The Burrowers (2013) s01e03 Episode Script

Part 3

We think we know Britain's wildlife.
But there's a secret world beneath our feet.
A hidden kingdom teems with millions of burrowing creatures, their lives shrouded in mystery.
Why do they live underground? Where do they sleep? And 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 like this and observe what it's up to It's beyond my dreams.
It's summer now, but in spring our young burrowers took some giant steps.
Our baby water voles braved their first swim.
But are they ready for the wild? If they don't acquire these skills, they simply won't survive.
Our seven orphan cubs had their first taste of the night air.
This is a momentous moment.
But can they learn to speak badger? That's like a cat hiss.
Our first rabbit litters ventured out of their burrow, but how will the warren adjust to the next wave of bunnies? It's as if the rabbits are deliberately spacing themselves out.
We have an unprecedented window on the lives of the burrowers.
Delve deeper into this magical world with me, Chris Packham, as we ask in this concluding programme: how do young burrowers grow up and leave home? We've got about 50 rabbits in here.
It's gone tremendously well.
Summer has arrived in Britain's south west where, in Somerset, we created a home for seven orphaned badgers.
And 100 miles away at our Devon base, a riverbank burrow for a family of water voles and a large-scale warren for an ever-growing community of rabbits.
We've been documenting every aspect of their lives since winter.
Welcome to Burrowers Central.
Now it was nine months ago that our exciting project began here and, if I'm honest with you, we didn't know too much about our burrowers' lives underground.
Since then, we've learned a tremendous amount, including some fascinating new science.
That said, there's a lot more we still want to know.
It's summer now and our young burrowers are facing their toughest challenge yet.
Very soon, all of our young burrowers will be leaving to find new homes of their own.
We'll watch as they prepare, as our badgers work out how to dig a new sett, as our young water voles learn how to stock up for winter and work as a team and as our rabbits discover safety in numbers.
Our animals aren't aware that we've made their outdoor spaces predator-proof, but they're now all spending more time cautiously exploring.
So why are they outside so much? 'We can find out in the fields around our Devon base.
'This is the one time of year when the full extent of the burrowing world reveals itself 'on the surface, 'but to see what's going on, you need special thermal imaging equipment.
' At night, the countryside comes alive as burrowers of all kinds leave the safety of their burrows to take advantage of the abundance of food.
There are 75 million burrowers in the UK.
That includes 30 million moles, 300,000 badgers and 45 million rabbits.
These numbers are staggering.
They outnumber us by a wide margin.
And the most astonishing thing? These estimates are just for their winter populations.
In the summer, when they finish breeding, things go wild.
At this time of year, the young that have been growing up inside their burrows throughout spring come out in their droves.
And one particular burrower outnumbers them all.
Our rabbit warren began in winter with just 10 adults.
Now there are already more than 30.
The females, like Pipkin and Hazel, have now led their winter litters outside.
And inside, they've already filled their breeding chambers with a whole new second wave of kits.
The question is why do rabbits breed so fast? And why in these synchronised waves? 'Our rabbit expert, Dr Sasha Norris, is on hand to help work out what's going on.
' The thing is, their extraordinary ability to reproduce in vast numbers - breed like rabbits - is implicitly important because, in summer, when the vast majority of their young are coming above ground, everything else is breeding.
You've got fox cubs, baby buzzards, nestfuls of stoats.
Virtually everything likes a bunny burger.
They cleverly time when they have their young so that all the baby bunnies are out at the same time and this means predators can't eat all of them, so some will survive.
It's called predator swamping.
As each wave of young rabbits emerges from the warren, the waiting predators are overwhelmed.
Nevertheless, just one in ten rabbits will survive to see their first birthday, but those that do are enough for the warren to continue.
Even if there's a fox frenzy, a buzzard bonanza, some of them will get through.
The big mystery is how do rabbits synchronise these waves of young? Well, it turns out that it's all down to one individual - the top buck - and in our warren that's Thumper.
And we witnessed exactly how he dutifully fulfils his role, back in winter, when the first litters of the season were born.
As the top female, Hazel, went into labour, Thumper was close by.
He's there.
You can see his shadow.
The shadow of his ears on the wall! The shadow of Thumper, guarding his new family.
It might look as if Thumper is simply being an attentive father, but he's not.
Just seconds after the babies are born, he does something quite astonishing.
Thumper is already sowing the seed for the next generation.
But we mustn't see this as any form of brutality.
She wants to be mated.
This is the process they want.
Maximum reproduction at any time.
She's in the process of giving birth and already she must be chemically communicating that she's able to be impregnated again, that she's receptive.
She's just stopped and he's in straight away.
They have such high mortality, so many die so young, that the only way to ensure she has surviving offspring is to keep on breeding.
So while she's feeding these young, she's going to be growing inside her a new litter.
Ultimately, it's a survival strategy that works for this species.
Indeed.
Constant reproduction.
Maximising the rate of that.
And our buck doesn't stop there.
Thumper mates with all of the other females immediately after they give birth.
In doing so, he ensures that all of their litters arrive at the same time.
So in the wild, each generation would exit the warren in a wave, to swamp the awaiting predators.
Thumper is the metronome of the warren.
As numbers expand, we'll find out how our increasing horde of rabbits organise themselves.
At Secret World Wildlife Rescue, it's nearly a month since our seven orphaned badgers moved in.
There were three females and four males, but sexual maturity is months away.
And since the big female that we named Lunar led their first steps outside in spring, they've become truly nocturnal.
They're now regularly exploring al fresco each and every night.
But as dawn approaches, they retreat to the comfort of the sett.
Down here, they're either resting like old sleepyhead Truffle or it's all rough and tumble.
This play fighting that we see here looks like a lot of fun, but this is preparation for their life ahead.
They're learning here how to bite, who to bite, how to flee and make sure you don't get attacked.
This badger, Bramble, was once the smallest.
An outsider, she struggled to fit in.
But now she's nearly as big as the others and much more confident, even vying for leadership with Lunar.
In the last week, their play has got much more intense.
'Bramble bites Lunar around the tail, the neck and the ears.
'It looks brutal, even painful, 'but how can we be sure that things haven't turned sour? 'Well, the giveaway is this mouth half open gesture.
'It's known as a play face.
' This is really important because in the security of the burrow here, these animals are learning about each other.
This is a learning process, which is all about their survival.
In the wild, our young cubs will meet strangers, aggressive badgers from other territories who could cause them harm.
So will our young group know how to tell friend from foe? In truth, only time will tell.
At Burrowers Central, our small Devon farm, our water vole riverbank is in full summer bloom.
Inside the burrow, it's a busy time.
Our two adult residents, Mr Ratty, the brown male, and Bonnie, the black female, still have a turbulent relationship.
But it doesn't seem to matter.
They've already produced a litter of three.
Ratty Junior and his siblings have grown fast.
Just three weeks old, they're already the equivalent of teenagers.
And behaving like them.
They don't seem to have much respect for the old man.
But inside, there's even more exciting news.
Bonnie is nesting again.
Vole expert Derek Gow thinks we've really convinced her that she's living in a riverbank.
She's taken out flood insurance.
We've got this one nest here which we think has the young in, but Bonnie and Ratty have also filled other chambers with grass.
Is this typical of voles? Studies have shown that one water vole can have 2-3 nests.
In part, it's an adaptation to flood events.
If the river rises by a metre and these chambers flood, it makes a lot of sense to have nests further up.
What we also know is females, when they move their babies, can sometimes kick out the animals that are in there.
There's a wonderful tale from Wiltshire of a female water vole observed saving its babies from flood waters and she took them to the nest of a male, pushed him out, and started putting her babies in there.
It's an adaptation, in part, to flood events and a very sensible thing to do in this riverbank environment.
Days later, in one of the nests, we finally spot her second litter.
Five more pups.
It's fantastic news.
Like their older brothers and sisters, they'll eventually be released.
Ours are a Scottish breed and they're destined for the Black Isle, north of Inverness.
Over 15 years, Derek has worked to reverse the dramatic decline of the water vole in Britain.
They've disappeared from 90% of the areas where they were once common.
Here, with practised care, he brings water voles back to Cornwall for the first time in 20 years.
But before our voles are ready to enter the wild, there's some serious growing up to do.
And for Ratty Junior and his sisters, the arrival of younger siblings will be life-changing.
Soon there will be no more room at the inn.
Just a short walk from Riverbank Burrow, our rabbit warren is now a frenzy of baby bunnies.
With the second generation almost ready to go outside, the third generation can't be far away.
Our warren is reaching capacity.
But how will our rabbits behave when real estate is at a premium? We want to know what to expect.
'Intriguingly, there could be some clues at our concrete cast of an abandoned wild rabbit warren.
' For me, this is an absolute revelation.
I'm really excited by this.
It was such a simple idea.
Find an abandoned rabbit warren, fill it with concrete and then excavate it.
And look - you can appreciate immediately the structure.
Can this fascinating arrangement reveal clues as to how rabbits cope with the summer squeeze? There's only one way to find out.
We're taking things to a whole new level.
With experts in 3D mapping, we scan the structure with a gizmo that fires lasers 250,000 times a second.
The result is an exact 3D model of the warren.
And we can examine it from every angle.
So can we use it to unearth any patterns in the apparent chaos? Was the warren dug at random or did the rabbits plan it in this way? With our data, teams of scientists led by Exeter University's Dr Dave Hodgson produced some fascinating insights.
I like to think of the warren as if we were zooming in from outer space.
What I did was I added a grid to this to simplify it and turn it into a graphical model of the warren.
Stripped out all of the dirty reality and simplified it into just distances, nodes, entrances.
Like pure maths.
What we find is actually relatively clear, I think, to the eye which is that these distances between chambers or from entrances are really quite even.
There's no section of the warren system where you find very short distances.
OK.
So it's as if the rabbits are deliberately spacing themselves out in this warren.
'Dave even thinks he's worked out how the warren might have grown over an estimated three decades 'from a single scrape into a home for some 50 rabbits.
' It does appear that the rabbit warren has developed in three phases, probably generational changes.
So what we can see here is what we believe to be the original section of the warren.
It's got large chambers and several entrances in a very connected network of burrows.
There's a second phase to the warren and I compare this to urban sprawl.
If we have a historic city centre here with lots of alleyways, we have much larger warrens with fewer cave-ins.
The chambers themselves have more connections, implying more traffic of rabbits.
There's a third phase to this as well, which is less clear.
We don't understand this quite so well - some rabbits that don't enjoy company, perhaps, stretching the warren system out.
This is probably the newest part of the structure.
'This expansion is seasonal.
With each summer breeding boom, 'the females dig out new nesting chambers and new tunnels.
'But how did the warren begin in the first place? 'Perhaps our rabbits can provide the answer.
' Our orphaned badgers are showing all the signs that they've become a well-bonded badger family.
But will they fit in to the wider badger community? I'm here in the New Forest, not far from a badger sett where there's a social group I'm very familiar with.
What we are hoping is that when we release our cubs into the wild they'll assimilate into a social group like this.
Badgers from neighbouring groups can be aggressively territorial.
Fights between males are even sometimes fatal, so it's vital that our young cubs understand the warning calls.
(Now normally they would learn a lot of that behaviour from their parents.
(Badger adults spend a lot of time rearing and looking after their cubs.
(And this makes me wonder what will happen with our little orphans.
(Will they be able to learn how to socialise? (Because if they don't, that might be a problem in the future.
) 'Our replica sett is the perfect place to test whether badgers can instinctively tell a friendly call 'from a hostile one.
'I've asked our badger expert Dr Chris Cheeseman along to help.
'And I've got one of my favourite playlists for us all to enjoy.
' Chris, I have here a little mix, a megamix in fact, of badger calls and sounds.
I've got badchat, bark, chirp, chitter, churr, cluck, coo, growl.
I'm going to start off by playing a chirping sett, which they will hear.
We've heard them do it.
Let's see if we get a response.
Look at that.
This one's got up and he's looking out.
Look, he's listening.
That was a sleeping badger a few seconds ago and now he's out here having a good look round.
This is the excited play noise.
They're showing interest.
It's sounds that they recognise.
You can see that.
"Where's that coming from? Where are those other badgers making that sound?" That worked brilliantly.
Shall we try with another call? I'd be interested to see the hiss reaction.
That's more of an aggressive sound.
OK.
Or, "Back off, keep away.
" Shall we go for the hiss? Yeah.
OK.
Look at this one.
He's backing off.
He's backing off, look at that.
That one's doing exactly what you'd expect.
And the other one behind.
He's backing right into the corner.
That's Bramble, actually.
Right.
That's like a cat hiss.
Yeah.
"Keep away.
" Definitely cautious, I would say.
The backing off was there for the first few seconds.
OK.
Shall we try one more? Look at this.
Flat out.
Yeah, try a bark.
A bark.
OK, let me have a look here.
Bark.
Are you ready for barking? Yeah.
Oh, yes, look at that.
Look at this one, running around.
They're all waking up now.
This one's actually fleeing the chamber.
That's definitely a retreat.
'Our orphan badgers aren't sexually mature, but how would they respond to the best badger chat-up lines?' There's a churr that's made by the female badger that gets males terribly excited.
And there's a churr that's made by the male badger that gets females excited.
What about that? Yeah.
I can't imitate it, I'm afraid.
Just as well! I don't want to see you accosted here by either sex! But when you see them, the females can say, "Back off!" They have a little That means, "No, leave me alone.
Not interested.
" What's interesting with this group is that they haven't all had the opportunity to hear those calls.
Some of them responded far more demonstratively to calls of adult badgers that they might have heard.
The other orphans haven't.
We may have even taught them a few things, but to survive in the wild these badgers will have to build up that repertoire so that they can communicate effectively and play their role in badger society.
Each of our burrowing species has evolved a different strategy to try to ensure the better survival of its young once they get out into the wider ecosystem.
Each of these strategies is very different.
Think about the badgers.
They are trying to evolve a social hierarchy which will help stabilise their group in the future and also help when it comes to investing in parental care.
The rabbits couldn't be more different.
For them it's breed like mad.
The more bunnies the better to try to survive the onslaught of all of those predators.
But another of our smaller burrowers seems to have a far more organised strategy when it comes to the survival of the entire colony.
'Here at Escot Park, there's a thriving community of water voles.
'It's the last of its kind in Devon.
'There are literally hundreds of burrows all along the riverbank.
'Each one is home to a little family like ours.
'And if you know where to look, there are clues that hint at the water voles' strategy for survival.
' Look at this! Wow.
This is really interesting.
Looking around me, I can see none of this plant at all within visible range, so the animals have snipped these into little portable packages and they've taken them and put them down here to store them so that they can eat at their leisure in a safe spot.
That's really, really neat.
'By creating these larders, water voles can keep feeding all year round, 'but how do they learn what to store and how to use it?' In our riverbank burrow, whilst Bonnie is inside suckling her second litter, first-born Ratty Junior and both of his sisters are now completely self-sufficient.
They're eating 80% of their body weight every single day.
And they're already instinctively making food stores of their own, both outside on the riverbank and inside the burrow.
But what makes a good snack on the go and what's a store cupboard staple? This was the question that we had in mind when we built their burrow.
So vole expert Derek Gow introduced a wide variety of vegetation to their river.
This is a real favourite.
These are the roots of flag iris and we'll plant quite a lot.
'And now the footage we've captured can show us which choices the water voles are making.
' Something innate is there that enables them to identify a species and its ability to be stored.
They must have to learn that as youngsters now, somehow.
Could it be that it's a taste thing? Could it be as simple as that? Something in that root appeals to them and they use it as a result.
A pattern is already emerging.
Mum Bonnie has taught her young well.
Ratty Junior and his sisters are eating up their greens - perishable grasses.
But inside the burrow, they store foods with a longer shelf life - roots, tubers and bark.
And most intriguing of all, the whole family seem to be working together to build up their larders.
Completely different strategy than our rabbits.
Much fewer individuals that have to play a role in this community because if they don't store this food, the entire community could be in jeopardy through the winter.
Yeah.
They may not make it themselves, as we know.
Many won't.
They have very short lives.
We know from studies that an old male water vole is about two.
And an old female is slightly over a year.
Many of the animals gathering this material aren't going to live long enough to use it.
But the key thing for them is that the colony survives.
That's kind of neat that that very survival is dependent on these young voles now learning what to eat and what to store later.
Isn't it? Absolutely critical.
The young water voles seem to be making good progress, but there's still some way to go before they can be released.
They've got to learn fast, to learn how to build nests, how to cut food, bring it back to the burrows and store it.
If they don't acquire these skills very early on, they won't survive.
In our rabbit warren, the second wave of rabbits are now outside.
And the third batch have arrived.
As a result, the dynamics of the warren are changing.
Top female Hazel keeps churning out babies in the penthouse chamber that she picked out in winter.
To appreciate how well she's chosen, you only need to look at the accommodation the females below her in the pecking order have had to make do with.
One of them, Beatrix, is trying to raise a family in what is effectively a busy highway and a favourite duelling spot for our two males.
Sasha and I want to understand what's happening.
Now here they are, chasing through again.
What's interesting about this particular nest site is there's a lot of activity.
It's a bit like Piccadilly Circus.
Not the ideal place to have young! That's because this is not the top dog.
It's one of the sub-optimal burrows.
Exactly, yeah.
'Beatrix has made her choice to put her kits at risk in a busy part of the warren.
'But for other subordinate females, there is another option.
'Moving out.
This is Acorn.
Her place is at the very bottom of the rabbit pecking order.
She's been excluded from the main warren by all of the other females.
In the wild, living outside like this would be a huge risk.
Acorn would be completely exposed to predators.
Out here, unaware that our fences protect her, she starts to dig.
Like the other females, her instinct is to breed.
Some of the young ones are only practising their digging skills, but could Acorn be digging a breeding chamber, what we call a stop? And could this be a clue as to how whole new warrens begin life? At our concrete cast, there's an amazing parallel.
Our team of human burrowers have unearthed a second, much smaller burrow.
Smaller, but no less interesting.
I think this started where a subordinate had been kicked out of the main part of the warren and come here to do her own thing.
Yeah.
It's not the ideal scenario to raise your young.
The dominant female will always choose to put her kits in the safest part of the main warren, but this was still part of the main social group.
It's not very far away.
Ultimately, I imagine, this would have expanded and these tunnels led to more chambers and perhaps even headed back in this direction and joined up with that part of the warren.
This satellite warren is situated just a stone's throw from the main one.
It's possible that it was a subordinate female that created it.
The implications are fascinating.
The dominant rabbit at the top of the hierarchy, like Hazel, may rule the warren, but the sub-dominant rabbits like Acorn are the unlikely heroes.
I'm excited by all of this because I like to think of animals playing by rules.
I don't think they can afford to do things necessarily by accident and not by design.
I suppose, ultimately, it's all about hope.
Sub-dominant animals could, at some stage in the future, find a place to start their own warren and ultimately it might survive and succeed.
So you might say that from tiny acorns whole new warrens can grow.
Back in Somerset, our young orphaned badgers are doing well without parents.
But without their mother's milk, their fur thins as they grow.
They need to get onto a natural diet and there's one particular juicy superfood they need to learn to get their paws on - earthworms.
Our badger expert, Chris Cheeseman, has devised their next test.
He's buried pockets of earthworms around their enclosure.
So can they instinctively sniff out this most essential of badger snacks? Well, this is an intriguing experiment.
We've provided them with their favourite natural food and they've found these earthworms, the first time they've been confronted with what will be, in the wild, their main staple food.
Earthworms must be irresistible.
Bramble is in a digging frenzy.
Badgers find them by smell and they quickly grab it with their incisor teeth and pull it gently out of the hole, toss it back, a couple of bites and swallow.
And I've watched a badger feeding at night and in the space of one feeding session, which is about two hours long, it ate 1,083 Lumbricus terrestris.
Now these earthworms are about three grams each.
You multiply that.
That's over three kilograms of earthworms.
The badger was visibly distended, like a barrel.
These badgers are already showing that they're finding this food, they can smell them, they're eating them exactly the way you'd see in the wild.
It's a very good sign that they are perfectly capable of finding, hopefully, their main food source, which is going to be worms.
Now it's great news that our young cubs are getting so fond of dining out, but in the process they're learning another tough lesson.
They're picking up stowaways and inadvertently carrying them into their sett.
Parasites! All badgers host a plethora of lice, fleas and ticks.
For our group, the itch is nothing that a good scratch can't relieve, but in the wild it can get much worse.
Badger fleas infest their bedding and have special hooked claws to cling on to their wiry fur.
Our badgers will have to work out how to keep this troublesome parasite at bay.
Fleas are well adapted to the badger's own lifestyle.
And they need a badger to suck blood from, get a blood meal.
And they also need somewhere to lay their eggs.
They do it in the badger's nest.
The eggs hatch out in the bedding, the larvae will develop there.
When they hatch into fleas, off they go again, find an adult badger to suck blood from.
That's the life cycle, basically.
So there are implications here.
The bedding could be a complete repository of parasites.
That's got to be surely why the badgers are so keen on removing it, changing it, upgrading it.
It is indeed.
Wild badgers have an ingenious way of keeping badger fleas out of their beds.
They're often to be seen at the surface, pulling their bedding out into the open air.
There, they leave it for a few days before dragging it back into the sett.
Now when it's out there, exposed to sunlight and desiccation, drying.
That will kill the larvae! It'll kill the larvae and make it hard for fleas to survive.
So it's a good way of keeping that parasite burden down to take your bedding out and air it.
'But will our orphans know how to air their bedding? 'It's a vital badger skill they'll need to master.
'So far, we've only provided them with hay, 'but by giving them a choice of materials, we can also see 'how they react and which ones they prefer.
' We've gone for hay, dry grass, we've gone for bracken, which is very, very common.
They do bring in fresh green bedding.
One that's frequently brought in, and it really is smelly, is garlic.
Wild garlic.
The smell must be incredibly pungent.
I'm sure the fleas don't particularly like it.
I can buy into that theory.
I've seen that other animals will choose types of aromatic plant.
Birds will bring them into their nests for their anti-parasite or anti-bacteria properties.
Quite cautious, that, isn't it? Yeah.
Having a good sniff, look.
That's also very interested.
Look at that.
And the garlic.
Having a good sniff.
Yeah, look at that.
Not so sure about that.
He's blowing his nose off the garlic.
There was a definite response.
Bramble came straight in.
Initially cautious, but then went to that new hay and the others have piled in.
They seem to be enjoying it.
There's tremendous interest, sniffing these smells.
Theirs is a world of smell.
Yeah.
"Where has this come from?" To a badger, it must be a cacophony of smells.
And new smells for them.
Absolutely.
They've never experienced any of these things, except the hay.
But Lunar is down here sniffing away furiously again at this mixture of grass and bluebells.
Did you see the way she stuffed her nose in? Yeah.
It was really, "What is this?!" Getting a lungful of a completely new experience.
'It'll be a week or two before our cubs get used to their new bedding.
'When we return, we'll see whether they've been able to work out how to beat the parasites.
' Back at our water vole riverbank at Burrowers Central, there's been a major development.
Bonnie has kicked Ratty Junior and his sisters out of the burrow.
Perhaps with the arrival of her second litter, it's all got too much at home.
Outside, they're on their own.
In our protected enclosure, they're quite safe from predators.
But it's the perfect dress rehearsal for the challenge they'll face when they're released into the wilds of Scotland.
'I'm back at Escot Park with Derek.
It's the site of one his most successful release programmes 'and where water voles now thrive.
' There's a burrow coming out.
Yeah, loads of burrows here.
Some right up in the trees here.
Big ones.
Yeah.
'What's happening to Bonnie's first litter seems to be typical of what's happening here 'to every water vole household.
' The animals start to force each other out.
Initially, this will take the form of little squeaking fights and pushing each other away.
Some take the hint and leave home.
But like teenagers the world over, others take a bit more persuasion.
'In an empty riverbank, young voles simply dig out new burrows next door, but in existing colonies, 'things get a lot more complicated.
' So if our family here is rapidly expanding in numbers and another is just down the river slightly further, at a certain point they could meet.
They're absolutely going to meet.
It's a very important process.
They will not willingly breed with animals they're closely related to.
We don't exactly know how they detect this degree of relatedness.
It may be a pheromone exchange so they won't breed with their uncles or fathers It's part of the process.
Part of the process is they have to meet other animals.
Even though they're pugnacious and territorial and will not willingly accept other animals in, some of those animals have to come in or populations simply don't survive.
What if you get a really bumper number of animals here? They meet up and they carry on breeding, then where do they go? Then what happens is that you basically have the animals They're forced by population pressure out into the wider landscape.
You get a starburst-type phenomena.
They just go boom.
'This starburst effect would be the perfect outcome for Derek 'with all the young moving out into neighbouring burrows and breeding.
'The whole riverbank would then explode into life, creating a honeycomb of burrows, 'packed full of water vole families.
'And the more burrows they create, the more food stores there'd be 'and the greater the chance that the whole colony would survive to breed another year.
'But all of that depends on young water voles learning how to dig.
'Can our youngsters work out how to create a new home? 'Well, at first, they look to Dad for answers.
'As Mr Ratty forages outside, he digs himself small boltholes, 'places to escape if there's a predator looming.
'Ratty Junior watches intently, 'but it's one of his sisters who gets her teeth into it first.
' Just three weeks after they were born, one of our young voles is already on the property ladder.
Back at our badger sett, Chris Cheeseman's returned to see how they got on with their bedding challenge.
Inside the burrow, things are eerily quiet.
There's no sign of the badgers or their new bedding.
I'm absolutely amazed that these badgers have removed pretty well all of the bedding that we put in the artificial nest chambers.
We've got a piece of a nice bedding ball here, which is some of the hay that was introduced.
That's been gathered up and brought outside.
That's what we'd hoped for.
But aside from the hay, where's all the other more flea-resistant bedding? And where, for that matter, are the badgers? Well, as we scroll through the footage of the previous few nights, there are signs of something very exciting.
In the middle part of our outdoor enclosure, our badgers are seen investigating an old log.
Lunar digs away the dirt and then disappears right down inside.
She emerges and then slowly pulls out some bedding.
And this explains everything.
Perhaps this is our badger family's way of telling us that they're ready to go.
They've developed natural behaviours and they seem to have moved on.
They've now abandoned this and gone outside into the compound and seem to have established the beginnings of what we think might be a sett.
This has been a tremendously rewarding experience for us all, to see the way these cubs have been brought in from the wild at a very young age.
They've bonded as a social group, they've developed natural behaviours and I don't think it's going to be long before they're ready for release into the wild.
There's even better news - after getting the all-clear in their tests for TB, our young orphans have passed their final challenge.
They are going to be released back into the wild at a secret location because of the pressures on badgers in the UK at the moment.
Having watched them and having watched them mature and forge these bonds, I think there's a very good chance that our young badgers are going to make it out in the big wide world.
'It's my last chance to bid farewell to Mr Ratty, Bonnie and their young family.
'Their home is now bursting with life and soon their offspring will head off 'to start their new lives in Scotland.
'And across the farm, what began with 10 adult rabbits rattling around in a giant warren 'has become a bumper crop.
' Sasha, the project's coming to an end.
We've got about 50 rabbits.
It's gone tremendously well.
We've witnessed all of their breeding habits, but now we've got this population of rabbits to look after.
Yeah.
If you think back to the beginning, there's a nervousness.
You just never know if animals will like the habitat you provide for them.
It's brilliant.
What's the future for them now? Most of them will go back to a breeder.
They'll have lovely homes.
And a few rabbits will stay here and live in this rabbit utopia.
'At the start of the project, we had an empty field, a few plans and a big ambition.
'We shifted hundreds of tons of earth 'and created something quite unprecedented.
'A Wind In The Willows for the 21st century.
'A whole new way of looking beyond Britain's hidden frontier of natural wonders.
' We've seen things we could never dare dream we would have done before we began.
And we've also met an incredible cast of characters, too.
'Among them, my favourite badger, Bramble, 'who went from a tiny outsider to becoming a key part in our close-knit band of badgers.
' It's been a truly wonderful experience and a privilege to have studied these animals in a facility that's given me an insight that I've never seen before.
'And then there was Mr Ratty and Bonnie, who gave us a unique view 'of the water vole's tempestuous temperament, but also did their bit for water volekind.
' You read old textbooks and you know they use their forward-pointing teeth for burrowing.
We've never seen excavating soil with their teeth before.
It's been a privilege and pleasure to watch.
'And our rabbits, from Hazel to Acorn, all of them demonstrating admirably 'why they're such extraordinary survivors.
' Some of the loveliest moments have been the most subtle.
For example, when two females meet each other and just gently touch noses.
It speaks volumes about the nature of their relationship.
'And then, of course, there's top male Thumper, without whom none of this would be possible.
' We've unearthed the secrets of an underground kingdom that we knew so little about.
It really has been a remarkable journey.
If you've enjoyed the world of our burrowers and you'd like to see more, there's plenty available on our website, where we've put together the most fascinating behaviour of the series.
I've also produced a few guides to spotting burrowers where you live.
Learn how to spot badgers, water voles, rabbits, foxes and moles.
That's all on