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0:00:00 > 0:00:05- Rural Wales offers some of the most - spectacular scenery in Britain.
0:00:08 > 0:00:12- But the countryside - offers much more than just views.
0:00:12 > 0:00:15- It's home - to some our best-loved wildlife.
0:00:16 > 0:00:20- But one group of mammals - lives a secret life.
0:00:22 > 0:00:25- By burrowing miles - of subterranean tunnels...
0:00:26 > 0:00:30- ..the way these animals - live their lives...
0:00:30 > 0:00:35- ..has been a mystery until now.
0:00:35 > 0:00:39- We're going to do something - that has never been done before.
0:00:39 > 0:00:44- By uncovering some of these - burrowers' tunnels and chambers...
0:00:44 > 0:00:48- ..we're going to recreate - an artificial habitat.
0:00:48 > 0:00:51- For the first time ever...
0:00:51 > 0:00:55- ..we'll get an insight into - their secret subterranean lives.
0:00:55 > 0:01:01- We'll discover what water voles - do in their tunnels every day...
0:01:02 > 0:01:07- ..how rabbits cope with nurturing - dozens of offspring each year...
0:01:07 > 0:01:10- ..and how small badgers - learn to cope...
0:01:11 > 0:01:13- ..with the big world - beyond the sett.
0:01:13 > 0:01:17- Join me, Iolo Williams, - as we venture...
0:01:17 > 0:01:21- ..to the magical, hidden, - subterranean world of the burrowers.
0:01:43 > 0:01:45- To begin our journey underground...
0:01:46 > 0:01:51- ..we've travelled to a farm near - the Dartmoor National Park in Devon.
0:01:51 > 0:01:55- Among the animals and buildings - you'd expect to see on a farm...
0:01:56 > 0:01:59- ..is something completely unique.
0:01:59 > 0:02:02- The biggest artificial burrow - ever to be created.
0:02:07 > 0:02:10- I've been watching - and studying wildlife all my life...
0:02:11 > 0:02:14- ..but never animals - that live underground.
0:02:14 > 0:02:18- Doing that - would have been too invasive.
0:02:18 > 0:02:20- But for the first time ever...
0:02:20 > 0:02:26- ..we've created habitats - for four very different burrowers.
0:02:27 > 0:02:29- Over recent months...
0:02:29 > 0:02:33- ..a team of cameramen, - scientists and experts...
0:02:33 > 0:02:36- ..has been filming - and studying burrowers...
0:02:37 > 0:02:40- ..and analysing the footage...
0:02:40 > 0:02:43- ..to reveal interesting facts - and tales.
0:02:44 > 0:02:48- Some of the facts have been - a revelation for the experts.
0:02:49 > 0:02:52- Our rabbit expert is Ceri Morris...
0:02:52 > 0:02:57- ..a mammal ecologist who works - for Natural Resources Wales.
0:02:59 > 0:03:03- It's incredible to see - their world inside the chambers.
0:03:06 > 0:03:09- We're used to seeing rabbits - in the countryside.
0:03:09 > 0:03:13- Rabbits are among most common - mammals in the British Isles.
0:03:14 > 0:03:18- But we know next to nothing - about their habits underground...
0:03:19 > 0:03:22- ..which is the most important time - in their lives.
0:03:23 > 0:03:25- They're expert burrowers...
0:03:25 > 0:03:28- ..and we have a great deal - to learn about them.
0:03:31 > 0:03:36- Britain's best-known warrens - are off the Pembrokeshire coast.
0:03:36 > 0:03:38- Skomer Island and Skokholm Island.
0:03:39 > 0:03:43- The Normans introduced rabbits - to the island in the 13th century...
0:03:44 > 0:03:47- ..to provide a regular supply - of meat and fur.
0:03:49 > 0:03:54- The next burrower is different - from the rabbit in many ways.
0:03:54 > 0:03:59- Firstly, - it's a rare creature nowadays.
0:03:59 > 0:04:03- It also burrows - around riverbanks and under water.
0:04:04 > 0:04:09- Nobody knows more about water voles - than Dyfrig Jones.
0:04:10 > 0:04:14- For years, we've watched them - and searched for their tracks.
0:04:15 > 0:04:17- You never see the system.
0:04:18 > 0:04:20- You never see - the network of chambers.
0:04:21 > 0:04:24- You never see a nest like that.
0:04:24 > 0:04:29- This is the first time you can start - putting all the pieces together.
0:04:29 > 0:04:33- Archive footage of water voles - is very rare...
0:04:33 > 0:04:38- ..but we hope to discover how they - use their lair, how they mate...
0:04:39 > 0:04:41- ..and how they raise their young.
0:04:42 > 0:04:44- Data like this is important...
0:04:44 > 0:04:49- ..in helping us repopulate our - riverbanks with voles once again.
0:04:51 > 0:04:55- The last of the burrowers - is perhaps the hardest to study.
0:04:55 > 0:05:01- Badgers are timid nocturnal mammals - that are industrious at night.
0:05:01 > 0:05:04- Badgers are monitored - by Owen Bidder on a daily basis.
0:05:05 > 0:05:07- They've done quite well.
0:05:07 > 0:05:11- They've nestled near the branches - and roots of the tree.
0:05:11 > 0:05:14- Badgers in the wild - burrow underground...
0:05:14 > 0:05:18- ..close to branches and roots...
0:05:18 > 0:05:21- ..to provide a structure - for their tunnels.
0:05:22 > 0:05:25- It looks as though we've succeeded - in creating a sett...
0:05:26 > 0:05:29- ..that is acceptable to the badgers.
0:05:29 > 0:05:33- Only time will tell - if they reveal their secrets.
0:05:48 > 0:05:51- The research work began in winter...
0:05:52 > 0:05:54- ..with a visit - to Bicton Park in Devon.
0:05:55 > 0:05:58- Rabbit numbers - have had to be controlled there.
0:05:58 > 0:06:03- One rabbit warren had been vacated - and provided a perfect insight...
0:06:04 > 0:06:06- ..into how rabbits - design their habitats...
0:06:07 > 0:06:11- ..how deep they burrow - and how complicated the tunnels are.
0:06:11 > 0:06:15- Park manager Cliff Cogger - was on hand to help us.
0:06:15 > 0:06:18- By smoking the warren, - it was possible to see...
0:06:19 > 0:06:21- ..how many entry holes there were.
0:06:22 > 0:06:26- There were 13 holes altogether - in the warren, but why so many?
0:06:26 > 0:06:29- To avoid predators, of course.
0:06:29 > 0:06:32- Animals that kill - and feed on other animals.
0:06:32 > 0:06:35- The rabbits know their way around...
0:06:35 > 0:06:38- ..unlike the predators, - so it's easy to escape.
0:06:38 > 0:06:40- But how deep is the warren?
0:06:41 > 0:06:43- We've enlisted the help - of another expert.
0:06:44 > 0:06:46- A ferret fitted with a GPS system.
0:06:52 > 0:06:57- At its deepest, the warren - reaches 2.5 metres underground.
0:06:58 > 0:07:01- By inserting a camera - into the tunnels...
0:07:01 > 0:07:06- ..we can establish - that they're 20cm wide...
0:07:06 > 0:07:11- ..with a few leading to a chamber - measuring the size of a football.
0:07:13 > 0:07:17- Using the data from the warren, - we now have a design...
0:07:18 > 0:07:20- ..to build a warren of our own.
0:07:20 > 0:07:23- One thing is very clear.
0:07:23 > 0:07:26- The warren will have to be big.
0:07:26 > 0:07:28- Very big.
0:07:30 > 0:07:34- These animals burrow - with great force and instinct.
0:07:35 > 0:07:39- What's easy for them - is much more difficult for us.
0:07:42 > 0:07:45- Building the rabbit warren - started in winter.
0:07:46 > 0:07:50- Heavy machinery was needed to dig - a hole larger than a tennis court.
0:07:50 > 0:07:56- To replicate its size, - the interior had to be to scale...
0:07:56 > 0:07:59- ..and as close as possible - to a real warren.
0:07:59 > 0:08:02- Hopefully, our rabbits - will react naturally...
0:08:03 > 0:08:06- ..and bear their young - in the warren...
0:08:06 > 0:08:11- ..so that we can see how they - go about their lives underground.
0:08:16 > 0:08:17- In addition to that...
0:08:18 > 0:08:23- ..we must be able to see and film - what the mammals do nocturnally.
0:08:23 > 0:08:25- Cameramen devised a way...
0:08:26 > 0:08:31- ..to light and film - within the chambers and tunnels.
0:08:31 > 0:08:34- In order to set lighting levels...
0:08:34 > 0:08:38- ..cuddly toys were used - to represent the rabbits.
0:08:42 > 0:08:44- These are the rabbits...
0:08:44 > 0:08:47- ..that will eventually - enter the warren.
0:08:48 > 0:08:53- They're partially-tamed rabbits. - They're getting used to my presence.
0:08:53 > 0:08:56- We couldn't use wild rabbits.
0:08:57 > 0:09:02- If you grouped wild ones together - in a very confined space...
0:09:02 > 0:09:05- ..they would fight, - often to the death.
0:09:05 > 0:09:10- They're ferocious animals - and quite nasty, to be honest.
0:09:10 > 0:09:15- Partially-tamed rabbits - must be used for this purpose.
0:09:20 > 0:09:20- .
0:09:23 > 0:09:23- Subtitles
0:09:23 > 0:09:25- Subtitles- - Subtitles
0:09:31 > 0:09:34- As the work continues - on the rabbit warren...
0:09:34 > 0:09:37- ..work began - on an artificial habitat...
0:09:37 > 0:09:40- ..for another burrower - with completely different needs.
0:09:41 > 0:09:43- The habitat - is much more complicated.
0:09:44 > 0:09:46- It's the smallest - of our burrowers...
0:09:47 > 0:09:49- ..but they burrow with such force...
0:09:49 > 0:09:53- ..that a concrete foundation - is required for the den.
0:09:58 > 0:10:01- Our next subject is the water vole.
0:10:04 > 0:10:07- But how do they - build their burrows...
0:10:07 > 0:10:09- ..meet each other and mate?
0:10:09 > 0:10:13- Those are some of the questions - we're hoping to answer.
0:10:15 > 0:10:18- But we have one fundamental problem.
0:10:18 > 0:10:22- No-one knows - how water voles build their dens...
0:10:23 > 0:10:26- ..so we decided - to perform an experiment...
0:10:26 > 0:10:28- ..that has never been tried before.
0:10:29 > 0:10:32- Letting the voles themselves - show us.
0:10:34 > 0:10:40- Two water voles burrowed - in a box of sand for a month.
0:10:40 > 0:10:42- They created their own lair.
0:10:43 > 0:10:47- For the first time, - we've been able to establish...
0:10:47 > 0:10:50- ..the size and form - of a water vole's den.
0:10:53 > 0:10:57- This is the first time - you can piece together the jigsaw.
0:10:59 > 0:11:01- It's interesting to see.
0:11:01 > 0:11:06- It's very complicated, - much more so than I expected.
0:11:07 > 0:11:10- I foresaw a tunnel and two - chambers, but there are many.
0:11:11 > 0:11:14- The two nests, - one there and one over there...
0:11:14 > 0:11:18- ..are quite far away - from the point of entry.
0:11:18 > 0:11:22- Yes, and what I'd like to see - is this in three dimension.
0:11:23 > 0:11:27- You could see if it was built - on different levels then.
0:11:27 > 0:11:30- If you think about a dyke, - a brook or a canal...
0:11:30 > 0:11:35- ..you have that depth, - from the bottom of the brook...
0:11:35 > 0:11:37- ..all the way up to the bank.
0:11:38 > 0:11:41- It'd be lovely to see - the different levels they use.
0:11:41 > 0:11:46- But I suspect that this is - a good example of their habitat.
0:11:46 > 0:11:51- Space has been restricted - because it's in a box.
0:11:51 > 0:11:55- Imagine if you were near - a ditch or a canal...
0:11:55 > 0:11:59- ..where you might have a depth - of 10 metres or 15 metres.
0:11:59 > 0:12:03- Imagine how much burrowing - these small creatures must do...
0:12:03 > 0:12:06- ..in order to create this network.
0:12:06 > 0:12:07- They're very industrious.
0:12:07 > 0:12:10- They're very industrious.- - Two things stand out for me.
0:12:10 > 0:12:12- The two nests.
0:12:13 > 0:12:18- This isn't very deep, yet the nests - are as high up as they can be.
0:12:18 > 0:12:24- We're very aware that the nesting - chambers are higher up in the den.
0:12:24 > 0:12:27- If you think - about a canal or a ditch...
0:12:27 > 0:12:30- ..from the surface of the water - to the bottom...
0:12:31 > 0:12:34- ..there's sure to be - a depth of three to five metres.
0:12:34 > 0:12:38- We know that they enter their dens - in the water...
0:12:38 > 0:12:41- ..and climb to the nesting chambers.
0:12:41 > 0:12:44- They're usually higher up - in the structure...
0:12:44 > 0:12:48- ..in a mud mound - or whatever they choose to nest in.
0:12:49 > 0:12:53- There are features missing - from this example.
0:12:53 > 0:12:55- Usually, there are more holes.
0:12:56 > 0:12:59- There's a point of entry - to this network of chambers...
0:13:00 > 0:13:03- ..and tunnels - from one chamber to another.
0:13:03 > 0:13:07- But there is usually - at least one other tunnel...
0:13:07 > 0:13:10- ..serving as an escape route - to dry land.
0:13:13 > 0:13:16- There's an opening at water level - and another higher up.
0:13:17 > 0:13:19- That's usually the case.
0:13:19 > 0:13:21- The more information we collate...
0:13:22 > 0:13:26- ..about the importance of these - different chambers to them...
0:13:26 > 0:13:30- ..the more we can do to preserve - the habitat in which they live...
0:13:31 > 0:13:34- ..and areas - where we'd like them to repopulate.
0:13:34 > 0:13:38- This information - is vitally important.
0:13:43 > 0:13:47- Using the data - from the sand box experiment...
0:13:47 > 0:13:51- ..we can create an artificial - habitat for the water vole.
0:13:52 > 0:13:54- It must be by a river...
0:13:54 > 0:13:58- ..with a network of tunnels - and rugby ball-sized chambers.
0:14:02 > 0:14:08- This is where - we'll be filming the water voles.
0:14:08 > 0:14:12- It's not quite finished, - The lads are still working on it.
0:14:12 > 0:14:15- There'll be water - where I'm standing now...
0:14:16 > 0:14:18- ..while this is the riverbank.
0:14:18 > 0:14:23- They'll fill these holes - with plants, rushes...
0:14:23 > 0:14:25- ..vegetation and so on.
0:14:25 > 0:14:28- The tunnels themselves...
0:14:28 > 0:14:32- ..are entered from this opening - and another one further along.
0:14:33 > 0:14:35- They lead to this shed...
0:14:35 > 0:14:39- ..where we'll film the animals - underground.
0:14:45 > 0:14:49- The sand box showed us - that water voles...
0:14:49 > 0:14:52- ..build an orderly network - of tunnels.
0:14:52 > 0:14:55- We've one more lair to build.
0:14:55 > 0:14:58- A badger sett.
0:15:09 > 0:15:15- The badger sett - was constructed in Somerset...
0:15:15 > 0:15:19- ..on the site of the Secret World - wildlife rescue centre.
0:15:19 > 0:15:23- The centre - offers a unique opportunity...
0:15:23 > 0:15:28- ..to house homeless badgers - sent there from all over the UK.
0:15:28 > 0:15:31- Every winter, - veterinary nurse Sara Cowen...
0:15:31 > 0:15:35- ..cares for dozens of stray badgers.
0:15:35 > 0:15:41- If they're strong enough by summer, - they're released into the wild.
0:15:41 > 0:15:46- This year, Sara has agreed - to let the badgers live and breed...
0:15:46 > 0:15:49- ..in an artificial sett built by us.
0:15:49 > 0:15:51- A badger of this size...
0:15:52 > 0:15:56- ..stands a better chance of survival - if it's in a group.
0:15:56 > 0:16:02- Six badgers will be introduced - to the sett to form a new family.
0:16:02 > 0:16:05- To have any hope - of surviving in the wild...
0:16:05 > 0:16:08- ..they must learn - to rely on each other.
0:16:13 > 0:16:16- While the badgers - settled in their new home...
0:16:16 > 0:16:21- ..I met Rhys Gwyn, - a Snowdonia National Park warden...
0:16:21 > 0:16:25- ..to learn more - about how badgers live in the wild.
0:16:26 > 0:16:31- It's always the same when you - start looking for animal tracks.
0:16:31 > 0:16:33- You start noticing little signs.
0:16:33 > 0:16:38- Marks where badgers have burrowed - in the ground for insects...
0:16:38 > 0:16:41- ..scratch marks on trees...
0:16:42 > 0:16:44- ..badger droppings...
0:16:44 > 0:16:50- ..or even signs of where - they've dragged ferns into the sett.
0:16:50 > 0:16:53- You can see - where they've been foraging.
0:16:53 > 0:16:57- It's just a matter of noticing - these signs around the place.
0:16:57 > 0:16:59- There's bound to be...
0:16:59 > 0:17:02- ..a lot of earth - beneath our feet here.
0:17:02 > 0:17:05- From the height - of the fence nearby...
0:17:06 > 0:17:10- ..you can see that a lot of earth - has been dug up here.
0:17:10 > 0:17:13- This is small compared to some.
0:17:14 > 0:17:16- This is one hole, one entry point.
0:17:16 > 0:17:19- How many are there in total - and where are they?
0:17:20 > 0:17:25- It's hard to tell because there are - so many openings between the rocks.
0:17:25 > 0:17:30- In lowland areas, a sett - could easily have 50 openings.
0:17:31 > 0:17:34- How many badgers live in this one?
0:17:34 > 0:17:36- From what I've seen...
0:17:36 > 0:17:39- ..there's one large boar...
0:17:39 > 0:17:41- ..and one sow.
0:17:42 > 0:17:44- They have two offspring.
0:17:45 > 0:17:50- I've also seen one younger female - that wasn't born this year.
0:17:50 > 0:17:53- How far would these badgers wander?
0:17:53 > 0:17:55- How far would these badgers wander?- - It depends on the territory.
0:17:56 > 0:18:00- The size of the territory depends - on how much food is available.
0:18:00 > 0:18:06- In lowland areas, territories - tend to be relatively small.
0:18:06 > 0:18:10- In Scotland, where extensive - research has been carried out...
0:18:11 > 0:18:16- ..you'll find territories - ranging from 130 to 300 hectares.
0:18:16 > 0:18:18- They're sprawling territories.
0:18:19 > 0:18:22- In lowland areas, - territories are about 30 hectares.
0:18:23 > 0:18:26- That's enough to sustain - a large family of badgers.
0:18:26 > 0:18:29- You're holding a mixture.
0:18:29 > 0:18:32- What exactly is it - and what do you do with it?
0:18:32 > 0:18:36- One way of establishing - the size of badgers' territory...
0:18:37 > 0:18:39- ..is by leaving food out for them.
0:18:39 > 0:18:42- They're particularly fond - of peanut butter...
0:18:43 > 0:18:47- ..mixed with something sweet - like syrup or honey...
0:18:47 > 0:18:50- ..containing - harmless plastic pellets.
0:18:50 > 0:18:55- They pass through the body, so that - when they mark their territory...
0:18:56 > 0:18:59- ..those pellets can be seen clearly - in their droppings.
0:18:59 > 0:19:04- By using - different-coloured pellets...
0:19:04 > 0:19:07- ..and leaving them - in different areas...
0:19:07 > 0:19:13- ..we can establish the territories - of each badger family.
0:19:13 > 0:19:17- We'd better spread that about - and return in a couple of days.
0:19:17 > 0:19:18- Where do you leave it?
0:19:18 > 0:19:21- Where do you leave it?- - Close to the hole.
0:19:21 > 0:19:23- Do you leave it all there?
0:19:23 > 0:19:26- No, a little here - and some more near another hole.
0:19:27 > 0:19:29- That should do it.
0:19:29 > 0:19:34- So we'll leave that for now - and return in three days' time...
0:19:34 > 0:19:38- ..to see if we can spot the pellets - in the droppings.
0:19:38 > 0:19:40- Off we go then.
0:19:44 > 0:19:48- Now that we have an idea - of the scale of a badger sett...
0:19:48 > 0:19:53- ..we must build a network - of tunnels and larger chambers...
0:19:54 > 0:19:57- ..since badgers - are very sociable creatures.
0:20:06 > 0:20:09- There's no time to waste.
0:20:09 > 0:20:12- Another small badger - has reached the centre.
0:20:12 > 0:20:15- It's the smallest of them all.
0:20:15 > 0:20:19- She was found freezing and - whimpering in a corner of a field.
0:20:20 > 0:20:26- Will the five that have lived - together for a period of time...
0:20:26 > 0:20:28- ..accept the new addition?
0:20:28 > 0:20:31- If she's not accepted - by the group...
0:20:31 > 0:20:34- ..life will be difficult for her.
0:20:34 > 0:20:37- Returning her to the wild - would be impossible.
0:20:44 > 0:20:48- Back on the farm in Devon, the first - of our new habitats is ready.
0:20:49 > 0:20:53- After being delayed by the weather, - everything is finally in place...
0:20:54 > 0:20:57- ..and the rabbits - have started to settle in.
0:20:58 > 0:21:03- This is my first chance to go - inside to see the rabbit warren.
0:21:04 > 0:21:07- It's like stepping - into a subterranean world!
0:21:07 > 0:21:08- Let's go in.
0:21:27 > 0:21:32- Wow! This is what - a proper rabbit warren looks like.
0:21:35 > 0:21:37- It could have been - dug from the earth.
0:21:38 > 0:21:43- This has been modelled - on an actual rabbit warren.
0:21:43 > 0:21:48- You can see that it's a network - of tunnels and different chambers.
0:21:48 > 0:21:50- At the moment...
0:21:51 > 0:21:53- ..it houses ten rabbits.
0:21:53 > 0:21:56- Two males and eight females.
0:22:08 > 0:22:12- The first burrowers - have moved into their new home...
0:22:12 > 0:22:14- ..and we're almost ready...
0:22:15 > 0:22:18- ..to introduce - the water voles and badgers...
0:22:18 > 0:22:20- ..to their new homes too.
0:22:21 > 0:22:24- Next week, we'll discover - if the animals have settled in.
0:22:25 > 0:22:27- Will the rabbits be ready to mate?
0:22:27 > 0:22:30- How will the water voles - adapt to their new home?
0:22:31 > 0:22:35- And will the new family of badgers - welcome the stray into the fold?
0:23:04 > 0:23:06- S4C Subtitles by Adnod Cyf.
0:23:06 > 0:23:06- .