Original subtitles

Squirrels, one of our most familiar wild residents...

..but is there more to these cheeky characters than first meets the eye?

They've managed to become one of the world's most widespread animals.

There are squirrels and that can survive a deep freeze...

SQUEAKS

..communicate in complex languages...

..and outwit their greatest enemies.

RATTLING

Now, they're catching the attention of the world's top scientists.

This is a really special animal.

It's kind of a three-dimensional spatial genius.

To uncover the squirrel's incredible talents,

we are going to work with the experts...

Squirrels are one of the most agile animals on Earth.

..put them to the test on a specially-designed assault course...

..and see the world through the eyes of an orphan,

as he develops the skills he needs to get back to the wild.

It's time to meet the high-flying,

nut-loving, clever creatures we should never underestimate...

..the Super Squirrels.

The squirrel family is surprisingly large.

There are almost 300 different species.

They are found in a huge range of habitats...

..from frozen Arctic tundra...

..to baking deserts.

Some live underground...

..others high in the treetops...

..and a few can even take to the air.

This adaptability has seen them conquer the globe...

..and colonise almost every continent on Earth.

Possibly the most loved of all is the iconic Eurasian red squirrel.

This tree squirrel was once widespread across Europe,

northern Asia and Siberia,

especially in ancient conifer forests.

But in several countries, their numbers have plummeted,

and they are under threat.

In the UK, 75% of the remaining

red squirrels are found here, in Scotland.

With the species in decline,

every single red squirrel is precious...

..and one has just been rushed in.

Look at you!

So small.

This is a baby red squirrel.

It's the smallest red squirrel I've ever seen.

It looks to be maybe about five days old.

He has no hair, eyes closed, pretty much pinkie form.

SHE LAUGHS

The tree holding his nest was cut down.

He will now be totally dependent on his new surrogate mum,

Sheila McAllister.

Sheila's worked at the National Wildlife Rescue Centre

for five years.

She and the team look after nearly 10,000 animals every year,

from foxes to otters.

All right...

Sheila is a specialist in caring for red squirrels and releasing

them into the wild...

..but this one is the youngest yet, and very vulnerable.

So, the next 48 hours for this wee guy is going to be quite extreme.

He's going to need a lot of care to get him through.

Definitely, out in the cold, he wouldn't have survived by himself.

In the wild, he'd be tucked up inside a nest.

Tree squirrels build nests from twigs, moss, bark and leaves.

The nest is known as a drey.

It keeps the young warm and safe from predators for the first three

months of their lives.

At this age, they are totally dependent on their mother's care.

This little orphan will rely on Sheila instead.

She will feed him milk every hour for the next couple of days,

even through the night.

It's a critical time, but they're already beginning to bond.

So, we've decided to name him Billy, after Billy Connolly,

and my job over the next few days will be to keep him nice and warm,

regular feeds,

and just overnight care to make sure he is getting all the food

and comfort that he needs.

There you go. Nice and snug.

This is a rare chance to follow a red squirrel as he grows up.

If it all goes well,

we'll see Billy reach key milestones in his development,

and go back to the wild.

The decline of the Eurasian red squirrel has several causes,

including loss of habitat...

..and the arrival of a competitor...

..the eastern grey squirrel.

It's native to the east coast of the United States,

but was introduced to the UK in the 1800s.

Since then, it's thrived,

and outcompeted the smaller red for habitat and food.

Thanks to its adaptability,

the great squirrel has become one of the most prolific on Earth.

DOGS BARK

Their agility is impressive to watch,

but some of their most remarkable moves go unseen, up in the trees.

Wildlife film-maker and squirrel fanatic Douglas Parker is obsessed

with finding out more about their aerial acrobatics.

He wants to bring grey squirrels down to our level and put them

to the test.

I want to build the ultimate obstacle course to highlight all of

these incredible superpowers that they have.

I want to test their physical progress, and to do that,

I'm going to get obstacles which highlight their grip,

highlight their balance, highlight their leaping ability,

and just to show that it's not just climbing around on branches.

You know, it's really, really, really impressive.

So, Doug set to work,

with a bit of expert help...

..designing and building the ultimate squirrel assault course

to show what they can do up in the trees.

Eight obstacles...

..each designed to test a different treetop skill...

..with the prize of hazelnuts as a reward.

To get onto the course,

the squirrels need to complete the first obstacle...

..Overhang.

The squirrels must leap up and navigate the overhanging wood

to reach the nuts on the platform.

At the centre of it all, Doug settles into a hide.

So, what I have done to get the squirrels to go around the course

obstacle by obstacle is put food

stashes at the end of every single one.

So, once the food is eaten at the first obstacle,

it will then have to get to the second obstacle to get the food.

And it's not long before the first contender arrives.

Early signs looking good.

It's safe to say we've got some hungry squirrels.

Within hours,

several squirrels have worked out the overhang to get the nuts.

It's quite clear that once these squirrels have figured out how to

tackle an obstacle, they just perfect that movement.

And before Doug even expected it,

they are straight on to the next obstacle...

..Pendulum.

They're over to the other side in no time.

I cannot believe how easily it just got round that.

They're using just one central pendulum

and blinding speed to get across.

Doug's course is already showing how quickly squirrels learn.

Working out how to solve a problem is a key squirrel skill...

..wherever they live.

The grasslands of western America...

..home to a very different sort of squirrel...

..the California ground squirrel.

They live in burrows, where they can have their pups in safety.

But burrows are no barrier to their greatest enemy...

..the Pacific rattlesnake.

The snakes use infrared sensors to detect the heat of

warm-blooded prey, so there's nowhere to hide.

With pups to defend, a female squirrel must face the snake.

She flicks stones.

It doesn't look like the smartest move,

but it's a deliberate and cunning ploy.

By provoking it, a squirrel can listen to the frequency and speed

of the rattle...

RATTLING

..and this reveals how big, how warm,

and how aggressive the snake is.

After listening, the squirrel can work out what to do.

She pumps extra blood into her tail, and waves it repeatedly.

The blood flow in her tail

is normally used to help regulate temperature...

..but here she knows that the extra heat will be sensed by

the rattlesnake, and it makes her seem bigger.

It works.

Solving problems like this

can increase a squirrel's chances of survival.

It is something the pups will need to learn, too.

Squirrel babies have to grow up fast.

In Scotland, just three weeks have gone by,

but the change in Billy the orphan squirrel is clear.

Hey, little guy.

Hello.

When she's not at work,

Sheila brings him home to give him the 24 hour care he needs.

Billy's doing really well.

He's feeding really good, gaining weight daily.

Billy's just opened his eyes just last night,

so he's still not quite sure of the light,

and he still squints his wee eyes.

So, he's just adjusting, and everything is still developing.

He's starting to really look like a proper little red squirrel now.

He's clearly thriving, and he's already developing one

of his most vital life skills - his grip.

The grip that Billy has is really important because it's going to

keep him in those trees.

You can see that, even so small,

he's got a good bit of strength in him.

He kind of hooks these nice wee claws into you...

..which have grown superfast, as well.

At this stage, they would still be in the nest,

and they would be pretty inactive, so they would just be, like,

really kind of exercising amongst themselves.

Without his mother or siblings to interact with,

Sheila will have to help Billy practise his grip.

Oh, are you going up here?

Good lad.

In the wild, having strong claws and a firm grip is a matter of

life and death up in the canopy.

It's a difficult place to manoeuvre.

No two branches are ever the same,

and conditions constantly change with the weather and the seasons.

Their aerial abilities are so impressive,

they've even got the attention of the world's leading scientists.

Professor Robert Full is an expert in robotics.

Here at the University of California, at Berkeley,

he's already taken ideas from cockroaches...

..and bush babies...

..and now he can see the potential for squirrel-inspired robots.

Part of our motivation is to understand the most agile animals,

and squirrels are certainly among the most agile.

Imagine if we could understand the fundamental principles of how the

squirrels move through these complex, unstructured environments,

and then translate them to robots -

robots that, in a disaster area,

would be able to read and jump through gaps,

and climb on wires to quickly enter

an area in order to find individuals.

To study the squirrels in detail,

the team use a portable wall out in the woods.

They stick perches to it, which represent branches of the tree.

A steady supply of nuts attract the wild squirrels in to play.

Bob is discovering that their aerial acrobatics

depend on their decision-making.

For example, one of the tasks we had is, how could they determine where

to jump on branches or rods that are of difference stiffnesses?

Some are really springy, and some are very stiff.

What would they do in order to make

the best choice of jumping to the perch?

When it's very stiff, they run out very far and only jump a little bit.

That's the sort of best decision.

But when a branch is very bendy, they make a different choice.

They decide to only go a little way and then take a longer jump.

So, they make a very good decision,

in terms of their jumping capability.

All these choices are made in a split second.

Bob is hoping to understand these decisions for the breakthrough

he wants in designing robots.

But his experiments have shown something else too.

If they do get it slightly wrong,

it's their grip that can save the day.

Even if they don't land perfectly on the perch,

they have the ability to manoeuvre their body such that they're able to

grip and grab on with their claws,

so that they don't fall,

and then they can swing back up on the perch to get their peanut.

It's a brilliant demonstration of their grip in action...

..and something Bob hopes

to replicate with his robots in the future.

One squirrel needs a good grip more than most.

The jungles of southern India are home to the Malabar giant squirrel.

This remarkable-looking squirrel

is one of the most colourful members of the squirrel family.

It's also one of the largest.

At a metre long,

it's almost as big as this lion-tailed macaque.

The two compete for food, so meetings aren't always friendly.

Luckily, there are more of these huge jackfruit around,

so they don't need to share.

Being such a heavyweight

makes the Malabar giant squirrel's grip particularly impressive.

It means they can hang upside down while they feed.

They also use their grip to run down trees headfirst.

To help them do this, they have a special adaptation -

an unusually flexible ankle joint

allows the foot to rotate almost 180 degrees.

It's the equivalent of standing with both feet pointing backwards,

and means that, whether they are going down or up,

their claws are always able to grip on.

This treetop technique is used by all tree squirrels...

..whether large...

..or small,

and Billy's grip and strength has come on leaps and bounds.

He is just over seven weeks now,

so we can see he has changed quite a lot.

He has got this great bushy tail,

and his agility's really coming on.

He's getting very active, and quite a handful.

To make sure Billy can go back to the wild,

he needs to meet some of his own kind.

Here, sweet pea.

And Sheila is now caring for another youngster of similar age.

Are you hungry? Yeah.

This is Annie.

She's from Inverness.

She was caught by a dog

and the owner handed her in to the vets.

So, luckily, she doesn't have any injuries,

and for the size of her, she is doing pretty well.

It's an important moment for Billy.

Who's this?

He's scared.

At this age, in the wild, the squirrels would have siblings,

and they would also have their mother, so it's just that contact,

and being able to express natural behaviours, and just have playtime.

So, it really going to benefit Billy,

as he has never had any contact with another squirrel.

They already seem to be pushing each other to new heights.

He's off. It's a good sign.

Come on, Annie. Woohoo!

Annie...

Where are you going, Billy?

What's your next move?

Hey!

Young red squirrels learn a lot from interacting with their families...

..but other species have taken living together to the extreme.

These are prairie dogs, a type of ground squirrel.

They live in a large colonies, called towns...

..on the open plains of North America.

The advantage of living in numbers

is there are more eyes to keep a lookout.

When a coyote is spotted...

SQUEAKS LOUDLY

..they use a complex language to warn the others.

SQUEAKS

Their call communicates more than just a warning.

It identifies the type of predator, too,

so they can take the right evasive action.

So, this coyote might be better off trying its luck elsewhere.

These prairie dogs, it seems, like to do things differently.

They eat mostly plants -

not the diet you'd expect from a squirrel -

and that's down to their size.

Big animals don't lose as much body heat

to the environment as smaller ones,

so, as one of the larger squirrels,

prairie dogs don't have to use as much energy to keep warm...

..and can survive on a less nutritious diet.

It's a lifestyle that suits them down to the ground.

What's in here?

Smaller squirrel species like Billy need a lot more calories.

Do you need some?

That's why they depend much more on nuts, which are high in fat.

Are you going to take it? Good boy.

These almonds are 49% fat, ideal for a growing squirrel.

So, Billy has just started to eat nuts.

He's like a wee secret eater, though.

He just hides out in his bed, and he'll eat underneath the covers.

Last night was the first night I've seen him actually sit upright

and eat a nut, which is quite a good stage for him.

For now, he can only eat soft nuts without the shells.

Although all his teeth are through, they are still developing.

A squirrel's front teeth never stop growing.

That's to counteract the wear from a lifetime of relentless chomping.

Red squirrel teeth grow around 20cm a year,

so in Billy's lifespan,

his teeth may grow as much as two metres.

Next, his tooth enamel will harden.

It's a critical moment,

because then he will be able to cope with the hardest nuts in nature.

Once he starts eating the nuts in the shell and being able to break

through this, then we're quite happy for him

to be going to the wild, then.

Nuts are also the favourite food of the grey squirrel...

..and at the assault course, Doug is relying on this to entice

the squirrels on to the next obstacle...

..Lily Pads.

The squirrels must leap between the coloured discs.

The blue discs are solid.

The red discs are wobbly.

The idea is that they'll learn

the difference and just use

the stable blues to get across.

But this obstacle is much harder than the ones before.

The squirrels will get to the start of the Lily Pads,

quite literally just have a look at it,

and think, no, not a chance,

and just completely give up before they even give it a go.

Others have given it a go

but fallen off halfway, which is what I was expecting.

It's a very tough obstacle.

Part of the learning process

is testing things out and making mistakes.

But with winter approaching, the squirrels are hungry and motivated.

So quick.

So quick. Oh, my gosh!

And finally, they find their own way of getting across.

The squirrels have figured out an incredible solution.

They take one step on the reds

and two steps to steady themselves on the blue.

So they go one, one-two, one, one-two, one, one-two,

using speed and agility to overcome the cognitive problem.

Driven by their desire to fatten up for winter,

they've combined their grip, agility and persistence...

..and earnt their prize of a nice, big hazelnut.

All around the world,

the coming of winter poses a real challenge to squirrels.

There's little food around, and the cold temperatures mean using more

energy than ever to keep warm.

But the super squirrels have come up with some ingenious ways of

surviving the toughest time of year.

Here in Alaska...

..deep underground...

..the arctic ground squirrel has a particularly radical solution.

It's hibernating.

It drops its heart rate,

breathing and body temperature and survives on stored fat alone...

..but that's not the really clever bit.

This little squirrel can handle the coldest temperatures of any mammal.

Even underground, it reaches -26 Celsius.

The squirrel's body temperature drops below freezing,

yet it doesn't freeze.

We still don't know exactly how.

What scientists have discovered is, every two to three weeks,

the squirrels shiver to warm themselves

to a more typical 36 degrees.

This temporary warmth is just about enough

to keep it going through winter.

Spring arrives...

..and the ground squirrel finally ventures out.

It's eaten nothing for a full eight months.

Thanks to this remarkable strategy,

it's avoided the lean months of winter altogether.

Other ground squirrels have come up with a different strategy.

In North America,

chipmunks will sleep for days at a time through winter.

But when they wake, they need food to stay alive.

Luckily, thanks to that hard shell, nuts store pretty well.

So they gather nuts throughout autumn...

..and stockpile them.

Chipmunks make hundreds of trips

backwards and forwards to their larder.

It takes a lot of time and energy.

Flexible cheek pouches make the task slightly easier...

..fitting in up to seven nuts at the time.

But there's a problem -

other chipmunks that want to steal your stash.

Any hoard must be defended, even if it means fighting for it.

With the thief seen off, the precious stockpile is safeguarded.

It's everything a chipmunk needs to get through the winter.

Nuts are such a valuable resource that theft is rife.

So, to avoid pilfering,

the tree squirrels have come up with a different tactic.

They don't risk putting all their nuts in one basket -

they bury each one separately.

It's a strategy known as scatter hoarding.

But when hunger strikes,

how on earth do the squirrels manage to find them again?

It's a question that intrigues Dr Mikel Delgado

at the University of California, at Berkeley.

Her university campus is home

to a thriving population of fox squirrels,

a species native to the eastern side of North America.

They provide the ideal opportunity for Mikel to discover what happens

to each nut once it's buried.

We really don't know how long it stays where it was buried.

We don't know who retrieves it

and whether it gets reburied or eaten, or stolen.

I think a lot of people do think that they're just

burying a nut wherever and they might find it later,

but this is really a question of survival for them.

To find answers, Mikel needs to make each nut trackable.

So she drills a minute hole...

..and inserts a tiny microchip.

To make them easier for her to spot,

she paints the nuts with bright yellow, nontoxic paint...

..and puts them out for the squirrels.

Squirrels are nut connoisseurs,

so Mikel watches carefully to see if her modified nuts pass inspection.

The initial moment that a squirrel receives a nut and starts

assessing it, they're making a lot of decisions.

Should I eat it now? Should I save it for later?

Is this a nut that might go bad if I bury it?

In which case, it's much better to eat it now.

They typically do two assessment behaviours,

so you'll see paw manipulation where they rotate the nuts in their mouth

and paws,

and that allows them to see if it's been infested

by a weevil or other insect,

and they're probably also assessing the weight,

and then shortly after that, they usually do a head flick.

That allows the squirrel to again determine, is this a good nut?

Is it old? Is it fresh? Does it have a lot of food inside?

And so those are the behaviours that they use to make their decisions

about where to bury a nut.

Her nuts pass the test.

Mikel scans the site where the nut

is buried to record the precise spot.

We saw a squirrel here earlier and now we're just checking to get the

exact location with the scanner.

And now we will triangulate this location using different landmarks

and a compass, so we can find it tomorrow or a week from now.

Using her notes, Mikel can rescan

every single nut throughout the winter.

The ones that are moved are assumed to have been remembered and eaten

or possibly stolen.

The nuts that are never retrieved are assumed to be forgotten.

The results are remarkable.

A year and a half later, we can see how many nuts had been forgotten.

In my study, the squirrels buried around 300 nuts.

Of those nuts, about 10% of them were forgotten.

So the flip of that is that squirrels are probably remembering

and locating about 90% of the nuts

they buried, which is actually quite good.

Mikel only supplied 300 micro-chipped nuts...

..but fox squirrels bury many more,

up to 10,000 a year each.

So, scaling Mikel's work up suggests they can remember the exact location

of up to 9,000 nuts.

Impressive stuff.

So is there something special about the fox squirrel's brain that allows

them to do this?

Dr Lucia Jacobs thinks there is.

Also at Berkeley, Lucia leads research on

the evolution of brains and cognition.

This is the Berkeley fox squirrel,

and this species is a scatter hoarder.

And this species is a California ground squirrel.

You can see they're pretty much the same size,

and these are both species that are actually found in Berkeley,

and what's interesting about pairing

the ground squirrel and the fox squirrel,

you can actually see, even from their skulls,

how the brain size is larger in the fox squirrel.

That's a general pattern that's been shown, that the tree squirrels

have larger brains.

Remembering where they've left their nuts requires a bigger brain.

There's also another reason why tree squirrels are so blessed

in the brain department.

Arboreal animals have larger brains

than animals that live on the ground,

and it's just because living in trees is a much more complicated

environment, and so you see that across all kinds of different

mammals, the more they're living

in a complex, three-dimensional environment,

the larger the brain.

And that's not all.

Tree squirrel brains are able to do something truly astonishing.

So, what you may not know about squirrels is that

in the fall, their brains get bigger.

So that squirrel in your backyard,

in the fall has a bigger brain than the same squirrel did earlier

in the year.

This is because they have to make a huge mental map of where all their

nuts are hidden,

and that takes brain power.

By springtime, when food is plentiful again,

the brain goes back down to its smaller size.

Overall, Lucia thinks the squirrel brain is pretty impressive.

Squirrels are very smart animals, they are very long-lived,

even under natural conditions, of five years,

but in captivity, 15 to 20 years,

and usually animals, the longer they live, the larger their brains.

After all these years with squirrels, they really are special.

In fact, they are just...

The more I study them, the more special they become.

Alongside fox squirrels,

grey squirrels are one of the smartest of all.

Recent research even suggests that this brainpower is what allows them

to outcompete the red squirrel.

So at the assault course,

Doug has decided to put their memory and cognitive abilities to the test.

The Maze.

There's only one way through,

so the squirrels will have to ignore the dead ends

and learn the right route.

WHISPERING: What are you going to do?

Sniffing around.

No nuts up there.

Step one is finding the route through.

Step two is remembering it.

Oh, my word!

Wow!

In just 15 minutes,

a squirrel has figured it out and begins to perfect its route.

It's clear that once the squirrel has completed an obstacle,

it remembers how it did that obstacle,

so, when it comes to doing it next time round,

it doesn't waste any time figuring out its route.

It's a brilliant demonstration of intelligence and memory...

..and the squirrels have definitely earned their reward.

In the space of just eight weeks,

Billy has developed many of these squirrel skills,

and it's now time to put them all together.

To stand a chance of living back in the wild,

he must leave the security of Sheila's bedroom.

There's an enclosure back at the rescue centre,

which has been modified to house Billy and fellow squirrel, Annie.

It's really good because we can set it up with loads of different

branches, hanging branches, and branches just going across,

and it also gets them used to the elements,

as well as having a sheltered area.

It's been set up with everything a squirrel could want,

but this is still a huge moment for Billy,

and Sheila doesn't know how he'll react.

Hi, guys. You're OK.

Hi, Billy. Do you want to come out?

Where are we? Come on.

So, Billy has never encountered anything outdoors.

He came into us with his eyes closed.

There we go.

Billy and his companion Annie don't seem too nervous.

Billy's over there. He's on his first branch.

He's venturing out into the light.

And before long, he's taking it all in his stride.

I can see Billy's quite happy -

he's going round and exploring everything.

At times, he'll just kind of stop and he's quite quiet,

and that's when he's a bit unsure,

but he's doing really well, he's jumping around

and he's gripping onto everything really well.

He's doing good.

The network of branches inside the enclosure is higher up and further

apart than Billy has ever experienced before.

It's to help him master his next challenge,

the most difficult and dangerous thing

that all tree squirrels have to do -

large leaps.

Jumping between branches avoids a trip all the way down to the ground

to get to another tree.

It saves a great deal of energy,

and, despite the risk involved, these incredible feats of acrobatics

are an everyday part of treetop life.

Their leaping is so impressive that Dr Greg Burns has spent the last

four years trying to understand how they can physically do it.

If you imagine that this animal is jumping 8-10 feet,

that's 8-10 body lengths, that's a huge, huge jump.

Here at his lab in Siena College, New York,

Greg's enlisted an assistant to find out more.

OK, so this is Cedar. This was an orphaned squirrel that we raised.

It was found on campus maybe two months ago,

and so he's a juvenile grey squirrel.

He is about three months old, maybe.

We've hand-raised it from a baby and got it to train to jump a little bit

in the lab here and we're going to learn some things about the

biomechanics of jumping.

As soon as he's big enough,

Cedar will gradually be released back into the wild.

For now, he's honing his skills by jumping between two platforms

in return for his favourite nuts.

There we go. Whoa! Too far!

Here's a big nut.

And Greg is analysing the mechanics of his leap,

with interesting results.

When it jumps, it jumps with a maximum force

of about ten body weights.

Compared to you or I, I did a standing jump

of about six or seven feet and I can produce about one and a half,

two body weights, maybe, tops.

So they're much, much more powerful jumpers.

Greater power equals a longer jump.

To produce more power, they have

especially large leg muscles.

The muscles act like

an elastic band.

So, squirrels crouch to pre-stretch them

for an extra little snap of force.

The next stage is flight.

It will then very quickly extend its hindlimbs.

Its forelimbs will reach out

and basically start reaching towards the target.

The target is the landing platform, which Greg has modified.

It measures the pressure Cedar puts down through his paws on impact...

..and reveals the force would easily be enough for Cedar to hurt himself.

And when they land, they can land with a force of about

15 body weights, and so they need to find ways to basically reduce that

landing force and one of the things they do is they make sure they get

all four limbs on the ground at the same time.

This spreads the landing force between all four feet.

Bending their legs also helps absorb more of the impact.

Greg has discovered that combining these adaptations allows

grey squirrels like Cedar to complete huge leaps.

It's the equivalent of a human jumping two bus lengths

from a standing start.

But there's another squirrel who beats that record.

In the far north of America, this nocturnal member of the

squirrel family searches for fungi, its favourite food.

But fungi is spread in random patches through the forest and the

squirrel has to cover large distances to find it.

So, this squirrel has evolved a special talent.

The northern flying squirrel is just 16cm long

and weighs less than a typical smartphone.

Yet, it can leap up to 45m between trees.

Its wings allow it to glide through the canopy.

They are an incredible piece of aeronautical engineering.

The main membrane stretches between

their wrists and ankles,

and another smaller membrane

between the ankles and tail.

Combined, they form a parachute.

Flying squirrels have the longest limbs of all the squirrels,

to make their parachute as large as possible.

A piece of cartilage on the end of the wing gives them an upturned tip.

This reduces drag and increases stability.

It's the reason many aeroplanes have

upturned tips on their wings, too.

The result is these incredibly long leaps at speeds of up to 20mph...

..allowing the squirrels to travel widely through the forest.

In the UK, at the assault course, the squirrels need to make their own

leap of faith, as their very last test.

As well as the obstacles they've done before,

the squirrels are facing the Tightrope...

..Rolling Branch...

..and Windmill,

before their final 3m Mega Leap

to the giant stash of nuts at the end.

These wily grey squirrels have had plenty of practice now,

and are becoming experts at some of the obstacles,

but will one be able to string it all together

and complete the course in full?

WHISPERING: There's definitely one individual standing out

from the rest, and he's just shown up.

OK.

Come on.

OK.

Across the Lily Pads...

Into the Maze...

He's got the first half of the obstacle course down.

Tightrope...

OK, this individual looks like he's going to do it.

Rolling Branch...

Windmill...

Come on, come on! You can do it.

Oh, he made it look so easy!

OK, this squirrel's made it all the way around. It's the final bit.

It's the final jump.

He's done it. You absolute star!

We've found our super squirrel.

One individual has completed this entire course.

It's had to use every squirrel super skill -

intelligence, memory,

determination, problem-solving,

and mind-blowing physical agility.

It's easy to see just why these animals are totally unmatched

in their treetop homes.

As the grey squirrels finally piece everything together

at the assault course,

in Scotland, Billy is about to take his final step too.

At 15 weeks old, Sheila thinks he's ready to go back into the wild.

So, Billy and Annie are about to be given their freedom.

So, we are en route with Billy and co.

So this is release day, so a big day for the guys.

So we've got a great location for releasing them.

There's 50 acres of woodland, which will provide plenty of food

and space for the squirrels.

At this age in the wild, he would be fully independent from his mother,

but Sheila won't be cutting all ties just yet.

I've got a little parting gift for Billy.

This is some whole hazelnuts. They don't want to eat them now.

It just means they can store them away

and keep them for the wintertime.

She'll put out nuts daily through his first winter...

..so he can retrieve and store them.

Now it's time for the biggest step of his life.

The transport box allows Billy to get used to his new surroundings,

while feeling safe and hidden inside.

With the door open, he can leave when he's ready.

So, he's just coming to the front, and having a wee peek,

just trying to suss everything out, and then going back in again!

He's coming out. He's got his nose.

Bye, Billy.

Now, it's up to him.

He's going so high!

It looks like Billy has the speed a wild squirrel needs,

and his instinct to head high into the trees is a good one.

It was good. That was nice.

He went off quite calm, and had a good look around.

He manoeuvred really well in the tree.

I was quite happy with that.

He jumped out of the box quite relaxed,

and just that grip on the tree,

he manoeuvred round the tree and up to the top in no time at all.

And Billy won't be alone.

I would say it's a job well done.

Billy's really came along.

He's had quite a journey and, yeah,

he's just kind of proved he's a wee champion.

Back in the wild, Billy will draw on all the skills he developed

during his time with Sheila...

..the same survival skills that make all squirrels so special.

Their perseverance in pursuit of food...

..their extraordinary aerial agility...

..phenomenal problem-solving...

..and the cunning required to outsmart predators.

It's these amazing abilities

that have allowed the super squirrels to thrive

and become one of the most successful animal families

on the planet.