Original subtitles

Home to this Lausanne albatross chick.

He's ready to make his maiden flight to the open ocean.

But there can be no room for error.

They've travelled a thousand kilometres to get

here, arriving just in time for the fledging season.

Leaving will be the most dangerous journey of his life.

But it's his neighbours, black-footed albatross chicks, that go first.

A splash landing.

Just what the sharks are waiting for.

Now it's his turn.

With the summer winds picking up, conditions

are finally right for him to spread his wings.

And fly.

He's airborne.

For the first time in his life.

But when the breeze suddenly drops, so too does the chick.

Without wind, he's helpless.

A very lucky escape.

He's off.

He may not touch land again for five years.

As he travels hundreds of thousands of

kilometres across the ocean, searching for food.

Our planet is solar-powered.

The sun's rays take eight minutes to reach us.

But due to the Earth's tilt, they don't strike its surface evenly.

This solar energy arrives in varying amounts at different times of the year,

depending on where it strikes.

And in the Northern Hemisphere, the huge increase

that comes with summer triggers countless journeys.

In early July, the flower meadows of Europe receive

more sunlight than at any other time of the year.

And that makes it a very busy time for honeybees.

Few animals work harder to exploit the summer's riches.

To make just half a kilo of honey.

A colony of bees must fly 90,000 kilometres and visit over a million flowers.

And we have taken advantage of their labours for thousands of years.

In this domestic hive in Germany, 60,000 bees

are working together as one superorganism.

And with the larger queen laying an egg every 30

seconds, it's a colony that is now bursting at the seams.

There could be another 40,000 bees developing in this hive.

And there just isn't enough room for them all.

The superorganism has to split.

Those in the leaving party gather at the entrance.

And when they reach a critical mass, they begin to swarm.

They must find a new home.

But the first stop is just a staging post, close to the hive.

In a few minutes, 30,000 bees gather around

the queen, who is now shielded by the swarm.

Out in the open, they're vulnerable to the elements.

So the race is on to find somewhere else to live.

Scouts set off, looking for a suitable home.

A tree hole that is just the right size, height and angle to the sun.

This one looks possible.

But too shady.

Too small.

Already taken.

Now, what about this one?

It looks promising.

Yes, this will do nicely.

So it's back to the staging post to convince the rest of the colony.

And she does that by dancing.

The angle of her waggle dance relative to the sun

tells them in which direction the hole can be found.

While the duration lets them know how far away it is.

And the better the spot, the more intense her performance.

Others return to advertise their finds.

But their moves just don't cut it, compared to hers.

Interest grows around her.

And more bees set out to inspect the new hole.

It's house hunting by committee.

It seems they agree.

And they return to spread the news to the rest of the swarm.

To do so, the scouts must touch every bee in turn.

And, incredibly, in just half an hour, all 30,000 of them are ready to leave.

On arrival, each bee fans a pheromone across the

forest, helping others to find the new nest site.

More and more arrive at the new location.

All joining in to spread the chemical message.

Within a few hours, the entire swarm has made the move.

Bees are only able to move like this when the sun's energy provides

them with enough food to rebuild their colony from scratch.

So, for the next few weeks, they will need to be as busy as, well, a bee.

In July, the further north you go, the more daylight there is.

And for just a brief period, this increase in solar power turns the Arctic tundra

into a rich grassland, attracting more than a million snow geese.

They've travelled the length of North America, a distance of 5,000 kilometres,

and they've come here to breed.

Arctic summers are short, so the geese start laying straight away.

The female sits tight on the nest.

While the male keeps an eye out for enemies.

And he doesn't have long to wait.

Arctic foxes live here the year round, and they eagerly await the return of the geese.

The foxes' survival depends on a steady supply of food.

And they're not afraid of eggs.

But snow geese only lay one clutch a year.

And they defend it with their lives.

Nonetheless, a single fox may steal over 1,000 eggs in a season.

Despite these losses...

...plenty of eggs do hatch.

It may be the height of summer, but it's still the Arctic.

So the goslings stay with mother to keep warm.

But there's only so much room under one wing.

Still, it's better to keep out of the way...

...when the tundra's larger residents pass through.

Caribou themselves pose little risk.

But they do bring problems.

Grizzly bears follow them... ...in the hope of an easy meal.

And their presence causes a stir within the colony.

Any chick in its path is hoovered up.

With things getting dangerous, it's time to get out of the way.

It's time for these chicks to start their life on the move.

The family heads for the safety of the water.

In just eight weeks, when the sun's power starts to wane here...

...the goslings will make their first flight south...

...all the way to the Gulf of Mexico.

Not all animals migrate as the seasons change.

Lions control the same territory year in, year out.

So this pride in East Africa's Serengeti...

...relies on prey coming to them.

Right now, it's the height of the dry season...

...and the long grass plains where these lions live...

...are relatively empty.

But things are about to change.

Heading towards them are hundreds of thousands of wildebeest.

Together, they make up the biggest terrestrial migration on Earth.

The herd eats its way through nearly 5,000 tons of grass a day...

...which means they have to keep on the move.

Something the lions have been counting on.

The long, dry grass is of little nutritional value...

...but the herd must pass through it.

And the lions know that.

The grass provides a very effective cloak of invisibility.

To prevent her scent being detected... ...the lioness approaches from downwind.

Stalking...

...and stopping.

Every movement...

...considered.

One careless step... ...could reveal her presence.

Any disturbance in the grass... ...could be a potential threat for the herd.

That's just a guinea fowl.

A false alarm.

Or... ...perhaps not.

She's almost perfectly placed.

Just 20 meters from her target.

After months with little to eat... ...this is a vital meal.

The pride will need to make the most of the migration...

...while it's passing through.

Soon, the herds will have left the lion's territory...

...moving north in their never-ending search... ...for fresh grazing.

In August, the Northern Hemisphere... ...is at its warmest.

And on Canada's Vancouver Island... ...there's one animal...

...whose life cycle depends on these higher temperatures.

As day breaks over Cedar Lake...

...something is stirring in its depths.

Tadpoles here... ...spend their nights hiding in deep, cool water.

Now, with the sun up... ...they set off across the lake.

Initially...

...in hundreds.

Then... ...thousands.

All are heading for the sunlit shallows.

Here... ...the water is five degrees warmer... ...than in the lake's depths.

And that will speed their transformation into toads.

But when night falls... ...they head back... ...to the safety of the deep.

Until... ...the next morning.

Every day... ...they repeat the journey.

Sun...

...swim...

...feed...

...repeat.

It seems perfect.

Except others take advantage... ...of their daily routine.

Dragonfly larvae.

They are ambush predators.

With extendable jaws.

And they have voracious appetites.

Blind leeches patrol the muddy bottom.

Once they catch something...

...they suck out its blood.

Throughout the summer...

...the tadpoles continue their daily commute.

Until...

...after a few weeks...

...they start to look like tiny toads.

By harnessing the sun's energy... ...they've grown quickly.

Now... ...they stop their daily routines... ...and prepare for their journey...

...into the forest.

Here too...

...predators await.

Garter snakes... ...specialize in eating amphibians.

Though they rarely have as much choice... ...as this.

Eventually... ...the sheer numbers of young toads... ...overwhelm the snakes.

The survivors spread out... ...into the forest... ...where they'll spend...

...the next four years.

Until... ...it's time for them... ...to head back to the lake...

...to breed.

By mid-summer...

...there is little snow left... ...in America's Pacific Northwest.

Meltwater fills the rivers...

...ready to carry travelers...

...who make what is perhaps...

...the most extraordinary... ...and demanding journey... ...tackled by any animal.

Sockeye salmon... ...and they're heading upriver... ...to breed.

After three years feeding... ...in the Bering Sea...

...they find their way across... ...hundreds of kilometers of ocean...

...guided by the Earth's magnetic field... ...and their astounding ability...

...to recognize the taste of the river... ...in which they hatched.

They are one of the few fish in the world... ...that can move from saltwater...

...into fresh.

And over the next month... ...they will travel 200 kilometers upstream...

...past Lake Iliamna... ...to their spawning pools just beyond.

It's the last journey... ...these salmon will ever make.

As they enter the river... ...they stop eating...

...putting all their efforts... ...into battling the current.

Swift rapids and high waterfalls...

...do not stop them.

Four weeks into their journey... ...their bodies begin to change.

Flashes of red appear in their flanks.

These are their breeding colors... ...and the redder the fish...

...the fitter they are.

A few more weeks... ...and they're barely recognizable.

The jaws of the males... ...have become hooked beaks...

...which they will use to fight for a mate.

But their spawning pools... ...are still nearly 100 kilometers away.

And just upriver... ...there are predators... ...ready to intercept them.

Bears depend on the annual salmon run...

...to fatten up for the winter ahead.

Now

they're very, very hungry.

During the migration... ...an adult bear can eat 40 salmon a day.

The salmon are quick and agile.

But as the water gets shallower...

...the advantage swings in favor of the bears.

And the bears are not afraid... Several kilometers upstream...

...the fish finally reach... ...Lake Iliamna.

One of the last pristine waterways... ...in America.

Their spawning pools lie just upstream.

But for now the sockeye linger... ...while the females' eggs...

...complete their development.

...are not yet over.

These waters are the home... ...of the only freshwater seals... ...in America.

The salmon haven't eaten... ...in eight weeks.

But they can still out-swim... ...these predators.

The seals switch strategy... ...and start to hide... ...in plain sight.

In a rarely seen behavior... ...they wait for the salmon... ...to come to them.

Surprisingly... ...they ignore the males... ...right in front of them.

And go for the females... ...who are laden with... ...calorie-rich eggs.

But for every... ...salmon that's taken...

...thousands... ...get through.

Mattered and bruised... ...from their long journey... ...they have at last reached...

...their spawning pools.

Once here, males and females... ...pair up and together...

...fight for the best nest sites.

They mate.

It's the only time... ...they will ever do so.

They've given everything... ...to complete this epic migration.

Their lives...

...the nutrients... ...from their decaying bodies...

...fertilize the water.

A sacrifice... ...that ensures the next generation...

...will have the very best start... ...in life.

August in the... ...High Arctic.

After three months of continuous... ...daylight, little is left... ...of the sea ice.

And that makes life... ...very hard for this... ...ice bear.

And her eight-month-old cubs.

Three months ago... ...they were hunting blubber-rich seals... ...out on the ice.

Now they're forced to swim... ...continuously for days on end...

...in search of... ...whatever food they can find.

Polar bears use five times... ...more energy when swimming... ...than walking.

And that is beginning... ...to take its toll... ...on her smallest cub.

Oh!

He's finding it hard to keep up.

But his mother is too hungry... ...to wait for long.

She can smell food somewhere... ...on this island.

And the dive-bombing... ...gulls are a sign... ...that she's close.

For the largest land carnivore... ...on Earth, these chicks...

...are not much of a meal.

Though they would be a much-needed... ...boost for the cubs.

If they can get down to it... ...before it's gone.

The weaker cub...

...is not very sure-footed.

By the time he's caught up... ...it's too late.

With food... ...so scarce...

...there is no time for rest.

The climb back up...

...should be easy.

Certainly... ...his sibling seems to take it... ...in his stride.

But after that long swim... ...the weaker cub has little energy left.

Unable to follow... ...he panics... ...and heads in the wrong direction.

A slip here... ...would mean a 15-meter fall... ...onto the rocks below.

His mother takes no notice... ...of his problems.

So desperate is she for another meal.

His survival depends... ...on staying close to his mother.

If he can't keep up...

...she will be forced to abandon him.

He's made it...

...only to find... ...that he must still... ...keep going.

It's a journey this young cub... ...may not survive.

With summer sea ice melting earlier... ...than we've ever known...

...polar bears are having to spend... ...more of their year swimming.

For animals... ...used to traveling across ice... ...these changes may well...

...prove to be too great.

6,000 kilometers south of the Arctic... ...the summer sun...

...is also heating the shallow waters... ...of the Persian Gulf.

Making the sea here... ...the hottest on the planet.

Attracts the ocean's... ...biggest fish.

A whale shark.

After a journey... ...of thousands of kilometers...

...it's arrived in time... ...for one of the best feeding events... ...of its year.

And it's heading... ...to a particular spot.

The waters... ...of the Al Shaheen... ...oil fields.

The platforms act... ...as reefs...

...providing a home for hundreds...

No vessels are allowed... ...within half a kilometer... ...of each rig.

So creating marine sanctuaries... ...where fish can spawn in safety.

Tuna are among them.

They can only breed...

...when the water is 25 degrees Celsius... ...or more.

So in summer...

...when the Gulf is at its hottest...

...they gather together...

...and release hundreds of millions... ...of eggs.

The water's surface... ...becomes thick with spawn.

And that is what the whale shark... ...has crossed oceans for.

Taking in water... ...through its meter-wide mouth...

...it collects the eggs.

More sharks arrive... ...to join the feast.

And this... ...is the hottest sea... ...on Earth.

And after feeding for a few hours... ...each morning...

...the whale sharks will have to return... ...to the cooler depths.

At the height of the spawning season... ...there may be over a hundred...

...per square kilometer.

It's one of the largest gatherings... ...of whale sharks on the planet.

And all the more remarkable... ...that it was only recorded...

...for the first time in 2010.

Back in the Serengeti...

...a million wildebeest and zebra... ...are still on the move...

...following the sun and rain... ...in search of fresh grazing.

And in amongst the throng...

...new life.

This zebra foal... ...and his family... ...travel amongst the wildebeest...

...for safety.

He is just four weeks old.

And keeping pace with the herd... ...is a daily struggle.

Yet his biggest hurdle... ...lies just ahead.

The Mara River.

Its fast-flowing waters... ...claim the lives of...

...a thousand animals a year.

Crossing it will be a major trial... ...for a foal... ...that has never swum before.

The herd nears... ...the river's edge.

None wants to be the first to cross.

But as numbers increase...

...pressure mounts... ...on those at the front.

Once one commits... ...the floodgates open.

But the foal and his family wait.

Many wildebeest... ...drown in the crush.

Still... ...the zebra hold back.

And with good reason.

Five metre long Nile crocodiles...

...amongst the... ...biggest in Africa.

These giant reptiles... ...may not have eaten... ...since this time last year.

With so many targets... ...from which to choose...

...they can afford to take their time.

Soon, perhaps...

...the crocodiles will have taken their fill.

No such luck.

The zebra can wait... ...no longer.

They must stay... ...with the herd.

So, the young foal... ...must now...

...swim for his life.

... ... ... ...