0:00:13 > 0:00:14East Africa,...
0:00:16 > 0:00:19..and something is stirring in the grass.
0:00:26 > 0:00:30These male widow birds are desperately flinging
0:00:30 > 0:00:32themselves into the air...
0:00:33 > 0:00:35..all to try and impress the ladies.
0:00:40 > 0:00:43One female flies in for a closer look whilst
0:00:43 > 0:00:49he proudly shows off around a grassy palace, built purely for effect.
0:00:57 > 0:01:01Animals will go to extraordinary lengths to win a mate.
0:01:03 > 0:01:06There are show-offs and romantics...
0:01:09 > 0:01:15..singers and dancers, even some who resort to brute force.
0:01:19 > 0:01:23The challenges of winning a perfect partner create some of the most
0:01:23 > 0:01:26beautiful and spectacular sights in the natural world.
0:01:28 > 0:01:32Yet it's also a far more complex contest than we might imagine.
0:01:35 > 0:01:40Beneath the surface lies a web of intrigue, surprising strategy
0:01:40 > 0:01:42and fascinating biology.
0:01:47 > 0:01:52Science is slowly revealing what it takes to win at the mating game.
0:02:04 > 0:02:09The Arctic, millions of square miles of empty ice.
0:02:15 > 0:02:18Polar bears are normally solitary.
0:02:18 > 0:02:21You might think that even finding a partner in this desolate
0:02:21 > 0:02:23landscape would be a real challenge.
0:02:26 > 0:02:30But they have an excellent sense of smell
0:02:30 > 0:02:33and can detect another bear from miles away.
0:02:42 > 0:02:46Male bears can spend weeks tracking the scent of a female
0:02:46 > 0:02:47who's ready to mate.
0:03:10 > 0:03:12They sniff closely to size each other up.
0:03:19 > 0:03:23She'll raise her cubs alone, devoting herself to them
0:03:23 > 0:03:28for two, even three years. It's a huge commitment of time
0:03:28 > 0:03:32and effort, so it's vital to pick a male who will provide strong
0:03:32 > 0:03:34and healthy genes for her offspring.
0:03:38 > 0:03:41It looks as though she's going to put this potential suitor
0:03:41 > 0:03:42through his paces!
0:03:46 > 0:03:49She leads him up and down the slopes.
0:03:49 > 0:03:51It's as if she's testing his fitness.
0:04:01 > 0:04:03They start to play.
0:04:08 > 0:04:12Courtship is one of the few times that adult animals play together.
0:04:48 > 0:04:51This slope is rather steep for the heavier male.
0:05:01 > 0:05:05It's no good. He can't quite manage it.
0:05:14 > 0:05:18But she seems to have decided that he might be The One...
0:05:19 > 0:05:21..whilst he seems to have lost interest.
0:05:28 > 0:05:31It's her turn to do the chasing
0:05:31 > 0:05:34and she's got a few tricks up her sleeve.
0:05:58 > 0:06:01That was enough to entice him up again!
0:06:30 > 0:06:32Now that she's reeled him in,
0:06:32 > 0:06:35she goes straight back to giving him the run-around.
0:06:39 > 0:06:43Choosing partners who can prove how fit and strong they are
0:06:43 > 0:06:48is a useful strategy in the mating game, and it's often the females
0:06:48 > 0:06:52who do the choosing and the males who have to make all the effort.
0:06:55 > 0:06:59In the tropical forests of New Guinea, one male is dedicated to
0:06:59 > 0:07:02making an unforgettable first impression.
0:07:05 > 0:07:10The six-plumed bird of paradise is cleaning his display ground.
0:07:12 > 0:07:15He obsessively tidies every fallen leaf.
0:07:17 > 0:07:20His stage must be meticulously tidy
0:07:20 > 0:07:23for what will be an incredible performance.
0:07:30 > 0:07:33A few attractive berries to help decorate the floor.
0:07:39 > 0:07:42His final touch is hardly ever seen.
0:07:44 > 0:07:47Might he think he's found a bit of old snake skin?
0:07:47 > 0:07:51Some scientists believe he's trying to add the scent of a snake to
0:07:51 > 0:07:56ward off predators. For others, it's a cleaning cloth
0:07:56 > 0:07:58and he's polishing a perch for a female.
0:08:11 > 0:08:15Later, he uses a bigger bit of rag and does the same.
0:08:17 > 0:08:21Only strong, healthy and well-fed males can afford the time
0:08:21 > 0:08:25and effort for the most meticulous preparation
0:08:25 > 0:08:29and, in theory, they're the ones with better genes to pass on.
0:08:30 > 0:08:34He'll have a highly critical audience, so it's time to
0:08:34 > 0:08:36rehearse the main act.
0:09:33 > 0:09:35His dance steps perfected,
0:09:35 > 0:09:38he's ready to start the show for real.
0:09:41 > 0:09:43He spots a female nearby,
0:09:43 > 0:09:46so quickly goes to get more berries to tempt her in.
0:09:53 > 0:09:56Disaster! He's left his polishing rag on the dance floor.
0:10:03 > 0:10:07It's perfect for her nest! She flies off without even
0:10:07 > 0:10:12seeing his dance. He delivers his berries too late.
0:10:12 > 0:10:15He never got a chance to win her heart
0:10:15 > 0:10:17and he lost his precious polishing cloth.
0:10:19 > 0:10:20Back to work.
0:10:25 > 0:10:29For a choosy female, displays are an excellent way to assess
0:10:29 > 0:10:31the qualities of a potential partner.
0:10:34 > 0:10:38They're full of clues as to how good the male's genes might be.
0:10:45 > 0:10:49Physical features, like those extraordinary feathers,
0:10:49 > 0:10:53might also be a sign of how strong and successful this male is.
0:10:59 > 0:11:01It's all a matter of taste.
0:11:01 > 0:11:05Different species are attracted to different features.
0:11:06 > 0:11:11As fussy females favour particular attributes, they become exaggerated
0:11:11 > 0:11:17over generations, leading to ever more elaborate and extreme displays.
0:11:17 > 0:11:20Fancy feathers, red faces,...
0:11:22 > 0:11:24..blue faces,...
0:11:26 > 0:11:27..large noses.
0:11:28 > 0:11:31Beauty is all in the eye of the beholder...
0:11:34 > 0:11:38..and it's not just stunning visuals that can win a mate.
0:11:41 > 0:11:44Off the tropical paradise of Tonga, you can hear
0:11:44 > 0:11:47perhaps the loudest love song in the world.
0:11:47 > 0:11:55WHALE SONG
0:12:07 > 0:12:11Male humpback whales repeat each other's songs
0:12:11 > 0:12:15and add to them, so they become ever more complex and beautiful,
0:12:15 > 0:12:18showing off their memory as well as sheer volume.
0:12:32 > 0:12:36Listening carefully to this song is a female humpback whale.
0:12:36 > 0:12:38She's here with last year's calf
0:12:38 > 0:12:41and is ready to conceive another one.
0:12:43 > 0:12:46He stops singing and follows her.
0:12:46 > 0:12:50He may sing to her again but not if he thinks other males are close by.
0:12:53 > 0:12:57They start to get to know each other. It's an old-fashioned,
0:12:57 > 0:12:59slow-motion waltz.
0:13:20 > 0:13:24Such beautiful movement is rarely seen.
0:13:24 > 0:13:27Dance in the animal world is little understood.
0:14:17 > 0:14:21But their courting ballet is about to be cut short.
0:14:25 > 0:14:29Rival males have detected that something is going on.
0:14:29 > 0:14:34They arrive in force, a mob on the dance floor, set on disruption.
0:14:40 > 0:14:42Each male tries to get beside the female
0:14:42 > 0:14:45and to intimidate the others.
0:14:45 > 0:14:48The 35-tonne males are set on a fight.
0:14:58 > 0:15:03Animals that can seem so tender in a moment become so aggressive.
0:15:05 > 0:15:08The mating game has become a battle.
0:15:12 > 0:15:17They smash into one another. They tail-slap and bellow.
0:15:39 > 0:15:43Most of this is just show, throwing their weight around.
0:15:54 > 0:15:58It's over. The biggest male has won.
0:16:02 > 0:16:04She will accept the outcome,
0:16:04 > 0:16:08the male who's most likely to father the strongest offspring.
0:16:08 > 0:16:12In the end, it was fighting that proved a better test than
0:16:12 > 0:16:13singing or dancing.
0:16:20 > 0:16:25Competition is a big part of the mating game and, inevitably,
0:16:25 > 0:16:27it can lead to physical aggression.
0:16:29 > 0:16:34BELLOWS
0:16:34 > 0:16:37Full of testosterone and laden with weaponry,
0:16:37 > 0:16:40males push each other to the limit.
0:17:12 > 0:17:16Size and strength are the ultimate test of virility,
0:17:16 > 0:17:21but fighting is a dangerous, even life-threatening, strategy.
0:17:21 > 0:17:25So, animals will go to great lengths to avoid a fight if they can.
0:17:28 > 0:17:33American bison graze peacefully together for much of the year.
0:17:46 > 0:17:50But when the mating season arrives, the atmosphere changes.
0:17:54 > 0:17:59The males begin to taste the air to pick up the scent of any female
0:17:59 > 0:18:01who might be ready to mate.
0:18:06 > 0:18:09Before a fight, competing males walk in parallel,
0:18:09 > 0:18:11assessing one another.
0:18:11 > 0:18:13Pumped up with testosterone,
0:18:13 > 0:18:15they paw the ground to show off their strength.
0:18:17 > 0:18:20They spray the earth with their urine and then roll in it
0:18:20 > 0:18:22so that they reek of their own hormones.
0:18:38 > 0:18:42These ritual displays can put off rival males without having to
0:18:42 > 0:18:45resort to a potentially dangerous fight.
0:18:47 > 0:18:49But it doesn't always work.
0:18:56 > 0:19:00Even then, most fights are resolved in a matter of seconds.
0:19:00 > 0:19:05A few, however, escalate into full-scale battle.
0:19:15 > 0:19:19Weighing almost a tonne, they use power and speed to try
0:19:19 > 0:19:21and push each other off their feet.
0:19:28 > 0:19:31This male is lucky to escape a fatal stabbing.
0:19:34 > 0:19:38For the winner, the prize is a whole harem of females.
0:19:42 > 0:19:47But, sometimes, the way to win is not to fight for females
0:19:47 > 0:19:49but to fight for something the females want.
0:19:55 > 0:19:59On the other side of the world, an idyllic English riverside is
0:19:59 > 0:20:01the setting for one such story.
0:20:11 > 0:20:15Here, there is a creature that flirts with suicide
0:20:15 > 0:20:17to woo his paramour with the perfect gift.
0:20:18 > 0:20:23The delicate Banded Demoiselle knows that what every girl wants
0:20:23 > 0:20:27is fast-flowing water, rich in life-giving oxygen,
0:20:27 > 0:20:30as the best place to lay her eggs.
0:20:30 > 0:20:34Each male, in his shining, metallic armour, is prepared to
0:20:34 > 0:20:38fight for the best patch in a graceful, aerial competition.
0:21:25 > 0:21:31The victor has won a patch where the river riffles round a fallen branch,
0:21:31 > 0:21:34faster-running water that is just what the ladies are looking for.
0:21:38 > 0:21:41But how can he prove that this is a good spot?
0:21:43 > 0:21:48He flings himself at the water, using his own body to show the flow.
0:21:50 > 0:21:52It's a high-risk strategy.
0:21:52 > 0:21:55He might drown or be snatched by a hungry fish.
0:22:06 > 0:22:09If she's satisfied, she'll accept him.
0:22:20 > 0:22:23All his hard work has paid off.
0:22:23 > 0:22:27She gives their eggs the best possible start in life,
0:22:27 > 0:22:30laid on plants in oxygen-rich water.
0:22:37 > 0:22:41A true romantic hero who has risked his life,
0:22:41 > 0:22:46and all because the lady loves the perfect place to lay her eggs.
0:22:49 > 0:22:53So, some males fight for females, whilst others,
0:22:53 > 0:22:57like the Demoiselle, fight for something the females want.
0:22:57 > 0:23:00And there are just a few animals where males fight for a prize
0:23:00 > 0:23:03that seems almost arbitrary.
0:23:03 > 0:23:08Topi, an African antelope, gather each year for a very unusual
0:23:08 > 0:23:11and highly ritualised contest.
0:23:13 > 0:23:15The males start by putting on war paint.
0:23:26 > 0:23:30By plastering their horns with mud, they're trying to be more
0:23:30 > 0:23:34intimidating to other males, and maybe more attractive to females.
0:23:34 > 0:23:36The dirtier, the better.
0:23:42 > 0:23:46The males compete in a loose circle called a lek.
0:23:46 > 0:23:49Each fights for a patch of land as close as possible
0:23:49 > 0:23:51to the centre of the arena.
0:23:58 > 0:24:01There's nothing particularly special about the middle, but in the
0:24:01 > 0:24:07ritual of the topi's mating game, it's become symbolically important.
0:24:07 > 0:24:11They fight for the centre because, well, because it's the centre.
0:24:24 > 0:24:27Eventually, each male has won his patch,
0:24:27 > 0:24:30and the females are more likely to choose a partner who is
0:24:30 > 0:24:32closer to the heart of the arena.
0:24:35 > 0:24:37The mating rituals go on for many days.
0:24:37 > 0:24:40The males dare not leave their territories
0:24:40 > 0:24:42in case rivals should claim them.
0:24:43 > 0:24:46And they have to fight repeatedly to retain their position.
0:24:47 > 0:24:51As the days pass, they become ever more exhausted.
0:25:26 > 0:25:30There is a real, physical cost to this competition.
0:25:35 > 0:25:39Hyenas are quick to take advantage of the weak and exhausted topi.
0:26:16 > 0:26:19Yet, in spite of the circling hyenas,
0:26:19 > 0:26:22the male topi will stay close to their places on the lek.
0:26:23 > 0:26:28To flee would mean losing any chance in the mating game.
0:26:44 > 0:26:46It's a risky game to play.
0:26:56 > 0:26:59Some males choose a rather different strategy.
0:27:00 > 0:27:05In the dry forests of Madagascar are some that have chosen to be
0:27:05 > 0:27:06lovers, not fighters.
0:27:08 > 0:27:12Ring-tailed lemurs live in troops of around a dozen individuals
0:27:12 > 0:27:15in which the females rule the roost.
0:27:19 > 0:27:23This morning, the ladies can choose from a line-up of hopeful males.
0:27:27 > 0:27:30Welcome to the lemur lounge bar.
0:27:36 > 0:27:41The boys are on parade, hoping to be the chosen one.
0:28:10 > 0:28:15They are sizing each other up, this particular morning, with excitement.
0:28:20 > 0:28:26One of the females is on heat. It's her choice and she's unpredictable.
0:28:26 > 0:28:32A chance for fatherhood is up for grabs. Fights quickly break out.
0:28:37 > 0:28:41The object of their affection just sits and waits.
0:28:48 > 0:28:50Whilst the squabbles continue,
0:28:50 > 0:28:56one sneaky young male sees an opportunity to make his move.
0:28:56 > 0:28:59He hopes to win her heart by more subtle means.
0:29:02 > 0:29:05With an air of nonchalance, he settles down
0:29:05 > 0:29:11and begins to smear scent onto his tail from glands on his wrists.
0:29:15 > 0:29:19The perfume he wafts over her will tell her a lot about what
0:29:19 > 0:29:22he has to offer as a potential partner.
0:29:23 > 0:29:27And he just might offer something that the other males don't.
0:29:37 > 0:29:39He may not be the strongest fighter,
0:29:39 > 0:29:44but very latest science suggests that his scent might contain
0:29:44 > 0:29:48clues to a different strength, his ability to fight illness
0:29:48 > 0:29:52and parasites which he could pass on to her offspring.
0:30:06 > 0:30:08She's still not convinced.
0:30:08 > 0:30:11Maybe she should wait for the outcome of the fight.
0:30:17 > 0:30:19The battle continues, unresolved.
0:30:24 > 0:30:26So, she leads him off to somewhere quieter.
0:30:34 > 0:30:38His sneaky seduction has finally won her over
0:30:38 > 0:30:41and they head off for some undercover love.
0:30:52 > 0:30:55Whether by fighting or by sneakier means,
0:30:55 > 0:31:01it's often males who seem to do the hard work in the mating game.
0:31:01 > 0:31:04But it's not always as one-sided as you might think.
0:31:12 > 0:31:16These mountain gorillas are headed up by a dominant male,
0:31:16 > 0:31:18the silverback.
0:31:18 > 0:31:22He's head of a family of females and youngsters.
0:31:22 > 0:31:27It will have taken him many years to win this prestigious position.
0:31:27 > 0:31:30GORILLAS HOOT AND SCREAM
0:31:37 > 0:31:42There is a young female who's recently joined his group.
0:31:42 > 0:31:46She wants the silverback to father her children.
0:31:46 > 0:31:50She's just come into season and she has only a couple of days
0:31:50 > 0:31:51when she's fertile.
0:31:51 > 0:31:53There's no time to waste
0:31:53 > 0:31:56but she's going to have to work hard to get his attention.
0:31:58 > 0:32:03She stares at him, a brazenly flirtatious act in itself.
0:32:03 > 0:32:07She tightens her lips into a smile and gazes straight into his eyes.
0:32:10 > 0:32:14This is gorilla seduction at its least subtle.
0:32:50 > 0:32:54But he doesn't seem to be won over by her shameless tactics.
0:32:56 > 0:32:59The whole family watch to see what happens next.
0:33:05 > 0:33:08The young female decides to try a different tactic.
0:33:09 > 0:33:13There are two teenagers, black-backed, immature males,
0:33:13 > 0:33:15and she flirts with them.
0:33:15 > 0:33:19She positions herself between the two rival boys.
0:33:19 > 0:33:22Both are interested in her.
0:33:23 > 0:33:25She's a tease.
0:33:25 > 0:33:28As she joins one, the other watches, grunting in jealous fury.
0:33:28 > 0:33:33She solicits both males but doesn't actually mate with either.
0:33:33 > 0:33:37She only has eyes on the big prize and, sure enough,
0:33:37 > 0:33:40the silverback hears and comes charging in.
0:33:42 > 0:33:45With a little subterfuge, she gets her man.
0:33:58 > 0:34:02The silverback will offer more than just good genes to her offspring.
0:34:04 > 0:34:08Any children that are his will get his protection
0:34:08 > 0:34:09as part of the family.
0:34:11 > 0:34:14Perhaps best to make absolutely sure.
0:34:25 > 0:34:30It's all for this, a helpless mountain gorilla baby,
0:34:30 > 0:34:32one of only a few hundred left.
0:34:39 > 0:34:43The family bonds in mountain gorillas are strong.
0:34:46 > 0:34:49The silverback's role as father goes beyond protection.
0:34:51 > 0:34:55He's babysitter, punch ball and role model, too.
0:35:24 > 0:35:27When both parents stick around to protect
0:35:27 > 0:35:32and rear the offspring, the mating game becomes more complex.
0:35:32 > 0:35:36It's no longer just about strong and healthy genes
0:35:36 > 0:35:40but about choosing a partner who will help to raise the youngsters.
0:35:42 > 0:35:45And that can seem like finding one in a million.
0:36:00 > 0:36:04The party here, on Lake Bogoria in Tanzania, is perhaps
0:36:04 > 0:36:08the greatest gathering of courting couples in the animal world.
0:36:17 > 0:36:20Thousands of flamingos dance together,
0:36:20 > 0:36:23all looking for Mr or Mrs Right.
0:36:35 > 0:36:39Eye colour and feathers are important. The brighter, the better.
0:36:46 > 0:36:49Once you've caught someone's eye, it's about choosing a partner
0:36:49 > 0:36:52who will be loyal, who will stick around.
0:36:54 > 0:36:57Flamingos seem to prefer birds similar to themselves.
0:37:05 > 0:37:08But the dance may reveal much deeper insights into each other.
0:37:10 > 0:37:13Many animals find symmetry attractive,
0:37:13 > 0:37:14and the mirrored movements
0:37:14 > 0:37:19and co-ordinated head turns may help find a mate that is more compatible.
0:37:36 > 0:37:38It's vital to make the right choice.
0:37:40 > 0:37:43Flamingos nest in the middle of soda lakes.
0:37:47 > 0:37:49These are swamps of caustic mud.
0:37:49 > 0:37:51It's one of the hottest places on Earth.
0:37:54 > 0:37:58It's a trek to the nearest food and fresh water,
0:37:58 > 0:38:01and you can't leave the nest in the sun.
0:38:01 > 0:38:05That means raising the chick is impossible for a single parent.
0:38:05 > 0:38:07Working together is crucial.
0:38:15 > 0:38:18It gets up to 50 degrees Celsius out here.
0:38:18 > 0:38:21This is parenting at its toughest,
0:38:21 > 0:38:25so, the choice of partner made in the dance needs to be right.
0:38:56 > 0:39:00After a short time, the chicks form a creche,
0:39:00 > 0:39:04safety in numbers as they learn to stand on their own two feet.
0:39:05 > 0:39:09And, eventually, they set off to find fresh water.
0:39:09 > 0:39:13Their parents abandon them, though they're still only chicks.
0:39:16 > 0:39:18They have to find their own way
0:39:18 > 0:39:21out of the hellhole in which they were born.
0:39:21 > 0:39:24They have no family to help them now, only each other.
0:39:35 > 0:39:38But there are animals where the family is a far more
0:39:38 > 0:39:40permanent institution.
0:39:41 > 0:39:44Here, the mating game needs teamwork to win.
0:39:44 > 0:39:52HOWLING
0:39:57 > 0:40:02February in Yellowstone, bitterly cold and food is scarce.
0:40:02 > 0:40:05Alone, a wolf would struggle to hunt.
0:40:11 > 0:40:15Their prey, elk, are many times a wolf's size,
0:40:15 > 0:40:19so, to survive out here, the wolves work as a family team.
0:40:21 > 0:40:24Offspring stay with their parents for many months,
0:40:24 > 0:40:28learning how to survive and to help raise the next litter.
0:40:28 > 0:40:29The alpha couple need their help.
0:40:29 > 0:40:34Winter is mating season and they need to be fit and healthy.
0:40:34 > 0:40:38The male is dark, the pack mother grey.
0:40:38 > 0:40:40They defend the group and lead the hunts.
0:40:47 > 0:40:49BUGLING
0:40:50 > 0:40:53The pack spreads out to head off the elk.
0:40:53 > 0:40:56Hunting strategy is passed down, learned
0:40:56 > 0:40:59and refined within families and generations.
0:41:03 > 0:41:08The father leads one team. The mother intercepts a panicking elk.
0:41:18 > 0:41:22BUGLES
0:41:30 > 0:41:32They all share the spoils.
0:41:44 > 0:41:48But all is not quite as collaborative as it seems.
0:41:48 > 0:41:52This pack strategy works well for the alpha couple but not quite
0:41:52 > 0:41:54so well for last year's offspring.
0:41:56 > 0:41:59The youngsters could have their own pups, but for the alpha couple,
0:41:59 > 0:42:04that would mean more mouths to feed and less for their litter.
0:42:05 > 0:42:07So, the alpha couple
0:42:07 > 0:42:11will actively discourage last year's offspring from mating.
0:42:11 > 0:42:13But one of their daughters has other ideas.
0:42:15 > 0:42:19Skulking behind the pack is a lone male wolf.
0:42:19 > 0:42:23He has no territory of his own but follows the family,
0:42:23 > 0:42:28scavenging leftovers and looking for opportunities.
0:42:28 > 0:42:30He's spotted one, the young daughter.
0:42:39 > 0:42:43The intruder could be in with a chance, as long as he's not caught.
0:42:43 > 0:42:45The pack leader could kill him.
0:42:51 > 0:42:59HOWLS
0:43:06 > 0:43:09While the pack is distracted by a bison,
0:43:09 > 0:43:12the temptation for the young female is too great,
0:43:12 > 0:43:15and she sneaks away to join the mysterious stranger.
0:43:19 > 0:43:23It's risky but it could be her only chance to get close
0:43:23 > 0:43:24to a potential mate.
0:43:56 > 0:44:00When mating, wolves lock together,
0:44:00 > 0:44:04unable to separate for half an hour to ensure fertilisation.
0:44:05 > 0:44:09Not so good if you're about to be caught by your dad.
0:44:09 > 0:44:12The affair was always destined to be a short one.
0:44:45 > 0:44:47After a painful separation,
0:44:47 > 0:44:51her new mate is chased away with his tail between his legs.
0:45:05 > 0:45:08The wayward daughter is chastised for her behaviour.
0:45:10 > 0:45:13Eventually, though, she'll be accepted back into the family.
0:45:16 > 0:45:19Having her own pups would be the best way for her to pass
0:45:19 > 0:45:23on her genes but it might threaten the success of the alpha couple.
0:45:23 > 0:45:25There's a tension between them.
0:45:35 > 0:45:38And the more we learn about how animals behave,
0:45:38 > 0:45:42the more it seems that behind the facade of seemingly perfect
0:45:42 > 0:45:46animal partnerships lurk darker secrets,
0:45:46 > 0:45:49the truth of which are only now coming to light.
0:46:22 > 0:46:25Lar gibbons in the forests of Thailand.
0:46:27 > 0:46:31They seem to be the perfect couple, musical and monogamous.
0:46:34 > 0:46:42WHOOPING AND SINGING
0:46:46 > 0:46:49Their duet is a renewal of their partnership
0:46:49 > 0:46:51and proclaims their home territory.
0:46:51 > 0:46:54They stay together to raise a family.
0:47:05 > 0:47:07But appearances can be deceptive.
0:47:09 > 0:47:12They're surrounded on all sides by neighbours,
0:47:12 > 0:47:15and gibbons can sometimes stray.
0:47:15 > 0:47:18It turns out that as many as one in ten matings
0:47:18 > 0:47:20may not be with their partner.
0:47:21 > 0:47:26Some scientists think there may be a reason for a female's infidelity.
0:47:26 > 0:47:29A quick liaison may serve to convince other neighbouring
0:47:29 > 0:47:33males that they could be the father of her offspring,
0:47:33 > 0:47:36and this might stop them attacking the youngsters.
0:47:39 > 0:47:44Maybe a little infidelity actually helps protect the family.
0:47:53 > 0:47:55Whatever the reason for straying,
0:47:55 > 0:47:59their affairs don't seem to be a problem for their partnership.
0:47:59 > 0:48:00They'll remain together.
0:48:12 > 0:48:17And this is not the only example of a flexible relationship that
0:48:17 > 0:48:21can be more advantageous to animals than a purely monogamous one.
0:48:23 > 0:48:27The dry forests of western Madagascar are a harsh place
0:48:27 > 0:48:28to bring up a family.
0:48:28 > 0:48:32But there is one bird who's come up with a cunning plan.
0:48:34 > 0:48:37This is the vasa parrot.
0:48:37 > 0:48:39She has a tree hole full of chicks,
0:48:39 > 0:48:43but food is scarce and she can't feed them all by herself.
0:48:51 > 0:48:56From a high perch, she issues a summons across the forest.
0:48:56 > 0:49:01BIRDCALL
0:49:06 > 0:49:09She's not the prettiest-looking bird.
0:49:09 > 0:49:12During breeding, her sleek, black feathers fell out
0:49:12 > 0:49:14and her skin underneath is orange.
0:49:14 > 0:49:17But her trashy appearance doesn't deter suitors.
0:49:21 > 0:49:23A male answers her call.
0:49:23 > 0:49:28They've been courting for many weeks and mated regularly.
0:49:28 > 0:49:31They greet with a head-swaying dance that seems to say
0:49:31 > 0:49:34"you are the only one for me".
0:49:54 > 0:49:57Then he passes food to her.
0:50:02 > 0:50:06Suddenly, he leaves and another male turns up.
0:50:18 > 0:50:20And another male.
0:50:20 > 0:50:24She has mated with them all and she accepts his offerings, too.
0:50:25 > 0:50:29In fact, she may have up to six males on the go at once.
0:50:29 > 0:50:31They all feed her.
0:50:32 > 0:50:36Each male may believe that he is the father to her chicks.
0:50:36 > 0:50:38With a graceful tete-a-tete,
0:50:38 > 0:50:42she seems to reassure each of them that he is the special one.
0:50:58 > 0:51:01Then it's back to the nest with all the food.
0:51:01 > 0:51:04Her clutch is of mixed parentage.
0:51:06 > 0:51:11Perhaps here, three of the males out of the six are genuine fathers,
0:51:11 > 0:51:14and the other three duped.
0:51:14 > 0:51:18In this game, she is the real winner with several doting fathers
0:51:18 > 0:51:20to help feed her children.
0:51:20 > 0:51:22A cunning ploy.
0:51:25 > 0:51:31So, does everyone cheat at the mating game? Well, maybe not.
0:51:31 > 0:51:34True monogamy, animals that stay together for ever
0:51:34 > 0:51:37and remain faithful, is certainly very rare.
0:51:39 > 0:51:42But there may be a few perfect partnerships.
0:51:42 > 0:51:46One may be found in New Caledonia in the South Pacific.
0:51:48 > 0:51:49These are Kagu,
0:51:49 > 0:51:53flightless birds that stay together as a couple for life.
0:52:04 > 0:52:08Both parents work together to look after one chick.
0:52:08 > 0:52:11This is the dad, pitting his wits against a worm.
0:52:28 > 0:52:30Spot the chick.
0:52:34 > 0:52:36The camouflage is effective.
0:52:38 > 0:52:40Less effective is getting the food in.
0:52:58 > 0:53:01Feeding babies can take a lot of patience.
0:53:04 > 0:53:07Some of the young from previous years stay in the territory
0:53:07 > 0:53:12and help defend any chicks from predators or neighbouring Kagu.
0:53:12 > 0:53:15Several birds all help guard one chick.
0:53:15 > 0:53:20SQUAWKING AND SINGING
0:53:20 > 0:53:22Each morning, they sing together.
0:53:23 > 0:53:27They work as a team and chase away any intruders.
0:53:27 > 0:53:31SQUAWKING AND SINGING
0:53:31 > 0:53:35The Kagu's relationship is solid and the bonds of commitment
0:53:35 > 0:53:39are passed down to the offspring, forming a strong family unit.
0:53:41 > 0:53:44But the Kagus also seem to be quite the romantics.
0:53:51 > 0:53:55Each year, the male rekindles the flame with this lifelong mate.
0:54:03 > 0:54:07She's seen it all before but it's still important to remind her.
0:54:14 > 0:54:17After all, no-one likes to be taken for granted.
0:54:23 > 0:54:25They may be committed for life
0:54:25 > 0:54:27but it seems he still wants her to know
0:54:27 > 0:54:29that she's the only one for him.
0:54:40 > 0:54:43Throughout the animal kingdom, the mating game is
0:54:43 > 0:54:47full of extraordinary behaviour and surprising sophistication.
0:55:02 > 0:55:07Even fighting isn't simple but overlaid with ritual and sacrifice.
0:55:10 > 0:55:13For some animals, it's all about playing the field.
0:55:18 > 0:55:21Others may be searching for more commitment in a partner,
0:55:21 > 0:55:22one who will stick around.
0:55:25 > 0:55:28Some are carefully chosen for a brief liaison.
0:55:41 > 0:55:45Others form bonds that can last a lifetime.
0:55:48 > 0:55:52And there are a few that remain truly faithful.
0:55:54 > 0:56:00But is it all just a game or is there ever something more?
0:56:00 > 0:56:03Do these bonds ever go beyond physical need?
0:56:11 > 0:56:15In the heart of Australia is a rather unlikely
0:56:15 > 0:56:18candidate for ultimate animal romantic.
0:56:25 > 0:56:29This is a shingleback, a skink,
0:56:29 > 0:56:33known here in Australia as the sleepy lizard.
0:56:35 > 0:56:38A female catches the eye of a male.
0:56:38 > 0:56:42He courts her by gently nudging her and licking her.
0:57:03 > 0:57:06They will stay together for two months
0:57:06 > 0:57:09and then they'll separate for the rest of the year.
0:57:10 > 0:57:16But despite this time apart, the couple's bond remains strong.
0:57:16 > 0:57:18The following year, they will somehow
0:57:18 > 0:57:21manage to find each other in order to mate once more.
0:57:21 > 0:57:25As far as we know, they remain faithful for the rest
0:57:25 > 0:57:29of their lives, sometimes for more than 20 years.
0:57:29 > 0:57:32Even when one of them dies, they're reluctant to move on.
0:57:34 > 0:57:36Shinglebacks are slow and vulnerable.
0:57:37 > 0:57:40If one half of a pair gets run over,
0:57:40 > 0:57:44the other has been seen waiting by its side for days.
0:57:46 > 0:57:49It seems the bond between them endures, even after death.
0:57:51 > 0:57:55Surely, this is more than just a mating game?
0:57:55 > 0:57:59Certainly, there's much more about animal relationships
0:57:59 > 0:58:01that still waits to be discovered.
0:58:06 > 0:58:08Subtitles by Red Bee Media Ltd