The animal world is full of spectacle and wonder.
But what's it like to be right in the heart of the action?
To find out, our team of spy creatures goes undercover.
They not only look like the animals they film -
they behave like them, too.
Armed with the latest camera technology...
..they are heading across the globe.
From the heat of the tropics...
..to the lands that lie in the north.
From the islands of the southern seas...
..to the snow and ice of the frozen poles...
..our spies reveal the astonishing variety of life
that thrives there
from inside their world.
On this assignment, our spy creatures
explore life in the temperate zone -
the lands that lie between the tropics
and the Arctic Circle.
In this northern realm,
animals find extraordinary ways to cope
with the changing seasons
and the surprising opportunities they bring.
In the mountains of Japan, winters can be harsh
and temperatures can fall far below zero.
The Japanese macaque
is the only monkey that can survive this far north.
Here, volcanic springs bring comforting warmth.
A mountain spa.
The perfect spot to luxuriate.
A new member has just joined their health club.
Spy Macaque is already making friends.
A youngster, just nine months old.
The spa has another new recruit.
One that can film the monkeys' bathing rituals
both from above and below.
It's already capturing unique behaviour.
As a mother grooms her baby,
she lets warm water penetrate deep into its fur.
The hot tub is a place
to socialise and strengthen friendships.
It's a shared activity.
You scratch my back, I'll scratch yours.
The troupe has a clear hierarchy.
Who grooms who helps keep everyone in their place.
It's also a chance to relax.
Nearby, winter sports are on offer.
The young males love play fighting.
MACAQUES SCREECH
One day they'll leave the troupe to join another.
Testing their strength helps prepare them for that moment.
Today, they have a chance to play with a snowball.
One that can film.
Rather than play, he admires his reflection in its lens.
Nearby, games are almost over.
In the spa, Spy Monkey is still making friends,
including the curious baby.
But when social position is everything,
you can't always choose who your friends are.
It's Mum who decides.
The spa not only gives warmth,
it gives therapy,
helping them de-stress.
It's used most by the females,
especially those who are pregnant.
As females never leave the troupe,
they pass the custom down through the generations.
The troupe's young males will soon be gone.
For now, a favourite pastime is disturbing the peace.
The baby isn't so quick off the mark.
And Mum is nowhere to be seen.
But what mother would ever really leave her baby?
Now, a special kind of warmth.
One only a mother can offer.
But there goes her chance to relax.
While it's still winter in Japan,
the mountains of northwest Mexico
are having their first taste of spring.
It's the setting for perhaps
the most beautiful wildlife spectacle of all.
One that requires a unique spy creature.
The blue-throated hummingbird is native to these forests.
This spy version hovers just like the real thing.
In the heart of this grove,
half a billion monarch butterflies lie sleeping.
They have travelled from as far as Canada
to escape the cold northern winter.
How they return to this exact spot is a mystery.
Like the butterflies, hummingbirds feed on nectar.
So our spy isn't seen as a threat.
While resting,
they cluster together
to conserve precious warmth.
But as winter ends,
the sun warms their fragile wings.
Once they reach a critical 13 degrees Celsius,
they start to fly.
As the day warms,
the forest comes to life.
Spy Hummingbird won't harm these delicate butterflies.
Its moving parts are shielded to keep them safe.
Butterflies can even safely land on its wings.
It soon captures something quite extraordinary.
What starts as a trickle soon becomes a stream.
Then grows into a cascade.
A spectacle that has rarely been filmed.
And our spy is harmlessly in the very heart of it.
Beauty also lies in the detail.
After five months spent hibernating,
each monarch must take a drink.
It will convert their fat stores to vital sugars.
Fuel for the long journey that lies ahead.
Re-energized, they begin their migration
back to North America.
The journey will involve three successive generations,
each completing a new stage of the journey.
Only the last will return in the autumn.
It's a relay race across the generations
of up to 6,000 miles.
How they return to this exact same grove remains a mystery.
In Alaska, at the other end of North America,
spring is only just starting to arrive.
Here, bald eagles rule the skies.
Including, for now, a spy.
At this time of year, the glaciers are volatile,
bringing danger to the life that thrives here.
As the sun rises higher each day,
the spring melt begins.
Already, cracks have started to form.
Soon the sea ice will be gone.
The resident harbour seals now haul out on ice cast from a glacier.
With spring, humpback whales also start to arrive.
They migrated north from California
to enjoy the feeding opportunities now found here.
Sea otters gather in huge rafts -
up to 2,000 in all.
The nursing mothers congregate in the areas now free of ice.
Spy Sea Otter joins them in their floating nursery.
She's immediately accepted
by these notoriously shy creatures.
It's a privileged insider's view
of the most sociable otter of all.
Here, they not only have company -
there are more eyes to spot danger.
The spring melt
makes the glaciers unstable.
The icefall creates a rolling wave
up to ten metres high.
It may still be a danger
over a kilometre away.
In the turmoil,
mothers and pups are easily separated.
They must find refuge away from the glacier.
In a cove, they find a solution
to the turbulent waters.
Kelp offers the moorings they need.
It's just a matter
of how best to attach themselves.
But even this beginner is having success.
As the ice vanishes,
more kelp beds will soon appear.
The otters can enjoy
the upcoming summer in peace.
Spring has also reached Manitoba
in central Canada.
It marks the beginning
of an extraordinary awakening.
These are garter snakes.
After hibernating together underground,
they emerge in their thousands.
Remarkably, all are male.
They warm themselves in the sun,
preparing for the moment
when the females emerge.
This one has a camera.
Our spy is entering a world governed by smell.
Snakes use their tongues to pick up scent.
All are searching for females.
When the males detect a likely partner,
they swarm all over her,
desperate to be the first to mate.
But Spy Snake is witnessing
something quite extraordinary.
Although there are no females here,
the males are still swarming.
And even more are joining the scrum.
Nearby, others have also
picked up the scent.
Soon, there's no stopping them.
As everyone piles in, Spy Snake
becomes buried in the growing ball of snakes.
Then, in the middle,
the reason for the knot of serpents.
An impostor -
a male that smells like a female.
He's deliberately attracting the males.
His aim is to share their warmth.
By fooling them into embracing him,
he becomes superheated -
a huge gain for a cold-blooded reptile
looking for a mate.
Finally, there she is.
Her perfume is far stronger
than the impostor.
Nothing beats the real thing.
The warmest males are already hot on her trail.
But the superheated impostor leads the charge.
Here, snakes that impersonate females
get ahead in the mating game.
Best leave them to it.
Summer has arrived
in the forests of southern Germany.
The season of plenty
for a secretive and industrious creature.
The only clue to its presence -
a carefully constructed woodpile.
This is the time
beavers raise their young.
Making the most of the lush vegetation that summer brings.
They recognise each other by smell.
Rubbing noses confirms their friendship.
They pair for life
and live together as a family.
They are wary of strangers.
Newcomers enter at their own risk.
Somehow, Spy Beaver must win them over.
But first, he must pass the odour test.
Real beavers have scent glands
that tell family from foe.
As our spy doesn't smell like a beaver,
he's free to explore.
Their lodge has a concealed entrance...
..that lets them come and go
without being seen.
Keeping a low profile hides them
from predators like lynx and foxes.
On the bank, a new spy
is there to greet her.
Beavers are strict vegetarians
and Spy Baby Beaver
is surrounded by willow -
their favourite meal.
Her teeth are coloured orange
by iron deposits that strengthen them.
They are also self-sharpening
and slice through wood like a knife.
Beavers can fell 300 shrubs and trees each year,
clearing old growth and helping
to maintain their entire ecosystem.
For now, the youngsters
leave it all to the grown-ups.
They spend most of their time at play.
Wrestling is a rarely filmed pastime.
Beavers also have friends.
A muskrat.
This mini-me lives alongside the beavers,
and even shares their lodge.
Wherever the beaver goes,
the muskrat follows.
Being ten times smaller
means the best food
is usually out of reach.
But while the beaver does the hard work,
the muskrat can sit back.
This is what friends are for.
Beavers with young
are always on high alert.
A false alarm.
But always best to err
on the side of caution.
After a fright,
grooming is a comfort for everyone.
By creating a layer of air
between skin and underfur,
it provides insulation.
Harmony is soon restored.
While the muskrat
just keeps himself busy.
For Mum, a well-earned massage
after a hard day's work.
As early summer arrives,
Baha, California becomes the focus
of a great natural gathering.
Here, brown pelicans patrol
some of the richest fishing grounds in the world.
There's a new member of the flock.
A spy on the wing.
One that can film the fishing party
wing tip to wing tip.
Clear, warm currents
create plankton blooms.
Huge fish shoals are found.
It's just a matter
of spotting them from the air.
Then taking them by surprise.
But where fishing is easy,
everyone wants a piece of the action.
Bottlenose dolphins.
By spreading out, they increase
their chances of finding a shoal.
Dolphins are intensely curious.
They leap to check out
the strange bird that's following them.
Here, it's not just dolphins
that take to the air.
Mobula rays.
Why they leap is a mystery.
But it might be a signal to show where food has been found.
For where rays are jumping, huge blooms of plankton are not far away.
And rays converge in their tens of thousands to feed.
The aerial view may be astonishing,
but more wonder lies below.
Spy Ray gets closer than any human diver can.
Deep into the heart of the shoal.
With a spy swimming among them
and a spy in the sky,
our cameras capture an event never filmed before.
As the rays circle, they create a vortex,
concentrating the plankton inside.
At every turn, more plankton is sucked into the centre.
They just have to scoop it up.
When they feed near the surface,
they use a different technique.
Ripples pass through the masses,
like a subaquatic Mexican wave.
Soon, the leaping starts again.
For Spy Ray, it's a case of, if you can't beat them, join them.
As the day ends, our spy keeps leaping with the best of them.
GULLS CRY
It's midsummer in Alaska.
The fishing season for grizzly bears.
THEY GROWL PLAYFULLY
With uncanny timing,
mother bears bring their cubs to a remarkable event.
Soon, a million salmon will pass up this river to spawn.
BEAR HUFFS
This year, a newcomer is joining them.
With his teddy-bear looks and camera eye, he's well prepared.
Late arrivals must be quick.
The best fishing spots will soon be taken.
BEAR GRUNTS
Our spy also has a quick way down.
He's now in prime position.
Risky, when a mother bear is still staking out her claim.
SHE SNORTS
SHE SNIFFS
But he seems to have got away with it.
For all, it's a waiting game.
The tide is out, and the river empty.
But her cubs have yet to master the art of patience.
They head out to the estuary to search for the salmon.
Leaving mother bear to bide her time.
Spy Bald Eagle is already on their trail.
Bears can smell fish up to 20 miles away.
By following their nose, they soon find where the salmon are gathering.
With fish everywhere,
just how hard can it be to catch one?
Finally, after all that effort.
Older bears know better than to waste their energy.
They've learnt that salmon arrive on the high tide.
But the first is not what it seems.
Spy Salmon swims just like the real thing.
It, too, is ready to run the gauntlet of the bears.
In its wake are countless sockeye salmon.
They've travelled thousands of miles
to spawn in the river where once they were born.
The salmon bottleneck beneath the falls,
before taking a leap into the unknown.
A prime spot for fishing.
Bears can see underwater.
Useful for targeting.
With so many fish, it's like bobbing for apples.
They can eat over 30 salmon a day,
and almost double their weight in the fishing season.
They soon become fussy, picking the most nutritious treats,
like the skin and head.
But any good party can attract unwelcome guests.
THEY GRUNT
They have good reason to feel nervous.
Males can kill cubs.
One mother makes a stand.
SHE GROWLS FEROCIOUSLY
She's joined by another.
THEY GROWL
He may be powerful, but he's no match for a mother's fury.
He won't be back in a hurry.
Now that the cubs have nothing to fear,
why not tackle a bear of their own?
Grab the paw first...
That showed him.
Now the killer bite.
Maybe not.
SPY BEAR GRUNTS
Meanwhile, Spy Salmon has been left high and dry.
Surely a better bet.
Never mind, there's always one that gets away.
As summer draws to an end, Istanbul and Turkey
sets the scene for another great spectacle.
White storks are heading south to escape Europe's upcoming winter,
when food will be hard to find.
Half a million will make the perilous journey to Africa
of up to 8,000 miles.
They have a fellow traveller.
He joins them in the thermals that rise from the ground below.
Spy Stork's broad wings are designed to ride these natural elevators,
just like the real birds.
WIND GUSTS
The twisting columns of hot air
offer the storks a free ride upwards.
WIND GUSTS
Once they reach the top of one thermal,
they simply glide to another.
They head to the city with hardly a wing flap.
Good move.
The roads and buildings of Istanbul reflect the heat,
creating huge thermals
which carry them upwards
even higher than before.
Riding only on hot air, they can reach heights of nearly a mile.
They need the altitude.
They now face the riskiest part of their journey.
Because thermals don't form over water.
As they try to glide,
there's nothing to give them the lift they need.
Those who hadn't gained enough height on land
soon drop from the sky.
To avoid plunging into the sea,
they must flap their heavy wings.
They start burning body fat
just to stay airborne.
Consuming 20 times more energy
than when they glide.
If a wing so much as touches the water, they will fall in and drown.
They are battling for their lives.
Then, suddenly, a lifeline.
An outcrop rising from the sea.
Just enough sun-baked rock
to create the thermals they so desperately need.
It's a free ride upwards that saves their lives.
In this way, storks use islands as stepping stones
to help survive the crossing.
Travelling only by day,
it can take four weeks before they arrive over the plains of Africa.
BIRDSONG
Here, they'll have all the insects and other food they need
as they wait out Europe's upcoming winter.
BIRDSONG
In England, the early-morning mist
signals that autumn has finally arrived.
And with it, the greatest and most colourful transformation in nature.
The trees survive the winter
by taking back nutrients and chlorophyll from the leaves.
What's left behind are the autumn hues.
The leaves that once fed the trees are then discarded.
Grey squirrels are among the many preparing themselves
for the changing season.
CROWS CAW
Spy Squirrel is poised and ready with his camera eye.
Well, nearly ready.
Along with his spy nut,
other disguised cameras are strewn
across the forest floor.
In autumn, squirrels stock up their winter larder.
Each may bury around 10,000 nuts.
In an amazing feat of memory,
they may retrieve 4,000 of them.
With so many nuts to find, competition is rife.
HIGH-PITCHED SHRIEKING
Every nut is a gift for would-be thieves.
CROWS CAW
In fact, around a fifth of all squirrels steal from others.
That'll do nicely.
It's one thing to steal a nut -
another to keep hold of it.
It's not just squirrels feeling the seasonal change.
Autumn is the rutting season for red deer.
By breeding now, they will have their young in the summer.
Their stag.
He tries to gather together
as many hinds as he can.
Perhaps 20 in all.
Spy Squirrel is right in the middle of his herd.
But the stag has other things on his mind.
STAG BELLOWS
In the rutting season, he has his work cut out.
Rounding up his straying hinds
is a constant battle.
But he has an even bigger challenge - a rival.
STAG BELLOWS
A bevy of hinds is just what he's looking for.
Females will go with the strongest stag.
STAG BELLOWS
The rival must fight to prove his mettle.
STAGS BELLOW
Battle lines are drawn.
One mistake could prove fatal.
Whoever gains most ground wins.
Victory for the reigning stag.
STAG BELLOWS
Spy Squirrel may be worse for wear,
but he still captures one final shot of the champion.
STAG BELLOWS
For the squirrels, there's still one last nut
they've yet to get their paws on.
Another trophy to squirrel away.
Back in Germany, among the beavers,
autumn is also well underway.
It won't be long until the winter sets in.
Before then, their lodge must undergo some maintenance.
Spy Beaver investigates.
It's the beavers' busiest time of year.
They scour the river for building material.
Stones help stabilise the lodge against flooding.
Preparing their home for winter is everyone's responsibility.
Sticks and logs bring strength to the structure.
It can also be used to plug holes
and reduce leaks to the main chamber.
Small sticks are used to fill in the gaps.
To cap it all, a thatch of turf helps weatherproof the roof.
On the river bank, the whole family is hard at work
collecting food and nesting material.
Even the youngsters do their bit.
The beavers must harvest what they can before winter sets in.
Everything must be ferried back home.
The muskrat uses grass as nesting material
to furnish his own quarters in the lodge.
As winter approaches, the beavers redouble their efforts.
And the muskrat gets ever more ambitious.
With everyone working flat-out,
they'll soon be ready for the upcoming winter.
They'll spend most of it safely tucked up inside.
As the year comes to an end,
the snows have returned to Japan.
Already, the macaques are huddling together for warmth.
Once more, their social life
revolves around the hot tub.
Our spies are at the end of their mission.
Sweet dreams soon come to all.
Time-out for our spy creatures, too.
Next time - our spies travel to the islands of the southern seas
to meet yet more extraordinary animals.