0:00:08 > 0:00:12Mile upon mile of snow and ice.
0:00:12 > 0:00:14A winter wonderland.
0:00:16 > 0:00:18Completely deserted.
0:00:19 > 0:00:21Well, almost.
0:00:23 > 0:00:26This is the setting
0:00:26 > 0:00:30of one of nature's most spectacular journeys.
0:00:30 > 0:00:32It's truly the edge of nowhere.
0:00:32 > 0:00:35Where we're going, there aren't any roads -
0:00:35 > 0:00:39just miles and miles of this.
0:00:50 > 0:00:58There are animals that can survive up here, of course, but one above all is the master.
0:00:58 > 0:01:02Welcome to the land of the caribou.
0:01:22 > 0:01:26For the caribou, movement is a way of life.
0:01:28 > 0:01:32Every year, each individual caribou, young and old,
0:01:32 > 0:01:38will travel over 2,000 miles, heading north in spring and back south in the autumn.
0:01:38 > 0:01:40It's no easy option.
0:01:42 > 0:01:44First, there's the predators...
0:01:46 > 0:01:48..and appalling weather...
0:01:51 > 0:01:57..and other challenges this extreme environment will throw at them as they struggle north.
0:02:07 > 0:02:10So why go on such an odyssey?
0:02:10 > 0:02:14And how do they survive such an extreme test of endurance?
0:02:19 > 0:02:21Well, to find out...
0:02:21 > 0:02:24this year, we're going with them.
0:02:31 > 0:02:37I'm going to travel any way I can, and do whatever it takes to keep up.
0:02:42 > 0:02:46This way I hope to discover something of what they go through
0:02:46 > 0:02:50and find out why travelling is the caribou's passport to survival.
0:02:54 > 0:02:59To understand what caribou are up against, I need to keep in touch with the herd.
0:03:00 > 0:03:04And one of the best ways to do that is to follow a single animal.
0:03:04 > 0:03:07Well, we're going to try.
0:03:11 > 0:03:17But how are we going to follow a single animal in a herd of 120,000?
0:03:17 > 0:03:19They all look identical.
0:03:26 > 0:03:31Well, first we have to find the herd at the most southerly end of their migration in spring,
0:03:31 > 0:03:35just before their long trek north.
0:03:35 > 0:03:38Then we need to call on the experts.
0:03:38 > 0:03:41For the last ten years, scientists in Canada
0:03:41 > 0:03:45and the USA have been studying one particular caribou herd.
0:03:45 > 0:03:47It's called the Porcupine herd.
0:03:50 > 0:03:54We're joining Martin Kienzler, who is part of an international operation.
0:03:54 > 0:04:01Martin and his team are attaching satellite collars to caribou so they can track their travels remotely.
0:04:03 > 0:04:08This year, they're particularly interested in how pregnant females cope,
0:04:08 > 0:04:13because the future of the entire herd depends on them completing this journey.
0:04:19 > 0:04:21This is one of our girls.
0:04:23 > 0:04:25We've named her Claudia.
0:04:29 > 0:04:31Neck, 46.
0:04:31 > 0:04:35Martin and his team quickly measure her vital statistics
0:04:35 > 0:04:41to build her personal profile, including taking a bit of blood to confirm that she's pregnant.
0:04:44 > 0:04:46On with the satellite collar.
0:04:46 > 0:04:50Now we can track her every move remotely.
0:04:58 > 0:05:00And there she goes -
0:05:00 > 0:05:04with 700 kilometres of some of the world's harshest terrain ahead of her.
0:05:08 > 0:05:14That's over 400 miles of heavy going - and probably carrying a calf, as well.
0:05:19 > 0:05:23The thing is, we don't know if she is pregnant for sure.
0:05:23 > 0:05:27But this blood sample will hopefully give us the good news.
0:05:27 > 0:05:29So where are we, then?
0:05:31 > 0:05:36Right now, we're with Claudia in the Yukon Territory of Canada.
0:05:36 > 0:05:38But remember, she's not alone.
0:05:38 > 0:05:42She's with over 120,000 others
0:05:42 > 0:05:46and soon they'll all be on the move, trekking all the way up
0:05:46 > 0:05:53to the Arctic National Wildlife Refuge in Alaska over 400 miles away.
0:05:53 > 0:05:59But why? Why make such a dangerous and difficult journey?
0:05:59 > 0:06:03For the answer, we have to turn the clock back to the autumn,
0:06:03 > 0:06:08when an event took place that set this entire incredible journey in motion...
0:06:10 > 0:06:12..the rut.
0:06:14 > 0:06:18The caribou rut only lasts around ten days, but during that time,
0:06:18 > 0:06:23around 80% to 90% of all the females will become pregnant.
0:06:33 > 0:06:38With conception, an unstoppable chain of events is set in motion.
0:06:40 > 0:06:45In 228 days, the pregnant females will give birth,
0:06:45 > 0:06:48but they can't give birth here.
0:06:51 > 0:06:56There's too many predators, and there's not enough quality food.
0:06:56 > 0:07:00This is why the herd must travel north.
0:07:04 > 0:07:08Back to the present and now it's April.
0:07:08 > 0:07:12We're still here in the Yukon to join the caribou as they start their incredible journey.
0:07:14 > 0:07:18Only problem is, they haven't budged. They're late.
0:07:20 > 0:07:24Now, the satellite collar that Claudia is wearing is pretty spectacular.
0:07:24 > 0:07:28But it wouldn't be any use to us if we couldn't get the information
0:07:28 > 0:07:32that it's beaming into space while we're out in the field.
0:07:32 > 0:07:36So we've got another piece of kit here, and that's this.
0:07:36 > 0:07:39It's a satellite pager.
0:07:39 > 0:07:44Now, I have got the co-ordinate for Claudia.
0:07:44 > 0:07:49She still hasn't started her journey yet. She's still very much where we collared her.
0:07:49 > 0:07:54We don't know why she hasn't started, but spring seems to be coming very late this year,
0:07:54 > 0:07:58and the snow around this area is still very, very deep.
0:08:00 > 0:08:05Whatever the reason for the caribou's delayed start, it's a worry.
0:08:05 > 0:08:08This whole journey runs on a tight schedule.
0:08:08 > 0:08:13The caribou have a series of deadlines to meet if they're to reach the calving area on time.
0:08:13 > 0:08:18And if they miss these deadlines, it will put the calves and the mothers in great danger.
0:08:18 > 0:08:22Every delay increases the risk.
0:08:22 > 0:08:26Anyway, we can't start our journey until the caribou start theirs.
0:08:26 > 0:08:28So we'll just have to wait, too.
0:08:32 > 0:08:36It's a good time to meet the locals and get a feel for this place.
0:08:36 > 0:08:40The Yukon is a real wilderness and I need to know how to look after myself.
0:08:43 > 0:08:47I'm building what they call a quinzee - a snow shelter -
0:08:47 > 0:08:50and I'm actually gonna sleep in it tonight.
0:08:55 > 0:08:58The branches keep me off the snow.
0:09:01 > 0:09:03And the skins will help keep me warm.
0:09:03 > 0:09:06- Got some more bedding here, Steve. - Oh, wow!- Yep.
0:09:06 > 0:09:10'They're about the best thermal insulators in the world.'
0:09:11 > 0:09:14I think I can live with this.
0:09:14 > 0:09:18'What are they? You guessed it - caribou skins.'
0:09:20 > 0:09:23To be honest, it's going to be a flippin' nightmare!
0:09:25 > 0:09:31My extreme survival teacher is Faye Chamberlain, who's an experienced hunter and trapper.
0:09:31 > 0:09:37She's lived up here for 28 years, living out in the wilderness for weeks at a time.
0:09:37 > 0:09:40Faye has to be totally self-sufficient.
0:09:40 > 0:09:42I try to travel as light as possible.
0:09:42 > 0:09:47- For example, if I don't have sunglasses and I'm out on the land, I'll grab some birch bark...- Yeah.
0:09:47 > 0:09:51- ..and make myself one of these... - STEVE LAUGHS
0:09:51 > 0:09:56- ..basically to keep... Yeah. - Let me have a go at that. Yeah, they're great, actually.
0:09:56 > 0:10:00- Have you ever had to wear these? - No, never had to.
0:10:00 > 0:10:01THEY LAUGH
0:10:01 > 0:10:03- OK.- But I would.
0:10:03 > 0:10:07Oh, yeah. Snow blindness can end up getting you killed. But...
0:10:07 > 0:10:09- Yeah.- ..as a fashion statement...
0:10:11 > 0:10:16If I'm going to stay in a quinzee, you know, you're gonna have to have a long-burning candle.
0:10:16 > 0:10:22- But if you don't have any of those, this is the real homemade jobby here.- Sardine tin, is it?
0:10:22 > 0:10:25Yeah, it's a sardine tin with a piece of lamp wick and some lard.
0:10:25 > 0:10:29You're gonna use it for a little heating and lighting in there.
0:10:29 > 0:10:32So that'll stay lit all night, will it?
0:10:32 > 0:10:36- No, you'll have a bit of larch wood. That'll burn down, but that'll add to it.- Yeah.
0:10:36 > 0:10:39Got some salmon strips here, if you'd like one.
0:10:39 > 0:10:42'Now, I've been vegetarian most of my life,
0:10:42 > 0:10:46'but to survive out here, you've gotta be prepared to eat anything.'
0:10:46 > 0:10:48And this has been dried, has it?
0:10:48 > 0:10:50This has been dried.
0:10:50 > 0:10:56Well, soaked in a little bit of a salt brine, and then smoked and then dried on the rack. Yup.
0:10:58 > 0:11:01That's weird. I haven't had fish since I was a kid, really.
0:11:01 > 0:11:07Well, the people have been doing it for thousands of years, and the land is like their larder.
0:11:07 > 0:11:09Oh, hello, you.
0:11:09 > 0:11:10Do you want some of that?
0:11:10 > 0:11:13So what are the threats to the herd, then?
0:11:13 > 0:11:18- Well, of course there's global warming...- Yes. - That's a big one.
0:11:18 > 0:11:22And also potential development in the coastal plain
0:11:22 > 0:11:27- on their migration, and the calving grounds, especially.- Yeah.
0:11:27 > 0:11:31And that could really have drastic consequences for the caribou.
0:11:31 > 0:11:34'The temperature's plummeting.
0:11:34 > 0:11:37'Maybe this wasn't such a good idea!'
0:11:37 > 0:11:39Now, this new coat is fantastic.
0:11:39 > 0:11:44- That's amazing.- Yeah, this is kinda made out of caribou. Yeah.
0:11:44 > 0:11:50I feel, you know, when I get a caribou, I like to think I'm prolonging their life and spirit
0:11:50 > 0:11:53- by using as much as I can.- Yeah.
0:11:53 > 0:11:58So these are the hides, and I put wolverine around for the ruffs, cos it doesn't frost so much.
0:11:58 > 0:12:03- And is it warmer than one of these down jackets? - Oh, by far, by far. Yeah.
0:12:03 > 0:12:08- So do you think I'm going to be comfortable tonight?- Oh, yeah. You're going to be snug as a bug.
0:12:08 > 0:12:12It's about 20 below tonight, so it'll be what we call a two-dog night up here.
0:12:12 > 0:12:14- A two-dog night?- Yeah.
0:12:14 > 0:12:18For every ten degrees below zero, you add on a dog,
0:12:18 > 0:12:20to snuggle up with you to keep you...
0:12:20 > 0:12:22Oh, right. OK, OK.
0:12:24 > 0:12:28That's going to be OK. Here we go.
0:12:32 > 0:12:35OK. So I'm in my quinzee.
0:12:37 > 0:12:40The only light I have is this candle.
0:12:41 > 0:12:43It's not too bad, actually.
0:12:43 > 0:12:48But the thermometer I've got in here is just creeping up, up, up.
0:12:48 > 0:12:52It's now at minus four, and who knows how high it's going to get?
0:12:52 > 0:12:54So I don't think warmth's going to be a problem.
0:12:54 > 0:12:56Good night!
0:12:58 > 0:13:00'Big mistake!
0:13:00 > 0:13:05'That candle gave me light, of course, but it was also the central heating.'
0:13:05 > 0:13:06Ugh!
0:13:10 > 0:13:13It's just turned midnight
0:13:13 > 0:13:16and things are getting a bit chilly in here.
0:13:16 > 0:13:18I might have to...
0:13:18 > 0:13:21put a few more layers on and see how I get on.
0:13:26 > 0:13:29I think it's time to call it a day.
0:13:29 > 0:13:33I'd like to stay out longer but, er...
0:13:33 > 0:13:38you know when the cold kind of gets to your bones, and you just can't sleep?
0:13:38 > 0:13:40Well, that's it.
0:13:40 > 0:13:42The wind is...
0:13:42 > 0:13:44blowing quite wild outside...
0:13:46 > 0:13:48..and, er...
0:13:48 > 0:13:51I just need
0:13:51 > 0:13:52a warm bed.
0:13:54 > 0:13:57I think I've done... I've done my bit.
0:13:57 > 0:14:00Here am I, trying to convince... I'm just freezing cold.
0:14:00 > 0:14:02I want a nice bed!
0:14:06 > 0:14:07Sorry,
0:14:07 > 0:14:10I just couldn't hold out any longer.
0:14:10 > 0:14:14If I have to sleep out again on this journey, I'll know to keep that candle burning.
0:14:19 > 0:14:23Well, despite so little sleep, I feel great this morning,
0:14:23 > 0:14:27because Claudia's co-ordinates show she's on the move at last.
0:14:29 > 0:14:34The pregnant females are at the lead, and the rest of the herd follows.
0:14:34 > 0:14:39But now there are only five weeks till the calves are due.
0:14:41 > 0:14:44This will be a race against time.
0:14:55 > 0:14:58They're off, so I'm off, too!
0:15:10 > 0:15:16Believe it or not, I did seriously think about actually trying to walk alongside Claudia and her mates.
0:15:17 > 0:15:20But it's knackering!
0:15:28 > 0:15:31It is...
0:15:31 > 0:15:33totally sapping.
0:15:33 > 0:15:37You just have to get into the rhythm and keep plodding on.
0:15:37 > 0:15:41It's almost like continually falling forward, and,
0:15:41 > 0:15:48as long as you keep picking the foot up and falling on to it, you're going to keep going.
0:15:58 > 0:16:01Well, you've got to have a break occasionally.
0:16:01 > 0:16:04'Or permanently, in my case.
0:16:04 > 0:16:06'I'm just not built to travel this way.'
0:16:10 > 0:16:14Unlike the caribou, who are in a league of their own.
0:16:14 > 0:16:21In terms of energy usage, they can out-perform any other land animal that's ever been studied.
0:16:21 > 0:16:24You get a lot of miles to the gallon with a Porcupine caribou.
0:16:26 > 0:16:29How do they do it? Well, they distribute their weight
0:16:29 > 0:16:34evenly across those big feet so they don't sink so far into the snow.
0:16:34 > 0:16:41It's obvious there's absolutely no way I would be able to run with the caribou.
0:16:41 > 0:16:44And by the way, caribou do need to run.
0:16:46 > 0:16:49We're not the only ones trying to follow them.
0:17:04 > 0:17:06These are special wolves.
0:17:08 > 0:17:14Instead of having a territory in one place, these wolves have evolved to travel,
0:17:14 > 0:17:19to migrate with the herd, constantly on the lookout for any opportunities to make a kill.
0:17:34 > 0:17:38It's tough, but the wolves keep a health-check on the Porcupine herd,
0:17:38 > 0:17:41weeding out the weak or old animals.
0:18:21 > 0:18:22IT CAWS
0:18:24 > 0:18:30Escaping wolves can be another hold-up, and they're already so late starting.
0:18:34 > 0:18:38So where do Claudia and all the pregnant mums stand right now?
0:18:39 > 0:18:42Well, she's making slow progress
0:18:42 > 0:18:47but seems to be heading towards the northernmost town up here, Old Crow.
0:18:47 > 0:18:50So I guess we'd better head there, too.
0:18:51 > 0:18:54Easier said than done. The weather has turned awful.
0:18:55 > 0:18:57This is serious for us all.
0:18:57 > 0:19:00It's proper Yukon winter weather.
0:19:01 > 0:19:04It's minus 40 out there now.
0:19:06 > 0:19:10Of course, caribou are built to withstand these extremes.
0:19:10 > 0:19:15They have compact bodies, insulating, hollow fur,
0:19:15 > 0:19:18and they don't need to shiver till it's below minus 40 degrees.
0:19:18 > 0:19:21They just sit it out.
0:19:46 > 0:19:48Phew, we made it!
0:19:48 > 0:19:50Old Crow.
0:19:50 > 0:19:53All I want now is a hot mug of tea to warm me up.
0:19:58 > 0:20:00Old Crow is a unique place.
0:20:00 > 0:20:04For a start, the town has no roads to it at all.
0:20:04 > 0:20:06You have to fly or sledge in.
0:20:06 > 0:20:11It's the only community in the Yukon that can't be reached by car.
0:20:14 > 0:20:18Old Crow owes its very existence to the caribou.
0:20:18 > 0:20:20It's built on their migration route.
0:20:20 > 0:20:25There's archaeological evidence of caribou bones cut and shaped by humans
0:20:25 > 0:20:30going back tens of thousands of years, and the Gwitchin people who still live here
0:20:30 > 0:20:34still live off the caribou, which provide them with food and clothes.
0:20:36 > 0:20:40In recent years, the Porcupine herd have streamed right through the village by now.
0:20:40 > 0:20:43But this year, they're late.
0:20:43 > 0:20:46We need some expert advice.
0:20:48 > 0:20:54Everyone's an expert on caribou in Old Crow, but it's the elders who have the real wisdom.
0:20:55 > 0:21:01The man we need to see is out of town at his hunting cabin, waiting for the caribou to arrive.
0:21:01 > 0:21:05And the best way to get there? You've guessed it!
0:21:07 > 0:21:09How many dogs are you gonna give me?
0:21:09 > 0:21:12- Seven.- Seven.
0:21:12 > 0:21:14Seven's a lot for me.
0:21:14 > 0:21:17'Now, I've done this before, but it was a long time ago.
0:21:17 > 0:21:20'And even then, I was, well, rubbish!'
0:21:20 > 0:21:23There's an assumption that I know what I'm doing.
0:21:23 > 0:21:29I don't know where that's come from, but the first corner's going to be an absolute doozy.
0:21:35 > 0:21:38This is what most people think that dogs are going to be like.
0:21:38 > 0:21:43These dogs are absolutely mad keen to go, but wait till we let them go.
0:21:43 > 0:21:45Then listen to what they're like.
0:21:45 > 0:21:47OK, dogs, OK.
0:21:47 > 0:21:49DOGS IMMEDIATELY GO QUIET
0:21:53 > 0:21:55Not quite what you'd expect, is it?
0:21:57 > 0:21:59Good dogs!
0:22:15 > 0:22:17'So who exactly are we going to meet, then?
0:22:17 > 0:22:22'Stephen Frost is a Gwitchin elder, and his life is still wrapped up
0:22:22 > 0:22:25'with the coming and the going of the caribou.
0:22:25 > 0:22:30'He's the repository of maybe thousands of years of knowledge about the caribou migration.
0:22:30 > 0:22:33'If anyone can help us, Stephen can.'
0:22:58 > 0:23:01Whoa...
0:23:01 > 0:23:05- Hello, Steve.- Hello, Stephen! - You're welcome here.
0:23:05 > 0:23:08- Thank you very much. - My name is Steve, too.
0:23:08 > 0:23:11- Oh, excellent. - Did you have a good trip?- Eventful.
0:23:11 > 0:23:13Didn't you do well today?
0:23:13 > 0:23:15Teddy, Daisy...
0:23:15 > 0:23:17Let's have a look at your feet,
0:23:17 > 0:23:21and set everybody free in excitement.
0:23:21 > 0:23:24'Stephen Frost is 73 years old.
0:23:24 > 0:23:29'His life still revolves around the caribou, much as his ancestors' did for thousands of years.
0:23:29 > 0:23:36'He hunts them, uses their skin for clothing, makes shoes and the warmest coats in the world.'
0:23:36 > 0:23:40Man, are you ever an expert at swinging that axe!
0:23:43 > 0:23:47'The mysteries of the caribou migration run in his blood.
0:23:49 > 0:23:53'When scientists get stuck, they often turn to Stephen for advice.'
0:23:53 > 0:23:59I think this is probably not the best way to come, but you seem to know what you're doing.
0:23:59 > 0:24:03- I'll follow you.- Well, somebody got to know what they're doing, I guess!
0:24:03 > 0:24:05I think we know who that is!
0:24:08 > 0:24:12Yeah. Follow the local. That's the way to do it.
0:24:13 > 0:24:18'This river right outside Stephen's cabin is the Porcupine River.
0:24:18 > 0:24:24'It gives its name to the Porcupine herd, because the entire herd must cross it on their way north.'
0:24:24 > 0:24:28- Where are the caribou now? Why aren't they here? - This year's a bit late.
0:24:28 > 0:24:31There's an awful lot of snow.
0:24:31 > 0:24:35But had it not been late, the caribou should have been
0:24:35 > 0:24:43crossing the Porcupine above Old Crow, you know, maybe ten, 12 to 50 miles up already.
0:24:43 > 0:24:48But it's late, and that's because of the snow. Only because of the snow.
0:24:48 > 0:24:52If they're still late because of this deep snow, is that going to be a problem?
0:24:52 > 0:25:00If the caribou don't get up there, then by nature they don't have calves where they're supposed to,
0:25:00 > 0:25:05making it easier for the wolves and bears to get them.
0:25:05 > 0:25:11So in a late year, we've known caribou to even calf
0:25:11 > 0:25:17before they hit the river, and it's most likely then they will never make it up there.
0:25:17 > 0:25:21OK. The calves are going to really struggle, I suppose, to keep up with Mum.
0:25:21 > 0:25:23Yeah. They probably won't make it.
0:25:23 > 0:25:27And how long have the Gwitchin been actually hunting here?
0:25:27 > 0:25:32I dunno. I don't know if anyone could answer that right.
0:25:32 > 0:25:35About 40,000 years?
0:25:35 > 0:25:38- I don't think you were here then! - No!
0:25:38 > 0:25:44Me, neither. But it's been a long, long time.
0:25:47 > 0:25:51The caribou should have been here by now.
0:25:51 > 0:25:55They just keep on slipping further behind schedule.
0:25:55 > 0:25:58Everything's stacked up against them -
0:25:58 > 0:26:06the weather, the terrain, the wolves and, if that wasn't enough, as the weather warms up
0:26:06 > 0:26:09there's something else.
0:26:17 > 0:26:20The winter may have been an exercise in extreme survival,
0:26:20 > 0:26:24but at least the caribou didn't have bears to contend with.
0:26:27 > 0:26:32The bears were all hibernating throughout the winter, but now they emerge from their dens.
0:26:34 > 0:26:38After five or six months underground, they're hungry.
0:26:41 > 0:26:47Bears are surprisingly fast, but Claudia is young and healthy.
0:26:47 > 0:26:49She should be able to outpace them.
0:26:55 > 0:26:59And there's more. As the weather warms up, the ice melts,
0:26:59 > 0:27:05turning the snow to slush and the frozen rivers into death traps.
0:27:33 > 0:27:36And the Porcupine River is melting, too...
0:27:43 > 0:27:48..with Claudia stuck on the wrong side.
0:27:48 > 0:27:51Crossing the river like this would be suicide.
0:27:53 > 0:27:56Yet another delay.
0:28:10 > 0:28:13She hesitates for three days.
0:28:13 > 0:28:16Is she looking for a safe place to cross?
0:28:18 > 0:28:22Isn't it amazing what those satellite collars reveal?
0:28:22 > 0:28:26Without them, scientists would know nothing of this sort of behaviour.
0:28:37 > 0:28:42At last, Claudia's satellite co-ordinates show that she crosses safely along with the others.
0:28:57 > 0:29:00Let's hope she can make up for lost time.
0:29:05 > 0:29:08Meanwhile, we've got problems of our own.
0:29:08 > 0:29:11'Something's come up.
0:29:11 > 0:29:16'The whole point of Claudia's journey is for her to find somewhere safe to give birth to her calf.
0:29:16 > 0:29:21'And everything we're doing is based on the assumption she's pregnant.
0:29:21 > 0:29:22'But is she?
0:29:22 > 0:29:27'Remember when we were collaring her with Martin Kienzler right at the beginning?
0:29:27 > 0:29:30'We took blood samples to see if Claudia was pregnant.
0:29:30 > 0:29:35'Well, we don't have the results yet, so we have no way of knowing if she's pregnant or not.
0:29:38 > 0:29:43'The only way to find out is to try and find her and see for ourselves.'
0:29:48 > 0:29:51- How are you doing? - I'm doing good.- Hey, Martin.
0:29:51 > 0:29:54We flew over thick fog on the way here.
0:29:54 > 0:29:57'We've managed to convince Martin Kienzler to come to our aid.
0:29:57 > 0:30:00'He's kindly dropped everything to join us.
0:30:00 > 0:30:03'And we've got the legendary Stephen Frost.
0:30:03 > 0:30:08'So we've got the latest science, coupled with the traditional knowledge of the Gwitchin people.'
0:30:08 > 0:30:12OK, so we're all together. We've got a chopper with a full tank of fuel.
0:30:12 > 0:30:14Rock and roll!
0:30:30 > 0:30:34'So how are we going to find her?
0:30:34 > 0:30:39'It's the double whammy - the old and the new.
0:30:39 > 0:30:41'Technology first.
0:30:41 > 0:30:47'As well as a satellite link, Claudia is beaming a radio signal all the time.'
0:30:47 > 0:30:50- So Claudia is nine miles this way. - OK.
0:30:50 > 0:30:55Well, hopefully she's going to be up on one of these ridges, or up on a ridge.
0:30:55 > 0:30:58'We know she's down here somewhere.'
0:30:58 > 0:31:01Yeah, there's some down there on that ridge.
0:31:01 > 0:31:03Oh, there we go, we've got her.
0:31:03 > 0:31:05Fairly close, too.
0:31:07 > 0:31:11- I can land right here...- Yup. - ..if you want. Shall I try it?
0:31:11 > 0:31:13Yeah. OK.
0:31:13 > 0:31:15All right. 30 seconds.
0:31:18 > 0:31:20Bump, bump.
0:31:21 > 0:31:25'Once we're down on the ground, it's a whole new ball game.
0:31:25 > 0:31:29'Now we need the experience of someone who's spent their life amongst caribou -
0:31:29 > 0:31:32'someone who can think like a caribou.'
0:31:32 > 0:31:38You know, they seem to be coming straight this way, so they could follow that trail.
0:31:38 > 0:31:41Or there's one down here.
0:31:41 > 0:31:47I wonder if we could move this stuff to that little timber area, because if they see us out here, you know.
0:31:47 > 0:31:49Yeah, right away.
0:31:49 > 0:31:54'Ancient skills and modern technology - it's a good combination.'
0:32:12 > 0:32:15They're just gonna come out right there...
0:32:16 > 0:32:19- ..on this...- Oh, yes, yes. Right.
0:32:19 > 0:32:24'This is the first time I've really seen the herd properly.
0:32:24 > 0:32:28'It's easy enough to say there's over 120,000 animals in the herd,
0:32:28 > 0:32:31'but you can't really visualise what that means.
0:32:31 > 0:32:33'It's just mind-boggling.'
0:32:38 > 0:32:41(Just listen to them!)
0:32:41 > 0:32:44(That tapping sound is their tendons clicking.)
0:32:48 > 0:32:50(She's so close!)
0:32:55 > 0:33:03Our caribou, Claudia, is in here somewhere, amongst these hundreds of caribou.
0:33:03 > 0:33:07We've been so lucky because they've just come and surrounded us.
0:33:07 > 0:33:13We've got caribou all around us, just slowly plodding their way north.
0:33:13 > 0:33:15Really peaceful.
0:33:15 > 0:33:19All we can hear is the clicking of their tendons,
0:33:19 > 0:33:24and they've got within a few hundred feet and haven't been bothered by us,
0:33:24 > 0:33:29so that's really nice, just to be able to see them on their migration.
0:33:29 > 0:33:35And when we leave them now, they'll just keep going, for hundreds and hundreds of miles.
0:33:39 > 0:33:42It's hard to grasp how many there are.
0:33:42 > 0:33:46They just keep coming, layer upon layer, streaming past.
0:33:48 > 0:33:52Picking out Claudia's gonna be much more tricky than I thought,
0:33:52 > 0:33:56but if we don't see her, we won't know if she's pregnant or not.
0:33:56 > 0:34:00She just walked right on by.
0:34:00 > 0:34:04We just missed her. She's in that line of trees there.
0:34:04 > 0:34:06We can see all the caribou that are with her.
0:34:12 > 0:34:15I think she was, like you say, in that main body...
0:34:17 > 0:34:21a few, 500 yards, and slowly getting further. It's...
0:34:21 > 0:34:25- That's pretty good, though. - Oh, you know, we came that close.
0:34:27 > 0:34:28Well, you know,
0:34:28 > 0:34:32with the caribou moving the way they are, you know,
0:34:32 > 0:34:34I think we might have another chance yet.
0:34:34 > 0:34:39To be honest, I'm not sure there is any realistic chance of seeing her -
0:34:39 > 0:34:44there are just so many of them, and they're all really spread out.
0:34:44 > 0:34:46But, we've got to keep trying.
0:34:46 > 0:34:49Everyone's gone to so much trouble, we can't give up now.
0:35:04 > 0:35:10We've managed to get just ahead of them again, with a better vantage point this time.
0:35:14 > 0:35:17There's lots of them down there now.
0:35:35 > 0:35:38There she is. Got her.
0:35:38 > 0:35:40- You've got her?- Yeah.- Excellent!
0:35:51 > 0:35:54That's extraordinary, we've found her!
0:35:56 > 0:35:59Just look at her tummy - she certainly looks pregnant to me.
0:36:01 > 0:36:04But the real giveaway is she's still got her big antlers.
0:36:04 > 0:36:08If she wasn't pregnant, they'd have fallen off by now, like some of the others.
0:36:17 > 0:36:24On a sunny day like today, it's hard to imagine what Claudia has been through already.
0:36:24 > 0:36:27Blizzards, the river crossing.
0:36:27 > 0:36:30Not to mention fending off wolves and grizzlies.
0:36:30 > 0:36:36But at the moment, all that's on her mind is getting to those calving grounds in time.
0:36:43 > 0:36:47That's probably the last we're going to see of her
0:36:47 > 0:36:54for however long it's going to take her to get to the calving grounds.
0:36:54 > 0:36:57That's if she can get to the calving grounds.
0:36:57 > 0:37:01If she hadn't been pregnant, the fact that's she's almost
0:37:01 > 0:37:04three weeks behind schedule wouldn't have mattered.
0:37:04 > 0:37:08But now we know for sure she is, she needs to get to the safety
0:37:08 > 0:37:12of the Arctic Refuge to give birth in just two weeks.
0:37:13 > 0:37:16You know, I don't think she's going to make it.
0:37:20 > 0:37:25Where Claudia and the herd are going now we just can't follow.
0:37:25 > 0:37:29It's out of helicopter range and there's no human habitation at all.
0:37:29 > 0:37:32All we can do is watch her progress from her collar
0:37:32 > 0:37:37and hope and pray that the little dot keeps moving day on day.
0:37:40 > 0:37:46As they get much further north there will be some good news.
0:37:46 > 0:37:50The caribou will leave the shadowing wolf packs behind.
0:37:55 > 0:37:59As it's now spring, it's time for the wolves to give birth.
0:37:59 > 0:38:02But to do that, they need to dig a den.
0:38:05 > 0:38:09Further north, the ground is frozen solid all the year round
0:38:09 > 0:38:15so the wolves have to den where the ground is still soft enough to dig out a safe haven for their cubs.
0:38:25 > 0:38:29The wolves might have to stop, but the caribou have to push on.
0:38:34 > 0:38:40They haven't got that far to go in terms of total distance, but these girls are heavily pregnant.
0:38:40 > 0:38:44You can see it. Imagine if you were, say, eight-months pregnant,
0:38:44 > 0:38:52and you had to walk, sometimes run, over wet, muddy ground and slushy snow for about 150 miles.
0:38:52 > 0:38:54No wonder they're slowing down.
0:38:59 > 0:39:03And the weather's continuing to warm up.
0:39:06 > 0:39:11It's an uncomfortable time for animals used to surviving extreme cold.
0:39:11 > 0:39:15They seek out patches of snow to help keep them cool.
0:39:32 > 0:39:35We can't go where Claudia and the herd are going now.
0:39:35 > 0:39:39No roads, no towns, nothing.
0:39:39 > 0:39:42But we can get ahead and wait for her.
0:39:42 > 0:39:47So we're overtaking Claudia and heading for the only town there is up there,
0:39:47 > 0:39:50close to where Claudia should have her calf.
0:39:54 > 0:40:00Welcome to Kaktovik airport, gateway to The Arctic National Wildlife Refuge.
0:40:04 > 0:40:07A comfortable taxi ride to my five-star hotel.
0:40:14 > 0:40:16Ah, we like the look of that!
0:40:16 > 0:40:18'No expense spared!'
0:40:25 > 0:40:27Right, it's 5th June.
0:40:27 > 0:40:30This is a very important day in Claudia's calendar
0:40:30 > 0:40:33because this is the week she's most likely going to give birth.
0:40:33 > 0:40:40And in fact, over the last few days her plot positions have started to slow down in terms of movement.
0:40:40 > 0:40:44So, we can only assume that she's either going to give birth
0:40:44 > 0:40:48imminently, or she already has, and has now got a calf in tow.
0:40:48 > 0:40:52The problem is, she's not at the traditional calving grounds.
0:40:52 > 0:40:54She's in the wrong place.
0:40:54 > 0:40:59With all the delays, Claudia's only just reached the north coast.
0:40:59 > 0:41:03She's still in Canada, 100 miles from the core calving area.
0:41:10 > 0:41:13But you can't stop nature.
0:41:13 > 0:41:18Around half of all the female caribou give birth on the same day,
0:41:18 > 0:41:22and pretty much all of them will deliver within the week.
0:41:22 > 0:41:25It's all synchronised to minimise the chance
0:41:25 > 0:41:29of a predator getting your calf because there are so many around.
0:41:32 > 0:41:36As you might expect with caribou, the calves are up and running,
0:41:36 > 0:41:40well tottering, within a couple of hours of being born.
0:41:46 > 0:41:51Once she's steadied up, she'll hardly stop moving for the rest of her life.
0:42:11 > 0:42:13Pretty soon they find their feet.
0:42:13 > 0:42:18When they're just one day old, a caribou calf can easily outrun a human!
0:42:26 > 0:42:32The youngsters may be pretty nimble on their feet, but there's a new threat on the horizon.
0:42:39 > 0:42:46Golden eagles target young caribou and there's little chance of a calf outrunning this aerial attack.
0:43:04 > 0:43:06One in ten calves get taken.
0:43:24 > 0:43:31It takes the herd and Claudia another three weeks to get to the heart of the Arctic Refuge,
0:43:31 > 0:43:37dodging eagles, being hassled by bears, crossing rivers.
0:43:44 > 0:43:47Lots of little legs trying to keep up.
0:43:53 > 0:43:55Many calves will fall by the wayside.
0:44:09 > 0:44:12But what about Claudia's calf?
0:44:16 > 0:44:21All we can do is wait in Kaktovik with bated breath.
0:44:21 > 0:44:23Will Claudia make it?
0:44:23 > 0:44:25And has her calf survived?
0:44:27 > 0:44:30There's only one way to find out.
0:44:30 > 0:44:33We're going for one final rendezvous with our heroine.
0:44:40 > 0:44:46She's travelled well over 400 miles, all the way up from the Yukon.
0:44:46 > 0:44:52It's taken her a gruelling 10 weeks, crossing some of the most hostile terrain on Earth.
0:44:52 > 0:44:57Now Claudia's here, only 40 miles south of us.
0:45:08 > 0:45:11Going for a rendezvous is easier said than done.
0:45:11 > 0:45:14No helicopters are allowed in the refuge.
0:45:14 > 0:45:21The only way in is via this one little plane - flown by this one pilot.
0:45:21 > 0:45:25But Tom is one of the few people who'd be willing to take on a mission like ours,
0:45:25 > 0:45:30because there's a bit of a problem. We'll come back to that later.
0:45:39 > 0:45:46You have to get up here, up into the heavens to see one of the most awesome sights in all nature.
0:45:46 > 0:45:50- Look at this, man. We're in 'em good now...- Oh, my hat, yeah...
0:45:50 > 0:45:56Hey Tom, right on. There's thousands of them here. Thousands and thousands and thousands.
0:45:56 > 0:46:00Ah, they're peppered everywhere, aren't they? Lots of calves.
0:46:00 > 0:46:03Loads of calves. That's good to see.
0:46:12 > 0:46:15The entire porcupine herd on the move.
0:46:15 > 0:46:17They cover the earth.
0:46:17 > 0:46:20A living carpet of caribou.
0:46:22 > 0:46:27OK, so by now they're a slightly moth-eaten carpet of caribou,
0:46:27 > 0:46:31but finally you can see what this migration is all about.
0:46:31 > 0:46:35This is what they're here for.
0:46:35 > 0:46:38The caribou are stuffing their faces.
0:46:43 > 0:46:47The vegetation that's been hidden away all winter explodes into action,
0:46:47 > 0:46:53with 24-hour sunlight producing masses of high-protein food,
0:46:53 > 0:46:55enough even for the entire porcupine herd.
0:46:57 > 0:47:01The mothers use it to make the richest milk among land mammals,
0:47:01 > 0:47:06and they all build up the fat and muscle they lost on the long trek north.
0:47:15 > 0:47:19OK, back on board, I can reveal our little problem.
0:47:19 > 0:47:21We've got nowhere to land!
0:47:21 > 0:47:24No, seriously, there's no landing strips at all!
0:47:24 > 0:47:27We just have to find somewhere to land as best we can -
0:47:27 > 0:47:30a bit of grass beside a river, a mud flat, whatever.
0:47:30 > 0:47:35It's totally down to the judgment and skill of Tom.
0:47:35 > 0:47:38And even he seems to be having second thoughts.
0:47:38 > 0:47:41I'm not going into a... I mean, it would be stupid
0:47:41 > 0:47:44to go into a place for the first time without...
0:47:44 > 0:47:48It's too rocky. There's only one place up here we're going to go and check out.
0:47:48 > 0:47:50We might have a problem here.
0:47:51 > 0:47:54We'll go try to find some place.
0:47:59 > 0:48:02- That'll do it.- Yeah.
0:48:14 > 0:48:15Nice one, Tom!
0:48:18 > 0:48:22What an incredible, incredible spot!
0:48:22 > 0:48:24Just take a look down there.
0:48:31 > 0:48:34That is stunning!
0:48:41 > 0:48:45So, we're on our own. But Tom will be round and about.
0:48:45 > 0:48:48If he sees anything useful, he'll radio us.
0:49:02 > 0:49:07We had to land 10 miles away from the herd, so it'll take us about four hours to reach them.
0:49:09 > 0:49:12Absolutely stunning views all around.
0:49:12 > 0:49:15We're in the middle of nowhere.
0:49:18 > 0:49:23This might be paradise, but there is one small fly in the ointment.
0:49:23 > 0:49:28As soon as you stand still, you're getting absolutely swamped by mosquitoes as well,
0:49:28 > 0:49:32which is something that the caribou are obviously feeling.
0:49:32 > 0:49:36So we are effectively honorary caribou for the next few hours.
0:49:41 > 0:49:43Mozzie bites down my face.
0:50:02 > 0:50:05Hang on a minute, are those caribou down there?
0:50:09 > 0:50:11Look at that!
0:50:11 > 0:50:14They stretch as far as the eye can see!
0:50:18 > 0:50:21But these mozzies are really getting bad.
0:50:24 > 0:50:29They're irritating enough for me, but for the caribou, they can be a serious problem.
0:50:33 > 0:50:38The caribou have a three-week window to feed like crazy before the mosquitoes hit.
0:50:38 > 0:50:43Because when they hatch out in their millions, they drive the caribou to distraction.
0:50:53 > 0:50:59Incredibly, a caribou can lose as much as two and a quarter pints of blood in a single day.
0:51:03 > 0:51:07They seek relief by searching out cool and windy areas,
0:51:07 > 0:51:11and stick together in mass aggregations to avoid being bitten.
0:51:20 > 0:51:27By being constantly on the move, that means less time to eat and that also affects their health.
0:51:38 > 0:51:40And there are still bears up here.
0:51:45 > 0:51:48Mind you, they're not quite such a threat any more.
0:51:50 > 0:51:56When the calves were born, the bears hit up to six youngsters a day.
0:51:59 > 0:52:02But now the calves are strong.
0:52:02 > 0:52:04They can easily outrun a bear.
0:52:08 > 0:52:11Look at those waves of disturbance.
0:52:11 > 0:52:13It looks like shoals of fish, doesn't it?
0:52:13 > 0:52:15Darting away from sharks or seals.
0:52:37 > 0:52:41Right then, we're much closer now.
0:52:41 > 0:52:46Can we find Claudia and see whether her calf has made it?
0:52:48 > 0:52:51Our caribou are just over that ridge.
0:53:05 > 0:53:07Well, this is why we came here.
0:53:07 > 0:53:10They're over there - caribou as far as you can see.
0:53:10 > 0:53:12That is the porcupine herd.
0:53:12 > 0:53:17They've travelled 400 miles across some of the harshest terrain to get here.
0:53:17 > 0:53:23All we've got to do is find one - one red collar somewhere in all of them.
0:53:34 > 0:53:38Well, it was worth it.
0:53:38 > 0:53:42There are thousands upon thousands of them.
0:53:44 > 0:53:48Look at the tiny calves - they're beautiful.
0:53:48 > 0:53:52When we saw them, down in the Yukon in the snow,
0:53:52 > 0:53:57then they were forming a big line, travelling.
0:53:57 > 0:54:02Now they're here, they might be in a big herd but well spread out.
0:54:02 > 0:54:07And they're just feeding their faces and there are lots and lots of calves.
0:54:17 > 0:54:19But I can't see any red collars.
0:54:24 > 0:54:27The only thing we can do is keep scanning for her.
0:54:30 > 0:54:38But we've placed ourselves really well, cos I think they're gonna come right under our noses.
0:54:44 > 0:54:49Some of them are really close, but no sign of Claudia.
0:54:59 > 0:55:02The numbers are just too overwhelming.
0:55:05 > 0:55:08We did find her once, so it was worth a try.
0:55:08 > 0:55:11But I guess we'll just never know about that calf.
0:55:13 > 0:55:16PROPELLERS WHIR
0:55:17 > 0:55:20I forgot, our eye in the sky!
0:55:23 > 0:55:27'There's still caribou here. There's still caribou.
0:55:27 > 0:55:30'All the way down here there's caribou.'
0:55:30 > 0:55:33Well, good. Don't scare 'em away!
0:55:33 > 0:55:38'About as far as the eye can see, there's caribou all along here.'
0:55:40 > 0:55:44Then this bolt from the blue from a caribou biologist on board.
0:55:46 > 0:55:51'Er, we've just confirmed that Claudia does indeed have a calf.'
0:55:51 > 0:55:55- Oh boy, that's good news. - 'So, just to let you know that Claudia has a calf.'
0:55:55 > 0:55:57Fantastic.
0:56:02 > 0:56:04Oh, that's fantastic. We just lost you now.
0:56:04 > 0:56:06But thanks a lot. We'll see you later.
0:56:18 > 0:56:24So, Claudia's calf made it, despite that arduous trek from Canada.
0:56:24 > 0:56:27It was all worth it.
0:56:29 > 0:56:34It's been amazing to share this incredible journey with these caribou,
0:56:34 > 0:56:38as they've travelled all the way from their wintering grounds to here,
0:56:38 > 0:56:40in the Arctic National Wildlife Refuge.
0:56:40 > 0:56:46What's been so special is being able to experience some of the hardships they've faced on the way.
0:56:46 > 0:56:50I know I haven't actually got to see Claudia since I got here,
0:56:50 > 0:56:55but it's enough for me to know that Claudia's out there behind me,
0:56:55 > 0:56:58somewhere, safe, and even had a calf.
0:56:59 > 0:57:05For me, my journey's ended here, but for the caribou, constant movement is a way of life.
0:57:05 > 0:57:12They're going to turn their noses down south and pretty soon start the whole process all over again.
0:57:12 > 0:57:17I'd love to go with them, but there's no keeping up with caribou.
0:57:24 > 0:57:29For Claudia's calf, this is just the beginning of a lifetime on the move.
0:57:29 > 0:57:33Her first big hurdle is over. She's survived the first month.
0:57:35 > 0:57:40Now she faces the biggest journey of her life - the long haul south.
0:57:42 > 0:57:46As with all the animals in Incredible Journeys,
0:57:46 > 0:57:51Claudia and her calf are still writing their own story.
0:58:08 > 0:58:13Subtitles by Red Bee Media Ltd - 2007
0:58:13 > 0:58:16E-mail us at subtitling@bbc.co.uk