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THUNDER

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Fresh water.

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Some animals can't breed without it.

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But correctly predicting its arrival

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can be the difference between
success...

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..and disaster.

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A giant African bullfrog.

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He's the size of a dinner plate,

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and he weighs half a kilo.

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He's been buried for the last six
months.

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Now he needs to find a mate...

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..and he doesn't have long.

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The newly-arrived rains have created
pools that trigger

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this year's mating jamboree.

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He's not the first to the party.

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And what is more, it will be all
over within the next 24 hours.

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This pool is already crowded with
males,

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like a downtown bar on a Friday
night.

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The females will soon arrive, ready
to lay their eggs.

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So this is where a male needs to be.

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But the battle-scarred faces are a
warning.

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This pond is not for the
faint-hearted.

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The males occupy the centre of the
pond and fight to hold

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a place there.

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Their calls will attract females,
but they will have to get

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to the centre if they're to meet the
strongest males.

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So if a male is going to mate,
that's where he needs to be.

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Which, for a latecomer, means
running the gauntlet.

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As any prize-fighter knows,

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dodging the hits is all part

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of winning the bout.

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And by doing what frogs do best,

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he reaches the centre unscathed.

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But his victory may not last long.

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New contenders are arriving.

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And this is one of those they've all

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been waiting for - a female.

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She wants to get to the centre too.

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After all, that's where she will
meet the strongest males.

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Swimming there underwater is her
best chance

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of reaching them.

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If a male is to mate, he must stay
in the centre.

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And he won't be able to do that
without a fight.

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These battles are no-holds-barred

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and could even be fatal.

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The latecomer accepts defeat.

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Not everyone can win in the mating
game.

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So it's his rival who holds the
centre of the pond

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and gets the females.

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The pool will soon dry up.

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So for this year, at least,

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he's missed his chance.

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Patagonia.

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On the high plateau,

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the spring thaw reveals

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a land of lakes.

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The water here comes not from rains,

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but from melting snow and ice.

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One of the rarest birds in the world
travels long distances to get

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here and breed.

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A hooded grebe, one of just 700 that
still survive.

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This is a female, so she's extremely
important if this species

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is to survive.

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She doesn't fight to claim a mate.

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She dances.

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The most experienced males are the
best dancers

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because they've done all this
before.

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So her challenge is to mate with one
of them.

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To do that,

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she will have to prove that she too
can dance.

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Just getting noticed would be a
start.

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Couples are pairing off all around,

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but her calls go unanswered.

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SHE CALLS

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Two is company, and as perhaps she
should have known,

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three is a crowd.

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A solitary male must be a better
possibility...

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..but he's not keen either.

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The lakes will freeze again before
long,

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so an invitation to dance is a very
welcome sign.

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THEY CALL

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But a rival for his affections
brings it to a swift end.

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And just as she was getting started.

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It's not going well.

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And if she can't have him...

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Perhaps finding a gift for him will
help.

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If she can find a partner, they will
nest among the milfoil

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plants when its flowers appear on
the water surface.

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Presenting strands of it is part of
the courtship ritual.

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She just needs to find someone to
give it to.

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His bending over backwards is
perhaps a sign

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that he is not interested.

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But who's this?

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FLAMENCO MUSIC PLAYS

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Could he be the dance partner that
she's been looking for?

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The timing of her moves is crucial.

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His precision shows that he's danced
this routine before,

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and more importantly, that he has
already been a parent.

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It's looking good.

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Finally, having completed the
performance,

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she seals their bond

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with a strand of milfoil...

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..a symbol of their commitment to
the work ahead.

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And one of hope for the survival of
this most endangered of birds.

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THEY CALL

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Many species migrate to lakes

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at a specific time in order to
breed.

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And for some, doing so comes at
great cost.

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This female sockeye salmon started
from far out in the Pacific Ocean

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and then continued up one of
Alaska's great rivers

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for a further 160 miles in order to
reach Iliamna Lake.

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Her arrival coincides with that of
others.

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Lots of them.

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Every summer, over three and one
half million sockeye come

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here. It's the largest salmon run in
the world.

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When they entered fresh water, they
stopped feeding,

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so the bodies of the females now
have room for developing eggs.

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But their energy is dwindling, and
they have yet to reach

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the spawning grounds that lie
upstream beyond the lake.

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But now they face more immediate
threats.

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While they try desperately to evade
the grizzly bears

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that attack them from the lakeshore,

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another threat comes from deep
water.

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Iliamna Lake is home to freshwater
seals.

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Despite these onslaughts,

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great numbers of the migrants
survive

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and swim on upstream, undeterred.

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There are far more salmon

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than the predators can eat.

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At last, they reach the shallow
streams.

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So far on their journey, there has
been safety in numbers.

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But now, at the spawning ground,

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it's every fish for itself.

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A female starts digging a nest

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and quickly attracts the attention
of a male.

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Quivering his fins is a male's
version of a pick-up line.

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She has a mate for now, but with
more fish

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continuing to arrive,

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room for nests is running out.

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Rival females try to steal her mate,
her nest or both.

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But she quickly sees them off.

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Nests now cover the stream bed.

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She releases her eggs...

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..he fertilises them...

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..and their work is done.

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But she doesn't start on a return
journey.

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This was always a one-way trip.

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None of the salmon, male or female,

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has eaten since leaving the ocean...

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..and now their exhausted bodies
begin to collapse.

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Pacific salmon only breed once

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in their lives, and having done so,

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they die.

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They seemed inexhaustible while
being driven

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by the urge to reproduce.

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These have won the mating game.

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But it cost them their lives to do
so.

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Salmon from the Pacific migrate

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in their search to find a safe place

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to lay their eggs.

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But when suitable sites for nests
are particularly rare, competition

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can get intense.

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These are the Appalachian Mountains
in the eastern United States.

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Here, in just a very few rivers,
live monsters

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with a truly ancient ancestry.

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Some call them snot otters...

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..others mud devils.

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Their most common name, however, is
hellbender.

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But common they are not.

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Hellbenders are very rare indeed.

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This male is very well camouflaged,
and he rarely moves.

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So in practice, he's almost
invisible.

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Hellbenders are a kind of giant
salamander.

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He may grow up to 60 centimetres
long.

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They're usually very shy,

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but during the few weeks each year

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when summer turns to autumn and the
river starts to flow

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more strongly, the hellbenders start
to move around.

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He's looking for somewhere to nest -

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a rock, but not just any rock.

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This particular slab he knows well.

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He's chosen it before.

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Such rare, heavier stones don't get
easily washed away.

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The space underneath it is well
hidden and the current flowing

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swiftly through it will bring the
oxygen needed

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for developing eggs.

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The females are already on the move,

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battling their way upstream towards
him.

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He just needs to hold on to his den
until they get there.

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But every year other males arrive to
challenge him.

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They come at him from all sides.

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They're even lining up to try and
take over his den.

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But as he fights, the strong current
carries him away from the den

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and another rival sees a chance.

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Back in the nick of time.

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Exhausting.

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00:20:29,320 --> 00:20:32,920
But this is the time when he has to
secure a mate.

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With temperatures dropping, the
turbulent winter water becomes

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00:20:42,520 --> 00:20:45,640
rich in oxygen needed by developing
eggs.

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00:20:48,560 --> 00:20:51,640
These days, increasing erosion of
the land

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00:20:51,640 --> 00:20:54,960
is blocking hellbender dens with
sediment.

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00:20:54,960 --> 00:20:58,760
So now this one, more than ever, is
worth fighting for.

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He's been forced out of his home.

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00:21:26,080 --> 00:21:29,880
But after all he's been through,
he's not about to concede.

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His rival gives up.

206
00:21:46,560 --> 00:21:48,360
He is still the boss.

207
00:21:57,440 --> 00:22:00,880
And now, at last, a welcome visitor.

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00:22:04,360 --> 00:22:07,960
He greets her with what is known to
hellbender watchers

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00:22:07,960 --> 00:22:11,000
as a courtship kiss.

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00:22:11,000 --> 00:22:13,400
Her belly is full of eggs

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00:22:13,400 --> 00:22:15,600
and she slips in beside him.

212
00:22:20,520 --> 00:22:25,600
Then strangely, after days of
brawling,

213
00:22:25,600 --> 00:22:29,000
rival males are also allowed to
enter.

214
00:22:33,800 --> 00:22:37,320
Perhaps he's now too exhausted to
fight

215
00:22:37,320 --> 00:22:40,120
or has some strategy we don't know
about.

216
00:22:45,040 --> 00:22:48,720
Other females then visit the den and
add their eggs

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00:22:48,720 --> 00:22:52,400
to the communal clutch, which he
will protect.

218
00:22:55,200 --> 00:22:59,760
He has become a baby-sitter for the
whole hellbender community.

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00:23:02,320 --> 00:23:07,400
In the freshwater world, it's often
the males who look after the young.

220
00:23:10,520 --> 00:23:13,960
But even when these duties are left
to one parent,

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00:23:13,960 --> 00:23:18,200
the mating game may still demand
carefully timed coordination.

222
00:23:19,600 --> 00:23:21,640
THUNDER RUMBLES

223
00:23:25,800 --> 00:23:30,080
In South America, water levels
across the Amazon basin rise

224
00:23:30,080 --> 00:23:32,480
and fall with the seasonal rains.

225
00:23:38,840 --> 00:23:42,880
If this male splash tetra is going
to mate successfully,

226
00:23:42,880 --> 00:23:45,280
he needs the water level to rise.

227
00:23:47,760 --> 00:23:50,120
It's low at the moment,

228
00:23:50,120 --> 00:23:54,240
but every drop of rain brings it
closer to his requirements.

229
00:24:10,000 --> 00:24:15,240
As the rain begins to ease, he tries
to find out if he's high enough yet.

230
00:24:25,880 --> 00:24:30,360
A few well-aimed splashes help him
to estimate the distance.

231
00:24:36,840 --> 00:24:39,600
He's looking for a place

232
00:24:39,600 --> 00:24:42,160
where a female can lay her eggs away
from predators.

233
00:24:46,160 --> 00:24:48,840
But to assess the situation
properly,

234
00:24:48,840 --> 00:24:51,880
he does something truly
extraordinary.

235
00:25:03,960 --> 00:25:06,680
The water he splashes on to the leaf

236
00:25:06,680 --> 00:25:10,440
momentarily delays his fall back
into the river.

237
00:25:15,200 --> 00:25:18,000
Now he turns his attention to a
female.

238
00:25:21,520 --> 00:25:24,880
Because what comes next needs the
two of them.

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00:25:33,960 --> 00:25:36,040
If they're to mate successfully,

240
00:25:36,040 --> 00:25:38,680
they must hit the leaf
simultaneously.

241
00:26:01,800 --> 00:26:06,920
After she's laid her eggs, he
spreads his jaw and fins

242
00:26:06,920 --> 00:26:10,960
to help him cling on just long
enough to fertilise them.

243
00:26:27,280 --> 00:26:31,040
This extraordinary way of laying
keeps the eggs safe

244
00:26:31,040 --> 00:26:33,840
from underwater predators.

245
00:26:33,840 --> 00:26:37,240
But for him, it creates one final
challenge.

246
00:26:40,400 --> 00:26:44,200
Out of the water, the eggs are in
danger of drying out.

247
00:26:48,040 --> 00:26:49,480
Problem solved.

248
00:26:51,760 --> 00:26:55,680
With the female gone, he alone takes
the responsibility

249
00:26:55,680 --> 00:26:59,240
for ensuring their eggs will stay
wet

250
00:26:59,240 --> 00:27:01,760
until they hatch in a few days'
time.

251
00:27:04,560 --> 00:27:08,960
The splash tetra pair had to
synchronise their moves,

252
00:27:08,960 --> 00:27:13,760
but in other cases, the mating game
requires thousands of individuals

253
00:27:13,760 --> 00:27:15,400
to work in harmony.

254
00:27:17,720 --> 00:27:20,360
In the Great Rift Valley of East
Africa,

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00:27:20,360 --> 00:27:24,200
fractures in the Earth's crust have
been filled with fresh water

256
00:27:24,200 --> 00:27:27,320
over millions of years by the annual
rains.

257
00:27:29,920 --> 00:27:31,960
But in many of these lakes,

258
00:27:31,960 --> 00:27:34,040
the water doesn't stay fresh for
long.

259
00:27:36,560 --> 00:27:39,960
Scalding volcanic waters from deep
below ground

260
00:27:39,960 --> 00:27:43,280
carry up salts dissolved from the
rocks.

261
00:27:46,200 --> 00:27:50,320
Not much is able to live in these
caustic lakes.

262
00:27:50,320 --> 00:27:52,960
But one kind of bird flocks to them.

263
00:27:57,320 --> 00:28:00,560
Lesser flamingos gather here in
millions

264
00:28:00,560 --> 00:28:03,560
to feed on the microscopic algae
that develop

265
00:28:03,560 --> 00:28:05,840
in these super salty waters.

266
00:28:34,240 --> 00:28:39,040
A male flamingo must be well-fed
before he can mate.

267
00:28:42,760 --> 00:28:46,160
And the algae and other
microorganisms that flourish

268
00:28:46,160 --> 00:28:51,240
in these briny waters are the only
things that lesser flamingos eat.

269
00:28:57,800 --> 00:29:01,520
But these organisms also contain
toxins.

270
00:29:03,280 --> 00:29:06,120
The birds do not digest these
substances,

271
00:29:06,120 --> 00:29:09,160
but store them in their plumage out
of harm's way.

272
00:29:09,160 --> 00:29:11,920
And it's these that turns them pink.

273
00:29:13,400 --> 00:29:17,320
The more well-fed he is, the rosier
he becomes

274
00:29:17,320 --> 00:29:20,440
and the more attractive he is to his
potential mate.

275
00:29:28,240 --> 00:29:30,040
As the water gets deeper,

276
00:29:30,040 --> 00:29:33,440
the flamingos have to find new ways
to collect their food.

277
00:29:51,040 --> 00:29:54,080
He's getting pinker with every
mouthful.

278
00:29:57,840 --> 00:30:00,360
There is a female out there for him,

279
00:30:00,360 --> 00:30:04,440
but he can only find her when she
and all his friends in the flock

280
00:30:04,440 --> 00:30:07,760
are pink enough to begin their
courtship dance.

281
00:30:13,440 --> 00:30:18,080
Each morning, the birds gather
around the hot springs to drink

282
00:30:18,080 --> 00:30:21,320
and show off their newly pink
feathers.

283
00:30:21,320 --> 00:30:24,640
It's a chance to see who is ready
for dancing.

284
00:30:28,160 --> 00:30:30,360
With his plumage in proper order,

285
00:30:30,360 --> 00:30:34,400
he's keen to get the party started
and show off to a female.

286
00:30:42,120 --> 00:30:45,800
After weeks of feeding, with the
whole flock in full colour,

287
00:30:45,800 --> 00:30:50,360
it seems that everyone is finally in
the mood.

288
00:30:59,360 --> 00:31:02,520
Dance fever spreads throughout the
flock.

289
00:31:04,040 --> 00:31:07,400
And, at last, the performance
begins.

290
00:31:12,200 --> 00:31:14,960
Both males and females are dancing.

291
00:31:19,800 --> 00:31:23,000
Groups merge and co-ordinate their
courtship.

292
00:31:33,800 --> 00:31:36,600
Laying their eggs at exactly the
same time

293
00:31:36,600 --> 00:31:39,920
maximises their chicks' chance of
survival,

294
00:31:39,920 --> 00:31:42,000
and dancing together ensures

295
00:31:42,000 --> 00:31:44,440
that they're all in sync with one
another.

296
00:31:51,280 --> 00:31:54,080
If two birds find what they're
looking for,

297
00:31:54,080 --> 00:31:56,280
they leave the dancing group.

298
00:31:58,320 --> 00:32:02,560
Exactly how a partner is chosen, we
don't fully understand.

299
00:32:03,760 --> 00:32:07,600
But it seems that some flamingos try
to select a partner

300
00:32:07,600 --> 00:32:11,400
with the same shade of pink as
themselves,

301
00:32:11,400 --> 00:32:14,360
though how they judge that is still
a mystery.

302
00:32:35,480 --> 00:32:39,080
Lesser flamingos may have to wait
many years

303
00:32:39,080 --> 00:32:43,320
before the water conditions are
right to enable them to mate.

304
00:32:45,560 --> 00:32:48,840
But there are lakes where securing a
mate

305
00:32:48,840 --> 00:32:51,880
can be a year-round preoccupation.

306
00:32:54,880 --> 00:32:59,560
Lake Tanganyika in East Africa is
enormous,

307
00:32:59,560 --> 00:33:02,440
deep and warm.

308
00:33:02,440 --> 00:33:05,320
And it's been this way for millions
of years.

309
00:33:07,360 --> 00:33:11,680
Long-term stability allows long-term
mating strategies.

310
00:33:13,160 --> 00:33:17,240
This pile of shells, for example, is
constantly getting bigger.

311
00:33:19,720 --> 00:33:22,480
It's likely to be several decades
old.

312
00:33:23,680 --> 00:33:27,480
It's certainly older than the
current ruler,

313
00:33:27,480 --> 00:33:29,640
a male callipterus fish.

314
00:33:36,520 --> 00:33:39,040
He is an underwater architect

315
00:33:39,040 --> 00:33:42,880
and busy collecting empty snail
shells to add to his castle.

316
00:33:56,840 --> 00:34:00,440
His pile is home to over 20 females,

317
00:34:00,440 --> 00:34:02,840
who lay their eggs inside the
shells.

318
00:34:07,880 --> 00:34:11,560
He does his best to ensure that they
only mate with him.

319
00:34:13,160 --> 00:34:15,480
And doing so is a full-time job.

320
00:34:27,240 --> 00:34:29,840
There are eels here

321
00:34:29,840 --> 00:34:33,080
that would happily make a meal of a
shell full of eggs.

322
00:34:39,360 --> 00:34:41,880
But not if the king can prevent it.

323
00:35:00,160 --> 00:35:03,800
He stole this castle of shells from
a previous owner.

324
00:35:05,560 --> 00:35:07,920
And if he lets his guard down,

325
00:35:07,920 --> 00:35:10,680
someone will certainly take it from
him.

326
00:35:22,520 --> 00:35:26,640
Gangs of marauding bachelors are a
constant nuisance.

327
00:35:34,520 --> 00:35:37,600
And while the king of the shell
castle is busy

328
00:35:37,600 --> 00:35:39,280
proving how tough he is...

329
00:35:40,600 --> 00:35:42,800
..he's being watched by a sneak.

330
00:35:46,600 --> 00:35:50,480
He belongs to the same species, but
he's a dwarf.

331
00:35:52,160 --> 00:35:55,000
He won't grow any bigger and he's
ready to mate.

332
00:35:56,200 --> 00:35:59,440
He just needs to get near enough to
a female.

333
00:36:01,200 --> 00:36:05,280
He is only one 50th of the weight of
the king

334
00:36:05,280 --> 00:36:09,080
and if he can reach a shell with a
female inside,

335
00:36:09,080 --> 00:36:12,760
he's small enough to slip inside and
mate with her.

336
00:36:23,240 --> 00:36:24,480
Busted.

337
00:36:26,440 --> 00:36:27,960
Back to square one.

338
00:36:33,680 --> 00:36:37,840
Every now and then, the king has to
tackle someone his own size.

339
00:36:40,320 --> 00:36:44,000
A serious contender is attempting to
overthrow him.

340
00:36:45,360 --> 00:36:47,560
Could this be a chance for the
dwarf?

341
00:37:01,800 --> 00:37:03,040
He's close.

342
00:37:09,240 --> 00:37:12,680
Once inside with the female, he can
fertilise her eggs

343
00:37:12,680 --> 00:37:15,880
without the king ever knowing that
he's been there.

344
00:37:21,640 --> 00:37:23,720
He might not be the biggest fish,

345
00:37:23,720 --> 00:37:28,200
but he's definitely got one of the
cheekiest strategies in the lake.

346
00:37:30,480 --> 00:37:34,520
These shenanigans continue month
after month,

347
00:37:34,520 --> 00:37:38,240
thanks to the lake's extremely
stable environment.

348
00:37:41,520 --> 00:37:45,920
But some environments in southern
Africa are far from stable.

349
00:37:48,400 --> 00:37:52,520
The grassy plains in Zambia change
radically every year.

350
00:37:55,000 --> 00:37:56,400
They flood.

351
00:37:59,560 --> 00:38:04,080
Many are home to lechwe, one of the
most aquatic of antelopes.

352
00:38:09,240 --> 00:38:13,600
With hooves that splay out wide and
extra-strong hind legs,

353
00:38:13,600 --> 00:38:17,880
this female is able to travel across
even deep swamps.

354
00:38:21,800 --> 00:38:25,240
But their watery world is now
shrinking.

355
00:38:25,240 --> 00:38:27,240
It hasn't rained in months.

356
00:38:29,600 --> 00:38:35,040
Before long, these swamp meadows on
which the lechwe depend will be dry.

357
00:38:37,880 --> 00:38:41,400
They turn into dusty plains with
just a few

358
00:38:41,400 --> 00:38:43,160
small, muddy water holes.

359
00:38:49,360 --> 00:38:52,960
This is the best time for a female
to find a mate.

360
00:38:57,320 --> 00:38:58,840
In a few months' time,

361
00:38:58,840 --> 00:39:02,160
when her young are born, things will
be easier.

362
00:39:03,440 --> 00:39:06,480
So it's at this point that she
starts to think

363
00:39:06,480 --> 00:39:07,960
about getting a partner.

364
00:39:12,720 --> 00:39:17,520
Most of the time, male and female
lechwe live quite separate lives.

365
00:39:21,680 --> 00:39:24,520
She is now at her most fertile,

366
00:39:24,520 --> 00:39:28,400
and she starts to leave the safety
of the female herd.

367
00:39:31,600 --> 00:39:34,480
Alone, she's more vulnerable,

368
00:39:34,480 --> 00:39:36,840
and the long, dry grass away

369
00:39:36,840 --> 00:39:40,480
from the swamp can only too easily
conceal a lion.

370
00:39:45,080 --> 00:39:48,760
She mustn't stay away from the other
females for long.

371
00:39:54,280 --> 00:39:57,600
To survive here, you must be fit and
strong,

372
00:39:57,600 --> 00:40:00,760
and those are exactly the
characteristics

373
00:40:00,760 --> 00:40:02,320
she values in a mate.

374
00:40:04,840 --> 00:40:09,160
The best place to find a male with
such qualities is even further

375
00:40:09,160 --> 00:40:10,640
away from the water.

376
00:40:13,240 --> 00:40:16,320
Out here on the dry plains, the
males are already

377
00:40:16,320 --> 00:40:17,920
competing for females.

378
00:40:26,760 --> 00:40:30,080
Stabbing the ground with his horns
is a male's way

379
00:40:30,080 --> 00:40:32,280
of demonstrating his strength.

380
00:40:40,960 --> 00:40:43,080
His next move is more direct.

381
00:40:58,760 --> 00:41:00,680
She remains unconvinced,

382
00:41:00,680 --> 00:41:03,040
but this performance has caught

383
00:41:03,040 --> 00:41:05,200
the attention of a rival male.

384
00:41:16,000 --> 00:41:18,560
She's here to mate with the
strongest male,

385
00:41:18,560 --> 00:41:22,680
and these battles will help her
decide which one that is.

386
00:41:29,280 --> 00:41:31,120
But they'd better get a move on.

387
00:41:31,120 --> 00:41:34,040
There are plenty of other males that
she could choose.

388
00:41:45,520 --> 00:41:47,480
Having seen off his rival,

389
00:41:47,480 --> 00:41:49,760
he resumes his overtures to her.

390
00:41:58,000 --> 00:42:01,640
Perhaps because they're vulnerable
when they get together, their union

391
00:42:01,640 --> 00:42:03,400
is very brief.

392
00:42:08,120 --> 00:42:12,600
Afterwards, he tries to remain
close, but she has other ideas.

393
00:42:17,520 --> 00:42:20,560
Her instinct is to seek safety in
numbers.

394
00:42:22,600 --> 00:42:25,360
She's got what she came for and she
heads back

395
00:42:25,360 --> 00:42:27,240
to the female herd.

396
00:42:31,920 --> 00:42:35,240
She's started her pregnancy at just
the right time

397
00:42:35,240 --> 00:42:39,640
to give her offspring, when it
arrives, the best start in life.

398
00:42:45,840 --> 00:42:50,720
In Brazil, this wetland, the
Pantanal, also dries out every

399
00:42:50,720 --> 00:42:54,120
year, and this is the time when,

400
00:42:54,120 --> 00:42:56,320
like the lechwe, caiman breed.

401
00:43:00,560 --> 00:43:05,040
But if he is to survive long enough
to mate, this male will have to find

402
00:43:05,040 --> 00:43:06,440
water of some kind.

403
00:43:08,560 --> 00:43:12,080
The pool he came from has now dried
up.

404
00:43:12,080 --> 00:43:15,120
If he doesn't find a new one, he
will die.

405
00:43:19,960 --> 00:43:23,360
The land is littered with the
remains of those who didn't reach

406
00:43:23,360 --> 00:43:24,840
water in time.

407
00:43:32,400 --> 00:43:34,760
But he is heading for one place

408
00:43:34,760 --> 00:43:36,800
where he knows that water

409
00:43:36,800 --> 00:43:39,560
will remain throughout the dry
season.

410
00:43:47,920 --> 00:43:49,280
He's made it.

411
00:43:56,920 --> 00:43:59,640
And he is not the only one to have
done so.

412
00:44:05,120 --> 00:44:07,440
So have thousands of others.

413
00:44:16,880 --> 00:44:19,480
And it's not only water that's here.

414
00:44:21,280 --> 00:44:23,120
There are females as well.

415
00:44:37,560 --> 00:44:40,240
Late afternoon is a time to bask.

416
00:44:49,400 --> 00:44:51,840
And although the dwindling pool

417
00:44:51,840 --> 00:44:54,480
is now very crowded, they tolerate

418
00:44:54,480 --> 00:44:56,520
CAIMAN GRUNTS
each other...

419
00:44:56,520 --> 00:44:58,600
..for the time being.

420
00:45:10,600 --> 00:45:13,000
But by first light,

421
00:45:13,000 --> 00:45:14,760
the mood has changed.

422
00:45:16,920 --> 00:45:20,680
Surviving the drought is no longer a
male's top priority.

423
00:45:22,160 --> 00:45:26,160
If babies are to hatch out when the
high water returns and life

424
00:45:26,160 --> 00:45:29,440
is easier, he needs to mate soon.

425
00:45:31,400 --> 00:45:34,760
And if he's to do that, he must
claim a patch of this water

426
00:45:34,760 --> 00:45:36,000
as his own...

427
00:45:37,400 --> 00:45:40,080
..because there isn't room for
everyone.

428
00:45:47,800 --> 00:45:52,640
All around, males begin to assert
their dominance.

429
00:46:01,440 --> 00:46:03,880
The newcomer must stand his ground

430
00:46:03,880 --> 00:46:06,240
if he wants to remain a contender.

431
00:46:09,680 --> 00:46:12,680
But he must also know when to back
down.

432
00:46:14,680 --> 00:46:16,800
And there is usually someone

433
00:46:16,800 --> 00:46:18,760
smaller for him to pick on.

434
00:46:29,160 --> 00:46:33,000
By mid-morning, an uneasy calm
descends.

435
00:46:37,040 --> 00:46:39,760
The newcomer has secured a patch.

436
00:46:42,120 --> 00:46:46,360
But he still has to convince a
female that he's worth mating with.

437
00:46:50,360 --> 00:46:52,800
CAIMAN GRUNTS
And he has a plan.

438
00:46:54,560 --> 00:46:57,160
It starts with a grunt.

439
00:46:57,160 --> 00:47:00,480
GRUNTING CONTINUES

440
00:47:00,480 --> 00:47:05,520
The next part of his courtship song,
we can't hear, but we can see it.

441
00:47:31,040 --> 00:47:34,760
It is not the muscular movement of
his body that make

442
00:47:34,760 --> 00:47:36,120
the water dance,

443
00:47:36,120 --> 00:47:38,560
but the low frequency of his call.

444
00:47:44,160 --> 00:47:47,080
This song contest may be inaudible

445
00:47:47,080 --> 00:47:49,760
to us, but not to female caiman.

446
00:47:59,120 --> 00:48:01,880
It attracts them from far and wide.

447
00:48:22,680 --> 00:48:25,680
Despite his rival's best efforts,

448
00:48:25,680 --> 00:48:28,320
it is the newcomer who seems

449
00:48:28,320 --> 00:48:30,880
to be getting it right,

450
00:48:30,880 --> 00:48:34,000
because he's got company.

451
00:48:38,680 --> 00:48:41,040
The water is so murky that actual

452
00:48:41,040 --> 00:48:42,960
mating is rarely visible...

453
00:48:44,520 --> 00:48:47,960
..but every now and then two caiman
appear a little more interested

454
00:48:47,960 --> 00:48:49,680
in one another,

455
00:48:49,680 --> 00:48:53,400
and something is clearly going on
below the surface.

456
00:49:05,360 --> 00:49:07,760
Timing is crucial...

457
00:49:07,760 --> 00:49:09,760
THUNDER RUMBLES

458
00:49:09,760 --> 00:49:12,440
..as it is for all animals that come

459
00:49:12,440 --> 00:49:15,160
to breed in those variable and only

460
00:49:15,160 --> 00:49:19,160
too unpredictable of the Earth's
environments,

461
00:49:19,160 --> 00:49:21,000
its fresh waters.

462
00:49:40,160 --> 00:49:44,280
In order to tell the story of the
breeding migration of red salmon,

463
00:49:44,280 --> 00:49:47,640
the Mating Game team had to choose
the best location.

464
00:49:50,680 --> 00:49:55,640
After months of research, assistant
producer Olly Scholey struck gold.

465
00:49:56,800 --> 00:49:59,760
So the reason we've come on this
shoot really stems back to me

466
00:49:59,760 --> 00:50:01,920
just sitting on Instagram on a
Sunday evening

467
00:50:01,920 --> 00:50:06,040
and just scrolling through pictures,
and I saw this one photo

468
00:50:06,040 --> 00:50:10,720
of Iliamna Lake that Jason had taken
and was just completely sold on

469
00:50:10,720 --> 00:50:12,960
coming here to film red salmon.

470
00:50:12,960 --> 00:50:16,120
There's gin-clear water, and you can
just immediately see

471
00:50:16,120 --> 00:50:19,360
in that picture that there's a
really fascinating spawning dynamic

472
00:50:19,360 --> 00:50:20,720
going on here.

473
00:50:21,960 --> 00:50:25,080
Jason Ching is a local salmon
biologist

474
00:50:25,080 --> 00:50:28,080
and world-renowned wildlife
photographer.

475
00:50:28,080 --> 00:50:33,120
He has taken the crew to the exact
location where he took his picture.

476
00:50:37,360 --> 00:50:41,440
Cinematographer David Reichert is
hoping to film the details

477
00:50:41,440 --> 00:50:43,800
of the salmon courtship as never
before.

478
00:50:45,720 --> 00:50:49,360
Filming underwater, one of the big
struggles is the visibility,

479
00:50:49,360 --> 00:50:51,600
being able to see a nice, sharp
image.

480
00:50:51,600 --> 00:50:55,640
So when I saw the picture from here,
that was really exciting for me.

481
00:50:55,640 --> 00:50:59,000
To be able to work in that kind of
water is... You know

482
00:50:59,000 --> 00:51:02,360
you're going to be bringing home
really beautiful stuff.

483
00:51:02,360 --> 00:51:06,520
The crew also want to capture the
spectacle of this huge salmon run

484
00:51:06,520 --> 00:51:07,720
from the air...

485
00:51:09,560 --> 00:51:12,080
...and this aerial perspective shows
them

486
00:51:12,080 --> 00:51:14,440
something completely unexpected.

487
00:51:15,520 --> 00:51:17,960
Just keep it down. Yeah, you've got
control.

488
00:51:19,040 --> 00:51:22,160
Hang on, hold up. There's a seal,
bottom left.

489
00:51:22,160 --> 00:51:24,760
OK, I'm moving forward.

490
00:51:24,760 --> 00:51:29,960
Freshwater seals, an incredibly rare
animal, were predating

491
00:51:29,960 --> 00:51:33,400
upon the salmon as they kind of
bunched up in this river mouth.

492
00:51:33,400 --> 00:51:35,680
Oh, he's right on one.

493
00:51:35,680 --> 00:51:40,320
This seal behaviour has never been
filmed before, and the crew now

494
00:51:40,320 --> 00:51:43,960
have to overcome the far harder
challenge of documenting

495
00:51:43,960 --> 00:51:46,120
it from underwater.

496
00:51:46,120 --> 00:51:48,280
He's away down...

497
00:51:48,280 --> 00:51:51,120
Freshwater seals are extremely shy,

498
00:51:51,120 --> 00:51:53,440
so in order to do this, the crew

499
00:51:53,440 --> 00:51:55,920
need to use remote cameras.

500
00:51:55,920 --> 00:51:58,840
Hopefully, these are going to
capture that seal behaviour,

501
00:51:58,840 --> 00:52:01,080
seals attacking the salmon,

502
00:52:01,080 --> 00:52:03,800
and that'll go with the incredible

503
00:52:03,800 --> 00:52:06,360
drone shots that we've already got.

504
00:52:10,200 --> 00:52:12,920
Stop. Yep. Perfect.

505
00:52:12,920 --> 00:52:15,440
Oh, it looks good, mate.

506
00:52:15,440 --> 00:52:17,280
Horizon's good.

507
00:52:17,280 --> 00:52:20,280
So if they come in, if they come in
and feed here,

508
00:52:20,280 --> 00:52:22,760
we're going to get some pictures.

509
00:52:25,320 --> 00:52:27,520
Here he comes, here he comes.

510
00:52:27,520 --> 00:52:29,440
He's just sniffing around right now.

511
00:52:29,440 --> 00:52:31,800
So we've just started getting some

512
00:52:31,800 --> 00:52:33,880
little bits of the seals coming in,

513
00:52:33,880 --> 00:52:36,760
but we're not quite in the right
place. We haven't been in quite the

514
00:52:36,760 --> 00:52:39,080
right place, but now we've
positioned

515
00:52:39,080 --> 00:52:41,760
it right where we think that this
seal is going to stop

516
00:52:41,760 --> 00:52:45,080
and wait and then jump up and grab a
fish.

517
00:52:45,080 --> 00:52:46,680
Fingers crossed, it works.

518
00:52:46,680 --> 00:52:48,200
Coming in.

519
00:52:48,200 --> 00:52:51,480
OK, he's getting in a good place for
this one. Yeah.

520
00:52:51,480 --> 00:52:54,840
After days of catching mere
glimpses... That's a good shot.

521
00:52:54,840 --> 00:52:58,920
..the crew finally have their
cameras in the perfect position.

522
00:52:58,920 --> 00:53:02,600
Oh, good, good, good, good, good,
good, good, good, good! Oh! Oh!

523
00:53:02,600 --> 00:53:05,360
Oh, so close! He missed!

524
00:53:05,360 --> 00:53:07,600
So, there he is. See him coming up
there?

525
00:53:09,320 --> 00:53:10,960
He might be about to charge again.

526
00:53:10,960 --> 00:53:12,960
Oh! Got him!

527
00:53:14,840 --> 00:53:16,520
Oh, mate, on both cameras!

528
00:53:18,760 --> 00:53:20,880
It's a great success, but it was

529
00:53:20,880 --> 00:53:23,040
only going to be a matter of time

530
00:53:23,040 --> 00:53:25,360
before the crew meet the salmon's

531
00:53:25,360 --> 00:53:27,720
other predators.

532
00:53:29,240 --> 00:53:31,600
BEAR GRUNTS
There's a bear.

533
00:53:40,400 --> 00:53:43,960
Oh. Get ready with the cameras. OK.

534
00:53:43,960 --> 00:53:46,920
It's dangerous to surprise a
grizzly,

535
00:53:46,920 --> 00:53:48,800
so Olly lets the bear know

536
00:53:48,800 --> 00:53:50,640
that the crew are close.

537
00:53:51,640 --> 00:53:54,640
Hey, bear! Hey, bear!

538
00:53:54,640 --> 00:53:57,080
I'm watching this bear. Yeah.

539
00:53:57,080 --> 00:53:58,680
Hey, bear. Hey, bear.

540
00:53:59,800 --> 00:54:01,800
That's close enough.

541
00:54:01,800 --> 00:54:04,040
Hey, bear. Hey, bear.

542
00:54:04,040 --> 00:54:05,600
You stay back.

543
00:54:05,600 --> 00:54:07,880
Like, obviously, hindsight is a
lovely thing.

544
00:54:07,880 --> 00:54:11,600
We're probably a bit too close to
the river and to all the fish.

545
00:54:11,600 --> 00:54:13,920
I think we just need to move back a
little bit and just stay

546
00:54:13,920 --> 00:54:15,200
a bit further away.

547
00:54:16,480 --> 00:54:19,040
This is his river, not our river,

548
00:54:19,040 --> 00:54:21,600
so we'll let him catch his lunch.

549
00:54:23,080 --> 00:54:25,560
I mean, it could be amazing because
we've got this really

550
00:54:25,560 --> 00:54:28,360
clear water. We could get some
really unique shots of bears walking

551
00:54:28,360 --> 00:54:30,960
through salmon and actually able to
see the whole bear.

552
00:54:30,960 --> 00:54:33,920
The slight downside to that is
either the bear treads on the camera

553
00:54:33,920 --> 00:54:36,440
or grabs it or does anything to it.

554
00:54:36,440 --> 00:54:39,520
It's... Basically the plan is to put
quite an expensive camera

555
00:54:39,520 --> 00:54:42,480
underneath the feet of a charging
bear.

556
00:54:42,480 --> 00:54:43,520
So...

557
00:54:44,920 --> 00:54:49,240
David positions the remote cameras
in deeper water in the hope

558
00:54:49,240 --> 00:54:52,240
of capturing an extremely rare
perspective

559
00:54:52,240 --> 00:54:54,120
of a hunting grizzly bear.

560
00:54:57,400 --> 00:54:59,960
Still coming? Yeah. Maybe get out.

561
00:55:04,240 --> 00:55:05,920
OK, got him. Oh, nice!

562
00:55:06,960 --> 00:55:09,600
Yes! OK, we got him.

563
00:55:09,600 --> 00:55:13,240
It works, and they capture a
salmon's-eye view of one

564
00:55:13,240 --> 00:55:17,840
of the biggest challenges they face
on their breeding migration.

565
00:55:21,960 --> 00:55:25,280
Although the plan for getting the
camera close to the bear works

566
00:55:25,280 --> 00:55:27,360
maybe a little bit too well!

567
00:55:35,600 --> 00:55:38,600
We have to look at one upside down
now because the bear's completely

568
00:55:38,600 --> 00:55:41,000
HE LAUGHS
rolled it!

569
00:55:41,000 --> 00:55:42,400
Is it intact?

570
00:55:42,400 --> 00:55:46,600
Miraculously, the camera survives,
and it's now time for David

571
00:55:46,600 --> 00:55:49,080
to finish telling the salmon story

572
00:55:49,080 --> 00:55:51,400
by trying to film them spawning.

573
00:55:58,240 --> 00:56:01,840
So we have found just a magical part
of the world.

574
00:56:03,800 --> 00:56:06,800
Just the amount of activity here,

575
00:56:06,800 --> 00:56:09,040
it's just epic, what is happening.

576
00:56:13,400 --> 00:56:15,400
What has really surprised me

577
00:56:15,400 --> 00:56:17,360
about spending so much time

578
00:56:17,360 --> 00:56:19,800
with these salmon is really how

579
00:56:19,800 --> 00:56:22,240
intricate this behaviour is.

580
00:56:22,240 --> 00:56:24,920
There's so much going on with these

581
00:56:24,920 --> 00:56:26,920
fish as they compete

582
00:56:26,920 --> 00:56:29,040
to be really the mating pair.

583
00:56:32,520 --> 00:56:36,200
Yeah, fish... Like, fish sex is, you
know... I feel,

584
00:56:36,200 --> 00:56:38,640
HE LAUGHS
like, a little awkward...

585
00:56:38,640 --> 00:56:41,240
..watching that for hours, but they
don't seem

586
00:56:41,240 --> 00:56:43,160
to care, so I guess it's cool.

587
00:56:44,920 --> 00:56:47,280
With some luck and some ingenuity,

588
00:56:47,280 --> 00:56:49,360
the team capture almost every

589
00:56:49,360 --> 00:56:51,880
challenge that the red salmon must

590
00:56:51,880 --> 00:56:53,640
overcome in order to win

591
00:56:53,640 --> 00:56:55,120
the mating game.

592
00:57:02,240 --> 00:57:04,240
Next time...

593
00:57:04,240 --> 00:57:06,920
The need to breed drives all life,

594
00:57:06,920 --> 00:57:08,560
but the challenges faced

595
00:57:08,560 --> 00:57:09,880
are by no means equal.

596
00:57:11,120 --> 00:57:13,040
Some in the mating game must

597
00:57:13,040 --> 00:57:15,120
overcome overwhelming odds

598
00:57:15,120 --> 00:57:17,760
to have any chance of success,

599
00:57:17,760 --> 00:57:20,720
and the changes WE are creating

600
00:57:20,720 --> 00:57:22,880
are the greatest challenge of all.

601
00:57:22,880 --> 00:57:25,000
PANDA WHINES