Seven Worlds, One Planet

One continent on our planet changes

more dramatically than any other.

THUNDER RUMBLES

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.

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.

TWIG SNAPS

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.

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.

SQUAWKING

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 ofjust two hours.

WHIMPERS

GRUNTS

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

This is their first-ever trip to the seaside.

In a few hours, the tide will return.

So, they must keep up with Mum.

WHIMPERS

SQUEALS

Here's something tasty -

crabs.

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.

SQUEALS

But now, this family is not alone.

An adult male.

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

GRUNTS

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.

SQUEALS

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

And at this time of year is 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.

GROWLS

An American badger.

The pups have never seen one before.

And badgers eat pups.

A burrowing owl.

It also knows that badgers are dangerous.

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.

CHIRPS

The mother sounds the alarm.

CHIRPS

Adults know the danger all too well.

CHIRPS

SCREECHES

Four pups make it to safety below.

But their mother dare not wait above ground any longer.

GROWLING

FLIES BUZZ

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