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0:00:00 > 0:00:05- Rural Wales offers some of the most - spectacular sights 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 of our best-loved wildlife.
0:00:16 > 0:00:20- But one group of mammals - is living a secret life.
0:00:22 > 0:00:25- By burrowing tunnels - miles underground...
0:00:26 > 0:00:30- ..the way these animals live - their lives beneath the surface...
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's 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 > 0:00:50- For the first time ever...
0:00:51 > 0:00:55- ..we'll get an insight - into their secret lives underground.
0:00:57 > 0:01:01- We'll discover what water voles - do every day in their tunnels...
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.
0:01:42 > 0:01:46- Nine months have passed - since we first began filming.
0:01:46 > 0:01:51- At first, no-one was sure - how things would develop.
0:01:51 > 0:01:56- But over the months, we've learned - all kinds of interesting things...
0:01:56 > 0:01:59- ..as well as a few new discoveries.
0:01:59 > 0:02:02- With the onset of summer, - the young burrowers prepare...
0:02:03 > 0:02:06- ..for their biggest challenge yet - - leaving the sett.
0:02:07 > 0:02:10- The orphaned badgers - have got to know each other well.
0:02:11 > 0:02:17- They've already ventured outdoors. - The eventual aim is to release them.
0:02:17 > 0:02:21- With no parents to teach them, will - they know what to do in the wild?
0:02:22 > 0:02:27- The water voles have also been - outside and swam for the first time.
0:02:27 > 0:02:30- They've all gained weight...
0:02:30 > 0:02:33- ..but their lives - are about to change for good.
0:02:34 > 0:02:36- The rabbit warren - is overrun with kits...
0:02:37 > 0:02:39- ..with more and more - born each week.
0:02:40 > 0:02:42- How do the mothers - care for their young?
0:02:43 > 0:02:46- What will happen - to all these burrowers...
0:02:47 > 0:02:50- ..as their numbers - perpetually increase...
0:02:50 > 0:02:53- ..creating - more competition for food?
0:02:56 > 0:03:00- Burrowers usually hide - during the daytime...
0:03:01 > 0:03:03- ..which is vital to their survival.
0:03:04 > 0:03:07- Although we don't see them, - they are there.
0:03:08 > 0:03:11- To get an idea of their numbers...
0:03:11 > 0:03:15- ..summer nights are conducive - to learning how they live.
0:03:15 > 0:03:17- We must be able to see in the dark.
0:03:18 > 0:03:22- The countryside comes alive at night - as burrowers leave their dens...
0:03:22 > 0:03:26- ..and venture into a world that's - totally different in daylight.
0:03:26 > 0:03:31- There are 75 million burrowers - in the British Isles.
0:03:31 > 0:03:35- 45 million rabbits, 30 million - moles, 300,000 badgers...
0:03:36 > 0:03:39- ..and 245,000 foxes.
0:03:39 > 0:03:43- There are more burrowers - than people on these isles.
0:03:43 > 0:03:45- What's extraordinary...
0:03:45 > 0:03:49- ..is that these are - population numbers in winter...
0:03:50 > 0:03:53- ..before they've given birth - to their young.
0:03:53 > 0:03:56- Numbers soar - during spring and summer.
0:03:56 > 0:04:00- The summer months are crucial - for young burrowers.
0:04:00 > 0:04:02- Every generation must find a den...
0:04:03 > 0:04:07- ..and learn to compete against - a multitude of other animals.
0:04:08 > 0:04:13- How is it possible to survive - among 150 million other animals?
0:04:21 > 0:04:23- At the beginning of summer...
0:04:24 > 0:04:27- ..the rabbit warren - produces a high number of kits.
0:04:28 > 0:04:33- In the wild, nine out of every 10 - rabbits die within the first year.
0:04:33 > 0:04:39- It's vital, therefore, that they - produce as many young as possible.
0:04:41 > 0:04:45- The experiment began in winter - with nine rabbits.
0:04:45 > 0:04:47- Two bucks and seven does.
0:04:47 > 0:04:51- But we weren't sure - if all of them would breed.
0:04:51 > 0:04:56- We also didn't know if the dominant - ones would retain their dominance...
0:04:56 > 0:04:59- ..or be superseded by other rabbits.
0:05:00 > 0:05:02- Nine months later - and the dominant female...
0:05:03 > 0:05:06- ..has retained her position - as head of the warren.
0:05:07 > 0:05:09- She claims - the warren's highest chambers.
0:05:10 > 0:05:11- In a group like this...
0:05:12 > 0:05:17- ..the status of individuals - within that group is very important.
0:05:17 > 0:05:22- That's right, the dominant female...
0:05:22 > 0:05:25- ..chooses - the best nest in the warren...
0:05:26 > 0:05:27- ..which is at the top.
0:05:28 > 0:05:33- She decides - who's allowed to nest in the warren.
0:05:34 > 0:05:38- The second doe in the pecking order - nests at the bottom.
0:05:38 > 0:05:42- It's far more dangerous - in terms of predators and floods.
0:05:42 > 0:05:45- Some rabbits aren't allowed in.
0:05:45 > 0:05:50- They are prohibited from - even entering the rabbit warren.
0:05:50 > 0:05:53- It's a complicated hierarchy.
0:06:00 > 0:06:03- In the den - of the small orphaned badgers...
0:06:04 > 0:06:09- ..it's obvious that the animals have - come together as one big family.
0:06:12 > 0:06:14- Once the orphans were found...
0:06:14 > 0:06:19- ..they were brought to the Secret - World rescue centre in Somerset.
0:06:19 > 0:06:21- In six weeks' time...
0:06:22 > 0:06:26- ..they will live outside the - artificial habitat we've created.
0:06:26 > 0:06:31- They're stronger and more playful, - biting each other's ears and tails.
0:06:32 > 0:06:36- Though they're playing, is there a - deeper significance to these games?
0:06:36 > 0:06:39- The truth is, - this is a learning process.
0:06:39 > 0:06:43- How to bite, who to bite, - how to overpower an attacker...
0:06:43 > 0:06:46- ..and how to avoid an attack.
0:06:46 > 0:06:49- This teaches them - how to live in a social group.
0:06:52 > 0:06:56- Usually, the young would learn these - life skills from their parents.
0:06:56 > 0:07:00- So we must try and guess - how our badgers will behave...
0:07:00 > 0:07:02- ..once they're released.
0:07:04 > 0:07:08- Last week, Owen visited the RSPCA...
0:07:09 > 0:07:12- ..where one group - was being prepared for release.
0:07:14 > 0:07:18- The badgers have since settled - in the countryside.
0:07:18 > 0:07:23- Owen is tracking them by following - the signal from their collars.
0:07:27 > 0:07:31- Originally, the badgers were - released into an artificial sett...
0:07:31 > 0:07:34- ..that we created for them.
0:07:35 > 0:07:38- On the first night, - they moved out of there...
0:07:38 > 0:07:42- ..and found a natural vacant sett...
0:07:43 > 0:07:46- ..or rather, two vacant setts, - in this habitat.
0:07:46 > 0:07:49- It's a positive outcome so far.
0:07:50 > 0:07:52- I think they'll claim this habitat.
0:08:01 > 0:08:05- This is the artificial sett - we created for the badgers.
0:08:06 > 0:08:09- These pipes - have been embedded into the soil.
0:08:09 > 0:08:13- I think - because the pipes are there...
0:08:13 > 0:08:16- ..the badgers - haven't been able to dig.
0:08:17 > 0:08:21- Instead, they've found a vacant sett - at the top of the hill.
0:08:41 > 0:08:45- We observed the badger - walking along this path...
0:08:45 > 0:08:49- ..trailing his tail on the floor.
0:08:49 > 0:08:52- He was leaving his scent behind.
0:08:53 > 0:08:59- We believe that's his way - of marking his territory.
0:08:59 > 0:09:04- He's saying, - "This is my path and my territory.
0:09:04 > 0:09:07- "If you're another badger, - be aware of that."
0:09:08 > 0:09:12- More than likely, this path - is very important in this territory.
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0:09:32 > 0:09:32- Subtitles
0:09:32 > 0:09:34- Subtitles- - Subtitles
0:09:44 > 0:09:49- Soon, the water voles - will be released into the wild.
0:09:49 > 0:09:53- I'm in Penclacwydd, one of the best - sites in Wales to see water voles.
0:09:54 > 0:09:58- I'm meeting Dyfrig Jones to discover - what will happen to the voles...
0:09:58 > 0:10:00- ..once they're released.
0:10:04 > 0:10:08- This is the type of habitat - you'd expect to see...
0:10:09 > 0:10:12- ..if you went to - the south of England...
0:10:12 > 0:10:16- ..but here in Wales, - this type of habitat is rare.
0:10:16 > 0:10:20- The uplands are different - but you'll find them there too.
0:10:21 > 0:10:23- The characteristics are similar...
0:10:24 > 0:10:27- ..in terms of the river banks...
0:10:27 > 0:10:31- ..and the ditches - that are found in Wales's uplands.
0:10:32 > 0:10:35- The vegetation is different...
0:10:35 > 0:10:38- ..but at certain times - of the year...
0:10:38 > 0:10:43- ..it becomes a rich supply of food, - sugar and general nutrients.
0:10:43 > 0:10:45- When I was a child...
0:10:46 > 0:10:48- ..water voles were very common.
0:10:48 > 0:10:52- Their numbers have since dwindled, - so what's happened?
0:10:53 > 0:10:56- If you think about the type - of habitat they occupied...
0:10:57 > 0:11:01- ..they were drawn to riverbanks - and long, winding streams.
0:11:01 > 0:11:07- That long stretch of habitat - was teeming with various wildlife.
0:11:07 > 0:11:12- Changes in the land in terms of - agricultural or urban development...
0:11:12 > 0:11:19- ..have meant that the continuous - stretch of habitat has been lost.
0:11:19 > 0:11:21- That's one reason.
0:11:21 > 0:11:24- Compare that with American mink...
0:11:24 > 0:11:28- ..that have been released - into Wales's rivers and thrived.
0:11:29 > 0:11:34- They have a systematic approach.
0:11:34 > 0:11:38- They begin at one end of the stream - and eat everything in sight.
0:11:38 > 0:11:42- Those populations are then lost.
0:11:45 > 0:11:47- At first, - the pair didn't get along.
0:11:47 > 0:11:52- But eventually they mate - and produce three offspring.
0:11:52 > 0:11:57- The young soon venture to the river, - which is part of their habitat.
0:12:04 > 0:12:05- As they play outside...
0:12:06 > 0:12:08- ..the mother creates another nest.
0:12:09 > 0:12:13- It's only been three weeks since - the mother spawned her first litter.
0:12:14 > 0:12:16- Now she's preparing - to give birth again.
0:12:17 > 0:12:21- The water voles are content - within our artificial habitat.
0:12:21 > 0:12:26- There's plenty of shade and food - and no predators to fear.
0:12:26 > 0:12:29- But the situation - is very different in the wild.
0:12:29 > 0:12:31- Many die within the first year.
0:12:32 > 0:12:35- 70% of them die...
0:12:35 > 0:12:40- ..from malnutrition, floods - and fatal attacks from predators.
0:12:41 > 0:12:44- The water voles - we've been tracking...
0:12:45 > 0:12:48- ..are part of - a conservation programme.
0:12:48 > 0:12:51- Eventually, they'll be - re-introduced into the wild.
0:12:52 > 0:12:55- What do you look for - before releasing them?
0:12:55 > 0:12:58- You release them in family groups.
0:12:59 > 0:13:02- There are two or three - in a family group...
0:13:02 > 0:13:05- ..that have - established themselves over time.
0:13:05 > 0:13:08- They're released - into a diverse habitat.
0:13:09 > 0:13:14- They must have banks - so that they can burrow into them.
0:13:14 > 0:13:17- They must also - have varied vegetation...
0:13:18 > 0:13:22- ..that they can feed from - and use as shelter...
0:13:22 > 0:13:25- ..throughout the year.
0:13:25 > 0:13:27- They must have plenty of room...
0:13:28 > 0:13:33- ..if you're releasing - family groups of more than six...
0:13:34 > 0:13:37- ..in order for them to repopulate.
0:13:37 > 0:13:42- You might have to find - one or two miles of ideal habitat...
0:13:42 > 0:13:44- ..that they can occupy.
0:13:44 > 0:13:48- But it must be considered - a long-term measure.
0:13:48 > 0:13:53- You have to return the following - year or the year after that...
0:13:53 > 0:13:56- ..to release others into the wild.
0:13:56 > 0:13:59- Whatever you do...
0:13:59 > 0:14:02- ..you must bear in mind - what's already there.
0:14:02 > 0:14:04- Are there - water voles there already?
0:14:05 > 0:14:07- It's a question of genetics.
0:14:07 > 0:14:12- It comes down to metapopulations. - They're crucial.
0:14:12 > 0:14:15- If you disregard that aspect...
0:14:15 > 0:14:18- ..and have no connection - between these habitats...
0:14:19 > 0:14:21- ..the area becomes isolated...
0:14:21 > 0:14:25- ..and that's the worst thing - you can do for this species.
0:14:36 > 0:14:38- Back in the rabbit warren...
0:14:39 > 0:14:42- ..the rabbits are breeding - as quickly as the voles.
0:14:42 > 0:14:45- While they're lucky - to survive one season...
0:14:45 > 0:14:50- ..the rabbits have developed - a very clever strategy.
0:14:50 > 0:14:53- As the dominant female - delivers her first litter...
0:14:54 > 0:14:56- ..the dominant male stays outside.
0:14:56 > 0:14:59- The minute the kits are born...
0:14:59 > 0:15:04- ..the male returns to the mother - and mates with her again.
0:15:04 > 0:15:08- This might seem strange to us...
0:15:08 > 0:15:11- ..but it's completely natural - for rabbits.
0:15:11 > 0:15:15- A doe can become pregnant - half an hour after giving birth.
0:15:15 > 0:15:19- The male knows this and takes - advantage of the situation...
0:15:20 > 0:15:22- ..before the other males do.
0:15:22 > 0:15:25- The mother collects - a big ball of fur and straw...
0:15:26 > 0:15:30- ..to lay at the opening before - leaving in order to feed and rest.
0:15:31 > 0:15:35- That really surprised me.
0:15:35 > 0:15:40- Once she's given birth to her young, - the buck approaches her...
0:15:40 > 0:15:42- ..and mates with her straightaway.
0:15:43 > 0:15:46- Yes, and she becomes pregnant again.
0:15:46 > 0:15:49- They produce litters every month...
0:15:49 > 0:15:55- ..so that they can birth - lots of offspring during the season.
0:15:55 > 0:16:00- Because animals eat them, they must - produce as many as possible.
0:16:00 > 0:16:02- This raises another question.
0:16:02 > 0:16:07- With the water voles, - they breed at such a rate...
0:16:07 > 0:16:11- ..they quite literally - breed to death.
0:16:11 > 0:16:13- Why doesn't that happen to rabbits?
0:16:15 > 0:16:18- Nursing their young is effortless.
0:16:18 > 0:16:22- They come in and feed them milk - for three minutes a day...
0:16:22 > 0:16:24- ..before going back out to feed...
0:16:24 > 0:16:29- ..so that they can have more babies - and keep themselves healthy.
0:16:29 > 0:16:34- They make sure they're in optimum - health by taking lots of breaks.
0:16:34 > 0:16:36- Resting helps them.
0:16:36 > 0:16:39- It's a - completely different technique.
0:16:40 > 0:16:43- The only way rabbits survive...
0:16:43 > 0:16:46- ..and avoid attacks - from predators...
0:16:46 > 0:16:48- ..is to keep their numbers high.
0:16:48 > 0:16:53- They produce more rabbits - than predators are able to catch.
0:16:53 > 0:16:57- This is crucial in summer - when the young leave the warren.
0:16:57 > 0:17:00- It's also breeding season...
0:17:00 > 0:17:04- ..for foxes, stoats - and birds of prey and their chicks.
0:17:04 > 0:17:08- When the kits - leave the warren en masse...
0:17:08 > 0:17:12- ..it makes it impossible - for predators to kill them all.
0:17:12 > 0:17:14- Some are sure to survive.
0:17:24 > 0:17:28- On Skokholm Island - off the Pembrokeshire coast...
0:17:28 > 0:17:33- ..suitable land and food - for rabbits is hard to come by.
0:17:33 > 0:17:35- Ceri and I visited the island...
0:17:36 > 0:17:40- ..to see how rabbits survived - under such difficult circumstances.
0:17:40 > 0:17:45- You come to these islands - and see so many rabbits.
0:17:46 > 0:17:50- What's responsible - for limiting their numbers?
0:17:50 > 0:17:52- Is it food?
0:17:52 > 0:17:55- Food is one thing - but it's also down to space.
0:17:56 > 0:17:59- With so many, - they run out of room in the end.
0:18:00 > 0:18:03- They don't like - being too close to each other.
0:18:03 > 0:18:08- They also need a place to nest - and they can't burrow into rocks.
0:18:08 > 0:18:11- That answers my question.
0:18:12 > 0:18:15- There are many in this area here...
0:18:16 > 0:18:20- ..while there none in that - rockier terrain in the distance.
0:18:21 > 0:18:24- It's much easier - to burrow in this area.
0:18:24 > 0:18:29- They're also responsible - for this ecosystem.
0:18:29 > 0:18:32- They call it - a rabbit-maintained ecosystem.
0:18:33 > 0:18:36- A habitat maintained by rabbits - and nothing else.
0:18:36 > 0:18:40- They're more important - on islands than on the mainland.
0:18:40 > 0:18:42- They are the grazers.
0:18:45 > 0:18:49- During summer, thousands of rabbits - compete for food.
0:18:49 > 0:18:52- But when the does - are under pressure...
0:18:52 > 0:18:57- ..they can prevent pregnancies by - reabsorbing embryos from the womb...
0:18:57 > 0:18:59- ..back into the body.
0:19:03 > 0:19:08- Though there are no voracious - mammals to kill the rabbits here...
0:19:09 > 0:19:13- ..they become the prey of birds - that eat them as a snack.
0:19:16 > 0:19:18- As you walk around the island...
0:19:19 > 0:19:22- ..animals have been slaughtered - here and there.
0:19:22 > 0:19:26- You see the remains of birds - and rabbits, similar to this.
0:19:26 > 0:19:29- There's nothing much left - of the rabbit...
0:19:30 > 0:19:32- ..only a little fur and bones.
0:19:32 > 0:19:36- I'd say it was killed - by the great black-backed gull.
0:19:37 > 0:19:39- Yes, probably.
0:19:39 > 0:19:41- In spite of this...
0:19:42 > 0:19:46- ..I'd say an island such as this - is a safe environment for a rabbit.
0:19:46 > 0:19:50- On the mainland, rabbits are - the prey of many different animals.
0:19:51 > 0:19:55- Foxes, stoats, polecats and weasels.
0:19:56 > 0:19:59- But there are no other mammals - on this island apart from mice.
0:20:00 > 0:20:04- They're safe in terms of - mammal-eating predators.
0:20:04 > 0:20:08- When it comes to birds, - seagulls in particular...
0:20:09 > 0:20:12- ..as well as other species, - they eat rabbits too.
0:20:12 > 0:20:14- Yes, buzzards eat them.
0:20:15 > 0:20:18- If the seagulls are able - to pull them out of their burrows...
0:20:19 > 0:20:21- ..other animals finish them off.
0:20:22 > 0:20:26- There's added pressure - for rabbits that live on islands...
0:20:26 > 0:20:30- ..since thousands of birds - burrow and nest underground...
0:20:30 > 0:20:33- ..whilst competing - for the best holes.
0:20:34 > 0:20:39- I know that some birds - are able to burrow underground.
0:20:39 > 0:20:42- The Manx shearwater - and the puffin, for instance.
0:20:43 > 0:20:46- But they prefer using - an old rabbit warren.
0:20:46 > 0:20:49- It's easier - if the hole is already there.
0:20:49 > 0:20:53- They adapt the holes - that are already there.
0:20:53 > 0:20:55- The island's warden told me...
0:20:55 > 0:20:59- ..that he'd seen a puffin - enter a rabbit hole...
0:20:59 > 0:21:02- ..and come out with - a tiny pink rabbit.
0:21:02 > 0:21:07- He threw it out, went back in - and tossed out another six of them.
0:21:07 > 0:21:11- It's strange, isn't it? - He wanted that hole for himself.
0:21:11 > 0:21:15- He tossed them aside - as if they were fur or dirt.
0:21:15 > 0:21:18- He threw them out - and claimed it as his own.
0:21:18 > 0:21:20- They're competitive.
0:21:36 > 0:21:38- I'll insert this rod slowly.
0:21:40 > 0:21:44- There's a camera - with a small red light on top.
0:21:44 > 0:21:46- I'm about half a metre inside.
0:21:47 > 0:21:50- There's something there. - Something white.
0:21:50 > 0:21:52- We can see it now.
0:21:52 > 0:21:56- It's a Manx shearwater. - Do you see the head?
0:21:56 > 0:22:00- Yes, it's a Manx shearwater.
0:22:05 > 0:22:08- It's impossible - to tell if it's male or female.
0:22:08 > 0:22:11- One of them - goes fishing for three days...
0:22:11 > 0:22:14- ..while the other - looks after the egg.
0:22:14 > 0:22:19- It comes back in the middle of - the night when it's pitch black...
0:22:19 > 0:22:23- ..and if the male's been away, - he'll take over from the female...
0:22:24 > 0:22:26- ..while she goes fishing.
0:22:26 > 0:22:29- When it's hatched, they return - more often at night with food.
0:22:30 > 0:22:33- There are more than - 100,000 pairs on this island.
0:22:33 > 0:22:35- It's incredible, isn't it?
0:22:36 > 0:22:40- It's hard to tell if a rabbit - has started burrowing this hole...
0:22:40 > 0:22:45- ..and the bird has adapted it or if - the bird has dug the hole itself.
0:22:45 > 0:22:48- We can't tell by looking at it.
0:22:48 > 0:22:53- There are rabbit droppings nearby - which suggests it was a rabbit.
0:22:53 > 0:22:56- We've had an insight - into the secret life of rabbits.
0:22:57 > 0:23:01- We've also had a glimpse of the - secret life of a Manx shearwater...
0:23:01 > 0:23:06- ..a bird that spends most - of spring and summer underground.
0:23:19 > 0:23:22- Next week's episode - is the last in the series.
0:23:22 > 0:23:26- We'll be reflecting on - what we've learnt and discovered...
0:23:26 > 0:23:29- ..during this unique experiment.
0:23:57 > 0:23:59- S4C subtitles by Adnod Cyf.
0:23:59 > 0:23:59- .