Summer: Earth's Seasonal Secrets

Every year, spectacular seasons transform our planet.

They are the driving force of all life on Earth.

Bringing opportunities and huge challenges.

Spring bursts with new life.

But it's a race to grab fleeting chances.

Summer is all about glorious abundance.

But the heat can push animals to their limits.

Autumn is nature's great gold rush.

But competition is fierce.

Winter creates a frozen wonderland...

..and only the most resourceful will survive.

In every corner of the planet,

animals rise to overcome the seemingly impossible...

..and use extraordinary tricks...

..to thrive against the odds...

..as the seasons create the greatest shows on earth.

Summer.

The flowers are blooming, the sun is shining, the days are long.

But the living isn't always easy.

These sweltering days have their challenges.

The competition for summer's bounty

can push every creature to its limits.

So the first challenge is making sure you grab your share.

Across the world, nature is at its most lavish.

For insects, the explosion of flowers creates a banquet.

The more the sun warms the flowers,

the more nectar they produce.

For a little honeybee, these are busy times.

Every working bee is a female.

Between them, they'll visit 2 million flowers

to collect enough nectar to make just one cupful of honey.

In a woodland in Minnesota,

this colony of 40,000 honeybees is hard at work.

Summer's honey will be stored away to keep them going over winter.

Each bee might only make a 12th of a teaspoon of honey in her whole life.

She won't give it up lightly.

But they're being watched.

A black bear cub.

He needs to more than double his weight over summer

to survive a five-month winter hibernation.

A mouthful of honey and bee grubs is packed with calories.

But there's a technique to getting it and he hasn't learnt it.

He's soon surrounded by angry bees...

..and is way out of his depth.

Fortunately, his mother is an expert.

The stings are ferocious

but her fur is so thick she simply shakes the bees off.

But her bare face is more vulnerable.

She can stand the attack just long enough to grab a honeycomb.

For the bears, this is a valuable meal.

They must take any chance they can to fatten up during summer.

They're mostly vegetarian, but right now they'll eat anything.

Bees, grubs, honeycomb, the lot.

It might look like a disaster for the bees...

..but all is not quite lost.

Each bee will eat her own weight in the remaining honey

to keep her going while they rebuild their home.

Summer is full of golden opportunities

but you have to grab them while you can...

..because some of them are truly fleeting.

The Canadian Rockies.

In these northern mountains, summer doesn't last long.

It's only August, but it could be snowing by September.

So flowers rush to bloom while it's still warm.

But someone is picking them.

A pika.

She's the miniature cousin of a rabbit.

And she's doing something that no other animal does.

She's building a haystack.

In winter, her home could be under half a metre of snow...

..so she's creating a makeshift larder

so she can dine on flowers during the long winter months.

She really is making hay while the sun shines.

She's very choosy.

She'll only pick what's in season when it's at its most nutritious.

She eats some and stores some

and she even adds some toxic plants to the hoard.

They'll act as a natural preservative over winter.

Over these few weeks of summer,

she might make 14,000 trips down to the flower meadows.

But it's a slog going up and down the mountainside.

Maybe there's an easier way.

A neighbouring pika has started building his own haystack just down the slope.

As soon as his back is turned,

his devious little neighbour helps herself.

The rightful owner comes back

just in time to see his precious winter supplies

disappearing round the corner.

And he is furious.

MR PIKA SQUEAKS

Thieving is rife around here in summer...

..and every pika has to be constantly on guard.

But it's not just other pikas you have to watch.

The bighorn sheep know an easy meal when they see one.

Without her vital supplies, she won't survive the Canadian winter,

so it's straight back to work to get some more.

Summer might be a time of abundance, but with such competition...

..it pays to be a little bit cunning.

And in the forests of southern Madagascar,

one animal has come up with an ingenious strategy.

A ring-tailed lemur.

All around, the trees are full of huge bugs.

They're cicadas, and in the summer rainy season they're out in force.

They drink the tree sap, extract the sugar...

..and then excrete great jets of honeydew.

And for the lemurs, that is a sign to start hunting.

These fat little insects are rich in protein - a lemur's summer treat.

But there's a problem.

Cicadas fly and they're pretty hard to catch.

The effort can outweigh the reward.

But there is an easier way.

A giant wasp.

A specialist in hunting cicadas.

She paralyses it with her sting

and then drags it to her underground larder.

All the lemur has to do is watch where the wasp hides it...

..and then go and dig it up.

A treat like this is only available for a short time...

..and it tastes so much sweeter

when someone else does the hard work for you.

Summer feasts are often fleeting

and sometimes making the most of them requires not just cleverness but sheer bravery.

On the Serengeti in Eastern Africa, a massive herd is on the move,

following the arrival of lush summer grass.

A million wildebeest, zebra and antelope.

And all these animals attract flies.

Billions of them.

For a rainbow lizard, this could be paradise.

While the herds are around, the air will be full of flying food.

All the lizard has to do is grab the flies with his sticky tongue.

But it's not as easy as it looks.

There might be a simpler way to catch them.

If you're brave enough.

Because it's not just wildebeest that attract flies.

But how can you possibly get close enough to reach them?

Lions are the world's least active big cats.

They rest for a good 18 hours a day, so there's plenty of opportunity.

But you need to hold your nerve.

The brighter, more dominant blizzard should take the lead

but, while he's still thinking about it,

a smaller lizard seizes the moment.

Lions can be testy.

They're not likely to eat the lizards,

but one swipe with a paw that size

and it would be game over.

So you need to choose your moment.

Got one.

The lizards start to up the ante.

The secret is to move fast

and to know when to stop.

When times are this good and there's plenty of food,

some animals turn their thoughts to starting a family.

These long days of summer are the perfect time to look for a mate.

But that brings challenges of its own.

For some, it's a time to get back together with an old flame.

On Heron Island in northern Australia,

a pair of noddy terns sit and bob their heads,

getting to know each other again after a few months apart.

The warm days of high summer are the time to raise a family but it's good

to take a moment to get reacquainted.

On the Great Barrier Reef, the rising warmth of the water

is the cue to get a parrotfish couple in the mood.

The male takes the lead,

gently brushing her fins as he dances around her.

But, for a crowd of surgeon fish, it's just one big party.

The females rise to the surface and release their eggs

and the males dash to be the first to fertilise them with a puff of sperm.

Summer is a time to flaunt yourself.

You're never going to find a partner if you hide yourself away.

But there's one animal that lives in such a hidden place

its astonishing summer courtship has only just been discovered

by the outside world.

In the isolated forests of Mount Mabu in Mozambique,

butterflies are emerging after the summer rains.

As soon as their wings dry, they will set out in search of a mate.

Hundreds of thousands of butterflies are ready to breed

but they won't find their perfect partner in a forest this dense.

Their only option...

..is to head for the open air.

They follow rivers upstream,

travelling higher and higher up the mountain.

It can take hours.

But finally they break out into the light.

They've reached a treeless mountaintop,

the only open space around.

Now the fun can begin.

The males must show off their flying strength to win a female

and fight off rivals.

They only have about an hour each day when conditions are just right.

Finally, they'll return to the depths of the forest

and the females will lay their eggs.

But they've had their moment in the sun.

For some animals, pairing up is a much less gentle affair.

In the deserts of the Middle East,

it's all about strength and endurance.

For a male Nubian ibex, courtship is highly competitive.

It's late summer. On these barren slopes in eastern Israel,

life is tough at the best of times.

As the temperatures soar, it's about to get tougher.

The females need to give birth in spring, so they must mate soon.

And the males know it.

For most of the year these big males live quiet lives...

but not now.

For weeks these males will hardly eat.

They won't do much at all except try to beat each other up.

The toughest ibex gets all the females,

so it's all about the fight.

These are young bucks, evenly matched.

They can go on like this for an hour or more.

But neither of these is going to win.

The females only have eyes for this strong, experienced male,

with his enormous horns.

The younger males never had a chance.

For now they can only practise.

But, eventually, one of them will fight his way to become the next champion male.

For one animal, summer courtship is an even more spectacular event.

But success is all about timing.

On Christmas Island in the Indian Ocean summer brings

what is probably the most dramatic mass emergence in the world.

Christmas Island crabs.

They've spent months hiding away in the forest, all alone.

It's only now, in the rainy days of a tropical summer,

that they venture out.

They need moisture in the air or they'll dry out.

So when the humidity is over 85%, out they come.

There may be more than 40 million of them

and they're heading straight for the beach.

It can take them a week to get there...

..but their hormones kick-start a sugar rush in their bodies

and, after months of inactivity,

they're now dashing along at 300 metres an hour.

At the coast, they pair up.

Once they've mated, each female needs to get her eggs into the water.

As night falls on the high tide, the final push starts.

Their babies need to start their lives in the sea.

But there's a problem. These mothers can't swim.

If they get washed away, they drown.

So they paddle into the shallows and shimmy out their eggs from there.

Then it's the long walk back to the safety of the forest.

To wait for next summer's rains.

After just a few frantic weeks,

40 million crabs simply vanish among the trees.

One of the world's most epic breeding events is all over for another year.

The summer sun gives life a burst of energy.

But when it's highest in the sky, it also brings roasting heat.

So the next challenge summer throws out is keeping your cool.

So how do you keep the temperature down?

Lions can overheat in the hottest part of the day.

So they sleep through it,

turning their bellies to the air to catch a cooling breeze.

In the Australian Outback, where temperatures can hit 50 degrees,

red kangaroos lick their arms.

The saliva cools them, just like sweat does.

Koalas hug trees to stay chilled.

Trees stay cooler in the summer

and a koala can avoid overheating

just by lying up against one.

In a drying Zambian river a hippo wallows in mud

to keep cool while it's waiting for a summer rains.

But it also sweats out a unique red liquid that acts as sun cream.

But when it comes to sheer heat, deserts break all records.

To live in these superheated places you have to be built for it.

Daybreak in the Arabian desert

and a dabb lizard is using the sun's warmth

to warm up after a chilly night.

At this time of day his scales are black to absorb most heat.

But as the temperature rises he starts to overheat.

And he undergoes a remarkable transformation.

The dark pigment in his skin

gets gradually paler to reflect the sun's heat.

After a few minutes,

he can finally saunter off a completely different colour.

And totally chilled.

But there are some desert animals that face an even tougher summer.

The Sahara Desert.

This is one of the hottest places on earth.

Summer temperatures can reach nearly 60 degrees centigrade.

But in this sweltering place there are the ultimate desert survivors.

These are silver ants - the toughest on Earth.

They're built for life in this natural furnace.

Their extra-long legs raise their bodies off the hot sand

and, when they run, they're the fastest ants on earth.

But their secret weapon is their hairy bodies.

New science has revealed that these hairs are shaped like tiny prisms.

Perfectly reflecting the sun and stopping the ants overheating.

Being the world's only hairy ant

means they can stay busy clearing sand

and looking for food in the full glare of the roasting midday sun.

They spin round, taking bearings from the sun

so they don't get lost in the burning desert.

Other insects aren't nearly so tough.

This fly has keeled over.

And that's what these ants are looking for.

It means they can feast on easy victims

and stay safe from attack themselves.

No other predators could cope with this sort of heat.

But even silver ants have their limits.

If their bodies go above precisely 53.6 degrees, they will die.

They can only stay out in the sun for ten minutes.

And they're running out of time.

Some are already expiring.

They need to get back underground... fast.

Just in time.

But you don't need to live in the desert to feel the heat of high summer.

Even when you get down towards Antarctica,

the coldest place on the planet, you can still overheat.

It's the middle of a long breeding season for king penguins

and on the island of South Georgia in the South Atlantic Ocean

400,000 gasping birds are crowded together.

It's one enormous creche.

In midsummer, temperatures can hit a balmy 17 degrees.

And the penguins are feeling it.

The dense coat of feathers that keeps them warm in the sub-Antarctic winter

is far too hot for the height of summer.

Everyone is sweltering.

Even the neighbouring elephant seals

are throwing wet sand over themselves to cool off.

The adult penguins can head off to fish in the refreshing South Atlantic.

But the chicks still have their downy winter overcoat.

They can lose some heat through their enormous feet

but not enough.

These chicks take more than a year to fledge

and it'll be another two months before they can swim properly.

So they take a tentative dip in a chilly glacier stream.

But it's a bit choppy and it's hard to stay on your feet.

So they find an alternative.

A muddy pool, just cool enough to be refreshing.

Now THAT was fun!

When the heat builds, keeping cool is a challenge for everything.

But the burning sun doesn't just overheat animals.

It also draws the water from the land.

And when your world is in danger of drying out

it brings a whole new set of challenges.

This is Namibia in southern Africa.

It's getting late in the dry season.

The increasing heat will bring tropical summer thunderstorms

but there's no sign of rain yet.

Then suddenly, out of nowhere, there's life.

Crowds appear as if by magic.

But there seems to be nothing for them.

They're here because there's an ancient underground spring.

Even when everything has turned to dust,

it bubbles to the surface and never runs completely dry.

At this time of year, when everything is waiting for summer rains,

it's like the promised land.

Every day hundreds of animals gather from miles around,

all jostling together for this precious chance of a drink.

It's like the world's most exotic bar.

But with all these animals crowded together,

it brings dangerous attention.

Lions.

The herds are spooked.

But all the lion wants right now is a drink.

And nobody is going to stand in her way.

The shortage of water means predators and prey must all drink alongside each other.

When the summer rains finally fall there will be plenty of water and the crowds will vanish.

But, for now, this is a life-saver.

Just when everything seems bone dry,

refreshment can come from the most unlikely places.

In the Sonoran Desert of Arizona and New Mexico,

it might not rain at all for five months.

But this saguaro cactus took precautions long ago.

These giants only live in this one desert,

and they're totally tuned in to its seasons.

Last time it rained,

this giant among cacti sucked up the sudden flood of water

and its pleated trunk expanded like a concertina.

Its main roots are shallow,

but they spread out 30 metres all around its base.

Its trunk is so huge it could have five tonnes of water

packed away inside.

It not only survives...

..it thrives.

As the weeks go on and the drought tightens, it flowers.

And then at the height of summer,

with its carefully gathered store of water,

it produces the most luscious fruit.

In the desert, that makes it a lifeline.

There are visitors from far and wide.

There may be 60 different types of animal reliant on its generosity.

Birds,

insects...

..even desert tortoises rush to the feast.

And just when the fruit is running out,

the heat of high summer brings a sudden change.

Thunderstorms.

North America's summer monsoon.

THUNDER CLAPS

The cactuses get to replenish their reserves.

To survive summer's toughest times,

sometimes you just have to wait for it to change.

But sometimes you have to go and get what you need.

To find summer's greatest riches

some animals will travel thousands of miles.

Literally, to the ends of the Earth.

Millions of sooty shearwaters fly all the way from New Zealand

to raise their babies in Alaska.

Just because the summer seas are full of fish.

Humpback whales swim more than 3,000 miles from Hawaii

to spend summer in the same rich Alaskan waters.

It's the longest mammal migration on Earth.

But it's not just the big animals

that make the most adventurous trips.

This is the smallest migrating bird in the world.

A calliope hummingbird.

His wings are only four centimetres long

and he weighs less than a penny.

But he's just flown 3,000 miles to get here.

He's come all the way up from Mexico

to the mountains of Wyoming.

Just for the flowers!

Here in North America, there are richer pickings

than back at home in the heat of Mexico.

Here, he can drink his own weight in nectar every day.

But this is a popular summer destination for hummingbirds.

You have to be prepared to fight for your flower patch.

A rufous hummingbird is twice his size,

but the calliope male is feisty.

He's not going to let anyone muscle in.

The summer bounty is so good here

it's where the hummingbirds choose to raise their little ones.

And they don't get much littler than this.

The nest is barely the size of an egg cup.

The babies are already bursting out of it.

Their father doesn't get involved in childcare.

It's down to their mother to get them fed,

pumping a mixture of nectar and insects

straight from her beak into their throats.

But she's in a hurry.

In about three weeks, she will be off back to Mexico for the winter.

The chicks will fledge soon,

but neither parent will wait for them.

These young hummingbirds will have to find their own way back to Mexico

all by themselves.

Nearly 3,000 miles on almost nothing but nectar.

That's quite a start to life.

But that's nothing compared with the long haul flight made by this Arctic tern.

It's the longest migration of any animal on Earth.

He's flown all the way from Antarctica

and he'll spend the summer here in Svalbard, in the Arctic -

a 44,000 mile round trip,

from the bottom of the planet to the top.

But what could be worth such a mammoth journey?

The long hours of summer daylight mean the seas are full of life.

As much fish as you could possibly want.

And the terns flock here in their thousands.

He brings a little gift for his lifelong partner.

By the time they get back to Antarctica

it will be summer again there.

Their lives are lived in an endless summer.

No other animal spends longer in the sunshine.

And they've come back here to raise their chicks.

It seems like an adventurous thing to do,

bringing up your family on the road.

But the summer feeding is so good here,

in three weeks these chicks will have grown

more than five times heavier.

And they don't waste a morsel.

This chick was up and running less than three days after it hatched.

But in about a month it's going to have to fly the massive return trip

to the other end of the world.

Over its lifetime it could clock up a total of 1.5 million miles.

It's certainly ambitious.

These epic summer trips are worth it

when you're trying to give your family the best start in life.

And sometimes it takes a monumental effort.

In the warm waters off northern Australia,

a green turtle is about to come ashore.

She's coming back to the very beach where she was born.

She might have swum 1,500 miles to get here.

And she's not alone.

At the height of summer,

there might be more than 20,000 females landing on this one island.

It's the world's biggest gathering of green turtles.

These females may be 50 years old,

but they're still raising babies.

They come ashore when the temperature is just right for their eggs.

When night falls,

it's a scramble to find a nesting place in the warm sand.

Each expectant mother carefully digs out a hole with her back flipper.

But with hundreds of mothers choosing this perfect moment to lay their eggs,

there's a problem.

In the rush to dig their nests,

they almost bury each other in sand.

But they haven't come all this way to give up now.

They might lay more than 100 eggs.

These mothers won't ever see their babies.

At daylight they'll go back to the sea.

They will leave it to the warmth of the sand to do the rest.

After two months, the eggs hatch.

And the warmth has had an extraordinary effect.

If the sand was over 30 degrees centigrade,

the baby turtles will hatch as females.

Under 28 degrees, and the babies will all be male.

These little turtles' lives have already been predestined

by the strength of the summer sun.

This turtle is on the start of her own epic migration.

But one summer, after 30 years at sea,

she'll be back to this very beach.

But one young animal has to take an even riskier long-distance trip.

On a warm day in midsummer

it has to take the biggest gamble of its life.

On the Hawaiian atoll of French Frigate Shoals,

young black footed albatrosses are getting to grips

with their two-metre wingspan.

They've spent the last five months preparing for this one moment.

Their parents have already left and there's nothing to eat.

They're on their own

and ahead of them is a 1,500 mile journey north

to better summer fishing grounds.

First, they have to get airborne.

But even that takes some practice.

There's not much of a run-up.

Their very first flight will need a take off over water.

And in the shallows there's something waiting for them to fail.

Tiger sharks.

They know full well these young albatrosses will be around here in summer

and learning to fly.

They gather on the very day the chicks take their clumsy maiden flight.

And they wait.

Every young bird has to leave the island.

There's no alternative.

It's do or die.

A lucky escape for one.

Another prepares to launch.

There's no going back now.

It's vital not to land in the water.

From here, take off is even harder.

This young albatross has to make an almighty effort.

She's done it.

If she's lucky, she'll spend the next 40 years roaming the ocean.

But on this one day in this one summer

she's made the right start.

Summer moves on,

and life is getting ready for the next seasonal challenge.

As autumn kicks in in the mountains of North America,

pikas will finish their collecting.

In the forests,

black bears will be getting ready

to spend the next five months fast asleep.

And the king penguin chicks will feel their world cool down

as their long winter approaches.

Summer is all about seizing the moment

and enjoying nature's most lavish bounty.

Life is busy.

And it might have its challenges.

But there are pleasures, too.

Autumn is just around the corner

so you need to make the most of the good times while they're here.