life as a single parent.
0:13:58 > 0:14:03A good, secure home can also be a very effective lure
0:14:03 > 0:14:06with which to attract a female.
0:14:06 > 0:14:09Red-headed weavers nest in colonies,
0:14:09 > 0:14:15and the yellow-headed females keep an eye on what they are building
0:14:15 > 0:14:34before committing themselves.
0:14:41 > 0:14:45A lot of work goes into each nest.
0:14:45 > 0:14:51It's important the weaves be tight - too loose and the eggs might drop through.
0:14:55 > 0:14:59When one is finished and ready for judging,
0:14:59 > 0:15:03the male perches hopefully beside it.
0:15:13 > 0:15:17She clearly doesn't think much of this one.
0:15:25 > 0:15:51This, however, is good enough to warrant an internal inspection.
0:15:51 > 0:15:55each of which holds chicks he has fathered.
0:15:57 > 0:16:01Each female, by choosing him as a mate,
0:16:01 > 0:16:05has provided her young with the best genes available,
0:16:05 > 0:16:11and he has quadrupled the number of his offspring.
0:16:11 > 0:16:16But some birds construct even bigger buildings to impress females,
0:16:16 > 0:16:23and to see the most spectacular you have to come to the forests of the islands north of Australia.
0:16:23 > 0:16:31Some females can be persuaded to mate for rewards that are more abstract than mere food and lodging.
0:16:31 > 0:16:55There's a kind of bird here in New Guinea whose females select a male not for a meal ticket,
0:16:59 > 0:17:03He has a passion for interior decoration.
0:17:03 > 0:17:08His hut - almost big enough for me - is neither a home nor a nursery.
0:17:08 > 0:17:12It's a gallery for displaying his artistic creations
0:17:12 > 0:17:16to visiting females.
0:17:16 > 0:17:23These flowers come from a creeper that's only just started to bloom - great if you like colour.
0:17:23 > 0:17:26And he loves it!
0:17:36 > 0:17:39The iridescent wing-cases of beetles
0:17:39 > 0:17:44also appeal to him and he has amassed an impressive collection.
0:17:44 > 0:18:09But they're always in need of rearrangement to show them off
0:18:09 > 0:18:13with a slightly different artistic sense.
0:18:13 > 0:18:19If a female decides these are the best jewels, then she'll mate with the owner.
0:18:28 > 0:18:32So here, where living is easy,
0:18:32 > 0:18:37a female is not bowled over by food or accommodation, but by beauty.
0:18:37 > 0:18:43And beauty can be found not only in jewels, but in costumes.
0:18:46 > 0:18:48This is Bulwer's pheasant,
0:18:48 > 0:18:52and he has got spectacular wattles.
0:18:52 > 0:18:56He's impressive enough normally,
0:18:56 > 0:19:16but when she is around he gets very excited indeed!
0:19:19 > 0:19:24Impressive though he is, she is very critical.
0:19:28 > 0:19:32He's not good enough, it seems.
0:19:34 > 0:19:38Another pheasant - Temminck's tragopan.
0:19:38 > 0:19:42His costume jewellery is even more elaborate.
0:19:49 > 0:19:53And if you've got it, why not flaunt it?
0:20:26 > 0:20:29than is possessed by any other bird.
0:20:49 > 0:20:54The argus pheasant has the largest of all tail feathers,
0:20:54 > 0:20:59and wing feathers that are certainly as spectacular.
0:21:08 > 0:21:12And what can rival the train of a peacock?
0:21:12 > 0:21:38The costume put on specially for courtship dances by the African widowbird
0:21:38 > 0:21:43It's hazardous exposing yourself like this, even if you can fly.
0:21:43 > 0:21:50You're making yourself an easy target for a hawk and there are many around here in Kenya.
0:21:52 > 0:21:58Evidently the matings a male gets from displaying in this fashion
0:21:58 > 0:22:01make the risk worthwhile.
0:22:11 > 0:22:15Up in the frozen north, on the Arctic tundra,
0:22:15 > 0:22:19life is too rigorous to allow such extravagance.
0:22:19 > 0:22:23Here, males display in a more modest way.
0:22:26 > 0:22:47The buff-breasted sandpiper - no spectacular plumes for him.
0:22:49 > 0:22:53Flashes like these can be seen a good 200 yards away.
0:22:53 > 0:22:56A female has got the message.
0:23:05 > 0:23:08She's definitely interested.
0:23:16 > 0:23:19Now there are three females.
0:23:19 > 0:23:22It's time to reveal all!
0:23:32 > 0:23:36He reinforces his appeal with quiet clicking calls.
0:24:00 > 0:24:05Now there are four females with male number one. This hardly seems fair.
0:24:07 > 0:24:10Number two's wings don't appeal!
0:24:14 > 0:24:18So he comes over to where the action is.
0:24:24 > 0:24:28The females don't know which way to turn.
0:24:42 > 0:24:47But number one won't allow anyone else on his pitch for long.
0:24:47 > 0:25:07There's not room on this part of the tundra for two.
0:25:07 > 0:25:10only too often leads to physical violence.
0:25:12 > 0:25:15Scotland.
0:25:15 > 0:25:22Here in the pine forests of the Highlands, fights between males are among the most violent of all.
0:25:27 > 0:25:31The capercaillie is the biggest of grouse.
0:25:35 > 0:25:38The arenas where the males display
0:25:38 > 0:25:43are vigorously contested, and the best, in the end,
0:25:43 > 0:25:48is claimed by the most powerful male who will defend it against anyone.
0:26:24 > 0:26:28But here's a really serious rival.
0:26:33 > 0:26:37He is being very reckless indeed.
0:26:56 > 0:27:03Birds can get very badly injured in battles like these, and even die from their wounds.
0:27:03 > 0:27:08But the rewards they're fighting for are very great.
0:27:08 > 0:27:30This is the most important moment of their year.
0:27:30 > 0:27:35And they seem to agree on who the champion is.
0:27:43 > 0:27:47Runners-up are almost always rejected,
0:27:47 > 0:27:52while the winner attracts almost more mates than he can deal with.
0:27:58 > 0:28:03Some males make the job of the females in choosing them easier
0:28:03 > 0:28:07by gathering together and displaying in groups.
0:28:07 > 0:28:12And there's one bird in the Brazilian rainforest
0:28:12 > 0:28:16who has the oddest way of impressing a female.
0:28:16 > 0:28:19It's called the calf bird.
0:28:41 > 0:28:44They compete with calls.
0:28:44 > 0:28:49The sound is greatly amplified by air sacs on their throats.
0:29:04 > 0:29:09This assembly is 100 feet above the ground, high in the canopy,
0:29:09 > 0:29:16so high that very few people have seen the birds performing this incredible chorus, let alone film it.
0:29:46 > 0:29:54The females look exactly the same as the males - as you might expect as costumes aren't used to compete.
0:30:00 > 0:30:04When a female flies down to the best branch,
0:30:04 > 0:30:08all the males call with renewed intensity.
0:30:17 > 0:30:20More females arrive.
0:30:34 > 0:30:58She tells the male she has chosen him by giving him a peck on the neck.
0:30:58 > 0:31:02That's the idea!
0:31:04 > 0:31:07And then he notices a second female.
0:31:07 > 0:31:09Call as they might,
0:31:09 > 0:31:13none of the other males get a look in.
0:31:17 > 0:31:25The calf bird has a cousin whose males also display in groups. They compete not with sound, but colour.
0:31:25 > 0:31:28The cock-of-the-rock.
0:31:44 > 0:31:48The males assemble in groups of a dozen or so,
0:31:48 > 0:32:10perching low down on lianas, watching out for females
0:32:19 > 0:32:24The female is dull-coloured. She has no use for bright feathers.
0:32:27 > 0:32:31Her arrival at the display ground has an immediate effect.
0:32:31 > 0:32:34The males flop down.
0:32:34 > 0:32:38Each one owns a particular patch of ground - his court -
0:32:38 > 0:32:41on which he, and he alone, displays.
0:32:46 > 0:32:51Each now has the problem of how to persuade her to land beside him,
0:32:51 > 0:32:57and a cock-of-the-rock's idea for doing that is to bounce... competitively.
0:33:18 > 0:33:23Once again, a peck on the neck says, "I'm yours".
0:33:23 > 0:33:28And, once again, the male is not very quick on the uptake.
0:33:30 > 0:33:33But he gets there eventually.
0:33:33 > 0:33:38After this is over, she will go off and rear her chicks by herself.
0:33:42 > 0:33:44Another female.
0:33:48 > 0:33:51She makes exactly the same selection.
0:33:57 > 0:34:04By gathering together, the males make sure that the females know where the marriage market is,
0:34:04 > 0:34:07but the price of doing so
0:34:07 > 0:34:08is that only one or two males will make a sale.
0:34:08 > 0:34:31He is captain of this team and he whistles to summon other members.
0:34:36 > 0:34:38The team is complete
0:34:38 > 0:34:41and the show begins.
0:34:43 > 0:34:49They want to prove that they are the best team of acrobats in the area.
0:34:49 > 0:34:56A female arrives to get a close-up view of the performance from the actual dancing perch.
0:34:56 > 0:34:59If she is sufficiently impressed,
0:34:59 > 0:35:02she will mate with the captain.
0:35:02 > 0:35:07But why should he be helped? Because if something happens to the captain,
0:35:07 > 0:35:12one of them might inherit his title. Maybe not a large chance,
0:35:12 > 0:35:17but it's better than performing solo and having no chance at all.
0:35:49 > 0:35:54If the lady decides to accept him, she will mate with him nearby.
0:35:54 > 0:35:59She will fly away and he will keep on dancing, hoping for more success.
0:35:59 > 0:36:03He will never knowingly see his offspring.
0:36:03 > 0:36:08But not all polygamous birds are so neglectful of their duties.
0:36:08 > 0:36:11Here on the pampas of Argentina
0:36:11 > 0:36:14lives another male with many wives
0:36:14 > 0:36:18who takes his nursery duties very seriously indeed.
0:36:18 > 0:36:23These eggs are all looked after by one single male,
0:36:23 > 0:36:26and even now
0:36:26 > 0:36:49he is trying to entice another female to come here to add to this huge clutch.
0:37:02 > 0:37:06He settles down to continue incubating.
0:37:09 > 0:37:16And one of the females with whom he mated yesterday is now ready to lay.
0:37:28 > 0:37:33She settles down within a yard or so of the nest.
0:37:36 > 0:37:39An egg is on its way.
0:38:04 > 0:38:11Because the male has taken total charge of the nest, the females can be just as promiscuous as he is.
0:38:11 > 0:38:18And that female having laid here, will now be going away to find another male with another nest
0:38:18 > 0:38:22to see if he'll accept another egg.
0:38:22 > 0:38:26That's unusual behaviour for a male -
0:38:26 > 0:38:31taking total responsibility for incubation and chick rearing.
0:38:31 > 0:38:34On the tundra of the Arctic, however,
0:38:34 > 0:38:39another species has taken this reversal of roles further still.
0:38:42 > 0:38:44These are red phalaropes.
0:39:12 > 0:39:15that's typical male behaviour.
0:39:15 > 0:39:21But the truth becomes apparent when you see them mating.
0:39:21 > 0:39:27It's the duller one who mounts on the other's back who is the male.
0:39:33 > 0:39:36THAT is the female.
0:39:38 > 0:39:43HE now goes back to the nest that HE has already built.
0:39:43 > 0:39:48The brighter coloured female comes back to him several days thereafter
0:39:48 > 0:39:52to mate again and add more eggs to the nest.
0:39:53 > 0:39:56While SHE sits, HE stands aside.
0:40:22 > 0:40:27But mating openly with multiple partners is the exception.
0:40:27 > 0:40:33In most species, both parents are needed to bring up the young,
0:40:33 > 0:40:39so most birds remain as a pair at least during the breeding season.
0:40:39 > 0:40:46An indication that this is the basis of their relationship is that the sexes are broadly similar.
0:40:46 > 0:40:51But even so, living as a pair doesn't preclude
0:40:51 > 0:40:54a little infidelity now and then.
0:40:57 > 0:41:03Perhaps the most bizarre behaviour of all takes place in the gardens of England -
0:41:03 > 0:41:07and it seems that until recently, nobody even noticed.
0:41:08 > 0:41:28A young female hedge sparrow, a dunnock, ready to lay.
0:41:28 > 0:41:31The pair often feed together -
0:41:31 > 0:41:35a devoted couple if ever you saw one.
0:41:47 > 0:41:50He seldom lets her out of his sight
0:41:50 > 0:41:54for she is not as faithful as she might be.
0:41:56 > 0:41:59There's a third bird around, Beta,
0:41:59 > 0:42:02another, younger male.
0:42:02 > 0:42:07He's not popular with Alpha and they're continually squabbling.
0:42:08 > 0:42:13Sometimes the fights can get quite vicious and feathers fly.
0:42:17 > 0:42:40But, in spite of that, Beta stays around,
0:42:40 > 0:42:42calling quietly to her.
0:42:45 > 0:42:48She joins him
0:42:48 > 0:42:53and now, while Alpha is preoccupied with feeding,
0:42:53 > 0:42:55she and Beta get together.
0:42:55 > 0:43:00Twirling her tail invitingly, in a split second they mate.
0:43:05 > 0:43:08Beta flies away.
0:43:08 > 0:43:12But now, out in the open,
0:43:12 > 0:43:16she is courting Alpha with that same old tail twirling.
0:43:16 > 0:43:20He takes precautions to ensure his paternity.
0:43:22 > 0:43:25He pecks her genital opening...
0:43:52 > 0:43:54And now he mates with her,
0:43:54 > 0:43:59and it will be his sperm that will fertilise her eggs.
0:44:01 > 0:44:07She has kept two males happy, who will help feed the young when they hatch.
0:44:07 > 0:44:12Alpha has made sure that he will be the father of the eggs she will lay,
0:44:12 > 0:44:15or, at any rate, most of them.
0:44:15 > 0:44:20But it's here in the southeast woodlands of Australia
0:44:20 > 0:44:27that infidelity reaches its most astounding, indeed you might say, its ultimate height.
0:44:28 > 0:44:33And it occurs among the families of this dazzling little bird -
0:44:36 > 0:44:39the superb fairy wren.
0:44:41 > 0:45:01He is an attentive male, courting his female with little gifts of food.
0:45:01 > 0:45:05One of them dances for her, flaring the blue fans on his cheeks.
0:45:10 > 0:45:15Yet another male is also flirting with her.
0:45:21 > 0:45:25And here's another.
0:45:30 > 0:45:34And she selects one of them.
0:45:42 > 0:45:47But her first established male is not around to see all this.
0:45:47 > 0:46:09He is visiting a female neighbour, and he's carrying a bouquet,
0:46:09 > 0:46:12pays off too.
0:46:13 > 0:46:17Now he's back at his own nest with his first mate,
0:46:17 > 0:46:22looking after the chicks the nest now contains.
0:46:28 > 0:46:34So the female fairy wren chooses the flashiest males to father her chicks,
0:46:34 > 0:46:40and allows her partner only just enough matings to ensure he helps to feed the family.
0:46:40 > 0:46:45And while the males may have chicks in as many as six nests,
0:46:45 > 0:46:49they may not have a single one in the nest they tend.
0:46:49 > 0:46:56They say it's a wise child that knows its own father, but that's never truer than in the bird world.
0:47:00 > 0:47:20But extreme infidelity, like polygamy, is not widespread among birds.
0:47:30 > 0:47:34Males and females conduct their courtship on equal terms,
0:47:34 > 0:47:40and when they are convinced they are compatible
0:47:40 > 0:47:43they work together to build a nest.
0:47:43 > 0:47:48Protected by water, and with a strong mate to see off intruders,
0:47:48 > 0:47:53these swans will probably hatch their egg successfully. But for many,
0:47:53 > 0:47:58they are entering the most difficult part of their lives.
0:47:58 > 0:48:03They will have to be extremely ingenious to raise a family,
0:48:03 > 0:48:09as we'll see in the next programme in The Life Of Birds.
0:48:48 > 0:48:53Subtitles by BBC - 1998