0:00:11 > 0:00:13Now, what would you say if I were to tell you
0:00:13 > 0:00:15that a freshwater mussel
0:00:15 > 0:00:19was one of THE most devious animals on the planet?
0:00:20 > 0:00:22Well, I know what you're thinking, you're thinking,
0:00:22 > 0:00:25"Is that honestly the best he can do?
0:00:25 > 0:00:29"Starting the programme with a mollusc, a watery snail?"
0:00:29 > 0:00:33Well, let me ask you for something. The next two minutes of your life.
0:00:33 > 0:00:35Because if you give them to me,
0:00:35 > 0:00:39I can promise to show you something utterly remarkable.
0:00:39 > 0:00:42You see, when it comes to looking after her young,
0:00:42 > 0:00:45this little mussel has a big problem.
0:00:48 > 0:00:49Like all mothers,
0:00:49 > 0:00:54she wants to provide her precious offspring with food and protection.
0:00:54 > 0:00:59But in a fast-flowing, barren river, that's an impossible challenge.
0:01:02 > 0:01:06Unless she can enlist help from an unsuspecting neighbour.
0:01:08 > 0:01:10Like, say, a bass.
0:01:12 > 0:01:18But first of all, she's got to well and truly dupe it. Just watch this.
0:01:20 > 0:01:24Hidden inside her shell is something extraordinary.
0:01:34 > 0:01:36The perfect fish lure.
0:01:38 > 0:01:43An incredible copy of the small fishes she lives alongside.
0:01:46 > 0:01:50Which happen to be the bass' favourite prey.
0:01:57 > 0:01:58It's totally tricked.
0:02:02 > 0:02:04And when the bass attacks...
0:02:06 > 0:02:10..the mussel fires her young straight into its face.
0:02:13 > 0:02:16Because this is exactly where she wants them.
0:02:16 > 0:02:20You see, her little ones snap shut on the fish's gills,
0:02:20 > 0:02:22where they feed on nutrients from its blood.
0:02:25 > 0:02:28Her brood are safe.
0:02:28 > 0:02:31And when they're big enough, they drop down to the riverbed
0:02:31 > 0:02:33and grow into adults.
0:02:35 > 0:02:37She's pulled off the perfect con.
0:02:39 > 0:02:40The most extraordinary thing is
0:02:40 > 0:02:43that this mussel doesn't even have any eyes.
0:02:43 > 0:02:48She can't even see the fish she's mimicking in minute detail
0:02:48 > 0:02:52to get exactly what she wants.
0:02:52 > 0:02:57This is a very sneaky solution to a childcare conundrum.
0:02:58 > 0:03:04It's transformed the modest mussel into a master of deception.
0:03:04 > 0:03:07And it turns out that this mussel isn't the only one
0:03:07 > 0:03:11tricking other animals to start and raise a family.
0:03:27 > 0:03:30All animals face the same ultimate challenge.
0:03:30 > 0:03:34They've got to successfully produce the next generation.
0:03:34 > 0:03:36But it's far from straightforward.
0:03:39 > 0:03:41They have to win a mate...
0:03:42 > 0:03:44..and then care for their young...
0:03:46 > 0:03:47..to make sure they survive.
0:03:50 > 0:03:54So, how do animals increase their chances in the minefield
0:03:54 > 0:03:56of the mating game?
0:03:56 > 0:03:58Would they lie, cheat,
0:03:58 > 0:04:02even steal from one another just to get an advantage?
0:04:02 > 0:04:05Come on! Of course they would.
0:04:09 > 0:04:13Join me as I met seductive sneaks...
0:04:15 > 0:04:17..love rats
0:04:17 > 0:04:20and some very dysfunctional families.
0:04:22 > 0:04:25Animals doing whatever it takes to survive.
0:04:39 > 0:04:43'The first problem animals face is finding a mate.
0:04:44 > 0:04:47'But this is far from straightforward.'
0:04:51 > 0:04:54You see, many animals live in complex social groups,
0:04:54 > 0:04:58where only certain individuals are allowed to breed.
0:05:00 > 0:05:03Take these long-tailed macaques, for example.
0:05:03 > 0:05:07Somewhere in this group is a dominant male, the alpha male.
0:05:07 > 0:05:09And he enforces his dominance
0:05:09 > 0:05:12for the right to mate with all of the females here.
0:05:14 > 0:05:15SNARLING
0:05:17 > 0:05:20So amongst many types of animals, when it comes to mating,
0:05:20 > 0:05:22there are rules.
0:05:22 > 0:05:25But, of course, we're talking about deception here,
0:05:25 > 0:05:27so those rules are made to be broken.
0:05:32 > 0:05:36So, how are those animals at the bottom of the pecking order
0:05:36 > 0:05:38going to get what they want?
0:05:44 > 0:05:46BIRDSONG
0:05:54 > 0:05:55A mob of red kangaroos.
0:05:57 > 0:06:01This male is a long way down in the group's hierarchy.
0:06:04 > 0:06:08If he wants to have young, he's going to have to take on this guy.
0:06:13 > 0:06:15The alpha male.
0:06:17 > 0:06:21Only he has the right to mate with the females in this group.
0:06:23 > 0:06:26Now, our young male could choose the hard way.
0:06:28 > 0:06:29The honest way.
0:06:31 > 0:06:33And fight his way to the top.
0:06:36 > 0:06:39But it could take years to grow strong enough
0:06:39 > 0:06:42to dominate his rivals.
0:06:42 > 0:06:44And it's risky.
0:06:45 > 0:06:48With a kick that can crush bone,
0:06:48 > 0:06:50kangaroo fights can end in serious injury.
0:06:54 > 0:06:57So instead, he opts for Plan B.
0:06:59 > 0:07:01Cheat.
0:07:03 > 0:07:06If the alpha male isn't looking...
0:07:09 > 0:07:11..and it's always worth checking...
0:07:18 > 0:07:19..he takes a chance.
0:07:23 > 0:07:29This illicit liaison is also in the interest of the female.
0:07:29 > 0:07:31By mating with other males,
0:07:31 > 0:07:34she's mixing up the group's gene pool,
0:07:34 > 0:07:37which could give her offspring an advantage.
0:07:39 > 0:07:44The crafty pair have got scot clean away with it
0:07:44 > 0:07:47and the old alpha male has absolutely no idea
0:07:47 > 0:07:51that he may not have fathered the next generation.
0:07:57 > 0:08:00This sneaky strategy is seen right across the world.
0:08:00 > 0:08:02BIRDSONG
0:08:05 > 0:08:09Take this blackback gorilla in Uganda.
0:08:10 > 0:08:13The only way that he can become a father
0:08:13 > 0:08:16is to try going behind the silverback's back.
0:08:21 > 0:08:26In fact, research shows that 15% of mountain gorillas
0:08:26 > 0:08:29aren't fathered by the dominant male at all.
0:08:31 > 0:08:34So it's a successful tactic.
0:08:36 > 0:08:40Despite the risk of getting caught in the act.
0:08:40 > 0:08:41HOOTING
0:08:46 > 0:08:47ROARING
0:08:53 > 0:08:57Breaking the rules gives males low in the pecking order
0:08:57 > 0:08:59a chance to continue their line.
0:09:00 > 0:09:04But for most males, the biggest challenge is convincing
0:09:04 > 0:09:07a female to mate with him in the first place.
0:09:08 > 0:09:13And some of them have come up with incredibly calculated cons
0:09:13 > 0:09:14just to get their attention.
0:09:16 > 0:09:19'One of nature's greatest cheats lives here.
0:09:21 > 0:09:24'The grasslands of the Maasai Mara.'
0:09:30 > 0:09:31Where predator and prey...
0:09:34 > 0:09:36..are locked in a battle to survive.
0:09:39 > 0:09:42But remarkably, one animal has turned
0:09:42 > 0:09:46this ever-present danger to his advantage.
0:09:46 > 0:09:50He's the sneakiest pick-up artist on the plains.
0:09:53 > 0:09:54The topi.
0:09:56 > 0:09:58Africa's unlikely Lothario.
0:10:02 > 0:10:05The topi are gathering for the breeding season.
0:10:07 > 0:10:11But playing the mating game here...isn't easy.
0:10:16 > 0:10:20Fortunately, topi are ever-alert to the danger.
0:10:25 > 0:10:29With ears pricked and a knowing stare,
0:10:29 > 0:10:32they warn the herd with a loud snort.
0:10:32 > 0:10:33SNORT!
0:10:35 > 0:10:37SNORT!
0:10:38 > 0:10:39SNORT!
0:10:41 > 0:10:43SNORT!
0:10:43 > 0:10:45SNORT!
0:10:46 > 0:10:48Once her cover's blown...
0:10:49 > 0:10:53..a lioness has no chance of sneaking up unnoticed.
0:10:56 > 0:10:58So it's back to the matter at hand.
0:11:00 > 0:11:03And time is running out.
0:11:03 > 0:11:08You see, female topi are only in season for one day of the year.
0:11:10 > 0:11:14And they have a whole herd of prospective partners to choose from.
0:11:16 > 0:11:19So competition between these males is intense.
0:11:30 > 0:11:33Losing a fight means making do with
0:11:33 > 0:11:36a position on the outskirts of the herd,
0:11:36 > 0:11:40where it's much harder to attract a mate.
0:11:43 > 0:11:47Fortunately, a female is passing by.
0:11:49 > 0:11:52It's his big chance to impress.
0:12:06 > 0:12:08But she barely notices him.
0:12:15 > 0:12:21He's going to have to try something a bit more, well, underhand.
0:12:23 > 0:12:27First, he scans the scene.
0:12:27 > 0:12:30No sign of danger.
0:12:30 > 0:12:35Which makes what he's about to do very devious indeed.
0:12:35 > 0:12:36SNORT!
0:12:36 > 0:12:38SNORT!
0:12:38 > 0:12:40SNORT!
0:12:40 > 0:12:42SNORT!
0:12:43 > 0:12:46This alarm call will stop any female in her tracks
0:12:46 > 0:12:50because it means that a predator must be nearby.
0:12:50 > 0:12:52SNORT!
0:12:52 > 0:12:54But it's a complete con.
0:12:56 > 0:13:00A false alarm just to keep her close.
0:13:01 > 0:13:04And by delaying a female just a little bit,
0:13:04 > 0:13:09he gives himself another vital chance to mate.
0:13:12 > 0:13:14And she is none the wiser.
0:13:17 > 0:13:20Now, male topi who use this trick, and many of them do,
0:13:20 > 0:13:26get on average three more matings with every female that they fool.
0:13:29 > 0:13:35OK, it may be dishonest, but it works.
0:13:37 > 0:13:40And you know the really smart bit?
0:13:40 > 0:13:45They don't use these false alarm calls outside of the breeding season.
0:13:45 > 0:13:49So our two-faced topi never gets caught crying wolf.
0:13:54 > 0:13:59So a strategically-timed trick can keep a female close at hand.
0:14:02 > 0:14:04But other ladies are far more demanding.
0:14:07 > 0:14:10And to win their attention, males have to pull off
0:14:10 > 0:14:14the most elaborate deceptions in the natural world.
0:14:23 > 0:14:26'The outback - tough, unforgiving.
0:14:27 > 0:14:29HE EXHALES
0:14:29 > 0:14:32'Just like one of its female residents.
0:14:35 > 0:14:37'And in an attempt to impress her,
0:14:37 > 0:14:42'one male has created something truly extraordinary.'
0:14:46 > 0:14:49But this designer has a devious side.
0:14:51 > 0:14:56I give you the one and the only great bowerbird.
0:15:01 > 0:15:04'Yes! He's one of nature's greatest architects.
0:15:06 > 0:15:09'But this isn't a nest, it's a bower.
0:15:10 > 0:15:13'It's built purely to impress a female.'
0:15:17 > 0:15:20It's designed to entice her, to intrigue her,
0:15:20 > 0:15:24to keep her around long enough to give him a chance to mate.
0:15:26 > 0:15:30I think it's a fair comparison to say that this bower is
0:15:30 > 0:15:33a bit like the male's internet dating profile.
0:15:33 > 0:15:36It's something that he's got to tinker with,
0:15:36 > 0:15:39fiddle with until he gets it exactly right.
0:15:39 > 0:15:41Because it's got to work.
0:15:41 > 0:15:44It's got to attract a member of the opposite sex.
0:15:46 > 0:15:49But let's be honest, we all know how this game works.
0:15:49 > 0:15:52Dating profiles are always improved
0:15:52 > 0:15:56with a few, let's say, embellishments.
0:15:58 > 0:16:00And our bird has done something similar.
0:16:00 > 0:16:03He's built something sneaky into his bower.
0:16:04 > 0:16:07An incredible visual trick.
0:16:09 > 0:16:10Let me demonstrate.
0:16:25 > 0:16:28By taking objects that we know the scale of
0:16:28 > 0:16:32and playing with the perspective, we can trick the mind
0:16:32 > 0:16:37and make it think that they've magically changed size.
0:16:37 > 0:16:40It's an illusion we called forced perspective.
0:16:44 > 0:16:47And the bowerbird's curious construction
0:16:47 > 0:16:49is using just this technique.
0:16:51 > 0:16:54An abandoned bower can show us how.
0:16:54 > 0:17:00The design of the bower is based around this central avenue here,
0:17:00 > 0:17:04which opens out on to an arena at each end.
0:17:04 > 0:17:08And that's made up of small grey or white objects.
0:17:08 > 0:17:10And we call it the gesso.
0:17:10 > 0:17:14There are some more objects, a pile of stones right in the centre here.
0:17:14 > 0:17:17The male hopes that the female will watch him
0:17:17 > 0:17:22from that spot as he displays outside, on that arena.
0:17:24 > 0:17:27But recently, scientists have discovered that the male has
0:17:27 > 0:17:31created an extraordinary illusion.
0:17:31 > 0:17:35And it's all down to the arrangement of the objects on the gesso.
0:17:35 > 0:17:41Take a look. Those closest to the avenue entrance are quite small.
0:17:41 > 0:17:46Those halfway across are a little larger.
0:17:46 > 0:17:52And those furthest away are the biggest of all.
0:17:53 > 0:17:57So let's see how this tricks a prospective mate.
0:18:03 > 0:18:05She's inside the bower.
0:18:06 > 0:18:10In just the position for the illusion to work.
0:18:14 > 0:18:19Now, usually, the further things are away from us, the smaller they look.
0:18:21 > 0:18:28But our bowerbird has reversed this with his gradient of stones.
0:18:28 > 0:18:31And when the female stands in the bower...
0:18:32 > 0:18:36..it changes how the world is supposed to look.
0:18:39 > 0:18:43And just like us looking at the cars,
0:18:43 > 0:18:46or other forced-perspective illusions...
0:18:48 > 0:18:53..it takes her a while to make sense of what she's seeing.
0:18:55 > 0:19:01And this makes her stay a few crucial seconds longer.
0:19:03 > 0:19:05His beautiful illusion is enhanced
0:19:05 > 0:19:09by the movement of objects that he tosses in front of it.
0:19:09 > 0:19:10Watch this.
0:19:40 > 0:19:43Come on, you have to admire the lengths he's going to
0:19:43 > 0:19:45to pull his bird.
0:19:45 > 0:19:47SQUAWKING
0:20:00 > 0:20:02Success!
0:20:04 > 0:20:07This is the first time that any animal on earth
0:20:07 > 0:20:12has been seen to be using the illusion of forced perspective.
0:20:14 > 0:20:18It's an illusion, it's a strategy that works.
0:20:18 > 0:20:22What a bird! What...a bird!
0:20:28 > 0:20:33Remarkable new science is revealing that animals across the world...
0:20:35 > 0:20:40..are using mind-bending optical illusions in the mating game.
0:20:42 > 0:20:44In the forests of South America...
0:20:45 > 0:20:48..this male wire-tailed manakin
0:20:48 > 0:20:51displays to a mate with his bright colouration.
0:20:52 > 0:20:56And he's got a neat trick to maximise his assets.
0:21:00 > 0:21:02Now, take a look at this.
0:21:02 > 0:21:05What would you say if I told you that this strip
0:21:05 > 0:21:10running across the centre of the panel was all the same colour?
0:21:10 > 0:21:13You might disbelieve me because your eyes, like mine,
0:21:13 > 0:21:15are probably telling you
0:21:15 > 0:21:18that it's darker at this end and lighter at this.
0:21:18 > 0:21:21But I can prove that we've got it wrong.
0:21:21 > 0:21:25If I take the strip off and hold it down here,
0:21:25 > 0:21:29you can see that it is indeed all the same colour.
0:21:29 > 0:21:33And this is an example of the simultaneous brightness
0:21:33 > 0:21:35contrast effect.
0:21:40 > 0:21:45And the sneaky manakin is using just this illusion.
0:21:47 > 0:21:51He needs to appear to be as bright, as vivid as possible.
0:21:53 > 0:21:58Yet he displays in dark shadows under the rainforest canopy.
0:22:00 > 0:22:02So, why on earth would he do that?
0:22:05 > 0:22:07Let's imagine each of these discs
0:22:07 > 0:22:12represents a male brightly-coloured bird of the same species.
0:22:12 > 0:22:15I'll put the first one of these male birds on here
0:22:15 > 0:22:20and then I'll put the second one displaying over here, in the shade.
0:22:20 > 0:22:22And look at that.
0:22:22 > 0:22:24There's absolutely no doubt at all
0:22:24 > 0:22:29that the bird that's displaying in the shade looks much brighter.
0:22:29 > 0:22:33And this isn't down to the way we receive things optically,
0:22:33 > 0:22:37it's down to the way that our brains, and those of the birds,
0:22:37 > 0:22:39register contrast.
0:22:39 > 0:22:43It is a mind-blowing effect.
0:22:44 > 0:22:47A shady and successful deception.
0:22:50 > 0:22:55Visual trickery gives some males the edge when it comes to attraction.
0:22:57 > 0:23:01But most use a far more straightforward approach.
0:23:01 > 0:23:04Simply be THE biggest.
0:23:06 > 0:23:09# Get up, get on up
0:23:09 > 0:23:11# Get up, get on up...#
0:23:11 > 0:23:15Despite all the debate, I can tell you that when it comes to
0:23:15 > 0:23:20impressing the opposite sex, size really does matter.
0:23:23 > 0:23:26It helps females make a choice.
0:23:26 > 0:23:28Because it's an honest representation
0:23:28 > 0:23:31of the male's underlying strength and fitness.
0:23:33 > 0:23:35It's a foolproof plan.
0:23:36 > 0:23:39Well, unless, of course, you can cheat the system.
0:23:47 > 0:23:50Meet the fiddler crab.
0:23:53 > 0:23:58This one enormous claw means that he's a male.
0:24:02 > 0:24:05Eyeing up the beach, he's looking for a mate.
0:24:07 > 0:24:11And his oversized appendage is the way to win her over.
0:24:12 > 0:24:15So he takes pride in its appearance.
0:24:16 > 0:24:21All he has to do is wave it in the air to attract a passing female.
0:24:23 > 0:24:25The problem is...
0:24:26 > 0:24:28..there's a little competition.
0:24:35 > 0:24:37Look at it, it's heaving with them.
0:24:37 > 0:24:43Sometimes, you can find 45 crabs in one square metre of mud.
0:24:58 > 0:25:00Now, when the females are receptive,
0:25:00 > 0:25:03they leave their burrows to size up the local talent.
0:25:09 > 0:25:13And whilst most of the males sport an average appendage,
0:25:13 > 0:25:15others are rather better endowed.
0:25:19 > 0:25:23Which goes down pretty well with the females.
0:25:25 > 0:25:30# Baby, here I am I'm the man on the scene
0:25:30 > 0:25:35# I can give you what you want But you got to go home with me. #
0:25:35 > 0:25:39And begs the question, how does the less-equipped male actually compete?
0:25:43 > 0:25:47He needs to make his claw stand out in the crowd.
0:25:49 > 0:25:51But how?
0:25:51 > 0:25:54Well, scientists noticed that these crabs
0:25:54 > 0:25:57are very particular about their neighbours.
0:25:59 > 0:26:01Let me show you something.
0:26:01 > 0:26:06It's a little optical illusion that might explain what's going on here.
0:26:06 > 0:26:10And all I need is a small, round stone.
0:26:17 > 0:26:20If we copy the stone
0:26:20 > 0:26:23and surround one with larger stones
0:26:23 > 0:26:25and one with smaller stones,
0:26:25 > 0:26:31the stone on the left appears smaller than that on the right.
0:26:31 > 0:26:32But if we switch sides...
0:26:34 > 0:26:36..the other stone appears smaller.
0:26:38 > 0:26:40This is a trick of visual perception
0:26:40 > 0:26:43and it's known as the Ebbinghaus illusion.
0:26:48 > 0:26:52If a crab could surround itself with smaller males,
0:26:52 > 0:26:55then this trick might just work.
0:26:55 > 0:26:59Because its claw would look larger than it really is,
0:26:59 > 0:27:02just like the stone.
0:27:02 > 0:27:04The question is, though,
0:27:04 > 0:27:09how could an animal like a crab go about organising something like that?
0:27:13 > 0:27:18Well, he can't just wander around and stand next to a smaller-clawed crab
0:27:18 > 0:27:22to make his look bigger, he's got to stay near his burrow.
0:27:22 > 0:27:24It's vital for his survival.
0:27:28 > 0:27:31It's his bolthole at high tide.
0:27:33 > 0:27:35And to escape from predators.
0:27:42 > 0:27:47So instead, he does something extraordinary.
0:27:47 > 0:27:49He manipulates his neighbours.
0:27:50 > 0:27:55If a rival male moves into the territory next door
0:27:55 > 0:27:58and it's got a small claw,
0:27:58 > 0:28:02then the central crab doesn't bother to challenge it at all.
0:28:02 > 0:28:05It will only challenge a new neighbour
0:28:05 > 0:28:07if it arrives with a large claw.
0:28:11 > 0:28:13And it doesn't stop there.
0:28:15 > 0:28:19You see, he'll also defend his small-clawed neighbours
0:28:19 > 0:28:22by driving out any intruder with a large claw.
0:28:28 > 0:28:31All for his own gain.
0:28:31 > 0:28:34Because if he can permanently surround himself
0:28:34 > 0:28:37with small-clawed neighbours,
0:28:37 > 0:28:43then his average claw will appear relatively much larger.
0:28:43 > 0:28:46Simple and beautiful.
0:28:46 > 0:28:52And I can actually see it happening right here, now, in front of me.
0:28:55 > 0:29:00It's a very sneaky solution from a very crafty crustacean.
0:29:04 > 0:29:07I love it when it's the little things that really get you going.
0:29:07 > 0:29:12Not the tigers, the dolphins or the chimpanzees, but the crabs.
0:29:12 > 0:29:16How many times have you not looked at a crab?
0:29:16 > 0:29:18Just thought, "Well, it's a crab".
0:29:18 > 0:29:20And yet their life histories,
0:29:20 > 0:29:24their lifestyles are incredibly fascinating.
0:29:24 > 0:29:29I mean, waving your claw about and making it look bigger.
0:29:29 > 0:29:32It's brilliant. It's absolutely brilliant.
0:29:40 > 0:29:44From artful illusions, let's move on to blatant cheats.
0:29:48 > 0:29:51You see, some males will go to extreme lengths
0:29:51 > 0:29:54to trick the competition and beguile the girl.
0:29:59 > 0:30:03And to start the next generation,
0:30:03 > 0:30:08one animal is even breaking the fundamental laws of nature.
0:30:12 > 0:30:15'The Brouage wetlands are the stronghold
0:30:15 > 0:30:17'of a spectacular bird of prey.
0:30:18 > 0:30:21'The marsh harrier.'
0:30:26 > 0:30:30In the breeding season, this male has a problem.
0:30:33 > 0:30:37Competition with other males over breeding territories is intense.
0:30:37 > 0:30:39SQUAWKING
0:30:43 > 0:30:46But he has an extraordinary solution.
0:30:49 > 0:30:54In fact, a ground-breaking discovery has completely changed
0:30:54 > 0:30:58everything I thought I knew about this bird.
0:30:58 > 0:31:00Take a look at this.
0:31:00 > 0:31:05This is what I'd call a pretty typical adult male marsh harrier.
0:31:05 > 0:31:10It's got these grey panels in its wings and this plain grey tail.
0:31:10 > 0:31:13And I'd have said that was a male. I'd be pretty certain about that.
0:31:13 > 0:31:15I'd have said that this one was a female.
0:31:15 > 0:31:17It's a much browner bird
0:31:17 > 0:31:22and it has these pale leading edges to the wings here and a pale head.
0:31:22 > 0:31:26I'd have said it was a female, but I'd have been wrong.
0:31:26 > 0:31:31You see, this isn't a female, it's a male in disguise.
0:31:33 > 0:31:35Since he became an adult,
0:31:35 > 0:31:40this male has grown feathers that make him look like a female.
0:31:42 > 0:31:46It's remarkable because in many species, the harriers included,
0:31:46 > 0:31:51males and females deliberately look different.
0:31:53 > 0:31:56It's called sexual dimorphism.
0:31:58 > 0:32:00Both sexes use these visual cues
0:32:00 > 0:32:04to know how to behave towards one another.
0:32:05 > 0:32:09Whether to fight, or to flirt.
0:32:10 > 0:32:16So, why would this bird intentionally put on this pretence?
0:32:16 > 0:32:19What's going on here really is quite extraordinary.
0:32:19 > 0:32:22And scientists have been studying these birds
0:32:22 > 0:32:25to see why they're doing something so extreme.
0:32:25 > 0:32:29And the results they've come up with are truly remarkable.
0:32:31 > 0:32:34'I'm in the middle of a male marsh harrier's territory.
0:32:34 > 0:32:38'And using these models, I'm going to conduct an experiment.'
0:32:40 > 0:32:44Under the strict guidance of the scientist working here,
0:32:44 > 0:32:48I'm introducing an intruder into this territory
0:32:48 > 0:32:50in the form of this decoy,
0:32:50 > 0:32:53which has been very accurately painted
0:32:53 > 0:32:58to look like a typical, traditionally-marked male marsh harrier.
0:33:05 > 0:33:07'Here's the resident male.'
0:33:13 > 0:33:15During the breeding season,
0:33:15 > 0:33:19male marsh harriers are fiercely protective of their nesting sites.
0:33:21 > 0:33:23He's spotted the decoy.
0:33:31 > 0:33:33Legs down, talons out.
0:33:35 > 0:33:37SQUAWKING
0:33:37 > 0:33:40This is a clear threat to the intruder.
0:33:42 > 0:33:44Who he sees as a rival.
0:33:46 > 0:33:49'But what happens if we put out a different decoy?
0:33:50 > 0:33:53'Enter the female mimic.
0:33:58 > 0:34:00'How's he going to react to this one?'
0:34:01 > 0:34:06Here is our male. It's drifting over the reeds now.
0:34:07 > 0:34:09Here it is, here it is.
0:34:09 > 0:34:12Right over the decoy.
0:34:12 > 0:34:15And there's no doubt at all that he saw that decoy.
0:34:15 > 0:34:19There was no aggression there at all. He just drifted past.
0:34:21 > 0:34:26Pretending to be female stops these male birds from being attacked.
0:34:26 > 0:34:30Using their devious disguise, they sneak past other males
0:34:30 > 0:34:35and right over their turf without any conflict.
0:34:37 > 0:34:42Then they set up their own territory right on the doorstep
0:34:42 > 0:34:44of a typical-coloured male.
0:34:47 > 0:34:52'But, of course, the ultimate goal for these males is still to breed.'
0:34:53 > 0:34:54So, how does that work?
0:34:57 > 0:35:02Well, when our cheat meets a real female, he switches tactics.
0:35:02 > 0:35:04SQUAWKING
0:35:04 > 0:35:09Just like a typical male, he courts her with an elaborate sky dance.
0:35:12 > 0:35:15She has no doubts at all that he's a male bird.
0:35:22 > 0:35:24'They settle down to raise the next generation.'
0:35:26 > 0:35:29He gets access to prime hunting grounds
0:35:29 > 0:35:33and can bring up his chicks without any conflict.
0:35:33 > 0:35:35It's great, isn't it?
0:35:35 > 0:35:38This uniquely sneaky strategy
0:35:38 > 0:35:41means that the cross-dressing male
0:35:41 > 0:35:45has a much easier time when it comes to rearing his family.
0:35:45 > 0:35:48But you know the most remarkable thing of all?
0:35:48 > 0:35:51It's such a successful strategy
0:35:51 > 0:35:56that 40% of the male marsh harriers in this population
0:35:56 > 0:36:00are now using it to their advantage.
0:36:03 > 0:36:07These marsh harriers are committed to their cross-dressing colouration
0:36:07 > 0:36:08for their entire lives.
0:36:16 > 0:36:18But in the ocean, there is
0:36:18 > 0:36:21an animal that can change its disguise in just an instant.
0:36:27 > 0:36:33Giant Australian cuttlefish, up to a metre long, are gathering to breed.
0:36:36 > 0:36:38The marble-coloured females
0:36:38 > 0:36:43draw in their tentacles to show that they're impressed by a male.
0:36:44 > 0:36:47The big guys with bold,
0:36:47 > 0:36:50striped courtship patterns dominate this crowd.
0:36:52 > 0:36:55They guard females underneath their bodies.
0:36:59 > 0:37:04A small male has a tough time even getting a look-in.
0:37:04 > 0:37:08The dominant male sees him off with an eight-legged arm-wrestle.
0:37:15 > 0:37:20But this little chancer is about to pull off his party trick.
0:37:23 > 0:37:27He draws in his tentacles to look like a female.
0:37:31 > 0:37:37But that's not all. He even changes his pattern to complete the con.
0:37:47 > 0:37:52Using this devious drag act, he slips underneath the male.
0:37:53 > 0:37:59As far as the big guy's concerned, he's now protecting another female.
0:38:00 > 0:38:05But beneath him, our cross-dresser is mating with his female!
0:38:07 > 0:38:12And he's ensured that at least some of the next generation belong to him!
0:38:20 > 0:38:23These elaborate illusions, tricks and cons
0:38:23 > 0:38:28give animals an advantage when it comes to mating.
0:38:29 > 0:38:34But there's a bigger challenge ahead once their little ones are born.
0:38:35 > 0:38:37WAVES CRASH
0:38:42 > 0:38:45To make sure their offspring survive,
0:38:45 > 0:38:51animals have to provide food, shelter and protection around the clock.
0:38:52 > 0:38:56It's a massive investment of time and energy.
0:38:58 > 0:39:01So perhaps it's no surprise that some of them
0:39:01 > 0:39:06have found very sneaky ways to reduce these childcare costs.
0:39:08 > 0:39:11Introducing the emperor tamarin.
0:39:20 > 0:39:21Ouch!
0:39:21 > 0:39:25They're called emperor tamarins because of this extraordinary
0:39:25 > 0:39:26moustache here.
0:39:26 > 0:39:29Reminiscent of a Chinese emperor.
0:39:29 > 0:39:32And as you can see, they're a very small monkey species,
0:39:32 > 0:39:36which means they can occupy a very particular niche.
0:39:36 > 0:39:40They can reach right to the end of the thinnest little twigs,
0:39:40 > 0:39:44where they forage for fruits and also for insects.
0:39:44 > 0:39:49But, of course, being small does also come with some disadvantages.
0:39:49 > 0:39:52Particularly when it comes to having your young. Ouch!
0:39:58 > 0:40:02Emperor tamarins live in the rainforests of South America.
0:40:05 > 0:40:10This female, named RC because of her radio collar, is a new mum.
0:40:15 > 0:40:16These tamarins are tiny.
0:40:18 > 0:40:20So to make childbirth easier,
0:40:20 > 0:40:24they have two smaller twins rather than one large baby.
0:40:27 > 0:40:29Nevertheless, together,
0:40:29 > 0:40:33these twins weigh about 50% of her own body weight.
0:40:37 > 0:40:39That's a bit like me carrying a couple of...
0:40:39 > 0:40:42Well, not just carrying a couple of toddlers around,
0:40:42 > 0:40:45but leaping around in the branches of a tree,
0:40:45 > 0:40:47carrying a couple of toddlers.
0:40:47 > 0:40:49It's a real burden.
0:40:49 > 0:40:51A burden on their ability to find food for themselves
0:40:51 > 0:40:53and successfully rear those young.
0:40:53 > 0:40:55They need some help.
0:40:57 > 0:41:02And to get it, RC has been very devious indeed.
0:41:07 > 0:41:11Scientists have discovered that she's at the centre
0:41:11 > 0:41:12of an elaborate con.
0:41:16 > 0:41:20They use coloured beads to identify the males in the group.
0:41:20 > 0:41:22This one is Purple Beads.
0:41:24 > 0:41:27RC mated with him five months ago.
0:41:29 > 0:41:32And he's arrived to help bring up the babies.
0:41:39 > 0:41:42That's good news. The childcare is now split 50/50.
0:41:46 > 0:41:52But hang on. Red Beads has also reported for childcare duty.
0:41:57 > 0:42:03And finally, No Beads is also taking a turn looking after the twins.
0:42:08 > 0:42:13Now, with childcare covered, RC can finally forage.
0:42:15 > 0:42:20Getting food for herself and to help produce milk for the twins.
0:42:23 > 0:42:26The question is, how on earth has she enlisted so much help?
0:42:28 > 0:42:30Well, back in the breeding season,
0:42:30 > 0:42:34it turns out that RC didn't just mate with Purple Beads.
0:42:41 > 0:42:45She deliberately mated with Red Beads.
0:42:46 > 0:42:48And No Beads, as well.
0:42:50 > 0:42:52It's created such confusion
0:42:52 > 0:42:57that now, none of the males actually know who's the daddy.
0:43:02 > 0:43:05But if there's any possibility that the twins are theirs,
0:43:05 > 0:43:09then, of course, it makes sense to invest in looking after them.
0:43:10 > 0:43:14So they all chip in with the childcare.
0:43:14 > 0:43:18By playing the genetics to her advantage,
0:43:18 > 0:43:21RC has elicited more than enough help.
0:43:23 > 0:43:27It's an absolutely brilliant maternal monkey con.
0:43:27 > 0:43:29It's magnificent.
0:43:29 > 0:43:31It's hats off to the tamarin.
0:43:40 > 0:43:42So two-timing tactics
0:43:42 > 0:43:45are a way of shirking some parenting responsibilities.
0:43:49 > 0:43:53But other cheats have managed to get out of childcare altogether.
0:43:54 > 0:43:56BIRDSONG
0:43:59 > 0:44:03And this plays out as one of the darkest deceptions of all.
0:44:06 > 0:44:09Meet the greater honeyguide.
0:44:09 > 0:44:11CHIRPING
0:44:13 > 0:44:19As its name suggests, it guides people to honey-filled bees' nests.
0:44:27 > 0:44:30The deal is that both sides get a reward.
0:44:34 > 0:44:39So our honeyguide seems a caring, sharing kind of bird.
0:44:39 > 0:44:43But when it comes to parenting, she has a sinister secret.
0:44:44 > 0:44:48Because she doesn't do any at all.
0:44:49 > 0:44:52And the key is conning another species.
0:44:54 > 0:44:58An unsuspecting pair of little bee-eaters.
0:45:03 > 0:45:07Their nest is just inside an abandoned aardvark burrow.
0:45:12 > 0:45:17It's pitch-black in here, but with the help of specialist cameras,
0:45:17 > 0:45:21we can reveal the extraordinary events inside this nest.
0:45:26 > 0:45:29The bee-eaters incubate their precious eggs around the clock.
0:45:33 > 0:45:37Each is barely the size of a fingernail.
0:45:37 > 0:45:39But look closer.
0:45:42 > 0:45:46The slightly larger one is the egg of our honeyguide.
0:45:49 > 0:45:53Her devious plan has already been laid.
0:45:54 > 0:45:58You see, honeyguides are brood parasites.
0:45:58 > 0:46:01Much like another bird we're very familiar with.
0:46:04 > 0:46:06The Eurasian cuckoo.
0:46:10 > 0:46:13They lay their eggs in other birds' nests.
0:46:14 > 0:46:17And apart from a small size difference,
0:46:17 > 0:46:19they mimic them perfectly.
0:46:21 > 0:46:24The parents, in this case, a pair of reed warblers,
0:46:24 > 0:46:29are completely fooled, and they incubate them all.
0:46:30 > 0:46:34Leaving the female cuckoo completely free of any responsibility.
0:46:37 > 0:46:40Back in Africa, it's a similar story.
0:46:45 > 0:46:48The doting bee-eaters care for all of the eggs.
0:46:48 > 0:46:52But the honeyguide has a new problem.
0:46:53 > 0:46:58Her chick needs the bee-eater's sole attention to survive.
0:47:01 > 0:47:03So, how is she going to orchestrate that?
0:47:12 > 0:47:17One of the eggs has hatched, and it's the honeyguide's.
0:47:19 > 0:47:21Exactly as she intended.
0:47:24 > 0:47:30Our honeyguide incubated her egg inside her body before laying it.
0:47:32 > 0:47:35Ensuring that it hatched first.
0:47:39 > 0:47:42The bee-eaters have been completely duped.
0:47:44 > 0:47:49They believe this colossal chick is their helpless first-born
0:47:49 > 0:47:52and they do everything they can to care for it.
0:47:55 > 0:47:56Keeping it warm...
0:47:57 > 0:48:00..and working tirelessly to find it food.
0:48:09 > 0:48:12But as the other eggs near their hatching date...
0:48:13 > 0:48:16..all of this is about to change.
0:48:21 > 0:48:25Above ground, the cuckoo chick has an extremely underhand way
0:48:25 > 0:48:27of dealing with the competition.
0:48:30 > 0:48:34The imposter's innate response to unhatched eggs...
0:48:35 > 0:48:36..is quite extraordinary.
0:48:39 > 0:48:42It heaves them straight out of the nest.
0:48:51 > 0:48:52Removing the problem.
0:48:54 > 0:48:58And ensuring that it gets all of the food.
0:48:59 > 0:49:01Until it's old enough to fledge,
0:49:01 > 0:49:05no matter how...big...it gets.
0:49:14 > 0:49:19But our honeyguide chick can't kick out the other eggs.
0:49:19 > 0:49:21It's deep underground in a burrow.
0:49:21 > 0:49:25And these eggs are now starting to hatch.
0:49:31 > 0:49:33It needs another way.
0:49:37 > 0:49:41And the chick's solution would make its scheming mother proud.
0:49:50 > 0:49:55It's been growing a very specialised razor-sharp bill.
0:50:06 > 0:50:10Now, remember, it can't even see its rivals.
0:50:10 > 0:50:12But it takes a stab in the dark.
0:50:17 > 0:50:20This is pure instinct at play.
0:50:23 > 0:50:27One by one, each of its foster siblings is killed.
0:50:29 > 0:50:32This behaviour is a shocking new discovery.
0:50:32 > 0:50:35But it's also a strategy that works.
0:50:39 > 0:50:43The honeyguide chick now has the bee-eater's undivided attention
0:50:43 > 0:50:45until it's ready to leave the nest.
0:50:48 > 0:50:53As for the adult honeyguide, well, not only has she got out
0:50:53 > 0:50:54of the effort of raising a family,
0:50:54 > 0:50:57she never even sees her own chick.
0:50:59 > 0:51:05Surely the most devious childcare plan that's ever been hatched?
0:51:12 > 0:51:16Crafty cuckooing has to be the sneakiest way
0:51:16 > 0:51:18of avoiding parenting duties.
0:51:21 > 0:51:25But even the most dedicated parents face a problem.
0:51:25 > 0:51:29Because, often, their offspring are also trying to trick them.
0:51:31 > 0:51:35You see, all young animals have their own agenda.
0:51:36 > 0:51:40They want more time, more food and more attention.
0:51:41 > 0:51:43More than their parents want to give.
0:51:51 > 0:51:56In nature, there's always an underlying conflict between parents
0:51:56 > 0:51:57and their offspring.
0:51:57 > 0:51:59A form of competition.
0:52:01 > 0:52:04At times, the adults don't want to feed the young
0:52:04 > 0:52:07quite as much as those young would like.
0:52:09 > 0:52:13But I've got to tell you that some youngsters have come up with
0:52:13 > 0:52:16an extraordinary scheme to get what they want.
0:52:22 > 0:52:23These bold and boisterous
0:52:23 > 0:52:26black and white birds are called pied babblers.
0:52:26 > 0:52:30These striking four birds here are the adults.
0:52:32 > 0:52:37Hiding in the shelter of the bushes are the plainer brown youngsters.
0:52:39 > 0:52:42But don't be fooled by their dowdiness.
0:52:42 > 0:52:45These young chicks are out to trick their own parents.
0:52:47 > 0:52:49BABBLERS SQUAWK
0:52:52 > 0:52:55They already have the whole family running around after them.
0:52:58 > 0:53:02Their parents and the older siblings are working relentlessly
0:53:02 > 0:53:03to satisfy their appetites.
0:53:14 > 0:53:17But as far as they're concerned, that's still not enough.
0:53:20 > 0:53:25So, is there anything that they could possibly do that would get them
0:53:25 > 0:53:26any more food?
0:53:28 > 0:53:30Well, yes.
0:53:30 > 0:53:31Actually, there is.
0:53:33 > 0:53:35But it's pretty outrageous.
0:53:38 > 0:53:41It involves the babblers' predators.
0:53:42 > 0:53:46The Kalahari is a dangerous place to live.
0:53:46 > 0:53:51So, for a young bird, staying hidden is by far the safest option.
0:53:53 > 0:53:58And yet, this is when they do something very strange indeed.
0:53:58 > 0:54:01Rather than hiding from predators,
0:54:01 > 0:54:04it's almost as if they've got a death wish.
0:54:25 > 0:54:30These two youngsters have hopped right out into the open.
0:54:30 > 0:54:32And they're making lots of noise.
0:54:33 > 0:54:36This is asking for trouble, surely,
0:54:36 > 0:54:40because they're very vulnerable to any predator.
0:54:40 > 0:54:42Why would they be doing that?
0:54:42 > 0:54:45Well, there's a reason for everything in nature.
0:54:47 > 0:54:52Surely, there's got to be some method in this madness?
0:55:01 > 0:55:02There is.
0:55:02 > 0:55:07A remarkable new discovery is revealing a manipulative masterplan.
0:55:08 > 0:55:10Consider the scenario.
0:55:10 > 0:55:11We've all seen it.
0:55:11 > 0:55:14A child having a tantrum in a supermarket aisle.
0:55:14 > 0:55:17What it's doing is making a scene in public
0:55:17 > 0:55:20so it might just get its bag of sweets.
0:55:20 > 0:55:23And that's exactly what's going on here.
0:55:23 > 0:55:28These chicks are trying to extort food from their parents.
0:55:32 > 0:55:35And I'm going to demonstrate exactly how they're doing it,
0:55:35 > 0:55:39with the predator warning call of one of the babblers' neighbours.
0:55:41 > 0:55:44I've got the alarm call of a starling.
0:55:44 > 0:55:46So, I'm going to play this to these babblers
0:55:46 > 0:55:48and see what their reaction is.
0:55:48 > 0:55:51Obviously, if they know the alarm call,
0:55:51 > 0:55:53they'll think that there's a predator present.
0:55:55 > 0:55:56AGITATED BIRD CALL
0:55:58 > 0:56:01Well, they didn't... They didn't need much of that, did they?
0:56:01 > 0:56:05Clearly, these adults recognise that predator alarm call.
0:56:07 > 0:56:10But just look at the chicks.
0:56:10 > 0:56:13They're still out in the open, calling for food.
0:56:16 > 0:56:19Now, to stop all of this noise attracting
0:56:19 > 0:56:20the attention of predators,
0:56:20 > 0:56:23the adults rush out to feed them.
0:56:23 > 0:56:25They're trying to keep them quiet.
0:56:28 > 0:56:30And by using this strategy,
0:56:30 > 0:56:36the chicks can get fed an incredible nine times more food.
0:56:37 > 0:56:41These chicks are blackmailing their parents.
0:56:41 > 0:56:42It's despicable,
0:56:42 > 0:56:44but wonderful.
0:56:47 > 0:56:51Surely, these are the ultimate con artists?
0:56:53 > 0:56:56Tricking their family from almost the moment they're born.
0:57:02 > 0:57:06Parents all over the world have always suspected that they were
0:57:06 > 0:57:08being blackmailed by their kids.
0:57:08 > 0:57:12And, as this ground-breaking study shows, it's certainly the case.
0:57:13 > 0:57:16Pied babbler, take a bow.
0:57:23 > 0:57:26So, whether they're avoiding predators...
0:57:26 > 0:57:27..finding food...
0:57:28 > 0:57:30..or starting a family...
0:57:31 > 0:57:36..we've met the devious animals that will stop at nothing...
0:57:36 > 0:57:39..to get ahead in the game of life.
0:57:42 > 0:57:47They really are the world's sneakiest animals.
0:57:52 > 0:57:55I've been amazed, in fact, I've got to tell you I've been staggered
0:57:55 > 0:57:59at the lengths they'll go to to transform their appearance,
0:57:59 > 0:58:00or their behaviour.
0:58:00 > 0:58:05I mean, you might have thought that only humans could be that crafty.
0:58:05 > 0:58:07But, no.
0:58:07 > 0:58:12Let's celebrate the illusionist, the con artist, those thieves.
0:58:12 > 0:58:16The species that use spectacular deception
0:58:16 > 0:58:21and incredible ingenuity to ensure their survival.
0:58:21 > 0:58:25It's hats off to the natural born hustlers.