The Burrowers (2013) s01e02 Episode Script
Part 2
('We think we know Britain's) wildlife '.
.
but there's a secret world beneath our feet.
'A hidden kingdom teams with millions of burrowing creatures, 'their lives shrouded in mystery.
'Why do they live underground? 'Where do they sleepand eat? 'And how do they raise their young? 'Their secret subterranean world remained unseen '.
.
until now.
' Wow! Look at this! This is our vision come true.
'We are breaking new ground in natural history.
'We've unearthed real animal burrows.
'And created three lifelike replicas of our own.
'A rabbit warren, 'a water vole burrow 'and a badger sett.
' To be able to crouch here, this far away from a little badger and observe what it's up to - it's beyond my dream! 'It's spring now, but winter was a busy time for our burrowers.
'Our rabbits have bred, 'but will their young learn the skills they need to survive?' It's quite a brave moment for these little things.
'Our two water voles got off on the wrong paw, 'but are things looking up?' If there ARE babies in there, that's where they'll be.
'And our seven orphaned badger cubs have begun to bond as a group, 'but can they master the badger basics?' This is the first time they've had the opportunity to dig! 'And we uncover the dark secrets of the burrower that can do this!' Phenomenal! Hopefully, people may see moles in a different light.
'We have a window on their lives like never before.
'Explore this magical world with me, Chris Packham, 'as we ask in this programme, 'how do young burrowers grow up inside the burrow 'and prepare for their first taste of fresh air?' This is a momentous moment in the lives of these young badgers.
'It's spring in Britain's Southwest 'where, in a unique experiment, we've built three replica burrows.
'Our badger sett is now home to a family of seven playful orphans.
'And 100 miles away, on a small Dartmoor farm, 'we've created a riverbank burrow for a pair of water voles 'and a vast warren, big enough for a whole community of rabbits - 'all under the watchful eye of a team of the country's 'of top filmmakers and naturalists.
' Welcome to Burrower Central, here in Devon.
It's six months since our unique project began here and already we've learned so much new science.
But having said that, there's a lot more that we want to know yet.
It's springtime now and our young burrowers face their biggest challenge yet - taking their first steps into the outside world.
'Our burrows aren't just underground.
'They're all equipped with protected outdoor spaces.
'We know from the wild that spring is when young emerge from the burrow 'for the very first time.
'How will our young burrowers prepare for the outside world? 'We'll watch as our badger cubs learn to communicate '.
.
as our newborn rabbits find their way 'out of the labyrinth of the warren, 'and as the next generation of young water voles grow up 'and get ready to leave home.
' We ask, what role does the burrow play at this important stage of our burrowers' lives? Will it provide them with the skills to survive outside? 'There's a major clue that our ten rabbits 'have enjoyed their first month in our warren.
'They've been breeding like rabbits.
'Led by head buck Thumper '.
.
the two squabbling males 'have already sired seven litters between them.
'Hazel is the top female.
'And like nearly every adult doe in the warren, 'she has a litter of her own.
' There is something enchanting and magical about this rabbits' nest.
It's pulsing with young rabbits.
We can't see them.
They're completely hidden by the fur, but they're all down there, huddling to stay warm.
We're not entirely sure how old they are.
Maybe a week or just over.
It'll only be a few days, then they will start to come out of the nest and explore the rest of the warren.
Then it won't be long until they look like this - a fully fledged bunny.
'At two weeks, these seven kits 'have reached the next stage of development.
'They belong to Pipkin.
'Despite only suckling from Mum for three minutes a day, 'they've matured rapidly.
'Rabbit milk is one of the most nutritious in the animal kingdom.
'They've gained sight, 'can now hear 'and they weigh five times the amount they did at birth.
'And now that their fur is fully developed, 'they can leave the warmth of the nest and take their first steps.
'For the moment, at least, 'they don't go beyond their mother's chamber.
' This is going to give us an extraordinary opportunity to see these animals raised.
A view that no other naturalist could have ever had - looking at rabbits underground, going about their natural business.
'Their parents are from domestic stock, 'but they should behave as they would in the wild.
'Because our rabbit warren, like all of our burrows, 'is based on data from the real thing.
'They're the largest constructed burrows of their kind.
'We want to see for ourselves the enormous scale 'and structural design of a wild warren.
'So, six months ago at Devon's Bicton Park, 'we investigated an abandoned warren 'and began the most ambitious stage of our natural history project.
' We're going to fill this warren with concrete.
When it sets and we excavate it, we'll be able to see the anatomy of their architecture in full sculptural 3-D.
And that's pretty exciting.
'Battling one of the worst winters on record, 'we filled the empty warren with ten metric tonnes of concrete.
'And then left it to set.
'Now in spring, we're beginning 'the biggest wildlife excavation of its kind ever attempted in Britain.
'When we finish, we'll have the most detailed picture ever 'of the rabbits' secret subterranean world.
'It's going to take another week to reveal every corner.
' 'Our badger sett is located at Secret World Wildlife Rescue Centre in Somerset.
'It's been a few weeks since our cubs moved in.
'They're all rescued orphans, nursed back to health.
' 'Boisterous female Lunar 'is the eldest and biggest.
'She's established her position at the head of the group.
'She's still just the equivalent age of a human tweenager.
' This artificial sett that we built is the perfect rehabilitation environment for our young badgers, because it gives them the chance to learn in a natural setting about living together as a group.
That will be very important when it eventually comes to their release.
Of course, in the meantime, it also gives us a unique opportunity to delve into the secret life of badgers below ground.
'This is the cub we named Bramble.
'She'd been found alone and fighting for her life.
'One of the youngest and smallest cubs, 'she's had a tough time fitting into the group.
'Without the others, she's unlikely to survive 'when this group is released into the wild.
'It seems she's not quite ready yet to impress the boss, Lunar.
'She tries her luck first with a more relaxed cub' '.
.
Mr Sleepyhead himself, Truffle.
'The moment Truffle went into our burrow, he made a cosy bed.
' Their instinct is to make a nest so that they can stay warm, which is essential.
'And now, all he does is lie in it.
'Bramble follows suit.
'She cuddles up to her new brother and then has a snooze.
'But there are other challenges ahead.
'They'll all be tested for TB.
'And when they're old enough and fit to be released, 'they'll need to dig a sett of their own.
'But at just two months old, 'they've already begun to put their digging skills to the test.
' Just look at our little badgers! If you look closely - they're a bit busy at the moment - but you can see that they're natural born digging machines.
Look at the shape of their body.
Their narrow nose broadens over and tapers down.
Perfect for moving through the soil.
And their spine is arched.
This helps with their whole digging and shifting masses of soil.
And when they grow into adults - if they ever stop playing - these things can really shift soil, double their own bodyweight at a single time.
'Badgers don't just dig new digs.
'In the wild, their setts sometimes cave in.
'Burrowers can be buried alive 'if they don't know how to dig their way out.
'So, will our cubs know how to tunnel out of trouble? 'To find out, our badger expert, Dr Chris Cheeseman, 'wants to set them a challenge.
' Well, what we're trying to do here is we're creating a blockage between this chamber and the one next door.
There's a tunnel that links them.
Badgers love to dig in soft soils, typically sandstone, and it does collapse.
It's going to be interesting to see whether these badgers dig their way through.
'If our cubs can't master this skill, 'they simply won't survive in the wild.
'Only time will tell if they're up to the challenge.
' 'Back at Burrower Central, we've created another burrow 'for a completely different kind of burrower, 'an endangered British species, about which very little is known - 'the water vole.
'When we introduced a pair bred for conservation 'into our replica riverbank burrow, 'things didn't go quite as planned.
' There's an altercation going on between Mr Ratty and Bonnie.
'But after a difficult few days, we did spot something intriguing.
'They blocked up two of the three entrances into their burrow.
' They typically do this when they're about to, or have just given birth.
'And now, water vole expert Derek Gow 'has spotted an exciting new development - 'a large ball of grass in Bonnie's chamber.
' Derek, we can't peek into Bonnie's nest.
The risk of disturbance would be too great.
Which is quite frustrating, but we've got to behave.
What is likely to be going on in there? Well, the simple answer, of course, is "Who knows?" But What we know is that they make these large, coarse, almost rugby ball shaped nests.
In the inside are these tiny soft chambers, lots of very finely shredded material and moss.
These are the areas that the water voles give birth in and where the babies live when they're very small.
If there are babies in there, that's where they'll be.
'We don't have to wait long to find out.
'A few days later, through a small gap in Bonnie's nest, 'a tiny water vole pup reveals himself.
'Ratty junior!' 'Bonnie has a small litter of three pups, 'but she's still got her work cut out.
'They're blind and helpless, so she'll have to care for them 'until they can stand on their own four paws.
'On the other side of the farm 'in our rabbit warren, there are now over 20 young kits, 'all ready to explore their underground home.
'As they investigate THEIR burrow, we can finally get to grips 'with the full extent of our real warren in the wild.
'I've returned to Bicton Park, 'where the excavation of our concrete cast is now complete.
' I've been waiting for today for months.
For me, this is one of THE most exciting parts of our project.
We've learned a tremendous amount about the animals in our artificial burrows, in terms of behaviour.
What we haven't been able to do is map the actual burrows that they create in the wild.
Well, what lies over here I think might be one of the final pieces in our jigsaw of understanding their underground lives.
The only thing is, I wasn't entirely sure .
.
that it was going to work.
This is an absolute revelation.
I'm really excited by this.
It's such a simple idea - find an abandoned rabbit warren, fill it full of concrete then excavate it.
Look! You can appreciate immediately the structure.
The most profound thing is it makes me think that all of those times I was walking across the UK countryside, stepping over rabbit holes in the ground, I never knew what was beneath that soil.
And now, I can see it easily.
Question is, of course, what can we learn from this? 'A bird's-eye view shows us just how complex the warren is '.
.
with multiple living chambers 'and complex intersections.
'This warren has over 120 metres of tunnels 'and occupies the same floor space as the average new-build home.
'Our expert, Dr Sasha Norris, has already been investigating.
' I'm completely blown away by it.
I think it's absolutely incredible.
My first impressions are how much it looks like tree roots.
I guess you can expect that cos the tree and the rabbit are doing the same thing, trying to find their way through the soil.
There's going to be rocks, bits they just can't get through.
So they have to go sideways and you've got that organic shape.
It's beautiful, actually.
It's a rabbit sculpture.
Look at this, where the rabbits' claws have cut into the soil.
It's been preserved for ever, like the rabbits' Pompeii.
'So, what can this structure teach us about life underground 'for our baby rabbits? 'Navigating around this maze is an impressive feat for an adult rabbit.
'But for a tiny kit, a warren can be up to 4,000 times its size.
'Pipkin's litter are 18 days old 'and they're now ready to test the limits of the burrow.
'They've left their chamber 'and they venture out into the adjoining tunnels.
' Imagine being born in a warren like this, spending the first few weeks of your life entirely underground in a nest.
Then you branch out, following your way through these tunnels using only a sense of smell, no light whatsoever.
But this network of tunnels would suddenly come alive when all of those young left their breeding nest and started to move around.
There is a period when they're moving around inside the warren, not outside.
Then it would be like a A bunny bundle .
.
heaving party underground.
'As Pipkin's litter explore beyond their home chamber, 'they encounter other unrelated rabbits for the first time.
'In this rabbit nursery, all of the kids play together nicely.
'The same can't be said for their over-protective parents.
'Hazel and the other females have chosen nest chambers.
'And they defend them fiercely.
'Under stress, territorial mums can even kill kits from other litters 'that stumble into their path.
'So Pipkin's litter are going to have to become warren-wise, 'if they want to survive and make it into the outside world.
' 'Meanwhile, our badger expert, Chris Cheeseman, 'has set up a challenge for our young orphans.
'Are they natural born diggers?' Chris, it's going to be interesting to see this.
If they do anything, it's going to be instinctive.
They've not had opportunity to learn any of this from any adult badgers.
'One badger gets straight to work.
'No surprise, it's the head of the group, the big female, Lunar.
' Look at the power of the forelimbs.
That's a beautiful illustration of the way they can pick it up like a spade and shift a lot of soil.
Then the back limbs are just pushing it back, clearing it, basically.
They pull it underneath them, then they'll kick with the back legs just to clear it away.
'Lunar works away at the soil.
She's not the only one who's interested.
'Bramble, our small outsider, 'is keen to make an impression.
' Bramble's come in as well now, look.
Lunar's the dominant animal.
She's a bit bigger and a bit older.
Little Bramble, doing her share of the digging as well.
There's a desire to get through.
You can see there's a bit of excitement there.
"This is our way out.
We need to sort this.
" These are just young badgers, never had the benefit of learning from their mothers or other badgers in the group.
They're instinctively doing what comes naturally.
And they've broken through.
In no time at all.
What was that? Two or three feet of soil? Yeah.
They are powerful digging machines.
'Our orphaned badger cubs have proved that they can really burrow.
'It's a skill they'll need before they can be released.
'Best of all, Bramble has become a key member of the family.
'There is one more thing they'll have to learn 'before any of these badgers can take their first steps outside.
'They'll need to show they know how to defend their home.
'Whilst most of our burrowers are ready to step outside for the first time, 'there is one that's so specialist that it never has to leave.
' And for that, we had to employ a completely different approach.
That's because of the way that it uses its burrow in the wild.
'Our mystery creature gets everything it needs below ground.
'With some 30 million of them living in the UK, 'what are the secrets of its success? 'How does it eat, drink and even breathe? 'Well, to find out, we cast an abandoned burrow with concrete, 'just as we did for the rabbits, 'and unearthed a structure all the more extraordinary, 'when you consider that it was probably created by ONE animal 'in a single day.
' It's even more impressive when you consider the volume of soil that it shifted - up to 540 times its own bodyweight.
Now, that is a bit like me shifting this lot in a day - 40 tonnes of soil.
So, what is this curious creature? It's the mole.
Based on our burrow cast, we created a mole burrow of our own.
So, what we've got here are boxes with a closed system of tunnels which are as close to nature as possible and ideal for filming.
Our moles were rescued and have now been rehomed in our burrow.
They should feel at home.
It's completely enclosed and just like being underground.
So what can we learn about this ultimate burrower? One man who can help us is mole enthusiast Peter Stafford.
At the age of just 17, Peter captured a series of astonishing images that remain the only pictures of a wild mole nest ever shot.
This picture won him the title of Wildlife Cameraman of the Year in 1967.
Look at this! Yeah.
The detail in these images is phenomenal.
I know.
Absolutely extraordinary.
Look at this, powering along its tunnel.
Yeah.
Wonderful exploratory behaviour.
It's padding the surface with its nose as it comes forward.
That's amazing.
Look at that! You can see all its whiskers.
'Our exciting new view of moles moving through the soil 'backs up a theory that Peter has had about them for years.
' It's extraordinary footage.
I'd describe the motion of a mole through soil as a swimming action.
It pulls itself through, rather than digs its way through in the traditional way we think about burrowing.
'This swimming mole theory might seem unlikely '.
.
until you go underwater '.
.
and watch a common seal in action.
' Seals have very streamlined bodies for slipping easily and gracefully through the water.
Moles have streamlined bodies for pushing their way through the soil.
These animals don't have their limbs beneath their body, like many quadruped animals do to support their weight.
For seals, the water is supporting that bodyweight.
They have their forelimbs on the side of their body, just like moles do.
'To understand Peter's theory, you have to go below the surface 'and get down to the bare bones of his idea.
'A mole's skeleton is just like a miniature seal.
' The seal has its hands turned into these huge flippers for pushing through water.
Here we have a spade - or a shovel! By virtue of its sixth finger, which gives it incredible width.
A key feature is this modification of the forelimbs, isn't it? Yeah.
Exactly the same there.
That's an incredible piece of natural sculpture.
Very few people would say that was an arm bone! 'With a sixth finger on each of its front paws, 'short upper arms and reinforced shoulders, 'the mole moves through soil just as the seal moves through water, 'pushing the soil away with sideways strokes.
'This is what's known as "convergent evolution" - 'two completely different animals that have evolved in the same way.
' This is an animal that swims through the sea and here we have an animal which, through similar adaptations, swims through the soil.
That's exactly what they both do.
'But moles are solitary creatures, so we have to ask, 'why do they dig out such an extensive burrow? 'Well, it's not just a home.
It's a trap - 'one that earthworms regularly fall for.
'The mole's tiny eyes are virtually useless in the dark.
'Instead, it uses its nose.
'But not for smelling - for feeling.
'Its nose is covered with over 5,000 sensory cells called Eimer's organs.
'These are so sensitive they can feel the tiniest of vibrations - 'even the moment when a worm drops into the burrow.
'The mole pulls the worm through its enormous paws, 'forcing out any dirt, like toothpaste.
'And if it's not hungry, it bites off the head 'and uses venomous saliva to paralyse its prey.
'Which it then stores in a special chamber.
'A living larder, full of tasty earthworms that never spoil.
' Things are very quiet out here at the moment in the tank area.
Occasionally, we get to glimpse Ratty and Bonnie, but all of their litter are inside the burrows, doing the essential job of fattening-up first.
'A few days after we last saw them, 'our young voles are ready to move out of their nest.
'At just a week old, the babies are nearly half the size of Mum.
'That's like a newborn baby growing into a seven-year-old 'in just five days.
'So how is it that they've grown quite so fast? 'Suckling.
'Amazingly, four of Bonnie's teats are close to her armpits 'and this might be, like for other aquatic species, 'so her young can suckle IN the water.
'But Mother's milk is not enough on its own.
'In just a week, Ratty junior is already eating solids.
'In fact, all the pups are now raiding Mum's larder, 'and they are hungry.
'Water voles eat 80% of their own bodyweight every single day.
'So it won't be long before Mum's food store runs out.
'Soon, the young water voles will have to leave the burrow 'to forage for food themselves on the riverbank.
'If there's one thing water voles aren't too fussy about it's food.
'They'll eat up to 227 different types of plant, 'especially grasses, but so much roughage can be hard to handle.
' This is a highly magnified photograph of the surface of a blade of grass.
It's not smooth at all.
It's covered with all of these spines.
Here's another photograph which shows just one of those in close-up.
The material that makes up this spine is silica.
When we say "silica", think "sand".
Gliding that between your teeth makes life tough.
Our water voles have come up with some specialised adaptations to overcome this problem.
They've evolved some of the most formidable gnashers in the animal kingdom.
I have a water vole skull, Chris.
Lovely specimen.
Look at that! Fantastic! Displaying all the attributes of a rodent's skull.
Those sharp incisors.
The gap between those, where they can move the food around, once they've nibbled it off, then the molars.
I'm going to try to get a molar out.
These are unique.
Hard enamel round the outside and the soft bit in the centre creates these ridges.
They're constantly growing, that's the point.
They're constantly wearing down, on account of that vegetation.
Very hard abrasive material.
People don't realise how abrasive uncooked vegetation is.
It needs a solid grinding mass that's capable of breaking it down.
'Ratty junior has some of the toughest teeth in the mammal world, 'and they're constantly growing.
'He'll need them, so he can eat up all his greens.
'But also for the very thing that, like Dad, will define him 'as one of Britain's best burrowers - 'digging.
'He chomps through the soil, sucks it in, spits it out 'and then kicks it away with his paws.
'An adult water vole can excavate a tunnel system up to 70 metres long.
'It can gnaw through roots and even topple trees.
' I've felt the teeth of a water vole! You've probably felt the teeth of many! They can deliver a sharp a bite.
They can give you a scorcher of a bite! And what they also tend to do is, once they've bitten you, they get those little front paws and they hang on.
It's just not a fun experience! 'Inside our rabbit warren, Pipkin's litter are now three weeks old.
'They are much more adventurous and they're ranging right through the warren.
'They're getting to know this place like the back of their paw.
'But why? In our burrow, the kits are safe from predators.
'But they don't know that.
'Their wild instincts tell them 'to get to know every inch of their warren, for a very good reason.
' A burrow system like this protects them from most predators.
They simply can't get in.
But there is one that can get in - and often comes in for the kill.
'The stoat! 'It might be a tenth of the size of a rabbit, 'but this is rabbit enemy number one.
'Unlike larger hunters, the stoat can fit inside a rabbit warren.
'And once it makes a kill, it can sometimes stay there.
'A stoat, like this one in a replica burrow, 'will take up residence inside its victim's chamber 'and, in a horrifying twist, 'sometimes use the rabbit's carcass as a nest where it gives birth.
'Its victim doesn't just provide warmth for the young, 'it can also provide ample food for them as they begin to grow.
'But the rabbits have a trick left up their sleeve, 'revealed by our concrete cast of a warren, 'which shows that these tunnels aren't just a place to rest, 'but also full of escape routes.
' This has got seven different tunnels coming off it.
Some going down, some going sideways and up.
If you imagine you're being pursued by a stoat through the warren, at this point, you can really confuse them, can't you? You can go off in every direction.
You intimately know this highway of tunnels.
Because you live in it, you know how to get away.
From that predator.
'We built our warren inside a protected enclosure, 'so there's no chance of a stoat attack.
'Our young rabbits still spend every moment 'learning all of the complex intersections and secret pathways.
'But will they be ready for their biggest step of all?' 'One extreme way to avoid being eaten by any kind of predator 'is to spend your whole life underground, which is what moles do.
'Our moles will happily live out their lives in our replica burrow, 'just as they would in the wild.
'But living your whole life below the surface isn't easy.
'Like all mammals, the mole needs oxygen, 'and that's in short supply.
'There's so little down here that we wouldn't be able to breathe.
' To find out how moles cope with these really tough conditions, I've come to meet a completely different species of animal which, at first glance, you would think would have little in common with the mole, particularly as it's 1,000 times larger.
It's the alpaca.
It's a creature which survives in an incredibly hostile environment.
It prospers where other mammals really, really struggle.
At 4,000 metres up in the high Andes, there's 40% less oxygen than there is down here at sea level.
This presents mammals with all sorts of problems when it comes to breathing and respiring.
All animals need that oxygen, but what the alpacas have done is radically change their blood.
For a start, they've got many more red blood corpuscles.
This helps with the oxygen exchange.
They've also got a lot more haemoglobin, that chemical which transports the oxygen inside those blood cells.
Curiously, the mole has gone down exactly the same route.
It, too, has many more red blood corpuscles and a lot more haemoglobin.
It's not living at high altitude, but it's living in tunnels where there's only one third of the amount of oxygen that I'm breathing here in the fresh air.
The mole's life is a near complete mystery to us.
There is evidence at this time of year that some moles do venture above the surface, and we have to ask why.
The clues come, not from watching moles, but by looking at another completely unrelated animal.
Tawny owls, like many birds, produce pellets.
All of the bones, fur and feathers get compacted into that pellet, which is regurgitated through the mouth.
If we can recover their pellets and look inside them, we can see what's been on their menu.
So let's see what we've got here.
Here's a jawbone straight away.
Look at that! These are the teeth of an insectivore.
Very different than a rodent.
This is a mole jawbone.
How is a non-burrowing bird catching an animal that never surfaces? The bones are the biggest clue.
They're from juvenile moles that have been turfed out of their mother's burrow.
It's likely that these inexperienced burrowers simply lost their way and then, on the surface, become completely vulnerable to birds of prey.
What about that?! That's really neat.
We're learning something about the social behaviour of one animal through the diet of another! Pretty fantastic! And I'm really pleased with that bone.
'Our badgers now seem properly settled in their new residence.
'They've bonded as a group.
'Now they'll need to develop skills 'they'll need for encountering other badgers.
' It's perhaps not surprising, given they spend so much time down in the sett in the dark, that badgers don't rely upon their eyesight when it comes to recognising things and communicating.
It's their sense of smell which is most critical.
If you look very carefully at their face, you can see they've got these very long, quite broad snouts.
They've got big noses! You can see here, Bramble at the moment, is not looking at that soil, she's sniffing that soil.
They have this snuffling behaviour.
It's one of the things that defines the behaviour of badgers.
The reason that they're drawing in these massive intakes of breath is so that they can smell very quickly exactly what they're after.
But what are the scents they're so obsessed by? There's something that they're doing to each other with their hind quarters.
And the results seem irresistibly smelly to the others.
This is interesting stuff.
Look very carefully at Lunar, at what she's doing.
She's compressing the back part of her body down onto another animal.
What she's doing is scent marking that animal.
Badgers have sub-caudal glands at the base of their tail.
They carry a personal perfume.
She is anointing her other group member here, so they know who they've had an encounter with.
By scent marking the others, Lunar is reaffirming her status at the top of the group.
She, and all of our badgers, are leaving their perfumed calling card.
But they don't just scent mark each other.
They also leave scent on their droppings.
So what role could that play? What are these young badgers going to use that for out in the wider world? 'We can find out in the wild 'if we go to the place where badgers go to the toilet.
'They repeatedly use a series of latrines 'located on the periphery of their territory.
' It's fair to say that, to the bulk of our audience, this will look like an ugly pile of poo.
But to the badgers, this is like a veritable perfume counter! Well, this is part of a boundary latrine.
Badgers mark their boundaries by defecating in these latrines.
This is a scent beacon, which sends a message to other badgers in the neighbouring groups that this is "our patch" and that's yours and stay there! It is a mutually respected boundary marker, like a fence round your garden.
They're very active when they're defecating.
They get very excited.
I've seen groups of badgers.
Three have arrived at once.
This is fantastic fun, finding a latrine! Seeing who's been there, whether your rival's been there, digging a pit, adding your own.
Exactly right.
They do get really worked-up.
Almost frantically scratching around and smelling.
We can't smell it, unless you stick your nose right down there.
To a badger, this is really full of scents.
I'm going to give it a go.
It does have a characteristic smell.
It's not too strong, but it's characteristic.
Musty.
Yeah, musty.
Very different from a fox, which is much more bitter.
Once you've learned a smell, you can always tell.
I bet you couldn't tell between the different badgers.
Give me a chance.
That's Brian.
That's Yeah, Brian and Stan.
And Stan had a worm tandoori that night.
Definitely.
'Scent mark latrines are vitally important, 'because badgers from a family group usually don't take kindly 'to trespassers on their patch.
'Our badgers will need to recognise the scented latrines of their group 'to protect themselves in the future when they're released into the wild.
'With each wiggle of the end of her tail, 'Lunar demonstrates her scenting language skills 'and the others follow suit.
'Back at Burrower Central, 'Pipkin's litter are now nearly four weeks old.
'They're looking a lot less like baby bunnies 'and more like small versions of their mum.
'These physical features are vital to their survival above ground.
'Because these animals are hunted by just about everything.
' Look at her eyes.
Typically, predators have their eyes on the front of their face.
When they're looking forward, they can judge distance extremely well.
Important when you're about to grab something.
If you don't want to be grabbed, where do you put your eyes? On the sides and on the top of your head.
Pipkin here can see not only forward, to look out for the fox, and behind to look out for the fox, but also up at the same time, to look out for the buzzard.
So it's a very good adaptation.
The second thing - look at her ears.
At the moment, they're inactive.
When you watch a rabbit on the surface, its ears are always erect.
What's more, they can twist them in different directions at the same time.
They can listen for predators over here AND over there.
So, they've made physiological adaptations to avoid being eaten.
'The big moment has arrived.
'Pipkin's young are as ready as they'll ever be 'to undertake the journey 'they've spent the last four weeks preparing for.
'With Mum, Pipkin, leading the way, 'they venture into the outside world.
'But how will they take in the foreign sights and sounds 'and their first breath of fresh air? 'Sasha and I are waiting eagerly.
' Here they come, Chris.
Look at that! On the brink! It's quite a brave moment for these little things.
We know there aren't any predators in our enclosure, but they don't know that.
'Even without the threat of being eaten, 'the outside world is overwhelming.
'Bright sunshine.
New smells.
'New sounds.
'And boisterous adults.
'For some of Pipkin's litter, it's just too much.
'All they want to do is huddle for security.
'Mum is on hand to reassure them.
' Look how attentive she is here.
Head up the whole time.
She's not feeding at all.
She's looking around, constantly vigilant.
Occasionally, she's thumping away, to warn them.
They're all in a tight cluster, which is what you'd want.
The kits don't just look to Mum for protection.
This is interesting.
We've seen them grooming one another in the warren.
Now, they're all looking after one another.
That's a way of forming affiliations with other rabbits.
They don't just groom their own family.
They also groom other litters and adults.
This is how they tell each other that they're part of a group and maintain that group.
It's a behaviour called allogrooming.
Physical contact builds bonds and secures friendships, so everyone can watch out for danger.
Because outside the warren, security for a rabbit is a case of safety in numbers.
The more rabbits there are, the more eyes, the more ears, therefore, for the individual, the more time spent feeding.
Now look.
They're taking their first fresh meal, if you like.
Up until this point, they've been fed on milk.
What's interesting is they learn the right types of food to eat from the chemicals inside the milk that they drank in the warren.
So they know the flavour and they can pick up the scent and eat that to get them going? That's right.
Those plants won't be poisonous cos their mum ate them and survived.
I wonder what it's like, that first bite of a fresh leaf.
That must be a flavour sensation! 'Our kits' preparation for the outside has served them well.
'They've used their time in the burrow to grow 'and learn vital skills for survival.
'But there are still trials ahead.
'Life for an adolescent rabbit is fraught with challenges.
'Their instincts tell them to always be cautious.
'When one is spooked '.
.
everyone is back in their burrow, in just a few hops.
'At our riverbank burrow, the water voles are busy.
'Bonnie can be seen restocking the larder 'and Mr Ratty is taking his daily dip.
'So far, the youngsters haven't made an appearance outside.
' We've got to look at these, Derek, and think that the burrow has provided them with enough security to mature to the stage that they can be this independent this quickly.
They've taken on all the weight they require to be strong and fit enough.
Now, it's a more testing time.
They've got to find their own way in this world.
It's really something.
It's a remarkable thing to see.
'In just two weeks, that's half the time it took our baby rabbits, 'our young water voles are ready to step outside 'and take their first swim.
' 'After just a moment's hesitation 'our first young water vole is straight into the water.
'And then there were two.
'They love the water - and a good play.
'But where's Ratty junior? 'At first, he's not as confident as the others.
'But after a little comfort eating '.
.
he finally ventures out.
'He soon masters the water, 'although he hasn't quite mastered getting out.
'It's Mum, Bonnie, to the rescue, 'whilst his dad takes a more relaxed approach.
' This is a happy conclusion.
When you think about it, at last, the youngsters have come out into the wider world, into the water, and they're looking good.
There's something personally satisfying, I've got to say! Yeah.
It's really lovely.
It's delightful to see them behaving in this way.
They're just beautiful animals.
'There's only one group of burrowers still to step outside - 'the badgers.
'Our orphaned cubs are now three months old.
'In the wild, at around this age, 'cubs are encouraged to leave the sett by their mothers.
'But here, without parents to guide them, we open up the burrow 'and hope they'll take their first steps outside.
'It's the first real test of how well they've bonded as a group.
'Will they face the outside world together? 'As badgers are nocturnal, we have to wait until it's dark.
' This is a momentous moment in the lives of these young badgers.
It's the first time that they've come outside into the wide world.
Imagine the sensory overload! Look how busy Lunar is here, with her nose.
The first thing she's done is start snuffling in that soil.
It must be loaded with new smells.
'At first, it looks as if Lunar is on her own.
'But as night falls, another badger appears.
'And then Bramble follows, hot on their heels.
'Eventually, the whole group explores together.
'Now, it's a protected enclosure, but our orphans don't know that.
'Any strange scent or sound and they're on the alert.
'It's a great sign that our badgers are instinctively sensing danger.
'One cub has got a bit over-excited.
'Lunar can't resist a good romp.
' 'So, the seven cubs have taken a brave step, 'but that's enough for one night.
'Before long, they all head back inside, 'to the familiarity and comfort of their sett.
' We've had a fabulous few weeks with this amazing experiment.
We've learned a tremendous amount.
We've seen Ratty junior and his siblings, the water voles, have grown at a phenomenal rate.
Our young badgers learned all about scenting and digging before they stepped out.
Pipkin's litter developed a protective community before they, too, ventured out into the wider world.
One thing's for sure, we've seen all of our burrowers using their burrow to prepare them for life above ground.
This is a remarkable project and we've learned a tremendous amount about all the secret lives of these animals.
'Next time, how will our rabbits cope 'with a warren that's full to bursting?' For them, it's a case of "breed like mad".
'Will our young water voles be ready for life in the wild? 'And will our badgers learn to talk badger 'and be ready to leave the sett for good?' This looks like a lot of fun, but this is preparation for their life ahead.
If you're enjoying the world of our burrowers and you'd like to see more there's plenty available on our website.
We've put together the most fascinating behaviour that we've discovered throughout the series.
I've also produced guides to show you how to spot burrowers living where you live.
Learn how to spot badgers, water voles, rabbits, foxes and moles - That's all on
.
but there's a secret world beneath our feet.
'A hidden kingdom teams with millions of burrowing creatures, 'their lives shrouded in mystery.
'Why do they live underground? 'Where do they sleepand eat? 'And how do they raise their young? 'Their secret subterranean world remained unseen '.
.
until now.
' Wow! Look at this! This is our vision come true.
'We are breaking new ground in natural history.
'We've unearthed real animal burrows.
'And created three lifelike replicas of our own.
'A rabbit warren, 'a water vole burrow 'and a badger sett.
' To be able to crouch here, this far away from a little badger and observe what it's up to - it's beyond my dream! 'It's spring now, but winter was a busy time for our burrowers.
'Our rabbits have bred, 'but will their young learn the skills they need to survive?' It's quite a brave moment for these little things.
'Our two water voles got off on the wrong paw, 'but are things looking up?' If there ARE babies in there, that's where they'll be.
'And our seven orphaned badger cubs have begun to bond as a group, 'but can they master the badger basics?' This is the first time they've had the opportunity to dig! 'And we uncover the dark secrets of the burrower that can do this!' Phenomenal! Hopefully, people may see moles in a different light.
'We have a window on their lives like never before.
'Explore this magical world with me, Chris Packham, 'as we ask in this programme, 'how do young burrowers grow up inside the burrow 'and prepare for their first taste of fresh air?' This is a momentous moment in the lives of these young badgers.
'It's spring in Britain's Southwest 'where, in a unique experiment, we've built three replica burrows.
'Our badger sett is now home to a family of seven playful orphans.
'And 100 miles away, on a small Dartmoor farm, 'we've created a riverbank burrow for a pair of water voles 'and a vast warren, big enough for a whole community of rabbits - 'all under the watchful eye of a team of the country's 'of top filmmakers and naturalists.
' Welcome to Burrower Central, here in Devon.
It's six months since our unique project began here and already we've learned so much new science.
But having said that, there's a lot more that we want to know yet.
It's springtime now and our young burrowers face their biggest challenge yet - taking their first steps into the outside world.
'Our burrows aren't just underground.
'They're all equipped with protected outdoor spaces.
'We know from the wild that spring is when young emerge from the burrow 'for the very first time.
'How will our young burrowers prepare for the outside world? 'We'll watch as our badger cubs learn to communicate '.
.
as our newborn rabbits find their way 'out of the labyrinth of the warren, 'and as the next generation of young water voles grow up 'and get ready to leave home.
' We ask, what role does the burrow play at this important stage of our burrowers' lives? Will it provide them with the skills to survive outside? 'There's a major clue that our ten rabbits 'have enjoyed their first month in our warren.
'They've been breeding like rabbits.
'Led by head buck Thumper '.
.
the two squabbling males 'have already sired seven litters between them.
'Hazel is the top female.
'And like nearly every adult doe in the warren, 'she has a litter of her own.
' There is something enchanting and magical about this rabbits' nest.
It's pulsing with young rabbits.
We can't see them.
They're completely hidden by the fur, but they're all down there, huddling to stay warm.
We're not entirely sure how old they are.
Maybe a week or just over.
It'll only be a few days, then they will start to come out of the nest and explore the rest of the warren.
Then it won't be long until they look like this - a fully fledged bunny.
'At two weeks, these seven kits 'have reached the next stage of development.
'They belong to Pipkin.
'Despite only suckling from Mum for three minutes a day, 'they've matured rapidly.
'Rabbit milk is one of the most nutritious in the animal kingdom.
'They've gained sight, 'can now hear 'and they weigh five times the amount they did at birth.
'And now that their fur is fully developed, 'they can leave the warmth of the nest and take their first steps.
'For the moment, at least, 'they don't go beyond their mother's chamber.
' This is going to give us an extraordinary opportunity to see these animals raised.
A view that no other naturalist could have ever had - looking at rabbits underground, going about their natural business.
'Their parents are from domestic stock, 'but they should behave as they would in the wild.
'Because our rabbit warren, like all of our burrows, 'is based on data from the real thing.
'They're the largest constructed burrows of their kind.
'We want to see for ourselves the enormous scale 'and structural design of a wild warren.
'So, six months ago at Devon's Bicton Park, 'we investigated an abandoned warren 'and began the most ambitious stage of our natural history project.
' We're going to fill this warren with concrete.
When it sets and we excavate it, we'll be able to see the anatomy of their architecture in full sculptural 3-D.
And that's pretty exciting.
'Battling one of the worst winters on record, 'we filled the empty warren with ten metric tonnes of concrete.
'And then left it to set.
'Now in spring, we're beginning 'the biggest wildlife excavation of its kind ever attempted in Britain.
'When we finish, we'll have the most detailed picture ever 'of the rabbits' secret subterranean world.
'It's going to take another week to reveal every corner.
' 'Our badger sett is located at Secret World Wildlife Rescue Centre in Somerset.
'It's been a few weeks since our cubs moved in.
'They're all rescued orphans, nursed back to health.
' 'Boisterous female Lunar 'is the eldest and biggest.
'She's established her position at the head of the group.
'She's still just the equivalent age of a human tweenager.
' This artificial sett that we built is the perfect rehabilitation environment for our young badgers, because it gives them the chance to learn in a natural setting about living together as a group.
That will be very important when it eventually comes to their release.
Of course, in the meantime, it also gives us a unique opportunity to delve into the secret life of badgers below ground.
'This is the cub we named Bramble.
'She'd been found alone and fighting for her life.
'One of the youngest and smallest cubs, 'she's had a tough time fitting into the group.
'Without the others, she's unlikely to survive 'when this group is released into the wild.
'It seems she's not quite ready yet to impress the boss, Lunar.
'She tries her luck first with a more relaxed cub' '.
.
Mr Sleepyhead himself, Truffle.
'The moment Truffle went into our burrow, he made a cosy bed.
' Their instinct is to make a nest so that they can stay warm, which is essential.
'And now, all he does is lie in it.
'Bramble follows suit.
'She cuddles up to her new brother and then has a snooze.
'But there are other challenges ahead.
'They'll all be tested for TB.
'And when they're old enough and fit to be released, 'they'll need to dig a sett of their own.
'But at just two months old, 'they've already begun to put their digging skills to the test.
' Just look at our little badgers! If you look closely - they're a bit busy at the moment - but you can see that they're natural born digging machines.
Look at the shape of their body.
Their narrow nose broadens over and tapers down.
Perfect for moving through the soil.
And their spine is arched.
This helps with their whole digging and shifting masses of soil.
And when they grow into adults - if they ever stop playing - these things can really shift soil, double their own bodyweight at a single time.
'Badgers don't just dig new digs.
'In the wild, their setts sometimes cave in.
'Burrowers can be buried alive 'if they don't know how to dig their way out.
'So, will our cubs know how to tunnel out of trouble? 'To find out, our badger expert, Dr Chris Cheeseman, 'wants to set them a challenge.
' Well, what we're trying to do here is we're creating a blockage between this chamber and the one next door.
There's a tunnel that links them.
Badgers love to dig in soft soils, typically sandstone, and it does collapse.
It's going to be interesting to see whether these badgers dig their way through.
'If our cubs can't master this skill, 'they simply won't survive in the wild.
'Only time will tell if they're up to the challenge.
' 'Back at Burrower Central, we've created another burrow 'for a completely different kind of burrower, 'an endangered British species, about which very little is known - 'the water vole.
'When we introduced a pair bred for conservation 'into our replica riverbank burrow, 'things didn't go quite as planned.
' There's an altercation going on between Mr Ratty and Bonnie.
'But after a difficult few days, we did spot something intriguing.
'They blocked up two of the three entrances into their burrow.
' They typically do this when they're about to, or have just given birth.
'And now, water vole expert Derek Gow 'has spotted an exciting new development - 'a large ball of grass in Bonnie's chamber.
' Derek, we can't peek into Bonnie's nest.
The risk of disturbance would be too great.
Which is quite frustrating, but we've got to behave.
What is likely to be going on in there? Well, the simple answer, of course, is "Who knows?" But What we know is that they make these large, coarse, almost rugby ball shaped nests.
In the inside are these tiny soft chambers, lots of very finely shredded material and moss.
These are the areas that the water voles give birth in and where the babies live when they're very small.
If there are babies in there, that's where they'll be.
'We don't have to wait long to find out.
'A few days later, through a small gap in Bonnie's nest, 'a tiny water vole pup reveals himself.
'Ratty junior!' 'Bonnie has a small litter of three pups, 'but she's still got her work cut out.
'They're blind and helpless, so she'll have to care for them 'until they can stand on their own four paws.
'On the other side of the farm 'in our rabbit warren, there are now over 20 young kits, 'all ready to explore their underground home.
'As they investigate THEIR burrow, we can finally get to grips 'with the full extent of our real warren in the wild.
'I've returned to Bicton Park, 'where the excavation of our concrete cast is now complete.
' I've been waiting for today for months.
For me, this is one of THE most exciting parts of our project.
We've learned a tremendous amount about the animals in our artificial burrows, in terms of behaviour.
What we haven't been able to do is map the actual burrows that they create in the wild.
Well, what lies over here I think might be one of the final pieces in our jigsaw of understanding their underground lives.
The only thing is, I wasn't entirely sure .
.
that it was going to work.
This is an absolute revelation.
I'm really excited by this.
It's such a simple idea - find an abandoned rabbit warren, fill it full of concrete then excavate it.
Look! You can appreciate immediately the structure.
The most profound thing is it makes me think that all of those times I was walking across the UK countryside, stepping over rabbit holes in the ground, I never knew what was beneath that soil.
And now, I can see it easily.
Question is, of course, what can we learn from this? 'A bird's-eye view shows us just how complex the warren is '.
.
with multiple living chambers 'and complex intersections.
'This warren has over 120 metres of tunnels 'and occupies the same floor space as the average new-build home.
'Our expert, Dr Sasha Norris, has already been investigating.
' I'm completely blown away by it.
I think it's absolutely incredible.
My first impressions are how much it looks like tree roots.
I guess you can expect that cos the tree and the rabbit are doing the same thing, trying to find their way through the soil.
There's going to be rocks, bits they just can't get through.
So they have to go sideways and you've got that organic shape.
It's beautiful, actually.
It's a rabbit sculpture.
Look at this, where the rabbits' claws have cut into the soil.
It's been preserved for ever, like the rabbits' Pompeii.
'So, what can this structure teach us about life underground 'for our baby rabbits? 'Navigating around this maze is an impressive feat for an adult rabbit.
'But for a tiny kit, a warren can be up to 4,000 times its size.
'Pipkin's litter are 18 days old 'and they're now ready to test the limits of the burrow.
'They've left their chamber 'and they venture out into the adjoining tunnels.
' Imagine being born in a warren like this, spending the first few weeks of your life entirely underground in a nest.
Then you branch out, following your way through these tunnels using only a sense of smell, no light whatsoever.
But this network of tunnels would suddenly come alive when all of those young left their breeding nest and started to move around.
There is a period when they're moving around inside the warren, not outside.
Then it would be like a A bunny bundle .
.
heaving party underground.
'As Pipkin's litter explore beyond their home chamber, 'they encounter other unrelated rabbits for the first time.
'In this rabbit nursery, all of the kids play together nicely.
'The same can't be said for their over-protective parents.
'Hazel and the other females have chosen nest chambers.
'And they defend them fiercely.
'Under stress, territorial mums can even kill kits from other litters 'that stumble into their path.
'So Pipkin's litter are going to have to become warren-wise, 'if they want to survive and make it into the outside world.
' 'Meanwhile, our badger expert, Chris Cheeseman, 'has set up a challenge for our young orphans.
'Are they natural born diggers?' Chris, it's going to be interesting to see this.
If they do anything, it's going to be instinctive.
They've not had opportunity to learn any of this from any adult badgers.
'One badger gets straight to work.
'No surprise, it's the head of the group, the big female, Lunar.
' Look at the power of the forelimbs.
That's a beautiful illustration of the way they can pick it up like a spade and shift a lot of soil.
Then the back limbs are just pushing it back, clearing it, basically.
They pull it underneath them, then they'll kick with the back legs just to clear it away.
'Lunar works away at the soil.
She's not the only one who's interested.
'Bramble, our small outsider, 'is keen to make an impression.
' Bramble's come in as well now, look.
Lunar's the dominant animal.
She's a bit bigger and a bit older.
Little Bramble, doing her share of the digging as well.
There's a desire to get through.
You can see there's a bit of excitement there.
"This is our way out.
We need to sort this.
" These are just young badgers, never had the benefit of learning from their mothers or other badgers in the group.
They're instinctively doing what comes naturally.
And they've broken through.
In no time at all.
What was that? Two or three feet of soil? Yeah.
They are powerful digging machines.
'Our orphaned badger cubs have proved that they can really burrow.
'It's a skill they'll need before they can be released.
'Best of all, Bramble has become a key member of the family.
'There is one more thing they'll have to learn 'before any of these badgers can take their first steps outside.
'They'll need to show they know how to defend their home.
'Whilst most of our burrowers are ready to step outside for the first time, 'there is one that's so specialist that it never has to leave.
' And for that, we had to employ a completely different approach.
That's because of the way that it uses its burrow in the wild.
'Our mystery creature gets everything it needs below ground.
'With some 30 million of them living in the UK, 'what are the secrets of its success? 'How does it eat, drink and even breathe? 'Well, to find out, we cast an abandoned burrow with concrete, 'just as we did for the rabbits, 'and unearthed a structure all the more extraordinary, 'when you consider that it was probably created by ONE animal 'in a single day.
' It's even more impressive when you consider the volume of soil that it shifted - up to 540 times its own bodyweight.
Now, that is a bit like me shifting this lot in a day - 40 tonnes of soil.
So, what is this curious creature? It's the mole.
Based on our burrow cast, we created a mole burrow of our own.
So, what we've got here are boxes with a closed system of tunnels which are as close to nature as possible and ideal for filming.
Our moles were rescued and have now been rehomed in our burrow.
They should feel at home.
It's completely enclosed and just like being underground.
So what can we learn about this ultimate burrower? One man who can help us is mole enthusiast Peter Stafford.
At the age of just 17, Peter captured a series of astonishing images that remain the only pictures of a wild mole nest ever shot.
This picture won him the title of Wildlife Cameraman of the Year in 1967.
Look at this! Yeah.
The detail in these images is phenomenal.
I know.
Absolutely extraordinary.
Look at this, powering along its tunnel.
Yeah.
Wonderful exploratory behaviour.
It's padding the surface with its nose as it comes forward.
That's amazing.
Look at that! You can see all its whiskers.
'Our exciting new view of moles moving through the soil 'backs up a theory that Peter has had about them for years.
' It's extraordinary footage.
I'd describe the motion of a mole through soil as a swimming action.
It pulls itself through, rather than digs its way through in the traditional way we think about burrowing.
'This swimming mole theory might seem unlikely '.
.
until you go underwater '.
.
and watch a common seal in action.
' Seals have very streamlined bodies for slipping easily and gracefully through the water.
Moles have streamlined bodies for pushing their way through the soil.
These animals don't have their limbs beneath their body, like many quadruped animals do to support their weight.
For seals, the water is supporting that bodyweight.
They have their forelimbs on the side of their body, just like moles do.
'To understand Peter's theory, you have to go below the surface 'and get down to the bare bones of his idea.
'A mole's skeleton is just like a miniature seal.
' The seal has its hands turned into these huge flippers for pushing through water.
Here we have a spade - or a shovel! By virtue of its sixth finger, which gives it incredible width.
A key feature is this modification of the forelimbs, isn't it? Yeah.
Exactly the same there.
That's an incredible piece of natural sculpture.
Very few people would say that was an arm bone! 'With a sixth finger on each of its front paws, 'short upper arms and reinforced shoulders, 'the mole moves through soil just as the seal moves through water, 'pushing the soil away with sideways strokes.
'This is what's known as "convergent evolution" - 'two completely different animals that have evolved in the same way.
' This is an animal that swims through the sea and here we have an animal which, through similar adaptations, swims through the soil.
That's exactly what they both do.
'But moles are solitary creatures, so we have to ask, 'why do they dig out such an extensive burrow? 'Well, it's not just a home.
It's a trap - 'one that earthworms regularly fall for.
'The mole's tiny eyes are virtually useless in the dark.
'Instead, it uses its nose.
'But not for smelling - for feeling.
'Its nose is covered with over 5,000 sensory cells called Eimer's organs.
'These are so sensitive they can feel the tiniest of vibrations - 'even the moment when a worm drops into the burrow.
'The mole pulls the worm through its enormous paws, 'forcing out any dirt, like toothpaste.
'And if it's not hungry, it bites off the head 'and uses venomous saliva to paralyse its prey.
'Which it then stores in a special chamber.
'A living larder, full of tasty earthworms that never spoil.
' Things are very quiet out here at the moment in the tank area.
Occasionally, we get to glimpse Ratty and Bonnie, but all of their litter are inside the burrows, doing the essential job of fattening-up first.
'A few days after we last saw them, 'our young voles are ready to move out of their nest.
'At just a week old, the babies are nearly half the size of Mum.
'That's like a newborn baby growing into a seven-year-old 'in just five days.
'So how is it that they've grown quite so fast? 'Suckling.
'Amazingly, four of Bonnie's teats are close to her armpits 'and this might be, like for other aquatic species, 'so her young can suckle IN the water.
'But Mother's milk is not enough on its own.
'In just a week, Ratty junior is already eating solids.
'In fact, all the pups are now raiding Mum's larder, 'and they are hungry.
'Water voles eat 80% of their own bodyweight every single day.
'So it won't be long before Mum's food store runs out.
'Soon, the young water voles will have to leave the burrow 'to forage for food themselves on the riverbank.
'If there's one thing water voles aren't too fussy about it's food.
'They'll eat up to 227 different types of plant, 'especially grasses, but so much roughage can be hard to handle.
' This is a highly magnified photograph of the surface of a blade of grass.
It's not smooth at all.
It's covered with all of these spines.
Here's another photograph which shows just one of those in close-up.
The material that makes up this spine is silica.
When we say "silica", think "sand".
Gliding that between your teeth makes life tough.
Our water voles have come up with some specialised adaptations to overcome this problem.
They've evolved some of the most formidable gnashers in the animal kingdom.
I have a water vole skull, Chris.
Lovely specimen.
Look at that! Fantastic! Displaying all the attributes of a rodent's skull.
Those sharp incisors.
The gap between those, where they can move the food around, once they've nibbled it off, then the molars.
I'm going to try to get a molar out.
These are unique.
Hard enamel round the outside and the soft bit in the centre creates these ridges.
They're constantly growing, that's the point.
They're constantly wearing down, on account of that vegetation.
Very hard abrasive material.
People don't realise how abrasive uncooked vegetation is.
It needs a solid grinding mass that's capable of breaking it down.
'Ratty junior has some of the toughest teeth in the mammal world, 'and they're constantly growing.
'He'll need them, so he can eat up all his greens.
'But also for the very thing that, like Dad, will define him 'as one of Britain's best burrowers - 'digging.
'He chomps through the soil, sucks it in, spits it out 'and then kicks it away with his paws.
'An adult water vole can excavate a tunnel system up to 70 metres long.
'It can gnaw through roots and even topple trees.
' I've felt the teeth of a water vole! You've probably felt the teeth of many! They can deliver a sharp a bite.
They can give you a scorcher of a bite! And what they also tend to do is, once they've bitten you, they get those little front paws and they hang on.
It's just not a fun experience! 'Inside our rabbit warren, Pipkin's litter are now three weeks old.
'They are much more adventurous and they're ranging right through the warren.
'They're getting to know this place like the back of their paw.
'But why? In our burrow, the kits are safe from predators.
'But they don't know that.
'Their wild instincts tell them 'to get to know every inch of their warren, for a very good reason.
' A burrow system like this protects them from most predators.
They simply can't get in.
But there is one that can get in - and often comes in for the kill.
'The stoat! 'It might be a tenth of the size of a rabbit, 'but this is rabbit enemy number one.
'Unlike larger hunters, the stoat can fit inside a rabbit warren.
'And once it makes a kill, it can sometimes stay there.
'A stoat, like this one in a replica burrow, 'will take up residence inside its victim's chamber 'and, in a horrifying twist, 'sometimes use the rabbit's carcass as a nest where it gives birth.
'Its victim doesn't just provide warmth for the young, 'it can also provide ample food for them as they begin to grow.
'But the rabbits have a trick left up their sleeve, 'revealed by our concrete cast of a warren, 'which shows that these tunnels aren't just a place to rest, 'but also full of escape routes.
' This has got seven different tunnels coming off it.
Some going down, some going sideways and up.
If you imagine you're being pursued by a stoat through the warren, at this point, you can really confuse them, can't you? You can go off in every direction.
You intimately know this highway of tunnels.
Because you live in it, you know how to get away.
From that predator.
'We built our warren inside a protected enclosure, 'so there's no chance of a stoat attack.
'Our young rabbits still spend every moment 'learning all of the complex intersections and secret pathways.
'But will they be ready for their biggest step of all?' 'One extreme way to avoid being eaten by any kind of predator 'is to spend your whole life underground, which is what moles do.
'Our moles will happily live out their lives in our replica burrow, 'just as they would in the wild.
'But living your whole life below the surface isn't easy.
'Like all mammals, the mole needs oxygen, 'and that's in short supply.
'There's so little down here that we wouldn't be able to breathe.
' To find out how moles cope with these really tough conditions, I've come to meet a completely different species of animal which, at first glance, you would think would have little in common with the mole, particularly as it's 1,000 times larger.
It's the alpaca.
It's a creature which survives in an incredibly hostile environment.
It prospers where other mammals really, really struggle.
At 4,000 metres up in the high Andes, there's 40% less oxygen than there is down here at sea level.
This presents mammals with all sorts of problems when it comes to breathing and respiring.
All animals need that oxygen, but what the alpacas have done is radically change their blood.
For a start, they've got many more red blood corpuscles.
This helps with the oxygen exchange.
They've also got a lot more haemoglobin, that chemical which transports the oxygen inside those blood cells.
Curiously, the mole has gone down exactly the same route.
It, too, has many more red blood corpuscles and a lot more haemoglobin.
It's not living at high altitude, but it's living in tunnels where there's only one third of the amount of oxygen that I'm breathing here in the fresh air.
The mole's life is a near complete mystery to us.
There is evidence at this time of year that some moles do venture above the surface, and we have to ask why.
The clues come, not from watching moles, but by looking at another completely unrelated animal.
Tawny owls, like many birds, produce pellets.
All of the bones, fur and feathers get compacted into that pellet, which is regurgitated through the mouth.
If we can recover their pellets and look inside them, we can see what's been on their menu.
So let's see what we've got here.
Here's a jawbone straight away.
Look at that! These are the teeth of an insectivore.
Very different than a rodent.
This is a mole jawbone.
How is a non-burrowing bird catching an animal that never surfaces? The bones are the biggest clue.
They're from juvenile moles that have been turfed out of their mother's burrow.
It's likely that these inexperienced burrowers simply lost their way and then, on the surface, become completely vulnerable to birds of prey.
What about that?! That's really neat.
We're learning something about the social behaviour of one animal through the diet of another! Pretty fantastic! And I'm really pleased with that bone.
'Our badgers now seem properly settled in their new residence.
'They've bonded as a group.
'Now they'll need to develop skills 'they'll need for encountering other badgers.
' It's perhaps not surprising, given they spend so much time down in the sett in the dark, that badgers don't rely upon their eyesight when it comes to recognising things and communicating.
It's their sense of smell which is most critical.
If you look very carefully at their face, you can see they've got these very long, quite broad snouts.
They've got big noses! You can see here, Bramble at the moment, is not looking at that soil, she's sniffing that soil.
They have this snuffling behaviour.
It's one of the things that defines the behaviour of badgers.
The reason that they're drawing in these massive intakes of breath is so that they can smell very quickly exactly what they're after.
But what are the scents they're so obsessed by? There's something that they're doing to each other with their hind quarters.
And the results seem irresistibly smelly to the others.
This is interesting stuff.
Look very carefully at Lunar, at what she's doing.
She's compressing the back part of her body down onto another animal.
What she's doing is scent marking that animal.
Badgers have sub-caudal glands at the base of their tail.
They carry a personal perfume.
She is anointing her other group member here, so they know who they've had an encounter with.
By scent marking the others, Lunar is reaffirming her status at the top of the group.
She, and all of our badgers, are leaving their perfumed calling card.
But they don't just scent mark each other.
They also leave scent on their droppings.
So what role could that play? What are these young badgers going to use that for out in the wider world? 'We can find out in the wild 'if we go to the place where badgers go to the toilet.
'They repeatedly use a series of latrines 'located on the periphery of their territory.
' It's fair to say that, to the bulk of our audience, this will look like an ugly pile of poo.
But to the badgers, this is like a veritable perfume counter! Well, this is part of a boundary latrine.
Badgers mark their boundaries by defecating in these latrines.
This is a scent beacon, which sends a message to other badgers in the neighbouring groups that this is "our patch" and that's yours and stay there! It is a mutually respected boundary marker, like a fence round your garden.
They're very active when they're defecating.
They get very excited.
I've seen groups of badgers.
Three have arrived at once.
This is fantastic fun, finding a latrine! Seeing who's been there, whether your rival's been there, digging a pit, adding your own.
Exactly right.
They do get really worked-up.
Almost frantically scratching around and smelling.
We can't smell it, unless you stick your nose right down there.
To a badger, this is really full of scents.
I'm going to give it a go.
It does have a characteristic smell.
It's not too strong, but it's characteristic.
Musty.
Yeah, musty.
Very different from a fox, which is much more bitter.
Once you've learned a smell, you can always tell.
I bet you couldn't tell between the different badgers.
Give me a chance.
That's Brian.
That's Yeah, Brian and Stan.
And Stan had a worm tandoori that night.
Definitely.
'Scent mark latrines are vitally important, 'because badgers from a family group usually don't take kindly 'to trespassers on their patch.
'Our badgers will need to recognise the scented latrines of their group 'to protect themselves in the future when they're released into the wild.
'With each wiggle of the end of her tail, 'Lunar demonstrates her scenting language skills 'and the others follow suit.
'Back at Burrower Central, 'Pipkin's litter are now nearly four weeks old.
'They're looking a lot less like baby bunnies 'and more like small versions of their mum.
'These physical features are vital to their survival above ground.
'Because these animals are hunted by just about everything.
' Look at her eyes.
Typically, predators have their eyes on the front of their face.
When they're looking forward, they can judge distance extremely well.
Important when you're about to grab something.
If you don't want to be grabbed, where do you put your eyes? On the sides and on the top of your head.
Pipkin here can see not only forward, to look out for the fox, and behind to look out for the fox, but also up at the same time, to look out for the buzzard.
So it's a very good adaptation.
The second thing - look at her ears.
At the moment, they're inactive.
When you watch a rabbit on the surface, its ears are always erect.
What's more, they can twist them in different directions at the same time.
They can listen for predators over here AND over there.
So, they've made physiological adaptations to avoid being eaten.
'The big moment has arrived.
'Pipkin's young are as ready as they'll ever be 'to undertake the journey 'they've spent the last four weeks preparing for.
'With Mum, Pipkin, leading the way, 'they venture into the outside world.
'But how will they take in the foreign sights and sounds 'and their first breath of fresh air? 'Sasha and I are waiting eagerly.
' Here they come, Chris.
Look at that! On the brink! It's quite a brave moment for these little things.
We know there aren't any predators in our enclosure, but they don't know that.
'Even without the threat of being eaten, 'the outside world is overwhelming.
'Bright sunshine.
New smells.
'New sounds.
'And boisterous adults.
'For some of Pipkin's litter, it's just too much.
'All they want to do is huddle for security.
'Mum is on hand to reassure them.
' Look how attentive she is here.
Head up the whole time.
She's not feeding at all.
She's looking around, constantly vigilant.
Occasionally, she's thumping away, to warn them.
They're all in a tight cluster, which is what you'd want.
The kits don't just look to Mum for protection.
This is interesting.
We've seen them grooming one another in the warren.
Now, they're all looking after one another.
That's a way of forming affiliations with other rabbits.
They don't just groom their own family.
They also groom other litters and adults.
This is how they tell each other that they're part of a group and maintain that group.
It's a behaviour called allogrooming.
Physical contact builds bonds and secures friendships, so everyone can watch out for danger.
Because outside the warren, security for a rabbit is a case of safety in numbers.
The more rabbits there are, the more eyes, the more ears, therefore, for the individual, the more time spent feeding.
Now look.
They're taking their first fresh meal, if you like.
Up until this point, they've been fed on milk.
What's interesting is they learn the right types of food to eat from the chemicals inside the milk that they drank in the warren.
So they know the flavour and they can pick up the scent and eat that to get them going? That's right.
Those plants won't be poisonous cos their mum ate them and survived.
I wonder what it's like, that first bite of a fresh leaf.
That must be a flavour sensation! 'Our kits' preparation for the outside has served them well.
'They've used their time in the burrow to grow 'and learn vital skills for survival.
'But there are still trials ahead.
'Life for an adolescent rabbit is fraught with challenges.
'Their instincts tell them to always be cautious.
'When one is spooked '.
.
everyone is back in their burrow, in just a few hops.
'At our riverbank burrow, the water voles are busy.
'Bonnie can be seen restocking the larder 'and Mr Ratty is taking his daily dip.
'So far, the youngsters haven't made an appearance outside.
' We've got to look at these, Derek, and think that the burrow has provided them with enough security to mature to the stage that they can be this independent this quickly.
They've taken on all the weight they require to be strong and fit enough.
Now, it's a more testing time.
They've got to find their own way in this world.
It's really something.
It's a remarkable thing to see.
'In just two weeks, that's half the time it took our baby rabbits, 'our young water voles are ready to step outside 'and take their first swim.
' 'After just a moment's hesitation 'our first young water vole is straight into the water.
'And then there were two.
'They love the water - and a good play.
'But where's Ratty junior? 'At first, he's not as confident as the others.
'But after a little comfort eating '.
.
he finally ventures out.
'He soon masters the water, 'although he hasn't quite mastered getting out.
'It's Mum, Bonnie, to the rescue, 'whilst his dad takes a more relaxed approach.
' This is a happy conclusion.
When you think about it, at last, the youngsters have come out into the wider world, into the water, and they're looking good.
There's something personally satisfying, I've got to say! Yeah.
It's really lovely.
It's delightful to see them behaving in this way.
They're just beautiful animals.
'There's only one group of burrowers still to step outside - 'the badgers.
'Our orphaned cubs are now three months old.
'In the wild, at around this age, 'cubs are encouraged to leave the sett by their mothers.
'But here, without parents to guide them, we open up the burrow 'and hope they'll take their first steps outside.
'It's the first real test of how well they've bonded as a group.
'Will they face the outside world together? 'As badgers are nocturnal, we have to wait until it's dark.
' This is a momentous moment in the lives of these young badgers.
It's the first time that they've come outside into the wide world.
Imagine the sensory overload! Look how busy Lunar is here, with her nose.
The first thing she's done is start snuffling in that soil.
It must be loaded with new smells.
'At first, it looks as if Lunar is on her own.
'But as night falls, another badger appears.
'And then Bramble follows, hot on their heels.
'Eventually, the whole group explores together.
'Now, it's a protected enclosure, but our orphans don't know that.
'Any strange scent or sound and they're on the alert.
'It's a great sign that our badgers are instinctively sensing danger.
'One cub has got a bit over-excited.
'Lunar can't resist a good romp.
' 'So, the seven cubs have taken a brave step, 'but that's enough for one night.
'Before long, they all head back inside, 'to the familiarity and comfort of their sett.
' We've had a fabulous few weeks with this amazing experiment.
We've learned a tremendous amount.
We've seen Ratty junior and his siblings, the water voles, have grown at a phenomenal rate.
Our young badgers learned all about scenting and digging before they stepped out.
Pipkin's litter developed a protective community before they, too, ventured out into the wider world.
One thing's for sure, we've seen all of our burrowers using their burrow to prepare them for life above ground.
This is a remarkable project and we've learned a tremendous amount about all the secret lives of these animals.
'Next time, how will our rabbits cope 'with a warren that's full to bursting?' For them, it's a case of "breed like mad".
'Will our young water voles be ready for life in the wild? 'And will our badgers learn to talk badger 'and be ready to leave the sett for good?' This looks like a lot of fun, but this is preparation for their life ahead.
If you're enjoying the world of our burrowers and you'd like to see more there's plenty available on our website.
We've put together the most fascinating behaviour that we've discovered throughout the series.
I've also produced guides to show you how to spot burrowers living where you live.
Learn how to spot badgers, water voles, rabbits, foxes and moles - That's all on