All life is driven by the need to breed.
Though, for a few,
the odds of doing so are overwhelmingly against them.
The deep ocean.
The largest and least-populated habitat on Earth.
Those that live here appear to come from another world...
..and much of their lives are spent alone in the blackness.
So finding any potential partner is hard,
and getting the timing right is even harder.
Such an extreme game of chance
has led to one of the most bizarre strategies of all.
A fanfin anglerfish.
On her belly, she has what seems to be an odd-looking fin.
It is, in fact, a tiny parasitic male anglerfish.
When he met her,
it was his once-in-a-lifetime opportunity
to secure a mate.
So he bit into her.
His blood system fused with hers.
Now he is entirely dependent on her.
So much so, that when she dies, he will die, too.
Until then, his sole function in life is to fertilise her eggs.
This extreme commitment
ensures that both can succeed
in their bizarre version of the mating game.
Most creatures that play the mating game
must solve major problems if they are to succeed.
But among these sand dunes in Russia,
where howling winds can transform an unstable landscape,
the challenge for one animal
is almost overwhelming.
A male toad-headed agama.
He spends his entire life on this dune.
Once a year, he'll try to find a mate.
She would only be interested if he has a suitable burrow
in which she can lay her eggs.
But in his world of shifting sands,
good burrows are hard to come by.
And when the wind is strong,
they can be lost in a matter of minutes.
So he's keen to attract a female as quickly as he can.
And his black-tip tail is his way of doing so.
He's been noticed.
Now he must entice her back to his burrow.
Instead, she replies with an invitation of her own.
He tries again - with more vigour.
She still doesn't move.
Turns out...
..she already has a burrow...
..and is not about to abandon such a valuable property.
Which presents him with a dilemma.
Accepting her invitation may mean he gets a mate,
but leaving means he risks losing his burrow to a rival male.
What to do?
Desire gets the better of him,
and he hotfoots it over to her place.
But after a closer look...
..she decides he's not for her.
And while his back is turned...
..the worst has happened.
A rival male has spotted his unguarded burrow.
But he won't give it up without a fight.
Each flanks the other
and tries to make themselves look bigger.
The intruder is seen off...
..but it's a hollow victory.
The wind picks up, and sand engulfs the contested burrow.
As it disappears...
..so do his chances of success -
until the wind dies down, and he can try again.
Territory may be important for some...
..but the need to find a mate is vital for all.
One solution is to devote a lifetime to just one partner.
But that only works when there are enough to go round.
A Laysan albatross.
For over half the year,
she has scoured the vast Pacific alone,
searching for food.
And now she is returning
to her breeding grounds in Hawaii.
Laysans pair for life.
Repeated displays cement their long-term relationship.
It takes two adults to raise just one chick...
LAYSANS CALL
..so a partner willing to share the burden of parenthood
is the difference between success and failure.
But this female is on her own.
She was seduced and then abandoned by an unfaithful male.
Adulterous males play no further part
in looking after their extramarital eggs.
She cannot raise her chick alone.
She must find a partner.
All the available males here are already taken...
..but she hasn't exhausted her options just yet.
A new arrival catches her eye.
But she needs to discover
whether this is a partner she can rely on...
..and she does so by suggesting a dance.
THEY CALL
They seem a perfect match.
LOUD HONK
But it's a match with a difference...
..because her dance partner...
..is another female.
SHE CALLS AND TWITTERS
This duet confirms their commitment...
LOUD HONK
..to raising a chick together.
BOTH HONK
Within a few days,
she lays a single large egg.
The effort drains her of energy.
To recover, she must head back to sea to feed.
And while she's away, she is totally reliant
on her new-found partner to incubate her egg.
She must put all her trust in her if they are to succeed.
Three weeks later, she's back...
..well fed, and ready to take her turn.
But something is wrong.
Her precious egg has been pushed out of the nest.
It seems she couldn't trust her partner, after all.
Worse still...
..while she's been away...
..her partner has also laid an egg!
It turns out she, too, had mated
before entering this relationship.
But two eggs create a problem.
They can only incubate one...
..because both must take turns to feed.
HONK
The urge to incubate her own egg is overwhelming.
But the chick within
has grown cold, and died.
So she devotes herself
to the only egg left alive.
Her partner's.
Two months later...
TWITTERING, HONKING
Her decision pays off.
She is not related to the chick...
..but this seemingly selfless act
is part of her long-term strategy.
This female couple may be together
for half a century or more,
and will take turns
raising each other's chicks.
CHICK TWEETS
Adulterous males will always take advantage when they can.
But by alternating whose egg is incubated...
..both these females have found a way to achieve lifetime success.
Long-term relationships can increase the chances of success,
but some animals only get one opportunity to breed -
and that creates the highest-stakes game of all.
In the Sonoran Desert,
the Earth is starting to move.
A male digger bee.
He's spent his entire life underground...
..waiting for this moment to arrive.
It's the breeding season...
..and he's emerged with just one purpose.
To find a mate.
This is his only opportunity to do so.
Because, in a few days' time...
..he will be dead.
To give him an edge,
his sense of smell is among the best of all bees.
The female he's looking for
is still buried beneath the desert sand.
Her intoxicating perfume seduces him...
..even before she emerges...
..and it drives him crazy.
But a bigger rival is quick to displace him.
The odds are stacking up against him.
More males are arriving by the minute.
Like him, each needs to mate...
..and they will die trying.
If he is to succeed,
he must also do whatever it takes.
Once again, he picks up the scent of a female...
..and once again,
his rivals aren't far behind.
Just as he digs her out...
..they pounce.
As yet more join in,
he risks being trapped at the centre of the ball
and cooked alive by their body heat.
No longer able to defend her..
..he flees.
He's forced away from the battleground -
where there is little competition,
but far fewer females.
He picks up a scent no-one else has.
This is his last chance.
They mate immediately,
and he passes his sperm to her.
But this is far from the end of his story.
As long as her perfume lingers,
rivals will be attracted to mate with her...
..and he can't risk that happening.
He's already inseminated her,
yet it is only now
that he starts to court her.
He must convince her she needs no other than him -
and to do that, he seduces her
with a rasping call...
RASPING
..and may anoint her with his own scent.
Only when she shows no further interest in mating...
..and her heady perfume has gone...
..can he be sure that he is the only one
she will ever breed with...
..and he releases her.
For both of them,
their mating game is over.
She now devotes all her time
to being a responsible mother -
gathering pollen and nectar
for their offspring.
As for her seductive partner?
He will pay no further part in their lives.
He's fathered the next generation
and ensured no rival will replace him.
Time...
..to die.
Living long enough to mate
is a challenge faced by all animals.
But one creature is forced to travel extraordinary distances
to have any chance of doing so.
North America, in late summer.
Beneath the leaf of a milkweed plant,
a male monarch butterfly
is completing his final transformation.
As an adult,
he's driven by a single goal...
..the need to mate.
But he cannot do so yet.
And he cannot do so here.
His mating game is bound to the only plant
on which monarchs lay their eggs.
Milkweed.
Without it, monarchs cannot breed.
But winter is coming.
The milkweed here won't reappear until next summer,
and he cannot survive winter's extreme cold.
So he is forced to undertake one of the greatest migrations on Earth.
Driven ever southwards,
it's a gruelling journey of nearly 3,000 miles...
..and takes two months to complete.
His destination is a small mountain hillside in Mexico.
Hundreds of millions of monarchs
have made the same journey to this refuge.
They are all here
because only this forest has exactly the right conditions
for waiting out the winter.
Smaller males like him only just make it.
All must rely on their remaining reserves of energy
to survive until next spring.
So for those that arrive already exhausted,
the odds of doing so are against them.
A winter storm spells disaster.
Those already on the edge do not make it.
In spring, the sun's warmth brings the survivors
cascading back to life.
And among them, the small male.
All are now ready to breed.
Many will head north in search of milkweed
that is starting to reappear.
But not all are still capable of making that journey.
The smaller male is almost spent...
..so, to have any chance of breeding,
he resorts to a desperate strategy.
A drink gives him just enough for his final act.
Among those leaving their winter refuge,
he's looking for a large, healthy female.
One with enough strength to survive longer than him
and find the fresh milkweed.
He's spotted her.
Grabbing her, he clings on with all his remaining might
as he forces her to the ground.
Here, he mates.
It's a violent act, born of desperation.
But he has survived long enough to breed.
And in doing that,
he has beaten enormous odds.
Grabbing any chance to mate may be the difference
between winning and losing the mating game.
But sometimes, those that are defeated
still find a way to pass on their genes,
despite the impossible odds stacked against them.
It's spring in south Texas...
..and wild turkeys are coming together
at their traditional breeding grounds.
GOBBLING
Each year, colourful adult males - known as toms -
compete for female attention.
TURKEY CALLS
Calling...lets them know they've arrived.
The toms have a strict pecking order.
And this male...
..is at the very bottom of it.
So is his brother.
And at the top...
..their dominant brother.
As long as he is around,
the other two won't get a look in.
But that doesn't mean their mating game is over.
Instead, their strategy is to abandon their own desires,
and support their high-status sibling...
creating a formidable band of brothers.
It's the females that choose who they mate with.
They're all looking for the best male,
and they assess them on the splendour of their display.
With enough flamboyance,
the band of brothers can woo not just one female,
but all the hens here.
And their chances are greatest
when they display together.
With his two wingman by his side,
the dominant tom is out to impress.
But they aren't the only males that use teamwork.
A rival band of toms.
They, too, are looking to win over all the hens.
With so much at stake,
the band of brothers cannot give way.
But it's not the dominant Tom who takes a lead.
It's his low-ranking brothers
that peel off to intercept them.
As the feathers fly,
the high-ranking brother takes full advantage.
They try to keep their rivals at bay...
..so their brother can get on with mating.
It's all for one...
..and one for all.
Because each time he mates,
he also passes on many of the genes
he shares with his brothers.
So through the success of the dominant tom,
the siblings at the bottom of the pecking order
also succeed in the mating game...
..and all without ever mating themselves.
Waiting for the right moment to breed
is vital in any mating strategy...
..and many choose to do so in spring,
when food is readily available.
But mating during this period poses a sizeable challenge...
..especially if you ARE the menu.
Periodical cicadas.
About four centimetres long,
they don't bite or sting.
For many forest inhabitants,
that makes them the perfect meal.
Hundreds of cicadas perish before their mating game has even begun.
But millions more do survive,
overwhelming the predators as they gather in the canopy.
CACOPHONY OF CHIRPING
Here, they form the greatest mating choir on Earth.
Only the males sing.
SINGING
A female is enticed by a male's call...
CLICK! ..and responds...
..with a wing flick.
CLICK!
Each one lets him know she's interested...
CLICK!
..and draws him a little closer.
CLICK!
As they meet, his serenade changes.
SINGING
If it's still to her liking,
he'll get the chance to mate.
But this is only part of the strangest
and longest mating game of all.
Once she's mated, she bores into a tree
and lays up to 500 eggs
Two months later...
..newly hatched nymphs drop to the ground...
..bury themselves,
and attach to tree roots.
These cicadas won't be seen again for 17 years.
This remarkable strategy ensures that,
when they do re-emerge to breed,
their predators have long given up waiting.
And what's more - they all emerge at the same time
to once again overwhelm any predators that are around.
Their first instinct is to climb the nearest tree.
They cannot mate yet.
For that...
..they must take their adult form.
It takes time for soft white flesh to harden.
Until then, the newly formed adult cicadas are especially vulnerable.
Though, for this brood,
it isn't predators that they need to be most wary of.
It's their own kind.
In the 17 years they have lain hidden,
the forest above them has been transformed.
Many of the trees have been chopped down.
As a consequence, tens of thousands of cicadas
are forced to climb the few trees that remain.
In the crush, nymphs clamber over the emerging adults...
..and puncture...
POP, SQUELCH
..newly formed skin with their needle-sharp claws.
The wounds are fatal.
Soon the trees are surrounded
by mountains of the dead and the dying.
All have been prevented from mating by odds they could not overcome.
Their failure to breed is a result of rapid changes in their habitat...
..caused by the one species that rivals any animal on Earth
in its ability to breed successfully.
Us.
HORN BLASTS
In the last 17 years,
our population has increased
by over 1.4 billion.
We have overcome most of life's challenges...
..and, as a result,
we have become the most dominant species on the planet.
But our success has come at a cost.
We have converted wild habitat
to suit our needs...
..and have done so on an unprecedented scale.
One consequence of our actions
is that we have destroyed the ability of other species to breed.
And now we face a mass extinction of animals
like no other in human history.
If we are to help those that remain...
..we must figure out exactly what they need to play the mating game.
And until we do that,
we are creating an insurance policy, should the very worst happen.
Cryobanks.
A global network freezes and stores the DNA of many species...
..including those on the brink of extinction.
These blueprints for life
are a vital resource for both research and conservation...
..and are already being used to help those struggling to survive.
A male black-footed ferret.
He is searching for a mate in the last remnants
of the North American prairies.
But his chances of success are slim.
He is one of less than 400 left in the wild.
And all are descended from just seven individuals.
So even if he does find a mate,
they may be too closely related
to have healthy young.
But, thanks to science,
one very special ferret
may change his mating game forever.
Meet Elizabeth Ann.
She really is one of a kind...
..because Elizabeth Ann is a clone.
She has been created from the frozen cells
of a ferret that died over 30 years ago.
She isn't closely related to any of the other ferrets,
so the chances of producing healthy offspring with her are much higher.
Should we wish, we now have the ability
to breed any animal - or at least save its tissues
until we discover how.
But, in the world we have created,
there is more that is needed
to ensure long-term success in the mating game.
In China, scientific breakthroughs with captive breeding
have led to a remarkable success story...
..and a vital lesson.
A baby giant panda.
He is the first in 40 years
to be born into a world
where giant pandas are no longer endangered.
He's the product of a captive breeding programme
that began over half a century ago...
..and has now increased their population by more than 600.
But, in spite of that success,
there was a problem.
The young pandas were completely dependent on their keepers.
Ill-equipped to survive in the wild,
they didn't have the experience they needed to breed naturally.
And that was all because no-one fully understood
what giant pandas needed to play their mating game.
For decades, we assumed that we could breed captive-born pandas
by simply becoming matchmakers.
All we had to do was put a female panda...
..together with a male panda...
..and let nature take its course.
But nature...
..DIDN'T take its course.
It turns out that giant pandas
are extremely fussy about who they mate with.
If a female is paired with a male who...
..just doesn't do it for her...
..then the date fails completely.
Yet giant pandas have been on the planet
for at least two million years -
surely they can't be that bad at breeding!
Clearly, we were missing something.
Field research revealed that female pandas
need to choose a mate for themselves.
And to do that,
they need trees.
Adult giant pandas lead solitary lives
and only come together when it's time to breed.
Up here, a female can advertise when she's ready to mate...
SHE CALLS
..pick the best of the males she attracts...
..and avoid any she doesn't fancy.
These lessons are now changing how we help captive-bred giant pandas
to play a more natural mating game.
This mother was raised by keepers.
Her chances of going back to the wild have gone.
But for her spirited cub...
CUB SQUEAKS
..there is a brighter future.
By being raised by her mother
in a more natural environment - away from keepers -
she's learning the skills she will need to survive in the wild.
It'll be at least two years before she's ready.
But if she shows enough independence,
she will be released into native forest nearby,
and have a fighting chance of entering into the mating game
on her own terms.
And now, her odds of doing so have never been better.
In the last 40 years, the Chinese authorities
have doubled the amount of protected panda habitat,
and have even more planned.
And, remarkably, in the same time,
the wild population has increased by nearly a thousand.
All without a human matchmaker in sight.
Left alone, wild pandas have created almost twice the number
that the very best artificial breeding programme
could have created.
Turns out giant pandas aren't that bad at breeding, after all.
If we are to reverse our impact on the natural world,
the solution is simple and very clear.
We must protect and regenerate natural habitats.
If we can do that,
then the mating game can be relied upon
to create future generations.
To film animals' mating behaviour,
camera teams need to be in the right place at the right time.
Most mating behaviours are infrequent, fleeting,
and often unpredictable.
Perhaps the rarest breeding event
the Mating Game team attempted to film
only happens once in every 17 years.
Starting next week, billions - if not trillions - of tiny invaders
will begin their assault on nearly all of the country
east of the Mississippi River.
We are talking about Brood X Cicadas.
They've been laying in wait for 17 years
until the time and temperature is right to begin
their deafening descent upon millions of Americans.
There was a gazillion of them.
They were just swarming crazy.
And the noise - it was just fascinating.
They're so thick around the tree in my front yard,
that the...odour, the stench is to the point
where it's almost unbearable, at least for me.
And when they first was coming out, I thought they were disgusting
but now I kind of like them!
To film this emergence of periodical cicadas,
the crew teamed up with lifelong cicada expert John Cooley.
So how did I get interested in cicadas?
Well, as... As you can see, they're a lot of fun to play with,
and they always have some new trick up their sleeves,
and this one has really decided that he likes this microphone
an awful lot, and so he's going to attempt to mate with it.
This emergence has only happened three times in his lifetime,
so John has more reason than most to be present at the event.
John's knowledge is extensive,
but one unique skill proves most useful
when filming their mating strategies...
HE WHISTLES
That was an interference buzz.
..he can speak cicada.
Let's do it.
HE WHISTLES
This gives the crew a great advantage in their attempts
to capture the courtship rituals
of these remarkable insects.
I can whistle louder and more pure tone than the male cicadas,
so I can give kind of a supernormal stimulus
that will get the female to wing flick.
And I can also duet to myself - I can whistle and...
HE CLICKS ..do that to get the male to call.
So what I did was I kind of stepped into that interaction
to get the female to wing flick
and also to get the male back into a mode
where he was calling. So that was manipulated.
And there goes a bluebird! BIRD CALLS
HE LAUGHS Sorry.
Anybody who says they're not good flyers
has never watched exactly what happened there,
where he flew right to it.
That was what we call extremely persuasive calling, where it's...
..ta-ta-ta-ta-ta-daaaaaaah -
little stutters in the beginning and a little bit of abdomen waggle -
I hear you got that on there -
where he's just, you know, doing that.
Yeah, I film a lot of insects, but to get them to do something
on cue, just like that, is pretty special.
The crew wait until nightfall,
and John takes them to the exact place where he predicts
the cicadas will emerge.
We got a call saying this is a really good nymph area
and they are literally crawling everywhere.
It's like the ground is kind of boiling up.
You can hear them crackling. CRACKLING
It sounds like fire, or sort of leaves rustling.
They're just everywhere and they've been climbing us -
we've had to tuck our shirts in cos they're climbing up our shirts!
But, yeah, it's really cool.
I did not expect to see them in these crazy numbers.
There are so many cicadas coming out.
Oh, yeah, there's a lot going up me.
Cicada nymphs everywhere.
One got all the way up my pant leg, even up my shorts.
There just must be just tens of thousands,
if not hundreds of thousands of cicadas here.
But as the crew crack on with their filming,
John begins to notice some unsettling details.
Oh, look at the bubbles of lymph that are forming now
where you just got walked all over.
And this thing is just hanging by a foot
at the very delicate part of moulting.
Ohhh! Ohh! Ohh!
It's just... It's losing... a quarter of its body fluid.
This is really pretty extreme, what's going on here.
But, you know, it's...
It isn't set up or anything - this is just what's happening
and they're all going up this one tree.
There's nowhere else to go where we are -
we're standing on a parking lot
and the rest of it's sort of a backyard.
So this is... This is kind of one of the ways that humans
modify the landscape, that...
..may not work out so well for the cicadas.
This is not natural cicada habitat...
To the best of what we know,
these are species that like edges - forest edges -
but this is a little bit different.
Kirk's house, in this setting right here,
and a lot of the places we've seen are lawns with trees coming up.
And these trees are very good places for the cicadas to lay eggs,
they do quite well - a lot of eggs go in the ground here,
a lot of them survive -
but when they come out, they only have one place to go -
it's back to that tree.
And so these isolated trees concentrate the cicadas in a way
that a natural forest edge doesn't.
The cicadas' 17-year cycle evolved during a time
when their surrounding habitat was predictably constant.
But this is no longer the case in our modern world.
As trees disappear from their habitat,
so do John's opportunities to understand their behaviours.
HE WHISTLES
His lifetime of work does help the crew piece together
the cicadas' strategy as they create the next generation.
HE WHISTLES
Yeah. Oh, let these guys go up.
We got more. It's going to be good.
This is it, kids.
It does not get any better than that.
However, John's work is far from done.
He has already uncovered many mysteries
surrounding these amazing creatures.
But with only one chance every 17 years,
he will soon run out of time.
What's the biggest mystery left with periodical cicadas?
Why?
Biggest mystery in my book is...
..given that there are 5,000-6,000 species of cicadas on the planet,
fewer than ten doing this - what were the special circumstances
that caused these to have this kind of life history?
And I think, ultimately, that's going to be the question
that I will not be able to answer in my remaining life.
So... Go to it, future generations!