One continent on our planet changes more dramatically than any other.
North America.
Whole landscapes here
can be transformed
in a matter of minutes.
And all life has to be ready
to seize the moment.
Getting it wrong can be disastrous.
But time it correctly,
and there can be great rewards.
This is a land of opportunity.
Over 100 times the size of Great Britain,
North America stretches from
just above the equator
almost to the North Pole.
Temperatures can range
from 50 degrees Celsius
to minus 40.
The coldest wilderness of all
lies in the Arctic North.
Here, in Canada's Yukon Territory,
winter is brutal.
Many animals have travelled south
to avoid the worst of the cold.
For those which stay behind,
life becomes very hard indeed.
A Canadian lynx.
No other kind of cat anywhere
lives farther north than this one.
The search for food
could take him hundreds of miles.
IT GROWLS
A snowshoe hare.
This could be a chance.
He's lost the element of surprise.
And now there's a tangle of branches
between him and his prey.
Missed again.
More of his energy wasted.
Another hare.
This time, out in the open.
And another failure.
If he doesn't kill soon,
he may not survive
these winter months.
BIRD SCREECHES
But in North America,
change is never far away.
April, and billions of tonnes
of snow and ice
are starting to melt,
bringing new opportunities.
Much of the water drains southwards.
10,000 creeks join,
forming North America's
biggest river system.
The meltwaters travel 2,000 miles
down the Mississippi,
right through the heart of North America.
In the streams of Tennessee,
river chub are getting ready to breed.
This male is busy
building a mound of stones
in which, if he's lucky,
a female will lay her eggs.
As the river flows faster,
the work gets harder.
It's a good start.
But rivals are doing the same thing
and want some of his pebbles.
The intruder seen off,
and it's back to business.
A few finishing touches.
And then,
with the last of some 7,000 stones,
his nest is complete.
And, right on time,
here is a female.
But the mound
now needs one last feature.
A trench where she can lay her eggs.
And with a gentle shimmy
of his body,
he nudges her into position.
And she deposits her eggs
where they will be safe
from both currents and predators.
His work is done.
The eggs will hatch
and then his mound will be
slowly dismantled by the current.
So next year,
he'll have to start all over again.
Spring is now well on its way.
North America is wonderfully rich
in wild flowers.
There are over 10,000 species of them.
Hummingbirds fly up from the south
to feast on the nectar.
Along the North American coast,
the tides are the largest in the world.
The fragmented shoreline
forces sea water to rush up
narrow inlets.
And each time the tide retreats,
it opens a freshly stocked larder.
7,000 square miles
of extra coastline
is uncovered in the space
of just two hours.
A mother black bear is looking
for something suitable for her cubs.
This is their first-ever trip
to the seaside.
CUB YELPS
In a few hours,
the tide will return.
So they must keep up with Mum.
Here's something tasty -
crabs.
CUB YELPS
Big crabs can give a nasty nip.
So it's best to start off
with smaller ones.
During spring,
three quarters of the bears' food
comes from the beach.
But now, this family is not alone.
An adult male.
He's double her size,
and they're in his territory.
The cubs know that call.
It's time to head for safety.
Bears have poor eyesight,
but their sense of smell is acute,
and the male has detected intruders.
He knows exactly
which tree they are in.
If the cubs stay up there,
they'll be safe.
But they're losing
precious feeding time.
For now, he's content
to leave his scent mark.
A warning note for trespassers.
The family moves on.
For the cubs, lunch today
will have to be a takeaway.
The tide comes in.
And within minutes,
feeding time is over
for another day.
As the continent warms,
on a few special nights,
when the temperature is just right,
the forests of North America
put on a show.
Male fireflies
are taking to the air.
These insects are not,
in fact, flies.
They're a kind of beetle.
The light produced by the males
is the most energy-efficient on Earth.
Some species synchronise
their flashes to increase
the visibility of the message.
If a female sees
something she likes,
she returns the signal.
It looks as if
the message is working.
But the forest is booby-trapped
by orb-weaver spiders.
The firefly continues to glow,
even in death.
Other males see the flashes,
but not the dangers.
The spider's larder is filling up.
But for every firefly
that gets caught,
thousands avoid the traps.
And this male is lucky.
He's found a mate.
And over the course of the night,
millions will pair up.
There are over 150 different species
of fireflies in North America,
and each has its own flash code.
Once they're mated,
the females deposit their eggs
in the ground.
And for those that didn't find a mate,
their one chance has come and gone.
Little rain
reaches the heart of the continent.
For over a million square miles,
there's not a tree in sight.
Many of those living here
spend much of their time underground.
A prairie dog -
a kind of large, burrowing squirrel.
THEY SQUEAL
Sentinels keep watch,
ready to warn others of any danger.
And at this time of year,
there's a new generation to protect.
This mother has six pups.
The youngsters
constantly beg for food.
After all,
the pups aren't great at sharing.
But the prairie dogs
don't have the prairies to themselves.
An American badger.
The pups have never seen one before.
And badgers eat pups.
A burrowing owl.
It also knows
that badgers are dangerous.
OWL SQUAWKS
It too has young, and does not want
the badger anywhere near them.
Eventually, the badger gives up.
He sets off to look elsewhere.
If he can find a place
where the grass is higher than he is,
he will have a better chance.
IT CHIRPS
The mother sounds the alarm.
CHIRPING
Adults know the danger all too well.
Four pups make it
to safety below.
But their mother dare not wait
above ground any longer.
Half of all prairie dog pups
don't survive to adulthood.
Predators are not the only problem
faced by animals
living on these great plains.
Warm air sweeps up
from the Gulf of Mexico
and across the open prairies.
And here, with no mountains to block it,
it meets the frigid air
from the Arctic.
The results are spectacular.
As the air currents mix and swirl,
they build into one of nature's
most fearsome forces.
THUNDER CRASHES
Tornadoes.
These twisters spin
at speeds of up to 300mph.
The world's fastest wind.
Over 1,000 tornadoes
touch down here every year.
These drenching summer storms
are prevented from spreading westwards
by the Rocky Mountains.
Some peaks are over 4km high.
So, beyond them to the west,
much of the land remains parched.
The great American deserts
cover over 1 million square miles.
Here, roasted by the sun
and blasted by the wind,
the rocks disintegrate,
and mountains, particle by particle,
are reduced to sand.
These pillars are all that remain
of a plateau
where dinosaurs once roamed.
Few animals can now survive here.
In summer, as in all deserts,
the enemy is heat.
And it returns every day.
At seven in the morning,
the temperature is already
25 degrees Celsius.
The clock is ticking
for one unusual descendant
of the dinosaurs.
CHIRPING
A road runner.
Found only in the deserts of North America...
..built for life on the ground...
..he can run at over 20mph.
But the prey he seeks
are one step ahead.
The road runner's challenge
is picking the right target.
A Gila monster.
Too big.
By mid-morning,
it will be 40 degrees Celsius.
Even the smallest lizards
will soon head for cover.
A centipede.
Slim pickings for a morning's work.
Hunting should get easier,
and prey will stay out longer,
once the summer's peak
begins to fade.
On the East Coast,
summer is coming to an end.
Cold currents are sweeping along
the coast of Florida.
And with them come grey mullet,
on their migration to their spawning grounds in the south.
Millions of them,
and packed so tightly,
they stay in the water
like an oil slick.
Few people on the beach
are even aware of them.
The mullet keep as close
to the shore as possible.
For in deeper water,
there are predators.
Close to the beach,
they have to keep clear
of human swimmers.
But now, hunters from the open ocean
have detected them.
Tarpon, over two metres long
and weighing over 100kg.
To get close to the mullet in the shallows,
the tarpon turn on their sides.
Now the mullet can't see
their shining, silver flanks
until it's too late.
And feasting begins.
Blacktip shark arrive.
Pelicans join in.
But these attacks have little effect
on the immense shoals.
The mullet outnumber their enemies
by 10,000 to one.
So the great procession travels on
into the northern Atlantic Ocean,
where, at last, they will be able
to spawn in safety.
Autumn arrives in North America.
No mountain range spans
the continent from east to west,
so there is nothing to stop cold air
from the Arctic sweeping down unhindered,
as far south as Louisiana.
Autumn brings colour
to the southern swamps.
Here it has been hot and humid
for most of the year.
And now, these sub-zero temperatures
are something of a trial
for the local inhabitants.
An American alligator.
The alligator reacts to the chill
by slowing its heart rate
to barely one beat per minute.
It's a kind of energy-saving winter sleep.
But other creatures don't have this ability.
The largest inhabitants of the swamp.
A relative of the elephant.
A manatee.
A female provides milk for her calf
from a teat behind her flipper.
She might be able
to survive the chill
But her calf cannot.
So every autumn,
they need to find warmer waters.
They have a long journey ahead.
It could be hundreds of miles.
And she is not alone.
The warm waters they need to survive
come from an unusual source.
An immense underground river flows
through subterranean channels
in Florida's rocks.
In places, it comes to the surface
creating over 1,000 springs.
Now in winter, these springs
are ten degrees warmer
than the surrounding waters.
So, manatees come here every year
from far and wide.
They can get their back scrubbed.
And they socialise.
No-one is in much of a hurry.
And young manatees have a chance
to meet some surprising neighbours.
In summer, playing with an alligator
might be a dangerous game.
But now, at any rate,
the giant reptiles
are still too chilled
to react with any vigour.
Without these warm pools,
few of Florida's manatees
would be able to survive the winter.
But the waterways here are now
very popular with people, too.
And many manatees carry scars
inflicted by the propellers of boats.
Her calf has already
had its first scrape.
Every year, more than 100 manatees die from human causes.
As the human population of Florida grows, so wildlife is coming
under increasing pressure.
ENGINE REVS
Across North America, a million acres of wilderness
are lost every decade.
But it is in the far north of the continent that human beings
are affecting wildlife most critically.
RUMBLING
Canada is warming faster than any other country on Earth.
HUFFING
BEAR ROARS
Polar bears have always relied on sea ice for their hunting.
But summers are now getting longer and hotter.
For most polar bears, this is a time of starvation.
BEAR ROARS
On the shores of Hudson Bay, some bears are finding
a new source of food.
BIRDS HONK
They're all looking for the same thing,
and they have their own ways of catching it.
First, they must find the right rock.
Now they must wait.
BEAR SNIFFS
The tide comes in, bringing with it other northern giants.
WHALE HUFFS
Beluga whales.
THEY WHISTLE AND TRILL
Close to the shore, their calves should be safe
from the ocean-going predators such as orca.
Over 3,000 whales have gathered here.
The young male makes his move.
THEY WHISTLE
Polar bears are skilled marine hunters.
And beluga are slow swimmers.
As long as a whale can keep an eye on a hunting bear,
it should be safe.
WHALE HUFFS
This young bear is still learning.
More experienced bears know to be patient.
Success will depend on split-second timing.
WHALE HUFFS
A bite at the back of the head, and the kill is swift.
This extraordinary behaviour has only been reported here,
in this remote corner of North America...
..and only in the last few years.
This one small group of bears has found an ingenious way
of surviving the lean summer months.
But for others, it is not so easy.
We continue to transform our planet,
and the seasons are becoming less predictable.
Will the wildlife of North America be able to adapt?
Not only on this continent known for its change,
but in a rapidly changing world?
The North America crew heard reports of a rarely seen
polar bear hunting behaviour.
To film it, they set out in a small boat to navigate
the far corners of Canada's Hudson Bay.
But the weather here, on the Arctic Circle,
can be unpredictable.
THUNDER RUMBLES
We're out in the middle of Hudson Bay, and we have
a thunderstorm approaching.
The thing you don't want with a thunderstorm
is a metal boat and a big metal crane.
Hundreds of miles from help,
there's no chance of rescue here. THUNDER RUMBLES
So the crew head for safety.
LIGHTNING CRACKS
HE YELLS
RADIO: We can see 30k and then gusting up to 50 or 60, so
it's going to get a little nasty.
LIGHTNING CRACKS Whoa!
On land, they'll be safe from the storm.
But they need to be armed.
Polar bears have little fear of humans
and, at this time of the year, most are hungry.
With the bears at a safe distance, there's time for a quick moment
to celebrate cameraman John's 40th birthday.
# Happy birthday to you... #
We've come to what is probably one of the windiest shoots
I've ever done in my life.
This is the first time I've had a birthday on the beach.
You're kidding. Yeah. Ah.
And what a beach it is.
At the first sign of calm weather,
the crew head back out to look for a key part of the story.
Beluga whales.
With frigid waters and strong currents,
a thin rope will be cameraman Bertie's only lifeline.
WHALE SONG
Bertie can hear the belugas,
but he can't see them.
To communicate, the whales sing to each other through the murky water.
So, with this underwater microphone,
we're going to listen to what
these beluga whales are singing for Bertie.
WHALE SONG
Listening to their calls gives the crew an idea.
HE HUMS
Bertie tries enticing the belugas
closer with some tunes of his own.
HE HUMS
Despite some questionable singing,
it seems to be working.
HUMMING CONTINUES
Once reeled in, he shares the secret.
The moment I started singing Adele, they just went crazy.
HE CHUCKLES
It's the chorus, that's what gets them - every time.
With their boat the only feature for miles...
..it's not just beluga that come to check them out.
He's a young guy, really curious.
That's about as close as you can get to a polar bear.
INDISTINCT CHATTER
This bear is pulling our anchor off the bottom, and we're drifting
cos he's pulling...keeps pulling it up.
Hey, leave that anchor alone.
Leave it.
With all eyes on the bear,
the crew suddenly realise they have
a bigger problem to deal with.
CLANGING
Their boat has hit a rock.
Quentin, do you know where, exactly, the rock is?
ENGINE HUMS
Push that way. Yep.
Strong currents risk tipping the boat and
putting the crew in serious danger.
I mean, over the side here...
We're up on top of it, I think.
The team doesn't have long before
the falling tide will leave them stranded on the rock.
Is it moving or is it just swinging?
Hey, push your end. Push.
GRINDING
OK, we're off.
Whoo! A narrow escape.
Like all film crews, we kept wanting more and more
and, eventually, the boat got high-centred on a rock.
I didn't think about bears until I was back on the boat.
There's a bear in the water.
Yeah, oh, yeah. There are a couple right around us, yeah.
But with time running out,
there's little sign of the bears'
unique hunting strategy.
It's a waiting game - for both the bears and the crew.
Bear, bear, bear! Hey.
Straight off the front.
Finally, a big male in a promising position.
This is just the situation they've been looking for.
With one camera on the boat
and one in the air...
..the crew is hoping to cover the action from all angles.
I mean, it's just waiting for the right one in the right spot.
He's got one. It's slight, he's flailing. He's got one.
Let's get the anchor up, anchor up.
He's got it.
He's got it on the back of the head.
Right. He's got him by the tail now.
For the team, witnessing this life-and-death struggle is hard.
It's kind of shocking when it just happens in front of you like that.
It's amazing how powerful the bear is, to just grab an animal
that is designed to be in the water and be powerful,
and the bear just throws it around.
To see an animal lose its life is upsetting,
and the crew are left with mixed feelings.
We've really connected with these belugas,
so it's sad to see them die,
but that was a really spectacular bit of nature right there.
This footage adds to our understanding
of these ingenious animals.
In a changing world, one small group of polar bears has come up with
a remarkable strategy for survival.
Next time...
..the continent where wildlife puts on the greatest show on Earth.
THEY GROWL AND YELP
HIPPOS ROAR
Africa.
MUSIC: Out There by Sia and Hans Zimmer
# I don't want to walk alone
# I want to believe
# Can you hear my call?
# As love will speak to me. #