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S37 Ep4

A Squirrel's Guide to Success

Premiere: 11/14/2018 | 00:00:35 | Closed Captioning Icon

The squirrel family – from tiny chipmunks to big prairie dogs – is one of the most widespread on Earth. There are almost 300 species of squirrels that can glide through the air, outwit rattlesnakes, and survive the coldest temperatures of any mammal. Discover the secrets to their success.



About the Episode

From tiny chipmunks to big prairie dogs, the squirrel family is one of the most widespread on Earth. There are almost 300 species of squirrels that can glide through the air, outwit rattlesnakes and survive the coldest temperatures of any mammal. What is the secret to their success? Uncover the extraordinary abilities of these cheeky nut lovers as a filmmaker puts their problem-solving to the test on a specially designed obstacle course. Join some of the world’s top squirrel scientists who are making groundbreaking discoveries:from the brainy fox squirrel who can remember the location of 9,000 nuts, to the acrobatic gray squirrel whose tree-top leaps are the basis for new designs in robotics. See the world through the eyes of an orphan red squirrel called Billy as he grows up and develops all the skills he will need to be released back into the wild.

Noteworthy Facts:

  • There are nearly 300 species of squirrels in the world, living in a huge range of habitats, from the forest canopy to the Arctic tundra to the baking desert.
  • In the UK, the red squirrel population has plummeted by 95 percent. Seventy-five percent of the remaining red squirrels are found in Scotland.
  • More than three feet long in size, the Malabar giant squirrel can hang upside down while they feed and use their grip to run down trees headfirst. An unusually flexible ankle joint allows their feet to rotate almost 180 degrees.
  • A squirrel’s front teeth never stop growing to counteract the wear from a lifetime of relentless chomping.
  • To survive the frigid winters in Alaska, the Arctic ground squirrel hibernates by dropping its heart rate, breathing and body temperature and survives on stored fat alone. Every two to three weeks the squirrel will shiver to warm itself.
  • Squirrels are extraordinary leapers who can leap about 8-10 body lengths. Dr. Greg Byrnes, who has spent the last four years tracking squirrel’s movements in his lab at Siena College, learns that a squirrel’s leaping ability comes from their large leg muscles that act like an elastic band. To minimize the impact, they land with all four limbs on the ground at the same time.
  • The Northern flying squirrel is just six inches long and weighs the same as a typical smartphone. Yet, it can leap almost 150 feet between trees at speeds of up to 20 miles per hour. Its “wings,” a membrane that stretches between its wrists and ankles, and another smaller membrane between the ankles and tail, allow it to glide through the canopy. A piece of cartilage on the end of the “wing” gives them an upturned tip, which reduces drag and increases stability (many airplanes have upturned tips on their wings for the same reason).

Buzzworthy Moments:

  • To help combat the declining red squirrel population, Sheelagh McAllister, Head of Small Mammals at the National Wildlife Rescue Centre in Scotland, takes in a newborn red squirrel displaced from his nest. Naming him Billy, she weans and raises him at home until he is ready to be released back into the wild. McAllister and her team look after nearly 10,000 animals every year.
  • To defend her pups from a predatory rattlesnake, a California ground squirrel pumps extra blood into her tail and waves it repeatedly. The blood flow in her tail is normally used to help regulate temperature, but the extra heat is sensed by the rattlesnake, making her seem bigger than she really is.
  • Although chipmunks sleep for days at a time through the winter to save energy, when they wake they need food to stay alive. To prepare for this scenario, they gather nuts throughout autumn and stockpile them. Flexible cheek pouches make the task slightly easier; chipmunks can fit up to seven large nuts in their mouth at a time. They must also defend their hoard from other chipmunks; see one fight break out over a particular stockpile.
  • To avoid pilfering, tree squirrels don’t risk putting all their nuts in one basket; they bury each one separately in a strategy known as scatter hoarding. To learn how these squirrels are able to remember where they bury each nut, Dr. Mikel Delgado of the University of California at Berkeley inserts a tiny microchip into several test nuts. She discovers that Fox squirrels can remember and locate about 90 percent of the nuts they bury. Their brains grow larger than other species of squirrel, particularly during the fall season when nuts are plentiful.
  • Gray squirrels are one of the smartest species of all. Wildlife filmmaker Douglas Parker has found a unique way to demonstrate their adaptability. To get to a large pile of hazelnuts, wild gray squirrels must leap between the colored discs of an obstacle course constructed by Parker. Through trial and error, driven by their desire for nuts, these wily grays combine their grip, persistence, memory and problem-solving skills to get through the course.

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Special Thanks


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Original Funding Provided in Part by
The Arnhold Family In Memory Of Clarisse Arnhold
Sue and Edgar Wachenheim III
Kate W. Cassidy Foundation
Lillian Goldman Charitable Trust
Kathy Chiao and Ken Hao
Anderson Family Fund
Filomen M. D’Agostino Foundation
Rosalind P. Walter
The Halmi Family in memory of Robert Halmi, Sr.
Sandra Atlas Bass
Corporation for Public Broadcasting

Series Producer

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This program was produced by THIRTEEN Productions LLC, which is solely responsible for its content

© 2018 BBC


♪♪♪ NARRATOR: Squirrels.

One of the smartest, most adaptable, most successful creatures on the planet.

What are the secrets of their winning ways?

There are squirrels that can survive a deep freeze... [ Squeaking ] ...communicate in complex languages... and outwit their greatest enemies.

Now we'll explore their incredible talents by working with the experts.

FULL: Squirrels are one of the most agile animals on Earth.

JACOBS: This is a really special animal.

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

NARRATOR: 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 these high-flying, nut-loving, quick-thinking creatures and learn just what it takes to be such a great success.

♪♪♪ ♪♪♪ ♪♪♪ NARRATOR: The squirrel family is big and successful.

There are almost three hundred different species.

They've mastered a huge range of habitats, from frozen Arctic tundra... to baking deserts.

There are ground squirrels with homes in tunnels and burrows... ♪♪♪ ...tree squirrels living the high life in the canopy... ...and even flying squirrels that can glide effortlessly through the treetops.

This adaptability has enabled them to conquer the globe and colonize almost every continent on Earth.

♪♪♪ But one that is actually becoming rare 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're 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.

♪♪♪ McALLISTER: Look at you!

So small!

So this is a baby red squirrel.

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

It looks to be, maybe about 5 days old.

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

[ Chuckles ] NARRATOR: The tree holding his nest was cut down.

He'll now be totally dependent on his new surrogate mom, Sheelagh McAllister, the head of small mammals at the National Wildlife Rescue Centre of Scotland.

She and the Rescue Centre team look after nearly 10,000 animals every year, from foxes to otters.

McALLISTER: All right. There you go.

NARRATOR: Sheelagh is a specialist in caring for red squirrels and releasing them into the wild.

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

McALLISTER: So the next kind of 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.

NARRATOR: She'll 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.

McALLISTER: We've decided to name him Billy, and my job over the next few days would be to keep him nice and warm, regular feeds, and just overnight care to make sure that he is getting all the food and comfort that he needs.

There you go, nice and snug.

NARRATOR: 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.

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.

Females will have between one and six babies in a litter.

And the young are totally dependent on their mother's care.

All tree squirrels depend on a tree house throughout their lives.

But the ground squirrels have a different strategy for keeping their youngsters safe.

The rolling chaparral of California.

Home to the California ground squirrel.

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

The pups won't poke a whisker above ground until they're at least six weeks old.

♪♪♪ ♪♪♪ When they do venture out, the burrow is still an essential bolt-hole from predators like birds of prey and foxes.

But burrows are no barrier to their greatest enemy... the Pacific rattlesnake.

♪♪♪ [ Squeaks ] The snakes use infrared sensors to detect the heat of warm-blooded prey.

So there's nowhere to hide.

With pups to defend, a mother must face the enemy.

♪♪♪ ♪♪♪ She flicks stones.

It doesn't look like the smartest move, but it's a deliberate and cunning ploy.

By provoking the snake, a squirrel can listen to the frequency and speed of its rattle... and this reveals how big, how warm, and how aggressive the snake is.

After listening, the squirrel decides on her next move.

She pumps extra blood in to her tail and waves it repeatedly.

The blood flow in her tail is normally used to help regulate temperature.

But now she knows 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's something the pups will need to learn, too.

Squirrel babies have to grow up fast.

♪♪♪ Back in Scotland, just three weeks have gone by, but the change in Billy, the little orphan, is clear.


NARRATOR: When she's not at work, Sheelagh brings him home to give him the 24-hour care he needs.

McALLISTER: 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's -- he'll still squint his wee eyes so he's just adjusting and everything's still developing.

So 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.

McALLISTER: The grip that Billy has is really important, so 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 super-fast, as well.

At this stage, they would still be in the nest and they'd be pretty inactive, so they would just be like really kind of exercising amongst themselves.

NARRATOR: Without his mother or siblings to interact with, Sheelagh will have to help Billy practice his grip.

McALLISTER: Ooh! Are you going up here?

Good lad!

NARRATOR: 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 maneuver.

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 captured the attention of scientists studying how animals move.

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.

FULL: A 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 move and jump through gaps and climb on wires to quickly enter an area in order to find individuals.

NARRATOR: To study the squirrels in detail, the team uses a portable wall out in the woods.

They stick perches to it that represent branches of a tree.

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

Bob is discovering their aerial acrobatics depend on their decision-making.

FULL: For example, one of the tests we had is, how could they determine where to jump on branches or rods that are of different 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.

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

FULL: They decide to only go a little ways and then take a longer jump, so they make a very good decision in terms of their jumping capability.

NARRATOR: 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.

FULL: Even if they don't land perfectly on the perch, they have the ability to maneuver 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.

NARRATOR: 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 colorful members of the squirrel family.

It's also one of the largest.

♪♪♪ At more than 3 feet 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 plenty of these huge jackfruit around.

They don't need to share.

Being such a heavyweight makes the Malabar giant squirrel's grip particularly impressive.

And that allows them to 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're 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 have improved by leaps and bounds.

McALLISTER: He is just over seven weeks now, so we can see he has changed quite a lot.

He's got this great bushy tail and his agility's really coming on.

He's getting very active and quite a handful.

NARRATOR: To make sure Billy can go back to the wild, he needs to meet some of his own kind.

McALLISTER: Hey, sweetie.

NARRATOR: And Sheelagh is now caring for another youngster of similar age.



This is Annie.

She's from Inverness.

She was caught by a dog, and the owner handed her into the vet's, so luckily she doesn't have any injuries, and for the size of her, she's doing pretty well.

NARRATOR: It's an important moment for Billy.

McALLISTER: Who's this?

Don't be scared.

At this age, in the wilds, the squirrels would have siblings and they would also have their mother, so you know, it's just that contact and being able to express, like, natural behaviors and just have playtime.

So it's really going to benefit Billy, as he's never had any contact with another squirrel.

[ Chuckles ] NARRATOR: They already seem to be pushing each other to new heights.

-McALLISTER: He's off. -NARRATOR: It's a good sign.

McALLISTER: Come on Annie. Whoo-hoo.

Annie. Where you going, Billy?

What's your next move?


NARRATOR: 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 large colonies called towns all across 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... [ Squeaking ] ...they use a complex language to warn the others.

♪♪♪ Their call communicates more than just a warning.

It identifies the kind 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 due 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.

[ Thunder rumbles ] McALLISTER: What's in here?

NARRATOR: Smaller squirrels like Billy need a lot more calories.

McALLISTER: Do you need some?

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

McALLISTER: Are you going to take it?

Good boy.

NARRATOR: These almonds are 49% fat -- ideal for a growing squirrel.

McALLISTER: So Billy has just started to eat nuts.

He's like a wee secret eater though, like he just hides out in his bed and he'll eat underneath the covers.

Last night was the first night I've actually seen him sit upright and eat a nut, which is quite a good stage for him.

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

Although all his teeth have come through, they're 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 8 inches a year, so in Billy's life-span, his teeth may grow more than six feet!

Next, his tooth enamel will harden.

It's a critical moment, because then he'll be able to cope with the hardest nuts in nature.

McALLISTER: 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.


NARRATOR: Sheelagh hopes to release Billy into the wild during autumn at the time when nuts are plentiful.

But as with squirrels all around the world, winter, when it finally arrives, poses a real challenge.

There's little food around, and the cold temperatures mean using more energy than ever to keep warm.

But squirrels everywhere have come up with some ingenious ways of surviving the toughest time of year.

Here in Alaska... 3 feet 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 part.

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

Even underground, it reaches minus-15 degrees Fahrenheit.

The squirrel's body temperature also drops below freezing... yet the squirrel doesn't freeze.

We still don't know exactly how that's possible.

What scientists have discovered is, every two to three weeks, the squirrels shiver to warm themselves to a more typical 97 degrees.

This temporary warmth is just about enough to keep the squirrel going through winter.

Spring arrives, and the ground squirrel finally ventures out.

It's eaten nothing for a full eight months.

But thanks to this remarkable strategy, it's slept through the lean months of winter altogether.

♪♪♪ Other ground squirrels have a different strategy for success.

The chipmunks of North America.

One of the most endearing members of the squirrel family.

Their small size means they can't store enough fat to sustain a complete winter without eating.

So, although chipmunks will sleep for days at a time in winter to save energy, 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 pantry.

It takes a lot of time and energy.

Flexible cheek pouches make the task slightly easier... ...fitting in up to seven nuts at a time!

But there is a problem.

Other chipmunks that want to steal your stash.

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

♪♪♪ ♪♪♪ ♪♪♪ With the thief chased away, the precious stockpile is safe.

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

♪♪♪ But nuts are such a valuable resource, theft is rife.

So, to avoid pilfering, 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, the largest tree squirrel in North America.

They provide the ideal opportunity for Mikel to discover what happens to the nuts once they're buried.

DELGADO: 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, oh, burying a nut wherever and they might find it later, but this is really a question of survival for them.

NARRATOR: 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.

DELGADO: 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.

Well, they typically do two assessment behaviors.

So you'll see paw manipulation where they rotate the nut 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 behaviors that they use to make their decisions about where to bury a nut.

NARRATOR: Her nuts pass the test.

Mikel scans the site where the nut is buried to record the precise spot.

DELGADO: We saw a squirrel cache 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 that we can find it tomorrow or a week from now.

NARRATOR: Using her notes, Mikel can re-scan 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.

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

In my study, the squirrels buried around 300 nuts and of those nuts, about 10% of them were forgotten.

So the flip side of that is that squirrels are probably remembering and locating about 90% of the nuts they buried, which is actually quite good.

NARRATOR: It's even possible that some of the nuts that weren't retrieved were simply not needed and not forgotten at all.

Mikel only supplied three hundred microchipped nuts in her experiment, but fox squirrels bury many more.

Each one can stash up to 10,000 nuts a year.

Scaling Mikel's work up suggests fox squirrels can remember the exact location of up to nine thousand 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.

JACOBS: 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 -- 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.

NARRATOR: 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.

JACOBS: 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 that they're living in a complex three-dimensional environment, the larger the brain.

NARRATOR: And that's not all.

Tree squirrel brains are able to do something truly astonishing.

JACOBS: 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.

NARRATOR: This is because they have to make a huge mental map of where all their nuts are hidden, and that takes brainpower.

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.

JACOBS: Squirrels are very smart animals.

They're very long-lived, even under natural conditions of 5 years, but in captivity, 15 to 20 years.

And usually, animals, the longer they live, the larger the 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.

♪♪♪ NARRATOR: Alongside fox squirrels, gray squirrels are one of the smartest of all.

Their intelligence and adaptability to urban environments have allowed them to become one of the most prolific squirrels on Earth.

♪♪♪ Wildlife filmmaker Douglas Parker is a squirrel fanatic, and he's found a unique way to demonstrate just how smart these wily grays are.

Tucked away in an English woodland, he's devised the perfect test to see how they combine problem solving with their physical abilities.

Wild squirrels are attracted in by a large pile of hazelnuts.

But to get to the nuts, they must leap between the colored discs.

The blue discs stand firm.

The red discs are wobbly.

The idea is that they'll learn the difference, and just use the stable blues to get across.

But it's proving to be a very difficult challenge.

PARKER: The squirrels will get to the start... quite literally just have a look at it, and think, nah, 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.

NARRATOR: Part of the learning process is testing things out and making mistakes.

♪♪♪ ♪♪♪ But with their favorite nuts in plain sight, the squirrels are utterly determined.

PARKER: So quick, so quick. Oh, my gosh.

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

PARKER: 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.

NARRATOR: Driven on by their desire for nuts, they've combined their grip, persistence, memory, and problem-solving skills.

♪♪♪ ♪♪♪ And earned their prize of a nice, big hazelnut.

♪♪♪ In the space of just eight weeks, Billy has developed many of the skills he'll need to succeed.

Now it's time to put them all together.

To stand a chance of living back in the wild, he must leave the security of Sheelagh's bedroom.

There's an enclosure back at the rescue center, which has been modified to house Billy and his fellow squirrel, Annie.

McALLISTER: 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.

NARRATOR: It's been set up with everything a squirrel could want.

But this is still a huge moment for Billy, and Sheelagh doesn't know how he'll react.

McALLISTER: Hey, guys, you're okay.

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.

Here we go.

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

McALLISTER: Billy's over -- [Laughs] over there, he's on his first branch.

He's venturing out into the light. [ Chuckles ] NARRATOR: And before long, he's taking it all in his stride.

McALLISTER: We can see Billy's quite happy, he's going round and exploring everything.

At times, you know, 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 on to everything real well.

He's doing good.

NARRATOR: The network of branches inside the enclosure is higher up and farther 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 Byrnes has spent the last four years trying to understand how they can physically do it.

BYRNES: If you imagine this animal jumping 8 to 10 feet, that's, you know, 8 to 10 body lengths right, that's a huge, huge jump.

NARRATOR: Here at his lab in Siena College, New York, Greg's enlisted an assistant to find out more.

BYRNES: Okay, so this is Cedar.

This was an orphan squirrel that we raised.

It was found on campus maybe 2 months ago, and so he's a juvenile gray squirrel, he's about 3 months old maybe.

We've hand raised it from a baby and got it trained it jump a little bit in the lab here, and we can learn some things about the biomechanics of jumping.

NARRATOR: 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 favorite nuts.

BYRNES: Oh, there we go. Oh, too far.

Here's a big nut.

NARRATOR: And Greg is analyzing the mechanics of his leap, with interesting results.

BYRNES: When it jumps, it jumps with a maximum force of about 10 body weights.

Compared to you or I, I did a standing jump about 6 or 7 feet and I can produce about 1.5, 2 body weights, maybe, tops.

So they're much, much more powerful jumpers.

NARRATOR: 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.

BYRNES: It will then very quickly extend its hind limbs, its forelimbs will reach out and basically start reaching towards the target.

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

It measures the pressure Cedar puts down through his paws on impact... and reveals that the force would be enough for Cedar to hurt himself.

BYRNES: Then, 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 4 limbs on the ground at the same time.

NARRATOR: 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 gray 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 easily beats that record.

In the far north of America, a nocturnal member of the squirrel family searches for fungi, its favorite food.

But fungi are spread in random patches throughout the forest, and the squirrel has to cover large distances to find them.

So this squirrel has evolved a special talent.

It flies!

The northern flying squirrel is just six inches long and weighs the same as a typical smartphone.

Yet it can leap almost 150 feet between trees.

♪♪♪ Its 'wings' allow it to glide through the canopy.

Flying squirrels are an incredible piece of aeronautical engineering.

♪♪♪ A large membrane stretches between their wrists and ankles, and another smaller membrane runs 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 each 'wing' gives them an upturned tip.

This reduces drag and increases stability.

It's the reason many airplanes have upturned tips on their wings, too.

The result is these incredibly long leaps at speeds of up to 20 miles an hour... allowing the squirrels to travel widely through the forest.

Billy has been building up his strength and agility.

And now, he's ready to make the biggest leap of all.

♪♪♪ ♪♪♪ McALLISTER: 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.

♪♪♪ NARRATOR: There are 50 acres of woodland, which will provide plenty of food and space.

All Eurasian red squirrels range far and wide as they forage.

Their favorite foods are tree seeds.

Especially ones from pine cones.

And like most other tree squirrels, they have to bury nuts for winter.

By Billy's age, a wild squirrel would be fully independent from its mother.

But Sheelagh won't be cutting all ties just yet.

McALLISTER: So I've got a little parting gift for Billy.

This is some whole hazelnuts.

If they don't want to eat them now, it just means they can store them away and keep them for the wintertime.

NARRATOR: She'll put out nuts daily through his first winter so he can retrieve and store them.

Finally, 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.

McALLISTER: So he's just coming to the front and having a wee peek.

Just trying to suss everything out and then coming back in again.

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

Bye, Billy!

NARRATOR: Now it's up to him.

McALLISTER: He's gone so high!

NARRATOR: It looks like Billy has the speed a wild squirrel needs, and his instinct to head high into the trees is a good one.

McALLISTER: It was good, that was nice.

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

He maneuvered really well in the tree.

I was quite happy with that.

He jumped out the box quite relaxed and just that grip on the tree, maneuvered round the tree and up to the top in no time at all.

NARRATOR: And Billy won't be alone.

♪♪♪ McALLISTER: 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.

[ Chuckles ] NARRATOR: Back in the wild, Billy will draw on all the skills that he developed during his time with Sheelagh.

He'll find his own home range and build a drey for shelter.

Hopefully, by next year, he'll meet a mate and help bolster the numbers of red squirrels in the forest.

As he gets to grips with his new life, he'll rely on all the amazing abilities that have made squirrels one of the most successful animal families on the planet.

♪♪♪ NARRATOR: This is life in an African wild dog family.

Endless mouths to feed... and a gaggle of teenagers to control.

Two parents must keep everyone safe in an unforgiving wilderness.

These woodlands are full of lions, the dogs' mortal enemy.

They compete for the same food, and their war is never-ending.

♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪


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