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One continent on our planet changes

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more dramatically than any other.

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North America.

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Whole landscapes here can be transformed
in a matter of minutes.

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And all life has to be ready
to seize the moment.

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Getting it wrong can be disastrous.

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But time it correctly,
and there can be great rewards.

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This is a land of opportunity.

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Over 100 times the size of Great Britain,

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North America stretches from just above
the equator almost to the North Pole.

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Temperatures can range
from 50 degrees Celsius to minus 40.

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The coldest wilderness of all
lies in the Arctic north.

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Here, in Canada's Yukon Territory,
winter is brutal.

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Many animals have travelled south
to avoid the worst of the cold.

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For those which stay behind,

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life becomes very hard indeed.

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A Canadian lynx.

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No other kind of cat, anywhere,

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lives farther north than this one.

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The search for food could take him
hundreds of miles.

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A snowshoe hare.

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This could be a chance.

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He's lost the element of surprise.

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And now there's a tangle of branches
between him and his prey.

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Missed again.

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More of his energy wasted.

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Another hare...

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this time out in the open.

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And another failure.

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If he doesn't kill soon,
he may not survive these winter months.

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But in North America,

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change is never far away.

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April - and billions of tonnes of snow
and ice are starting to melt,

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bringing new opportunities.

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Much of the water drains southwards.

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10,000 creeks join, forming
North America's biggest river system.

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The meltwaters travel 2,000 miles
down the Mississippi,

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right through the heart of North America.

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In the streams of Tennessee,
river chub are getting ready to breed.

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This male is busy building
a mound of stones, in which,

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if he's lucky,
a female will lay her eggs.

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As the river flows faster,
the work gets harder.

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It's a good start,
but rivals are doing the same thing

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and want some of his pebbles.

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The intruder seen off,

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and it's back to business.

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A few finishing touches.

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And then, with the last
of some 7,000 stones,

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his nest is complete.

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And right on time, here is a female.

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But the mound now needs one last feature.

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A trench where she can lay her eggs.

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And with a gentle shimmy of his body,
he nudges her into position.

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And she deposits her eggs

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where they will be safe
from both currents and predators.

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His work is done.

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The eggs will hatch,

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and then his mound
will be slowly dismantled

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by the current.

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So next year,
he'll have to start all over again.

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Spring is now well on its way.

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North America is wonderfully rich
in wild flowers.

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There are over 10,000 species of them.

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Hummingbirds fly up from the south
to feast on the nectar.

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Along the North American coast,
the tides are the largest in the world.

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The fragmented shoreline
forces seawater to rush up narrow inlets.

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And each time the tide retreats,
it opens a freshly stocked larder.

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7,000 square miles of extra coastline

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is uncovered in the space of just
two hours.

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A mother black bear is looking
for something suitable for her cubs.

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This is their first ever trip
to the seaside.

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In a few hours, the tide will return.

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So they must keep up with Mum.

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Here's something tasty -

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crabs.

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Big crabs can give a nasty nip.

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So it's best to start off
with smaller ones.

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During spring, three quarters
of the bears' food comes from the beach.

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But now... this family is not alone.

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An adult male.

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He's double her size,
and they're in his territory.

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The cubs know that call.

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It's time to head for safety.

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Bears have poor eyesight,
but their sense of smell is acute,

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and the male has detected intruders.

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He knows exactly which tree they are in.

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If the cubs stay up there,
they'll be safe,

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but they're losing precious feeding time.

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For now,
he's content to leave his scent mark.

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A warning note for trespassers.

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The family moves on.

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For the cubs, lunch today
will have to be a takeaway.

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The tide comes in.

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And within minutes,
feeding time is over for another day.

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As the continent warms,

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on a few special nights,

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when the temperature is just right...

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the forests of North America
put on a show.

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Male fireflies are taking to the air.

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These insects are not, in fact, flies,
they're a kind of beetle.

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The light produced by the males
is the most energy-efficient on Earth.

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Some species synchronise their flashes

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to increase the visibility of the message.

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If a female sees something she likes,

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she returns the signal.

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It looks as if the message is working.

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But the forest is booby-trapped...

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by orb-weaver spiders.

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The firefly continues to glow,
even in death.

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Other males see the flashes,
but not the dangers.

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The spider's larder is filling up.

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But for every firefly that gets caught,

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thousands avoid the traps.

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And this male is lucky.

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He's found a mate.

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And over the course of the night,

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millions will pair up.

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There are over 150 different species
of fireflies in North America,

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and each has its own flash code.

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Once they're mated, the females
deposit their eggs in the ground.

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And for those that didn't find a mate,

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their one chance has come and gone.

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Little rain reaches
the heart of the continent.

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For over a million square miles,
there's not a tree in sight.

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Many of those living here
spend much of their time underground.

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A prairie dog - a kind of
large, burrowing squirrel.

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Sentinels keep watch,
ready to warn others of any danger.

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And at this time of year
is a new generation to protect.

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This mother has six pups.

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The youngsters constantly beg for food.

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After all,
the pups aren't great at sharing.

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But the prairie dogs don't have
the prairies to themselves.

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An American badger.

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The pups have never seen one before.

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And badgers eat pups.

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A burrowing owl.

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It also knows that badgers are dangerous.

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It too has young and does not want
the badger anywhere near them.

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Eventually, the badger gives up.

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He sets off to look elsewhere.

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If he can find a place
where the grass is higher than he is,

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he will have a better chance.

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The mother sounds the alarm.

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Adults know the danger all too well.

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Four pups make it to safety below.

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But their mother dare not
wait above ground any longer.

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Half of all prairie dog pups
don't survive to adulthood.

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Predators are not the only problem
faced by animals

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living on these great plains.

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Warm air sweeps up from the Gulf of Mexico
and across the open prairies.

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And here, with no mountains to block it,

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it meets the frigid air from the Arctic.

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The results are spectacular.

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As the air currents mix and swirl,

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they build into one of nature's
most fearsome forces.

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Tornados.

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These twisters spin at speeds
of up to 300mph,

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the world's fastest wind.

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Over 1,000 tornadoes
touch down here every year.

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These drenching summer storms

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are prevented from spreading westwards
by the Rocky Mountains.

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Some peaks are over four kilometres high,

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so, beyond them, to the west,
much of the land remains parched.

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The great American deserts
cover over a million square miles.

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Here, roasted by the sun and blasted
by the wind, the rocks disintegrate,

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and mountains, particle by particle,
are reduced to sand.

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These pillars are all that remain
of a plateau where dinosaurs once roamed.

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Few animals can now survive here.

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In summer, as in all deserts,

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the enemy is heat,

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and it returns every day.

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At seven in the morning

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the temperature
is already 25 degrees Celsius.

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The clock is ticking

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for one unusual descendant
of the dinosaurs.

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A roadrunner.

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Found only in the deserts
of North America.

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Built for a life on the ground.

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He can run at over 20mph.

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But the prey he seeks are one step ahead.

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The roadrunner's challenge
is picking the right target.

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A Gila monster -

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too big.

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By mid-morning,
it will be 40 degrees Celsius.

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Even the smallest lizards
will soon head for cover.

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A centipede.

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Slim pickings for a morning's work.

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Hunting should get easier

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and prey will stay out longer

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once the summer's peak begins to fade.

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On the East Coast,
summer is coming to an end.

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Cold currents are sweeping
along the coast of Florida.

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And with them
come grey mullet on their migration

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to their spawning grounds in the south.

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Millions of them -

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and packed so tightly,
they stain the water like an oil slick.

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Few people on the beach
are even aware of them.

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The mullet keep as close
to the shore as possible,

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for, in deeper water, there are predators.

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Close to the beach,

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they have to keep clear of human swimmers.

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But now hunters from the open ocean
have detected them.

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Tarpon - over two metres long
and weighing over 100 kilograms.

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To get close to the mullet
in the shallows,

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the tarpon turn on their sides.

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Now the mullet can't see
their shining silver flanks

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until it's too late.

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And feasting begins.

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Black-tipped shark arrive.

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Pelicans join in.

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But these attacks have little effect
on the immense shoals.

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The mullet outnumber their enemies
by 10,000 to one.

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00:34:54,840 --> 00:34:59,440
So the great procession travels on,
into the Northern Atlantic Ocean,

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where, at last,
they will be able to spawn in safety.

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Autumn arrives in North America.

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No mountain range spans the continent
from east to west,

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so there is nothing to stop cold air
from the Arctic

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sweeping down unhindered
as far south as Louisiana.

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Autumn brings colour
to the southern swamps.

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Here, it has been hot and humid
for most of the year,

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and now these sub-zero temperatures
are something of a trial

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for the local inhabitants.

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An American alligator.

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00:36:39,440 --> 00:36:43,800
The alligator reacts to the chill
by slowing its heart rate

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to barely one beat per minute.

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It's a kind of energy-saving winter sleep.

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But other creatures
don't have this ability.

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The largest inhabitants of the swamp.

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A relative of the elephant.

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A manatee.

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A female provides milk for her calf
from a teat behind her flipper.

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She might be able to survive the chill.

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But her calf cannot.

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So every autumn,
they need to find warmer waters.

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They have a long journey ahead -

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it could be hundreds of miles.

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And she is not alone.

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The warm waters they need to survive
come from an unusual source.

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An immense underground river

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flows through subterranean channels
in Florida's rocks.

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In places, it comes to the surface,
creating over 1,000 springs.

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Now, in winter,

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these springs are ten degrees warmer
than the surrounding waters.

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So manatees come here every year
from far and wide.

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And here they can relax.

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They can get their backs scrubbed.

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And they socialise.

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00:39:41,599 --> 00:39:44,519
No-one is in much of a hurry.

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And young manatees have a chance
to meet some surprising neighbours.

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In summer, playing with an alligator
might be a dangerous game.

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00:40:12,639 --> 00:40:13,960
But now, at any rate,

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00:40:14,000 --> 00:40:18,960
the giant reptiles are still too chilled
to react with any vigour.

253
00:40:37,840 --> 00:40:40,119
Without these warm pools,

254
00:40:40,159 --> 00:40:44,360
few of Florida's manatees
would be able to survive the winter.

255
00:40:46,559 --> 00:40:51,559
But the waterways here
are now very popular with people, too,

256
00:40:51,599 --> 00:40:56,519
and many manatees carry scars inflicted
by the propellers of boats.

257
00:40:58,679 --> 00:41:02,079
Her calf has already had its first scrape.

258
00:41:03,679 --> 00:41:08,199
Every year, more than 100 manatees die
from human causes.

259
00:41:17,079 --> 00:41:19,960
As the human population of Florida grows,

260
00:41:20,000 --> 00:41:23,360
so wildlife is coming
under increasing pressure.

261
00:41:26,119 --> 00:41:28,440
Across North America,

262
00:41:28,480 --> 00:41:32,000
a million acres of wilderness
are lost every decade.

263
00:41:48,760 --> 00:41:51,719
But it is in the far north
of the continent

264
00:41:51,760 --> 00:41:56,079
that human beings
are affecting wildlife most critically.

265
00:41:57,679 --> 00:42:02,039
Canada is warming faster
than any other country on Earth.

266
00:42:16,840 --> 00:42:21,719
Polar bears have always relied
on sea ice for their hunting.

267
00:42:26,639 --> 00:42:29,760
But summers are now getting longer
and hotter.

268
00:42:33,199 --> 00:42:34,599
For most polar bears,

269
00:42:34,639 --> 00:42:36,559
this is a time of starvation.

270
00:42:49,039 --> 00:42:50,840
On the shores of Hudson Bay,

271
00:42:50,880 --> 00:42:54,599
some bears are finding
a new source of food.

272
00:43:03,199 --> 00:43:06,559
They're all looking for the same thing,

273
00:43:06,599 --> 00:43:10,320
and they have their own ways
of catching it.

274
00:43:17,119 --> 00:43:20,360
First, they must find the right rock.

275
00:43:31,079 --> 00:43:32,920
Now they must wait.

276
00:43:43,639 --> 00:43:48,760
The tide comes in,
bringing with it other northern giants.

277
00:44:08,320 --> 00:44:10,079
Beluga whales.

278
00:44:14,599 --> 00:44:16,519
Close to the shore,

279
00:44:16,559 --> 00:44:21,960
their calves should be safe
from ocean-going predators such as orca.

280
00:44:24,199 --> 00:44:26,840
Over 3,000 whales have gathered here.

281
00:44:42,679 --> 00:44:45,000
A young male makes his move.

282
00:44:53,480 --> 00:44:57,000
Polar bears are skilled marine hunters...

283
00:44:59,800 --> 00:45:02,000
and beluga are slow swimmers.

284
00:45:42,679 --> 00:45:46,119
As long as a whale
can keep an eye on a hunting bear,

285
00:45:46,159 --> 00:45:47,480
it should be safe.

286
00:46:02,239 --> 00:46:04,360
This young bear is still learning.

287
00:46:11,639 --> 00:46:15,719
More experienced bears
know to be patient.

288
00:46:30,639 --> 00:46:34,519
Success will depend
on split-second timing.

289
00:47:18,639 --> 00:47:23,159
A bite at the back of the head,
and the kill is swift.

290
00:47:31,880 --> 00:47:35,519
This extraordinary behaviour
has only been reported here,

291
00:47:35,559 --> 00:47:38,519
in this remote corner of North America...

292
00:47:41,400 --> 00:47:43,400
and only in the last few years.

293
00:47:51,719 --> 00:47:56,280
This one small group of bears
has found an ingenious way

294
00:47:56,320 --> 00:47:59,559
of surviving the lean summer months.

295
00:48:13,320 --> 00:48:17,280
But for others, it is not so easy.

296
00:48:19,440 --> 00:48:23,000
We continue to transform our planet,

297
00:48:23,039 --> 00:48:26,239
and the seasons
are becoming less predictable.

298
00:48:29,599 --> 00:48:33,320
Will the wildlife of North America
be able to adapt?

299
00:48:34,559 --> 00:48:39,360
Not only on this continent,
known for its change,

300
00:48:39,400 --> 00:48:41,519
but in a rapidly changing world?

301
00:49:02,519 --> 00:49:04,880
The North America crew heard reports

302
00:49:04,920 --> 00:49:07,920
of a rarely seen
polar bear hunting behaviour.

303
00:49:10,239 --> 00:49:12,800
To film it, they set out in a small boat

304
00:49:12,840 --> 00:49:17,000
to navigate the far corners
of Canada's Hudson Bay.

305
00:49:19,679 --> 00:49:21,760
But the weather here,
on the Arctic Circle,

306
00:49:21,800 --> 00:49:23,320
can be unpredictable.

307
00:49:28,760 --> 00:49:34,440
We're out in the middle of Hudson Bay
and we have a thunderstorm approaching.

308
00:49:34,480 --> 00:49:39,239
The thing you don't want with
a thunderstorm is a metal boat

309
00:49:39,280 --> 00:49:40,480
and a big metal crane.

310
00:49:41,760 --> 00:49:46,280
Hundreds of miles from help,
there's no chance of rescue here,

311
00:49:46,320 --> 00:49:48,519
so the crew head for safety.

312
00:49:48,559 --> 00:49:50,239
Whoa!

313
00:49:51,760 --> 00:49:56,440
Let's see -
30K, and then gusting up to 50 or 60,

314
00:49:56,480 --> 00:49:58,880
so it's gonna get a little nasty.

315
00:50:01,159 --> 00:50:03,719
Oh!

316
00:50:16,480 --> 00:50:19,679
On land, they'll be safe from the storm,

317
00:50:19,719 --> 00:50:21,599
but they need to be armed.

318
00:50:24,400 --> 00:50:26,719
Polar bears have little fear of humans,

319
00:50:26,760 --> 00:50:29,599
and at this time of the year,
most are hungry.

320
00:50:31,840 --> 00:50:35,880
With the bears at a safe distance,
there's time for a quick moment

321
00:50:35,920 --> 00:50:39,280
to celebrate
cameraman John's 40th birthday.

322
00:50:39,320 --> 00:50:42,280
♪ Happy birthday to you. ♪

323
00:50:43,719 --> 00:50:46,159
We've come to what is probably
one of the windiest shoots

324
00:50:46,199 --> 00:50:48,239
I've ever done in my life.

325
00:50:48,280 --> 00:50:51,880
This is the first time
I've had a birthday on the beach.

326
00:50:51,920 --> 00:50:53,599
- You're kidding?
- Yeah.

327
00:50:53,639 --> 00:50:55,079
And what a beach it is.

328
00:50:57,800 --> 00:50:59,760
At the first sign of calm weather,

329
00:50:59,800 --> 00:51:03,639
the crew head back out
to look for a key part of the story.

330
00:51:07,199 --> 00:51:09,519
Beluga whales.

331
00:51:15,719 --> 00:51:18,679
With frigid waters and strong currents,

332
00:51:18,719 --> 00:51:23,280
a thin rope will be
cameraman Bertie's only lifeline.

333
00:51:37,199 --> 00:51:41,239
Bertie can hear the belugas,
but he can't see them.

334
00:51:43,159 --> 00:51:44,239
To communicate,

335
00:51:44,280 --> 00:51:47,679
the whales sing to each other
through the murky water.

336
00:51:48,960 --> 00:51:51,760
So, with this underwater microphone,

337
00:51:51,800 --> 00:51:55,760
we're going to listen
to what these beluga whales are singing

338
00:51:55,800 --> 00:51:57,039
for Bertie.

339
00:52:02,400 --> 00:52:06,239
Listening to their calls
gives the crew an idea.

340
00:52:06,280 --> 00:52:12,800
Bertie tries enticing the belugas closer
with some tunes of his own.

341
00:52:17,760 --> 00:52:20,800
Despite some questionable singing,

342
00:52:20,840 --> 00:52:23,400
it seems to be working.

343
00:52:35,000 --> 00:52:37,440
Once reeled in, he shares the secret.

344
00:52:37,480 --> 00:52:42,159
The moment I started singing Adele,
they just went crazy.

345
00:52:45,920 --> 00:52:49,199
It's the chorus, that's what gets them -
every time.

346
00:52:51,400 --> 00:52:54,400
With their boat
the only feature for miles,

347
00:52:54,440 --> 00:52:57,960
it's not just beluga
that come to check them out.

348
00:52:59,039 --> 00:53:01,719
Here's a young guy,
really curious.

349
00:53:01,760 --> 00:53:06,679
That's about as close as you can get
to a polar bear.

350
00:53:19,880 --> 00:53:22,719
This bear is pulling our anchor
off the bottom, and we're drifting

351
00:53:22,760 --> 00:53:24,559
cos he's pulling... keeps pulling it up.

352
00:53:26,199 --> 00:53:28,880
Hey, leave that anchor alone. Leave it.

353
00:53:34,280 --> 00:53:35,800
With all eyes on the bear,

354
00:53:35,840 --> 00:53:39,280
the crew suddenly realise
they have a bigger problem to deal with.

355
00:53:41,519 --> 00:53:43,679
Their boat has hit a rock.

356
00:53:43,719 --> 00:53:45,320
Do you know exactly where the rock is?

357
00:53:48,719 --> 00:53:50,039
Push it that way.

358
00:53:50,079 --> 00:53:52,320
Strong currents risk tipping the boat

359
00:53:52,360 --> 00:53:55,159
and putting the crew in serious danger.

360
00:54:04,960 --> 00:54:07,360
We're up on top of it, I think.

361
00:54:09,079 --> 00:54:10,559
The team doesn't have long

362
00:54:10,599 --> 00:54:14,320
before the falling tide
will leave them stranded on the rock.

363
00:54:14,360 --> 00:54:16,119
Is it moving or is it just swinging?

364
00:54:16,159 --> 00:54:19,159
- OK, push your end, push. Go on.
- See if we can...

365
00:54:21,599 --> 00:54:23,360
- OK, we're off.
- We're off?

366
00:54:23,400 --> 00:54:24,960
Whoo!

367
00:54:25,000 --> 00:54:27,239
A narrow escape.

368
00:54:27,280 --> 00:54:31,119
Like all film crews,
we kept wanting more and more,

369
00:54:31,159 --> 00:54:33,760
and eventually the boat
got high-centred on a rock.

370
00:54:35,480 --> 00:54:38,079
I didn't think about bears
until I was back on the boat.

371
00:54:38,119 --> 00:54:39,519
There was a bear in the water.

372
00:54:39,559 --> 00:54:41,719
Yeah, there are a couple right around us.

373
00:54:41,760 --> 00:54:42,920
Yeah.

374
00:54:48,519 --> 00:54:50,000
But with time running out,

375
00:54:50,039 --> 00:54:54,280
there's little sign
of the bears' unique hunting strategy.

376
00:54:56,840 --> 00:55:02,000
It's a waiting game,
for both the bears and the crew.

377
00:55:08,719 --> 00:55:11,559
Bear, bear, bear! Straight off the front.

378
00:55:11,599 --> 00:55:14,840
Finally, a big male
in a promising position.

379
00:55:19,159 --> 00:55:22,599
This is just the situation
they've been looking for.

380
00:55:22,639 --> 00:55:27,639
With one camera on the boat
and one in the air,

381
00:55:27,679 --> 00:55:30,760
the crew is hoping to cover the action
from all angles.

382
00:55:34,199 --> 00:55:37,079
Just waiting for the right one
in the right spot.

383
00:55:43,960 --> 00:55:48,320
He's got one. He's got one.
Let's get the anchor up, anchor up.

384
00:55:48,360 --> 00:55:50,599
He's got it.

385
00:55:55,039 --> 00:55:56,519
He's got it on the back of the head.

386
00:55:58,239 --> 00:55:59,880
He's got him by the tail now.

387
00:56:02,679 --> 00:56:07,239
For the team, witnessing
this life-and-death struggle is hard.

388
00:56:08,320 --> 00:56:10,119
Oh, it's kind of shocking

389
00:56:10,159 --> 00:56:13,000
when it just happens
in front of you like that.

390
00:56:14,360 --> 00:56:16,599
It's amazing how powerful the bear is -

391
00:56:16,639 --> 00:56:19,376
it just grabbed an animal that's designed
to be in the water and be powerful,

392
00:56:19,400 --> 00:56:20,920
and the bear just throws it around.

393
00:56:22,440 --> 00:56:26,639
To see an animal lose its life
is upsetting,

394
00:56:26,679 --> 00:56:30,360
and the crew are left with mixed feelings.

395
00:56:30,400 --> 00:56:33,000
We've really connected with these belugas,

396
00:56:33,039 --> 00:56:35,400
so it's sad to see them die,

397
00:56:35,440 --> 00:56:38,920
but that was a really spectacular bit
of nature right there.

398
00:56:40,559 --> 00:56:43,119
This footage adds to our understanding

399
00:56:43,159 --> 00:56:46,039
of these ingenious animals.

400
00:56:52,719 --> 00:56:54,920
In a changing world,

401
00:56:54,960 --> 00:56:58,559
one small group of polar bears has come up

402
00:56:58,599 --> 00:57:01,559
with a remarkable strategy for survival.

403
00:57:06,679 --> 00:57:07,880
Next time...

404
00:57:11,800 --> 00:57:15,840
the continent where wildlife
puts on the greatest show on Earth.

405
00:57:26,599 --> 00:57:28,239
Africa.